18 - Renal Tubules (online) Flashcards
roughly how much filtrate is produced in one day and what happens to it?
180L per day
- 179L reabsorbed
- 1 to 2L converted to urine
what is reabsorbed, partially reabsorbed or excreted in the urine?
only the most important ones
completely reabsorbed:
- glucose, amino acids, bicarbonate ions…
partially reabsorbed (regulated):
- water, sodium, potassium, chloride…
- urea (mostly excreted)
excreted:
- creatinine, drugs and drug metabolites
in healthy individuals, pathologies can change this (eg: diabetes)
compounds found in filtrate and lost in urine in a day
only need to vaguely know the ratios (table in GN)
Glucose: 162g F - none U (100% reabsorbed)
Sodium: 570g F - 4g U (>99% reabsorbed)
Uric acid: 8.5g F - 0.8 U (>99% reabsorbed)
Creatinine: 1.6g F - 1.6g U (0% reabsorbed)
Renal tubules
permeability and absorption differences
PCT: water permeable (most reabsorption here)
- glucose symporters (absorption)
- Na/H+ antiporters (H+ excretion)
D-LOH: water permeable
thick limb of A-LOH: impermeable to water
- Na-K-2Cl symporters (absorption)
- Cl- leakage channels (absorption)
- K+ leakage channel (excretion)
DCT: impermeable to water
CD: variably permeable to water
- Na leakage channels (absorption)
- K leakage channels (absorption)
blood supply inside the kidney
GN quiz
- from arcuate artery
- radial artery
- afferent arteriole
- efferent arteriole
- peritubular capillaries
- vasa recta (connecting branches)
- arcuate vein
reabsorption of water (renal)
(mechanisms and % reabsorbed through each)
water moves by osmosis
- follows it’s concentration gradient through semipermeable membrane
- driven by concentration of solutes in tubules vs interstitial fluid (high [solute] brings water when moving to low [solute])
90% reabsorption is obligatory (dragged by solutes)
- mostly in PCT and D-LOH
10% is facultative (changes depending on amount required)
- ADH makes collecting duct more permeable to water (allowing it to leave the duct to the body, urinate less)
solute absorption mechanisms
basic methods, not for specific solutes
most active area is PCT
paracellular (between tight junctions of cells)
transcellular (in and out of tubule cells):
- active transport (requires energy)
- primary: uses ATP alone
- secondary: uses energy and movement of other ions
- symporter: ion and molecule in same direction
- antiporter: ion and molecule in opposite direction
- diffusion (down concentration gradient)
- simple (through cell wall)
- facilitated (by transport proteins)
sodium reabsorption mechanisms
Passive:
- paracellular (small amount) lumen to interstitial fluid
- diffusion from lumen to cell
Secondary Active transport
Cell to interstitial fluid:
- sodium potassium pump - antiporter: 3Na for 2K
Lumen to cell:
- PCT- glucose symporter: 1 glucose and 2Na
- glucose into IS fluid by passive facilitated diffusion
- PCT- Na+/H+ antiporter: 1Na+ for 1H+
- bicarbonate produced, passive facilitated diffusion to IS fluid
- thick limb LOH- Na-K-2Cl symporter
- Cl leakage channel to IS fluid
- K leakage channel back to lumen
Leakage channels
- Collecting duct - Na from lumen to cell
Main consequences of kidney failure
- acidocis (low blood pH) due to build up of salts and ions
- edema (fluid build up) due to salt retention
- high potassium levels (hyperkalemia) can lead to cardiac arrest
female anatomy for urination
GN quiz
- ureter
- ureteral opening
- bladder
- detrusor muscle (smooth - involuntary)
- urethral opening
- trigone (area that remains relaxed, isn’t contracted by muscle)
- external urethral sphincter (striated - voluntary)
- deep transverse perineus muscle
- levator ani muscles
the micturition reflex
- bladder fills with 200-400mL of urine
- stimulates stretch receptors
- triggers autonomic reflex
- contract detrusor muscle
- (males only) relax internal urethral sphincter
- concious decision to relax urethral sphincter or keep it closed
- if pressure continues to build, muscle cannot keep it closed
