Digestive System - Human Anatomy and Physiology II, Notes | KINS 2532, Study notes of Physiology

Download Digestive System - Human Anatomy and Physiology II, Notes | KINS 2532 and more Study notes Physiology in PDF only on Docsity! Digestive System Digestive processes 1. Ingestion 2. Propulsion 3. Mechanical digestion 4. Chemical digestion 5. Absorption 6. Defecation 1. Digestive activity is provoked by mechanical and chemical stimuli When sensors are stimulated they initiate reflexes that: 1. Activate or inhibit glands that secrete into lumen and blood 2. Mix lumen contents and moves them along 2. Control of activity is extrinsic and intrinsic - either by short reflexes by local plexi (enteric) or by long reflexes through CNS and autonomic nn. - also through hormonal cells in various organs GI organs - surrounded by peritoneum - mesentery - retroperitoneal - intraperitoneal Splanchnic circulation - aa. that serve organs and hepatic portal circulation Layers of GI tract 1. Mucosa layers: 1. Surface epithelium 2. Lamina propria – loose areolar c.t. 3. Muscularis mucosae 2. Submucosa 3. Muscularis externa - smooth muscle 4. Serosa - visceral peritoneum - in esophagus, serosa is replaced by adventitia Saliva - 97-99% water - slightly acidic - contains: - amylase - electrolytes - IgA antibodies Control of salivation comes from parasympathetic fibers of facial and glossopharyngeal nn. Stimulated by chemoreceptors Digestive processes: Mouth Mechanical - mastication - high acidity causes small intestine to send signals to inhibit vagal nuclei, local reflexes - also activates sympathetic fibers causing constriction of pyloric sphincter Contractile activity of stomach - only about 3 ml are sent to duodenum at a time - Interstitial cells of Cajal act as pacemakers for contraction - rate is constant but initiation and force of contraction are controlled by enteric reflexes and gastrin - shape of pyloric region insures that only liquids and well-digested foods pass to duodenu Small intestine - villi, microvilli - lacteals, Pyer’s patches Intestinal juice - Secreted by goblet cells and cells of intestinal crypts - slightly alkaline to neutralize acidity of stomach Liver - composed of lobules formed by plates of hepatocytes - plates radiate around central vein - at each corner of the lobule, there is a portal triad -portal triad= 1. Portal arteriole 2. Portal venule 3. Bile duct - space between hepatocyte plates = sinusoid - both arterial and venous blood travel through sinusoid - Kupffer cells (macrophages) reside in sinusoids Hepatocytes: 1. Produce bile 2. Store glucose 3. Store fat-soluble vitamins 4. Detoxify (e.g. remove ammonia from blood) Bile - bile salts and electrolytes are most important functional components - bile salts emulsify fats Release of bile - when bile sphincter is closed, bile builds up and enters gall bladder - when fatty chyme enters duodenum, intestinal hormone stimulates gall bladder to contract Pancreas Acini - clusters of cells surrounding ducts, secrete pancreatic enzymes 1. Trypsin for proteins 2. Amylase for starch 3. Lipases for fats 4. Nucleases for nucleotides Pancreas continued: - Islets of Langerhans - alpha cells produce glucagon - beta cells produce insulin Large Intestine - mostly absorbs water - bacterial flora - break down cellulose - synthesize B-complex vitamins and vitamin K Chemical Digestion Carbohydrates (polysaccharides) – --begins in mouth with amylase which works until stomach acidity stops it --Breakdown continues in small intestine as pancreatic amylase works --The products are oligosaccharides (mostly maltose) composed of 2-8 linked monosaccharides --Brush border enzymes further digest into monosaccharides (e.g. maltase) Proteins --begins in stomach with pepsin which breaks down proteins into smaller polypeptides and free amino acids --In small intestine, pancreatic enzymes such as trypsin break down polypeptides into smaller pieces --Brush border enzyme carboxypeptidase removes one amino acid at a time Lipids - bile salts coat small fat droplets to make the molecules more accessible to enzymes - pancreatic lipases break down fats by removing 2 of the fatty acid chains yielding free fatty acids and and a monoglyceride Absorption --most nutrients are absorbed through active transport --In the case of proteins, they are coupled with sodium transport