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149 Cards in this Set

  • Front
  • Back
***what is the "really basic" function of the liver?
to regulate the concentration of substances in hepatic venules and in bile
what are the 5 major physiologic functions of the liver
1. THE major organ of metabolism
2. detox/excretion
3. storage of nutrients (glycogen/fat)
4. immune reaction/phagocytosis
5. synthesis of structural proteins
what two domesticated mammals don't have a gall bladder?
horse and rat
histologically, what is the major landmark to identify liver tissue?
the portal triad
what is the arrangement of cells in a liver lobule?
cords of hepatocytes separated by sinusoids
where does processed blood flow out of the liver lobule?
central venule
what is the functional unit of a liver lobule?
acinus
which zones of the liver lobule have the highest metabolism? Which have the lowest?
the periportal cells have the highest; the cells surrounding the central vein have the lowest.
what structures comprise the portal triad of the liver?
- portal vein
- bile duct
- hepatic artery
what chemical is commonly used to measure hepatic blood flow?
indocyanin
what can result from hepatic venule outflow obstruction?
- ascites
- hepatomegaly
- elevated transaminases
- jaundice
what can result from impaired intrahepatic blood flow?
- ascites
- espohageal problems
- hepatomegaly
- elevated transaminases
what can result from impaired blood inflow to the liver?
- esophageal problems
- spelnomegaly
- intestinal congestion
scarring of the liver
cirrhosis
true of false, the liver is a minor contributor to lymph?
false. It is the major lymph-producing organ, generating approximately 50% of lymph.
what things can happen if hepatic central venous pressure rises?
- increased fluid leakage into the lymph
- fluid leakage from the liver surface
- in extreme cases, portal back pressure and gut edema
the accumulation of protein enriched fluid in the peritoneal cavity as the result of fluid loss from the liver
ascites
***To what degree do liver cells differ from each other?
- all cells have specialized functions and differ morphologically, even those of similar cell types
- function is compartmentalized
how are liver cells functionally polarized?
- one pole is in contact with hepatic sinusoids and engages in nutrient exchange, oxygen exchange, secretion, etc.
- the other pole is in direct contact with the ECM and adhere to collagen
what are the two types of liver acini and what are their features?
- structural acinus: portal triads at each of 6 (variable) corners, cords of hepatocites, sinusoids, central venule, and protal triads; reflects the vascular drainage of the liver

- functional acinus: portal triad in the center. Functionality is centralized around (1) the most oxygenated blood and (2) the portal vein.
what are the three components of the liver functional acinus, and what do they do?
1. central zone (periportal) - the most metabolically active cells because of oxygenation

2. midzonal region - hepatocytes between the portal triads and central venules; less metabolically active than the periportals and has different physiologic activity

