In recent years, there has been a noticeable shift by governments towards investing more resources in public transport systems like buses and trains rather than expanding road infrastructure. Several compelling reasons underpin this strategic move, and overall, this trend should be seen as largely positive due to its environmental, economic, and social benefits.
Firstly, one significant reason for increased investment in public transportation is the urgent need to address environmental concerns. Expanding roads typically encourages greater car use, exacerbating traffic congestion and air pollution. Public shipping, by contrast, significantly reduces the number of vehicles on the roadway, thereby lowering greenhouse gas emissions and improving urban air quality. For instance, cities like Tokyo and London, which have highly developed public transit networks, demonstrate markedly lower pollution levels compared to car-dependent cities.
Secondly, economically, investing in public shipment offers superior returns compared to lane expansion. Efficient public transportation systems can reduce the costs associated with traffic congestion, including lost productivity, wasted fuel, and increased healthcare expenditures due to pollution-related illnesses. Moreover, infrastructure projects like new metro lines or rapid bus routes can stimulate local economies by creating jobs and promoting sustainable urban growth.
Additionally, public transportation enhances social equity by providing affordable and accessible mobility for all citizens, including those who cannot afford personal vehicles. It reduces socioeconomic disparities by ensuring that individuals from various backgrounds can equally access employment opportunities, education, and essential services. For example, comprehensive bus networks in many European cities ensure that disadvantaged communities remain well-connected to city centres and economic hubs.
However, it must be acknowledged that public shipment systems require substantial upfront investment and ongoing maintenance, which could strain government budgets. Nonetheless, the long-term benefits clearly outweigh these initial costs.
In conclusion, the shift towards prioritizing public transport over avenue building is driven by crucial environmental, economic, and social imperatives. Despite initial financial challenges, this trend represents a profoundly positive development, fostering healthier environments, vibrant economies, and fairer societies.
Normal Body Temperatures
Body Core Temperature and Skin Temperature
The temperature of the deep tissues of the body—the “core” of the body—usually remains very constant, within ±1°F (±0.6°C), except when a person has a febrile illness. Indeed, a nude person can be exposed to temperatures as low as 55°F or as high as 130°F in dry air and still maintain an almost constant core temperature. The mechanisms for regulating body temperature represent a beautifully designed control system. In this chapter we discuss this system as it operates in health and in disease.
The skin temperature , in contrast to the core temperature , rises and falls with the temperature of the surroundings. The skin temperature is important when we refer to the skin’s loss of heat to the surroundings.
Normal Core Temperature
No single core temperature can be considered normal because measurements in many healthy people have shown a range of normal temperatures, as shown in Fig. 74.1 , from less than 97°F (36°C) to greater than 99.5°F (37.5°C). The average normal core temperature is generally considered to be between 98.0°F and 98.6°F when measured orally and about 1°F higher when measured rectally.
A diagram of a thermometer with temperature ranges for different activities and conditions, with Fahrenheit and Celsius values. The diagram of a thermometer represents the relationship between body temperature in Fahrenheit and Celsius under different conditions. The chart includes temperature ranges for activities like strenuous exercise at 104 degrees Fahrenheit or 40 degrees Celsius, emotions or moderate exercise at 102 degrees Fahrenheit or 39 degrees Celsius, and the usual range of normal body temperature at 98 degrees Fahrenheit or 37 degrees Celsius. It also indicates lower temperature ranges, such as early mornings or in cold weather at 96 degrees Fahrenheit or 36 degrees Celsius. The chart labels different temperature conditions for various age groups and physical conditions, such as hard work, emotions, and moderate activity.
Estimated normal range of body “core” temperature.
Body temperature increases during exercise and varies with temperature extremes of the surroundings because the temperature regulatory mechanisms are not perfect. When excessive heat is produced in the body by strenuous exercise, the temperature can rise temporarily to as high as 101°F to 104°F. Conversely, when the body is exposed to extreme cold, the temperature can fall below 96°F.
Body Temperature is Controlled by Balancing Heat Production and Heat Loss
When the rate of heat production in the body is greater than the rate at which heat is being lost, heat builds up in the body, and the body temperature rises. Conversely, when heat loss is greater than heat production, body temperature decreases. Most of the remainder of this chapter is concerned with this balance between heat production and heat loss and the mechanisms by which the body controls this production and loss.
Heat Production
Heat production is a principal by-product of metabolism. In Chapter 73 , which summarizes body energetics, we discuss the different factors that determine the rate of heat production, called the metabolic rate of the body . The most important of these factors are listed again here: (1) basal rate of metabolism of all the cells of the body; (2) extra rate of metabolism caused by muscle activity, including muscle contractions caused by shivering; (3) extra metabolism caused by the effect of thyroxine (and, to a lesser extent, other hormones, such as growth hormone and testosterone) on the cells; (4) extra metabolism caused by the effect of epinephrine, norepinephrine, and sympathetic stimulation on the cells; (5) extra metabolism caused by increased chemical activity in the cells, especially when the cell temperature increases; and (6) extra metabolism needed for digestion, absorption, and storage of food (thermogenic effect of food).
Heat Loss
Most of the heat produced in the body is generated in the deep organs, especially the liver, brain, and heart, and in the skeletal muscles during physical activity. This heat is then transferred from the deeper organs and tissues to the skin, where it is lost to the air and other surroundings. Therefore, the rate at which heat is lost is determined almost entirely by two factors: (1) how rapidly heat can be conducted from where it is produced in the body core to the skin and (2) how rapidly heat can then be transferred from the skin to the surroundings. Let us begin by discussing the system that insulates the core from the skin surface.
Insulator System of the Body
The skin, the subcutaneous tissues, and especially the fat of the subcutaneous tissues act together as a heat insulator for the body. The fat is important because it conducts heat only one-third as readily as other tissues. When no blood is flowing from the heated internal organs to the skin, the insulating properties of the normal male body are about equal to three-quarters the insulating properties of a usual suit of clothes. In women, this insulation is even better.
The insulation beneath the skin is an effective means of maintaining normal internal core temperature, even though it allows the temperature of the skin to approach the temperature of the surroundings.
Blood Flow to the Skin From the Body Core Provides Heat Transfer
Blood vessels are distributed profusely beneath the skin. Especially important is a continuous venous plexus that is supplied by inflow of blood from the skin capillaries, shown in Fig. 74.2 . In the most exposed areas of the body—the hands, feet, and ears—blood is also supplied to the plexus directly from the small arteries through highly muscular arteriovenous anastomoses .
A diagram of skin circulation represents the epidermis, dermis, subcutaneous tissue, and blood vessels. The diagram shows a cross-section of skin layers. It labels the epidermis, dermis, and subcutaneous tissue. Arteries branch upwards. They deliver oxygenated blood to a network of capillaries in the dermis. The capillaries connect to veins. These veins carry deoxygenated blood away. In the subcutaneous tissue, a venous plexus appears. An arteriole-venule anastomosis, a direct connection between an artery and a vein, is also present. Each component has a label. The diagram illustrates the circulatory system within the skin.
Figure 74.2
Skin circulation.
The rate of blood flow into the skin venous plexus can vary from barely above zero to as great as 30% of the total cardiac output. A high rate of skin flow causes heat to be conducted from the body core to the skin with great efficiency, whereas reduction in the rate of skin flow can greatly decrease heat conduction from the core to very little.
Fig. 74.3 shows quantitatively the effect of environmental air temperature on conductance of heat from the core to the skin surface and then conductance into the air, demonstrating an approximate 8-fold increase in heat conductance between the fully vasoconstricted state and the fully vasodilated state.
A line graph and the relationship between heat conductance through the skin and environmental temperature with vasoconstriction and vasodilated states. The line graph represents a relationship between environmental temperature in Fahrenheit and heat conductance through the skin, which is adjusted by the vasoconstriction and vasodilated states. The graph illustrates that heat conductance remains relatively low in a vasoconstrictive state, even as environmental temperature rises. However, as the temperature increases and the body transitions to a vasodilated state, heat conductance increases rapidly, especially at higher ecological temperatures over 90 degrees Fahrenheit, which indicates enhanced heat dissipation. A dashed line represents the vasodilated state, while the vasoconstrictive state is shown with solid points.
Figure 74.3
Effect of changes in the environmental temperature on heat conductance from the body core to the skin surface (in °F).
Modified from Benzinger TH. Heat and Temperature Fundamentals of Medical Physiology . New York: Dowden, Hutchinson & Ross; 1980.
Therefore, the skin is an effective controlled “ heat radiator ” system , and the flow of blood to the skin is a most effective mechanism for heat transfer from the body core to the skin.
Control of Heat Conduction to the Skin By the Sympathetic Nervous System
Heat conduction to the skin by the blood is controlled by the degree of vasoconstriction of the arterioles and the arteriovenous anastomoses that supply blood to the venous plexus of the skin. This vasoconstriction is controlled almost entirely by the sympathetic nervous system in response to changes in body core temperature and changes in environmental temperature, as discussed later in the chapter.
