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123 Cards in this Set
- Front
- Back
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Name in order the organs of the alimentary canal, beginning at the mouth.
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- mouth
- pharynx - esophagus - stomach - small intestines (duedenum, jejenum, ileum) - large intestine (cecum, colon, rectum) - anus |
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Name and describe the general function of the accessory digestive organs.
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- teeth and tongue - mechanical digestion
- salivary glands, pancreas, liver and gallbladder - chemical digestion |
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Identify and describe the basic activities performed by the alimentary canal (e.g. ingestion) which aid the digestive process.
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- ingestion - taking materials into the digestive tract; usu. via mouth
- Propulsion - moving materials through alimentary canal (swallowing + peristalsis) - Mechanical digestion - breaking down large food particles into small ones via grinding and mixing (chewing, stomach churning, segmentation in s. intestine) - Chemical digestion - catabolic rxns where complex food mol are broken down via enzyme-catalyzed hydrolysis - Absorption - movement of digestive end products from lumen of GI tract into blood/lymph (mostly in small i.) - Defacation - discharging to the environment undigested/unabsorbed food material via the anus as feces |
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Identify the four tissue layers of the alimentary canal wall.
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- Mucosa
- submucosa - muscularis externa - serosa |
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Describe the first of the four tissue layers of the alimentary canal wall.
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- Mucosa (mucous membrane)
- epithelium (stratefied ET - secretes mucus, enzymes, hormones); innermost one - lamina propria (areolar CT - blood vessels, nerve endings, lymph vessels, MALT/mucosa associated lymphatic tissues, tonsils) - muscularis mucosae - mucosal smooth musc. produces folding for more surface area; produces local movements to change shape of lumen Functions: protect underlying tissue, absorb digested material; secrete mucous, digestive juices, hormones - then come the other layers: - submucosa, muscularis externa, serosa |
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Describe the second of the four tissue layers of the alimentary canal wall.
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Submucosa:
- loose CT - immediately surrounds mucosa - has blood vessels, lymphatics and nerves; vascular network carries away nutrients - contains submucosal plexus (part of enteric nervous system) - next come muscularis externa and serosa |
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Describe the third of the four tissue layers of the alimentary canal wall.
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Muscularis Externa (muscularis)
- segmentation and peristalsis - in mouth and pharynx = skeletal muscle - in the rest - two layers of musc. - circular and longitudinal - thickens at certain points = sphincters - contains myenteric plexus (part of enteric nervous system) - then comes the serosa |
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Describe the fourth of the four tissue layers of the alimentary canal wall.
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Serosa: (visceral peritoneum)
- protective outer layer of peritoneal cavity - has visceral and parietal layers - secretes peritoneal fluid into peritoneum to reduce friction b/w digestive organs - in esophagus and rectum, replaced by adventitia |
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Identify and describe the two basic motility patterns of teh alimentary canal.
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- peristalsis - propelling motion produced by alternate waves of contraction and relaxation of muscles in tract wall
- Segmentation - mixing type of movement which churns and mech. fragments materials in tract; due to rhythmic local contractions of muscularis layer |
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In what way do each of the two basic motility patterns contribute to the digestive process?
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- Peristalsis - propells food along the alimentary canal
- Segmentation - churns and mech. digests food |
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Identify the main blood vessels of the splanchnic circulation. What organs are served by each of the blood vessels named?
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- blood supply of digestive organs
- arteries that branch off the abdominal aorta: - branches of celiac trunk (hepatic, splenic + L. gastric artery) for lifer spleen and stomach - inferior and superior mesenteric arteries - for the s. and l. intestines - hepatic portal circulation - carries nurtient rich venous blood from digestive organs to the liver |
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What is the splanchnic circulation?
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- the blood supply of the digestive organs
- consists of arteries that branch off abdominal aorta |
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Name and locate the two nerve plexuses that make up the enteric nervous system.
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- Submucosal plexus - found in submucosa; contains ANS fibers and ganglia; regulates glands and smooth musc.
- Myenteric - in muscularis externa/muscularis; b/w smooth muscle layers; provides nerves to GI tract wall for GI tract motility |
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What is the general function of teh enteric nervous system?
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- has reflex arcs that help provide optimal digestive conditions (via osmo, chemo and mechano receptors)
- Submucosal - coordinate/regulate movements of mucosa, vasoconstriction/dilation of local blood vessels; secretory function of glands - myenteric - regulating motility of tract walls; helps regulate glandular secretions in lumen |
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How are motor impulses of the parasympathetic nervous system conducted to teh GI tract? What is the general effect of parasympathetic input on digestive function?
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- carried by vagus nerve
- "rest and digest"; increases motility and secretory activity of digestive system |
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How are motor impulses of the sympathetic nervous system conducted to the GI tract? What is the general effect of sympathetic input on digestive function?
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- conducted via the greater and lesser splanchnic nerves (T1-T5 roots)
- inhibits digestive activity |
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What is a mesentery? Describe the difference between intraperitoneal and retroperitoneal.
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- mesentery = a fused double layer of parietal peritoneum; functions to connect visceral and parietal peritoneun, anchor organs, encase lymphatics, blood vessels and nerves
- intraperitoneal - inside/encased by the mesentery - retroperitoneal organs - adhere to dorsal abdominal wall; have no surrounding mesentery (some parts of small intestine and large intestine, most of pancreas) |
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Describe the composition and function(s) of saliva.
