Gastrointestinal Physiology Flashcards
Intrinsic regulation involves (2) and is responsible for
local nervous and endocrine systems; specific GI functions
Extrinsic regulation involves (3) and is responsible for
CNS, ANS, endocrine system; broad promotion or inhibition of GIT activity
the myenteric plexus controls ________ and gets its sensory info from _________
motility; mechanoreceptors
the submucosal plexus controls _______ and gets its sensory info from __________ in ________
secretions; chemoreceptors; mucosa
What coordinates motor and secretory activity in the GIT
interneurons (between myenteric and submucosal plexus)
describe nerve endings in the ENS
no synapse; NT is released diffusely within tissue; motor axons end in varicosities
varicosities release _________, which are (2)
neurocrines; NTs or hormones
what enteric NTs are excitatory
acetylcholine, tachykinins (substance P)
substance P is involved in (2)
pain; vomiting (via CTZ in medulla)
what enteric NT peptides are inhibitory
somatostatin; NE/E; PACAP
what enteric NT non-peptides are inhibitory
NO, ATP
what enteric NT is inhibitory to muscle but stimulatory to glands
VIP (vasoactive intestinal peptide)
most of the GI tract is supplied by what nerve
vagus
the pelvic nerve supplies
descending colon and rectum (and bladder)
the vagus nerve uses what NT
ACh (stimulatory to gut muscle and secretions; vasodilates; relaxes sphincters)
sympathetic afferent nerves synapse in (2) ganglions
celiac and mesenteric
splanchnic nerves release what NT
NE (inhibits motility and secretions; contracts sphincters; vasoconstricts)
_________ afferent nerves (which are _________) mediate normal gut function, whereas ___________ afferent nerves (which are ___________) signal pathological conditions
vagal, parasympathetic; splanchnic, sympathetic
where is information from visceral afferents integrated
brainstem mainly
most GI functions are (conscious or subconscious)
sunconscious
T/F GI functions are completely subsconscious
F
intrinsic gut hormones are mainly _________ released from ________ cells
peptides; enteroendocrine
T/F enteroendocrine cells look alike because they each secrete multiple hormones
F; they look alike but each secretes a single hormone
enteroendocrine cells have what effects
autocrine, paracrine and endocrine
how are some GI hormones involved in cancers
some promote mucosal growth
cytokines released by the mucosal immune system affect gut (2)
mucosal immune system; motility and secretions
T/F the GIT is predominantly self-regulated by intrinsic nerves and hormones
T
what is transit time
time taken by food to travel from one gut location to another
what are the 4(5) functions of the GI tract and examples of each
- propel ingesta (peristalsis)
- retain ingesta (sphincter contraction)
- break up and mix ingesta (segmentation)
- circulate ingesta (segmentation)
T/F GI smooth muscle contains gap junctions to electrically couple the cells
T
what are the pacemaker cells of the GI smooth muscle
Interstitial Cells of Cajal (ICCs)
what are slow waves
ICCs intrinsically, rhythmically depolarize (and then repolarize)
T/F slow waves cause firing of APs and contraction
F; the waves are of subthreshold depolarization
when does contraction of GI muscle occurs
when slow waves coincide with excitatory NT release
slow waves determine _________ whereas NTs determine ___________
pattern of contraction; whether the contraction occurs or not
waves travel in what direction along GI smooth muscle
aborally
contractions in the proximal stomach are _________ whereas those in the antrum are __________
weak; strong
the peristaltic reflex is entirely _________
internal to the ENS
distention of a food bolus ____________ circular muscle proximally and ____________ circular muscle distally
stimulates (Ach, substance P); relaxes (ATP, NO, NE, VIP)
mouth/pharynx/larynx is controlled by ________, esophagus in ruminants/dogs is controlled by ________, esophagus in cats and horses is controlled by _________ and the stomach and intestines are controlled by ________
CNS; ANS; ANS/ENS (cranial vagus, caudal ANS/ENS); ENS
prehension means
grasping food
prehension is controlled by ________ muscles and involves cranial nerves (3)
skeletal; facial, glossopharyngeal, trigeminal
what can cause issues with mastication
poor dentition and gum disease
the voluntary stage of deglutition involves _________; the involuntary stage of deglutition involves __________ and cranial nerves
