kidney 2 Flashcards
blood in the Bowmans capsule entering proximal convoluted tubules
blood without cells, platelets, or big proteins
still has the same osmolarity, ions, glucose, amino acids, small proteins, urea etc.
tubular reabsorption
highly selective
- 100% of sugars and 99.5% of salts reabsorbed
- only excess amounts of required substances are not reabsorbed
- waste products are not reabsorbed and eliminated as urine
paracellular path
fluid and solutes can squeeze between cells
free reabsorption when pulled through osmotic gradients
common in the proximal convoluted tubule
transcellular path
goes across apical and basal membrane
may be facilitated fission or osmosis, may also be active transport, may also be secondary active transport
active transport
sodium, hydrogen, potassium, calcium, magnesium
mostly sodium, gradient used to drag things coupled with sodium
secondary active transport
glucose, amino acids
sodium used to power glucose and amino acids co transporters
also used for chloride and proton balance
pinocytosis
when small proteins leak through glomerular capillaries
reabsorption of amino acids
active - uses ATTP
by receptors and also random
active transport is saturable
Tmax
anything involving a carrier or pump has a maximum rate of activity
important for diabetes mellitus - saturated glucose transporters which causes glucose to be lost to urine
only important in pathological states
passive transport
CL, urea, phosphate, sodium, calcium, magnesium, water
cannot be saturated, rate dictated by
- electrochemical gradient
- permeability
- time
anion drag NA+ created passive Cl- reabsorption
urea
- resorption of everything else in the tubule creates a urea gradient, favouring urea resorption
osmosis
- leafiness is regulated by tight junctions and aquaporins
- PCT - very leaky so water follows quickly, no time to establish osmotic gradient from Na pumping
ascending loop of Henle
has no aquaporins
has tight junctions between cells
osmolarity can be changes
DCT/CT/CD
distal convoluted tubule, collecting tubule and collecting duct variable permeability
segmentation of nephron function - Na reabsorption
most reabsorbed immediately passively and actively at proximal convoluted tubule
1/4 reabsorbed at the loop of henle - obligatory, not regulated
regulated by hormonal control at the distal tubule, small portion of sodium reabsorption
reabsorption of glucose, amino acids and small proteins in the nephron
all nutrients reabsorbed in the proximal tubule
endocytosis also occurs here to recapture proteins
H2O reabsorption
mostly reabsorbed in the proximal tubule because it follows sodium
loop of henle dilutes the renal filtrate by reabsorbing more sodium than water
water may be reabsorbed in the distal tubule or collecting duct - depending on hormonal ocontrol
proximal convoluted tubule
2/3 of sodium, chloride, potassium, water
100% of glucose and amino acids
secretes wastes, and protons
extensive brush border to increase surface area for exchange
heterogeneity of the PCT
first half - Na resorbed by co-T with glucose, amino acids
second half - little glucose and AAs remain, Na reabsorbed with Cl
secretions at the proximal convoluted tubule
NH3, bile salts, oxalate, urate, catecholamines, penecillin, salicylates, creatinine, etc
does omolality change across the PCT
no
reabsorbing sodium but equally reabsorbing water so osmolality doesn’t change
loop of henle
- descending - thin - no brush borders, few mitochondria, and minimal levels of metabolic activity, highly permeable to water, doesn’t not pump any salts only water moves due to many aquaporins
- ascending - thick - no aquaporins, impermeable to water, active resorption of sodium, chloride, and potassium
thick ascending limb
powered by sodium potassium pumps
sodium 2 chloride potassium co transporter - drags 2 chlorides and 1 potassium when a sodium is allowed through
a leaky potassium channel lets a lot of potassium out
an electrical gradient is established which its used to drag cations through paracellular diffusion - brings magnesium, calcium
sodium 2 chloride potassium co co transporter
drags 2 chloride and 1 potassium for every sodium that is allowed through
is a salt sensor - what is used to sense salts to regulate tubular glomerular feedback
dilution of tubular fluid
impermeable to water and losing ions - therefore becomes very dilute
distal convoluted tubule
2 cell types
- intercalated cells - secrete protons
- principle cells - reabsorb sodium and secrete potassium
later distal collecting tube and cortical collecting duct
- reabsorb sodium, secrete potassium - aldosterone
- H+-ATPasse secretes H+
- H2O permeability controlled by ADH - impermeable->permeable
- impermeable to urea - almost all the urea that enters these segments passes on to CD - excreted in the urine (exc. some urea reabsorption in medullary CDs)
medullary collecting duct
- reabsorbs <10% off the filtered water/Na
- final site for processing urine
- same functions of DCT/CCT, variable H2O permeability (ADH), can secrete H+
- unlike the cortical CT - urea is permeable
- urea is reabsorbed into medullary interstitium, increased osmolarity in this region - concentrated urine
producing dilute urine
thick ascending limb is waterproof and salts are reabsorbed, when kept waterproof, urine will be dilute
producing concentrated urine
- open aquaporins
- obligatory urine volume - some fluid required
- selective waterproofing - leaky distal collecting tubule, collecting tubule and collecting duct - so H2O is reabsorbed from the normally impermeable tubule segments
- a hyper osmotic renal medullary interstitial - provides the osmotic gradient for H2O resorption
generating hyper osmotic medullary interstitium
- urea impermeable ascending loop of henle, distal collecting tubule, collecting tubule
- water reabsorbed from distal collecting tubule, rapidly increases concentration of urea
- urea permeable inner medullary collecting ducts
- urea diffuses into the renal interstitium
- urea transporters
maintains increased urea concentration in the tubular fluid even though urea is being reabsorbed
why don’t peritubular capillaries dilute the medullary gradient
- the medullary blood flow is low - if there was normal flow salts would be picked up and carried out of the kidney
vasa recta blood flow is so slow that the blood is able to equilibrate - vasa recta countercurrent exchange - minimises solute washout