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- Composition - mosly H2O, dissolved solutes (electrolytes, salivary amylase, mucins, lysozyme, defensins); slightly acidic
- Functions - clean teeth, dissolve food chem. so we can taste; keep mouth moist; antibacterial; salivary amylase has digestive function of polysaccharides |
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How is the secretion of saliva controlled?
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- innervated by both parts of ANS
- rate of secretion + composition varies in response to sensory stimuli (sight/smell/thought of food, presence of food in mouth = PNS vs. scared; dry mouth = SNS) |
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Describe the structure and function of the esophagus.
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- muscular tube; collapsed when not in use
- cardiac/gastroesophaeal sphincter usu. tonically constricted; only relaxes to swallow - only a passageway; no digestion occurs |
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What purpose is served by the lower esophageal sphincter?
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- also called cardiac sphincter and gastroesophageal sphincter
- relaxes to allow bolus to be propelled into stomach - usu. tonically constricted to prevent gastric juice reflux |
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Describe the swallowing reflex - noting especially the stimuli which trigger swallowing and the motor responses involved.
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- bolus pushed into oropharynx @ back of mouth
- touch receptors in pharynx walls and uvula triggered - soft palat rises (close off nasopharynx) - larynx rises (epiglottis over glottis to cover airway) - peristaltic contractions along pharyngeal and esophageal walls (move bolus over esophagus) - cardiac sphincter relaxes - bolus plunked into stomach |
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When do each of the dentitions normally begin to appear? At what age are they typically complete? Whe complete, how many teeth do they have?
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- primary - deciduous teeth (baby/mild teeth); grow in until about 24 mo.; 20 teeth in total
- permanent - between 6-12 years baby teeth fall out; new ones in by end of adolescence (wisdom teeth b/w 17-25yrs); usu. 32 teeth total |
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Humans have two dentitions. What are they?
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- primary dentitions - baby/mild teeth
- permanent dentitions |
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Distinguish between the following serous membranes: visceral peritoneum, parietal peritoneum, mesentery... (see part two).
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- visceral peritoneum - covers external surfaces of most digestive organs, continuous with parietal peritoneum
- parietal peritoneum - continuous with visceral; lines the body wall; peritoneal cavity/potential space exists b/w these two serous membranes - mesentery - double layer of peritoneum (sheet of 2 serous membranes fused back to back); extends to digestive organs from body wall; provides routes for blood vessels, lymphatics, nerves; holds organs in place; stores fat |
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Distinguish between the following serous membranes: greater omentum, lesser omentum, mesocolon... (see part one).
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- two specific mesenteries
- lesser omentum - rund from liver to lesser curvature of stomach; there it becomes continjous with visceral peritoneum covering stomach - greater omentum - drapes inferiorly from greater curvature of stomach to cover s. intestine coils; runs dorsally/superiorly; wraps spleen + transverse portion of l intestine; blends with mesocolon; has many fat deposits and lymph nodes - mesocolon - dorsal mesentery that secures the large intestine to the parietal peritoneum of posterior abdominal wall |
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What are the functions of the stomach?
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- store food for gradual delivery to SI
- mix food material with gastic juice (convert it to chyme - pepsin secreted for beg. of protein digestion, gastic lipase secreted but not active till pH changes) - limited absorption (small amt. of H2O, glucose, some ions, lipid soluble substances like alcohol); from lumen to blood/lymphatic vessels found in submucosa |
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Name and locate the main regions of the stomach.
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- cardiac region - surrounds where the esophagus converges on stomach
- fundus - part that projects above the esophagus joining place - body - middle; main part - pyloric region - distal part (distal, narrowed portion of the regions is called pylorus) - pyloric sphincter - tonically contracted |
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What is the function of the pyloric sphincter?
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- found in pylorus
- tonically contracted - controlls the rate of gastric emptying |
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Name the simple columnar ET cells which line the stomach and describe their functions.
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- make up the stomach mucosa
- rest on lamina propria (layer of loose CT) - secretes alkaline mucous (protective from gastric juices and food) - has deep gastric pits in it - lead to gastric glands in lamina propria (that secrete and procuce gastric juice) |
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What are the gastric glands, and where are they located?
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- found in lamina propria (loose CT layer) of mucosa of stomach
- secrete and produce gastric juice - deep gastric pits in stomach mucosa leads to the glands |
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Identify the three types of exocrine gland cells located in the gastric glands.
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- mucus neck cells - secrete acidic mucous; thought to be stem cells that differentiate and replenish other gastric gland cells/surface mucus cells
- parietal cells - mainly in middle region of gastric gland; secrete intrinsic factor and HCl - chief cells - found deep in gastric glands; secrete pepsinogen (inactive form of pepsin); activated by stomach acids; also secrete a bit of gastric lipase - a fourth gland cell = G cells = enteroendocrine cell; secretes gastrin (causes gastric glands to secrete more and stimulates gastric emptying) |
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Identify and describe the function of the secretory products of each of the three types of exocrine gland cells located in the gastric clands.
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- Mucous neck cells - acidic mucous; don't know why; also might be the stem cells for the other gastric cells
- Parietal cells - intrinsic factor (needed for vit B12 absorption); HCl (strong acid kills ingested microbes, denatures most ingested proteins, needed for initial pepsin activation; then pepsin activates itself) - note: the G cells/enteroendocrine cells secrete gastrin - gastric glands secrete more |
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Describe the mechanism by which parietal cells secrete HCl into the gastric juice.