movement of the bolus into the oropharynx by the tongue; movement of the bolus from the oropharynx to the esophagus; cranial nerves 5, 7, 9, 10, 12
the upper esophageal sphincter is called the
cricopharyngeal sphincter
what is an important roleof the cricopharyngeal sphincter that prevents colic
prevents swallowing of air, which can cause colic
what propels food from pharynx to stomach; what muscle type and nerves are involved
peristalsis in the esophagus; striated mostly; vagus
T/F with fragmentation,there is net forward movement
F
functions of saliva (5)
lubricates; digests (amylase and lipase); antibacterial (lysozyme); grooming; thermoregulation
salivation is stimulated by ________ (what molecule) and inhibited by ________ (what molecule)
the facial nerves that control salivation are (2)
Ach (released by glossopharyngeal and facial); NE/E
two broad categories that stimulate salivation
ANS (and CNS) and natural stimuli
acini in salivary glands secrete (4)
mucus, enzymes, electrolytes (Na, Cl), water
when dehydrated, aldosterone stimulates _________ (2) to be reabsorbed in the salivary gland and _________ (2) to be secreted; this makes the saliva (2)
Na/Cl reabsorbed; K/HCO3 secreted; saliva becomes hypotonic and neutral to alkaline
parotid salivary glands primarily have ________ secretion
serous
ruminant saliva characteristics
voluminous, alkaline, high in Na and HCO3; helps buffer rumen contents
roles of the stomach (4)
stores food, breaks down food, starts digestion (HCl and proteolytic enzymes), released chyme
stomach movements are controlled by (3)
ANS, ENS, gut hormones
the _________ of the stomach is responsible for storage
proximal part (antrum and most of body)
the _______ of the stomach is responsible for churning and mixing
antrum
as food enters, the proximal stomach ______ due to ________ innervation
relaxes; vagus
T/F salivary enzymes can digest food throughout the entire stomach
F; only in the proximal stomach
stomach motility is controlled by (2)
ENS and vagus (PSNS)
what controls that only small particles can leave the pylorus
significant smooth muscle tone in the pylorus
gastric emptying is promoted by ______________ factors and inhibited by ________________ factors
gastric factors (secretion of gastrin due to stretch and composition of food); duodenal factors (that reflect newly arrived bolus such as low pH, high osmolarity)
once chyme enters the duodenum, it inhibits further emptying of the stomach by stimulating (3)
Afferent neurons in vagus -> decrease vagal tone/increase sympathetic tone
Afferent ENS cells
Secretion of cholecystokinin and somatostatin (from duodenal enteroendocrine cells)
what is the migrating motor complex? when does it occur
occurs between meals; pylorus relaxes and a strong wave of peristalsis sweeps the antrum, forcing less digestible food out en masse to the duodenum and colon
cyclical release of ______ from the ____ stimulates the migrating motor complex
cyclical release of motilin from the SI (stimulated by ACh)
during vomiting, intercostal and abdominal muscles __________ whereas stomach muscles _______
contract; relax
the pH of vomited food is _________ and comes from the ________ stomach whereas the pH of regurgitated food is _________ and comes from the _______ stomach
<5; distal; >7; proximal
The cardiac glands consist of
mucous cells
The fundic glands consist of
mucous cells, parietal cells, chief cells, enteroendocrine cells, mast cells
The pyloric glands consist of
mucous cells, a few G cells, a few parietal cells
surface mucous cells in all areas of the stomach secrete
neutral to alkaline mucous
parietal cells secrete (2)
HCl and intrinsic factor
chief cells secrete
zymogens
parietal cells contain receptors for (6)
ACh (+), histamine (+), gastrin (+), CCK (+), somatostatin (-), secretin (-)
what is the best method to inhibit gastric acid secretion by parietal cells
proton pump inhibitors; eventually H+ concentration rises high enough that CA catalyzes the reverse reaction
T/F we manipulate transport of Cl to the lumen as a way to inhibit gastric acid production
F; we only manipulate H+ secretion
Chief cells secrete _______________ zymogens, which are cleaved by ______________ into ______ enzymes that digest ___________
inactive (pro-enzyme); HCl; active; proteins
In monogastric animals the inactive zymogen is ____________ which becomes __________ once activated by HCl
pepsinogen; pepsin
In ruminants the inactive zymogen is ___________ which becomes __________ once activated by HCl
prochymosin; chymosin
chymosin is found in the __________ of ruminants
abomasum
