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All the four cutaneous sensory modalities can be elicited from the areas that contain only naked nerve endings erectile dysfunction doctors albany ny buy nizagara 100 mg. Thermoreceptors these receptors are sensitive to changes in the temperature of the skin popular erectile dysfunction drugs purchase nizagara 25 mg overnight delivery. Accordingly, there are two types of thermoreceptors: the warmth receptor and the cold receptor. Important Mechanoreceptors Pacinian Corpuscles these are mechanoreceptors located in the skin and deep tissues. Nociceptors They respond to painful stimuli, the stimuli that are harmful (damages the tissue or threaten to produce damage) to the organism. There are two types of nociceptors: A-mechanical nociceptors and C-polymodal nociceptors. Structure Pacinian corpuscle consists of a body composed of concentric layers (lamellae) much like an onion. The cell body of this A fiber lies in the dorsal root ganglion and the axon enters the spinal cord through dorsal root. The fiber is myelinated but the ending which lies in the concentric lamellae of the Pacinian corpuscle is unmyelinated. Function this is a rapidly adapting mechanoreceptor capable of receiving high frequency vibration. The distal end of the axon, not the lamellae of the Pacinian corpuscle is the actual transducer. Thus, when the concentric lamellae are stripped away, the force applied to the nerve ending continues to result in the genesis of receptor potential. The characteristic of the ending is that it is branched to form a complex structure inside the corpuscle. Ruffini Endings these are smallest mechanoreceptors present in both glabrous and hairy skin. The myelinated nerve fiber and its unmyelinated endings branch out to form a complex expanded structure. Function these are slowly adapting receptors that usually receive the sensation of crude touch. The fibers are myelinated but lose their myelin sheath before entering the epidermis. The afferent ending branches to form cup like flattened structures called Merkel disks which synapses with the special modified cells, the Merkel cells. The Merkel cells along with the Merkel disk are combinely called as Merkel apparatus or Iggo-dome receptor (because they elevate the epithelium of the skin). Structure these are encapsulated receptors into which the primary afferent nerve penetrates. The capsule is made up of modified cells that encircle the branched unmyelinated endings of A myelinated nerve fiber. Function these are rapidly adapting mechanoreceptors that mediate the sensation of touch and pressure. Function Merkel disks are slowly adapting mechanoreceptor that senses touch-pressure. Because the Merkel cells form a synaptic junction like structure with the Merkel disks, they are assigned the role of primary electromechanical transduction. Golgi-Mazzoni Corpuscle these are first identified in the tendons and muscles, but afterward also found in skin. Sinus Hair Follicle these are associated with hairs having large diameter and erectile tissue at the base surrounding the follicle. Nonsinus Hair Follicle these are associated with spray like terminals resembling Ruffini endings. Receptor Potential Receptors convert environmental energy into action potential in the sensory nerves. On application of stimulus (change in energy), a potential change is observed in the receptor. When the stimulus intensity is increased, the magnitude of the potential is proportionately increased. When it reaches about 10-15 mV, the action potential is generated in the sensory nerve.

