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Because of their elasticity generic shuddha guggulu 60caps without prescription, the aorta and large arter- tions in the face of a variety of challenges order shuddha guggulu 60 caps with visa, such as exercise shuddha guggulu 60 caps lowest price, ies are distended by each injection of blood from the heart buy discount shuddha guggulu 60caps on-line. Unfortunately, failure of the cardiovascular system to per- Several regulatory mechanisms normally keep aortic form normally occurs all too often. In developed countries, pressure within a narrow range, providing a pulsatile but 210 CHAPTER 12 An Overview of the Circulation and Hemodynamics 211 Blood flows from capillaries into venules and small veins. These vessels have larger diameters and thinner walls than the companion arterioles and small arteries. When the smooth muscle in their walls contracts, the vol- ume of blood they contain is reduced. These vessels, along with larger veins, are referred to as capacitance vessels. The pressure generated by the contractions of the left ven- tricle is largely dissipated by this point; blood flows through the veins to the right atrium at much lower pres- sures than are found on the arterial side of the circulation. The right atrium receives blood from the largest veins, the superior and inferior vena cavae, which drain the entire body except the heart and lungs. The thin wall of the right SVC atrium allows it to stretch easily to store the steady flow of Aorta blood from the periphery. Because the right ventricle can receive blood only when it is relaxing, this storage function of the right atrium is critical. The muscle in the wall of the right atrium contracts at just the right time to help fill the IVC right ventricle. Contractions of the right ventricle propel blood through the lungs where oxygen and carbon dioxide are exchanged in the pulmonary capillaries. Pressures are much lower in the pulmonary circulation than in the sys- temic circulation. Blood then flows via the pulmonary vein to the left atrium, which functions much like the right atrium. The thick muscular wall of the left ventricle devel- ops the high pressure necessary to drive blood around the systemic circulation. The mechanisms that regulate all of the above anatomic elements of the circulation are the subject of the next few chapters. In this chapter, we consider the physical princi- ples on which the study of the circulation is based. In con- trast, the circulations of the organs other than the lungs are in Hemodynamics is the branch of physiology concerned parallel; that is, each organ receives blood from the aorta and re- with the physical principles governing pressure, flow, re- turns it to the vena cava. Exceptions are the various “portal” circu- sistance, volume, and compliance as they relate to the car- lations, which include the liver, kidney tubules, and hypothala- diovascular system. SVC, superior vena cava; IVC, inferior vena cava; RA, right few chapters to explain the performance of each part of the atrium; RV, right ventricle; LA, left atrium; LV, left ventricle. Smooth muscle in the relatively thick walls Between Pressure and Flow of small arteries and arterioles can contract or relax, causing large changes in flow to a particular organ or tissue. Pressure is of their ability to adjust their caliber, small arteries and ar- force applied over a surface, such as the force applied to terioles are called resistance vessels. The prominent pres- the cross-sectional surface of a fluid at each end of a rigid sure pulsations in the aorta and large arteries are damped by tube. The height of a column of fluid is often used as a the small arteries and arterioles. For example, the pressure at the bot- steady in the smallest arterioles. The height of a column of mer- ies are small enough that red blood cells flow through them cury (Fig. They are numerous enough so that every cell it is dense (approximately 13 times more dense than wa- in the body is close enough to a capillary to receive the nu- ter), and a relatively small column height can be used to trients it needs. The thin capillary walls allow rapid ex- measure physiological pressures. For example, mean arte- changes of oxygen, carbon dioxide, substrates, hormones, rial pressure is equal to the pressure at the bottom of a col- and other molecules and, for this reason, are called ex- umn of mercury approximately 93 mm high (abbreviated change vessels.
The median umbilical ligament buy shuddha guggulu 60 caps on-line, a fibrous remnant of the embryonic urachus (see Developmental Exposition shuddha guggulu 60caps sale, pp purchase 60caps shuddha guggulu with amex. The base of the urinary bladder receives the ureters 60 caps shuddha guggulu with visa, and the urethra exits at the inferior angle, or apex. The region surrounding the urethral opening is known as the neck of the urinary bladder. The internal trigone lacks rugae; it is therefore smooth in appearance and remains rel- atively fixed in position as the urinary bladder changes shape trigone: L. Urinary System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 686 Unit 6 Maintenance of the Body Urinary bladder Urinary bladder Urethra Prostatic part of urethra Membranous part of urethra Bulbourethral gland (b) Corpus cavernosum penis Spongy part of urethra (a) FIGURE 19. It consists of a prostatic part that passes through the prostate, a membranous part that passes through the urogenital diaphragm, and a spongy part that passes through the penis. Urinary System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 19 Urinary System 687 The second layer of the urinary bladder, the submucosa, The urethra of the male serves both the urinary and repro- functions to support the mucosa. At the neck of the urinary bladder, can be identified in the male urethra: the prostatic part, the the detrusor muscle is modified to form the superior (called the membranous part, and the spongy part (fig. It appears only on the superior surface of the urinary the neck of the urinary bladder. The portion of the urethra re- bladder and is actually a continuation of the parietal peritoneum. The external urethral sphincter muscle The autonomic nerves serving the urinary bladder are de- is located in this portion. Sympathetic innervation arises from The spongy part of the urethra is the longest portion (15 the last thoracic and first and second lumbar spinal nerves to cm), extending from the outer edge of the urogenital diaphragm serve the trigone, urethral openings, and blood vessels of the uri- to the external urethral orifice on the glans penis. Parasympathetic innervation arises from the sec- surrounded by erectile tissue as it passes through the corpus spon- ond, third, and fourth sacral nerves to serve the detrusor muscle. The ducts of the bulbourethral