Basic Physics of Heat Loss From the Skin Surface
The various methods by which heat is lost from the skin to the surroundings are shown in Fig. 74.4 . They include radiation, conduction , and evaporation .
A diagram of the mechanisms of heat loss from the human body includes radiation, evaporation, conduction, and air currents. The diagram depicts heat transfer from a seated person. The illustration represents a person seated at a table. Text labels point to the person's body with percentages that indicate heat transfer occurs through different mechanisms. From top to bottom, the labels read radiation, 60 percent, evaporation, 22 percent, conduction to air, 15 percent, and conduction to objects, 3 percent.
Radiation Causes Heat Loss in the Form of Infrared Rays
As shown in Fig. 74.4 , about 60% of total heat loss is by radiation in a nude person sitting inside at normal room temperature.
Most infrared heat rays (a type of electromagnetic ray) that radiate from the body have wavelengths of 5 to 20 micrometers, 10 to 30 times the wavelengths of light rays. All objects that are not at absolute zero temperature radiate such rays. The human body radiates heat rays in all directions. Heat rays are also being radiated from the walls of rooms and other objects toward the body. If the temperature of the body is greater than the temperature of the surroundings, a greater quantity of heat is radiated from the body than is radiated to the body, and heat loss from the body occurs.
Conductive Heat Loss Occurs By Direct Contact With an Object
As shown in Fig. 74.4 , only minute quantities of heat, about 3%, are normally lost from the body by direct conduction from the surface of the body to solid objects , such as a chair or a bed. Loss of heat by conduction to air , however, represents a sizable proportion of the body’s heat loss (~15%), even under normal conditions.
Heat is actually the kinetic energy of molecular motion, and the molecules of the skin are continually undergoing vibratory motion. Much of the energy of this motion can be transferred to the air if the air is colder than the skin. Once the temperature of the air adjacent to the skin equals the temperature of the skin, no further loss of heat occurs in this way because now an equal amount of heat is conducted from the air to the body. Therefore, conduction of heat from the body to the air is self-limited unless the heated air moves away from the skin , so new, unheated air is continually brought in contact with the skin, a phenomenon called air convection .
Convective Heat Loss Results From Air Movement
Heat from the skin is first conducted to the air and then carried away by the convection air currents.
A small amount of convection almost always occurs around the body because of the tendency for air adjacent to the skin to rise as it becomes heated. Therefore, in a nude person seated in a comfortable room without gross air movement, about 15% of the person’s total heat loss occurs by conduction to the air and then by air convection away from the body.
Cooling Effect of Wind
When the body is exposed to wind, the layer of air immediately adjacent to the skin is replaced by new air much more rapidly than is normal, and heat loss by convection increases accordingly. The cooling effect of wind at low velocities is about proportional to the square root of the wind velocity . For example, a wind of 4 miles per hour is about twice as effective for cooling as a wind of 1 mile per hour.
Conduction and Convection of Heat From a Person Suspended in Water
Water has a specific heat several thousand times greater than air, so each unit portion of water adjacent to the skin can absorb far greater quantities of heat than can be absorbed by air. Also, heat conductivity in water is much greater than in air. Consequently, it is impossible for the body to heat a thin layer of water next to the body to form an “insulator zone” as occurs in air. Therefore, if the temperature of the water is below body temperature the rate of heat loss to water is usually many times greater than the rate of heat loss to air.
Evaporation
When water evaporates from the body surface, 0.58 Calorie (kilocalorie) of heat is lost for each gram of water that evaporates. Even when a person is not sweating, water still evaporates insensibly from the skin and lungs at a rate of about 600 to 700 mL/day. This insensible evaporation causes continual heat loss at a rate of 16 to 19 Calories per hour. Insensible evaporation through the skin and lungs cannot be controlled for purposes of temperature regulation because it results from continual diffusion of water molecules through the skin and respiratory surfaces. However, loss of heat by evaporation of sweat can be controlled by regulating the rate of sweating, as discussed later in this chapter.
Evaporation Is a Necessary Cooling Mechanism at Very High Air Temperatures
As long as skin temperature is greater than the temperature of the surroundings, heat can be lost by radiation and conduction. However, when the temperature of the surroundings becomes greater than that of the skin, instead of losing heat, the body gains heat by both radiation and conduction. Under these conditions, the only means by which the body can rid itself of heat is by evaporation .
Therefore, anything that prevents adequate evaporation when the surrounding temperature is higher than the skin temperature will cause the internal body temperature to rise. This phenomenon occurs occasionally in human beings who are born with congenital absence of sweat glands. These people can tolerate cold temperatures as well as people with normal sweat glands, but they can become severely stressed and die of heatstroke in tropical zones because, without the evaporative refrigeration system, they cannot prevent a rise in body temperature when the air temperature is greater than that of the body.
Clothing Reduces Conductive and Convective Heat Loss
Clothing entraps air next to the skin in the weave of the cloth, thereby increasing the thickness of the air zone adjacent to the skin and decreasing the flow of convection air currents. Consequently, the rate of heat loss from the body by conduction and convection is greatly depressed. A usual suit of clothes decreases the rate of heat loss to about half that from the nude body, but arctic-type clothing can decrease this heat loss to as little as one-sixth.
About half the heat transmitted from the skin to the clothing is radiated to the clothing instead of being conducted across the small intervening space. Therefore, coating the inside of clothing with a thin layer of metal, such as silver or gold, which reflects radiant heat back to the body, makes the insulating properties of clothing far more effective than otherwise. By using this technique, clothing for use in the Arctic can be decreased in weight by about half.
The effectiveness of clothing in maintaining body temperature is almost completely lost when the clothing becomes wet because the high conductivity of water increases the rate of heat transmission through cloth 20-fold or more. Therefore, one of the most important factors for protecting the body against cold in Arctic regions is extreme caution against allowing the clothing to become wet. Indeed, one must be careful not to become overheated because sweating in one’s clothes makes them much less effective thereafter as an insulator.
The Hypothalamus and Sympathetic Nervous System Regulate Sweating
Stimulation of the anterior hypothalamus-preoptic area in the brain either electrically or by excess heat causes sweating. The nerve impulses from this area that cause sweating are transmitted in the autonomic pathways to the spinal cord and then through sympathetic outflow to the skin.
It should be recalled from the discussion of the autonomic nervous system in Chapter 61 that the sweat glands are innervated by cholinergic nerve fibers (fibers that secrete acetylcholine but that run in the sympathetic nerves along with the adrenergic fibers). These glands can also be stimulated to some extent by epinephrine or norepinephrine circulating in the blood, even though the glands themselves do not have adrenergic innervation. This mechanism is important during exercise, when these hormones are secreted by the adrenal medullae and the body needs to lose increased amounts of heat produced by the active muscles.
Mechanism of Sweat Secretion
In Fig. 74.5 , the sweat gland is shown to be a tubular structure consisting of two parts: (1) a deep subdermal coiled portion that secretes the sweat, and (2) a duct portion that passes outward through the dermis and epidermis of the skin. As is true of many other glands, the secretory portion of the sweat gland secretes a fluid called the primary secretion or precursor secretion ; the concentrations of constituents in the fluid are then modified as the fluid flows through the duct.
A diagram of the process of sweat secretion, absorption of ions, and primary secretion in the skin. The diagram depicts the sweat secretion and absorption process in the skin. It includes the gland responsible for the primary secretion of protein-free filtrate. The duct, where absorption occurs, mainly of sodium and chloride ions, and the pore, through which sweat exits. The diagram also depicts the dermis and epidermis and the sympathetic nerve's connection to the gland.
Sweat gland innervated by an acetylcholine-secreting sympathetic nerve. A primary protein-free secretion is formed by the glandular portion, but most of the electrolytes are reabsorbed in the duct, leaving a dilute, watery secretion.
The precursor secretion is an active secretory product of the epithelial cells lining the coiled portion of the sweat gland. Cholinergic sympathetic nerve fibers ending on or near the glandular cells elicit the secretion.
The composition of the precursor secretion is similar to that of plasma, except that it does not contain plasma proteins. The concentration of sodium is about 142 mEq/L and that of chloride is about 104 mEq/L, with much smaller concentrations of the other solutes of plasma. As this precursor solution flows through the duct portion of the gland, it is modified by reabsorption of most of the sodium and chloride ions. The degree of this reabsorption depends on the rate of sweating.
When the sweat glands are stimulated only slightly, the precursor fluid passes through the duct slowly. In this case, essentially all the sodium and chloride ions are reabsorbed, and the concentration of each falls to as low as 5 mEq/L. This process reduces the osmotic pressure of the sweat fluid to such a low level that most of the water is also reabsorbed, which concentrates most of the other constituents. Therefore, at low rates of sweating, such constituents as urea, lactic acid, and potassium ions are usually very concentrated.
