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149 Cards in this Set
- Front
- Back
***what is the "really basic" function of the liver?
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to regulate the concentration of substances in hepatic venules and in bile
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what are the 5 major physiologic functions of the liver
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1. THE major organ of metabolism
2. detox/excretion 3. storage of nutrients (glycogen/fat) 4. immune reaction/phagocytosis 5. synthesis of structural proteins |
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what two domesticated mammals don't have a gall bladder?
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horse and rat
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histologically, what is the major landmark to identify liver tissue?
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the portal triad
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what is the arrangement of cells in a liver lobule?
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cords of hepatocytes separated by sinusoids
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where does processed blood flow out of the liver lobule?
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central venule
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what is the functional unit of a liver lobule?
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acinus
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which zones of the liver lobule have the highest metabolism? Which have the lowest?
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the periportal cells have the highest; the cells surrounding the central vein have the lowest.
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what structures comprise the portal triad of the liver?
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- portal vein
- bile duct - hepatic artery |
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what chemical is commonly used to measure hepatic blood flow?
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indocyanin
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what can result from hepatic venule outflow obstruction?
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- ascites
- hepatomegaly - elevated transaminases - jaundice |
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what can result from impaired intrahepatic blood flow?
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- ascites
- espohageal problems - hepatomegaly - elevated transaminases |
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what can result from impaired blood inflow to the liver?
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- esophageal problems
- spelnomegaly - intestinal congestion |
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scarring of the liver
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cirrhosis
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true of false, the liver is a minor contributor to lymph?
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false. It is the major lymph-producing organ, generating approximately 50% of lymph.
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what things can happen if hepatic central venous pressure rises?
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- increased fluid leakage into the lymph
- fluid leakage from the liver surface - in extreme cases, portal back pressure and gut edema |
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the accumulation of protein enriched fluid in the peritoneal cavity as the result of fluid loss from the liver
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ascites
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***To what degree do liver cells differ from each other?
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- all cells have specialized functions and differ morphologically, even those of similar cell types
- function is compartmentalized |
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how are liver cells functionally polarized?
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- 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 |
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what are the two types of liver acini and what are their features?
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- 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. |
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what are the three components of the liver functional acinus, and what do they do?
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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 |
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what is the "streaming liver theory?"
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hepatocytes originate near portal triands and move toward central venue, where they are apoptosed. This takes about 150 days in a human.
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what 3 things dictate the activity of a liver cell?
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1. position in the acinus
2. oxygen and nutrient supply (periportal cells use them up first) 3. differential gene expression |
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which cells in the liver are most affected if oxygen or nutrient supply are diminished?
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the centrilobular zone (cells closest to the central venule) because the periportal cells use up the nurtients and oxygen first
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what are the predominant energy processes used by the liver just after eating and during fasting (e.g. before a meal)
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- after eating, more carbs --> glycolysis
- fasting, gluconeogenesis and glycogenolysis |
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how do periportal hepatocytes differ in their carbohydrate metabolism versus centilobular hepatocytes?
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COMPARTMENTALIZED
- periportal: glycogenolysis and gluconeogenesis - centrilobular: glycolysis and glycogen synthesis |
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what three major things does the hepatocyte do with glucose once it is inside the cell?
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1. hepatocyte metabolism
2. glycogenesis 3. lipogenesis |
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What five major ways does the liver use fatty acids?
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1. oxidation for metabolic energy
2. converted to trigs by esterification 3. synthesized into phospholipids 4. synthesized into cholesterol 5. synthesized into VLDLs |
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how do periportal hepatocytes differ in their lipid metabolism versus centilobular hepatocytes?
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- periportal: cholesterol synthesis
- centrilobular: lipogenesis |
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what is the major organ for protein synthesis and what is the major protein?
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- liver
- albumin |
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what is the primary function of the liver with regards to protein metabolism?
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to maintain a constant level of free amino acids in the bloodstream
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how do amino acids move from the plasma to the hepatocytes?
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active transport
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what happens to excess amino acids in the liver?
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- deaminated and converted to fats or carbs
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where, specifically in the liver lobule is ammonia converted to urea?
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the proximal half to 2/3rd of the acinus
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what causes hepatic encephalopathy?
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inadequate ammonia detoxification by the liver
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true or false, the liver synthesizes immunogloubulins?
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false. The liver does make a protein for IgA, however.
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name five major proteins made in the liver
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1. albumin
2. glycoproteins 3. clotting factors 4. fibrinogen 5. secretory component of IgA |
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what is the physiological purpose of putting a sugar residue onto a protein to make a glycoprotein?
