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140 Cards in this Set
- Front
- Back
***true or false: endopeptidase cleaves trypsinogen to trypsin in the duodenum?
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false. ENTEROpeptidase does this.
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what two enzymes cleave trypsinogen to trypsin?
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1. enteropeptidase
2. trypsin |
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what is the function of trypsin?
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to cleave zymogens secreted into the intestinal lumen to active enzymes. Also, it cleaves trypsinogen to trypsin.
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where is secretin produced and released? What stimulates its secretion? What are its effects?
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- produced and released by the first few cm of the duodenum in response to gastric acid
- stimulates the ducts of the exocrine pancreas to produce copious amounts of bicarb - weak stimulator of bile and pancreatic enzymes |
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where is CCK produced and released? What stimulates its secretion? What are its effects?
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(cholecystokinin)
- produced by most of the duodenum in response to the presence of digesta in the lumen - stimulates the acini of the exocrine pancreas to secrete enzyme-rich fluid - is a weak stimulator of bicarb secretion |
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how do secretion and CCK affect each other?
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they augment each others' release
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in non-ruminants, where is the primary site of digestion? Where is the primary site of absorption?
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Both in the small intestine
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what are the major functions of the small intestine in ruminants?
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- fat digestion
- required for protein digestion and absorption - water and electrolyte reabsorption |
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what are the two anatomical structures of the small intestine most responsible for increasing its surface area?
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microvilli and glycocalyx
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what four anatomical features allow very efficient digestion and absorption by the small intestine?
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1. high surface area
2. "loose" tight junctions 3. high surface area basolateral membranes 4. capillaries and lacteals very close to the lateral spaces |
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what inhibits CCK secretion?
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loss of substrates from the late jejunum
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what inhibits secretin secretion?
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negative feedback (e.g. pH)
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what are the two main "aims" of the digestive phase of small intestinal motility?
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1. promote digestion and absorption
2. move digesta aborally at an appropriate rate |
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what is the predominate mechanism that the small intestine uses to mix digesta with enzymes?
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segmentation
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by what two means of controlling motility does the small intestine allow adequate time for digestion and absorption?
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1. the duodenal pacemaker
2. retentive form of gut motility to allow time for absorption |
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what are the two mechanisms by which the small intestine moves digesta at an appropriate rate?
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1. "regular" peristalsis, where digesta progresses only short distances.
2. peristaltic rush, where particularly strong waves respond to obstruction (much like secondary peristalsis of the esophagus) |
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what is the interdigestive phase of small intestine motility?
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the "housekeeper" modified peristalsis, that cleans out larger particles
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what is the function of the muscularis mucoase in small intestine motility?
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"waves" the intestinal villi in the "soup" of digesta
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characterize the connection of the ileum to the large intestine
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it is an ileocolic or ileocecal spincter that is held tonically closed, and must relax to allow digesta to enter the large intestine
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what are the two neural controls and function of those controls of small intestinal motility?
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1. intrinsic: myentric plexuses - intraintestinal communication
2. extrinsic: ANS - "influences" the myenteric plexuses |
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how does CCK influence small intestinal motility? Secretin?
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They both increase motility. Remember that these two enzymes work in concert.
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obstruction of the intestines caused by failure of peristalsis
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ileus
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what are the two types of diarrhea that occur in the small intestine?
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hypermotile and hypomotile
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what are the four general phases of digestion and absorption in the small intestine?
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1. luminal phase
2. mucosal ("membranous") phase 3. intracellular phase 4. absorption |
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what are the main chemical components in the luminal phase of digestion in the small intestine?
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pancreatic and/or gastric enzymes
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why is the luminal phase of digestion in the small intestine generally not sufficient to allow absorption of nutrients?
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because the particles are still too large. Only monomers, dimers, and trimers can be absorbed.
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in the mucosal phase, what organ produces the enzymes used for digestion, and where are the enzymes located?
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they are produced by the small intestine only and bound to the glycocalyx.
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what is the maximum size of digesta that can be absorbed by the small intestine?
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trimers
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by what two routes can digesta pass from the small intestinal lumen to the basolateral space/interstitium?
