By T. Xardas. Hawaii Pacific University. 2018.

Each adrenal • Reproductive maturity and function gland has two parts purchase 100mg sildenafil with mastercard causes of erectile dysfunction in young adults, the medulla and • Metabolism the cortex purchase sildenafil 75 mg with mastercard erectile dysfunction doctor milwaukee. Each part has a different • Adjustment to internal and external function. Overproduction or underproduction of It is divided into two parts, the ante- one hormone can affect a number of oth- rior and the posterior lobes. Insufficient amounts of the parathy- function of regulating the production and roid hormone in the blood can cause spasm secretion of another hormone. If parathyroid hormone is to ed by the thyroid gland, regulates the rate be effective, vitamin D must be present. When the level of thy- (medulla) secretes the hormones epineph- roxine in the blood is high, metabolism rine and, to a lesser extent, norepinephrine speeds up; when it is low, metabolism slows at times of stress to enable the body to pre- down. These Parathyroid hormone, which regulates the hormones increase the heart rate, increase concentrations of calcium and phosphate muscle tone, and constrict blood vessels in the body, is secreted by the parathyroid in times of stress. Excessive amounts of the parathy- adrenal glands (cortex) secretes hormones roid hormone in the blood can result in the called steroids, which regulate many essen- demineralization of bone, causing bones to tial functions, such as electrolyte and become fragile so that they are easily bro- water balance, metabolism, immune re- Pituitary Thyroid Parathyroid glands Adrenal gland Kidney Pancreas Ovaries (female) Testes (male) Figure 9–1 Endocrine System. Conditions of the Endocrine System 261 sponses, and inflammatory reactions. The Hyperthyroidism (Graves’ Disease, adrenal cortex is essential to life. If it is dys- Thyrotoxicosis) functional, death will occur within a few days unless the hormones that it normal- Manifestations of Hyperthyroidism ly secretes are replaced. Hyperthyroidism is the overproduction The anterior lobe of the pituitary secretes of thyroid hormone because of hyperfunc- thyroid-stimulating hormone (TSH) (which tion of the thyroid gland. Hyperthyroid- is necessary for thyroid function), growth ism results in an increased metabolic rate. The posterior lobe of the pituitary ingestion of the hormone or inflammation gland stores hormones produced in the of the thyroid gland (thyroiditis) rather hypothalamus. Antidiuretic hormone (ADH), than from an overactive thyroid gland which increases water reabsorption by the (Woeber, 2000). Other Special cells within the islets of Langer- symptoms of hyperthyroidism include hans in the pancreas produce the hormones restlessness, irritability, nervousness, and insulin and glucagon, which are necessary weight loss. The increased rate of metab- for the metabolism of carbohydrates, pro- olism causes intolerance to heat; thus, teins, and fats. Hormones produced by the environmental temperatures that seem testes and ovaries are important not only comfortable to others seem unbearably to reproductive function, but also to nor- warm to individuals with hyperthy- mal growth and development. Exophthalmos (abnormal pro- trusion of the eyeball) may also develop CONDITIONS OF THE with hyperthyroidism. Once exophthal- ENDOCRINE SYSTEM mos develops, the effects are permanent, giving individuals a wide-eyed and startled A number of medical conditions result- appearance. With early diagnosis and ing from endocrine dysfunction constitute treatment, hyperthyroidism usually caus- a major health problem (Wilson, 2001). Because symptoms of endocrine condi- tions are often similar to those associated with a number of mental disorders, some Treatment and Management of endocrine conditions may go unrecog- Hyperthyroidism nized or misdiagnosed as psychiatric disorders. Likewise, administration of hor- In hyperthyroidism, treatment is direct- mones in treatment of an endocrine defi- ed toward curtailing the secretion of the ciency may have side effects similar to thyroid hormone. Clearly, that blocks the production of the hor- the endocrine system, in addition to reg- mone may be used. Symptoms usually ulating internal body functions and main- subside within weeks or months after the taining homeostasis, has a role in human treatment begins. Hypothyroidism Radioactive iodine destroys cells that pro- duce thyroid hormone, and symptoms The goal of treatment of hypothy- usually subside within weeks or months. Consequently, a primary mode of viduals to become hypothyroid, however, treatment is replacement therapy. The which requires that they take thyroid medication of choice for thyroid hormone medication for life.

