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Lect 4 (mixing and propulsion in git)

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GIT 4

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Lect 4 (mixing and propulsion in git)

  1. 1. INGESTION OF FOOD: • Hunger: is an intrinsic desire that the person needs to ingest enough food. • Appetite: Is the type of food that a person preferentially seeks.
  2. 2. MASTICATION (CHEWING): • The teeth is responsible for chewing. • The anterior teeth (incisors) provide a strong cutting action, and the posterior teeth (molars) provide a grinding action. • Chewing reflex is done by rebound contraction. • Most of the muscles of chewing are innervated by the motor branch of the fifth cranial nerve.
  3. 3. SWALLOWING (DEGLUTITION): • Is a complicated mechanism, principally because the pharynx subseries respiration and swallowing. • Swallowing can be divided into: (1) A Voluntary Stage. (2) A Pharyngeal Stage. (3) An Esophageal Stage.
  4. 4. • The esophagus functions primarily to conduct food rapidly from the pharynx to the stomach. • The esophagus normally exhibits two types of peristaltic movements: 1- Primary peristalsis 2- Secondary peristalsis 1- Primary peristalsis: • Is simply continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagus during the pharyngeal stage of swallowing. • 8 to 10 seconds, 5 to 8 seconds (gravity pulling). • If the primary peristaltic wave fails to move all the food then secondary peristaltic waves initiates.
  5. 5. 2- Secondary peristalsis: • Result from distention of the esophagus itself by the retained food. • Initiated partly by: A. intrinsic neural circuits in the myenteric nervous system. B. Glossopharyngeal and vagal efferent nerve fibers. • Function of the Lower Esophageal Sphincter (Gastroesophageal Sphincter) = prevent significant reflux of stomach contents into the esophagus. • Additional Prevention of Esophageal Reflux by Valvelike Closure of the Distal End of the Esophagus.
  6. 6. • stomach
  7. 7. MOTOR FUNCTIONS OF THE STOMACH: (1) storage of large quantities of food until the food can be processed in the stomach, duodenum, and lower intestinal tract. (2) mixing of this food with gastric secretions until it forms a semifluid mixture called chyme. (3) slow emptying of the chyme from the stomach into the small intestine at a rate suitable for proper digestion and absorption by the small intestine.
  8. 8. STORAGE FUNCTION OF THE STOMACH:
  9. 9. MIXING AND PROPULSION OF FOOD IN THE STOMACH: • Gastric glands of the stomach secretes the digestive juices. • The long presence of food causes mixing waves which is a weak peristaltic constrictor waves. • every 15 to 20 seconds. • Powerful peristaltic action potential–driven constrictor rings that force the antral contents under higher and higher pressure toward the pylorus. • “Retropulsion”: is the combination of pyloric squeezing and constrictive peristalsis in the stomach. • Hunger Contractions: when the stomach has been empty for several hours or more. And the whole stomach contracts. • Hunger pangs: mild pain in the pit of stomach.
  10. 10. STOMACH EMPTYING: • “Pyloric pump”: Is promoted by intense peristaltic contractions in the stomach antrum. Control of Stomach Emptying: 1- Stomach factors: • Degree of filling. • Effect of gastrin. 2- Duodenal factors (inhibitory feedback): • Enterogastric inhibitory nervous feedback reflexes. • Hormonal feedback by Cholecystokinin (CCK).
  11. 11. • Hormone gastrin from the G cells of the antral mucosa. • Cause secretion of highly acidic gastric juice by the stomach glands. • Gastrin likely promotes stomach emptying. • Increased food volume in the stomach promotes increased emptying from the stomach. • Stretching of the stomach wall does elicit local myenteric reflexes in the wall • Multiple nervous reflexes are initiated from the duodenal wall (enteric nervous system, inhibitory sympathetic nerve fibers in stomach, inhibation vagus nerves in stomach). • Hormones cholecystokinin from mucosa of the jejunum. • Inhibitor to block increased stomach motility caused by gastrin. • Secretin and glucose-dependent insulinotropic peptide, also called gastric inhibitory peptide (GIP).
  12. 12. MOVEMENTS OF THE SMALL INTESTINE
  13. 13. MIXING CONTRACTIONS (SEGMENTATION CONTRACTIONS): • The contraction of the intestine they divide the intestine into spaced segments that have the appearance of a chain of sausages. • Chyme is propelled through the small intestine by peristaltic waves. • Peristaltic activity of the small intestine is greatly increased after a meal. • chyme into the duodenum, causing stretch of the duodenal wall.
  14. 14. • Factors that enhance the intestinal motility are: 1. gastrin, 2. CCK, 3. insulin, 4. motilin, and 5. serotonin. • Factors that inhibit the intestinal motility are: 1. secretin 2. glucagon