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the sugar residue determines which cell will use it.
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synthesis of which of the six clotting factors are dependent on Vitamin K?
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all of them
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what major problem can happen in the deficiency of vitamin K?
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the inability of the liver to synthesize clotting factors and thus the animal can bleed to death.
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why is vitamin K important in the synthesis of clotting factors?
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it is required for the synthesis of a special amino acid residue.
(glutamic acid is converted to gamma-carboxyglutamic acid) |
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what chemical causes the polymerization of fibrinogen to fibrin?
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thrombin
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what is the molecule "tagged onto" proteins for non-lysosomal degradation?
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ubiquitin
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what hormones stimulate protein degradation by the liver?
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glucagon, catecholamines, glucocorticoids
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what is the basic process of detoxification by the liver?
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The toxic substance goes through a Phase I reaction, then a Phase II reaction, which makes them water-soluble, and excreted in the bile
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what is induction and what change in intracellular structure accompanies it?
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resistance to drugs by increased ability to detoxify in the liver. SER hypertrophy is seen in induction.
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what is the liver's role in immunity?
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- Kupffer cells are very good at phagocytosing bacteria
- The liver produces the secretory component of IgA |
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what are the two major functions of bile?
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1. facilitation of fat digestion and absorption
2. elimination of waste products from the circulation |
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what makes poop brown-green?
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bile
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why is conjugation of bile necessary?
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conjugation allows bile to be water soluble and fat soluble to emulsify fat (in micelles) in the small intestine and facilitate absorption
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what are the six basic components of bile?
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1. water
2. bile salts 3. bilirubin 4. cholesterol 5. lecithin 6. electrolytes |
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what is the precursor molecule for bile salts?
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cholesterol
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to what two locations does the liver transport bile?
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1. small intestine
2. gall bladder |
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true or false, the gallbladder is muscular and can secrete amounts of bile based on what is needed?
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true
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true or false, the gallbladder actively dilutes bile to make more of it?
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false. The gallbladder concentrates bile to make it more potent
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what are the three major factors controlling gallbladder contraction?
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1. cholecystokinin (CCK)
2. vagal and ENS innervation 3. amount of dietary fat |
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true or false, most bile is reabsorbed in the small intestine by passive and active transport?
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true.
Duodenum and jejumum: passive Ileum: active |
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what is the major component of gallstones?
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cholesterol
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true or false, bile activity can be either enzymatic or non-enzymatic, depending on function?
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false. It is non-enzymatic.
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Name NINE functions of the alimentary tract (yes, nine)
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1. ingestion
2. digestion 3. absorption 4. elimination 5. detox 6. bacterial housing/management 7. immune function 8. secretion 9. endocrine function |
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what is the most essential function of bacterial housing and management in the lower GI tract?
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to keep bacteria out of the blood and small intestine
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what is secreted by the alimentary tract?
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- hormones
- HCl - bicarb - enzymes - electrolytes - "water" |
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what is the difference between digestion and absorption
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digestion is the mechanical or chemical breakdown of food into smaller components. Absorption is taking those components and putting them into the system.
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true or false, digestion and absorption, by and large, are controlled by the same set of stimuli?
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false. they are controlled by completely different and distinct processes.
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what are the three phases of digestion?
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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 |
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what is the one phase of absorption?
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1. Transport phase - passage into the vascular system
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what are the three regulators of the GI tract
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1. neuroendocrine - the intrinsic ENS of the GI tract
2. CNS - parasympathetic (vagus & pelvic nn.) and sympathetic (splanchnic & hypogastric nn.) 3. GI reflexes |
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in what direction do GI reflexes generally move?
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oral to aboral
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true or false, the CNS, under extreme circumstances can completely override the ENS and GI reflexes?
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false
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what is the name of and distribution of GI endocrine tissue?
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- APUD or enteroendocrine cells
- dispersed diffusely through the stomach, SI, and pancreas. - most abdundant orally; decreases aborally |
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what class of hormones are the GI endocrine horomones?
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peptide/protein
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where are GI endocrine hormones secreted?
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into the basolateral membrane, where they can diffuse and have autocrine, panacrine, or exocrine effects
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what electrolytes are secreted by the stomach?
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only H+ and Cl- to any significant extent
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what are the four major ions absorbed and/or secreted by the intestines?
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Na, K, Cl, HCO3
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what are the three general goals of electrolyte transport in the gut?
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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 |
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what three major features of the gut facilitate the movement of ions and water?
