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16 Cards in this Set
- Front
- Back
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what are the sources of fluid coming to the large intestine?
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injested water, gastric secretions, intestinal secretions, pancreatic/galbladder secretions.
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on the intestinal vili: what part secretes, what part absorbs?
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the crypts excrete, the apical tops absorb.
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glucose transport into the intestinal cells: what's the driving force, and what other substance acts the same way? by what general mechanism do they exit the BL?
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Na+/Glucose coupled co-transport. This also works for neutral amino acids. this should be in the small intestine.
getting out the BL into the blood requires specific transporters. |
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sodium, chlorine, potassium, and bicarb: talk about the large and small intestine: where do you get net secretion and net absorption?
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small intestine: absorbs all electrolytes, secretes bicarb.
large intestine: a lot like saliva: absorbs Na and Cl, secretes net K+ and bicarb. so, both secrete HCO3 and absorb sodium and chloride. remember that the colon spits out potassium (poop is hyperkalemic), whereas the small intestine sucks it up. |
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intestinal cells: what does increasing cAMP or cGMP or Ca++ do?
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All of these messengers decrease absorption and increase secretion.
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what are our 4 major groups of Na+ transporters in the large and small intestine?
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most Na+ is absorbed from the gut via Na+/Glucose and Na+/Amino Acid co-transporters after eating meals (post-prandial)
having glucose and amino acids helps absorb salt. Also note that Na+ is actively "resorbed" (kicked out the BL side) by the Na/K ATPase. between meals, most salt is absorbed via the Na+/H+ exchanger in the jejunum and ilium. Also, the ENaC channel (blocked by amiloride). |
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what channels along the gut are important for pH balance?
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the Na/H+ exchangers
also, the HCO3-/Cl- exchangers. |
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what's nifty about the way you ACTIVELY secrete acid in the stomach and ACTIVELY resorb potassium in the colon?
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it's the same transporter.
The stomach's parietal cells have a K+/H+ antiporter (K+ in, H+ out) to make acid in the lumen. the colon has the same guy: this time, more to save K+ at the last minute. weird 'cause poop is hyperkalemic, but maybe it stops it from being too hyperkalemic? |
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how does increasing Ca++ or cAMP in our intestinal secretion cells change things?
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these up secretions.
they do it by activating BL K+ leak channels, which make the lumen (-). This drive out Cl-, which pulls Na+ across tight junctions, which then raises the luminal osmolarity. water rushes out = ups secretion. |
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what's the general term for something that illicits the excretion of water and salts from the intestines? what general categories are there?
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secretogogues!
these can be: hormones/neurotransmitters bacterial enterotoxins immune system products laxitaves. |
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what are some actual important secretogogues, and what pathways do they work through?
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enterotoxins include heat stable and heat liable toxins (STa = heat stable).
Heat liable works through cAMP/PKA, as does VIP. These use the BACK DOOR (BL). Heat stable works through cGMP (think shigatoxin makes you gimpy). seratonin works through Ca++ (DID/IP3/PLC). all of these up secretion. note that these secretogogues increase salt secretion and STOP absorption. NOTE: absorpatagogues are aldosterone, sympathetics, neuropeptide yy, are all absorptigogogues. somatostatin too. |
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what's up with Ca++ absorption?
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tied to vitamin D.
Vitamin D increases the number of Ca++ channels on the apical membrane of the intestines. Also increases the synthesis of Ca++ channels. This lets in more calcium to the cell. NOTE: there's CALBINDIN: this binds up the intracellular calcium and keeps it from being too high and poisonous to the cell. Ca++ gets out the BL |
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aside from water, what can be absorbed in the large intestine?
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short chain fatty acids, digested by bacteria and the products go into our blood stream. this causes gas.
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what are the components of poop?
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100mL water, 25-50g solids.
mostly: bacteria (30%) fiber (30%) lipids (10-20%) organic matter K+ and HCO3- |
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what makes up farts?
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nitrogen
hydrogen C02 Methane oxygen |
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what's the most important feature of vitamin D? what are our Ca++ channels?
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vitamin D ups the secretion of calbindin.
note that intake of Ca++ into the cell is through a Ca++ channel. Export is a Ca++ ATPase. Also, a Na+/Ca++ exchanger. |
