Renal 2 Tubular Function and Micturition Flashcards
what is the function of the nephron?
3 primary functions: filtering, reabsorbing, secreting.
The glomerulus filters blood. Reabsorption occurs along in the convoluted tubules and Loop of Henle. Secretion occurs in the PCT & DCT, and collecting duct. Anything not reabsorbed (urea) becomes the urine + is secreted through the collecting duct.
what materials are completely reabsorbed from the filtrate?
glucose, amino acids and bicarbonate
what materials within the filtrate are regulated and partially reabsorbed?
water, sodium, potassium, chloride
what materials from waste are excreted as waste?
urea, creatinine, drugs, drug metabolites
which section of the Loop of Henle is water-permeable?
the descending limb; lots of water reabsorption and when we reabsorb substances like Na+, K+, or a.a.’s and glucose, water follows it
which section of the Loop of Henle is impermeable to water?
the thicker ascending limb; ions are still pulled out of the filtrate for reabsorption but water cannot follow it
collecting duct
able to modify water reabsorption in the presence of ADH (reabsorb water, w/o ADH water in filtrate ends up in bladder)
interlobular artery
become afferent arterioles feeding the glomerulus
arcuate artery
become efferent arterioles away from the glomerulus, dives down into glomerulus to form peritubular capillaries
recta vasa
straight vessels that collect the stuff we want back
obligatory water reabsorption
occurs when water is “obliged” to follow the solutes being reabsorbed, as aquaporins are always present in the PCT
facultative water reabsorption
aquaporins are inserted in collecting ducts only if ADH is present
where does most obligatory reabsorption occur?
PCT and descending LOH (tubules permeable to water)
where does most facultative reabsorption occur?
in the collecting duct
osmosis and the PCT
movement of water will always be able, linked to passive reabsorption of a number of ions as well as the waste product urea
- by the end of the PCT most organic solutes have been reabsorbed as well as 65% of the water
passive transport
the movement of substances across a cell membrane without the use of energy by the cell, simple diffusion or facilitated diffusion, or leak channels
passive sodium reabsorption
from high [ ] in fluid to low [ ] in tubule cells; sodium may pass through via paracellullar route and pull water with it to end up in the blood
what type of epithelium is the apical border of the tubular cell?
simple cuboidal epithelium
paracellular route
between epithelial cells of PCT
transcellular route
substances pass through the cytoplasm of the PCT epithelial cells and out their base
primary active transport
active transport that relies directly on the hydrolysis of ATP
secondary active transport
uses energy of the movement of ions down their concentration gradient to transport other solutes (like ions and larger uncharged molecules like glucose or a.a.’s)
symporter
when the secondary active transport protein moves both the ion and the solute in the same direction
antiporter
when the secondary active transport protein moves the ion in one direction and the solute in the opposite direction
what do both active transport mechanisms require?
a carrier protein to assist the movement of ions + other solutes
active sodium reabsorption
across apical membrane:
- leakage channels present allowing sodium to come in due to [ ] gradient
when sodium gets inside we do not want [ ] to continually build up (can’t let it continually come in)
- pumped out with sodium-potassium pump
- keeps [Na+] low in cell which allow use of symporters and leak channels for sodium to bring it back
active glucose reabsorption
- occurs in PCT
- gluc. symporter allows Na+ to go down [ ] gradient and has binding sites for 2 Na+ and 1 glucose
- binding changes conformation and allows Na+ to drag 1 glucose in and goes inside tubular cell
- Na+ needs to be pumped out to prev. build up (and K+ in)
transport is couple w/ Na+/K+ pump and facilitated diffusion
why can’t glucose build up inside the cell?
glucose attracts water, therefore it uses a facilitated diffusion transporter on the basolateral membrane allowing glucose to go down [ ] gradient
- moves from cell to bloodstream, followed by water
Na+/H+ antiporter in the PCT
- Na+ into absorptive cell and H+ out
- movement powered by Na+ [ ] gradient (high in filtrate, low in cell)
- H+ came from dissociation of H2CO3 (metabolically active process)
- antiporter uses sodium to kick out H+ to slowly help correct acidosis
- sodium then kicked out of cell using ATP pump to prev. buildup
- HCO3- being generated inside the apical cell has facilitated diffusion transporter that moves it across its [ ] gradient (low in blood)
- HCO3- disappears w/ Na+ into bloodstream
symport system at thick limb of LOH
- water-impermeable
- Na+-K+-2Cl- symporter is a protein allowing Na+ to walk down [ ] gradient which pulls in the other two solutes
- sodium [ ] fixed w/ ATP pump
- chloride leakage diffusion channel: as Cl- build up in cell, channel allows it to leak back into blood (water does not follow)
- potassium: can leak out from high to low [] back into filtrate and keep symporter running
- K+ leak channels may be present
- more Cl- than Na+ on side, helps drive cation movement across paracellular route (attractive forces)
sodium reabsorption in the collecting duct
- there are Na+ leak channels in the collecting duct
- Na+ [ ] regulated w/ ATP pump
- potassium may sometimes build up in blood (can be allowed to leak out of cell across apical membrane, leakage channels inserted there)
- if potassium needs to be conserved, leakage channels will be inserted on basolateral membrane (ensures return to blood)
what can happen from kidney failure?
salts and waste products like urea build up and the blood pH goes down
how does massive edema occur?
due to salt retention
acidemia
results from inability to secrete acids
what can occur with elevated potassium levels?
cardiac arrest b/c the heart depends on K to stabilize
- too much k on the outside of cell results in the heart having a hard time to maintain and reset RMP
structures of the bladder
detrusor muscle, ureteral openings, trigone, internal and external urethral sphincter, deep transverse perineus muscle, levator ani m
where is the bladder situated?
just behind the pubic symphisis/pubic bone