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The two gonadotropin receptors are in serum and do not exhibit pulsatile secretion of LH cheap 20mg levitra super active visa best erectile dysfunction pills treatment. Pul- linked to G proteins and adenylyl cyclase for the produc- satile injections of GnRH restore LH and FSH secretion tion of cAMP from ATP levitra super active 20mg with mastercard erectile dysfunction doctors in maine. FSH pulses tend to be smaller in count for all of the actions of LH and FSH on testicular amplitude than LH pulses, mostly because FSH has a longer cells. These generating GnRH pulsatility is unknown, the presence of a factors activate the promoter region of the genes of pulse generator in the hypothalamus has been postulated. Similar signal-transducing events oc- pothalamus and is responsible for the synchronized and cur in Sertoli cells that regulate the production of estradiol. The activity of The testis converts testosterone and some other androgens the pulse generator is modified by several factors. For ex- to estradiol by the process of aromatization, although estra- ample, castration causes a large increase in basal LH levels diol production is low in males. Therefore, the pulse generator may be mature sperm, inhibin (a protein produced by Sertoli cells tonically inhibited by testosterone. However, GnRH neu- that suppresses FSH secretion), and androgen-binding pro- rons lack receptors for gonadal steroids, suggesting that tein. Activin and follistatin production by testicular cells in humans is currently being investigated. GnRH Is Secreted in a Pulsatile Manner GnRH GnRH in the hypothalamus is secreted in a pulsatile man- ner into the hypothalamic-hypophyseal portal blood. GnRH pulsatility is ultimately necessary for proper func- tioning of the testes because it regulates the secretion of FSH and LH, which are also released in a pulsatile fashion (Fig. Continuous exposure of gonadotrophs to GnRH results in desensitization of GnRH receptors, lead- ing to a decrease in LH and FSH release. Therefore, the pulsatile pattern of GnRH release serves an important physiological function. The administration of GnRH at an improper frequency results in a decrease in circulating con- LH centrations of LH and FSH. Most evidence for GnRH pulses has come from animal studies because GnRH must be measured in hypothalamic- 1 2 3 4 5 6 7 8 9 hypophyseal portal blood, an extremely difficult area to Time (hr) obtain blood samples in humans. Since discrete pulses of GnRH are followed by distinct pulses of FSH and LH, A diagram of the pulsatile release of GnRH FIGURE 37. Between the sev- Steroids and Polypeptides From the enth month of pregnancy and birth, the testes descend Testis Regulate LH and FSH Secretion through the inguinal canal into the scrotum. The location of the testes in the scrotum is important for sperm production, Testosterone, estradiol, inhibin, activin, and follistatin are which is optimal at 2 to 3 C lower than core body tempera- major testicular hormones that regulate the release of the ture. Two systems help maintain the testes at a cooler tem- gonadotropins LH and FSH. One is the pampiniform plexus of blood vessels, diol, and inhibin reduce the secretion of LH and FSH in the which serves as a countercurrent heat exchanger between male. Activin stimulates the secretion of FSH, whereas fol- warm arterial blood reaching the testes and cooler venous listatin inhibits FSH secretion. The second is the cremasteric mus- Testosterone inhibits LH release by decreasing the se- cle, which responds to changes in temperature by moving cretion of GnRH and, to a lesser extent, by reducing go- the testes closer or farther away from the body. Estradiol formed from exposure of the testes to elevated temperature, fever, or testosterone by aromatase also has an inhibitory effect on thermoregulatory dysfunction can lead to temporary or per- GnRH secretion. Acute testosterone treatment does not al- manent sterility as a result of a failure of spermatogenesis, ter pituitary responsiveness to GnRH, but prolonged expo- whereas steroidogenesis is unaltered. The testes are encapsulated by a thick fibrous connec- Removal of the testes results in increased circulating lev- tive tissue layer, the tunica albuginea. Replacement therapy with physiologi- contains hundreds of tightly packed seminiferous tubules, cal doses of testosterone restores LH to precastration levels ranging from 150 to 250 m in diameter and from 30 to 70 but does not completely correct FSH levels. The tubules are arranged in lobules, separated by tion led to a search for a gonadal factor that specifically in- extensions of the tunica albuginea, and open on both ends hibits FSH release. Examination of a cross section of a testis eventually isolated from seminal fluid.