The primary functions of the skin are pro- tection of the body from the external environment and dissipation or conservation of heat during body temper- ature regulation order 50mg sildenafil mastercard erectile dysfunction nofap. The skin has one of the lowest metabolic rates in the body and requires relatively little blood flow for purely nu- tritive functions sildenafil 25 mg visa erectile dysfunction world statistics. Consequently, despite its large mass, its resting metabolism does not place a major flow demand on the cardiovascular system. However, in warm climates, body temperature regulation requires that warm blood from the body core be carried to the external surface, where heat transfer to the environment can occur. Therefore, at typical indoor temperatures and during warm weather, skin blood flow is usually far in excess of the need for tissue nu- trition. The reddish color of the skin during exercise in a warm environment reflects the large blood flow and dila- tion of skin arterioles and venules (see Table 17. The increase in the skin’s blood flow probably occurs through two main mechanisms. First, an increase in body core temperature causes a reflex increase in the activity of sympathetic cholinergic nerves, which release acetyl- choline. Acetylcholine release near sweat glands leads to the breakdown of a plasma protein (kininogen) to form bradykinin, a potent dilator of skin blood vessels, which in- The vasculature of the skin. The skin vascu- creases the release of NO as a major component of the dila- FIGURE 17. Second, simply increasing skin tempera- lature is composed of a network of large arteri- oles and venules in the deep dermis, which send branches to the ture will cause the blood vessels to dilate. Arteriove- from heat applied to the skin from the external environ- nous anastomoses allow direct flow from arterioles to venules and ment, heat from underlying active skeletal muscle, or in- greatly increase blood flow when dilated. The capillary loops into creased blood temperature as it enters the skin. During mild to moderate exercise in a warm envi- ronment, skin blood flow can equal or exceed blood flow to Sweat glands derive virtually all sweat water from blood the skeletal muscles. Exercise tolerance can, therefore, be plasma and are surrounded by a dense capillary network in lower in a warm environment because the vascular resist- the deeper layers of the dermis. As explained in Chapter 29, ance of the skin and muscle is too low to maintain an ap- neural regulation of the sweating mechanism not only propriate arterial blood pressure, even at maximum cardiac causes the formation of sweat but also substantially in- output. One of the adaptations to exercise is an ability to creases skin blood flow. All the capillaries from the superfi- increase blood flow in skin and dissipate more heat. In ad- cial skin layers are drained by venules, which form a venous dition, aerobically trained humans are capable of higher plexus in the superficial dermis and eventually drain into sweat production rates; this increases heat loss and induces many large venules and small veins beneath the dermis. The vascular pattern just described is modified in the tis- The vast majority of humans live in cool to cold regions, sues of the hand, feet, ears, nose, and some areas of the face where body heat conservation is imperative. The sensation in that direct vascular connections between arterioles and of cool or cold skin, or a lowered body core temperature, venules, known as arteriovenous anastomoses, occur pri- elicits a reflex increase in sympathetic nerve activity, which marily in the superficial dermal tissues (see Fig. Heat loss contrast, relatively few arteriovenous anastomoses exist in is minimized because the skin becomes a poorly perfused in- the major portion of human skin over the limbs and torso. As long as the skin tem- If a great amount of heat must be dissipated, dilation of the perature is higher than about 10 to 13 C (50 to 55 F), the arteriovenous anastomoses allows substantially increased neurally induced vasoconstriction is sustained. However, at skin blood flow to warm the skin, thereby increasing heat lower tissue temperatures, the vascular smooth muscle cells loss to the environment. This allows vasculatures of the progressively lose their contractile ability, and the vessels 286 PART IV BLOOD AND CARDIOVASCULAR PHYSIOLOGY passively dilate to various extents. The reddish color of the plied by two umbilical arteries, which branch from the in- hands, face, and ears on a cold day demonstrates increased ternal iliac arteries, and is drained by a single umbilical vein blood flow and vasodilation as a result of low temperatures. The umbilical vein of the fetus returns oxygen To some extent, this cold-mediated vasodilation is useful be- and nutrients from the mother’s body to the fetal cardio- cause it lessens the chance of cold injury to exposed skin. Although many liters of oxy- inadequate clothing is worn, heat loss would be rapid and hy- gen and carbon dioxide, together with hundreds of grams pothermia would result. This large chemical exchange without cellular exchange is possible because the fetal and FETAL AND PLACENTAL CIRCULATIONS maternal blood are kept completely separate, or nearly so. The Placenta Has Maternal and Fetal The fundamental anatomical and physiological structure Circulations That Allow Exchange Between for exchange is the placental villus. As the umbilical arter- ies enter the fetal placenta, they divide into many branches the Mother and Fetus that penetrate the placenta toward the maternal system.