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1. intracellularly by secondary active transport
2. paracellularly through "leaky" tight junctions |
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describe the intracellular phase of digestion in the small intestine.
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- it occurs ONLY in the small intestine
- only dipeptides and tripeptides - they are converted to amino acid monomers |
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where do nutrients pass in small intestinal absorption after they enter the interstitium?
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blood and lymph
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what type of carbohydrate is indigestible by all domestic mammals?
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lignin
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where does most digestion of soluble carbohydrates occur in non-ruminants?
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small intestine
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what are the four major sites of carbohydrate digestion in non-ruminants and what enzymes are used?
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1. oral lumen - salivary amylase
2. gastric fundus - salivary amylase 3. enteric lumen (duodenum and jejunum) - pancreatic amylase 4. mucosal (jejunum) - small intestinal enzymes on the glycocalyx |
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where does luminal digestion of CHOs by pancreatic amylase take place in the non-ruminant?
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duodenum and jejunum
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which part of the small intestine exhibits the greatest mucosal digestion of CHOs in the non-ruminant?
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jejunum
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generally, how are CHOs moved intracellularly from the lumen of the small intestine?
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by secondary active co-transport with sodium. Note that only monosaccharides can enter the enterocytes and be absorbed.
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how do sugars move from the basolateral membrane of the luminal cells to the basal interstitium of the small intestine?
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facilitated diffusion
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what are major sources of protein absorbed in the small intestine?
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- dietary
- sloughed-off mucosal cells - digestive enzymes - (ruminant) microbial protein |
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what are the products of oral luminal digestion of protein?
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none. Protein digestion does not occur in the oral lumen.
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what are the products of gastric luminal digestion of protein in the non-ruminant?
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proteoses
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In the non-ruminant, what chemicals are used in the gastric luminal phase of protein digestion?
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gastric acid and gastric enzymes
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In the non-ruminant, where does the majority of protein digestion occur?
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small intestinal lumen is the largest
small intestine mucosa is also very important |
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what is the maximum size protein that can enter an enterocyte in the non-ruminant?
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tripeptide
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where are pepsins used, what do they digest, and what type of enzyme are they in the non-ruminant?
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pepsins are protein-digesting endopeptidases used in gastric luminal digestion.
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what are the two main types of pancreatic proteases and how do they differ in the non-ruminant?
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- endopeptidases: cleave proteins inside of the chain
- exopeptidases: cleave individual amino acids from the carboxyl ends of proteins |
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what proteases are present on the non-ruminant small intestinal mucosa and what do they do?
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- aminopeptidases - cleave individual amino acids from the N-position; produce mono-, di-, and tripeptides
- dipeptidases - produce dipeptides |
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where does the majority of dipeptide and tripeptide digestion occur in the non-ruminant?
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In the small intestine enterocytes.
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by what mechanisms are amino acids transported from the enterocyte to the blood in the non-ruminant?
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facilitated diffusion and Na-dependent co-transport
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by what mechanism are intact proteins absorbed by neonates?
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pinocytosis
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what is the term used for when a neonate can no longer absorb whole proteins?
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gut closure
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what three organs are primarily responsible for digestion of dietary fat?
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stomach, small intestine, liver
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what enzyme is used for the digestion of triglycerides in the gastric lumen?
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none
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where does enzymatic fat digestion occur in the non-ruminant?
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small intestine only
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what is the 7-step process of triglyceride digestion and absorption in the small intestine?
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1. emulsification by bile
2. enzymatic hydrolysis to fatty acids 3. micelle formation 4. uptake by the enterocyte 5. conversion back to triglyceride 6. formation of chylomicrons 7. absorption into the central lacteal |
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which energy-yielding nutrient has no mucosal phase of digestion?
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lipids
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true or false: emulsification of fat by bile is a form of mechanical digestion?
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true
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what are the main enzymes that digest triglycerides?
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1. pancreatic lipase
2. pancreatic co-lipase |
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what is the function of pancreatic co-lipase?
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"sweeps" bile out of the way so that pancreatic lipase, which can not enter a fat globule, can work.