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Neural control involves and arterial pressure regulation strongly influence cardio- sympathetic and parasympathetic branches of the auto- vascular control mechanisms buy 20mg levitra super active with visa impotence from priapism surgery. Blood volume and arterial the fight-or-flight response order 40 mg levitra super active with visa erectile dysfunction doctors in st louis mo, diving, thermoregulation, pressure are monitored by stretch receptors in the heart and standing, and exercise. Sympathetic fibers to the heart release NE, which binds Neural regulation of the cardiovascular system involves the to 1-adrenergic receptors in the sinoatrial node, the atri- firing of postganglionic parasympathetic and sympathetic oventricular node and specialized conducting tissues, and neurons, triggered by preganglionic neurons in the brain cardiac muscle. Stimulation of these fibers causes increased (parasympathetic) and spinal cord (sympathetic and heart rate, conduction velocity, and contractility. Afferent input influencing these neurons The two divisions of the autonomic nervous system tend comes from the cardiovascular system, as well as from other to oppose each other in their effects on the heart, and ac- organs and the external environment. Briefly, the heart is innervated by Blood vessels (except those of the external genitalia) re- parasympathetic (vagus) and sympathetic (cardioaccelera- ceive sympathetic innervation only (see Fig. Parasympathetic fibers release neurotransmitter is NE, which binds to 1-adrenergic re- acetylcholine (ACh), which binds to muscarinic receptors ceptors and causes vascular smooth muscle contraction and of the sinoatrial node, the atrioventricular node, and spe- vasoconstriction. Stimulation of parasympathetic the adrenal medulla, binds to 2-adrenergic receptors of fibers causes a slowing of the heart rate and conduction ve- vascular smooth muscle cells, especially coronary and locity. The ventricles are only sparsely innervated by skeletal muscle arterioles, producing vascular smooth mus- parasympathetic nerve fibers, and stimulation of these cle relaxation and vasodilation. Postganglionic parasympa- fibers has little direct effect on cardiac contractility. Some thetic fibers release ACh and nitric oxide (NO) to blood cardiac parasympathetic fibers end on sympathetic nerves vessels in the external genitalia. ACh causes the further re- and inhibit the release of norepinephrine (NE) from sym- lease of NO from endothelial cells; NO results in vascular pathetic nerve fibers. Therefore, in the presence of sympa- smooth muscle relaxation and vasodilation. Parasympathetic Sympathetic Vagus nerves Ganglion ACh ACh SA NE ACh AV NE NE ACh ACh Thoracic Adrenal medulla ACh ACh 90% E Most blood vessels 10% NE NE Lumbar Sacral Blood vessels of external genitalia ACh Spinal cord ACh FIGURE 18. ACh, acetylcholine; NE, norepi- nephrine; E, epinephrine; SA, sinoatrial node; AV, atrioventricular node. The central terminals for these receptors steady level of background postganglionic activity (tone). Neurons from the NTS project to the sympathetic vasoconstriction, cardiac stimulation, and RVL and nucleus ambiguus where they influence the firing adrenal medullary catecholamine secretion, all of which of sympathetic and parasympathetic nerves. This tonic activity is generated by excitatory signals from Baroreceptor Reflex Effects on Cardiac Output and Sys- the medulla oblongata. Increased pressure in the transected and these excitatory signals can no longer carotid sinus and aorta stretches carotid sinus barorecep- reach sympathetic preganglionic fibers, their tonic firing tors and aortic baroreceptors and raises their firing rate. For example, the stimulation of pain fibers entering the wall of the arch of the aorta, travel with the vagus (cra- the spinal cord below the level of a chronic spinal cord nial nerve X) nerves to the NTS. This results in increased The Medulla Is a Major Area for Cardiovascular parasympathetic neural activity to the heart and decreased Reflex Integration sympathetic neural activity to the heart and resistance ves- sels (primarily arterioles) (Fig. Since mean arterial pressure is the functions: product of SVR and cardiac output (see Chapter 12), mean • Generating tonic excitatory signals to spinal sympa- arterial pressure is returned toward the normal level. This thetic preganglionic fibers completes a negative-feedback loop by which increases in • Integrating cardiovascular reflexes mean arterial pressure can be attenuated. Neurons in the rostral ventrolateral nu- sulting in increased heart rate, stroke volume, and SVR; this cleus (RVL) are normally active and provide tonic excita- tory activity to the spinal cord. Specific pools of neurons within the RVL have actions on heart and blood vessels. RVL neurons are critical in mediating reflex inhibition or activating sympathetic firing to the heart and blood vessels. The cell bodies of cardiac preganglionic parasympathetic neurons are located in the nucleus ambiguus; the activity of these neurons is influenced by reflex input, as well as in- put from respiratory neurons. Respiratory sinus arrhythmia, described in Chapter 13, is primarily the result of the influ- ence of medullary respiratory neurons that inhibit firing of preganglionic parasympathetic neurons during inspiration and excite these neurons during expiration. The Baroreceptor Reflex Is Important in the Regulation of Arterial Pressure The most important reflex behavior of the cardiovascular system originates in mechanoreceptors located in the aorta, carotid sinuses, atria, ventricles, and pulmonary vessels. These mechanoreceptors are sensitive to the stretch of the walls of these structures.

