Ianowski - theme 5 Flashcards
Order of nephron bits:
Glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct.
Glomerulus:
Ultrafiltration. Small plasma molecules and water move from blood to nephron, driven by blood pressure. No cells enter the ultrafiltrate - low protein concentration. Podocytes control passage.
Renal corpuscle: components
Glomerulus and glomerular/Bowman’s capsule
Glomerular capsule:
Two layers. Outside layer keeps the capsule apart from everything else; inside layer does the actual filtering. Contains basement membrane between endothelial cells and podocytes.
Basement membrane:
Involved in filtration. It’s negatively charged so plasma proteins don’t get through. Lets through water, ions, waste, and glucose.
Rate of glomerular filtration:
115 mL/min, 7.5 L/hr
Proximal convoluted tubule: job
Reabsorption - 65% filtered water, 67% filtered sodium, some glucose and AAs
Secretion - protons for acid/base regulation, some organic molecules
Proximal convoluted tubule: how do job
Active transport - carrier mediated glucose and AA transport. Na/K pump produces sodium gradient, which can bring glucose as a +1.
Tm:
Tubular maximum. Transporters are saturated; filtered glucose appears in urine.
Absorption of protein in proximal tubule:
99% of protein is taken up again from the nephron. 1% may be excreted.
Receptor-mediated endocytosis of proteins in proximal tubule:
Proteins are marked for destruction by lysosomes, then AAs can be pushed into interstitial space
Loop of Henle: function
Establishes osmotic gradient in medulla. This allows water absorption (another 20%) from the collecting duct.
How much water is left in the urine after passing through proximal tubule and the loop of Henle?
15%. 85% has been taken up.
How does the loop of Henle establish osmotic gradient?
Descending limb is permeable to water and impermeable to NaCl. Filtrate becomes concentrated.
Ascending limb is impermeable to water. Actively transports Na out (Cl follows passively). Medulla fluid becomes concentrated, allowing the process in the descending limb to occur.
What kind of feedback loop is used in the loop of Henle?
Positive feedback. The more Na is pumped out in the ascending limb, the more water can be reabsorbed in the descending limb. The more water reabsorbed in the descending limb, the more stuff for the ascending limb to pump out. ***
Urea in the medulla:
Accumulates in the loop of Henle and gets peed out. ***
Vasa recta:
Blood vessels! Takes up excess water and solutes with countercurrent exchange.
This is glomerular blood, not reg blood, so it has a high protein concentration and sucks up water cuz proteins are thirsty.
Why does the vasa recta loop up instead of exchanging blood at the bottom?
Blood at the bottom has a high ion concentration, which you don’t want to lose. Follow the gradient back up to low concentration before feeding into vein.
Distal convoluted tubule: what it do
May dilute filtrate. Regulates Na/K in the blood by aldosterone-controlled Na transport and ADH-controlled water permeability.
Distal convoluted tubule: the parts
Collecting duct and interlobular vein
Collecting duct:
Concentrates urine using the medulla’s gradient. In high water concentration, ADH blocks water exchange so it can be peed out. In low water concentration, the gradient pulls water out of the urine.
I gotta ask again - what’s another name for vasopressin?
ADH, antidiuretic hormone. I KEEP FORGETTING AND I’M SORRY.