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what are the products of the complete digestion of a triglyceride by pancreatic lipase?
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2 FFAs and a monoglyceride
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what are the main components of a micelle in the small intestine?
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- bile
- cholesterol - free fatty acids - monoglycerides - vitamin A |
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where, in the intercellular phase of fat digestion, are fats assembled into triglycerides and then chylomicrons
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SER
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how are chylomicrons transported from the SER to the blood?
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1. Golgi puts it into a vesicle
2. vesicle fuses with the basolateral membrane 3. chlyomicron enters the central lacteal and into the lymphatic system 4. enters the blood via the thoracic duct |
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what is lipemia?
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chylomicrons in the plasma following a fatty meal
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how is bile recovered/reused in the small intestine?
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- about half is PASSIVELY absorbed in the jejunum
- the other half is reused - if it enters the ileum, it is ACTIVELY transported |
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why is the ileum important in fat digestion?
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because it recovers almost all of the bile that passes into it
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why is poop brown?
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bile
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what major function does the large intestine perform in all species?
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electrolyte and water absorption
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how does digestion occur in the large intestine, if any?
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fermentation
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what is the most significant immune function in the large intestine?
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plasma cells in the lamina propria produce IgA
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what part of the large intestine is not involved in digestion or absorption?
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rectum
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what are the major electrolytes absorbed by the large intestine and by what mechanism does this occur?
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- Na (and Cl) via Na-K-ATPase
- K via H-K-ATPase |
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how is digesta transported from the ascending colon into the cecum?
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retroperistalsis
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how is digesta retained in the cecum for water absorption and digestion?
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stationary haustral contractions
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the movement of large volumes of material from the cecum to the large intestine
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mass movement
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how does motility in the large intestine differ from the cecum?
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the large intestine does not use retroperistalsis (except in the delivery of digesta to the cecum in non-equids)
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true or false: defecation can be defined as a sustained colonic contraction
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false
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how is defecation initiated?
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defecation reflex, which is activated by the distention of the descending colon and/or rectum
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what components of the ANS are involved in defecation?
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afferent and efferent neurons are both parasympathetic and arise from the pelvic plexuses and pelvic nerves.
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what four major groups of muscles are involved in defecation? (yes, I know that this is a lovely subject)
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1. mass movement contractions of the colon
2. contraction of the longitudinal rectal muscles 3. anal sphincters 4. skeletal muscles such as the abs and diaphragm (squeeze!) |
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the two anal sphincters:
- name - muscle type - innervation - major function |
1. internal anal sphincter; smooth muscle; pelvic nerve; kept tonically contracted for continence
2. external anal sphincter; skeletal muscle; pudendal nerve; "oh no, next rest stop!" and closure of the anus after defecation |
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what is the rectosphincteric reflex?
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as fecal mass enters the rectum, defecation ensues.
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in the act of counteracting the urge to defecate, what must be counteracted and how is this accomplished?
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the rectosphincteric reflex "overrided" by contraction of the external anal sphincter and stretch relaxation of the rectum
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why do animals fart?
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1. swallowing of air
2. intraluminal flora |
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what nutrients are digested most by microbes?
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CHOs and protein (fat is only partially digested by microbes)
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what major vitamins are synthesized by fermenting microbes?
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B Vitamins
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what types of microbes are involved in fermentation and where are they located?
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bacteria - foregut and hindgut
protozoa - foregut and hindgut fungi - mainly foregut |
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***where in horses and ruminants is digesta stored for fermentation?
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ruminants - rumen
horses - ***ASCENDING*** colon and cecum |
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what five major physiological conditions are maintained by the fermenting animal to keep its microbial flora happy?
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1. anerobic conditions (required for fermentation)
2. temperature 3. pH (buffers) 4. osmolarity near 300 mOsm 5. removal of microbial waste products |
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how are microbial waste products handled by the animal (foregut and hindgut fermenters, specifically)?
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they are absorbed as nutrients
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why do horses require higher protein in their diets than ruminants
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because ruminants digest microbes as their protein source. Horses cannot use microbial protein because they are hindgut fermenters
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what are the major gases produced by microbial fermentation?