what does chymosin do in ruminants
digests kappa-casein, which curdles the milk, slowing transit time and allowing better digestion in young ruminants
what is the role of mast cells in the stomach
secrete histamine, which acts via H2 receptors on parietal cells to stimulate HCl secretion
what is the stimulus/signal for g cells to release gastrin
peptides, amino acids and calcium in the stomach lumen
gastrin stimulates (2)
HCl secretion from parietal cells directly; histamine release from mast cells (which indirectly causes parietal cells to secrete HCl)
During the cephalic (anticipation) phase of HCl secretion, release of _______ from ________ stimulates _______ receptors on ________ and _________ cells, which overall acts to ________ HCl secretion
ACh; vagus; muscarinic; parietal; G-cells; increase
During the gastric phase of HCl secretion, ______________ and ____________ trigger ______ release of _____; food in the stomach raises pH, which further stimulates __________
chemoreceptors and stomach distension; ENS; ACh (stimulates parietal directly and gastrin secretion); further increases gastrin secretion
what inhibits HCl secretion
- low pH inhibits gastrin secretion (which reduces parietal HCl secretion)
- chyme in duodenum triggers release of somatostatin (inhibits parietal HCl secretion) and secretin (stimulates somatostatin and PGE2, also triggers bicarb release)
the endocrine pancreas is responsible for __________ and the exocrine pancreas is responsible for ___________
regulation of blood glucose; secretion of digestive enzymes
pancreatic enzymes function best in what environment
neutral to alkaline
what pancreatic cells secrete HCO3 and H2O
centroacinar and duct
what is an indigestible carbohydrate
cellulose
most enzymatic digestion occurs by
hydrolysis (for lipids, carbs and proteins)
lipase hydrolyzes____ into ____ and requires
neutral lipids into fatty acids and monoglycerides; co-lipase
cholesterol esterase hydrolyzes
cholesterol esters
phospholipase function
splits fatty acids from phospholipids
pancreatic zymogens include
trypsinogen -> trypsin, chymotrypsinogen -> chymotrypsin; proelastase -> elastase; procarboxypolypeptidases -> carboxypeptidase
what activates intestinal zymogens
mainly trypsin
why doesn’t the pancreas digest itself (1)
secretes inactive zymogens; trypsin inhibitors released alongside zymogens (gets diluted in intestinal lumen)
when does EPI usually occur
secondary to chronic pancreatitis
pancreatic cells have receptors for
ACh (enzymes and HCO3), gastrin (enzymes), CCK (enzymes), secretin (HCO3)
decreased pH in the duodenum stimulates the release of
secretin (secretes HCO3)
increased peptides and fat in the duodenum stimulates
CCK secretion (gallbladder contraction and release of pancreatic enzymes)
proteins and Ca in the pylorus stimulates
gastrin release, which acts on parietal cells/M cells AND stimulates the release of pancreatic enzymes
what provides negative feedback on pancreatic enzyme/HCO3 secretion
rise in duodenal luminal pH; chyme digestion/absorption
what does splanchnic circulation supply
stomach, small intestines, colon, pancreas, liver, spleen
T/F the splanchnic circulation has some degree of autoregulation
T
approx 75% of blood flow in GIT is to
mucosa
two main molecules that increase bloodflow to the GIT are
prostaglandins and ACh
two main molecules that decrease bloowflow to the GIT are
NE and PGF
nutrient absorption and increased metabolic _______ bloodflow to the GIT
increase
gastric ulcers can be caused by
chemicals, pathogens, decreased gastric bloodflow (ex. inhibition of prostaglandins by NSAIDs and glucocorticoids)
villi are very sensitive to ________ because of __________
hypoxia (end-organs); countercurrent O2 exchange
mild ischemia causes _____________, moderate ischemia causes _________ and severe ischemia causes __________
diarrhea; ulceration and bleeding; perforation and peritonitis
why does decreased bloodflow lead to ulcers
HCO3 production and mucus production relies on water, which comes from blood supply
the 2 roles of bile are
lipid digestion and waste elimination
bile salts, which are made from _______________, act like __________ to ___________lipid droplets
cholesterol; detergents; disperse
in hepatocytes, bile acids are _____________, which ______________
conjugated to amino acids; inhibits reabsorption from the biliary tract and duodenum
bile acids are ____________ transported into hepatic canaliculi
actively
purpose of the gallbladder
stores and concentrates bile