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- b/c it's a strong acid, the H and the Cl- need to be secreted separatly into the stomach lumen
- CO2 + H2O = HCO3- + H+ - the H+ is pumped into the lumen by a H+/K+ ATPase pump; the K just leaks back out of cell - the HCO3- is transported into the blood by a HCO3-/Cl- antiporter; the Cl- is now in the cell and diffuses into the stomach lumen |
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Why is it necessary for parietal cells to expend energy (i.e., by H+/K+ proton pumps) in secreting H+?
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- they have to secrete HCl separatly (as H and Cl) into the stomach lumen
- they are pumping H+ against its concentration gradient, to create a strong acid in the stomach |
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How does HCl secretion by parietal cells produce the alkaline tide into the systemic blood?
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- b/c HCl is a strong acid, the H and the Cl- need to be secreted separatly into the stomach lumen
- CO2 + H2O = HCO3- + H+ - the HCO3- is transported into the blood by a HCO3-/Cl- antiporter; the Cl- is now in the cell and diffuses into the stomach lumen - all of the HCO3- that is diffusing into the blood creates a slight rise in pH around the stomach - the tide!!! |
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What cells of the gastric gland secrete gastrin? Why are these cells called enteroendocrine cells rather than exocrine cells?
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- G cells
- secretion functions as paracrines; to help regulate the digestive activities (releases paracrines which are local, and hormones which are systemic) |
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Describe the composition of gastric juice.
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- the secretions of the mucus neck, parietal, and chief cells
- mucous neck - acidic mucous - parietal - HCL and intrinsic factor for vit B12 digestion - chief cells - pepsinogen; activated by HCl, then self activates (positive feedback cycle) - mucus - secreted by surface mucous cells |
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What is the function of each of the following components of gastric juice: HCl; pepsin; mucous; gastrin.
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- HCl - kill microbes, denature proteins, activate pepsin @ first
- Pepsin - self-activating later on from pepsinogen; begins protein digestion by cleaving off single AAs @ end of polypeptide strands - mucous - protection from acid and foods - gastrin - stimulates gastric glands; causes inc. in gastric juice, pepsinogen and HCl secretion; part of hormonal control |
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What is the most important digestive enzyme in gastric juice?
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- pepsinogen - turns into pepsin
- cleaves off single ends of AA strands @ end of polypeptide strands |
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How does gastrin help regulate gastric gland secretion?
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- provides the hormonal control of gastric secretion (other two: intrinsic and extrinsic neural control)
- stimulates gastric glands: inc. in gastric juice, pepsinogen, HCl |
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Name the three phases of gastric secretion and describe the characteristics of each.
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- Cephalic phase (reflex phase) - before food enters somach; triggered by food related stimuli (smell etc); sensory input to hypothalamus increase vagal stimulation, inc. gastric juice and salivary glands; a conditioned reflex
- Gastric phase - when food reches stomach for 3-4 hours; distension activates stretch receptors in wall; local myenteric reflexes and long-loop/vagovagla relfexes release Ach, enhances gastric juice secretion (inc. gastrin and HCl secretion) - Intstestinal phase - when chyme gets to duodenum; mainly slows gastric emptying and secretion; enterogastric relfex; triggers additional intestinal hormones (secretin, cholecystokinin, gastric inhibitory peptide, vasoactive intestinal peptide |
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Identify the stimuli which trigger each of the phases of gastric secretion.
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- Cephalic phase - triggered by food related stimuli(sight, smell etc) lasts only a few min.; a conditioned reflex
- Gastric phase - triggered by distension/stretch of the stomach walls; food chemicals activate G cells (irritates, inc. pH, activates chemoreceptors which activate G cells); gastrin (secreted by G cells), ACh (released by PNS fibers), histamine (secreted by other enteroendocrine cells stimulated by PNS - when combined w/ACh and gastin, has BIG effect on HCl secretion), rising pH (caused by buffering action of proteins), caffine; moderate amts of alcohol; - parietal cells (HCl) are main target to make more gastric juice - Intestinal phase - chyme (with lots of H+ fats, partially digested proteins and irritants) stretches duodenum |
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How is gastric secretion inhibited?
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- decreasing pH (once the proteins/buffers are digested)
- SNS stimulation and shut off of PNS stimulation (so ACh isn't released from the PNS fibers and gastrin - which stimulates parietal cells to secrete HCl - , and histamine aren'e being secreted) - stomach walls no longer distended - so the stretch reflexes aren't working w/ the myenterix and vagovagal reflexes |
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What is the enterogastric reflex, and how is it triggered?
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- occurs during the intestinal phase
- an inhitbitory neural mechanism - constricts the pyloric sphincter to slow stomach emptying consists of 3 different reflex responses: - dec in vagal nuclei of medulla to slow gastric secretion, dec. in local reflexes in submucosal and myenteric plexuses to slow peristalsis, inc. in SNS fibers to pyloric sphincter to make it tighten - Triggers release of intestinal hormones/enterogastrones: secretin (inhibits gastric secretions and motility, influences pancreas), cholecystokinin/CCK (inhibits gastric motility/emptying), gastric inhibitory peptide/GIP (inhibits secretion/motility in stomach), vasoactive intestinal peptide/VIP (inhibits parietal cells, stimulates alkaline secretion in intestines) |
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What affect does the enterogastric reflex have on digestive activity (i.e., secretory activity and gastric motility)?