Conversely, when the sweat glands are strongly stimulated by the sympathetic nervous system, large amounts of precursor secretion are formed, and the duct may reabsorb only slightly more than half the sodium chloride; the concentrations of sodium and chloride ions are then (in an unacclimatized person) a maximum of about 50 to 60 mEq/L, slightly less than half the concentrations in plasma. Furthermore, the sweat flows through the glandular tubules so rapidly that little of the water is reabsorbed. Therefore, the other dissolved constituents of sweat are only moderately increased in concentration; urea is about twice that in the plasma, lactic acid about 4 times, and potassium about 1.2 times as concentrated as in plasma.
A significant loss of sodium chloride occurs in the sweat when a person is unacclimatized to heat. Much less electrolyte loss occurs, despite increased sweating capacity, once a person has become acclimatized.
Acclimatization of the Sweating Mechanism to Heat—The Role of Aldosterone
Although an unacclimatized person seldom produces more than about 1 liter of sweat per hour, a person exposed to hot weather for 1 to 6 weeks sweats more profusely, often increasing maximum sweat production to as much as 2 to 3 L/hr. Evaporation of this much sweat can remove heat from the body at a rate more than 10 times the normal basal rate of heat production. This increased effectiveness of the sweating mechanism is caused by a change in the internal sweat gland cells to increase their sweating capability.
Also associated with acclimatization is a further decrease in the concentration of sodium chloride in the sweat, which allows progressively better conservation of body salt. Most of this effect is caused by increased secretion of aldosterone by the adrenocortical glands, which results from a slight decrease in sodium chloride concentration in the extracellular fluid and plasma. An unacclimatized person who sweats profusely often loses 15 to 30 grams of salt each day for the first few days. After 4 to 6 weeks of acclimatization, the loss is usually only 3 to 5 g/day.
Heat acclimatization is transient and disappears in a few weeks if not maintained by repeated heat exposure.
Loss of Heat By Panting
Many animals have little ability to lose heat from the surfaces of their bodies, for two main reasons: (1) the surfaces are often covered with fur, and (2) the skin of most animals is not supplied with sweat glands, which prevents most of the evaporative loss of heat from the skin. A substitute mechanism, the panting mechanism, is used by many animals as a means of dissipating heat.
The phenomenon of panting is “turned on” by the thermoregulator centers of the brain. That is, when the blood becomes overheated, the hypothalamus initiates neurogenic signals to decrease the body temperature. One of these signals initiates panting. The actual panting process is controlled by a panting center that is associated with the pneumotaxic respiratory center located in the pons.
When an animal pants, it breathes in and out rapidly, and thus large quantities of new air from the exterior come in contact with the upper portions of the respiratory passages. This mechanism cools the blood in the respiratory passage mucosa as a result of water evaporation from the mucosal surfaces, especially evaporation of saliva from the tongue. Yet, panting does not increase the alveolar ventilation more than is required for proper control of the blood gases because each breath is extremely shallow; therefore, most of the air that enters the alveoli is dead-space air mainly from the trachea and not from the atmosphere.
Regulation of Body Temperature—Role of the Hypothalamus
Fig. 74.6 shows what happens to the body “core” temperature of a nude person after a few hours of exposure to dry air ranging from 30°F to 160°F. The precise dimensions of this curve depend on the wind movement of the air, the amount of moisture in the air, and even the nature of the surroundings. In general, a nude person in dry air between 55°F and 130°F is capable of maintaining a normal body core temperature somewhere between 97°F and 100°F.
A line graph depicts the relationship between atmospheric and body temperature. The line graph depicts the relationship between atmospheric temperature in degrees Fahrenheit and body temperature in degrees Fahrenheit. The graph illustrates that the body temperature gradually rises and reaches a plateau as the atmospheric temperature increases from around 30 degrees Fahrenheit to 100 degrees Fahrenheit. After this point, as the atmospheric temperature rises beyond 100 degrees Fahrenheit, body temperature sharply increases, which indicates a potentially dangerous rise in body temperature.
Figure 74.6
Effect of high and low atmospheric temperatures of several hours’ duration, under dry conditions, on the internal body core temperature (in °F). Note that the internal body temperature remains stable despite wide changes in atmospheric temperature.
The temperature of the body is regulated almost entirely by nervous feedback mechanisms, and almost all these mechanisms operate through temperature-regulating centers located in the hypothalamus . For these feedback mechanisms to operate, there must also be temperature detectors to determine when body temperature becomes too high or too low.
Role of the Anterior Hypothalamic-Preoptic Area in Thermostatic Detection of Temperature
The anterior hypothalamic-preoptic area contains large numbers of heat-sensitive neurons, as well as about one-third as many cold-sensitive neurons. These neurons are believed to function as temperature sensors for controlling body temperature. The heat-sensitive neurons increase their firing rate 2- to 10-fold in response to an increase of 10°C in body temperature. The cold-sensitive neurons, by contrast, increase their firing rate when body temperature falls.
When the preoptic area is heated, the skin all over the body immediately breaks out in a profuse sweat and the skin blood vessels over the entire body become greatly dilated. This response is an immediate reaction to cause the body to lose heat, thereby helping to return the body temperature toward the normal level. In addition, any excess body heat production is inhibited. Therefore, the hypothalamic-preoptic area serves as a thermostatic body temperature control center.
Receptors in the Skin and Deep Body Tissues Detect Temperature
Although the signals generated by the temperature receptors of the hypothalamus are extremely powerful in controlling body temperature, receptors in other parts of the body play additional roles in temperature regulation. This is especially true of temperature receptors in the skin and in a few specific deep tissues of the body.
Recall from the discussion of sensory receptors in Chapter 49 that the skin is endowed with both cold and warmth receptors. The skin has far more cold receptors than warmth receptors—in fact, 10 times as many in many parts of the skin. Therefore, peripheral detection of temperature mainly concerns detecting cool and cold instead of warm temperatures.
Although the molecular mechanisms for sensing changes in temperature are not fully understood, experimental studies in various animal models, including Drosophila (fruit flies), rodents, and cats, indicate that the transient receptor potential (TRP) family of cation channels , found in somatosensory neurons and epidermal cells, mediate thermal sensation over a wide range of temperatures ( Table 74.1 ).
Summary of Transient Receptor Potential (TRP) Proteins That Serve as Heat Sensors and Cold Sensors a
TRP Protein Temperature Activation Threshold (°C)
Heat Sensors
TRPV1 ≥42
TRPV2 ≥52
TRPV3 ≥32
TRPV4 ≥27
Cold Sensors
TRPC5 ≤25
TRPM8 ≤27
TRPA1 ≤17
When the skin is chilled over the entire body, immediate reflex effects are invoked and begin to increase the temperature of the body in several ways: (1) by stimulating shivering, with a resultant increase in the rate of body heat production; (2) by inhibiting sweating, if this is already occurring; and (3) by promoting skin vasoconstriction to diminish loss of body heat from the skin.
Deep body temperature receptors are found mainly in the spinal cord , in the abdominal viscera , and in or around the great veins in the upper abdomen and thorax. These deep receptors function differently from the skin receptors because they are exposed to the body core temperature rather than the body surface temperature. Yet, like the skin temperature receptors, they detect mainly cold rather than warmth. Thus, the skin and the deep body receptors are likely concerned with preventing hypothermia —low body temperature.
Posterior Hypothalamus Integrates Central and Peripheral Temperature Sensory Signals
Even though many temperature sensory signals arise in peripheral receptors, these signals contribute to body temperature control mainly through the hypothalamus. The area of the hypothalamus that they stimulate is located bilaterally in the posterior hypothalamus approximately at the level of the mammillary bodies. The temperature sensory signals from the anterior hypothalamic-preoptic area are also transmitted into this posterior hypothalamic area. Here the signals from the preoptic area and the signals from elsewhere in the body are combined and integrated to control the heat-producing and heat-conserving reactions of the body.
Neuronal Effector Mechanisms that Decrease or Increase Body Temperature
When the hypothalamic temperature centers detect that body temperature is either too high or too low, they institute appropriate temperature-decreasing or temperature-increasing responses. The reader is probably familiar with most of these procedures from personal experience, but special features are described in the following sections.
Temperature-Decreasing Mechanisms When the Body Is Too Hot
The temperature control system uses three important mechanisms to reduce body heat when the body temperature becomes too great:
1.
Vasodilation of skin blood vessels . In almost all areas of the body, the skin blood vessels become intensely dilated due to inhibition of the sympathetic centers in the posterior hypothalamus that cause vasoconstriction. Full vasodilation can increase the rate of heat transfer to the skin as much as 8-fold.
2.
Sweating . The effect of increased body temperature to cause sweating is demonstrated by the blue curve in Fig. 74.7 , which shows a sharp increase in the rate of evaporative heat loss resulting from sweating when the body core temperature rises above the critical level of 37.1°C (98.8°F). An additional 1°C increase in body temperature causes enough sweating to remove 10 times the basal rate of body heat production.