gallstones are commonly formed from
calcium carbonate; bilirubin salts
what is the stimulus for release of bile acids
fat in the duodenum triggers release of CCK from enteroendocrine cells
CCK ___________ the gallbladder sphincter and______________ gallbladder smooth muscle
relaxes; contracts
bile acids act like _______________, by _____________ surface tension at the fat globule surface
detergents; decreasing
after triglycerides are broken down into FFA and monoglycerides, what happens to them
combine with bile salt micelles and diffuse to the borders of intestinal epithelial cells
T/F bile salts can be recycled after transporting FFA/monoglycerides to the intestinal brush border
T; because they are not absorbed until they are in the ileum
what happens to a small percentage of bile salts and what is the consequence
deconjugated by anaerobic gut bacteria; excreted into feces
what is the consequence of bacteria from the colon colonizing the small intestine
deconjugation of a large quantity of bile salt -> wash into colon -> diarrhea
what happens to conjugated bile salts in the ileum
taken up by active Na/bile salt symporter; return to liver via portal vein
what 3 disorders would lead to increases in serum bile acids
- cholestasis
- decreased functional hepatic mass
- acquired or congenital vascular shunts
bile contains other molecules, such as
phospholipids, cholesterol, lipid-soluble waste, HCO3
how is jaundice an indicator of liver function
tells you that fat-soluble waste (i.e. bilirubin in this case) is not being properly eliminated
bile release is stimulated in response to what hormones/NTs (2)
CCK; ACh from vagus
what is digestion
breakdown of macromolecules into constituent monomers
what is absorption
transfer of nutrients from the intestinal lumen to the blood or lymphatics
T/F most polymers cannot cross the intestinal epithelium
T
movement of nutrients, ions and water occurs between what 4 compartments
intestinal lumen, cytosol, lateral space, blood/interstitial fluid
T/F water and ions can move through tight junctions between enterocytes
T (water can also move through aquaporins)
water is reabsorbed in normal states because
oncotic pressure is greater in capillaries than in the lateral space; it follows reabsorption of nutrients and ions
loss of intestinal villi causes diarrhea because
reduced area for absorption of nutrients and electrolytes; water stays in intestinal lumen (gets lost osmotically)
paracellular transport is (passive/active/both) whereas transcellular transport is (passive/active/both)
always passive; active or passive
K is absorbed via the ______________ route and occurs primarily in the _____________intestine
paracellular; distal (because there is a relatively higher concentration)
concentration and electrical gradients for Na are
inward
Three mechanisms by which sodium absorption occurs are
- symporters (drives glucose and amino acid absorption)
- antiporters (drives H excretion)
- simple diffusion (just absorbs Na; negligible)
nutrients are absorbed via _______________ route, and rely on __________ transport
transcellular; active
the 3 types of secretion in the digestive tract are
mucus (secreted through multicellular glands in mouth/pharynx/esophagus and unicellular glands in stomach/goblet cells)
specialized substances (such as digestive enzymes) secreted by tubular glands and macroscopic structures (liver, pancreas, salivary gland)
water and electrolytes (crypts of lieberkuhn in intestine)
how to crypt cells secrete water and electrolytes (3 steps)
1) passive influx of Na/Cl through Cl symporter
2) passive diffusion of Cl out of the cell through Cl channel
3) active pumping of Na out via Na/K pump
water follows the Cl osmotically
T/F bicarb is released by salivary glands and the pancreas
T
what are 3 ways that HCO3 is secreted
- Na/HCO3 symport (from blood to intestinal cell)
- HCO3 channels (limited; tightly regulated; result in H2O secretion and increased pH)
- HCO3/Cl antiporter (causes increased pH; important in herbivores)
T/F lignin cannot be digested
T
complex sugars include
lactose (glucose + galactose) ; sucrose (glucose + fructose); maltose, isomaltose, maltotriose (di and tri saccharides of glucose)
simple sugars include
glucose, galactose, fructose
simple sugars are absorbed by (2)
- Na co-transport (symporters; glucose and galactose)
- facilitated diffusion (uniporters; fructose)
glucose-Na symporter absorbs one glucose/galactose for every ____ sodium
2
T/F there is a very wide variety of membrane-bound peptidases that break down peptides into free amino acids and di/tri-peptides
