Renal 2: Reabsorption And Secretion Flashcards
What is secondary active transport?
When an ion or nutrient piggybacks on Na and passively passes through a membrane moving down the Na gradient. The Na/K pump keeps Na gradient. (Doesn’t req ATP)
What is the difference between paracellular and transcellular transport of water and solutes (happens during reabsorption)?
Paracellular: movement of some ions, water, and urea thru leaky tight junctions, into and thru the interstitial fluid then into the capillary.
Transcellular: ions and nutrients are transported across cells via Na/K pumps and passive transporters. Water is transported via aquaporins.
What are Aquaporins?
H2O transporters: Membrane proteins permeable to water. Enable transcellular water absorption. Found in most tissues. Sometimes regulated by hormones. Cell permeability to water depends on up or down reg. of aquaporins.
Where in the tubule are water and Na+ reabsorbed?
Throughout tubule
Where are glucose, amino acids, vitamins, reabsorbed?
The proximal convoluted tubule (PCT) is the only part of the tubule that reabsorbs these nutrients! It reabsorbs about 2/3+ of filtrate.
What is the “Transport Maximum”?
The transport maximum or Tm is a saturation level for a given solute. Re absorption of organic solutes through proximal tubule epithelial cells is limited by saturation of carrier proteins. (Glucose levels above Tm are excreted in urine. We only have a finite number of transporters; if # of glucose molecules exceeds # of transporters then we pee it out. This happens in Diabetes Mellitus - Mellitus = sweet)
What is secretion?
Things that aren’t/can’t be filtered, but that we need to excrete, are secreted. Most organic ions and drugs are protein bound and not filtered; instead they are secreted from the peritubular capillaries into the proximal convoluted tubule.
Why do protein bound waste metabolite need to be secreted?
In the glomerulus, dissociation is weak and therefore few ions are filtered; whereas in peritubular capillaries, blood flow is slow, permitting more dissociation from carrier proteins and adequate time for secretion.
What is clearance?
It is a flow rate (ml/min) that measures the effectiveness of your kidney at getting a substance out of the body: the volume of plasma from which a substance is completely cleared by kidneys per unit time.
How is clearance measured?
Amt. substance secreted = amount (filtered - reabsorbed + secreted)
It is the amt substance secreted/ time over the concentration of the substance in the plasma.
Urine/blood
What are some typical values of clearance for: Glucose Na+ Urea Inulin Creatinine
Glucose: 0 ml/min Na+: 0.9 (body wants it) Urea: 70 (only half cleared - we use our own urea) Inulin: 125 - highest clearance Creatinine: 140 - max (12% overestimate)
What is Inulin used for?
In glomerular disease Inulin is used to determine if kidney filtration (GFR) has been affected. Inulin is almost completely cleared from blood; so it estimates GFR because it is filtered, but not reabsorbed or secreted.
What is PAH (para-aminohippuric acid) clearance used to measure?
Estimates amt of plasma flow into kidney, not just amt filtered.
Estimates renal plasma flow (RPF) - it is used to determine if there have been changes in renal perfusion due to, ie. renal stenosis.
PAH is 90% cleared from plasma by both filtration and secretion BUT IT IS NOT REABSORBED.
What is glomerulonephritis and how does it impact GFR?
Acute: antigen/antibody (Ag/Ab) complexes block glomeruli. Often caused by strep infection. Usually recovers w/in 2wks
Chronic: Ag/Ab complexes plug up glomerular pores and inflammation and damage to capillaries leads to deposition of fibrous CT (what leads to what?). Can lead to irreversible loss of nephrons.