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Therefore safe levitra super active 40mg erectile dysfunction only with partner, the pulmonary circulation is not The primary function of the pulmonary circulation is to a regional circulation like the renal levitra super active 20mg mastercard impotence versus erectile dysfunction, hepatic, or coronary bring venous blood from the superior and inferior vena circulations. In addition to gas exchange, the pul- systemic vascular resistance has for the left ventricle. Each time an airway branches, Pulmonary vessels protect the body against thrombi the arterial tree branches so that the two parallel each other (blood clots) and emboli (fat globules or air bubbles) from (Fig. More than 40% of lung weight is comprised of entering important vessels in other organs. The total blood vol- emboli often occur after surgery or injury and enter the sys- ume of the pulmonary circulation (main pulmonary artery temic venous blood. Small pulmonary arterial vessels and to left atrium) is approximately 500 mL or 10% of the total capillaries trap the thrombi and emboli and prevent them circulating blood volume (5,000 mL). The pulmonary veins from obstructing the vital coronary, cerebral, and renal ves- contain more blood (270 mL) than the arteries (150 mL). Endothelial cells lining the pulmonary vessels release The blood volume in the pulmonary capillaries is approxi- fibrinolytic substances that help dissolve thrombi. Emboli, 337 338 PART V RESPIRATORY PHYSIOLOGY A Lung The lungs serve as a blood reservoir. Approximately 500 mL or 10% of the total circulating blood volume is in the Bronchus pulmonary circulation. During hemorrhagic shock, some of Pleura this blood can be mobilized to improve the cardiac output. Pulmonary artery The Pulmonary Circulation Has Pulmonary Unique Hemodynamic Features vein In contrast to the systemic circulation, the pulmonary cir- culation is a high-flow, low-pressure, low-resistance sys- B tem. The pulmonary artery and its branches have much Pulmonary arteriole thinner walls than the aorta and are more compliant. The Muscle strand pulmonary artery is much shorter and contains less elastin Alveolus and smooth muscle in its walls. The pulmonary arterioles Pulmonary venule are thin-walled and contain little smooth muscle and, con- sequently, have less ability to constrict than the thick- walled, highly muscular systemic arterioles. The pulmonary veins are also thin-walled, highly compliant, and contain little smooth muscle compared with their counterparts in Respiratory bronchiole the systemic circulation. Unlike the Alveolar capillary systemic capillaries, which are often arranged as a network of tubular vessels with some interconnections, the pulmonary capillaries mesh together in the alveolar wall so that blood flows as a thin sheet. It is, therefore, misleading to refer to pulmonary capillaries as a capillary network; they comprise a Parallel structure of the vascular and air- dense capillary bed. A, Systemic venous blood flows ceedingly thin, and a whole capillary bed can collapse if lo- through the pulmonary arteries into the alveolar capillaries and cal alveolar pressure exceeds capillary pressure. B, A mesh of capillaries surrounds each alve- ingly in their pressure profiles (Fig. As the blood passes through the capillaries, it gives up car- arterial pressure is 15 mm Hg, compared with 93 mm Hg in bon dioxide and takes up oxygen. The driving pressure (10 mm Hg) for pulmonary flow is the difference between the mean pressure in the pul- especially air emboli, are absorbed through the pulmonary monary artery (15 mm Hg) and the pressure in the left capillary walls. These pulmonary pressures are meas- monary vessel, gas exchange can be severely impaired and ured using a Swan-Ganz catheter, a thin, flexible tube with can cause death. A similar situation occurs if emboli are ex- an inflatable rubber balloon surrounding the distal end. The tremely numerous and lodge all over the pulmonary arterial balloon is inflated by injecting a small amount of air tree (see Clinical Focus Box 20. Although the Swan-Ganz Vasoactive hormones are metabolized in the pulmonary catheter is used for several pressure measurements, most circulation. One such hormone is angiotensin I, which is useful is the pulmonary wedge pressure (Fig. To activated and converted to angiotensin II in the lungs by measure wedge pressure, the catheter tip with balloon in- angiotensin-converting enzyme (ACE) located on the sur- flated is “wedged” into a small branch of the pulmonary ar- face of the pulmonary capillary endothelial cells. When the inflated balloon interrupts blood flow, the tion is extremely rapid; 80% of angiotensin I (AI) can be tip of the catheter measures downstream pressure. The converted to angiotensin II (AII) during a single passage downstream pressure in the occluded arterial branch repre- through the pulmonary circulation. In addition to being a sents pulmonary venous pressure, which, in turn, reflects potent vasoconstrictor, AII has other important actions in left atrial pressure. Metabolism of vasoactive hor- atrial pressures have a profound effect on gas exchange, and mones by the pulmonary circulation appears to be rather pulmonary wedge pressure provides an indirect measure of selective.