A line graph depicts the relationship between head temperature, heat production, and evaporative heat loss. The line graph depicts the relationship between head temperature in Celsius and the rate of heat production and evaporative heat loss in calories per second. As head temperature increases from 36.4 degrees Celsius to 37 degrees Celsius, heat production rises and peaks at around 37 degrees Celsius. At the same time, evaporative heat loss remains low. The heat production level decreases after it reaches 37 degrees Celsius, while evaporative heat loss sharply increases. This represents the body's response to regulate temperature through heat production and evaporation.
Figure 74.7
Effect of hypothalamic temperature on evaporative heat loss from the body and on heat production caused primarily by muscle activity and shivering (in °C). This figure demonstrates the extremely critical temperature level at which increased heat loss begins and heat production reaches a minimum stable level.
3.
Decreased heat production . The mechanisms that cause excess heat production, such as shivering and chemical thermogenesis, are strongly inhibited.
Temperature-Increasing Mechanisms When the Body Is Too Cold
When the body is too cold, the temperature control system institutes procedures opposite of those when the body is too hot:
1.
Skin vasoconstriction throughout the body . This vasoconstriction is caused by stimulation of the posterior hypothalamic sympathetic centers.
2.
Piloerection . Piloerection means hairs “standing on end.” Sympathetic stimulation causes the arrector pili muscles attached to the hair follicles to contract, which brings the hairs to an upright stance and produces “ goose bumps ” on the skin at the base of the hairs. This mechanism is not important in human beings, but in many animals, upright projection of the hairs allows them to entrap a thick layer of “insulator air” next to the skin, so transfer of heat to the surroundings is greatly reduced.
3.
Increased thermogenesis (heat production) . Heat production by the metabolic systems is increased by promoting shivering, sympathetic excitation of heat production, and thyroxine secretion, as discussed in the following sections.
Hypothalamic Stimulation of Shivering
Located in the dorsomedial portion of the posterior hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering . This area is normally inhibited by signals from the heat center in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord. Therefore, as shown by the sudden increase in “heat production” (see the red curve in Fig. 74.7 ), this center becomes activated when the body temperature falls even a fraction of a degree below a critical temperature level. It then transmits signals that cause shivering through bilateral tracts down the brain stem, into the lateral columns of the spinal cord, and finally to the anterior motor neurons. These signals are nonrhythmic and do not cause the actual muscle shaking. Instead, they increase the tone of the skeletal muscles throughout the body by facilitating activity of the anterior motor neurons. When the tone rises above a certain critical level, shivering begins. This reaction probably results from feedback oscillation of the muscle spindle stretch reflex mechanism, which is discussed in Chapter 55 . During maximum shivering, body heat production can rise to four to five times normal .
Sympathetic “Chemical” Excitation of Heat Production
As noted in Chapter 73 , an increase in either sympathetic stimulation or circulating norepinephrine and epinephrine in the blood can rapidly increase the rate of cellular metabolism. This effect is called chemical thermogenesis , or nonshivering thermogenesis . It results at least partially from the ability of norepinephrine and epinephrine to uncouple oxidative phosphorylation, which means that excess foodstuffs are oxidized and thereby release energy in the form of heat but do not cause ATP to be formed.
The degree of chemical thermogenesis that occurs in an animal is almost directly proportional to the amount of brown fat in the animal’s tissues. This type of fat contains large numbers of special mitochondria where uncoupled oxidation occurs, as described in Chapter 73 . Brown fat is richly supplied with sympathetic nerves that release norepinephrine, which stimulates tissue expression of mitochondrial uncoupling protein 1 ( UCP1 , also called thermogenin ) and increases thermogenesis.
Acclimatization affects the intensity of chemical thermogenesis; some animals, such as rats and mice that have been exposed to a cold environment for several weeks, exhibit a 100% to 500% increase in heat production when acutely exposed to cold, in contrast to unacclimatized animals, which respond with an increase of perhaps one-third as much. This increased thermogenesis also leads to a corresponding increase in food intake.
In adult human beings, who have only small amounts of brown fat, it is rare for chemical thermogenesis to increase the rate of heat production more than 10% to 15%. However, in infants, who do have greater amounts of brown fat in their interscapular space, chemical thermogenesis can increase the rate of heat production 100%, which is probably an important factor in maintaining normal body temperature in neonates.
Increased Thyroxine Output as a Long-Term Cause of Increased Heat Production
Cooling the anterior hypothalamic-preoptic area also increases production of the neurosecretory hormone thyrotropin-releasing hormone by the hypothalamus. This hormone is carried by way of the hypothalamic portal veins to the anterior pituitary gland, where it stimulates secretion of thyroid-stimulating hormone .
Thyroid-stimulating hormone in turn stimulates increased output of thyroxine by the thyroid gland, as explained in Chapter 77 . The increased thyroxine activates uncoupling protein and increases the rate of cellular metabolism throughout the body, which is yet another mechanism of chemical thermogenesis . This increase in metabolism does not occur immediately but requires several weeks’ exposure to cold to make the thyroid gland hypertrophy and reach its new level of thyroxine secretion.
Exposure of animals to extreme cold for several weeks can cause their thyroid glands to increase in size 20% to 40%. However, human beings seldom allow themselves to be exposed to the same degree of cold as that to which many animals are often subjected. Therefore, the quantitative importance of the thyroid mechanism in humans for adaptation to cold is still uncertain.
Isolated measurements have shown that metabolic rates increase in military personnel residing for several months in the Arctic; some of the Inuit, the indigenous people who inhabit the Arctic regions of Alaska, Canada, or Greenland, also have abnormally high basal metabolic rates. Further, the continuous stimulatory effect of cold on the thyroid gland may explain the much higher incidence of toxic thyroid goiters in people who live in cold climates than in those who live in warm climates.
“Set Point” for Temperature Control
In the example of Fig. 74.7 , it is clear that at a critical body core temperature of about 37.1°C (98.8°F), drastic changes occur in the rates of heat loss and heat production. At temperatures above this level, heat loss is greater than heat production, so the body temperature falls and approaches the 37.1°C level. At temperatures below this level, heat production is greater than heat loss, so body temperature rises and again approaches the 37.1°C level. This crucial temperature level is called the “set point” of the temperature control mechanism—that is, all the temperature control mechanisms continually attempt to bring the body temperature back to this set point level.
Feedback Gain for Body Temperature Control
As discussed in Chapter 1 , feedback gain is a measure of the effectiveness of a control system. In the case of body temperature control, it is important for the internal core temperature to change as little as possible, even though the environmental temperature might change greatly from day to day or even hour to hour. The feedback gain of the temperature control system is equal to the ratio of the change in environmental temperature to the change in body core temperature minus 1.0 (see Chapter 1 for this formula). Experiments have shown that the body temperature of humans changes about 1°C for each 25° to 30°C-change in environmental temperature. Therefore, the feedback gain of the total mechanism for body temperature control averages about 27 (28/1.0 − 1.0 = 27), which is an extremely high gain for a biological control system; the baroreceptor arterial pressure control system, by comparison, has a feedback gain of <2.
Skin Temperature Can Slightly Alter the Set Point for Core Temperature Control
The critical temperature set point in the hypothalamus above which sweating begins and below which shivering begins is determined mainly by the degree of activity of the heat temperature receptors in the anterior hypothalamic-preoptic area. However, temperature signals from the peripheral areas of the body, especially from the skin and certain deep body tissues (e.g., spinal cord and abdominal viscera), also contribute slightly to body temperature regulation by altering the set point of the hypothalamic temperature control center. This effect is shown in Figs . 74.8 and 74.9 .
A line graph depicts the relationship between internal head temperature and evaporative heat loss, with sweat and skin temperature indicated. The line graph illustrates the relationship between internal head temperature in degrees Celsius and evaporative heat loss in calories per second. As internal head temperature increases, evaporative heat loss rises, with a marked increase between 33 degrees Celsius and 39 degrees Celsius, where sweating begins. The set point for heat regulation is indicated, below which insensible evaporation occurs. Skin temperature is also shown at various points, with a drop in skin temperature as the internal head temperature decreases to 29 degrees Celsius. The graph helps to visualize how the body responds to changes in temperature by regulating heat loss through evaporation and sweating.
Effect of changes in the internal head temperature on the rate of evaporative heat loss from the body (in °C). Note that the skin temperature determines the set point level at which sweating begins.
Courtesy Dr. T.H. Benzinger.
Fig. 74.8 demonstrates the effect of different skin temperatures on the set point for sweating, showing that the set point increases as skin temperature decreases. Thus, for the person represented in this figure, the hypothalamic set point increased from 36.7°C when the skin temperature was higher than 33°C to a set point of 37.4°C when the skin temperature had fallen to 29°C. Therefore, when the skin temperature was high, sweating began at a lower hypothalamic temperature than when the skin temperature was low. Such a system is valuable because it is important that sweating be inhibited when the skin temperature is low; otherwise, the combined effect of low skin temperature and sweating could cause far too much loss of body heat.