3. centriolbular zone - hepatocytes arranged around the "central" venule, which is at the periphery of the FUNCTIONAL acinus; lowest metabolic activity because it is most distant from the oxygen source of the hepatic artery
what is the "streaming liver theory?"
hepatocytes originate near portal triands and move toward central venue, where they are apoptosed. This takes about 150 days in a human.
what 3 things dictate the activity of a liver cell?
1. position in the acinus
2. oxygen and nutrient supply (periportal cells use them up first)
3. differential gene expression
which cells in the liver are most affected if oxygen or nutrient supply are diminished?
the centrilobular zone (cells closest to the central venule) because the periportal cells use up the nurtients and oxygen first
what are the predominant energy processes used by the liver just after eating and during fasting (e.g. before a meal)
- after eating, more carbs --> glycolysis
- fasting, gluconeogenesis and glycogenolysis
how do periportal hepatocytes differ in their carbohydrate metabolism versus centilobular hepatocytes?
COMPARTMENTALIZED
- periportal: glycogenolysis and gluconeogenesis
- centrilobular: glycolysis and glycogen synthesis
what three major things does the hepatocyte do with glucose once it is inside the cell?
1. hepatocyte metabolism
2. glycogenesis
3. lipogenesis
What five major ways does the liver use fatty acids?
1. oxidation for metabolic energy
2. converted to trigs by esterification
3. synthesized into phospholipids
4. synthesized into cholesterol
5. synthesized into VLDLs
how do periportal hepatocytes differ in their lipid metabolism versus centilobular hepatocytes?
- periportal: cholesterol synthesis
- centrilobular: lipogenesis
what is the major organ for protein synthesis and what is the major protein?
- liver
- albumin
what is the primary function of the liver with regards to protein metabolism?
to maintain a constant level of free amino acids in the bloodstream
how do amino acids move from the plasma to the hepatocytes?
active transport
what happens to excess amino acids in the liver?
- deaminated and converted to fats or carbs
where, specifically in the liver lobule is ammonia converted to urea?
the proximal half to 2/3rd of the acinus
what causes hepatic encephalopathy?
inadequate ammonia detoxification by the liver
true or false, the liver synthesizes immunogloubulins?
false. The liver does make a protein for IgA, however.
name five major proteins made in the liver
1. albumin
2. glycoproteins
3. clotting factors
4. fibrinogen
5. secretory component of IgA
what is the physiological purpose of putting a sugar residue onto a protein to make a glycoprotein?
the sugar residue determines which cell will use it.
synthesis of which of the six clotting factors are dependent on Vitamin K?
all of them
what major problem can happen in the deficiency of vitamin K?
the inability of the liver to synthesize clotting factors and thus the animal can bleed to death.
why is vitamin K important in the synthesis of clotting factors?
it is required for the synthesis of a special amino acid residue.

(glutamic acid is converted to gamma-carboxyglutamic acid)
what chemical causes the polymerization of fibrinogen to fibrin?
thrombin
what is the molecule "tagged onto" proteins for non-lysosomal degradation?
ubiquitin
what hormones stimulate protein degradation by the liver?
glucagon, catecholamines, glucocorticoids
what is the basic process of detoxification by the liver?
The toxic substance goes through a Phase I reaction, then a Phase II reaction, which makes them water-soluble, and excreted in the bile
what is induction and what change in intracellular structure accompanies it?
resistance to drugs by increased ability to detoxify in the liver. SER hypertrophy is seen in induction.
what is the liver's role in immunity?
- Kupffer cells are very good at phagocytosing bacteria
- The liver produces the secretory component of IgA
what are the two major functions of bile?
1. facilitation of fat digestion and absorption
2. elimination of waste products from the circulation
what makes poop brown-green?
bile
why is conjugation of bile necessary?
conjugation allows bile to be water soluble and fat soluble to emulsify fat (in micelles) in the small intestine and facilitate absorption
what are the six basic components of bile?
1. water
2. bile salts
3. bilirubin
4. cholesterol
5. lecithin
6. electrolytes
what is the precursor molecule for bile salts?
cholesterol
to what two locations does the liver transport bile?
1. small intestine
2. gall bladder
true or false, the gallbladder is muscular and can secrete amounts of bile based on what is needed?
true
true or false, the gallbladder actively dilutes bile to make more of it?
false. The gallbladder concentrates bile to make it more potent
what are the three major factors controlling gallbladder contraction?
1. cholecystokinin (CCK)
2. vagal and ENS innervation
3. amount of dietary fat
true or false, most bile is reabsorbed in the small intestine by passive and active transport?
true.

