Term
| What are the results of digestion that are capable of being absorbed for the following: carbohydrates, fats, proteins. |
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Definition
1. monosaccharides
2. small peptides and amino acids
3. monoglycerides and FFAs |
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Term
| What is involved with luminal digestion? How about membrane or contact digestion? |
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Definition
1. digestion occurs in the GI tract with enzymes from the stomach, pancreas, etc
2. digestion occurs as nutrients make contact with the brush border of villi and the enzymes in the enterocytes break down the nutrients |
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Term
| What digestive enzymes are secreted by the salivary glands? The stomach? |
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Definition
1. α-amylase and lingual lipase
2. pepsin |
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Term
| What digestive enzymes are secreted by the pancreas? |
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Definition
| amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, lipase-colipase, phospholipase A2, and cholesterol esterase |
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Term
| What digestive enzymes are secreted by the intestinal mucosa? |
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Definition
| enterokinase, sucrase, maltase, lactase, trehalase, α-dextrinase (isomaltase), amino-oligopeptidase, and dipeptidase |
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Term
| What is the total surface areas of the small intestine? What contribute to the surface area? |
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Definition
1. 250-400 m^2
2. the length, the folds of Kerckring, the villi, and the microvilli |
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Term
| What does senescent mean? |
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Definition
| something has reached the end of its division/growth power; this is used to refer to enterocytes that migrate up the crypts to the microvilli and cross the border beyond which they cannot differentiate |
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Term
| What is the function of trehalase? |
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Definition
| it digests three-carbon sugars |
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Term
| What is the shape of the cells in the crypts of Lieberkühn? How about the cells of the villi? |
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Definition
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Term
| What happens to enterocytes when they reach the top of the villi and die? |
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Definition
| they are shed into the GI tract and become digested and absorbed |
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Term
| What are the cell types in a villus? |
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Definition
| secretory, endocrine, goblet, and mature absorptive epithelial |
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Term
| What four mechanisms are important in transporting substances across the intestinal cell? |
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Definition
a. active transport (primary and secondary)
b. passive diffusion
c. facilitated diffusion
d. endocytosis |
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Term
| What is the most important process in SI absorption? How is it achieved? Why is it so important? |
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Definition
1. the absorption of Na+
2. by the activity of Na+/K+ ATPases on the basolateral side of the membrane
3. it provides the energy for secondary transport for many other substances and provides the shift in osmotic pressure that allows absorption of a lot of water |
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Term
| What substances are absorbed in the stomach? The duodenum and jejunum? |
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Definition
1. ethanol and NSAIDs
2. fats, carbs, amino acids, vitamins, ions, water, and electrolytes |
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Term
| What substances are absorbed in the ileum? The colon? The rectum? |
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Definition
1. bile salts and vitamin B12
2. water and electrolytes
3. drugs such as steroids and salicylates |
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Term
| What barrier must a nutrient cross to be absorbed by the blood or lymph? |
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Definition
| the unstirred layer, glycocalyx, apical cell membrane, cytoplasm, basolateral membrane, intercellular space, basement membrane, and capillary wall or lymph vessel wall |
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Term
| Where does carbohydrate digestion begin? What is the rate-limiting step of carbohydrate absorption? |
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Definition
1. in the mouth with saliva; it continues in the stomach with acid and in the SI with pancreatic amylase; lactose and sucrose, however, are only digested by contact digestion
2. assimilation |
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Term
| What do the following break down into: starch, maltose, lastose, sucrose |
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Definition
1. maltose and then glucose
2. glucose
3. glucose and galactose
4. fructose and glucose |
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Term
| How are the following transported across the apical membrane: glucose, galactose, fructose. |
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Definition
1. secondary active transport with Na+ in SGLUT-1 using energy from Na+/K+ ATPase
2. same as 1
3 facilitated diffusion using GLUT-5 |
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Term
| What is a hexose transporter? Which ones transport by facilitated diffusion? Which ones transport by secondary active transport? |
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Definition
1. a transporter of a 6-carbon ring structure (sugars)
2. GLUTs 1-5
3. SGLUT-1 |
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Term
| What is lactose intolerance? What are its symptoms? How is it diagnosed? |
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Definition
1. a lack of brush border lactase
2. abdominal cramps, bloating, diarrhea, and flatulence
3. feed the patient lactose and look for glucose in the plasma |
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Term
| What is the consequence of absent SGLUT-1? |
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Definition
| the patient will have to be fed fructose to get his carbohydrates |
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Term
| Where does protein digestion begin? |
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Definition
| Stomach, followed by SI via endo- and exopeptidases, brush border oligopeptidases and dipeptidases, and cytoplasmmic dipeptidases |
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Term
| What is the activation/deactivation mechanism for proteolytic enzymes? |
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Definition
| enterokinase activates trysinogen, making trypsin; trypsin autocatalyzes and also activates other proenzymes; proteolytic enzymes digest themselves |
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Term
| How are protein break-down products absorbed? |
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Definition
| amino acids are absorbed by secondary active transport and facilitated diffusion; di- and tri- peptides are absorbed by different carrier systems, but are absorbed faster |
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Term
| What is pancreatic insufficiency? What causes it? |
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Definition
1. inability or decreased ability of the pancreas to produce digestive enzymes
2. pancreatitis or CF |
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Term
| What are possible problems a person might have that would prevent them from assimilating protein? |