A similar effect occurs in shivering, as shown in Fig. 74.9 . When the skin becomes cold, it drives the hypothalamic centers to the shivering threshold even when the hypothalamic temperature is still on the hot side of normal. Here again, the control system is valuable because a cold skin temperature would soon lead to a deeply depressed body temperature unless heat production were increased. Thus, a cold skin temperature actually “anticipates” a fall in internal body temperature and prevents it.
A line graph depicts the relationship between internal head temperature and heat production, shivering, and skin temperature. The line graph represents the relationship between internal head temperature in Celsius and heat production in calories per second. As the internal head temperature decreases, heat production rises due to mechanisms such as shivering. The graph represents skin temperature ranges from 20 Celsius to 31 Celsius at different levels of internal head temperature. The basal heat production level is indicated at the set point. As the body cools, heat production increases, with shivering that contributes significantly to the rise in heat production as skin temperature decreases.
Figure 74.9
Effect of changes in the internal head temperature on the rate of heat production by the body (in °C). Note that the skin temperature determines the set point level at which shivering begins.
Courtesy Dr. T.H. Benzinger.
Behavioral Control of Body Temperature
Aside from the subconscious mechanisms for body temperature control, the body has another temperature-control mechanism that is even more potent— behavioral control of temperature .
Whenever the internal body temperature becomes too high, signals from the temperature-controlling areas in the brain give the person a psychic sensation of being overheated. Conversely, whenever the body becomes too cold, signals from the skin and probably also from some deep body receptors elicit the feeling of cold discomfort. Therefore, the person makes appropriate environmental adjustments to reestablish comfort, such as moving into a heated room or wearing well-insulated clothing in freezing weather. Behavioral control of temperature is the only really effective mechanism to maintain body heat control in severely cold environments.
Local Skin Temperature Reflexes
When a person places a foot under a hot lamp and leaves it there for a short time, local vasodilation and mild local sweating occur. Conversely, placing the foot in cold water causes local vasoconstriction and local cessation of sweating. These reactions are caused by local effects of temperature directly on the blood vessels and also by local cord reflexes conducted from skin receptors to the spinal cord and back to the same skin area and the sweat glands. The intensity of these local effects is, in addition, controlled by the central nervous system, so their overall effect is proportional to the hypothalamic heat control signal times the local signal. Such reflexes can help prevent excessive heat exchange from locally cooled or heated portions of the body.
Regulation of Internal Body Temperature Is Impaired After the Spinal Cord Is Severed
If the spinal cord is severed in the neck above the sympathetic outflow from the cord, regulation of body temperature becomes extremely poor because the hypothalamus can no longer control either skin blood flow or the degree of sweating anywhere in the body. This is true even though the local temperature reflexes originating in the skin, spinal cord, and intraabdominal receptors still exist. These reflexes are extremely weak in comparison with hypothalamic control of body temperature.
In people with this condition, body temperature must be regulated principally by the patient’s psychic response to cold and hot sensations in the head region—that is, by behavioral control of clothing and by moving into an appropriately warm or cold environment.
Abnormalities of Body Temperature Regulation
Fever
Fever, which means a body temperature above the usual range of normal, can be caused by abnormalities in the brain or by toxic substances that affect the temperature-regulating centers. Some causes of fever (and also of subnormal body temperatures) are presented in Fig. 74.10 . They include bacterial or viral infections, brain tumors, and environmental conditions that may terminate in heatstroke.
A diagram of a thermometer shows a temperature scale that indicates the upper and lower limits of survival, with categories for temperature regulation and related health conditions. The diagram of a thermometer explains a temperature scale in Fahrenheit and Celsius, which illustrates different ranges for human survival and temperature regulation. The upper limit of survival is marked at 114 degrees Fahrenheit, where heatstroke, brain lesions, and fever therapy may occur. The usual range of standard temperature is between 98 degrees Fahrenheit and 100 degrees Fahrenheit. The diagram shows where temperature regulation becomes impaired, lost, or seriously impaired as the temperature decreases. The lower survival limit is indicated at 74 degrees Fahrenheit, where temperature regulation is lost. The diagram helps to understand the physiological limits for temperature regulation in the human body and the potential health risks.
Resetting the Hypothalamic Temperature-Regulating Center in Febrile Diseases—Effect of Pyrogens
Many proteins, breakdown products of proteins, and certain other substances, especially lipopolysaccharide toxins released from bacterial cell membranes, can cause the set point of the hypothalamic thermostat to rise. Substances that cause this effect are called pyrogens .
Pyrogens released from toxic bacteria or those released from degenerating body tissues cause fever during disease conditions. When the set point of the hypothalamic temperature-regulating center becomes higher than normal, all the mechanisms for raising the body temperature are brought into play, including heat conservation and increased heat production. Within a few hours after the set point has been increased, the body temperature also approaches this level, as shown in Fig. 74.11 .
A line graph depicts the body's temperature regulation response to a sudden change in thermostat set point. The line graph depicts the temperature of the body regulation when the thermostat set point is suddenly raised to a high value. The horizontal axis represents time in hours, and the vertical axis represents body temperature in Fahrenheit. Initially, the body temperature gradually increases as the set point rises, which leads to chills that include vasoconstriction, piloerection, epinephrine secretion, and shivering. At a crisis point, the body temperature peaks, followed by a sudden decrease in the thermostat set point, which triggers vasodilation and sweat to return the body temperature to normal.
Effects of changing the set point of the hypothalamic temperature controller.
Mechanism of Action of Pyrogens in Causing Fever—Role of Cytokines
Experiments in animals have shown that some pyrogens, when injected into the hypothalamus, can act directly and immediately on the hypothalamic temperature-regulating center to increase its set point. Other pyrogens function indirectly and may require several hours of latency before causing their effects. This is true of many of the bacterial pyrogens, especially the endotoxins from gram-negative bacteria.
When bacteria or breakdown products of bacteria are present in the tissues or in the blood, they are phagocytized by the blood leukocytes, by tissue macrophages , and by large granular killer lymphocytes , as discussed in Chapter 34 . All these cells digest the bacterial products and then release cytokines, a diverse group of pep
El Derecho Constitucional, es el ordenamiento jurídico fundamental y supremo, que organiza jurídica y políticamente al Estado, a través de la Constitución Nacional. Determina la forma del Estado y su forma de gobierno, competencias y atribuciones, fines estatales, derechos y garantías de los habitantes. Regula la organización de todo el derecho -ya que determina su validez y vigencia-, sentando principios básicos a través de Declaraciones, y determina las relaciones entre particulares, entre éstos y el Estado, y las obligaciones que de ellas se desprenden.
El derecho a la jurisdicción lo tienen todas las personas sean físicas o jurídicas, en la medida en que dispongan de capacidad para ser parte en un proceso judicial. Se trata de un derecho que debe ser ejercido por medio de las vías legales previamente establecidas. Este derecho se vincula en forma inescindible con la necesidad de jueces naturales realmente imparciales, probos e idóneos, con la existencia efectiva de órganos judiciales suficientes y con dotación de personal, recursos económicos y procedimientos adecuados.
El Superior Tribunal de Justicia tiene, en lo judicial, las siguientes atribuciones, con arreglo a las normas legales respectivas: Ejerce jurisdicción ordinaria y exclusiva en los siguientes casos: a) en las demandas por inconstitucionalidad de leyes, decretos, ordenanzas, reglamentos o resoluciones, que se promuevan directamente por vía de acción; b) en los recursos de revisión, en los casos que la ley lo establezca; c) en los conflictos entre los poderes públicos de la Provincia y en los que se suscitaren entre los tribunales de justicia con motivo de su jurisdicción respectiva; d) en los conflictos de las municipalidades entre sí y entre éstas y los poderes del Estado.
El juicio por jurados es un procedimiento judicial en el cual doce (12) ciudadanos y ciudadanas (seis hombres y seis mujeres), como integrantes de un jurado popular, deciden sobre la culpabilidad o no culpabilidad de otro ciudadano acusado de cometer un delito grave. Este sistema permite mayor imparcialidad ya que la decisión no está basada en una sola persona sino en un jurado accidental y heterogéneo de 12 personas que no está involucrado en el proceso judicial previo ni pertenece al Poder Judicial.
Es inviolable la defensa de la persona y de los derechos en todo procedimiento judicial. Nadie podrá ser juzgado por otros jueces que los designados de acuerdo con la Constitución y competentes según sus leyes reglamentarias; penado sin juicio previo fundado en ley anterior al hecho del proceso y substanciado conforme a las disposiciones de esta ley; ni considerado culpable mientras una sentencia firme no lo declare tal.
La persona a quien se le imputare la comisión de un delito por el que se está instruyendo causa tiene derecho, aun cuando no hubiere sido indagada, a presentarse al tribunal, personalmente o por medio de un defensor, para que se le informe sobre los hechos que se le atribuyen y las pruebas existentes en su contra. El imputado tendrá derecho a hacerse defender por abogados de su confianza o por el Defensor Oficial.
