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The neurolemmocytes of the regenera- Myelination tion tube are believed to secrete chemicals that attract the Neurons are either myelinated or unmyelinated buy 20 mg tadalis sx impotence existing at the time of the marriage. Even a severed major nerve may be sur- oligodendrocyte surrounds a portion of the axon or dendrite to gically reconnected and the function of the nerve reestablished if provide support and aid in the conduction of impulses (figs buy tadalis sx 20mg on-line finasteride erectile dysfunction treatment. The neuroglia that participate in the myelination rolemmocytes, and central axons are generally believed to have a process contain a white lipid-protein substance called myelin much more limited ability to regenerate than peripheral axons. As several neuroglia are positioned in sequence, a myelin layer that encloses the axon or dendrite is formed. Myeli- Astrocytes and the Blood-Brain Barrier nated neurons occur both in the CNS and the PNS. Myelin is Astrocytes are large, stellate cells with numerous cytoplasmic responsible for the color of the white matter of the brain and processes that radiate outward. These are the most abundant spinal cord and the white coloration of nerves. Capillaries in the brain, unlike those of most other organs, The outer surface of the myelin sheath is encased in a glycopro- do not have pores between adjacent endothelial cells. Molecules tein neurolemmal sheath that promotes neuron regeneration in within these capillaries must thus be moved through the en- the event that the neuron is injured. Each neurolemmocyte dothelial cells by active transport, endocytosis, and exocytosis. These gaps in the myelin vascular processes that surround most of the outer surface of the sheath and neurolemmal sheath are known as the neurofibril brain capillaries (fig. It is at the neurofib- enter neurons in the CNS, they may have to pass through both ril nodes that a nerve impulse is propagated along a neuron. Astrocytes, therefore, The myelin sheaths of the CNS are formed by oligoden- contribute to the blood-brain barrier, which is highly selective; drocytes. Unlike a neurolemmocyte, which forms a portion of some molecules are permitted to pass, whereas closely related the myelin sheath around only one axon, each oligodendrocyte molecules may not be allowed to cross the barrier. The blood-brain barrier presents difficulties in the chemother- apy of brain diseases because drugs that could enter other or- gans may not be able to enter the brain. Ranvier, French pathologist, 1835–1922 converted to dopamine in the brain. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 352 Unit 5 Integration and Coordination Classification of Neurons and Nerves Neurons may be classified according to structure or function. The functional classification is based on the direction of con- ducted impulses. Sensory impulses originate in sensory receptors and are conducted by sensory, or afferent, neurons to the CNS. Motor impulses originate in the CNS and are conducted by motor, or efferent, neurons to a muscle or gland (fig. Association neurons, or interneurons, are located be- tween sensory and motor neurons and are found within the spinal cord and brain. The structural classification of neurons is based on the number of processes that extend from the cell body of the neu- ron (fig. The spindle-shaped bipolar neuron has a process at both ends; this type occurs in the retina of the eye. They are called pseudounipolar (pseudo = false) be- cause they originate as bipolar neurons, but then their two processes converge and partially fuse during early embryonic development. Most sensory neurons are pseudounipolar and have their cell bodies located in sensory ganglia of spinal and cranial nerves. Multipolar neurons are the most common type and are characterized by several dendrites and one axon ex- tending from the cell body. Fibers within a nerve are held together and strengthened by loose connective tissue (fig. The entire nerve is surrounded and supported by connective tissue called the epineurium, which contains tiny blood vessels and, often, adipose cells. Perhaps less than a quarter of the bulk of a nerve consists of nerve fibers. More than half is associated connective tissue, and approximately a quarter is the myelin that surrounds the nerve fibers.