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CO2 and CH4
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how does the foregut and small intestine aid in fermentation in the hindgut in horses?
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partial digestion: acids, enzymes, soaking, and motility
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compare the digestion of sugars and starches by the small intestine of horses versus carnivores.
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not as efficient. Some of the sugar and starch is fermented.
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if the horse digests its protein in the small intestine, how do the microbes in its ascending colon and cecum get the protein that they need?
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From urea, secreted into the colonic lumen from the blood, and converted to ammonia by microbial urease. They use this ammonia to make proteins and amino acids for themselves.
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although amino acid absorption in the hindgut of the horse is minimal compared to its diet, why is it important?
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microbes synthesize essential amino acids
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what are the two flow-reducing anatomical features in the equine ascending colon?
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1. right colic flexure - major effect
2. pelvic flexure (note that sternal and diaphragmatic flexures are much more minor compared to the above two) |
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what are the four functional regions of the intestines of the horse as related to digestion?
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1. cecum
2. ventral colons 3. dorsal colons 4. descending colon |
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in the horse, what transfers digesta from the small to the large intestine?
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ileocecal orifice
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how does delivery of digesta to the cecum differ in the horse from other animals?
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it passes directly into the cecum via the ileocecal orifice. Thus, no retroperistalsis from the colon to cecum is present.
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what is the main job of the horse cecum and how is this accomplished?
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to mix the digesta to start fermentation. This is done by:
- frequent segmentation from hausta to haustra - occasionally, a retroperistaltic mass movement from cecal apex to base, which delivers digesta to the RVC via the ceocolic orifice |
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what are the three major types of colonic motility in the ventral and dorsal colons of the horse?
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much the same in the ventral colons versus the dorsal colons
1. haustral segmentation 2. propulsive peristalsis 3. retentive peristalsis |
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what is the function of propulsive peristalsis in the horse's ventral colons?
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to move digesta along the ventral colons and to the dorsal colons
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in the horse's ventral colons, where is the pacemaker for retentive peristalsis, and where is retentive peristalsis best-developed?
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- the pacemaker and particle sorting pyloris-like sphincter is at the pelvic flexure
- the LVC is best developed for retentive peristalsis |
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in the horse's dorsal colons, where does retentive peristalsis originate, and where is retentive peristalsis best-developed?
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originates at the right colic flexure
best developed in the RDC |
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why is there so much water movement in the colon of the horse?
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to absorb VFAs and to maintain osmolarity
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how is the large intestine buffered in the horse?
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bicarb and phosphate secreted by the ileum and by the crypts of the mid-to later ascending colon
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what are the two functions of bicarb and phosphate in the horse's ascending colon?
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1. buffer the pH
2. maintain osmolarity |
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how and why are fecal balls produced by the horse?
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by segmentation in the descending colon to reabsorb water and electrolytes
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what are the three time periods of natural bovine gastric development?
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1. "nonruminant"
2. transitional period 3. "adult" |
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what three major stimuli cause reflexive closure of the gastric groove in the juvenile ruminant?
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1. cephalic (anticipation of suckling)
2. salts in the pharynx (chemoreceptors) 3. the activity of suckling |
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what stimulates the gastric groove to close in adult ruminants?
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ADH (thirsty!)
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what stimulates papillae to develop in the rumen?
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VFAs
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what are the four major functions of the reticulorumen?
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1. promote fermentation by mixing and sorting digesta
2. prepare digesta for remastication and reinsalivation (reticulum) 3. absorb VFAs 4. eructation of gases released form fermentation |
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how does digesta move to the omasum and what is the basic function of the omasum?
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- sucks the digesta into itself
- "treats" digesta for passage into the abomasum |
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what are the three major places, in the rumen, where ruminal bacteria reside, and what do they do?
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1. in the fluid, free-floating to ferment dissolved nutrients
2. on food particles, mostly cellulose 3. on the epithelium to digest sloughed-off epithelial cells. |
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how do the bacteria associated with the ruminal epithelium differ from that of the other bacteria in the rumen?