T
once in the cytoplasm, what happens to absorbed di and tri-peptides
broken down into amino acids by cytosolic peptidases
amino acids are transported into the enterocyte by
at least 4 Na co-transporters
how are antibodies in colostrum absorbed
specialized enterocytes absorb by pinocytosis; reach SI intact because of low HCl and pancreatic enzyme secretion shortly after birth
a major form of dietary fats are
triglycerides
lipid soluble vitamins are
A, D, E, K
T/F the stomach and tongue produce some lipases that play a role in adult animals
F; play a role in suckling animals
lipids are absorbed by what mechanisms
fatty acid transporter protein; diffusion (when LCFA concentrations in the lumen are high); diffusion for most other lipids
once fats are absorbed into enterocytes, what happens
triglycerides reassembled and packaged into chylomicrons along with cholesterol
chylomicrons are coated with (3)
phospholipids, cholesterol and apolipoproteins
chylomicrons are absorbed into
lacteals -> lymphatics -> systemic circulation
electrolytes, minerals and metals are mainly absorbed in the
jejunum
T/F most ingested calcium is readily absorbed
F; most is excreted unabsorbed in feces
two mechanisms of calcium absorption are
- diffusion
- vitamin D dependent absorption (opens calcium channels in duodenum; increases expression of calbindin in the cytoplasm)
phosphorus is absorbed as
phosphate
under normal conditions, how is phosphorus absorbed
paracellular passive diffusion
how does vitamin D regulate phosphorus absorption
by insertion phosphorus, Na symporters in the apical membrane
how is iron absorbed
- receptors for protein-bound iron (bound to heme or lactoferrin)
- DMT-1 (iron and H+ symporter)
what molecule acts as the storage site for iron; how does it store iron
ferritin; as ferric iron (Fe3+)
what molecule acts as the transporter for iron in the blood
transferrin
uptake of iron into systemic cells differs from uptake of micelles in enterocytes because
the whole transferrin-iron complex is endocytosed; with micelles, the bile salts are not absorbed (only the fats)
when iron stores are high, the liver secretes
hepcidin (downregulates DMT-1 and transferrin)
what is measured to evaluate iron levels
plasma transferrin
how is copper and zinc absorbed
DMT-1 (along with iron)
how is Cu and Zn excreted
in bile and urine
how do you treat Zn sensitivtiy
copper supplementation
how is vitamin C absorbed
Na/vitamin symporter
how is vitamin B6 absorbed
passive diffusion
what needs to happen to vitamin B12 before it can be absorbed
needs to first be released from its protein carrier (by HCl and pepsin in the stomach/pancreatic enzymes in the SI)
how is vitamin B12 absorbed
binds to intrinsic factor in the ileum; complex then binds to receptors on enterocytes and are endocytosed
most electrolytes are absorbed best in the
ileum and colon
during coupled sodium/chloride transport, Na is exchanged for _______________ and chloride is exchanged for _____________
H+; HCO3- (Note: both are produced by water and CO2 via CA)
how is Cl absorbed in herbivores and why is it important
exchange of HCO3 for Cl-; raises the luminal pH which is important to keep a neutral environment when volatile fatty acids are being created by fermentation
bicarbonate is mainly reabsorbed in the form of
H2O + CO2; driven via Na/H antiporter
in horses, what is the junction between the SI and LI; is it normally open or closed
ileocecal sphincter; closed (only open during a peristaltic reflex)
what are the 3 functions of the cecum and colon
- absorb water and electrolytes
- store feces
- ferment and absorb undigested organic material
the 3 motility patterns in the cecum and colon are
segmentation, propulsion (peristalsis), retropulsion (retroperistalsis)
what 2 reflexes promote colonic emptying
gastrocolic and duodenocolic
colon secretions consist of
mucus and HCO3
how is mucus/HCO3 secreted in the colon
HCO3 channels; HCO3/Cl antiporter
T/F VFAs are passively reabsorbed
T
what vitamins are synthesized by colonic bacteria
B, K
how are electrolytes and water absorbed in the colon
via active absorption
diarrhea is
increased water content of feces
T/F the colon has a large capacity for water absorption, which is increased by aldosterone
T
the internal colonic sphincter is ___________ under _______________ contrtol
smooth muscle; ENS/PSNS (pelvic n)
the external colonic sphincter is _____________ under ________________control
skeletal; CNS/pudendal n.
