Loop Of Henle, DCT, Collecting Tubules Flashcards
……of Na & Cl,……of water, ……of HCO3- is reabsorbed in loop of Henle
25%
15%
10%
GR: K appears in urine although it is completely reabsorbed in loop of Henle
Due to secretion by DCT & CD
GR: ASCENDING loopf if Henle in known as diluting segment
As it retains water inside it causing osmolarity to drop of 100 mOsm at its end
Comparecpermeability if asc & desc loops of Henle
Desc: highly permeable to water but realtively impermeable to solutes including urea & Na
Asc: impermeable to water
In the thin ascending loop of Henle NaCl is reabsorbed by……..while in thick part the process is……by…&…(carriers)
Passive diffusion
Active
Na/K/2Cl cotrabsported & Na/H+ counter-transporter
The lumen of loop of Henle charge is…..
What is the result?
+8 mV
Mg & Ca diffuse from lumen to the interstitial fluid via the paracellular pathway
Mode of inheritance of Bartter’s syndrome is……caused by……results in…..
Autosomal recessive
Impaired function of Na/K/2Cl or K channels in luminal membrane or chloride channels in basolateral membrane
Mild hypovolemia, RAAS activation, hypokalemia, metabolic alkalosis
…….make the final adjustment of electrolyes & pH
DCT & CD
Describe events occurring in initial part of DCT
It reabsorbs most of ions including Na & Cl but is impermeable to water & urea.
It is called diluting segment because it also dilutes tubular fluid (osmolarity dec to 80 mOsm)
Mention events occurring in late part of DCT & CD
- Na+ reabsorption by aldosterone in exchange for K+ & H+
- Cl- reabsorotion either by passive diffusion or 2ry active co-transport with Na+
- Only 5% of filtered water is reabsorbed in late part of DCT & the osmolarity at its end and at beginning of CD is isosmotic (300 mOsm). This process is under control of vasopressin. This is called facultative water reabsorption.
Describe mechanism of actions of ADH
It acts on late DCT & CD, increases their permeability to water as it binds V2 receptor and activates Gs causing activation of adenyl cyclase and inc cAMP which activates PKA causing phosphorylation of several proteins allowing supapical vesicles containg aquaporin to fuse with apical membrane in principal cells inc permeability to water. So, water passes passively down the osmotic gradient in the hypertonic medullary interstitium created by counter current mechanism.
Describe H+ secretion in CT & CD
H+ is secreted mainly by 1ry active transport at luminal border by ATPase carrier or may be in exchange for K+ in cause of hypokalemia or acidosis.
-Bicarbonate diffsues at basolateral border in exchange for Cl-
-Bicarbonate is formed by intracellular carbonic anhydrase enzyme also H+ is formed
-H+ is secretion into lumen will stop if pH reaches 4.5 (limiting pH) but it is titrated by NH3 & HPO4- which is necessary in cases of acidosis to ensure loss of hydrogen in urine. This is Necessary in cases of acidosis to ensure loss of H+ in urine, as the role of bicarbonate is limited as 90% is reabsorbed in PCT & 10% in loop of Henle.
Describe secretion of K+ in DCT & CD
- Actively secreted, it is the source of urine K+ as most is reabsorbed before it
- K+ comes from peritubular capillaries and diffuses to interstitium by diffusion (passive) then its cellular entry occurs actively coupled to Na transport to interstitium (Na+/K+ pump). K+ diffuses from tubular cells to lumen passively (under conc gradient)
It is regulated by aldosterone
……is secrete in DCT & CD to combat acidosis
Ammonia
Mention the functional characteristics of distal tubule & cortical collecting duct
- Impermeable to urea compared to inner medullary CD
- Reabsorb Na & Cl- follows passively
- Actively secrete Ka+
- Intercalated cells of these nephron segments secrete hydrogen ions by 1ry active transport by H+-ATPase mechanism both H & K compete for secretion.
The rate of 2, 3 & 4 is under effect of aldosterone - Permeability of late distal tubuke & CCD to water is controlled by ADH but in its absence they are impermeable to water, this help control of urine concentration.