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Dorsal chip fractures of MRI has been clearly demonstrated to reveal occult frac- the hamate may be seen on the lateral radiograph purchase tadalis sx 20 mg overnight delivery erectile dysfunction medication natural. The de- tures 20mg tadalis sx overnight delivery erectile dysfunction washington dc, that is, those not demonstrable on conventional radi- gree of displacement is best appreciated on this image. When the clinical index of suspicion of hip frac- In the digits, AP, lateral, and oblique projections of the ture is high, particularly in the elderly, an MRI is often use- digit in question should be obtained. A limited examination may be performed, and in many lieve that the addition of a reverse (internal) oblique is patients without a hip fracture, MRI will demonstrate other helpful. The so-called baseball finger or mallet finger abnormalities about the hip that are responsible for the is a fracture of the dorsal aspect of the base of the distal symptoms. When taken in a timely fashion, MRI can es- phalanx of the digit, almost always accompanied by flex- tablish or exclude the diagnosis of fracture. This injury Stress and insufficiency fractures about the hip are al- may be purely tendinous, and manifested only by flexion so relatively common and may occur either in the young deformity at the DIP joint. Volar plate fractures are quite (fatigue fractures) or in the elderly with osteoporosis or common and are seen at the volar aspect of the base of other underlying disease (insufficiency fractures). These may be impossible to identify Conventional imaging signs may be subtle or non-exis- on PA radiographs but are usually evident on oblique or tent. Others will have no joints may be seen in association with volar plate injuries; findings on conventional imaging and the presence of the a dislocation may have been reduced prior to imaging. This is often accompanied by a fracture at the site the hip are not uncommon, particularly in athletes. The of avulsion and may require stress views for evaluation most common of these include avulsion fractures from when the injury is purely ligamentous. If the adductor the site of origin of the hamstring muscles (the ischial aponeurosis is entrapped within the joint (Stenner lesion), tuberosity), avulsions from the straight or reflected heads then surgery may be necessary. Ultrasound and MRI of the rectus femoris (seen at the anterior inferior iliac have been advocated for the diagnosis spine or in the supra-acetabular region), and avulsions of the lesser trochanter. Dislocations of the hip are most commonly posterior Specific Sites - Lower Extremity and are frequently associated with fractures of the poste- rior wall of the acetabulum. Osteochondral or shear frac- Hip tures of the femoral head (Pipkin fractures) occur where the femoral head strikes the acetabulum at the time of Fractures of the femoral neck may be displaced, with re- posterior dislocation. In a posterior dislocation, the sultant shortening and external rotation of the lower ex- hip is displaced posteriorly and often slightly superiorly; tremity. Although these are readily diagnosed by conven- the thigh is held in adduction. Much less common are an- tional imaging, at times there is an apparent radiolucen- terior dislocations of the hip, in which the femoral head cy in the femoral neck, suggesting that the fracture is is seen in a medial and inferior position; the thigh is held pathologic. The area of lucency is due to rotation of the fracture frag- Knee ments. When femoral-neck fractures are impacted, diag- nostic problems increase. The position of the hip is usu- Routine imaging includes at least two views, AP and lat- ally in valgus and these fractures may be recognized as eral. Tangential views of the patella and tunnel views may bands of density extending across the femoral neck or by be used to supplement these, particularly when joint ef- a “squared-off ” contour to the head-neck junction along fusions are demonstrable. Patients with im- be helpful in detecting fractures of the tibial plateau. If a lipohemarthrosis is demonstrable on hori- tertrochanteric region; the lesser trochanter may represent zon-beam images, this is presumptive evidence for an in- a separate bony fragment in these cases. In these cases, CT is often the most tures of the greater trochanter should raise the possibility expeditious way to demonstrate these fractures. In patients with CT may not be able to detect other intra-articular abnor- conventional images indicating an avulsion of the greater malities. For this reason, MRI may be even more useful trochanter, MRI should be preformed in order to evaluate as it can detect ligamentous injuries, meniscal tears and the intertrochanteric region for incomplete fracture.