the defacation reflex is called the
rectosphincteric reflex
what stimulates colonic peristalsis
relaxation of the internal sphincter via PSNS (pelvic n)
the three main plant (digestible) wall components are
cellulose, hemicellulose, pectin
major substrates for fermentation are
cell wall components of forages and starches in grains
how are carbohydrates fermented in ruminants
cellulase (on bacterial surface) breaks down cellulose/hemicellulose/pectin into monosaccharides, which are then absorbed by the bacteria
what are the waste products of bacterial carbohydrate fermentation and what is their purpose
VFAs; used by ruminant as a source of energy
in bacteria, monosaccharides are broken into
pyruvate, ATP, CO2 and NADH + H+
pyruvate in an aerobic environment yields
energy sources (ex. NADH, FADH, ATP and VFAs
most bacteria yield what VFA
acetate (and methane)
lactate is broken down into what
acetate and proprionate
the main VFAs absorbed by ruminants are
butyrate, acetate, proprionate
VFA provide what % energy to herbivores
60-80%
does a high grain or high fiber diet yield more VFA
high grain (but VFA in excess will damage the rumen)
VFAs are (carbs/lipids/proteins)
lipids
VFA absorption occurs in what parts of the ruminant stomach
rumen, reticulum and omasum
as pH drops, rumen papillae _________
grow longer (increase SA for VFA absorption)
how are VFAs absorbed at a normal rumen pH? what is the net effect
bind to H+ (present due to Na/H exchange); HVFA are not ionized and are therefore easily absorbed; acts to increase rumen pH
what is the fate of acetate, proprionate and butyrate as an energy source
acetate: directly used for energy or to produce lipids
proprionate: converted to glucose in liver and then used for energy
butyrate: converted to β-hydroxybutryic acid in rumen epithelial cells and then used as an energy source
β-hydroxybutyric acid is a
ketone
why can farmers feed ruminants low quality protein
bacteria convert any quality protein into high quality protein; when bacteria are digested by the ruminant, it provides high quality protein
T/F in ruminants, most amino acids are converted into acetate, proprionate and butyrate
T
branched-chain amino acids are converted into _______________, which can then be used as _________ for the ruminant or ___________ for the rumen microbes
branched chain VFAs, which can be used as an energy source for the ruminant or a growth factor for the rumen microbes
protein is ultimately converted to
NH3 (ammonia)
lipids are digested by microbes into
LCFAs
T/F ruminants obtain their nutrients by consuming bacteria and their wastes (ex. VFAs)
T
ruminants can consume bacteria when they
are flushed into the abomasum (after proliferating)
what can influence the amount of VFAs produced by a ruminant
relative abundance of protein and carbohydrate
T/F ruminants must synthesize almost all of the glucose that they require
T
too much grain (rapidly fermentable CHO) can have what consequence; this is called
acidify the rumen and alter rumen flora (increased proliferation of lactic-acid producing bacteria, which further decreases pH); grain overload
rumen bacteria can synthesize protein from what non-protein nitrogen sources
urea, nitrates, ammonia; combined with ketoacids to form amino acids
what is a sign that fermentation is complete
small dense particles sink from a loss of gas bubbles
particles move into the omasum when they are what diameter
2-3mm
the solid zone contains _______________, the slurry zone contains ______________and the liquid zone contains ___________
most recent ingesta (least fermented; moderately fermented ingesta; mostly thoroughly fermented ingesta and water
secondary contractions of the rumen cause
eructation; removes gas produced by fermentation by bringing it to the region of the esophagus
gases at the cardia stimulate
gas sensors, that trigger the vagal reflex (by bringing afferent info to the brainstem)
what can inhibit eructation and cause bloat
froth from young, green forage
what stimulates rumination (chewing cud)