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Histotechnology explores the ways in which tissues its existing structure cheap sildenafil 25mg overnight delivery erectile dysfunction treatment nz. Embedding the tissue in a supporting can be better stained and observed sildenafil 100 mg discount erectile dysfunction unable to ejaculate. In all of these disciplines, a medium such as paraffin wax usually follows fixation. The next thorough understanding of normal, or healthy, tissues is impera- step, sectioning the tissue into extremely thin slices, is followed tive for recognizing altered, or abnormal, tissues. Some tissues are fixed by rapid freezing and then sectioned while frozen, making embed- ding unnecessary. Frozen sections enable the pathologist to make Changes in Tissue Composition a quick diagnosis during a surgical operation. These are done fre- quently, for example, in cases of suspected breast cancer. Stain- Most diseases alter tissue structure locally, where the disease is ing is the next step. Some diseases, however, called general conditions, routinely used on all tissue specimens. They give a differential cause changes that are far removed from the locus of the disease. Practically all histological conditions can be ishment or nerve impulses are impaired. Higher magnification is caused by a disease of the nervous system like polio, or it can be used to clarify specific details. Further examination may be per- the result of a diminished blood supply to a muscle. Senescence formed with an electron microscope, which reveals the intricacy (se˘-ne˘′sens) atrophy, or simply senescence, is the natural aging of of cellular structure. Histological observation provides the foun- tissues and organs within the body. Disuse atrophy is a local at- dation for subsequent diagnosis, prognosis, treatment, and rophy that results from the inactivity of a tissue or organ. Necrosis (ne˘-kro′sis) is death of cells or tissues within the Tissue Transplantation living body. It can be recognized by physical changes in the dead In the last two decades, medical science has made tremendous ad- tissues. Necrosis can be caused by severe injury; physical agents vancements in tissue transplants. Tissue transplants are necessary (trauma, heat, radiant energy, chemical poisons); or poor nutri- for replacing nonfunctional, damaged, or lost body parts. When histologically examined, the necrotic tissue most successful transplant is one where tissue is taken from one usually appears opaque, with a whitish or yellowish cast. Gan- place on a person’s body and moved to another place, such as a grene is a massive necrosis of tissue accompanied by an invasion skin graft from the thigh to replace burned tissue of the hand. Follow- transplants between genetically identical individuals, the only ex- ing somatic death, tissues undergo irreversible changes, such as ample being identical twins. These transplants also have a high rigor mortis (muscular rigidity), clotting of the blood, and cool- success rate. Postmortem (after death) changes occur under individuals of the same species but of different genotype, and varying conditions at predictable rates, which is useful in esti- xenografts, or heterografts, are grafts between individuals of dif- mating the approximate time of death. An example of a xenograft is the transplant of a pig valve to replace a dysfunctional or diseased human heart valve. Tissue Analysis Both allografts and xenografts present the problem of a possible tissue-rejection reaction. When this occurs, the recipient’s immune In diagnosing a disease, it is frequently important to examine tis- mechanisms are triggered, and the donor’s tissue is identified as sues from a living person histologically. The reaction can be minimized by a biopsy (bi′op-se) (removal of a section of living tissue) is “matching” recipient and donor tissue. These drugs act by interfering removal is usually done on large masses or tumors. Unfortunately, im- (kyoo″ re˘-tazh′) involves cutting and scraping tissue, as may be munosuppressive drugs may also lower the recipient’s resistance to infections.

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