Most reabsorption occurs here.
Glucose, amino acids, at least 2/3 Na Cl and h2o (aquaporin 1) in isosmotic amounts.
2/3 of Ca
30% of Mg
80% of phosphate
50% of urea.
lactate citrate and other kerb's cycle intermediates and vitamins
Uptake of filtered proteins (multiligands or endocytic ligands)
Synthesis of ammonium
Divided into 3 segments
S2- secrete organic acids and bases
S3 - Straight proximal tubules
Early segments have loads of microvilli, hence rapid transcullular transport, paracellular pathway is leakier.
Later segments have slower rates of transcelullar reabsorption and paracellular pathways are tighter. i.e opposite.
1.2 Peritubular Reabsorption
Much lower than glomerular filtration
1.3 Glomerulotubular Balance
Constantcy of the fraction of sodium reabsorbed by proximal tubule despite changes in GFR
Due to change in peritubular Starling's forces.
Changes in filtered load of glucose and amino acids.
2 Loop of Henle
2.1.1 Thin Descending Limb
Very permeable to H20 due to AQP1
Maybe permeable to NaCL or urea.
Therefore, as stuff pass thru, water leaves lumen and osmolality increases.
In cortical nephrons 600mOSM/kg
2.1.2 Thin ascending limb
Impermeable to water
Highly permeable to NAcl and moderately permeable to urea.
No active transort.
Fluid becomes more dilute.
2.2 Thick Ascending
Impermeable to water, low urea permeability
Active NaCl transport.
Reabsorb Hco3 by H+ secretion
Low osmolality at end of thick aLH
3 Distal Convoluted Tubule and Connecting Tubule
Similar in function, connecting tubule is sensitive to several hormones
They are water impermeable,
low urea permeability, active NaCL reabsorption.
4 Collecting Duct
Made up of 2 cell types
Na reabsorption and K secretion
Responds to aldosterone and ADH
a intercalated cells reabsorb K and secrete H
b intercalated cells secretes Hco3
Without ADH, no water goes.
If ADH water goes into/
Only papillary segment is permeable to urea.
via UTA1 and UTA3 urea transporters
Stimulated by ADH
5 Water Balance
Water inputs from food, oxidation of food or liquid intake.
Water outputs form insensible loss, sweat, faeces, urine
Water balance is regulated by, thirst and drinking, the kidneys, inhibit or stimulate ADH
REgulated in specific areas in hypothalamus, with aid from cerebral cortex
Stimulated by increased osmolality
Fall in extracellular volume
Dryness of mouth and throat.
Dilute rine is achieved by taking solute out and leaving water behind.
From thin ascending loop of hence.
If there no ADH in collecting duct, it is water impermeable.
Thin/thick alb and DCT are always water impermeable.
To make a concentrated urine, it must have ADH and high medullary osmolalityh, so it makes collecting tubule collect water.