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- an inhitbitory neural mechanism
- constricts the pyloric sphincter to slow stomach emptying consists of 3 different reflex responses: - dec in vagal nuclei of medulla to slow gastric secretion, dec. in local reflexes in submucosal and myenteric plexuses to slow peristalsis, inc. in SNS fibers to pyloric sphincter to make it tighten - Triggers release of intestinal hormones/enterogastrones: secretin (inhibits gastric secretions and motility, influences pancreas), cholecystokinin/CCK (inhibits gastric motility/emptying), gastric inhibitory peptide/GIP (inhibits secretion/motility in stomach), vasoactive intestinal peptide/VIP (inhibits parietal cells, stimulates alkaline secretion in intestines) |
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Describe the composition of pancreatic juice.
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- watery, alkaline fluid
- Enzymes: -- trypsin, chymotrypsin, carboxypeptidase - all secreted in inactive form -- pancreatic amylase, pancreatic lipase, pancreatic nuclease - all secreted in active form but can't work until exposed to bile |
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Name and tell the function of each of the digestive enzymes secreted by the pancreas.
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- watery, alkaline fluid helps neutralize chyme
- Enzymes: -- trypsin, chymotrypsin, carboxypeptidase: digest proteins, secreted in inactive form, (tripsin activated by membrane bound enterokinase, tripsin activates the rest itself) -- pancreatic amylase (carb digestion except cellulose and bicarbonates?), pancreatic lipase (digests lipids), pancreatic nuclease (digests nucleic acids); all secreted in active form, but can only digest once exposed to bile |
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Where and how are the protein digesting enzymes in the pancreatic juice activated?
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- trypsin, chymotripsin, carboxypeptidase
- secreted in inactive form (trypsinogen, chymotripsinogen, procarboxypeptidase) - tripsin activated by membrane-bound enterokinase - once active, tripsin activates the rest itself |
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Describe the pathway pancreatic juice follows as it travels from acinar cells to the duodenum.
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- two portions of the pancreas: endocrine cells (secrete glucagon and insulin); exocrine (acinar cells secrete pancreatic juice)
- from acinar cells, wecrete products into ducts (pancreatic and accessory) - ducts empty into the duodenum |
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How is the secretion of pancreatic juice regulated?
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- local hormones and PNS (less important)
Hormones: - Secretin - stimulates secretion of juice rich in bicarbonate ions; acic pH of chyme = stimulus for secretin; target - the cells of the pancreatic duct - cholecystokinin (CKK) - stimulates secretion of juice rich in digestion enzymes; causes gallbladder contractions and sphyncter to open; stimulus: chyme rich in fat/proteins; target: aciner cells of pancreas that secrete the juice |
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What are the functions of the liver?
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- blood maintanance - detox; get rid of worn out rbcs and pathogens, make plasma proteins for transport, coagulation, blood volume, etc
- metabolic regulation (central role) - makes glycogen and stores it, can release glucose into blood, lipid metabolism, gluconeogensis - aids digestion via synthesis and secretion of bile |
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What organ produces bile?
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- the liver
- derived from cholesterol in the liver - function if to emulsify fat globules |
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Describe the histological organization of liver lobules.
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- basic unit: liver lobule
- hexagonal in shape; made of hepatocytes (specialized ET cells) arranged around a central bein - At the corner of each lobule is a portal triad - portal triad is made of: a branch of the hepatic artery that gives O2 rich blood to liver; a branch of hepatic portal vein that gives deox. blood from viscera that is rich in nutrients; a bile duct - Liver sinusoids - found b/w hepatocyte plates where blood from hepatic portal vein and hepatic artery mingle then go to the IVC (it's where systemic blood picks up nutrients); enhances liver's function of filtering blood and processing nutrients b/c they very slow leaky capillaries w/large diameters |
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What three structures comprise a portal triad?
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- At the corner of each lobule (the basic unit of the liver) is a portal triad
- portal triad is made of: a branch of the hepatic artery that gives O2 rich blood to liver; a branch of hepatic portal vein that gives deox. blood from viscera that is rich in nutrients; a bile duct |
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Name the two sources of blood supply to the liver. Describe the hepatic circulation.
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- Each portal triad is made of: a branch of the hepatic artery that gives O2 rich blood to liver; a branch of hepatic portal vein that gives deox. blood from viscera that is rich in nutrients; a bile duct
- Liver sinusoids - found b/w hepatocyte plates where blood from hepatic portal vein and hepatic artery mingle then go to the IVC (it's where systemic blood picks up nutrients); enhances liver's function of filtering blood and processing nutrients b/c they very slow leaky capillaries w/large diameters SO: blood enters through hepatic artery(O2) and hepatic portal vein (nutrients) mingles in liver sinusoids to let systemic blood pick up nutrients flows into central vein; leaves via hepatic veins, goes to IVC |
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Describe the composition of bile.
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- watery secretion
- bile pigments (bilirubin, biliverdin - the leftovers of rbcs) - bile salts (from cholesterol in liver) (made of lecthin/a phospholipid, cholesterol, and electrolytes) |
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What is the function of bile salts?
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- emulsify fat globules, keep lipids solublized
- costly to make, so not excreted; is recycled - bile salts (from cholesterol in liver) (made of lecthin/a phospholipid, cholesterol, and electrolytes) |
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From what breakdown product are bile pigments derived?
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- bilirubin and biliverdin
- from the iron in rbcs |
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What organ stores bile between digestive periods?
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- the gallbladder
- on inferior surface of liver - concentrates and stores bile |
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Name the ducts which comverge to form the common bile duct.
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- hepatocytes secrete into
- bile canaliculi - bile ductules - bile ducts (part of portal triads) - R+L hepatic ducts - common hepatic ducts - finally, the cystic duct from gallbladder joins common hepatic to form common bile duct |
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Name the ducts which converge to form the hepatopancreatic ampulla, the duct that conducts both bile and pancreatic juice into the duodenum.
