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- -Functional unit of the kidney
- -1 million nephrons per kidney
- -Each nephron has many cellular transport systems (both passive and active) for reabsorption and excretion of molecules, ions, and just about anything that travels in the plasma.
- -Two types of nephron- juxtamedullary nephrons, cortical nephrons.
- -comprise 15% of nephrons
- -less blood flows through these nephrons
- -Their loos of Henle are accompanied by special arterioles called vasa recta ("straight vessels")
- -role in reabsorption of solutes
- -formed by efferent arterioles (still arteriole blood when it leaves glomerulus -doesn't change to venous blood until peritubular capillary network)
- - Run parallel with ascending/descending loop of Henle
- -They don't concentrate plasma- they prevent it from becoming dilute.
- -Comprise 85% of nephrons
- -Largest volume of blood flows through here
- -Granular, homogenous in appearance - many glomeruli
- -Their loop of Henle is shorter (less involvement in concentration of urine compared to juxtamedullary nephrons)
- Surrounds glomerulus
- (Capillary network where the filtration occurs - this is the only spot where plasma filtration occurs in the nephron)
- Wider fenestrae (capillary pores) than normal systemic capillaries.
- -the space between Bowman's capsule and the actual capillary network
- -Stuff filtered out of Capillary blood accumulates here.
- -the filtrate is called the urinary ultrafiltrate or glomerular filtrate, and it contains everything that's in the blood except the plasma proteins and blood cells.
- ="cell with feet"
- -specialized epithelial cells that meet the basement membrane, and their "feet" encircle the outer perimeter of the capillaries.
- -Between the foot processes are slit pores, negatively charged passageways through which filtrate passes.
- These slit pores have a Negative aligning charge and because PPs tend to have negative charges, they're repelled back into the blood plasma.
3 steps in urine formation
- 1> Filtration
- 2> reabsorption
- 3> secretion
- -Determined by hydrostatic and oncotic capillary pressures and plasma permeability vs. filtering surface of the capillaries
- -Glomerular filtration rate (GFR) = Hydrostatic pressure pushing fluid out of afferent arteriole minus capillary oncotic pressure pulling fluid back into the capillary minus the hydrostatic pressure of the fluid already in Bowman's capsule pushing back at the capillary.
- -GFR can be directly affected by the Juxtaglomerular apparatus (JGA)
- -DEC afferent capillary hydrostatic P
- ->DEC filtrate flow rate through the loop of henle
- ->INC reabsorption
- ->INC capsule hydrostatic P and /or afferent art oncotic p
- ->DEC GFR
- ->GFR is directly proportional to blood pressure and frequency of urination
-happen all throughout the different "limbs" of the nephron.
-also occurs in different degrees throughout the nephron, but the most important and numerous secretions take place in the thick ascending limb of the loop of Henle and in the collecting duct.
Types of Transport proteins
- -Primary active transport aka energy mediated transport; need ATP to function (ex. Na+/ K+ pump)
- -can move solutes against an electrochemical gradient
- -Secondary active transport aka carrier-mediated diffusion aka facilitated diffusion (ex. co-, counter-, uni-transport)
- -do NOT need ATP for function. These membrane transport proteins use concentration/electrochemical gradients to their advantage.
An important principle to remember is unless a membrane is water-impermeable
- wherever Na+ goes, H2O will follow.
- except for Thick ascending
Functional differences between nephron segments
- PCT, Proximal Convoluted Tubule
- Function-Isoosmotic reabsorption of solute and H2O
- Diuretics cause an increase in urine production("Diarrhea of the urine")
- by decreasing solute reabsorption from the tubular lumen.
- -Because each segment of the nephron is functionally unique, there are diuretic drugs that can affect each segment individually.
- The luminal cells of the PCT have brush borders to INC their surface area and consequently INC their reabsorptive capabilities.