Digestion Lecture 1 PDF 2024-2025

 El-doctor Physiology DIGESTION The digestive system includes: 1) the digestive tract: extending from the oral opening to the rectal opening: (Mouth → Pharynx → E...

 El-doctor Physiology DIGESTION The digestive system includes: 1) the digestive tract: extending from the oral opening to the rectal opening: (Mouth → Pharynx → Esophagus → Stomach → Small intestine → large intestine) 2) associated glands → (Salivary - Pancreas - Liver) Digestive tract is essential for the ingestion and digestion of food through several mechanism: Mechanical As → mastication - deglutition "swallowing" - regurgitation - rumination - vomiting - intestinal movement - defecation. Enzymatic or chemical As → salivary, gastric, pancreatic and intestinal enzymes ✓ Present in secretion of the associated glands. Microbiological Through the action of microflora and protozoa ✓ Present in the ruminant animals. Gastrointestinal tract Extension Extending from esophagus to the rectal opening: (esophagus → stomach → small intestine → large intestine) Capacity The capacity and length of this tract varies greatly in different animals: In carnivores In herbivores It is short and relatively simple. In herbivores it is much larger and more complicated. ❖ In some herbivores The stomach is relatively simple, but the intestines are very much larger and of greater capacity. e.g horse and rabbit. Capacity of the different parts of the digestive tract in gallons. Animal Stomach Small intestine Large intestine Total capacity Cow 80 15 43 183 Horse 4 12 30 46 Sheep 5 2 1 8 Pig 2 2 3 7 Function  To assist in the acquisition of nutrients.  To prepare and digest nutrients.  To felicitate absorption of products of digestion.  As excretory organs to help in elimination of waste products.  As an endocrine gland influences digestion and other metabolic functions.  Motility of the GI tract. 1  El-doctor Physiology ❖ Neurohormonal control of gastrointestinal tract The autonomic innervation of the mammalian gastrointestinal tract is either parasympathetic or sympathetic. Parasympathetic (stimulation) Sympathetic (inhibition) The parasympathetic provide innervation via the vagus nerve to the: ✓ The sympathetic innervation produces inhibition of: (esophagus - stomach - small intestine - proximal part of large intestine). 1) Motility. The sacral segment of the spinal cord provides parasympathetic innervation to the: 2) secretion. (distal portion of the colon - the rectum - the internal anal sphincter) ✓ The postganglionic nerve fibers release acetylcholine which is generally considered to be stimulatory to 1) motor (muscular). 2) secretory activity. ❖ Hormonal control of gastrointestinal tract Hormonal control of gastrointestinal motility and secretion this includes large number of hormones as (gastrin, secretin, cholecystokinin - pancreozymin (CCK-PZ), glucagon, enterogastrone, enterocrinin and villikinin). 2  El-doctor Physiology Mechanical digestion Ingestion or It means the seizing and conveying of food into the mouth. prehension The animal obtains its food by use of a prehensile: a) Fore limb → (Primate - Raccoon) b) Snout → (Elephant) c) Tongue → (cow - ox) d) Lips → (Horse - sheep) ✓ highly developed prehensile organs allow a more careful selection of food. The dental arrangement also can be related to diet, and varies from that if the relatively toothless edentates to the presence of large incisors, canines, and molars in carnivores and even more highly specialized molars of herbivores. N.B: The sheep has a clefted upper lip, but in goat the upper lip is not clefted. Drinking Is the process by which the fluid is carried to the mouth. In cat & dog In other domestic animals The free end of the tongue is like a This process is made by suction. ladle structure. ✓ Through the aid of the tongue "produce negative pressure, while the lips are closed all round except for a small opening under the water. Sucking Is the process by which the milk in the teat is forced into the mouth of the suckling animal. ✓ By creating pressure gradient in the mouth by their tong. 3  El-doctor Physiology The Gastrointestinal Hormones Def Gastrointestinal hormones are polypeptides secreted from certain cells of G.I.T mucosa called APUD cells "Amine precursor uptake and decarboxylation” Groups The gastrointestinal hormones can divided into 3 main groups: Gastric family Secretin family Other peptides secreted from G.I.T. and the brain 1) gastrin 1) secretin 1) substance P 2) cholecystokinin pancreozymin 2) gastric inhibitory peptide (GIP) 2) neurotensin (CCK-PZ) 3) vasoactive intestinal peptide (VIP) 3) bombesin 4) enteroglucagon 4) enkephalin 5) somatostatin The Gastrointestinal Hormones Hormone Stimulus to secretion Tissue of origin Target tissue Action 1- Gastrin 1) St. of vagus N. gastric mucosa & secretory cells - smooth 1) Production of HCl. 2) peptides & proteins in stomach. duodenum (g cells) m. of stomach 2) Stimulates gastric motility 2- Secretin food & strong acid Duodenum mucosa & Pancreas - muscles of 1) St. pancreatic juice in the duodenum upper part of jejunum stomach "H2O + bicarbonate” (S cells) 2) Inhibit gastric motility 3- Cholecystokinin presence of fatty acids & amino small intestine (upper gallbladder - pancreas 1) Contraction of gallbladder pancreozymin acids in the duodenum. part) (I cells) 2) St. pancreatic juice (rich in (CCk-PZ) enzymes) 4- Gastric inhibitory Monosaccharides and fats in small intesitne gastric mucosa 1) Inhibit gastric secretion and peptide (GIP) duodenum (upper part) (I cells) and gastric muscles motility. 2) Stimulates Brunner's glands. 3) Stimulate insulin secretion 5- Vasoactive intestinal fats in duodenum duodenum it is found in GIT & 1) Increase blood flow peptide (VIP) brain tissues 2) Inhibit gastric secretion "HCl" 3) St. Pancreatic secretion. 4) St. insulin secretion. 6- Enteroglucogen carbohydrate in duodenum duodenum jejunum, pancreas Inhibit motility and secretion 2  El-doctor Physiology Hormones Stimulus to secretion Tissue of origin Target tissue Action 7- Enterogesterone Fat & hypertonic solution duodenum stomach Inhibit gastric secretion & "all peptide inhibit gastric activities" in duodenum motility 8- Somatostatin acid in gastric lumen. Mucosa of GIT. 1) Inhibit secretion of gastrin, Hypothalamus, secretin, VTP, GIP. D-cells of pancreas ----------- 2) Inhibit gastric motility & secretion 3) Inhibit pancreatic secretion, 4) Gallbladder contraction 9- Histamine 10- Prostaglandins Is present in a high concentration in gastric mucosa. It presents in gastric mucosa. - It stimulates gastric acid secretion "HCl" through it action on H2 receptors in oxyntic cells. - Inhibit gastric secretion. - It increase motility & produce vasodilation of GIT. - Increase intestinal motility and secretion.  It action is blocked by some drugs as cimetidine which used in treatment of peptic ulcer. - Produce V.D. of bl. vessels of GIT. Join us 5