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Phys4 GI Lect10
Phys4 Flux of electrolytes and Water
| Question | Answer |
|---|---|
| How is water MAINLY absorbed from the intestine? | PASSIVELY in the small intestine. **therefore fluid flux is dependent of food and electrolyte concentrations in the lumen as wall as osmotic pressures w/in the BL |
| Water volumes entering the small intestine, Large intestine, and exceted in a 24hr period | 1.Small: 7-10L. 2.Large: 600mL. 3.Excreted: 100mL. |
| How does the osmolality of the GI lumen compare with that of the plasma? | ISOTONIC |
| In a healthy GI tract, what undergoes a net secretion? Net reabsorption? | SECRETION: 1.K+. 2.HCO3-. ABSORPTION: 1.Na+. 2.Cl-. 3.Water |
| Compare the gall bladder and small intestine epithelium to that in the colon? | Small int and GB have LEAKY epithelium where as Colon has a relatively impermeable epithelium. **allows it to create large transepithelial gradients. |
| 5 mechanisms of Na+ reabsorption | 1.Sugar/Na or aa/Na symporters. 2.Na channels (Colon). 3.Na/Cl symporter. 4.Na/H+ exchanger. 5.Paracellular solvent drag (sig in jej and duo). |
| Key Na reabsorption in the Proximal bowel (Jejunum and Duodenum) | 1.Glucose or aa's symptorter and Na/H+ exchanger predominate. 2.paracellular solvent drag. **HCO3- is secreted into BL on the basolateral side. |
| Na reabsorption in the Ileum/ Distal Bowel | 1.Na/H+ exchanger (combines with HCO/Cl exchanger to form the COUNTER TRANSPORT). 2.Na/Cl- symporter. **There is also a Cl/HCO3 exchanger that secretes bicarb. This creates lots oc Cl- in the cell |
| Where are you more likely to see Na absroption via Glucose/Na or aa/Na symptorter? | Proximal bowel. **Less prevalent in distal bowel b/c the glu & aa's have mostly been absorbed. |
| How is K+ absorbed in the small intestine? Large intestine? | Passive diffusion paracellularly. **K+ is SECRETED in the large intestine |
| How is Na primarily reabsorbed in the colon? | Na+ channels. **Targets of Aldosterone. |
| Movement of K+ in the colon | Can be absorbed or secreted depending on lumenal content, but mostly secreted via movement through paracellular space.. **Basolateral membrane is permeable to K+ (only in colon). |
| What can happen to [K+] as a result of Diarrhea | K+ secretion will inc due to the inc driving gradient from the Inc flows (K secretion has a flow rate dependence). **this can result in a hypokalemic metabolic ACIDOSIS. |
| 4 things that Increase K+ secretion in the Colon | 1.High Flow rates (diarrhea). 2.cAMP (activated by cholera toxin & VIP). 3.cGMP. 4.Ca+ (Inc by serotonin). **they affect apical membrane more than basolateral membrane. |
| What accounts for the high alkaline pH of stool water? | The Cl/HCO3 exchanger which is present in both small and large intestine. |
| Water movement seen with a hypertonic (just after eating) GI lumen | Initially moves into the lumen, then more distally both solutes then water move back into the BL. |
| Water movement seen with a hypotonic GI lumen | Initially moves from the lumen into the BL, then distally there is Isotonic movement. |
| What is the major source of water and electrolytes found in stool suring diarrhea? | Small intestine |
| How do Epsom salt (MgSO4) laxatives work? | Draw plasma water into the lumen which loosens the stool. |
| Effect of Ca+, cAMP, and cGMP on the Crypt cells of both large and small intestine | Open up Cl- channels at the apical membrane. **Mostly seen in small intestine. As a result of the Cl- & Na secretion, large volumes of water will follow. |
| List the Normal and abnormal secretagogues that Inc Cl- secretion from the crypt cells | NORMAL: 1.ACh (Inc Ca+). 2.Secretin (Inc cAMP). 3.VIP (Inc cAMP). ABNORMAL: 1.Cholera Toxin (Inc cAMP). 2.E coli (Inc cAMP). |
| Secretory Diarrhea | Diarrhea resulting mainly from an Increased volume of secretion (which then draws out large volumes of water). **Also is partially due to dysfunctioning colon. |
| Causes of Secretory Diarrhea | 1.E.Coli. 2.Shigella Flexneri. 3.Salmonella. 4.Virbrio Cholerae (affects both large & small Int and Inc cAMP in crypts and Villus). |
| How is oral rehydration therapy used to treat secretory diarrhea? | It utilizes the co-transport of Na+ w/ aa's or glucose to increase water reabaroption in the small int. **Inc lumenal aa and glucose will enhance absorption. |
| Ca+ reabsorption w/in the Enterocyte | Enhanced by Vit D which stimulates Ca+ transport via CaBP (binding protein) which allows it to cross the brush boarder. Ca+ exits basolateral mem via: 1.Ca-ATPase. 2.Ca/Na exchanger. |
| Where is iron absorbed by enterocytes? | Duodenum. MUST be in Ferrous (Fe2+) form. **Brush boarder reductases reduce Ferric Fe3+ to Ferrous Fe2+ so it can cross the apical mem via DMT-1 transporter |
Created by:
WeeG
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