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Once the enzyme has hydroxylated carbon names generic tadalis sx 20mg with visa low cost erectile dysfunction drugs, which denote their function in steroid biosynthe- 17 of pregnenolone to form 17 -hydroxypregnenolone generic 20 mg tadalis sx amex erectile dysfunction protocol + 60 days, sis (see Table 34. Some molecules of 17 - gins with the formation of free cholesterol from the cho- hydroxypregnenolone undergo this reaction and are con- lesterol esters stored in intracellular lipid droplets. This action of cholesterol molecules enter the mitochondria, which are 17 -hydroxylase is essential for the formation of andro- located close to the lipid droplets, by a mechanism that is gens (19 carbon steroids) and estrogens (18 carbon not well understood. Evidence indicates that free choles- steroids), which lack the carbon 20–21 side chain. There- terol associates with a small protein called sterol carrier fore, this lyase activity of 17 -hydroxylase is important in protein 2, which facilitates its entry into the mitochon- the gonads, where androgens and estrogens are primarily drion in some manner. The appearance of significant adrenal an- cules bind to the cholesterol side-chain cleavage enzyme drogen secretion in children of both sexes is termed (CYP11A1), embedded in the inner mitochondrial mem- adrenarche. This enzyme catalyzes the first and rate-limiting re- it normally occurs before the activation of the hypothala- action in steroidogenesis, which remodels the cholesterol mic-pituitary-gonad axis, which initiates puberty. The ad- molecule into a 21-carbon steroid intermediate called preg- renal androgens produced as a result of adrenarche are a nenolone. The reaction occurs in three steps, as shown in stimulus for the growth of pubic and axillary hair. The first two steps consist of the hydroxylation Those molecules of 17 -hydroxypregnenolone that dis- of carbons 20 and 22 by cholesterol side-chain cleavage en- sociate as such from 17 -hydroxylase bind next to another zyme. Then the enzyme cleaves the side chain of choles- ER enzyme, 3 -hydroxysteroid dehydrogenase (3 -HSD terol between carbons 20 and 22, yielding pregnenolone II). This enzyme acts on 17 -hydroxypregnenolone to iso- and isocaproic acid. The cholesterol side-chain cleavage enzyme, leave the mito- product formed is 17 -hydroxyprogesterone (see Fig. This mecha- This intermediate then binds to another enzyme, 21-hy- nism is not understood. At this point, the further remodel- droxylase (CYP21A2), which hydroxylates it at carbon 21. The product formed is 11- ciculata and zona reticularis or the zona glomerulosa. These biosynthetic events are summarized in must be transferred back into the mitochondrion to be Figure 34. This enzyme hydroxylates 11-deoxycortisol on carbon 11, converting it into cortisol. The 11 -hydroxyl group is the molecular feature that con- Nomenclature for the Steroidogenic En- fers glucocorticoid activity on the steroid. Some of the pregnenolone molecules generated in cells Previous Current of the zona fasciculata and zona reticularis first bind to 3 - Common Name Form Form Gene hydroxysteroid dehydrogenase when they enter the endo- Cholesterol side-chain P450SCC CYP11A1 CYP11A1 plasmic reticulum. Some of these progesterone molecules are 3 -Hydroxysteroid 3 -HSD 3 -HSD II HSD3B2 hydroxylated by 21-hydroxylase to form the mineralocor- dehydrogenase ticoid 11-deoxycorticosterone (DOC) (see Fig. The 17 -Hydroxylase P450C17 CYP17 CYP17 11-deoxycorticosterone formed may be either secreted or 21-Hydroxylase P450C21 CYP21A2 CYP21A2 11 -Hydroxylase P450 CYP11B1 CYP11B1 transferred back into the mitochondrion. There it is acted C11 Aldosterone synthase P450C11AS CYP11B2 CYP11B2 on by 11 -hydroxylase to form corticosterone, which is then secreted into the circulation. Aldosterone Progesterone may also undergo 17 -hydroxylation in 17 -hydroxylation in these cells, and cortisol and adrenal the zona fasciculata and zona reticularis. Instead, the enzy- verted to either cortisol or the adrenal androgen an- matic pathway leading to the formation of aldosterone is drostenedione. Pregnenolone is converted by en- The 17 -hydroxylase is not present in cells of the zona zymes in the endoplasmic reticulum to progesterone and glomerulosa; therefore, pregnenolone does not undergo 11-deoxycorticosterone. The latter compound then moves CHAPTER 34 The Adrenal Gland 613 into the mitochondrion, where it is converted to aldos- adrenal glands by microorganisms or autoimmune disease. This conversion involves three steps: the hydroxy- This disorder is called Addison’s disease. If sufficient adrenal lation of carbon 11 to form corticosterone, the hydroxyla- cortical tissue is lost, the resulting decrease in aldosterone tion of carbon 18 to form 18-hydroxycorticosterone, and production can lead to vascular collapse and death, unless the oxidation of the 18-hydroxymethyl group to form al- hormone therapy is given (see Clinical Focus Box 34. In humans, these three reactions are catalyzed by a single enzyme, aldosterone synthase (CYP11B2), an Transport of Adrenal Steroids in Blood. As noted earlier, isozyme of 11 -hydroxylase (CYP11B1), expressed only in steroid hormones are not stored to any extent by cells of the glomerulosa cells. The 11 -hydroxylase enzyme, which is adrenal cortex but are continually synthesized and secreted.