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1. electrochemical gradients
2. high capillary permeability with low flow resistance 3. continuous flow through capillaries |
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what are the four passive transport mechanisms used by the gut?
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1. paracellular (through the "leaky" tight junctions)
2. ion channels 3. facilitated diffusion 4. solvent drag |
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what are the major substances transported by the gut with secondary active transport?
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- sodium
- chloride - potassium - bicarbonate - glucose (and other sugars) - amino acids |
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what is tertiary active transport?
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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. |
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how does regional absorption of water vary by species type?
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- Carnivores: greatest volume in the small intestine
- Horses: greatest volume in the large intestine - Ruminants and Pigs: intermediate |
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what is the primary reason that water flows in any particular direction in the gut?
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to keep the gut isoosmotic
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in carvnivores, why is water "secreted" into the gut in "early" intestine, but absorbed in the "late" intestine?
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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 |
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where, specifically, does most electrolyte absorption occur in the GI tract?
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the enteric luminal surface; brush borders increase the surface area
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what is the most important electrolyte involved in GI absorption?
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sodium
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in what three ways is chloride absorbed in the GI tract?
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- paracellular
- ion channels - secondary and tertiary active |
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how is bicarbonate directly absorbed in the GI tract?
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- an ion exchange mechanism
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in what two ways is postassium absorbed in the gut?
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- mainly passive paracellular diffusion
- H-K ATPase in the colon recovers the "last bit" when needed |
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what is the main function of the crypt cells in the intestinal tract?
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to SECRETE electrolytes and "water"
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what microanatomical structures of the intestines secrete electrolyte and by what physiological process does this occur?
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- the intestinal crypt cells
- a Na and Cl pumping mechanism on the basolateral membrane directed into the cells. Water follows. |
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Why is intestinal secretion important?
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to maintain the 300 mOsm value in the presence of large amounts of osmotically active particles.
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what are the two functions of mastication?
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1. divide food particles
2. mixes the food with saliva |
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what are the main components of saliva and species differences
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ALL:
1. water 2. salts 3. mucin: a slippery protein PIGS, apes, guinea pig, rodents: salivary amylase |
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what are the five major functions of saliva in non-ruminants?
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- moisten and lubricate food for sawllowing
- dissolve molecules for taste buds - cleanses mouth and teeth - antibiotic activity - (varies) digests starch with amylase |
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what controls secretion and what three things stimulate this process
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Secretion is controlled neurally:
1. parasympathetic input 2. object in mouth as a reflexive secretion 3. anticipation of food |
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what are the voluntary parts of deglutition?
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from tongue, pushing bolus to pharynx
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what initiates swallowing?
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involuntary pharyngeal receptors triggering swallowing centers
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what is the condition of esophageal sphincters when swallowing is not occuring?
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- held tonically closed
- they must relax to swallow |
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what are the two main functions of the upper esophageal sphincter?
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1. prevents reflux to pharynx during swallowing
2. prevents air entry into the esophagus during breathing |
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what is the function of the lower esophageal sphincter?
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prevents gastric reflux to the espohagus
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what is the difference between primary and secondary peristalsis?
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- primary is elicited by swallowing
- secondary is when food is stuck in the esophgaus and stretch recep |
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what are the two major causes of megaesophagus?
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1. failure of the lower esophageal sphincter to relax
2. a persistent right aorta |
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comment on the absorption in the simple stomach.
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- limited
- small amounts of water, some drugs (e.g. NSAIDs), ethanol :-) |
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what are the two basic types of mucus in the simple stomach and what is their function
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1. thick - protective
2. thinner - lubrication |
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what is the "milk curdling" enzyme of the stomach that is especially important in young animals?
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chymosin (rennin)
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what are pepsins, where are they secreted, and how are they activated?
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gasteric enzymes of the stomach, secreted as zymogens, are converted to their active form by gastric HCl
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an enzyme precursor secreted in the stomach that is activated by gastric acid
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zymogen
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***what is the action of gastric lipase?
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cleaves the lipid off of a lipoprotein. It does not digest the lipid!
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***where is gastrin produced, released, and what is its action?
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- 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 |
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what stimulates the secretion of gastrin?
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- luminal factors: protein digestion
- mural (muscular wall) factors: vagal discharge caused by gastric stretch and contraction - a POSTIVE FEEDBACK mechanism |
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what inhibits the secretion of gastrin?
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- luminal factors: increased gastric acid
- mural factors: loss of stomach wall stretch - hormonal factors released by small intestine: secretin, GIP (gastric inhibitory peptide) |
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where in the stomach is histamine produced, what stimulates it, and what effect does it have?