The cylindrical taste bud is salts (ammonium salts) initiate respiratory reflexes and are used to revive unconscious persons discount levitra super active 20 mg without prescription erectile dysfunction 24. However buy 20mg levitra super active erectile dysfunction medication and heart disease, because of the caustic nature composed of numerous sensory gustatory cells that are encapsu- of smelling salts and the irreparable damage it may cause to the un- myelinated olfactory hairs, it is seldom used in first aid treatment of an unconscious person. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 497 Vallate papilla Filiform papilla Lingual tonsil Epiglottis Fungiform papilla Palatine tonsil Root of tongue Vallate Taste buds Body papillae of tongue (b) Fungiform papillae Squamous Median epithelium groove of tongue Supporting cell Apex Filiform of tongue (a) papillae Gustatory cell Taste pore Gustatory microvilli Connective tissue (c) FIGURE 15. Each gustatory cell contains Taste buds are found only in the vallate and fungiform papil- a dendritic ending called a gustatory microvillus that projects to lae. The filiform papillae, although the most numerous of the the surface through an opening in the taste bud called the taste human tongue papillae, are not involved in the perception of taste. The gustatory microvilli are the sensitive portion of the re- Their outer cell layers are continuously converted into scalelike pro- ceptor cells. Saliva provides the moistened environment neces- jections, which give the tongue surface its somewhat abrasive feel. There are only four basic tastes,which are sensed most Taste buds are elevated by surrounding connective tissue acutely on particular parts of the tongue (fig. Three princi- sweet (tip of tongue), sour (sides of tongue), bitter (back of pal types of papillae can be identified: tongue),and salty (over most of the tongue,but concentrated • Vallate papillae. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 498 Unit 5 Integration and Coordination Sweet Sour Salty Bitter receptors receptors receptors receptors FIGURE 15. This diagram indicates the tongue regions that are maximally sensitive to different tastes. Trigeminal nerve Trigeminal ganglion Geniculate ganglion Lingual nerve Facial nerve Uvula Tongue Glossopharyngeal nerve Chorda tympani nerve Vagus nerve Laryngeal nerve FIGURE 15. The chorda tympani nerve is the sensory branch of the facial nerve innervating the tongue. Branches from the paired vagus (tenth cranial) nerves and the trigeminal (fifth cranial) nerves also provide some sensory innervation. The hypoglossal (twelfth cranial) nerve (not shown) provides motor innervation to the tongue. The lingual nerve transmits general sensory information from the tongue (hot, cold, pressure, and pain). Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 499 The sensory pathway that relays taste sensations to the brain mainly involves two paired cranial nerves (fig. Taste sensations passing through the nerves just Principal Functions Principal Functions mentioned are conveyed through the medulla oblongata and thalamus to the parietal lobe of the cerebral cortex, where they Eyelid: protection Lens cap: protection are interpreted. Conjunctiva: protection Lens filter: protection Cornea and lens: focus incoming Lens system: focuses incoming light Because taste and smell are both chemoreceptors, they com- light waves waves plement each other. We often confuse a substance’s smell with its taste; and if we have a head cold or hold our nose while eat- Iris and pupil: regulate amount of Variable aperture system: regulates ing, food seems to lose its flavor. Distinguish between papillae, taste buds, and gustatory mi- Pigment epithelium: maintains Black interior of camera: maintains crovilli. Which cranial nerves have sensory innervation associated Retina: contains photosensitive Film: material coated on one side with taste? What are the sensory pathways to the brain cones and rods that respond to with photosensitive emulsion where the perception of taste occurs? Formation of the sensory components of the eye is com- sider, for example, the extremely keen eyesight of a hawk, which plete at 20 weeks, and the accessory structures have been soars high in the sky searching for food, or the eyesight of the owl, formed by 32 weeks. Predatory species, such as cats, Objective 11 Describe the accessory structures of the eye have eyes that are directed forward, allowing depth perception. Objective 13 Describe the neural pathway of a visual Accessory Structures of the Eye impulse and discuss the neural processing of visual information. Accessory structures of the eye either protect the eyeball or en- able eye movement. Protective structures include the bony orbit, eyebrow, facial muscles, eyelids, eyelashes, conjunctiva, The eyes are organs that refract (bend) and focus incoming light and the lacrimal apparatus that produces tears. Eyeball move- rays onto the sensitive photoreceptors at the back of each eye. The spe- cialized photoreceptor cells can respond to an incredible 1 bil- lion different stimuli each second.

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