coarse feed, stretch, and VFA in rumen
T/F eructation involves contraction of the reticulum
F; regurgitation of cud involves reticulum contraction
reticulorumen motility is controlled entirely by
vagus
how does stretch stimulate rumen motility
moderate stimulates; excessive inhibits
a large rumen mat _____________ rumen motility
excessively low pH _____________rumen motility
elevated VFA ____________ rumen motility
elevated osmolarity ____________ rumen motility
gases at cardia stimulate __________________
stimulates
inhibits
inhibits
inhibits
eructation
what happens if cows are fed poor quality feed, especially in cold climates
stimulates food intake and movement of ingesta out of the rumen prematurely; gets impaction of abomasum
cold climates ______________
stimulate rumen motility
water half-life in the rumen is
15-20h
T/F little water moves across the reticulorumen epithelium
T
when do ruminant rumens become colonized by microbes
3-8th week if given access to solid feed
in adult cattle, reticular groove closure can occur in response to
ADH; water bypasses rumen and is absorbed faster in the SI
The abomasum does not ______________, but does secrete ____________, to digest _________
absorb nutrients; lysozyme; bacterial cell walls
horses have three adaptations to frequent grazing, which are
- production of large quantities of saliva
- loss of mucus production in proximal gastric fundus
- continual secretion of gastric acid
chewing in horses is important since; as a result, they are given a
they cannot regurgitate their feed; high-fiber diet
time horses spend chewing creates ___________, which buffer against _____________
saliva; gastric acid
2 issues with teeth problems in horses are
inappetence and decreased volume of saliva (which can lead to gastric ulceration)
in horses the proximal fundus is what kind of epithelium
stratified squamous
what are some problems with intermittent feeding of horses
- do not produce enough saliva to buffer rumen pH -> ulcers
- VFA production becomes cyclic in cecum/colon -> pH variation
- feed may be inadequately digested -> colic/diarrhea
the equine small intestine is adapted to a low _______, high _______ diet
starch; cellulose
in the small intestine of horses, digestion and absorption is _________
incomplete
what is a major difference in digestion in equids vs ruminants
in horses, microflora do not enter the intestine, so bacterial CHO, protein and lipid are lost in feces
what is a consequence of short transit time in horses
loss of protein, carbs and fat in feces
pacemakers of cecum/colon transit time in horses are
cecum, RVC, pelvic flexure
describe the enterosystemic fluid cycle in horses
fluid secretion into the intestines equals total extracellular fluid volume; almost all of this is reabsorbed via osmosis as nutrients are absorbed
T/F glucose is essentially the only energy source used by the CNS
T
mobilization of stored CHO begins how many hours after the last meal
4-6h
glucose ________ diffuses into cells via _______
passively; GLUT
glut transporters in liver and brain are; in other tissues they are
always active; responsive to insulin
inside a cell, how is glucose processed
glycolysis (to provide energy); glycogenesis; hexose monophosphate; glucuronate
in monogastric animals, ____________ fuels the electron transport chain; in ruminants ________________ fuels the electron transport chain
NADH; VFAs
how to VFAs fuel krebs in ruminants (2)
acetate/butyrate become acetyl-CoA
proprionate enters at a diff point
what is a major substrate for gluconeogenesis in ruminants and where is it diverted from
oxaloacetate; Krebs cycle
in the liver, phosphorylation of glucose is _________ by insulin and ____________ by lack of insulin
increased; decreased
the hexose monophosphate pathway is involved in production of __________________, reduction of ____________, and synthesis of _____________
fatty acids and steroids; glutathione; nucleic acids
the glucuronate pathway is involved in synthesis of ________________, _________________ and is required for some forms of _____________ metabolism