Thus vyvanse erectile dysfunction treatment order nizagara canada, regulated pathway is capable of secretion of large amount of hormones erectile dysfunction drugs and melanoma buy nizagara with visa, whereas constitutive pathway promotes secretory reserve. Endocrine gland senses biological activity of the hormone and accordingly modulates its secretion. This system operates mainly for control of hypothalamo-pituitary-target endocrine gland axis. The endocrine cells that secrete the hormone also sense the biological activity produced by the hormone: 1. When the biological effects are more, the hormone secretion decreases appropriately to maintain normal function of the hormone (Flowchart 52. For exam ple, cells of pancreas secrete insulin that acts on liver and skeletal muscles to regulate blood glucose concen tration. Complex or Hierarchical Feedback Control When the feedback regulation involves second or third order feedback loop or both, the control mechanism is called complex or hierarchical control. This multiorder or complex control system is the usual mechanism for regula tion of many hormone secretions: 1. In this system, the hormone secreted by first (upper) order gland stimulates secretion of second (middle) order gland. Secretion (usually, trophic hormones) of middle order gland stimulates secretion of final (lower) order gland or target gland. Secretion of target gland (target gland hormone) inhibits the secretion of first order or middle order glands (Flowchart 52. Also, secretion of middle order gland (trophic hormone) inhibits secretion of first order gland. As this is an integrated system of control of endocrine functions, disorder at any level of hierarchy influences the function of other levels. The major hormone axes regulated by hierarchial system of feedback control are: Hypothalamopituitarythyroid axis Hypothalamopituitaryadrenal axis Hypothalamopituitarygonadal axis. Loops of Negative Feedback Control Depending on the distance from which the hormone of the target gland inhibits the upper order glands, the inhibition is classified into long loop, short loop and ultrashort loop. In this control system, increase in hormone concentration in plasma stimulates further secretion of that hormone so that the hormone concentration increases steadily to reach a peak plasma level: 1. Other examples are oxytocin secretion during parturi tion, release of oxytocin during breastfeeding and release of melatonin in response to darkness. Alteration in secretion of gonadal hormones at puberty in both boys and girls is the example of developmental hormonal secretion. Example of seasonal variation is change in hormone concentration in different times in a year that mostly occurs due to environmental changes. Neural Control Endocrine glands are usually innervated by both the com ponents of autonomic nervous system: 1. Stimulation of sympathetic or parasympathetic system therefore alters the endocrine secretions. Secre tion of catecholamines from adrenal medulla in response to sympathetic stimulation is an example. However, the receptor types present in the endocrine tissue determine the final secretion from the gland. Besides, innervation of the endocrine tissues may also be cholinergic, serotonergic or dopaminergic depend ing on the neurotransmitter released at the nerve ending. Secretion of hormones in response to various stimuli like visual, olfactory, gustatory, tactile, etc. One of the examples is the milk ejection reflex in which suckling by the baby increases secretion of oxytocin that causes contraction of myoepithelial cells of the mammary gland. Mechanisms the variation in hormone secretion is due to many mecha nisms such as change in secretory pattern influenced by photic stimuli (light-dark variation), change influenced by sleep (sleep-wake variation) or change subjected to environmental alteration (seasonal variation). Examples are glucagon stimulating insulin secretion, angiotensin stimulating aldosterone secretion, somatosta tin inhibiting growth hormone secretion and so on. Chemical Control Secretion of hormone is influenced by various chemical stimuli such as concentration of blood gasses, acids, ions and osmolality.

The frequency of peristaltic wave is about 3 per minute in human being and the waves are conducted from body toward pylorus latest advances in erectile dysfunction treatment buy generic nizagara pills. The gastric slow wave has four phases that resem ble the action potentials of cardiac muscle erectile dysfunction needle injection video order discount nizagara on-line. However, it does not overshoot and last for a longer period (10 times that of cardiac action potential). The smooth muscles of stomach contract when the depolarization of the slow wave exceeds the threshold for contraction. The force of contraction depends on the degree, frequency and duration of depolarization. Greater the depolarization and longer the muscle cells remain depolarized (above threshold), greater is the force of contraction. If stomach is allowed to remain empty for a longer duration, contractions become vigorous. The antral contractions are intense in such a situa tion and are associated with the relaxation of pyloric sphincter. Gastric Relaxations Receptive Relaxation this is the relaxation of the fundus and body of the stom ach in response to chewing and swallowing of food. Because of receptive relaxation, the intragastric pressure does not rise in spite of accumulation of a large volume of food. Normally, gastric motility induced by vagal stimulation is mediated by cholinergic fibers. Receptive relaxation is vagally mediated and adaptive relaxation is mainly a vagovagal reflex. Adaptive and Feedback Relaxations There are other two types of gastric relaxations: adaptive and feedback. The adaptive relaxation is the relaxation of stomach triggered by distension of stomach. Receptive relaxa tion starts even before food reaches stomach whereas adaptive relaxation occurs in response to stretching of stomach wall. The feedback relaxation of stomach is a reflexive relaxation that occurs due to presence of food in proximal segment of small intestine. Acidic chyme and fatty acid in intestine inhibit gastric motility by both hormonal and neural mechanisms that cause feed back relaxation of stomach. It helps in propelling food into the antrum and mixing of food with gastric juice. Therefore, food does not enter the duodenum, rather is recirculated in the stomach. Peristalsis After about half an hour following gastric filling, gastric peristalsis starts. The pacemaker for gastric peristalsis is located in the middle of the stomach close toward greater cur vature. Reverse Peristalsis Sometimes in abnormal situations, peristalsis occurs in reverse direction, which starts in the lower parts of the body and proceeds toward esophagus. The lower and upper esophageal sphincters relax so that gastric content is forced out of esophagus and oral cavity. Note, pyloric sphincter is closed in step A, B, and C during which thorough mixing and grinding of food occurs and the food material is converted into chyme. In stage D, sphincter is partially opened that causes slow emptying of gastric content into duodenum. Usually, it occurs at a slow but controlled rate so that duodenum and jejunum comfortably accommodate and process the chyme at a desired rate. Retropulsion the terminal part of antrum exhibits rapid and forceful contractions that forces the chyme to be propelled back toward the proximal part of the antrum and body of the stomach. Retropulsion is very effective in mixing and grinding the larger food particles into smaller ones. Then, pyloric sphincter partially opens and gastric pump slowly pushes food into duodenum.