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- cystic duct from gallbladder had joined the common hepatic to form the common bile duct
- common bile joins the pancreatic duct to form the hepatopancreatic ampulla (found in wall of duodenum) - joined with the hepatopancreatic sphincter |
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How is bile release regulated?
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- concentrated and stored in the gallbladder during interdigestive periods using ion pumps
- cholecystokinin (CCK) - stimulates gallbladder to contract and hepatopancreatic sphincter to relax - releases bile into duodenum - CCK released when food comes into duodenum - CCK also one of the 2 hormonal regulations of pancreatic secretion (along with secretin), and it stimulates the aciner cells in the pancreas to secrete enzymes |
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Name and locate the three regions of the small intestine.
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- duodenum - first few inches
- jejunum - superior - illeum - inferior and last |
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Identify the sphyncter at the juncture of the ileum and the large intestine.
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- the ileocecal valve
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What structural modifications increase the internal surface area, and thus the absorptive ability of the small intestines?
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- Circular folds(plicae circularis) of the mucosa and submucosa; deep, permanent folds
- Villi - finger like folds of intestinal mucosa; lamina propria of villi has extensive capillary network of lacteals (lymph cap), specialized to pick up lipid digestive products - microvilli - cover lumenal surfaces of mucosa; create brush border; on apical surface of columnar cells on villi (brush border enzymes are embedded that help digestion) - intestinal crypts - in mucosa b/w villi; intestinal glands located in here (goblet cells - mucus, paneth cells - lysosome in saliva, tears etc, enteroendocrine cells - secretin, gastrointestinal peptide, VIP, CCK) |
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Why are the alkaline secretions of the small intestine and pancreas imporant?
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- they help neutralize the chyme coming in from the stomach
- this is needed to let the enzymes of the SI work |
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Name the brush border enzymes and describe their location. What role does each of the brush border enzymes play in nutrient digestion?
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- brush border = microvilli on apical surface of columnar cells on villi of mucosa
- bb enzymes - proteins embedded that help digestion - Enzymes: -- peptidases - split small peptides into individual AAs -- lipases - split lipids -- alpha-dextrinase and glucoamylase (oligosaccarideases) - digest CHO/carbs composed of 3+ simple sugars -- Dissaccharidases: maltase(maltose = 2 Glucose); sucrase (sucrose = glucose + fructose); lactase (lactose = glucose + galactose) |
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Describe the motility patterns of the small intestine.
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Two basic patterns:
- Segmentation - segments contract; relaxed on either side; food pushed into contact w/brush border for absorption; stretch of wall stimulates myenteric plexus which intensifies segmentation - Migrating motility complexes - weak peristaltic wave; passes over small segments (4 in); begins when stomach has emptied; slow peristaltic movement; wave takes 2 hrs to pass down duodenum to illium; chyme takes 3-5 hrs to get through |
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Identify the neural and hormonal factors which regulate movement of food residue from the ileum into the cecum.
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- gastroileal reflex - long reflex triggered by digestive activity in the stomach; stretch triggers myenteric plexus = forceful contractions and opening of sphincter
- Gastrin - causes relaxation of ileocecal valve (and also increases segmentation intensity in the ileum) |
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Describe the stimulus for secretion and the main action(s) of each of the following hormones: gastrin... (there are 3 main ones)
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- Gastrin - secreted by G cells(enteroendocrine cells) in stomach; causes gastric glands to increase their secretory activity (HCl from parietal cells etc) and stimulates gastric emptying; stretch in stomach walls causes myenteric and vagovagal reflexes, inc in PNS input releases ACh, which stimulates gastrin secretion
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Describe the stimulus for secretion and the main action(s) of each of the following hormones: secretin... (there are 3 main ones)
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- acidic pH of chyme stimulates it
- it targets the cells of the pancreatic duct to secrete juice rich in bicarbonate ions into the duodenum to neutralize the acidic chyme and let the enzymes work |
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Describe the stimulus for secretion and the main action(s) of each of the following hormones: CCK (cholecystokinin).... (there are 3 main ones)
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- stimulated by chyme rich in fat + proteins
- targets aciner cells in pancreas(the exocrine portion of the pancreas) to stimulate secretion of juic rich in digestion enzymes (trypsin, chymotrypsin, carboxypeptidase, pancreatic anylase, pancreatic lipase and pancreatic nuclease); causes gallbladder contractions and the hepatopancreatic sphincter to open and release bile from the liver into the duodenum |
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What effect does CCK have on secretory activity of the pancreas and gallbladder?
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- stimulated by chyme rich in fat + proteins
- targets aciner cells in pancreas(the exocrine portion of the pancreas) to stimulate secretion of juic rich in digestion enzymes (trypsin, chymotrypsin, carboxypeptidase, pancreatic anylase, pancreatic lipase and pancreatic nuclease); causes gallbladder contractions and the hepatopancreatic sphincter to open and release bile from the liver into the duodenum Random note: the pancreas is retroperitoneal (mostly) |
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Name and locate the four main regions of the large intestine.
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- Cecum - 1st place to collect material and compacts it
*appendix - vermiform appendix contains masses of lymphoid nodules - Colon - largest portion (ascending, transverse, descending, sigmoid); ascending and descending are retroperitoneal - Rectum - erect; 6 in; whortes part - Anal canal - exterior to abdominopelvic cavity, beginning where tube passes through uritogenital diaphragm; from level of pelvic floor to anus; has internal anal sphincter of smooth/involuntary muscle and external anal sphincter of skeletal/voluntary muscle |
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Describe the teniae coli and haustra.
