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Phys3 Basic tran Mec
Phys3 Basic transport mechanisms: Handling Organic Solutes
Question | Answer |
---|---|
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. |