Renal System Flashcards
Filtration
occurs within the renal capsule and the forces involved in filtration are blood pressure, capsular pressure and colloid osmotic pressure. Blood plasma is filtered from the arterial system into the lumen of the nephron. Formed elements (red and white blood cells) are not filtered.
renal fraction
The portion of the total cardiac output that flows through the kidneys
- 12-30% (average 21%)
glomerular filtration rate
amount of filtrate formed in all the renal corpuscles of both kidneys each minute
180L/day
Filtration Fraction
part of plasma that is filtered into lumen of Bowman’s capsules; average 19%
Average urine production/day
1-2L. Most of filtrate must be reabsorbed
filtration membrane
Keeps proteins and blood cells out of Bowman’s capsule. Mostly ions, water, fluids will enter since the membrane is permeable to smaller molecules.
filtration pressure
pressure gradient responsible for filtration; forces fluid from glomerular capillary across membrane into lumen of Bowman’s capsules
glomerular capillary pressure
blood pressure in glomerular capillary move fluid from blood into bowman’s capsule
(positive pressure system)
capsule pressure
pressure from lumen of Bowman’s capsule moves fluid from Bowman’s capsule into glomerular capillary
- push back on fluid trying to enter since there is already some there
- stops filtration
blood colloid osmotic pressure (BCOP)
The largest driving force for pulling fluid from the interstitial spaces back into the capillaries due to osmotic pressure of colloids in the blood
- greater at end of glom.caps than beginning
- negative pressure system in urine system
Filtration Pressure (FP)
FP = GCP - BCOP - CP
- Net flow if it’s positive
- No net flow if it’s negative
glomerular nephritis
proteins enter the filtrate and filtrate exerts an osmotic pressure, increasing volume of filtrate
high glomerular capillary pressure
is due to:
- low resistance to blood flow in afferent arterioles
- low resistance to blood flow in glomerular capillaries
- high resistance to blood flow in efferent arterioles (smaller diameter)
Increase filtration
dilate afferent arteriole (enter nephron) and constrict efferent arteriole (leave nephron) = increase GCP = increase FP = increase filtration
reabsorption in proximal tubule
- active transport moves Na from basilar membrane of PCT cell into If, which makes a concentration gradient out of the cell into IF, which Na follows from the apical membrane out
- filtrate volume reduced by 65% due to osmosis
- thru apical membrane: Na, Cl, glucose, AA, water
- thru basilar membrane (cotransport): Na, K, Cl, glucose, AA, water
Reabsorption in Loop of Henle
- LH descends into medulla; IF is high in solute = water moves out of lumen
- DLH is permeable to water, ALH is to solutes
- solutes leave ALH and enter descending vasa recta (Na by active transport then conc gradient of Na, K, Cl)
-Reduce volume by another 15% (80% total so far) - inside nephron = 100mOsm/kg
Cortex = 300mOsm/kg
Filtrate within DCT is more dilute than IF
reabsorption of DCT and CT
- Na from filtrate to tubule cells via conc gradient, then out of cell via active transport
- collecting duct from cortex into medulla
- water follow conc gradient from DCT and CD into IF
- DCT and CD have variable water permeability
solute concentration in nephron
- volume of filtrate decrease = urea conc increase
(40-60% urea reaborped into nephron) - urate ions, creatine, sulfate, phosphates, nitrates are highly toxic and need to be eliminated
tubular secretion
- Ammonia
- H, K, penicillin, PAH
secretion of H and K
- H secreted into filtrate by either peritubular caps into IF then epithelial cells of tubule or as a byproduct of HCO3
- ## Na and HCO3 cotransported out into peritubular caps
- H and K secreted into filtrate by countertransport in DCT ; Na and K by active transport; Na and HCO3 cotransported then diffuse into peritubular caps
urine production
in PCT: Na, etc, removed; water passively follow; filtrate volume reduced
in DLH: water exit passively, solute enter; filtrate reduced
in ALH: Na, Cl, K move out, water stays in
in DCT and CD: if ADH present water not reabsorb and urine diluted
urine concentration mechanism
lots of water: remove waste w/o rid of electrolytes = kidneys make lots of urine
dehydrated: kidneys make small volume of highly concentrated urine; removes waste
Urine variable concentration
- maintain high solute concentration in medulla
- countercurrent of LH
- control permeability of distal nephron
medullary concentration gradient
- concentrate urine/prevent large water loss kidneys maintain lots of solute in medulla
- IF conc is 300 in cortical region and 1200 at tip of pyramid
- depends on: LH and vasa recta countercurrent and distribution/recycle of urea
loops of henle
- DLH permeable to water (move out into IF)
- ALH permeable to solutes (move out in thin segment)
- Na, K, Cl active transport out of ALH into IF = water follows out (down conc gradient)
- since water has left the LH it is more concentrated with solute to travel into the medulla
countercurrent system
the LH and VR flow in opposite directions of each other
- water leave DLH and enter AVR
- solute out of ALH (thin) and enter DVR
- solutes out of (thick) ALH and enter DVR
- filtrate reduced to 100mOsm/kg at DCT
vasa recta
- remove excess water and solute from medulla
- walls permeable to water and solutes (blood flow towards medulla = water out and solute in)
- top of AVR and DVR are 300; bottom is 1200
- DVR: water out, solute in
- AVR: water in, solute out
- slightly more water and solute carried by medulla
urea
- reabsorbed from collecting duct into filtrate of DLH (permeable to urea)
- 40-60% passively diffuse out of CD into filtrate (urea constantly saturated headed to medulla)
- flows in cycle to maintain high conc in medulla
ADH and nephron
ADH bind to its receptor on tubular cell, which activated the G-protein, which activates adenylate cyclase, which increases water’s permeability to leave the nephron cell
- reduces flow of urine. controlling V and BP will go up
renin-angiotensin-aldosterone system
- renin (from kidney) > angiotesin (liver) into angiotesin II > adrenal cortex > increase K and aldosterone
- concentrates urine by reduce urine and increase plasma
- increase extracellular Na so water will follow
aldosterone
makes Na active transport out and K in = increase Na levels out therefore water leaves cell to be picked up by vasa recta
- decreases V
atrial natriuretic hormone (ANH)
- produced by RA when it gets too full (high BP)
- inhibit Na reabsorption and ADH production (now water not escape)
- increase urine volume production
- low venous return = low RA pressure
autoregulation
as systemic BP increases afferent arterioles dilate and prevent increase in renal blood flow
- increased blood flow of filtrate past macula densa sends signal to juxtamedullary apparatus to dilate afferent arterioles
sympathetic stimulation
norepinephrine (fight/flight)
- constrict small arteries and afferent arterioles = stop blood flow to kidney to reroute to more important muscles
- decrease renal blood flow and filtration formation
plasma clearance
volume of plasma cleared of a particular substance per minute
- estimate GFR and renal plasma flow
- which drugs/substances excreted by kidney
tubular load
total amount of substance that passes through filtration membrane into nephrons each minute
tubular maximum
max rate substances can be reabsorbed
- each substance has its own max
- glucose is generally lower than max unless diabetic
micturition reflec
-Enough stretch on walls and lots of frequency (signals from bladder per second) then micturition reflex (internal sphincter open and bladder contract)
-Sacral region