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- Teniae coli - 3 separate longitudinal bands of smooth muscle lying just beneath the serosa; contract and form the LI pouches
- Haustra - the scalloped edges; pouches - these are two of the three unique features of the LI; the other one is the epiploic appendages (little fat saccules) but we don't know what they do |
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Describe the motility patterns of the large intestine. What is the functional significance of each?
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- Haustral Churning - distension causes contraction, mixing and churning; slow segmentation-type contractions in haustra walls; facilitates H2O and electrolyte absorption
- Mass movements - powerful peristaltic waves pass over large areas of colon 3-4x/day usu. during or just after eating; triggered by distension/irritation of somach or SI/duodenum (the gastrocolic reflex); moves materials to rectum; produces urge to deficate; fiber = more volume = stronger movements |
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What is the function of mass movements (mass peristalsis) and the gastrocolix reflex?
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- Mass movements - powerful peristaltic waves pass over large areas of colon 3-4x/day usu. during or just after eating; triggered by distension/irritation of somach or SI/duodenum (the gastrocolic reflex); moves materials to rectum; produces urge to deficate;
fiber = more volume = stronger movements |
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What are the functions of the large intestine?
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- absorb H2O, electrolytes, vitamines produces by enteric bacteria
- produce and excrete feces |
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Describe the defecation reflex.
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- an autonomic reflex
- feces forced into rectum via mass movements, rectal walls stretched - sensory fibers take 2 pathways: - mediated by centers in sacral level of spinal cord; comes back by involuntary motor nerve; causes contraction in wall of rectum and distal LI and relaxation of internal anal sphincter - messages sent to cerebral cortex; processed; sent back via voluntary motor nerve; either relaxes or tightens external anal sphincter - if cerebral control says "don't poop" then the stretch receptors adapt after a few min and the walls relax till the next mass movement - this pattern is the same as for urination |
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What enzymes are involved in the hydrolysis of carboyhdrates, proteins, lipids and nucleic acids? In what regions of the GI tract are each of these enzymes active?
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- Carbs: salivary amylase(in the mouth and short time in stomach), pancreatic amylase (secreted into duodenum, breaks down to di and trisaccharides), brush border enzymes(trisaccharides cleaved by oligosaccharides, disaccharides cleaved by disaccharidases:maltase, sucrase, lactase....glucose main product)
- Proteins: pepsin (in stomach), pancreatic proteases and brush border proteases (in SI - trypsin, chymotripsin, carboxypeptidase) - Lipids - gastric lipase (in stomach, but limited); pancreatic lipases (in SI - esp. in duodenum and jejunum) - Nucleic acids - pancreatic nucleases (in SI); brush border enzymes(cleave resulting monomers) |
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Pepsin and pancreatic proteases are secreted in an inactive form. How are each of these types of enzymes activated?
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Pancreatic proteases: trypsin, chymotripsin, carboxypeptidase
- enterokinase on brush border in duodenum and jejunum activates trypsin - trypsin activates chymotrypsin and carboxypeptidase Note: Trip. and Chymo. break polypeptieds into smaller polypeptides; carboxy and brush border peptidases complete protein digestion into amino acids, dipeptides and tripeptides |
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What are the digestive end products of carbohydrates, proteins, lipids and nucleic acids?
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Carbs - simple saccharides (glucose, fructose, galactose)
Proteins - Amino Acids Lipids - fatty acids Nucleic Acids - nucleotides |
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How are the digestive end products of carbohydrates absorbed?
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- simple/mono saccharides
- facilitated diffusion of fructose through transport proteins in brush border, - Na+ linked cotransport of glucose and galactose: secondary active transport (e. provided by Na conc. gradient created by Na/K pumps on basolateral membranes); transporter carries 2 Na and 1 glucose; galactose competes w/glucose for the binding site - why gatorade and rehydration drinks work - b/c you need Na to be able to absorb glucose |
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How are the digestive end products of proteins absorbed?
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- duodenum and jejunum primary site of small peptide absorption (di and tripeptides):
-- H+ linked secondary active transport; H diffuses down conc. gradient symporting w/small peptides; H+/Na+ antiporters in brush border membrane maintain H+ conc; peptidases inside epithelial cells break down most peptides to AAs; absorption across basolateral membrane into blood cap. in villus and then to liver via hepatic portal circulation) is by simple or facilitated diffusion - Illeum is most active site for AA uptake: transported across brush border via mechanisms involving Na+-linked secondary active transport symporters; absorption across basolateral membrane by simple or facilitated diffusion into blood cap. in villus |
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How are the digestive end products of lipids absorbed?
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- mostly in jejunum and illium
- end products of lipid digestive products(monoglycerides and free fatty acids) interact with bile salts form micelles (bile salts, monoglycerides, fatty acids, phosophlipids/emulsifiers, cholesterol, fat-soluble vitamins) - transported as micelle to brush border; absorbed via simple diffusion - triglycerides resynthesized inside mucosal ET cells (2FAs + MGs = TGs) - TGs packaged by golgi apparatus, coated with proteins/emulsifiers ; now in form of chylomicrons - ejected from ET cells by exocytosis, diffuse into lacteals (lymphatic cap.) b/c too big for blood stream - carried to systemic circulation via thoracic duct |
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How are the digestive end products of nucleic acids absorbed?