La investigación penal preparatoria deberá impedir que el delito cometido produzca consecuencias ulteriores y reunir las pruebas útiles para dar base a la acusación o determinar el sobreseimiento. El Ministerio Público Fiscal practicará y hará practicar todos los actos de la investigación. Dirigirá a la Policía Judicial y podrá encomendarle diligencias, pero la dirección de la investigación y la responsabilidad de sus resultados estarán siempre a su cargo.
El juez de garantías podrá ordenar una pericia siempre que para conocer o apreciar algún hecho o circunstancia importante en la causa, sean necesarios o convenientes conocimientos especiales en alguna ciencia, arte o técnica. Los peritos deberán tener título de tales en la materia a que pertenezca el punto sobre el que han de expedirse. Si la profesión no estuviere reglamentada o no hubiere peritos diplomados, deberá designarse a persona de conocimiento o práctica reconocidos.
Las decisiones del Juez de Garantías o del Tribunal serán dadas a conocer como providencias, autos o sentencias. Dictará sentencia para poner término al proceso, después de su íntegra tramitación; auto, para resolver un incidente o artículo del proceso o cuando este Código lo disponga; y providencia en los demás casos. Las providencias se dictarán en el plazo de veinticuatro horas. Los autos y las sentencias, salvo disposición en contrario, en un plazo máximo de cinco y veinte días respectivamente.
with her husband,
with her husband,
with her husband,
with her husband,
with her husband,
grows up." 1973. Picasso 1973. printmaker, 1973. stage 1973. regarded 1973.
Cours complet – De la cellule à l’être humain
Licence 1 Psychologie – UE 2.3
Dr Lucas De Zorzi – Université de Lille (2024-2025)
Bloc obligatoire – 3 ECTS (≈ 75–90h de travail)
24h en présence
\~60h travail personnel (révisions, préparation aux épreuves)
\---
I. Introduction générale
1\. Objectifs du cours
Initier à la biologie cellulaire et à la psychobiologie.
Relier la cellule, base du vivant, à la compréhension des comportements humains.
2\. Attention et apprentissage
Multitâche numérique = baisse de performance (ex. SMS → -22 % sur les notes).
Gêne collective + perte d’efficacité.
👉 Conseil : limiter distractions numériques pendant les cours.
\---
II. La biologie : science de la vie
1\. Définition
Du grec bios (vie) + logos (science).
Étude scientifique du vivant.
2\. Sous-disciplines (niveaux d’organisation)
Population : écologie.
Organisme : physiologie.
Systèmes/organes : anatomie, physiologie.
Tissus : histologie.
Cellules : biologie cellulaire.
Molécules : biochimie, biologie moléculaire.
\---
III. Caractéristiques du vivant
A) Organisation cellulaire
Cellule = plus petite unité du vivant.
Capable de réagir, se reproduire, évoluer.
2 types :
Procaryotes : primitifs, sans noyau (ex. bactéries).
Eucaryotes : plus complexes, avec noyau (animales, végétales).
Cas particulier : virus → nécessite un hôte.
B) Métabolisme
Ensemble des réactions chimiques internes.
Permet :
Extraction et transformation d’énergie.
Synthèse de molécules et réserves.
Outils spécifiques : ADN/ARN, enzymes.
C) Reproduction
Division cellulaire :
Mitose : croissance, réparation.
Méiose : reproduction sexuée.
Mort programmée = apoptose.
D) Variation et évolution
Variabilité génétique (ADN différent au sein d’une même espèce).
Sélection naturelle → survie des individus avantagés.
Développement du cerveau → nouveaux comportements (mémoire, apprentissage, coopération).
\---
IV. Organisation de la cellule eucaryote
1\. Éléments principaux
Membrane plasmique.
Noyau.
Cytoplasme : cytosol + organites (mitochondries, RE, etc.).
2\. Composition chimique
Lipides ≈ 35 %.
Protéines ≈ 55 %.
Glucides ≈ 10 %.
👉 Protéines = fonctions essentielles (enzymes, structure, récepteurs).
👉 Association glucides/lipides/protéines → glycolipides, glycoprotéines.
\---
V. La membrane plasmique
1\. Structure
Bicouche de phospholipides :
Têtes hydrophiles (vers extérieur/intérieur aqueux).
Queues hydrophobes (au centre).
Cholestérol = stabilité.
Protéines membranaires : transmembranaires, périphériques.
Glucides orientés vers extérieur → glycocalyx.
2\. Modèle de Singer & Nicolson (1973)
Mosaïque fluide : hétérogénéité + mobilité.
3\. Rôles
Barrière sélective.
Communication intercellulaire.
Cohésion tissulaire.
\---
VI. Les échanges membranaires
1\. Transport de grandes molécules
Endocytose : entrée (nutriments, bactéries).
Exocytose : sortie (hormones, neurotransmetteurs).
→ Ensemble = transport cytotique.
2\. Transport de petites molécules
Diffusion simple : passive, selon gradient.
Diffusion facilitée : passive, via protéines.
Transport actif : contre gradient, nécessite ATP.
\---
VII. Les jonctions cellulaires
Jonctions serrées : barrière quasi étanche.
Jonctions communicantes (gap junctions) : canaux protéiques → échanges directs (ex. SNC).
Jonctions adhérentes/desmosomes : ancrage via cytosquelette (peau, cœur).
👉 Glycocalyx = identification, reconnaissance, adhérence. (Parfois marqueur tumoral).
\---
VIII. Le noyau
1\. Généralités
Présent uniquement chez les eucaryotes.
Contient l’ADN → information génétique.
2\. Nombre et forme
Généralement unique.
Exceptions :
Hépatocytes = 2.
Cellules musculaires = plusieurs.
GR = aucun.
3\. Structure
Enveloppe nucléaire (double membrane).
Nucléoplasme.
Chromatine (ADN + protéines).
Nucléole (ARN).
Pores nucléaires (échanges noyau ↔ cytoplasme).
4\. Fonctions
Activité hétérosynthétique : transcription ADN → ARNm → protéines.
Activité autosynthétique : réplication ADN → division cellulaire.
\---
IX. Psychobiologie : bases biologiques du comportement
1\. Définition
Étude des bases biologiques du comportement.
Interaction organisme ↔ environnement.
2\. Niveaux d’analyse
Social → Organique → Neuro → Réseaux → Cellules → Synapses → Molécules.
👉 Boucle : le social influence la biologie et réciproquement.
3\. Exemple
Système musculosquelettique = support du mouvement → condition du comportement.
\---
X. L’objet de la psychologie
1\. Définition
Antiquité : étude de l’âme (psyche).
Aujourd’hui : science du comportement et des processus mentaux.
2\. Objectifs
Objectiver la subjectivité (mesurer pensées, émotions, perceptions).
3\. Méthodes
Subjectives : auto-déclarations.
Objectives : mesures biologiques (rythme cardiaque, IRM, etc.).
👉 Importance de croiser les méthodes.
\---
XI. Problème corps-esprit : conceptions
Parallélisme (Leibniz) : corps/esprit parallèles, sans interaction.
Dualisme (Descartes, Bergson) : interaction mais réalités distinctes.
Monisme (Spinoza, Russell) : une seule réalité, deux aspects.
Matérialisme (Hobbes) : une seule réalité = matière.
Systémisme biopsychosocial (Engel) : modèle intégratif bio-psycho-social.
\---
XII. Importance du modèle biopsychosocial
Évite réductionnisme.
Approche globale des pathologies :
Dépression = inflammation (bio) + perte (psy) + isolement (social).
Anorexie = restriction (bio) + rapport au corps (psy) + pression sociale (social).
\---
✅ Conclusion générale
La biologie étudie la vie du niveau moléculaire au niveau populationnel.
La cellule est la base de tout vivant.
La psychologie moderne étudie comportements et processus mentaux, en lien avec leur base biologique.
Le modèle biopsychosocial est aujourd’hui la référence pour comprendre la santé, la maladie et le comportement.
📘 Cours complet – De la cellule à l’être humain
Licence 1 Psychologie – UE 2.3
Dr Lucas De Zorzi – Université de Lille (2024-2025)
Bloc obligatoire – 3 ECTS (≈ 75–90h de travail)
24h en présence
\~60h travail personnel (révisions, préparation aux épreuves)
\---
I. Introduction générale
1\. Objectifs du cours
Initier à la biologie cellulaire et à la psychobiologie.
Relier la cellule, base du vivant, à la compréhension des comportements humains.
2\. Attention et apprentissage
Multitâche numérique = baisse de performance (ex. SMS → -22 % sur les notes).
Gêne collective + perte d’efficacité.
👉 Conseil : limiter distractions numériques pendant les cours.
\---
II. La biologie : science de la vie
1\. Définition
Du grec bios (vie) + logos (science).
Étude scientifique du vivant.
2\. Sous-disciplines (niveaux d’organisation)
Population : écologie.
