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Phys3 Basic tran Mec

Phys3 Basic transport mechanisms: Handling Organic Solutes

QuestionAnswer
Difference b/w transcellular and paracellular Tran: requirees protein channels or transporter to cross from the lumen to the interstium. Para: movement from the lumen to the interstium occurs via tight junctions.
3 different carrier proteins 1.uniporter. 2.symporter. 3.antiporter/exchanger/counter transporter.
Dual function of Urea 1.Waste product to keep nitrogen balance. 2.Creates medullary osmotic gradient necessary for concentration/dilution of urine.
Normal BUN range 7-18mg/dl
Where does Abes like to go when he gets a new pistol? The BUN range
where is urea primarily reabsorbed? 1.Proximal tubule. 2.Inner Medullary CD (IMCD). **water reabsorption causes Inc tubular urea concentration.
where is urea primarily secreted? Loop of Henle, the medullary urea > tubular urea. **Thin limbs are impermeable to urea via tight junctions, UT-A2 transporters secrete urea into the tubule (ATLEAST as much that was reabsorbed in proximal tubule).
How does ADH cause urea reabsorption in the IMCD? 1.ADH activates cAMP. 2.UT1 is phosphorylated. 3.UT-A1 transporters allow crossing of apical membrane out of tubule. 4.UT-3 transporters: allow crossing basolateral membrane in PTC
Decreased flow's affect on urea More water has time to be reabsorbed which sets up a concentration gradient favoring reabsorption: 1.Dec secretion. 2.Inc reabsorption. 3.Inc BL urea (BUN).
Increased flow's affect on urea Water is moved quickly and less is reabsorbed, therefore the gradient for urea isn't as large: 1.Inc secretion. 2.Dec reabsorption. 3.Dec BL urea (BUN).
Where does the most glucose reabsorption occur? alomst 100% in the proximal tubule.
How does glucose cross the apical membrane to leave the tubule? glucose-Na symporter (SGLT). **Na+ concentration gradient used by SGLT is estabilished by a Na/K ATPase on basolateral membrane.
How does glucose cross the basolateral membrane to enter PTC Facilitated diffusion through: 1.GLUT2:early proximal tubule. 2.GLUT1:late proximal tubule.
What limits glucose reabsorption? Tubular maximum (Tm): 400mg/min. This is the plateau on the reabsorption curve. **Occurs at plasma glucose of 200mg/dl
what is normal plasma glucose? 90mg/dl
What does Tm represent? the filtered load at which the transporters will be saturated and any excess glucose will remain in the urine. **Occurs at 400mg/min when the plasma glucose reaches 200mg/dl
why does Splay, a curved approach to the Tm plateau, occur? B/c different nephrons reach Tm at different times depending on how large their glomerulus is.
What is the glucose clearance before Tm is reached? 0!!! b/c all is getting reabsorbed.
where does most aa reabsorption occur? aa's are 98% reabsorbed in the proximal tubule b/c they are freely filtered.
Does glucose of aa's have the higher Tm? GLUCOSE. aa's have a low Tm.
aa transport across the apical membrane 1.Na-driven transporters. 2.H-driven transporters. 3.aa exchangers.
aa transport across the basolateral membrane 1.Larger proteins: endocytosis. 2.very small peptides:broken down by lumenal peptidases. 3.di & tri-peptides: enter via PepT1 & broken down by cytoplasmic peptidases.
What happens to most hormones as they cross out of the tubule? Get degraded within the renal tubular cell rather than being absorbed. **Ex: Ang II & insulin.
What might you see in renal disease in terms of plasma hormone levels? Increased, due to decreased degradation of hormones.
What carboxylates get reabsorbed? 1.Pyruvate. 2.Lactate. 3.di & tri-carboxylate intermediates of the citric acid cycle.
What is mainly secreted in the proximal tubule 1.NE/Epi. 2.Dopamine. 3.Histamine. 4.Morphine. 5.Quinine. 6.PAH. 7.Bile salts.
Created by: WeeG
 

 



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