By J. Ugolf. Virginia University of Lynchburg. 2018.
The venous tamin B12 (together with intrinsic factor) orally or through injections order aleve 250mg otc pain treatment center of the bluegrass lexington ky, so that he or she will not develop pernicious anemia 500mg aleve otc pain management treatment center. This vein unites with the splenic vein to form the hepatic portal vein, which carries nutrient-rich blood to the liver (see fig. Describe the three stages of deglutition with reference to the structures involved. Describe the structure and function of the lower On the basis of function and histological structure, the small in- esophageal sphincter. Describe the modifications of the stomach that aid in me- mately 25 cm (10 in. Except for a short portion near the stomach, the duodenum is retroperitoneal. Its concave surface faces to the left, where it receives bile secretions from the liver and SMALL INTESTINE gallbladder through the common bile duct and pancreatic The small intestine, consisting of the duodenum, jejunum, and secretions through the pancreatic duct of the pancreas ileum, is the site where digestion is completed and nutrients are (fig. The surface area of the intestinal wall is increased by entry into the duodenum called the hepatopancreatic am- plicae circulares, intestinal villi, and microvilli. It is here that bile and pancreatic juice intestine and the way in which it is supported. The duodenal papilla can be opened or closed by the action of the sphincter of ampulla Objective 13 List the functions of the small intestine and (of Oddi). The duodenum differs histologically from the describe the structural adaptations through which these functions are accomplished. These Objective 14 Describe the movements that occur within the compound tubuloalveolar glands secrete mucus and are small intestine. It has pyloric sphincter of the stomach and the ileocecal valve that a slightly larger lumen and more internal folds than does opens into the large intestine. It is positioned in the central and the ileum, but its histological structure is similar to that of lower portions of the abdominal cavity and is supported, except the ileum. The fan- shaped mesentery permits movement of the small intestine but leaves little chance for it to become twisted or kinked. Enclosed within the mesentery are blood vessels, nerves, and lymphatic vessels that supply the intestinal wall. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 18 Digestive System 653 Duodenum Jejunum Intestinal v Ileum Tunica muscularis FIGURE 18. The terminal portion of the ileum empties • The three meter length of the small intestine. In a light micro- The products of digestion are absorbed across the epithelial lin- scope, the microvilli display a somewhat vague brush ing of the intestinal mucosa. Absorption occurs primarily in the jejunum, although some also occurs in the duodenum and ileum. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 654 Unit 6 Maintenance of the Body TABLE 18. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 18 Digestive System 655 Simple Intestinal villus columnar (lined with simple epithelium columnar epithelium) Lacteal Intestinal Capillary Lamina propria villus network Goblet cells Muscularis mucosa Intestinal crypt Duodenal glands Lymph vessel FIGURE 18. The terms brush border and microvilli are Venule Waldrop often used interchangeably in describing the small intestine. The intestinal villi are covered with columnar epithelial cells, among which are interspersed the mucus-secreting goblet FIGURE 18. Absorbed monosaccharides and amino acids enter the blood capillaries; absorbed fatty acids and cholesterols enter the lacteals. Intestinal villi are considered the functional units of the digestive system because absorption through these structures is how digested molecules enter the blood or lymph. Epithelial cells at the tips of the intestinal villi are continu- ously shed and are replaced by cells that are pushed up from the bases of the intestinal villi. The epithelium at the base of the in- testinal villi invaginates downward at various points to form nar- row pouches that open through pores into the intestinal lumen. These structures are called the intestinal crypts (crypts of Lieberkühn) (see fig. Mechanical Activities of the Small Intestine Contractions of the longitudinal and circular muscles of the small intestine produce three distinct types of movement: rhyth- mic segmentation, pendular movements, and peristalsis. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 656 Unit 6 Maintenance of the Body Rhythmic segmentations are local contractions of the cir- orly on the right side to a point just below the liver; it then cular muscular layer. They occur at the rate of about 12 to 16 per crosses to the left, descends into the pelvis, and terminates at the minute in regions containing chyme.
