By B. Ramon. Clayton College of Natural Health. 2017.
This is readily apparent from the fact that an organic substances are continually lost from the body as a adrenalectomized animal order viagra vigour 800mg visa, unlike its normal counterpart purchase viagra vigour 800mg with mastercard, result of perspiration, respiration, and excretion. Under normal con- diminishes, ATP generation by the cells becomes inade- ditions, these critical constituents of the body’s extracellu- quate to support life, and the animal eventually dies. Even 607 608 PART IX ENDOCRINE PHYSIOLOGY when fed a normal diet, an adrenalectomized animal typi- Zona glomerulosa cally loses body sodium and water over time, and eventu- Zona fasciculata Cortex: 80–90% ally dies of circulatory collapse. Its death is caused by a lack Zona reticularis of certain steroid hormones that are produced and secreted by the cortex of the adrenal gland. The glucocorticoid hormones, cortisol and corticos- Medulla: 10–20% terone, play essential roles in adjusting the metabolism of carbohydrates, lipids, and proteins in liver, muscle, and adi- pose tissues during fasting, which assures an adequate sup- ply of glucose and fatty acids for energy metabolism de- spite the absence of food. The mineralocorticoid hormone aldosterone, another steroid hormone produced by the ad- renal cortex, stimulates the kidneys to conserve sodium Catecholamines and, hence, body fluid volume. The glucocorticoids also enable the body to cope with Androgens physical and emotional traumas or stresses. The physiological importance of this action of the glucocorticoids is empha- Cortisol sized by the fact that adrenalectomized animals lose their ability to cope with physical or emotional stresses. Even when Aldosterone given an appropriate diet to prevent blood glucose and body sodium depletion, an adrenalectomized animal may die when exposed to traumas that are not fatal to normal animals. These hormones are the catecholamines, ep- androgen dehydroepiandrosterone, which is related chem- inephrine and norepinephrine, which have widespread ically to the male sex hormone testosterone. The molecu- effects on the cardiovascular system and muscular system lar structures of these hormones are shown in Figure 34. Many small arteries branch from the aorta and renal arteries and enter the cortex. These vessels give rise to capillaries that course radially through the cortex and ter- FUNCTIONAL ANATOMY OF THE minate in venous sinuses in the zona reticularis and adrenal ADRENAL GLAND medulla; therefore, the hormones produced by the cells of the cortex have ready access to the circulation. The human adrenal glands are paired, pyramid-shaped or- The cells of the adrenal cortex contain abundant lipid gans located on the upper poles of each kidney.
Since the Lewis hunting response increases heat loss from the body somewhat viagra vigour 800mg on-line, whether or not it is truly an example of acclimatization to cold is debatable purchase 800mg viagra vigour otc. However, Human Cold Acclimatization Confers a the response is advantageous because it keeps the extremi- Modest Thermoregulatory Advantage ties warmer, more comfortable, and functional and proba- The pattern of human cold acclimatization depends on the bly protects them from cold injury. It is partly for this reason that the occurrence of cold acclimatization in humans was con- troversial for a long time. Our knowledge of human cold CLINICAL ASPECTS OF THERMOREGULATION acclimatization comes from both laboratory studies and Temperature is important clinically because of the presence studies of populations whose occupation or way of life ex- of fever in many diseases, the effects of many factors on tol- poses them repeatedly to cold temperatures. At one time it was believed that humans must acclimatize to cold as lab- oratory mammals do—by increasing their metabolic rate. Fever Enhances Defense Mechanisms There are a few reports of increased basal metabolic rate Fever may be caused by infection or noninfectious condi- and, sometimes, thyroid activity in the winter. Pyrogens are substances that ports indicate the opposite response, consisting of a lower cause fever and may be either exogenous or endogenous. Such a response would spare metabolic most are microbial products, microbial toxins, or whole mi- energy and might be advantageous in an environment that croorganisms. The best studied of these is the lipopolysac- is not so cold that a blunted metabolic response would al- charide endotoxin of gram-negative bacteria. A thalamus (and perhaps elsewhere in the brain) to alter their lower core-to-skin conductance (i. This effect of climatization in which a reduction in the metabolic re- endogenous pyrogens is mediated by the local synthesis and sponse to cold occurred. This increased insulation is not due to subcutaneous fat (in fact, it has been observed in release of prostaglandin E2. Aspirin and other drugs that in- very lean subjects), but apparently results from lower blood hibit the synthesis of prostaglandins also reduce fever. In general, the cold liable indicator of the presence of disease that body tem- stresses that elicit a lower shell conductance after acclima- perature is probably the most commonly measured clinical tization involve either cold water immersion or exposure to index.