Duodenum and jejumum: passive
Ileum: active
what is the major component of gallstones?
cholesterol
true or false, bile activity can be either enzymatic or non-enzymatic, depending on function?
false. It is non-enzymatic.
Name NINE functions of the alimentary tract (yes, nine)
1. ingestion
2. digestion
3. absorption
4. elimination
5. detox
6. bacterial housing/management
7. immune function
8. secretion
9. endocrine function
what is the most essential function of bacterial housing and management in the lower GI tract?
to keep bacteria out of the blood and small intestine
what is secreted by the alimentary tract?
- hormones
- HCl
- bicarb
- enzymes
- electrolytes
- "water"
what is the difference between digestion and absorption
digestion is the mechanical or chemical breakdown of food into smaller components. Absorption is taking those components and putting them into the system.
true or false, digestion and absorption, by and large, are controlled by the same set of stimuli?
false. they are controlled by completely different and distinct processes.
what are the three phases of digestion?
1. Luminal phase - food is broken down in the lumen
2. Mucosal phase - food is broken down enzymatically in the small intestine on the surface of the enterocyte brush borders
3. Intracellular digestion - within the enterocytes of the small intestine
what is the one phase of absorption?
1. Transport phase - passage into the vascular system
what are the three regulators of the GI tract
1. neuroendocrine - the intrinsic ENS of the GI tract
2. CNS - parasympathetic (vagus & pelvic nn.) and sympathetic (splanchnic & hypogastric nn.)
3. GI reflexes
in what direction do GI reflexes generally move?
oral to aboral
true or false, the CNS, under extreme circumstances can completely override the ENS and GI reflexes?
false
what is the name of and distribution of GI endocrine tissue?
- APUD or enteroendocrine cells
- dispersed diffusely through the stomach, SI, and pancreas.
- most abdundant orally; decreases aborally
what class of hormones are the GI endocrine horomones?
peptide/protein
where are GI endocrine hormones secreted?
into the basolateral membrane, where they can diffuse and have autocrine, panacrine, or exocrine effects
what electrolytes are secreted by the stomach?
only H+ and Cl- to any significant extent
what are the four major ions absorbed and/or secreted by the intestines?
Na, K, Cl, HCO3
what are the three general goals of electrolyte transport in the gut?
1. provide the appropriate substrates for various processes (e.g. make gastric acid in the stomach; provide bicarb in the duodenum to neutralize the acid)
2. maintain the correct pH
3. maintain the correct "magic" osmolality of 300 OsM
what three major features of the gut facilitate the movement of ions and water?
1. electrochemical gradients
2. high capillary permeability with low flow resistance
3. continuous flow through capillaries
what are the four passive transport mechanisms used by the gut?
1. paracellular (through the "leaky" tight junctions)
2. ion channels
3. facilitated diffusion
4. solvent drag
what are the major substances transported by the gut with secondary active transport?
- sodium
- chloride
- potassium
- bicarbonate
- glucose (and other sugars)
- amino acids
what is tertiary active transport?
active transport that relies most directly on the gradient established by a secondary active transport.

Example:
- Primary Na-K-ATPase decreases sodium in the cell-->
- Secondary: Because of decreased sodium in the cell, Na from the lumen raises the level of bicarb in the cell by an Na-H symporter -->
- Tertiary: because of the high levels of intracellular bicarb, a Cl-bicarb antiporter transports chloride into the cell and bicarb out.
how does regional absorption of water vary by species type?
- Carnivores: greatest volume in the small intestine
- Horses: greatest volume in the large intestine
- Ruminants and Pigs: intermediate
what is the primary reason that water flows in any particular direction in the gut?
to keep the gut isoosmotic
in carvnivores, why is water "secreted" into the gut in "early" intestine, but absorbed in the "late" intestine?
the intestine wants to be isoosmotic:
- early in the intestine, there are more particles to dilute and thus more water is needed to keep it 300 mOsm
- late in the intestine, most of the particles have been absorbed, so water must be reabsorbed to keep the lumen 300 mOsm
where, specifically, does most electrolyte absorption occur in the GI tract?
the enteric luminal surface; brush borders increase the surface area
what is the most important electrolyte involved in GI absorption?
sodium
in what three ways is chloride absorbed in the GI tract?
- paracellular
- ion channels
- secondary and tertiary active
how is bicarbonate directly absorbed in the GI tract?
- an ion exchange mechanism
in what two ways is postassium absorbed in the gut?
- mainly passive paracellular diffusion
- H-K ATPase in the colon recovers the "last bit" when needed
what is the main function of the crypt cells in the intestinal tract?
to SECRETE electrolytes and "water"
what microanatomical structures of the intestines secrete electrolyte and by what physiological process does this occur?
- the intestinal crypt cells
- a Na and Cl pumping mechanism on the basolateral membrane directed into the cells. Water follows.
Why is intestinal secretion important?
to maintain the 300 mOsm value in the presence of large amounts of osmotically active particles.
what are the two functions of mastication?
1. divide food particles
2. mixes the food with saliva
what are the main components of saliva and species differences
ALL:
1. water
2. salts
3. mucin: a slippery protein