proteoglycans, vitamin C, hepatic
When pyruvate accumulates during exercise, it is converted into lactate and travels to the liver. In the liver, it is used to resynthesize glucose. This process is called
the Cori cycle
1) HDLs add __________ apoproteins to the chylomicron, making it a ______
2) ApoC activates what on the capillary endothelium
3) lipoprotein lipase does what
4) the chylomicron then loses _____, which signals for it to be absorbed by the __________ and recycled into _________; it may also be taken up by other cells that require ____________
apoC and apoE; VLDL
lipoprotein lipase
hydrolyzes TGs into LCFAs and monoglycerides
Apo C; liver; new VLDLs; new cholesterol
in adipose, LCFAs are ________; in other tissues they are _________
resynthesized into TGs; oxidized for energy
in order to be destroyed, chylomicron remnants must have
ApoE
HDLs are synthesized in (2)
liver and small intestine
The 2 functions of HDLs are to
retrieve ApoC and transfer ApoC/ApoE to new chylomicrons; transport cholesterol to the liver
the liver can do what to HDLs
endocytose them and incorporate their components to form new VLDLs
LCFAs created via the endogenous pathway are transferred through the blood on ___________________; triglycerides synthesized by the liver are transported through the blood stream by _____________
albumin; VLDLs
if the cell has sufficient energy, non-ruminants can divert what from the Krebs cycle for synthesis of LCFAs; this occurs in the ________
citrate; liver
in ruminants, what can be used to create LCFAs; this occurs in the ______________ and _______________
acetate; adipose and mammary tissue
in regards to mobilization of stored TG, insulin _______ and glucagon _________; thyroid hormone _____________ utilization of circulating lipids
inhibits; promotes; promotes
inherited defects in lipoprotein lipase can cause
hyperlipidemia
what are ketones
normal, water-soluble metabolites of lipids
ketones can be used in what context
in place of glucose to provide acetyl-CoA for Krebs
T/F acetone contributes to keto-acidosis
F; it is a weak acid, and is relatively volatile, so it is exhaled
T/F acetoacetate and B-hydroxybutyric acid are ketones that act as strong acids at normal blood pH
T
under normal conditions, ketones are used for _______ in ________ tissues
ATP production (converted back into acetyl-CoA); non-hepatic
T/F the liver is able to utilize ketones for energy
F
what is the main ketone in ruminants that contributes to ketacidosis
β-hydroxybutyric acid
For what 2 reasons are ruminants prone to keto-acidosis
- they have 2 sources (LCFAs from adipose and VFAs from fermentation)
- they must synthesize all of their glucose by diverting oxaloacetate, which causes more ketone formation when fat is mobilized
what are the main causes of keto-acidosis
Anything that mobilizes large amounts of fat
- starvation or anorexia
- lactation or late pregnancy
- insulin deficiency
T/F the most over-conditioned animals are least likely to develop keto-acidosis
F; they are the most likely
why does fat mobilization predispose animals to fatty liver? how does this coincide with gluconeogenesis in a state of anorexia
if TG formation exceed the hepatocytes ability to form VLDLs, lipid droplets form -> can destroy hepatocytes; in a state of anorexia, you also get diversion of oxaloacetate, which means the mitochondria take up less LCFA, and more is converted to TG in the cytoplasm
why are cows prone to fatty liver?
less efficient at exporting VLDLs AND they divert more oxaloacetate under normal conditions
give 3 reasons why pregnant or lactating ruminants are especially prone to fatty liver and ketosis
- less efficient at transporting VLDLs (buildup of TG more likely)
- divert more oxaloacetate (more formation of ketones; less use of LCFAs that can be converted to TGs)
- more prone to insulin resistance (more mobilization of LCFAs)
why might ketones appear in the urine
during ketosis, the absorption capacity of renal tubular epithelium is saturated