The tight junctions between the endothelial cells of capillaries are very tight and erectile dysfunction drugs mechanism of action purchase genuine nizagara online, therefore erectile dysfunction inventory of treatment satisfaction questionnaire purchase nizagara 100 mg visa, do not permit the passage of substances through them. Cerebral Blood Vessels Arterial Supply the brain receives blood supply from two major sources: 1. The vertebrobasilar system: Two vertebral arteries join to from the basilar artery, which finally merges into the circle of Willis. The internal carotid arteries: Two internal carotid arteries along with basilar artery form the circle of Willis. The circle of Willis, which is formed by basilar artery and two internal carotids, gives rise to three pairs of large vessels supplying the brain. The total cerebral blood flow is 750 mL per minute, which is about 14% of cardiac output. Note, two vertebral arteries unite to form basilar artery, which along with internal carotids form circle of Wills. Therefore, block in any of the artery results in ischemic damage to the part supplied by the artery. The arterial sample and the venous sample (from internal jugular bulb) are collected and the arterio venous difference is measured. Innervation of Cerebral Vessels Cerebral blood vessels are innervated by sympathetic, parasympathetic and sensory fibers. Using Radioactive Substances Radioactive substance usually used is radioactive Xenon (133Xe). The substance is injected into the carotid artery and the radioactivity of different areas of the brain is mea sured by placing scintillation counters around the skull. However, vasoconstriction effect of sympathetic stimulation on cerebral blood vessels is less marked. In this method, a short-lived radioisotope is used to label a substance, which is injected. Scintillation detectors placed on the head to monitor the Chapter 98: Regional Circulations 847 appearance and clearance of the tracer. The information from detectors is processed in a computer that quantifies the flow in a particular region of the brain. Rise in intracranial pres sure results in compression of cerebral arteries that decreases blood flow. Increase in arterial pressure as occurs during downward acceleration, increases arterial pressure in the head. As the cerebral blood vessels do not allow all the sub stances to enter into the brain tissue, the physician must know the penetrability of a drug into the brain tissue and accordingly prescribe the drug in proper concentration. Stroke: Interruption of blood supply to a part of the brain causes ischemic damage to that part. Neural Regulation Stimulation of sympathetic fibers causes vasoconstriction, but it is not important, as the vasoconstrictor system is not well developed in cerebral vascular bed. Stroke Types of Strokes There are two types of strokes: hemorrhagic and ischemic strokes. Hemorrhagic stroke usually occurs due to rupture of a branch of cerebral artery at the site of aneurysm. Acidosis, hypoxia, and hypercapnea in the brain tissue 848 Section 9: Cardiovascular System Treatment of Stroke the treatment of stroke includes antiexcitotoxic and fibrinolytic drugs. Therefore, it is important to diagnose and initiate the treatment of stroke at the earliest possible. Ischemia of brain tissue decreases glutamate uptake that increases local glutamate con centration. Glutamate causes excitotoxic neuronal damage of the brain tissue (excitotoxic lesion). Cessation of heart functions for more than a couple of minutes is life threatening. Therefore, it is essential to maintain an unin terrupted and adequate blood supply to the heart. Blood Supply Arterial Supply the heart is supplied by right and left coronary arteries that originate from the root of the aorta behind right and left cusps of aortic valve respectively. The right coronary artery principally supplies the right ventricle and the right atrium, and the left coronary artery supplies the left ventricle and the left atrium. Physiologically, there are no anastomoses between the right and left coronary arteries.