PIGS, apes, guinea pig, rodents: salivary amylase
what are the five major functions of saliva in non-ruminants?
- moisten and lubricate food for sawllowing
- dissolve molecules for taste buds
- cleanses mouth and teeth
- antibiotic activity
- (varies) digests starch with amylase
what controls secretion and what three things stimulate this process
Secretion is controlled neurally:
1. parasympathetic input
2. object in mouth as a reflexive secretion
3. anticipation of food
what are the voluntary parts of deglutition?
from tongue, pushing bolus to pharynx
what initiates swallowing?
involuntary pharyngeal receptors triggering swallowing centers
what is the condition of esophageal sphincters when swallowing is not occuring?
- held tonically closed
- they must relax to swallow
what are the two main functions of the upper esophageal sphincter?
1. prevents reflux to pharynx during swallowing
2. prevents air entry into the esophagus during breathing
what is the function of the lower esophageal sphincter?
prevents gastric reflux to the espohagus
what is the difference between primary and secondary peristalsis?
- primary is elicited by swallowing
- secondary is when food is stuck in the esophgaus and stretch recep
what are the two major causes of megaesophagus?
1. failure of the lower esophageal sphincter to relax
2. a persistent right aorta
comment on the absorption in the simple stomach.
- limited
- small amounts of water, some drugs (e.g. NSAIDs), ethanol :-)
what are the two basic types of mucus in the simple stomach and what is their function
1. thick - protective
2. thinner - lubrication
what is the "milk curdling" enzyme of the stomach that is especially important in young animals?
chymosin (rennin)
what are pepsins, where are they secreted, and how are they activated?
gasteric enzymes of the stomach, secreted as zymogens, are converted to their active form by gastric HCl
an enzyme precursor secreted in the stomach that is activated by gastric acid
zymogen
***what is the action of gastric lipase?
cleaves the lipid off of a lipoprotein. It does not digest the lipid!
***where is gastrin produced, released, and what is its action?
- produced by the APUD cells in the stomach
- released into the blood
- acts in increase acid and pepsin secretion in the stomach
- stimulates gastric motility
- small trophic effect on gastric mucosa
what stimulates the secretion of gastrin?
- luminal factors: protein digestion
- mural (muscular wall) factors: vagal discharge caused by gastric stretch and contraction
- a POSTIVE FEEDBACK mechanism
what inhibits the secretion of gastrin?
- luminal factors: increased gastric acid
- mural factors: loss of stomach wall stretch
- hormonal factors released by small intestine: secretin, GIP (gastric inhibitory peptide)
where in the stomach is histamine produced, what stimulates it, and what effect does it have?
- produced by gastric mast cells in response to gastrin or acetocholine
- has a panacrine effect to stimulate more gastrin release
what domestic mammals (besides humans) produce intrinsic factor, and what is its function?
- produced by pigs and rodents
- allows B12 absorption in the ileum
true or false: H and Cl are secreted separately in the stomach and require active transport
true
What is the basic process of HCl secretion into the gastric lumen?
1. carbonic anhydrase makes H+ and bicarb in the stomach from water and CO2
2. H-K ATPase actively transports H+ into the stomach and K+ out
3. The remaining bicarb is exchanged for a chloride in the blood by an antiporter
4. chloride is moved through a chloride channel in the apical membrane
what are the three main chemical regulators of gastric acid secretion?
1. Acetylcholine: vagal discharge induced by stretch and contraction receptors in the stomach wall up-regulates gastrin.
2. gastrin up-regulates acid
3. histamine up-regulates gastrin
true or false, maximal gastric acid release is accomplished when acetylcholine vagal receptors, gastrin receptors, and histamine receptors are simultaneously stimulated.
true
what is the most important mechanism that prevents the overproduction of gastric acid?
the negative feedback mechanism controlled by low pH of the gastric lumen.
- pH 2, acid slows down
- pH 1, acid stops
***which macronutrients (carbs, proteins, lipids) are significantly digested in the stomach?
all of them
what nutrients are almost completely digested chemically in the stomach
only protein