glands (Cow- The sensory receptors of the urinary bladder respond to disten- per’s glands) of the reproductive system attach to the spongy part sion and relay impulses to the central nervous system via the of the urethra near the urogenital diaphragm. The urinary bladder becomes infected easily, and because a woman’s urethra is so much shorter than a man’s, women are Micturition particularly susceptible to urinary bladder infections. It is a infection that involves the renal pelvis is called pyelitis; if it continues complex function that requires a stimulus from the urinary blad- into the nephrons, it is known as pyelonephritis. To reduce the risk of der and a combination of involuntary and voluntary nerve im- these infections, a young girl should be taught to wipe her anal re- gion in a posterior direction, away from the urethral orifice, after a pulses to the appropriate muscular structures of the urinary bowel movement. In young children, micturition is a simple reflex action that occurs when the urinary bladder becomes sufficiently distended. Urethra Voluntary control of micturition is normally developed by the time a child is 2 or 3 years old. Specialized urethral glands, embedded in average capacity of the urinary bladder is 700 to 800 ml. A vol- the urethral wall, secrete protective mucus into the urethral canal. The invol- stimulate stretch receptors and trigger the micturition reflex, cre- untary smooth muscle sphincter, the superior of the two, is the ating a desire to urinate. The lower sphincter, composed of third, and fourth sacral segments of the spinal cord. Following voluntary skeletal muscle fibers, is called the external urethral stimulation of this center by impulses arising from stretch recep- sphincter (fig. Stimulation of these muscles causes a rhythmic contrac- fice into the vestibule between the labia minora. The urethral tion of the urinary bladder wall and a relaxation of the internal orifice is positioned between the clitoris and vaginal orifice (see urethral sphincter. The female urethra has a single function: to transport ceived in the brain, but there is still voluntary control over urine to the exterior.
This chapter will consider the life history of a peptide transmitter cheap shuddha guggulu 60 caps online, comparing it to the classical transmitters such as the excitatory and inhibitory amino acids buy 60 caps shuddha guggulu visa, acetylcholine and the monoamines and then briefly review the main groups of peptides and their receptors and some of the possible functional aspects of peptides in the CNS cheap shuddha guggulu 60caps overnight delivery. Webster &2001 John Wiley & Sons Ltd 252 NEUROTRANSMITTERS cheap 60caps shuddha guggulu with mastercard, DRUGS AND BRAIN FUNCTION Figure 12. The study of the production of the propeptides have revealed a series of principles in that:. Some propeptides lead to the production of different, in terms of receptor affinities, peptides (substance P and neurokinin A act on neurokinin 1 and 2 receptors, respectively). Some propeptides produce multiple copies of similar peptides (met-enkephalin and leu-enkephalin act on the same delta opioid receptor). The whole process of production of a peptide is sluggish simply because the size of the precursor is so great. Once produced the precursor is packaged into vesicles and then transported down the axon to the terminal. Axonal transport is generally a slow process in that mm±cm/day is rarely exceeded. Thus in a long axon the arrival of the peptide at the release site at the terminal will not be quick. While the precursor is being transported it is processed further by peptidases within the vesicles that cleave the larger parent molecule into smaller fragments. It is easy to speculate that in an active neuron with a rapid firing pattern, the continued release of a peptide may eventually lead to depletion of the peptide occurring. If this also happens in the CNS it would provide a mechanism whereby the release and resultant receptor effects of a transmitter no longer match the firing pattern and demands of the neuron and so could contribute to long-term adaptations of neurons by a reduction in the time over which a peptide is effective. The release of some peptides may differ from that of other transmitters, depending on the firing rate of the neurons. The large vesicles needed to store a peptide may need a greater rate of depolarisation for membrane fusion and release of the contents. In the salivary gland the release of vasoactive intestinal polypeptide requires high-frequency stimulation whereas acetylcholine is released by all stimuli. Due to the complexities and problems of access to CNS synapses it is not known if the same occurs here but there is no reason why this should not. In sensory C-fibres a prolonged stimulus appears to be a prerequisite for the release of substance P. BREAKDOWN A peptide, once released, is not subject to reuptake like most transmitters, but is broken down by membrane peptidases. There are no known peptide transporters so that reuptake and re-use are not likely. The peptidases are predominantly membrane bound at the synapse and many are metalloproteases in that they have a metal moiety, most often zinc, near the active site. These enzymes are generally selective for particular 254 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION amino-acid sequences so that one peptidase may cleave a number of peptides if the amino-acid sequences overlap. A number of peptidases are found in the vasculature, including aminopeptidases and angiotensin-converting enzyme and any peptide with an acidic amino acid near the amino-terminal end of the peptide will be degraded after systemic administration. At a central synapse, the termination of action of a peptide relies on these peptidases. Thus, if there is considerable release at any one time, the peptide may saturate the enzyme(s) and so metabolism will not keep pace with release. Thus the peptide could escape the synapse where it was released and then diffuse through the tissue. The peptide may then act at sites distant from the neuron that released it, and these sites will be determined simply by receptors for the particular peptide. Consequently, volume transmission or non-synaptic effects may be important. This has been shown for lutenising hormone releasing factor (LHRH) in sympathetic ganglion cells where the peptide can act on neurons over distances of many hundreds of microns. In the CNS, the areas of spinal cord where neurokinins can be detected increase markedly when a prolonged intense peripheral stimulus is applied, suggesting saturation of peptidases allowing the intact transmitter to move through the tissue. Finally, one of the neurokinins, substance P, is found with calcitonin gene-related peptide (CGRP) in sensory neurons that terminate in the spinal cord.