  15. 15. • Function of the peristaltic intestinal wave is: 1. Spread of chyme to the intestinal mucosa. 2. Progression of chyme toward the ileocecal valve. • When reaching the chyme in the ileocecal valve they blocked for several hours until the person eat another meal then the gastroileal reflex begins which intensifies the peristalsis in the ileum and forces the remaining chyme through the ileocecal valve into the cecum of the large intestine.
  16. 16. • Peristalsis in the small intestine is normally weak. • Peristaltic rush is a “powerful and rapid peristalsis” caused by intense irritation to the intestinal mucosa as a result of infectious diarrhae. • The ileocecal valve prevents backflow from the colon to the small intestine. • Ileocecal sphincter is a thickened circular muscle. • Feedback control of the ileocecal sphincter: • When the cecum is distended, contraction of the ileocecal sphincter becomes intensified and ileal peristalsis is inhibited – delay emptying. Ex: 1. Inflamed appendix. 2. Partial paralysis of the ileum.
  17. 17. MOVEMENTS OF THE COLON
  18. 18. • The principal functions of the colon are: (1) absorption of water and electrolytes from the chyme to form solid feces. (2) storage of fecal matter until it can be expelled. The proximal half of the colon – absorption. The distal half of the colon – storage. Movement of colon is by two process: Mixing Movements—“Haustrations.” Propulsive Movements—“Mass Movements.”
  19. 19. Mixing Movements—“Haustrations”: • Same manner that segmentation movements occur in the small intestine. • This process done by means of contraction of circular muscles of large intestine, but in some cases leads to intestinal occlution. • The circular and lungitudinal muscels “which is formed by 3 strips called tenea coli” contractes leading to bulge feces outward into baglike sacs called haustrations. • Each haustration reaches peak intensity in about 30 seconds and then disappears during the next 60 seconds. • in the cecum and ascending colon they slowly propulse the colonic content. • 80 to 200 milliliters of feces are expelled each day.
  20. 20. Propulsive Movements—“Mass Movements”: • From the cecum to the sigmoid, mass movements can take over the propulsive role. • one to three times each day. • A mass movement is a modified type of peristalsis characterized: 1. a constrictive ring occurs in response to a distended or irritated point in the colon, usually in the transverse colon. 2. propelling the fecal material in this segment en masse further down the colon. • A series of mass movements usually persists for 10 to 30 minutes. • They then cease but return perhaps a half day later. • When they have forced a mass of feces into the rectum, the desire for defecation is felt.
  21. 21. Initiation of Mass Movements by Gastrocolic and Duodenocolic Reflexes: • These reflexes result from distention of the stomach and duodenum. • Irritation in the colon can also initiate intense mass movements. • A person with (ulcerative colitis) frequently has mass movements that persist almost all the time.
  22. 22. DEFECATION or EGECTION: • The rectum is empty of feces because a weak functional sphincter exists. • A sharp angulation contributes additional resistance to filling of the rectum. • When a mass movement forces feces into the rectum, the desire for defecation occurs immediately, including reflex contraction of the rectum and relaxation of the anal sphincters. • Continual dribble of fecal matter through the anus is prevented by tonic constriction of: (1) an internal anal sphincter (2) an external anal sphincter
  23. 23. • The external sphincter is controlled by nerve fibers in the pudendal nerve, which is part of the somatic nervous system and therefore is under voluntary, conscious, or at least subconscious control. • subconsciously, the external sphincter is usually kept continuously constricted unless conscious signals inhibit the constriction.
  24. 24. Defecation Reflexes: • Is done by Intrinsic reflex mediated by the local enteric nervous system in the rectal wall. 1. First feces enter the rectum. 2. Distention of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing feces toward the anus. 3. The internal anal sphincter is relaxed by inhibitory signals from the myenteric plexus. 4. If the external anal sphincter is also consciously, voluntarily relaxed at the same time, defecation occurs. • Parasympathetic fortified defecation reflex.
  25. 25. • Defecation signals entering the spinal cord initiate other effects, such as taking a deep breath, closure of the glottis, and contraction of the abdominal wall muscles. The peritoneointestinal reflex results from irritation of the peritoneum; it strongly inhibits the excitatory enteric nerves and thereby can cause intestinal paralysis, especially in patients with peritonitis. The renointestinal and vesicointestinal reflexes inhibit intestinal activity as a result of kidney or bladder irritation.

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