what are three major features that protect the stomach from digesting itself under acidic conditions?
1. very tight junctions
2. very high electrical resistance of the apical membranes that push away H+
3. thick mucous
why is protein digestion in the stomach critical?
because the pancreatic enzymes cannot digest large proteins
what are the four main functions of gastric motility?
1. filling/storage (stretch relaxation)
2. mechanical digestion (peristalsis and reverse peristalsis)
3. initiation of chemical digestion by mixing digesta with acid and pepsins
4. controlled emptying
what are the major functions of the gastric fundus?
- stretch relaxation to store volumes of food without increase in pressure
- mild peristalsis to slowly deliver food to body and antrum
- no mechanical mixing so species with salivary amylase can do their thing
where is the gastric pacemaker?
near the fundus
what is characteristic of the peristalsis in the body of the stomach?
strong for vigorous mixing
what is characteristic of the peristalsis in the pyloric antrum of the stomach?
really, really strong, grinding contractions to make small bits.
besides mechanical and chemical digestion, what is the other major function of the pyloric antrum?
- delivers small bits to the pylorus
- delivers bigger bits to the body of the stomach for further digestion
what is the size of the particle that gets through the pylorus during normal digestion?
< 2 mm
how does sympathetic stimulus affect the stomach during digestion?
slows gastric emptying
what comprises the enterogastric reflex?
- duodenal osmoreceptors
- hypertonic contents slow emptying
- isotonic contents maximize emptying
how does pH in the duodenum affect gastric emptying?
- anything below pH 3.5 stops; anything lower would be too acidic for the duodenum to neutralize.
how do small intestinal hormones affect gastric emptying?
slows it down
what are interdigestive contractions?
in between meals, moves larger objects (like tennis balls) into the duodenum
***what are the three phases of gastric secretion?
1. cephalic
2. gastric
3. intestinal
how does the cephalic phase of gastric secretion affect gastric activity and by what means?
- promotes gastric activity
- CNS-mediated (sight, smell, thought)
- increases motility and secretion
how does the gastric phase of gastric secretion affect gastric activity and what happens during this phase?
- promotes gastric activity
- local reflexes and responses to gastrin
- results from presence of food in the stomach
how does the intestinal phase of gastric secretion affect gastric activity and what happens during this phase?
- inhibits gastric activity (don't want to overload the duodenum)
- reflex negative feedback - enterogastric reflex
- hormonal feedback - GIP and CCK lower HCl, pepsinogen, motility
what is the regulator of conscious (skeletal muscle) GI motility?
spinal nerve innervation
what are the regulators of unconscious (smooth muscle) GI motility?
extrinsic factors: parasympathetic and sympathetic innervation; myenteric plexuses

intrinsic factors: hormones produced by the GI tract itself - most influence secretion, but some influence motility
what are the two critical components of intrinsic gut motility?
cooperation between:
1. inherent electrical activity of the smooth muscle cells
2. the gut's ENS
what acts as the pacemaker for gut slow wave contractions?
duodenum
true or false, the CNS cannot control GI slow waves, but ENS stimulation can increase, decrease, or stop them
false. The slow waves are completely independent of all nervous input
true or false: slow waves require neural input to make the gut wall contract.
true. slow waves are moving constantly, but they cannot cause a contraction by themselves
***what affects the contractility of intestinal smooth muscle?
- hormomes from APUD cells
and/or
- neuroregulatory substances from the ENS

they change the resting potential of the slow waves
how does parasympathetic stimulus affect GI motility?
- promotes GI secretion and motility
- relaxes GI sphincters and blood vessels
how does sympathetic stimulus affect GI motility?
- inhibits GI motility and secretion
- contracts sphincters and blood vessels
what are the two major functions of reverse peristalsis?
- get digesta into the cecum
- temporarily retain digesta in a particular region
non-progressive contractions of alternating segments of circular muscle layer in the intestines
mixing-segmentation

"gooshes" contents back and forth
holding digesta without allowing any movement
retention