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- nucleotides - (pentose sugar, phosphate ion and nitrogen-containing base) absorbed via active transport
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Describe the mechanism of Na+ linked secondary active transport of nutrients. Is the ATP expenditure involved in this type of nutrient absorption a direct or indirct expenditure? Explain.
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- Secondary - e. provided by Na+ conc. created by Na/K pumps on membranes
- indirect expenditure - because you're spending the energy to set up the Na conc gradient, and then that gradient provides the energy to move other substances (like glucose) across the membrane - ex. transporter carries 2 Na and 1 glucose across membrane - ex2. H diffuses down conc gradient symporting with small peptides (di and tripeptides) |
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What is the difference between a micelle and a chylomicron?
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- MIcelles - carry lipid digestive products to brush border for absorption (made of bile salts, monoglycerides, FAs, phospholipids/emulsifiers, cholesterol, fat-soluble vitamins); then the fats can be absorbed via simple diffusion
- inside mucosal ET cells triglycerides are resynthesized - Chylomicron - the new TGs are combined with other lipid matierals, coated with proteins/emulsifiers and packaged by golgi app.; ejected from ET cells by exocytosis; diffuse into lacteals/lymphatic cap; carried to systemic circulation via lyphatics and thoracic duct |
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How are chylomicrons carried from the intestines to the systemic circulation?
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- ejected from ET cells by exocytosis
- diffuse into lacteals/lymph. cap - carried to systemic circ via lymphatics - empty through thoracic duct |
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What is the function of lipoprotein lipase? Where in the circulatory system is it located?
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Functions:
-- can take FAs up to use or store it -- hydrolyzes TGs (TG = 3 FFA + glycerol); products diffuse into cell to be used as e. or stored as fat - Found in adipose tissue, muscle and heart (in the endothelium of the systemic capillaries in these places) - Note: chylomicron remnants circulate to liver for further metabolism (TG synthesis, gluconeogenesis, etc) |
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How is sodium absorbed in the GI tract?
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- absorbed along entire length of intestine (S + L)
- usu. diffuses across apical surface and then pumped across basolateral membrane by Na/K pumps (sets up e for secondary pumps and allows us to absorb H2O) - generally anions passsively follow e gradient of Na+: (but there are exceptions; HCO3- is actively secreted in proximal duodenum, in exchange for Cl- to provide a buffer; also secreted in ileum and LI) - HCO3- and Cl- are absorbed a lot in jejunum |
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How is potassium absorbed in the GI tract?
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- as water is absorbed in intestines b/c of sodium uptake, K more conc. in chyme
- now can be absorbed by simple diffusion - any disruption of H2O absorption interferes w/K+ absorption b/c NO way to actively absorb it - why dehydration = loss of potassium |
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How is water absorbed in the GI tract?
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- appx 9 L/day enters tract, only .1 L/day is lost in feces
- water moves in both directions freely via mucosa - water reabsorption coupled with solute (esp sodium) uptake |
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Where along the GI tract is the greatest amount of water absorbed?
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- most water absorbed in SI; (8.3 L)
- LI - absorbs about I L |
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ascites
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- the abnormal accumulation of peritoneal fluid in the peritoneal cavity
- can cause abdominal bloating; accompanies heart failure, liver disease, kidney disease Normal state: visceral and parietal peritoneum secrete fluid into cavity to reduce friction of organs; about 7 L/day secreted and reabsorbed |
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peristalsis
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propelling motion produced by alternate waves of contraction and relaxation of muscles in the tract wall
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segmentation
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mixing type of movement which churns and mechanicaly fragments materials in the digestive tract, occurs due to rhythmic, local contractions of the muscularis layer
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salivary amylase
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secreted in saliva
begins digestion of polysaccharides/starches/carbs - secreted by parotid, submandibular, sublingual glands |
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enteroendocrine cells
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Enteroendocrine cells are specialized endocrine cells of the gastrointestinal tract. They produce hormones such as serotonin[1], somatostatin, motilin, cholecystokinin, gastric inhibitory peptide, neurotensin, vasoactive intestinal peptide, and enteroglucagon.