Organisme : physiologie.
Systèmes/organes : anatomie, physiologie.
Tissus : histologie.
Cellules : biologie cellulaire.
Molécules : biochimie, biologie moléculaire.
\---
III. Caractéristiques du vivant
A) Organisation cellulaire
Cellule = plus petite unité du vivant.
Capable de réagir, se reproduire, évoluer.
2 types :
Procaryotes : primitifs, sans noyau (ex. bactéries).
Eucaryotes : plus complexes, avec noyau (animales, végétales).
Cas particulier : virus → nécessite un hôte.
B) Métabolisme
Ensemble des réactions chimiques internes.
Permet :
Extraction et transformation d’énergie.
Synthèse de molécules et réserves.
Outils spécifiques : ADN/ARN, enzymes.
C) Reproduction
Division cellulaire :
Mitose : croissance, réparation.
Méiose : reproduction sexuée.
Mort programmée = apoptose.
D) Variation et évolution
Variabilité génétique (ADN différent au sein d’une même espèce).
Sélection naturelle → survie des individus avantagés.
Développement du cerveau → nouveaux comportements (mémoire, apprentissage, coopération).
\---
IV. Organisation de la cellule eucaryote
1\. Éléments principaux
Membrane plasmique.
Noyau.
Cytoplasme : cytosol + organites (mitochondries, RE, etc.).
2\. Composition chimique
Lipides ≈ 35 %.
Protéines ≈ 55 %.
Glucides ≈ 10 %.
👉 Protéines = fonctions essentielles (enzymes, structure, récepteurs).
👉 Association glucides/lipides/protéines → glycolipides, glycoprotéines.
\---
V. La membrane plasmique
1\. Structure
Bicouche de phospholipides :
Têtes hydrophiles (vers extérieur/intérieur aqueux).
Queues hydrophobes (au centre).
Cholestérol = stabilité.
Protéines membranaires : transmembranaires, périphériques.
Glucides orientés vers extérieur → glycocalyx.
2\. Modèle de Singer & Nicolson (1973)
Mosaïque fluide : hétérogénéité + mobilité.
3\. Rôles
Barrière sélective.
Communication intercellulaire.
Cohésion tissulaire.
\---
VI. Les échanges membranaires
1\. Transport de grandes molécules
Endocytose : entrée (nutriments, bactéries).
Exocytose : sortie (hormones, neurotransmetteurs).
→ Ensemble = transport cytotique.
2\. Transport de petites molécules
Diffusion simple : passive, selon gradient.
Diffusion facilitée : passive, via protéines.
Transport actif : contre gradient, nécessite ATP.
\---
VII. Les jonctions cellulaires
Jonctions serrées : barrière quasi étanche.
Jonctions communicantes (gap junctions) : canaux protéiques → échanges directs (ex. SNC).
Jonctions adhérentes/desmosomes : ancrage via cytosquelette (peau, cœur).
👉 Glycocalyx = identification, reconnaissance, adhérence. (Parfois marqueur tumoral).
\---
VIII. Le noyau
1\. Généralités
Présent uniquement chez les eucaryotes.
Contient l’ADN → information génétique.
2\. Nombre et forme
Généralement unique.
Exceptions :
Hépatocytes = 2.
Cellules musculaires = plusieurs.
GR = aucun.
3\. Structure
Enveloppe nucléaire (double membrane).
Nucléoplasme.
Chromatine (ADN + protéines).
Nucléole (ARN).
Pores nucléaires (échanges noyau ↔ cytoplasme).
4\. Fonctions
Activité hétérosynthétique : transcription ADN → ARNm → protéines.
Activité autosynthétique : réplication ADN → division cellulaire.
\---
IX. Psychobiologie : bases biologiques du comportement
1\. Définition
Étude des bases biologiques du comportement.
Interaction organisme ↔ environnement.
2\. Niveaux d’analyse
Social → Organique → Neuro → Réseaux → Cellules → Synapses → Molécules.
👉 Boucle : le social influence la biologie et réciproquement.
3\. Exemple
Système musculosquelettique = support du mouvement → condition du comportement.
\---
X. L’objet de la psychologie
1\. Définition
Antiquité : étude de l’âme (psyche).
Aujourd’hui : science du comportement et des processus mentaux.
2\. Objectifs
Objectiver la subjectivité (mesurer pensées, émotions, perceptions).
3\. Méthodes
Subjectives : auto-déclarations.
Objectives : mesures biologiques (rythme cardiaque, IRM, etc.).
👉 Importance de croiser les méthodes.
\---
XI. Problème corps-esprit : conceptions
Parallélisme (Leibniz) : corps/esprit parallèles, sans interaction.
Dualisme (Descartes, Bergson) : interaction mais réalités distinctes.
Monisme (Spinoza, Russell) : une seule réalité, deux aspects.
Matérialisme (Hobbes) : une seule réalité = matière.
Systémisme biopsychosocial (Engel) : modèle intégratif bio-psycho-social.
\---
XII. Importance du modèle biopsychosocial
Évite réductionnisme.
Approche globale des pathologies :
Dépression = inflammation (bio) + perte (psy) + isolement (social).
Anorexie = restriction (bio) + rapport au corps (psy) + pression sociale (social).
\---
✅ Conclusion générale
La biologie étudie la vie du niveau moléculaire au niveau populationnel.
La cellule est la base de tout vivant.
La psychologie moderne étudie comportements et processus mentaux, en lien avec leur base biologique.
Le modèle biopsychosocial est aujourd’hui la référence pour comprendre la santé, la maladie et le comportement.
the nation is near and the road is still in line a short tale is told to the one in the hall she is still here and he is in the room the little star is on the rise in the night a dear one is here to share the story in detail the road is not hard and the land is still tall he shall retain the role and the idea in the heart the note is in the hand and the letter is to the side a solid line is drawn to start the tale in real time she said the story in a tone that is still dear
the nation is near and the road is still in line
a short tale is told to the one in the hall
she is still here and he is in the room
the little star is on the rise in the night
a dear one is here to share the story in detail
the road is not hard and the land is still tall
he shall retain the role and the idea in the heart
the note is in the hand and the letter is to the side
a solid line is drawn to start the tale in real time
she said the story in a tone that is still dear
El vídeo proporciona una manera eficaz para ayudarle a demostrar el punto. Cuando haga clic en Vídeo en línea, puede pegar el código para insertar del vídeo que desea agregar. También puede escribir una palabra clave para buscar en línea el vídeo que mejor se adapte a su documento.
Para otorgar a su documento un aspecto profesional, Word proporciona encabezados, pies de página, páginas de portada y diseños de cuadro de texto que se complementan entre sí. Por ejemplo, puede agregar una portada coincidente, el encabezado y la barra lateral. Haga clic en Insertar y elija los elementos que desee de las distintas galerías.
Los temas y estilos también ayudan a mantener su documento coordinado. Cuando haga clic en Diseño y seleccione un tema nuevo, cambiarán las imágenes, gráficos y gráficos SmartArt para que coincidan con el nuevo tema. Al aplicar los estilos, los títulos cambian para coincidir con el nuevo tema.
Ahorre tiempo en Word con nuevos botones que se muestran donde se necesiten. Para cambiar la forma en que se ajusta una imagen en el documento, haga clic y aparecerá un botón de opciones de diseño junto a la imagen. Cuando trabaje en una tabla, haga clic donde desee agregar una fila o columna y, a continuación, haga clic en el signo más.
La lectura es más fácil, también, en la nueva vista de lectura. Puede contraer partes del documento y centrarse en el texto que desee. Si necesita detener la lectura antes de llegar al final, Word le recordará dónde dejó la lectura, incluso en otros dispositivos.
Pour faire des chouquettes, fais bouillir 25cl d’eau avec 100g de beurre et une pincée de sel, ajoute 150g de farine d’un coup puis incorpore 4 œufs un à un. Forme de petits tas sur une plaque, saupoudre de sucre perlé et enfourne à 180°C pendant 20 minutes sans ouvrir la porte du four. Bon appétit!
Everything has come in apart from 24 copies of ‘The Great Expedition’ – (9780183245687). The publisher is currently out of stock. They did expect the title to be available by now, but unfortunately, they have a shipping delay, so are not yet able to fully confirm when they expect stock to arrive. Please confirm if you require these to be kept on order or if you wish these to be cancelled. My email address is operations@brownsbfs.co.uk
This type of typing test is perfect for schools. If you are a teacher and your want to prepare a typing lesson for your student, you can create one here and then send the page to your students. They will each be able to work on the text you have provided. If you are looking for a more complete solution, with lessons and monitoring of each student progress, try Typing School.
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Я думаю, что дружба играет очень важную роль в жизни. Друзья делают нашу жизнь радостнее и интереснее.
У каждого человека есть свой близкий друг. И конечно у меня тоже. Его зовут Куан. Мы познакомились десять лет назад, когда вместе учились в школе. Ему двадцать три года. Сейчас он живёт и работает в городе Хошимине.
