Digestive System Part # 3 Flashcards
(10 cards)
Functions of the Liver - Macromolecule factory
Carbohydrate metabolism - important in the synthesis and break down of glycogen. Lipid metabolism - storage of triglycerides, breakdown of triglycerides for ATP, synthesis of cholesterol, bile, and lipoproteins. Protein metabolism - removal of amines from amino acids and conversion of ammonia to urea. Processing of drugs and hormones - detoxifies alcohol and removes some drugs via bile production.Synthesis of bile salts - used to emulsify fats. Storage of nutrients - glycogen, iron, vitamins and minerals like copper. Phagocytosis - clean up, removal of wastes and bacteria, Stellate macrophages (aka Kupffer cells) preform phagocytosis.
Gallbladder -
Hangs just below the liver and is the size and shape of a small pear! Histology- has no submucosa, and mucosa is simple columnar epithelium. Functions to store and concentrate bile by absorbing water.
small intestine -
duodenum - located retroperitoneal, 12fingers in length (about 10 in) Jejunum - about 3 ft in lenght (middle section) Ileum - about 6 ft in length, end at the ileocecal valve (sphincter).
The small intestine is built for absorption due to increased surface space from circular folds, villi, and microvilli. The epithelium is simple columnar with special cells: enterocytes - (aka absorptive cells) - microvilli form on top of these cells. enterocytes cells absorb nutrients and secretion of brush boarder enzymes. Goblet cells - secret mucus. enteroendocrine cells - secrete secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP). duodenal glands - found specificalli in the submucosa of the duodemun, they secrete an alkaline mucus which helps neutralize the acidity of gastric juice. Paneth cells - secret lysozome.Paneth cells and enteroendocrine cells are located in the intestinal crypts that form the folds.
Brush border enzyme -
alpha - dextrinase - clips off one glucose at a time. maltase - cleaves maltose (2 glucose) and maltotriose (3 glucose)
maltose/maltotriose—maltase—–glucose
sucrase - converts surcrose into glucose and fructose.
lactase - converts lactose into glucose and galatose
aminopeptidase - cleaves amino acids from the amino terminus.
dipeptidase - converts dipeptides into 2 free amino acids
nucleosidases - takes the sugar off of a nucleotide.
phosphatases - take phosphate off of a nucleotide.
Note: carboxypeptidase is secreted by the pancrease and brush boader.
Mechanical digestion in the small intestine -
Segmentation - circular muscle alternately contracts and relaxes resulting in mixing of chyme with enzymes of the small intestine.
Peristalis - wave of contraction of the longitudinal muscle know as migrating motility complex (MMC) that occurs between meals.
Regulation of Intestinal Secretion and Motility - rest and digest parasympathetic
Affected by : Vagus nerve stimulation ( increases motility and secretion) Sympathetic stimulation (decreases motility)
Normally the ileocecal valve is closed, gastrin relaxes the sphincter. gastroileal reflex - food in the stomach (gastro) stimulates the movement of chyme fromthe small intestin (ileum) to the cecum by relaxing the ileocecal valve. Gastrin plays a key roll.
Absorption -Transport systems -
Very few substances are absorbed in the stomach: alcohol, lipid soluble drugs, and some water. 90% of all absorption occurs in the small intestine.
Simple diffusion - short chain fatty acids (10 - 12C’s), micelles with long chain fatty acids and monoglycerides, fat and water soluble vitamins. Facilitated diffusion - channel proteins facilitate movement of fructose. Secondary active transport with sodium - glucose, galactose, amino acids. Secondary active transport with hydrogen - dipeptided and tripeptides.
Lipid digestion - Lipid absorption - Water absorption - Electrolytes - Vitamins -
Lipid digestion : Large fat globules reduce the surface area for lipase. Bile salts emulisfy the gloubules by coating and creating small droplets and increase their surface area for lipase to act on. Emuslsification is not enzymatic. It dosent break bonds. Bile reduces the attraction that the fat molecules have for one anothe because bile salt is amphipathic.
Lipid absorption : Lipids are absorbed via formation of a micelle and chylomicron. Micelles are cages that form due to the amphipathic nature of bile salts. The micelle the diffuses into the phospholipid bilayer of the entercytes. Bile salts are absorbed as well and returned to the liver via enteroheptic circulation. Chylomicrons - triglycerides combine with protein and form a lipoprotein. Chylomicrons enter lacteals where they travel to the subcalvian vein. Lipoprotein lipase in the capillary endothelium break down chylomicrons into free fatty acids and glycerol that can be absorbed by tissue cells.
Water absorption - This absorption occurs via osmosis and is dependent upon the concentration of solutes. Water follows salt. Amino acids and electrolytes establish a concentration gradient for water to flow.
Electrolytes : secondary active transport - sodium movement is coupled with amino acid, glucose and galactose transport. Passive transport due to above - negatively charged ions such as chloride, iodine, and nitrate follow the positively charged ions. Actively transported - sodium,calcium,iron,magnesium,phosphate,and some potassium.
Vitamins - Fat soluble vitamins are absorbed in the micelle with lipids. Water soluble vitamins are absorbed by simple diffusion. B-12 must combine with intrinsic factor produced by the parietal cells.
Large intestines -
5 feet in length but large in diameter (2.5in) Cecum - first section of the large intestine that is pouch like, the worm - like appendix hangs from the cecum. Colon (4 sections and 2 bends) Ascending colon - first section on the right. Transverse colon - horizontal section. Decending colon - section on the left side. Sigmoid colon - S shaped that terminates at the rectum. Rectum - the last section of the alimentary canal, includes the anal canal, anal columns (folds inside the anal canal) and the anus. Right colic (hepatic) flexure - bend located just below the liver. Left colic (splenic) flexure - bend on the left just below the spleen.
Tenia coli - 3 bands of uneven thickening of the longitudinal muscle in the muscularis externa that act like drawstring to pull intestine into haustra (pouches). Mechanical digestion in Large intestine : Haustral churning -distention of the haustra results in their contraction which moves chyme along. Gastrocolic reflex - initiated by food in the stomach and results in mass peristalasis that moves the contents of the transverse colon into the rectum quickly.
Chemical digestion in the Large intestine - Defecation reflex -
No new enzymes are secreted by the body but bacteria that colonize the large intestine do produce enzymes (such as cellulase) which results in flatus (gas). In addition , bacteria synthesis vitamin K and several B vitamins. Water , electrolytes and vitamins are absorbed to form the feces.
Fecal mass in the rectum stimulates stretch receptors which send a signal via sensory neurons to the sacral spinal cord which send motor signals via parasympathetic fibers.
Motor pathway - a motor neuron (spinal reflex) from the spinal cord relaxes the involuntary (internal/smooth muscle) anal sphincter. With conscious control, a voluntary motor nerve from the cerebral cortex sends the signal to the (voluntary/skeletal muscle) external anal sphincter to relax. Valsalva maneuver - “bearing down” voluntary increase in pressure in the abdominal cavity by contraction of the abdominal wall, contraction of the diaphragm and closing the glottis. This maneuver also aids in childbirth.
Elimination communication - a relatively new toilet training practice that focuses on reduced use of diapers. The caregiver uses cues and timing to train the infant to void or defecate on command long before the control of the sphincters is established.