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Definition
| pancreatic insufficiency, congenital absence of trypsin, Hartnup's disease |
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Term
| What is the consequence of a congenital absence of trypsin? |
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Definition
| if there is no trypsin, none of the other pancreatic enzymes will be activated |
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Term
| What is Hartnup's disease? What are its consequences? |
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Definition
1. an inability to absorb neutral amino acids
2. the patient has reduced ability to absorb some amino acids, but can still get neutral amino acids through di- and tri- peptides |
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Term
| What are the most common sources of fiber? What is the difference between these fibers? |
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Definition
1. wheat and pectin
2. wheat decreases transit time of food and pectin increases transit time of food |
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Term
| After absorption, how is fructose processed? |
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Definition
| in the liver, it is turned into fru-1-phosphate, then into either glyceraldehyde or dihydroxyacetone; glyceraldehyde turns into GBP (glucose bisphosphate) and can enter gluconeogenesis to make glycogen or to make glycerol to start TG synthesis in the liver |
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Term
| How does trypsin work? Chymotrypsin? Carboxypeptidase? |
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Definition
1. cleaves peptide bonds on the carboxy side of a basic amino acid
2. cleaves on the amino side
3. cleaves the amino acids off the carboxy side |
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Term
| Define: sprue and tropical. |
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Definition
1. not being able to absorb something in your SI
2. typically bacteria or parasite; non-tropical is often idiopathic |
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Term
| What are the main processes that triglycerides must undergo to by absorbed? |
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Definition
| emulsification, enzymatic digestion into glyceride and FFAs, and reconstitution into TGs and chylomicron formation |
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Term
| What is a micelle? Steatorrhea? |
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Definition
1. a spherical formation of FFAs
2. fat in the stool
NOTE: steatorrhea can be an indicator of sprue is the fat is in the form of FFA (in which case it has been digested but not aborbed) |
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Term
| List the break-down products of the following: triglyceride, cholesterol-ester, and phospholipid. |
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Definition
1. either 1 2-mono-glyceride and 2 FFAs or 1 glycerol and 3 FFAs
2. 1 cholesterol and 1 FFA
3. 1 lysolecithin and 1 FFA |
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Term
| What breaks down a 2-monoglyceride? |
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Definition
| cholesterol ester hydrolase |
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Term
| What is malabsorption? What can cause it? |
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Definition
1. inability to absorb something, usually fat
2. motility disorders causing to rapid peristalsis, digestion disorders (pancreatitis or CF), or an absorption disorder (tropical or nontropical sprue) |
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Term
| Give examples of nontropical sprue. What is another name for nontropical sprue? What does it cause? |
|
Definition
1. allergy to gluten (wheat, rye)
2. celiac disease
3. destruction of the microvilli and sometimes to villi as well |
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Term
| On average, what is the volume of fluid entering the gut? How much is absorbed? How much is excreted? |
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Definition
1. about 9 L
2. about 8.8-8.9 L
3. 100-200 mL |
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Term
| What is the tonicity of chyme throughout the GI tract? |
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Definition
| isotonic except in some of the large intestine, where water is greatly reabsorbed |
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Term
| How is the majority of water and electrolytes absorbed? |
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Definition
| Basolateral Na+/K+ ATPases cause a Na+ gradient, so Na+ is reabsorbed by diffusion through water-filled channels, co-transport with amino acids or glucose, co-transport with Cl-, or counter-transport with H+, and Cl- and water follow the Na+ |
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Term
| What hormone greatly increases Na+ absorption in the gut? |
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Definition
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Term
| About how much total Na+ is absorbed daily? How much is typically taken in in the diet? How much is secreted in the small intestine? How much is absorbed from the intestine? How much is excreted in the feces? |
|
Definition
1. 15% of the total body Na+
2. 5-8 g/day
3. 20-30 g/day
4. 25-35 g/day
5. 0.1 g/day |
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Term
| How is water secreted into the lumen? |
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Definition
| increased osmotic pressure resulting from digestion of food and/or crypt cells actively secrete Cl- (whose channel is activated by cAMP, which will be followed by Na+, which will pull water into the lumen |
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Term
| What is the third leading cause of death by disease worldwide? What are some common causes of it? |
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Definition
1. diarrhea
2. infectious diarrhea, ulcerative colitis, drug-related diarrhea, or psychogenic diarrhea |
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Term
| What is cholera? What can it cause? What is its mechanism of action? What is the prognosis for it? What is the treatment for it? |
|
Definition
1. vibrio cholerae infection
2. cholera toxin stimulates secretion of water and electrolytes from crypt cells; patients may lose up to 10 L per day
3. the cholera toxin increases the cAMP to the CFTR, causing increased Cl- loss and increased Na+ and water loss in turn
4. untreated, 50% will die; treated, <1% would die
5. oral rehydration (glucose and electrolytes) |
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Term
| What stimulates net secretion in the following: mucosa epithelial cells, lamina propria cells, enteric neurons, blood? |
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Definition
1. serotonin, CCR, gastrin, and neurotensin
2. aracadonic acid, NO, bradykinins
3. ACh, serotonin, VIP, and substance P
4. VIP and prostaglandins |
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Term
| What stimulates a net absorption in the following: mucosa epithelial cells, lamina propria cells, enteric neurons, blood? |
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Definition
1. somatostatin
2. none listed
3. norepinephrine and neuropeptide Y
4. epinephrine, glucocorticoids, and aldosterone |
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Term
| What is lecithin? What does it do? |
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Definition
| a phospholipid secreted in the bile that emulsifies fats to assist in their absorption |
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Term
| What is feces composed of? Why is feces brown? |
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Definition
1. about 3/4 water and 1/4 solid matter; the solid matter has dead bacteria, fat, inorganic matter, protein, fiber, dried constituents of digestive juices, bile pigment, and epithelial cells
2. it contains breakdown products of bilirubin, which are brown |
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