У Куана короткие тёмные волосы и карие глаза. Он всегда носит очки. Мой друг добрый, умный, спокойный и очень честный.
У нас много общих интересов. Мы любим читать книги, играть в шахматы и гулять в парке. Иногда мы вместе смотрим фильмы.
Я считаю, что настоящая дружба — это доверие и уважение. Чтобы сохранить нашу дружбу, мы часто разговариваем, помогаем друг другу и проводим время вместе.
peo ple peo ple peo ple peo ple peo ple
peo ple peo ple peo ple peo ple peo ple
peo ple peo ple peo ple peo ple peo ple
peo ple peo ple peo ple peo ple peo ple
peo ple peo ple peo ple peo ple peo ple
When Not to Capitalize some writers overcapitalize; that is, they capitalize words that should not be capitalized. You need to learn to avoid using unnecessary capital letters. Rule one - A title or a family name that is preceded by a, the, or a possessive pronoun such as my is not capitalized Incorrect : Alice went to see the Dean. Correct : Alice went to see the dean. Correct: Alice went to see Dean Asher. Incorrect: She went with her Uncle. Correct: She went with her uncle. Correct: She went with her Uncle William. Rule two - The names of the seasons are not capitalized Incorrect: Both are going back to school in the Fall. Correct: Both are going back to school in the fall. Rule Three - A school subject is not capitalized unless it is the name of a specific course or a language. Incorrect: Alice wants to take a History course. Correct: Alice wants to take a history course. Correct: Alice wants to take American History 101 and Swahili. Rule Four - A direction word is not capitalized unless it refers to a specific place, such as a region of the country. Incorrect: They walked South to the administration building. Correct: They walked south to the administration building. Correct: Alice was born here, but William grew up in the South. Proper abjective- A descriptive word formed from a proper noun Rule Five- A geographic place is not capitalized unless it is part of a specific name you can find on a map. Incorrect: The school is next to a huge Lake. Correct: The school is next to a huge lake. Correct: The school is next Lake Ontario. Study tip- Proper nouns are sometimes abbreviated. When a word should be capitalized, its abbreviation should be capitalized too: Mount Shasta, Mt. Shasta.
911 operators serve as the critical first link in the emergency response chain. Often referred to as public safety dispatchers, these professionals are responsible for receiving emergency calls, assessing the situation, and coordinating the appropriate response. Their work demands precision, calm under pressure, and rapid decision-making. A single misstep can delay lifesaving assistance, making their role both high-stakes and indispensable.
When a call comes in, the operator must quickly determine the nature of the emergency. Is it a medical crisis, a fire, a crime in progress, or a traffic accident? Based on this assessment, they initiate contact with the relevant departments. For medical emergencies, operators dispatch paramedics or emergency medical technicians (EMTs), often while providing life-saving instructions over the phone. In cases involving fire, they alert the local fire department, ensuring that firefighters are equipped with the necessary details before arriving on scene.
Law enforcement is another key partner. When a crime is reported, 911 operators relay information to police officers, including suspect descriptions, vehicle details, and the urgency of the situation. In high-risk scenarios, such as active shooter incidents or domestic violence calls, operators may coordinate with specialized units like SWAT or crisis negotiation teams. Their ability to remain composed and relay accurate information can directly influence the outcome of these tense situations.
Beyond the core emergency services, 911 operators also interact with utility companies, animal control, and public works departments. For example, if a caller reports a downed power line or a gas leak, the operator must notify the appropriate utility provider while simultaneously ensuring public safety. In cases involving hazardous materials, coordination with environmental response teams may be necessary. These interactions require a deep understanding of local infrastructure and a network of contacts across multiple agencies.
Communication technology plays a vital role in this ecosystem. Modern dispatch centers use computer-aided dispatch (CAD) systems to log calls, track units, and share real-time updates. Geographic Information Systems (GIS) help operators pinpoint locations, especially when callers are unsure of their exact whereabouts. Integration with mobile networks allows for text-to-911 services, expanding accessibility for individuals who are deaf, hard of hearing, or in situations where speaking aloud could be dangerous.
Training for 911 operators is rigorous. It includes instruction in emergency medical dispatch, crisis communication, and legal protocols. Operators must also be familiar with the geography of their jurisdiction, local ordinances, and the capabilities of each department they interact with. Many undergo simulations that mimic real emergencies, helping them build the muscle memory needed to respond effectively under pressure.
Despite the challenges, the work of a 911 operator is deeply rewarding. They are the unseen heroes behind every siren, every rescue, and every life saved. Their collaboration with police, fire, medical, and municipal departments forms the backbone of public safety. Without their coordination, the entire emergency response system would falter.
Mechanics such as capitalization, punctuation, and spelling, is an important content area on the GED. Reasoning Through Language Arts test. Writing that is mechanically correct - that is, writing that has correct capitalization, punctuation, and spelling - always makes a better impression than writing that contains errors. When to Capitalize You probably already know that the first word in a sentence and the pronoun I are always capitalized. These additional rules will help you decide when to capitalize other words. proper noun - a word that names a specific person, place, or thing Rule one - Capitalize a proper noun, a word that names a specific person, place, group, or thing. William Boyle invented the credit card in 1951. He lived on Spark Street in West Hempstead on Long Island. Mr. Boyle worked for the Franklin National Bank. Rule two - Capitalize a proper adjective, a descriptive word that comes from the name of a specific person or place. Franklin's main competitor was First American Bank. Rule three - Capitalize a title that comes directly before a person's name. On the bank's board of directors was Mayor Graham. A depositor, Ms. Ailey, asked for credit to pay a big heating bill. Titles and family names (for example, mother, father, grandmother) are capitalized when they are used to address a person directly. Ms. Ailey saId, "How do you do, Mayor?" "Mr. Boyle, Sir, I would appreciate a line of credit, just like you give to wealthy depositors and businesses." Rule four - Capitalize the names of holidays, days of the week, and months of the year. Statements were sent out on the first Monday of the month. By New Year's Day in January 1952, Franklin National Bank had set up over 700 credit card accounts for its customers.
Mechanics such as capitalization, punctuation, and spelling, is an important content area on the GED. Reasoning Through Language Arts test. Writing that is mechanically correct - that is, writing that has correct capitalization, punctuation, and spelling - always makes a better impression than writing that contains errors. When to Capitalize You probably already know that the first word in a sentence and the pronoun I are always capitalized. These additional rules will help you decide when to capitalize other words. proper noun - a word that names a specific person, place, or thing Rule one - Capitalize a proper noun, a word that names a specific person, place, group, or thing. William Boyle invented the credit card in 1951. He lived on Spark Street in West Hempstead on Long Island. Mr. Boyle worked for the Franklin National Bank. Rule two - Capitalize a proper adjective, a descriptive word that comes from the name of a specific person or place. Franklin's main competitor was First American Bank. Rule three - Capitalize a title that comes directly before a person's name. On the bank's board of directors was Mayor Graham. A depositor, Ms. Ailey, asked for credit to pay a big heating bill. Titles and family names (for example, mother, father, grandmother) are capitalized when they are used to address a person directly. Ms. Ailey saId, "How do you do, Mayor?" "Mr. Boyle, Sir, I would appreciate a line of credit, just like you give to wealthy depositors and businesses." Rule four - Capitalize the names of holidays, days of the week, and months of the year. Statements were sent out on the first Monday of the month. By New Year's Day in January 1952, Franklin National Bank had set up over 700 credit card accounts for its customers. When Not to Capitalize some writers overcapitalize; that is, they capitalize words that should not be capitalized. You need to learn to avoid using unnecessary capital letters. Rule one - A title or a family name that is preceded by a, the, or a possessive pronoun such as my is not capitalized Incorrect : Alice went to see the Dean. Correct : Alice went to see the dean. Correct: Alice went to see Dean Asher. Incorrect: She went with her Uncle. Correct: She went with her uncle. Correct: She went with her Uncle William. Rule two - The names of the seasons are not capitalized Incorrect: Both are going back to school in the Fall. Correct: Both are going back to school in the fall. Rule Three - A school subject is not capitalized unless it is the name of a specific course or a language. Incorrect: Alice wants to take a History course. Correct: Alice wants to take a history course. Correct: Alice wants to take American History 101 and Swahili. Rule Four - A direction word is not capitalized unless it refers to a specific place, such as a region of the country. Incorrect: They walked South to the administration building. Correct: They walked south to the administration building. Correct: Alice was born here, but William grew up in the South. Proper abjective- A descriptive word formed from a proper noun Rule Five- A geographic place is not capitalized unless it is part of a specific name you can find on a map. Incorrect: The school is next to a huge Lake. Correct: The school is next to a huge lake. Correct: The school is next Lake Ontario. Study tip- Proper nouns are sometimes abbreviated. When a word should be capitalized, its abbreviation should be capitalized too: Mount Shasta, Mt. Shasta.