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Female Reproductive © The McGraw−Hill Anatomy 20 mg tadalis sx sale erectile dysfunction doctor dallas, Sixth Edition Development System Companies generic tadalis sx 20 mg overnight delivery erectile dysfunction pre diabetes, 2001 Chapter 21 Female Reproductive System 739 Clavicle Suspensory ligaments 1st rib Lactiferous sinus Nipple Pectoralis major muscle Lobule (cut) Areola Adipose tissue Mammary ducts Intercostal muscles Pectoralis minor muscle (b) Pectoral fascia Lactiferous duct Lobe Lactiferous sinus Lung Mammary duct (a) Suspensory ligaments FIGURE 21. In structure, the mammary glands, located in the breasts, are Each mammary gland is composed of 15 to 20 lobes, each modified sweat glands and are a part of the integumentary sys- with its own drainage pathway to the outside. In function, however, these glands are associated with the rated by varying amounts of adipose tissue. The amount of adi- reproductive system because they secrete milk for the nourish- pose tissue determines the size and shape of the breast but has ment of the young. The size and shape of the breasts vary consid- nothing to do with the ability of a woman to nurse. Each lobe is erably from person to person in accordance with genetic subdivided into lobules that contain the glandular mammary differences, age, percentage of body fat, or pregnancy. The mammary alveoli are the structures that berty, estrogen from the ovaries stimulates growth of the mam- produce the milk of a lactating female. Suspensory ligaments be- mary glands and the deposition of adipose tissue within the tween the lobules extend from the skin to the deep fascia overly- breasts. Mammary glands hypertrophy in pregnant and lactating ing the pectoralis major muscle and support the breasts. The lumen of each lactiferous duct expands near the Structure of the Breast nipple to form a lactiferous sinus. Milk is stored in the lactifer- ous sinuses before draining at the tip of the nipple. The surface of the areola may appear tions of the serratus anterior and external abdominal oblique bumpy because of the sebaceous areolar glands close to the sur- muscles (see figs. The breast overlies the lateral margin of the sternum, and the lateral color of the areola and nipple varies with the complexion of the margin of the breast follows the anterior border of the axilla. During pregnancy, the areola becomes darker in most axillary process of the breast extends upward and laterally toward women, and enlarges somewhat, presumably to become more the axilla, where it comes into close relationship with the axil- conspicuous to a nursing infant. This region of the breast is clinically significant be- Blood is supplied to the mammary gland through the perfo- cause of the high incidence of breast cancer within the rating branches of the internal thoracic artery, which enter the lymphatic drainage of the axillary process. Female Reproductive © The McGraw−Hill Anatomy, Sixth Edition Development System Companies, 2001 740 Unit 7 Reproduction and Development Mammary alveoli with Secretory secretions tubules Interlobular connective tissue (a) (b) FIGURE 21. Venous OVULATION AND MENSTRUATION return is through a series of veins that parallel the pattern of the Ovulation and menstruation are reproductive cyclic events that arteries. A superficial venous plexus may be apparent through the are regulated by follicle-stimulating hormone (FSH) and skin of the breast, especially during pregnancy and lactation. Sensory nerve endings in the nipple and areola are especially important Objective 13 Describe the hormonal changes that result in in stimulating the release of milk from the mammary glands to a ovulation and menstruation. Objective 14 Describe the structural changes that occur in Lymphatic drainage and the location of lymph nodes within the the endometrium during a menstrual cycle and explain how breast are of considerable clinical importance because of the these changes are controlled by hormones. About 75% of the lymph drains through the axillary process of the breast into the pectoral lymph nodes (fig. Some 20% of the Both ovulation and menstruation are reproductive functions of lymph passes toward the sternum to the internal thoracic lymph nodes. The remaining 5% of the lymph is subcutaneous and follows sexually mature females and are largely regulated by hormones the lymph drainage pathway in the skin toward the back, where it from the anterior pituitary and the ovaries. Both occur approxi- reaches the intercostal nodes near the neck of the ribs. The commonalities of the tissues making up these or- ondary oocyte that passes into the uterine tube. Ovulation typi- gans are that they are composed of highly metabolically active cally occurs from alternate ovaries. In addition, these cells are sensitive to chemicals—they have to be because they are hormonally regulated— divisions are initiated and the blastocyst implants on the uterine and thus, are also sensitive to carcinogens (cancer-causing agents). If the egg is not fertilized, the menstrual cycle is initiated usually 14 days after ovulation. The menstrual flow passes from the uterine cav- which milk passes during lactation.