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they use O2 from the blood of the ruminant
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how do ruminal fungi digest nutrients?
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they ferment plant fiber and physically digest them by breaking them apart with their hyphae
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what is the product of triglyceride fermentation in the rumen?
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FFAs and glycerol
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true or false: most ingested protein escapes fermentation by the rumen and is instead digested by the abomasum and small intestine?
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false. SOME dietary protein escapes the rumen. Most is fermented.
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what are the four major sources of urea in the ruminant?
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1. diffusion into rumen from the blood
2. ammonia given off by bateria is converted to urea by the liver and put back into rumen 3. saliva 4. feed additive |
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how does water enter the rumen?
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drinking only. Little to no luminal secretion.
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how does saliva vary with diet in the ruminant?
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the more roughage, the more saliva produced
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how is the rumen pH buffered?
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by buffers from the saliva
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what are the two basic functions of water in the reticulorumen?
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1. assists in sorting and movement of variously processed digesta
2. delivers microbes and digesta to omasum, abomasum |
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what are the six basic zones of the reticulorumen and where are they located?
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1. gas zone - upper part od dorsal sac
2. "bubbly" solid zone ("rumen mat") - floats on top of the fluid zones 3. ejection zone - near the cardia for eructation and regurgitation 4. slurry zone 5. liquid "non-bubbly zone" - finished fermenting 6. zone of potential escape - ventral parts of the reticulum and cranial sac; regurgitation or passage to omasum |
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by what three ways is ruminal motility controlled?
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1. endocrine (minor)
2. intrinsic nervous system - very complex 3. CNS - vagus nerve |
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what will happen to ruminal motility if the vagus nerve is cut?
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- the rumen will have uncoordinated contractions: poor mixing of digesta
- stretch receptors (and others) will not reach the brain, so the animal will keep eating - the ruminant will eventually die from bloat |
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what five physiological conditions of the rumen are monitored by the vagal nucleus?
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1. ruminal distention
2. consistency of the digesta 3. pH 4. concentration of VFAs 5. osmolarity (minor) |
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how does ruminal distention affect rumen motility
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slows it; bloat stops it.
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how does the fluidity of digesta affect rumen motility?
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more fluid - slower
more solid - faster and stronger |
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how does pH affect rumen motility?
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low (<5) slows so VFAs can be absorbed
high (>7) increases to promote fermentation |
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how does ruminal VFA concentration affect rumen motility?
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high VFA concentrations slows rumen motility
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how does the strength of reticulum contraction affect digestion?
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- moderate sorts digesta
- virorous sends fluid to omasum and coarse particles back to rumen |
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what are the four main waves of contraction of the rumen and their functions?
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1. caudally-directed peristaltic wave of the dorsal ruminal sac: mixes and sorts
2. caudally-directed peristaltic wave of the ventral ruminal sac: mixes and sorts 3. cranially-directed peristalic wave of dorsal sac: mixes, sorts, washes digesta into reticulum 4. cranially-directed peristalic wave of ventral sac: mixes, sorts, washes digesta into reticulum |
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what is the purpose of and process of secondary ruminal contraction?
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- eructation
1. cranially directed wave begins at caudal dorsal blind sac, moves over dorsal sac to cardia 2. cranial pillar elevates and cranial sac relaxes as wave approaches to drop liquid level. 3. lower esophageal sphincter relaxes and gas escapes |
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what is the process of regurgitation in the ruminant?
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1. rumen contracts, delivering bolus to the lower esophageal sphincter
2. lower esophageal sphincter relaxes and bolus enters esophagus 3. reverse peristalsis carries bolus to mouth 4. fluid reswallowed; bolus is remasitcated, resalivated, and swallowed |
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what is secreted into the ruminant saliva to buffer the rumen?
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phosphate and bicarb
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where are most VFAs absorbed by the ruminant, and what cell-type is involved in the absorption?
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stratified squamous epithelium of the ruminal papillae
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what is the most important enzyme secreted in the abomasum to digest bacterial cell walls?
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lysozyme
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