Studies using in unmyelinated nerve fibers by the cyto- polarized light and X-rays have shown that plasm of the sheath cells purchase aleve 500 mg mastercard eastern ct pain treatment center, and in myelinated the myelin sheath is made up of alternating nerve fibers by the myelin sheath (ABG2) buy 250mg aleve fast delivery natural pain treatment for dogs. Ac- Axon and sheath together are called the cordingly, the dark lines (major period line nerve fiber. The myelin sheath begins be- and intraperiod line) are regarded as layers hind the initial segment of the axon and of protein molecules and the light lines as endsjustbeforetheterminalramification. The sheath cells in the CNS are oligodendrocytes; in the peripheral nerves they are Schwann cells, which origi- nate from the neural crest (p. The myelin sheath of fresh, unfixed nerve fibers appears highly refractile and without struc- ture. The lipids are removed upon fixation, and the denatured protein scaffold remains as a gridlike structure (neurokeratin) (D3). At regular intervals (1–3mm), the myelin sheath is interrupted by deep constrictions, thenodesofRanvier(AB4F). Thesegmentbe- tween two nodes of Ranvier in peripheral nerves, the internode or interannular segment (F), corresponds to the expansion of one sheath cell. The cell nucleus (ADF5) and perinuclear cytoplasm form a slight bulge onthemyelinsheathinthemiddleofthein- ternode. Cytoplasm is also contained in ob- lique indentations, the Schmidt–Lanterman incisures (C, F6) (see also p. The mar- gins of the sheath cells define the node of Ranvier at which axon collaterals (E) may branch off or synapses may occur. Ultrastructure of the Myelin Sheath (G) The electron micrograph shows the axon enclosed by a plasma membrane, the ax- olemma; it is surrounded by a series of regu- larly spaced, concentric dark and light lines (period lines). The width of each lamella from one dark line to the next measures 120Å on average (1Å=0. As seen at higher magnification, the light lines are subdivided by a thin irregular Kahle, Color Atlas of Human Anatomy, Vol. Myelin Sheath 37 5 4 2 1 A Nerve fiber (according to von Möllendorff) 5 2 4 B Node of Ranvier, osmium stain (diagram) C Schmidt–Lanterman incisures 5 3 D Perikaryon of a Schwann cell E Axonal branching 5 4 6 4 1 F Internode (according to Cajal) 1 2 7 G Electron-microscopic views of the myelin sheath Kahle, Color Atlas of Human Anatomy, Vol. The groove deep- nates only one axon, an oligodendrocyte (B9) ens and its margins approach each other intheCNSmyelinatesseveralaxonsandwill and finally meet. In this way, a duplication later remain connected with several inter- of the cell membrane is formed, the mesaxon nodes via cytoplasmic bridges. The extent (A3), which wraps around the axon like a and shape of the cell becomes clear when spiral as the Schwann cell migrates around visualizing the internodes as being unfurled the encircled axon. The external mesaxon The term mesaxon is based on the term forms an external bulge (B10) starting from mesenterium, a thin duplication that is the cytoplasmic bridge. The myelin lamellae formed as a suspension band by the peri- terminate at the paranodal region (B11) toneum and encloses the intestine. As seen in the longitudi- ilar way, the Schwann cell forms a duplica- nal section, the innermost lamella termi- tion and envelops the axon. Like all plasma nates first and the outermost lamella covers membranes, the cell membrane of the the remaining endings, terminating directly Schwann cell consists of an outer and an at the node of Ranvier. At the ends of the inner dense layer of protein and a light lipid lamellae, the dense major period lines layer between them. Upon membrane du- widen into pockets filled with cytoplasm plication, the two outer protein layers come (B12). The axon of the central nerve fiber is into apposition first and fuse to form the in- completely exposed in the area of the node traperiod line (A4). There are no Schmidt–Lanter- membrane duplication becomes the five- man incisures in the CNS. With further encir- cling, the inner protein layers of the cell membrane make contact as well and fuse to form the dense major period line (A5). At the end of the process, the start of the duplica- tion lies inside the myelin sheath, the inter- nal mesaxon (AB6), while the end lies out- side, the external mesaxon (7 in A, B). Development of Unmyelinated Nerve Fibers (A) Unmyelinated nerve fibers (A8) are en- veloped by sheath cells, each of which en- circles several axons. The margins of the grooves may also form a membrane dupli- cation (mesaxon) but without fusion of the membrane layers. Myelin Sheath 39 4 6 7 1 3 5 2 8 A Development of the myelin sheath (according to Hamilton, Boyd and Mossman) 9 10 7 6 12 B Central nerve fiber, electron-microscopic diagram (according to Bunge) 11 C Oligodendrocyte with myelin lamellae (according to Bunge) Kahle, Color Atlas of Human Anatomy, Vol.