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During fetal development buy tadalis sx 20 mg cheap erectile dysfunction weed, its cells mingle with those of the anterior Knowledge Check lobe trusted 20mg tadalis sx erectile dysfunction just before intercourse, and in adults they no longer constitute a separate structure. What are some of the ways in which endocrine and ex- The neurohypophysis is the neural part of the pituitary ocrine glands differ structurally? How are the nervous and endocrine systems functionally which is in contact with the adenohypophysis, and the funnel- related? Also list the organs that serve other body functions, in addition to secreting hormones. Using diagrams, describe the mechanism of steroid hor- mone action and the mechanism of protein hormone ac- tion within cells. List the three kinds of hormones, give examples of each, into the nasal cavity) and describe their chemical compositions. Endocrine System © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 14 Endocrine System 461 Anterior Third ventricle cerebral artery Optic chiasma Cerebral cortex Hypothalamus Optic nerve Oculomotor nerve Pituitary stalk Trochlear nerve Posterior Anterior lobe lobe of of pituitary pituitary gland gland Sphenoidal Basilar artery sinus Sphenoid Sella turcica bone Waldrop (a) FIGURE 14. Endocrine System © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 462 Unit 5 Integration and Coordination Chromophobes Chromophils GH is regulated by growth hormone–releasing hormone (GH–RH) and growth hormone–inhibiting hormone (GH–IH), or somatostatin, from the hypothalamus. The precise mechanism of GH is not understood, but it seems to promote the movement of amino acids through cell membranes and the utilization of these substances in pro- tein synthesis. Pathological hyposecretion of GH during adolescence limits body growth, causing a type of dwarfism. In both of these conditions, body proportions are greatly distorted (see fig. In this condition, the soft tissues rapidly proliferate and certain body features, such as the hands, feet, nose, jaw, and tongue, become greatly distorted (see fig. TSH, frequently called thyrotropin, regulates the hormonal activity of the thyroid gland. Exposure to cold, cer- tain illnesses, and emotional stress may trigger an increased output of TSH. ACTH pro- through the infundibulum, along with minute neuroglia-like cells motes normal functioning of the adrenal cortex. The The pituitary gland is the structure of the brain perhaps most release of ACTH is controlled by a corticotropin-releasing subject to neoplasms. A tumor of the pituitary is generally de- hormone (CRH) produced in the hypothalamus. As with tected easily as it begins to grow and interfere with hormonal activity. If the tumor grows superiorly, it may exert sufficient pressure on the TSH, stress further influences the release of ACTH. In females, FSH plasm of the pituitary gland (hypophysectomy) may be performed transcranially through the frontal bone or through the nasal cavity regulates the monthly development of the follicle and and sphenoidal sinus. LH works with FSH, and to- Pituitary Hormones gether they are referred to as gonadotrophins, which means The pituitary gland releases nine important hormones. The first their target cells are located within the gonads or reproduc- seven in the following list are secreted by the anterior pituitary. In females, LH works with FSH in bringing The seventh is secreted by certain cells that are remnants of the about ovulation. The last two are produced in the hypothala- pus luteum and the production of another female sex hor- mus, transported through axons in the infundibulum to the pos- mone, progesterone (see chapter 21). The term trophic means “food”; it is hormone testosterone (see chapter 20). Endocrine System © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 14 Endocrine System 463 6. Prolactin is secreted in both males and females, but it functions primarily in females after parturition. Pro- lactin assists other hormones in initiating and sustaining milk production by the mammary glands. The hypothala- mus plays an important role in the release of this hormone through the production of prolactin-inhibiting hormone (PIH), now known to be dopamine. When PIH is secreted, the secretion of prolactin is inhibited; when PIH is not se- creted, prolactin is released. The exact action of MSH in humans is unknown, but it can cause darkening of the skin by stimulating the dispersion of melanin granules within melanocytes.

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Day hike the Lakes District of Chile to Patagonia of Argentina. Explore the culture and cuisine of the Andes while staying in comfortable cabins and hotels. Climb a volcano to see lava bubbling within its crater, hike through forests of ancient Araucarias, raft and learn and the art of fly fishing.
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