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- produced by gastric mast cells in response to gastrin or acetocholine
- has a panacrine effect to stimulate more gastrin release |
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what domestic mammals (besides humans) produce intrinsic factor, and what is its function?
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- produced by pigs and rodents
- allows B12 absorption in the ileum |
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true or false: H and Cl are secreted separately in the stomach and require active transport
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true
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What is the basic process of HCl secretion into the gastric lumen?
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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 |
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what are the three main chemical regulators of gastric acid secretion?
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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 |
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true or false, maximal gastric acid release is accomplished when acetylcholine vagal receptors, gastrin receptors, and histamine receptors are simultaneously stimulated.
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true
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what is the most important mechanism that prevents the overproduction of gastric acid?
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the negative feedback mechanism controlled by low pH of the gastric lumen.
- pH 2, acid slows down - pH 1, acid stops |
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***which macronutrients (carbs, proteins, lipids) are significantly digested in the stomach?
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all of them
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what nutrients are almost completely digested chemically in the stomach
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only protein
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what are three major features that protect the stomach from digesting itself under acidic conditions?
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1. very tight junctions
2. very high electrical resistance of the apical membranes that push away H+ 3. thick mucous |
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why is protein digestion in the stomach critical?
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because the pancreatic enzymes cannot digest large proteins
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what are the four main functions of gastric motility?
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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 |
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what are the major functions of the gastric fundus?
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- 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 |
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where is the gastric pacemaker?
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near the fundus
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what is characteristic of the peristalsis in the body of the stomach?
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strong for vigorous mixing
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what is characteristic of the peristalsis in the pyloric antrum of the stomach?
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really, really strong, grinding contractions to make small bits.
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besides mechanical and chemical digestion, what is the other major function of the pyloric antrum?
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- delivers small bits to the pylorus
- delivers bigger bits to the body of the stomach for further digestion |
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what is the size of the particle that gets through the pylorus during normal digestion?
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< 2 mm
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how does sympathetic stimulus affect the stomach during digestion?
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slows gastric emptying
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what comprises the enterogastric reflex?
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- duodenal osmoreceptors
- hypertonic contents slow emptying - isotonic contents maximize emptying |
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how does pH in the duodenum affect gastric emptying?
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- anything below pH 3.5 stops; anything lower would be too acidic for the duodenum to neutralize.
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how do small intestinal hormones affect gastric emptying?
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slows it down
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what are interdigestive contractions?
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in between meals, moves larger objects (like tennis balls) into the duodenum
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***what are the three phases of gastric secretion?
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1. cephalic
2. gastric 3. intestinal |
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how does the cephalic phase of gastric secretion affect gastric activity and by what means?
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- promotes gastric activity
- CNS-mediated (sight, smell, thought) - increases motility and secretion |
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how does the gastric phase of gastric secretion affect gastric activity and what happens during this phase?
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- promotes gastric activity
- local reflexes and responses to gastrin - results from presence of food in the stomach |
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how does the intestinal phase of gastric secretion affect gastric activity and what happens during this phase?
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- inhibits gastric activity (don't want to overload the duodenum)
- reflex negative feedback - enterogastric reflex - hormonal feedback - GIP and CCK lower HCl, pepsinogen, motility |
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what is the regulator of conscious (skeletal muscle) GI motility?
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spinal nerve innervation
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what are the regulators of unconscious (smooth muscle) GI motility?
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extrinsic factors: parasympathetic and sympathetic innervation; myenteric plexuses
intrinsic factors: hormones produced by the GI tract itself - most influence secretion, but some influence motility |
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what are the two critical components of intrinsic gut motility?
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cooperation between:
1. inherent electrical activity of the smooth muscle cells 2. the gut's ENS |
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what acts as the pacemaker for gut slow wave contractions?
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duodenum
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true or false, the CNS cannot control GI slow waves, but ENS stimulation can increase, decrease, or stop them
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false. The slow waves are completely independent of all nervous input
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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
|
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***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 |
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how does parasympathetic stimulus affect GI motility?
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- promotes GI secretion and motility
- relaxes GI sphincters and blood vessels |
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how does sympathetic stimulus affect GI motility?
|
- inhibits GI motility and secretion
- contracts sphincters and blood vessels |
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what are the two major functions of reverse peristalsis?
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- get digesta into the cecum
- temporarily retain digesta in a particular region |
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non-progressive contractions of alternating segments of circular muscle layer in the intestines
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mixing-segmentation
"gooshes" contents back and forth |
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holding digesta without allowing any movement
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retention
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