Rib Postganglionic axons that are destined for somatic struc- tures—such as sweat glands quality 250 mg aleve pain after lithotripsy treatment, pilomotor muscles order aleve 250 mg with mastercard back pain treatment videos, or blood Gray White vessels of the skin and skeletal muscles—leave the paraver- ramus ramus tebral ganglion in the gray ramus and rejoin the spinal Paravertebral nerve for distribution to the target tissues. Postganglionic sympathetic axons to the head, heart, and lungs originate in the cervical ganglion or upper thoracic paravertebral ganglia and make their way to the specific organs as identifiable, separate nerves (e. The pre- the cardiac nerves), as small-caliber individual nerves that ganglionic axons course through the spinal nerve and white ramus to the paravertebral ganglion. Synapse may group together, or as perivascular plexuses of axons with the postganglionic neuron may occur at the same spinal that accompany arteries. Postganglionic axons rejoin the The superior cervical ganglion supplies sympathetic ax- spinal nerve through the gray ramus to innervate structures in the ons that innervate the structures of the head. These axons limbs or proceed to organs, such as the lungs or heart, in discrete travel superiorly in the perivascular plexus along the carotid nerves. Structures innervated include the radial muscle of glion without synapsing in a paravertebral ganglion. Lesions that interrupt this pathway THE SYMPATHETIC NERVOUS SYSTEM produce easily detectable clinical signs (see Clinical Focus Preganglionic neurons of the sympathetic division origi- Box 6. The middle and inferior cervical ganglia innervate nate in the intermediolateral horn of the thoracic (T1 to organs of the chest, including the trachea, esophagus, T12) and upper lumbar (L1 to L3) spinal cord. Postsynaptic axons destined for the abdominal and pelvic Immediately after the ventral and dorsal roots merge to visceral organs arise from the prevertebral ganglia (see form the spinal nerve, the sympathetic axons leave the Fig. The three major prevertebral ganglia, also called spinal nerve via the white ramus and enter the paraverte- collateral ganglia, overlie the celiac, superior mesenteric, bral sympathetic ganglia (Fig. The paravertebral gan- and inferior mesenteric arteries at their origin from the aorta glia form an interconnected chain located on either side of and are named accordingly. These ganglia extend above and be- sympathetic innervation to the stomach, liver, pancreas, low the thoracic and lumbar spinal levels, where pregan- gallbladder, small intestine, spleen, and kidneys. Pregan- glionic fibers emerge, to provide postganglionic sympa- glionic axons originate in the T5 to T12 spinal levels. The deficits of function occur ipsilateral to the le- • Brainstem lesions, such as produced by strokes, which sion and include: interrupt the tracts that descend to the sympathetic neu- • Partial constriction of the pupil as a result of loss of sym- rons in the spinal cord pathetic pupillodilator action • Upper thoracic nerve root lesions, such as those pro- • Drooping of the eyelid, termed ptosis, as a result of loss of duced by excessive traction on the arm or from infiltra- sympathetic activation of Müller’s muscle of the eyelid tion of the nerve roots by cancer spreading from the lung • Dryness of the face as a result of the lack of sympathetic • Cervical paravertebral ganglia lesions from accidental or activation of the facial sweat glands. Johann Horner, a 19th century Swiss ophthal- traveling in the carotid periarterial plexus. Note the named paravertebral and solid lines, postganglionic axons by dashed lines. CHAPTER 6 The Autonomic Nervous System 113 superior mesenteric ganglion innervates the small and large Preganglionic sympathetic axons Adrenal intestines. The inferior mesenteric ganglion innervates the lower colon and rectum, urinary bladder, and reproductive organs. Chromaffin Adrenal cell medulla The Sympathetic Division Can Produce Local Vesicles or Widespread Responses The sympathetic division exerts a continuous influence on the organs it innervates. This continuous level of control is called sympathetic tone, and it is accomplished by a per- Vein sistent, low rate of discharge of the sympathetic nerves. When the situation dictates, the rate of firing to a particular organ can be increased or decreased, such as an increased firing rate of the sympathetic neurons supplying the iris to produce pupillary dilation in dim light or a decreased firing rate and pupillary constriction during drowsiness. The number of postganglionic axons emerging from the Blood capillary paravertebral ganglia is greater than the number of pregan- glionic neurons that originate in the spinal cord. Preganglionic sympathetic axons ter- preganglionic neurons by 100:1 or more. When stimulated, the chromaffin cells release epinephrine into the circulation. Divergence enables the sympa- and fatty acids, and blood cells which participate in the thetic division to produce widespread responses of many clotting and immune responses. The Fight-or-Flight Response Is a Result The Adrenal Medulla Is a Mediator of Widespread Sympathetic Activation of Sympathetic Function This response is the classic example of the sympathetic In addition to divergence, the sympathetic division has a nervous system’s ability to produce widespread activation hormonal mechanism to activate target tissues endowed of its effectors; it is activated when an organism’s survival is with adrenergic receptors, including those innervated by in jeopardy and the animal may have to fight or flee. The hormone is the catecholamine components of the response result from the direct effects of epinephrine, which is secreted with much lesser amounts sympathetic activation, while the secretion of epinephrine of norepinephrine by the adrenal medulla during general- by the adrenal medulla also contributes.
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