Most enteroendocrine cells are found in the islets of Langerhans, but they are also found in other locations. For example, the G cells (which secrete gastrin) are located primarily in the stomach Enteroendocrine cells are also found in the duodenum - G cells are one of the 4 types of gland cells in gastric glands (mucus neck, parietal, chief) - function as paracrines to regulate digestive activities |
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chyme
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Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum
- bolus converted to chyme in stomach |
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acini (acinar cells)
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- part of the exocrine portion of the pancreas
- secretes pancreatic juice into pancreatic an accessory ducts - juice: (alkaline; has trypsin, chymotrypsin, carboxypeptidase, pancreatic amylase, pancreatic lipase, pancreatic nuclease) - regulated by CCK/cholecystokinin |
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cholecystokinin(CCK)
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- trigger: chyme rich in fat + proteins
- targets aciner cells that secrete pancreatic juice; stimulates the secretion of juice rich in digestion enzymes - also causes gallbladder contractions and the sphincter to open |
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secretin
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stimulates secretion of pancreatic juice rich in bicarbonate ions
- alkaline tide (of the gastric cells) is ballanced by the output of bicarbonate, so that the blood pH is ballanced when going into duodenum targets cells of pancreatic duct - triggered by acidic pH of chyme |
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villi
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- finger-like folds of intestinal mucosa (inc. surface area of SI along with circular folds and microvilli)
- lamina propria of villi contains extensive cap network (including lactieals; lymph cap. specialized to pick up lipid digestive products which enter blood at thorasic duct) |
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microvilli
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- cover lumenal surfaces of mucosa in SI
- create the brush border - on apical surface of columnar cells on villi - brush border enzymes = proteins embedded that help digestion |
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brush border
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- covers lumenal surfaces of mucosa in SI
- microvilli create the brush border - on apical surface of columnar cells on villi - brush border enzymes = proteins embedded that help digestion - enzymes: peptidases (peptides to AA), lipases (lipids), alpha-dextrinase and glucoamylase (oligosaccharides - carbs w/more than 3 simple sugars), disaccharidases:maltase, sucrase, lactase |
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Peyers Patches
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(MALT) - Membrane associated lymphatic tissue
- lymphoid nodules - found in submucosa (areolar CT) of SI |
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MALT - mucosa-associated lymphatic tissue
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(MALT) - Membrane associated lymphatic tissue
- lymphoid nodules - found in submucosa (areolar CT) of SI |
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migrating motility complexes
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- weak peristaltic waves
- pass over small segments (4 in) - begin when stomach is empth - creates slow peristaltic movement - 1 of 2 basic motility patterns in SI (the other one is segmentation) - takes 2 hrs for contraction to travel from duodenum to illium - takes 3-5 hrs for chyme to get through |
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intestinal flora
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- the LI is home to millions of bacteria
- mostly bacteria, some yeasts - healthy symbiosis: bacteria ferment and break down complex carbs and proteins that we can't digest; by-product is that they synthesize vit K, thyamin, riboflavin and vit B-12 - fart: bacteria make H2, CO2, methyl sulfide, etc |
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haustral churning
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- one of 2 motility patterns of LI (the other one is mass movements)
- slow, segmentation-type contractions in haustra walls - distension causes contraction - slow mixing and churning facilitates absorption of H2O and electrolytes |
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deglutination
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to extract the gluten from
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dietary fiber
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Chemically, dietary fiber consists of non-starch polysaccharides such as arabinoxylans, cellulose and many other plant components such as dextrins, inulin, lignin, waxes, chitins, pectins, beta-glucans and oligosaccharides
Dietary Fiber (sometimes called roughage) is the indigestible portion of plant foods having two main components absorbs water, aids defacation |
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enteropeptidase
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- activates trypsin (a protein digesting enzyme from pancreas in the form of trypsinogen)
- synonym for membrane bound enterokinase possibly - trypsin then activates chymotripsonogen and procarboxypeptidase into chyotrypsin and carboxypeptidase - all of these digest proteins in the SI |
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hiatal hernia
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Hiatal hernia is a condition in which a portion of the stomach
protrudes upward into the chest, through an opening in the diaphragm. |
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emesis
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- vomiting
- the forceful expulsion of the contents of one's stomach |
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enterohepatic circulation
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Enterohepatic circulation refers to the circulation of biliary acids from the liver, where they are produced and secreted in the bile, to the small intestine, where it aids in digestion of fats and other substances, back to the liver
- ie. how bile salts travel.(?) |
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Describe the chemical digestion of carbohydrates, identifying the sites of digestion and the enzymes involved.
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- amylases: break down polysaccharides to di and trisaccharieds
-- salivary amylase - begins in mouth, short time in stomach; inactivated by acidic pH -- pancreatic amylase - secreted into duodenum; continue digestion of starch and glycogen; w/in 10 min starch becomes oligosaccharides, then eventually become di and tri - Brush Border Enzymes - in SI: -- Oligosaccharidases - cleave trisaccharides -- disaccharidases - cleave disaccharides (maltase: maltose to 2 glu; sucrase: sucrose to glu and fru; lactase: lactose to glu and gal) Absorption: -- facilitated diffusion of fructose thru transport proteins in brush border -- Na+ linked cotransport of glucose and gaoactose (2ndary active transport - carries 2 Na and 1 gluc) - move across basolateral membrane via facilitated diffusion, then diffuse into cap blood/hep. port. circ. |
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Describe the chemical digestion of proteins, identifying the sites of digestion and the enzymes involved.
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- Pepsin - in stomach acidity; breaks it into smaller polypeptide chains
- Pancreatic proteases/brushborder proteases - in SI -- trypsin, chymotripsin, carboxypeptidase (trypsin activated by enterokinase on brush b in duodenum and jejunum, then activates) - small peptides absorbed via H+ linked secondary active transport (H/Na) across brush membrane -- carbosypeptidase and brush border peptidases complete protein digestion into AA, di and tripeptides - absorption across basolateral mem. by simple or fac. diffusion |
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Describe the chemical digestion of lipids, identifying the sites of digestion and the enzymes involved.
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- gastric lipase in stomach - limited
- bile salts in SI = emulsion droplets - pancreatic lipases - cleave lipids into monoglycerides and FAs; mostly in duodenum and jejunum - absorption - end products of lipid digestion interact w/bile salts to for micelles - go to brush b. - absorbed via simple diffusion - put back together in mucosal ET cells into triglycerides; combined and coated to form chylomicrons - exit via exocytosis into lacteals - lipoprotein lipase( in adipose t. muscle and heart) hydrolyzes TGs in cap. into 3FA and glycerol |
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Describe the chemical cigestion of nucleic acids, identifying the sites of digestion and the enzymes involved
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- pancreatic nucleases - hydrolyze them in SI to nucleotide monomers
- brush border enzymes - cleave monomers into: pentose sugar, phosphate ion, nitrogen-containing base - end products absorbed via active transport |
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Describe the composition of intestinal juice.
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??????? - ask elise?
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