L20 Flashcards
Early distal tubule – budowa tkankowa wyjaśnic:
cuboidal epithelia, rich in mitochondria
Late distal tubule and collecting duct – budowa tkankowa wyjaśnic:
2 types of epithelia • Principal cells regulate Na+, K+ and water balance (ADH/aquaporins) • Intercalated cells regulate acid-base balance
Na+ reabsorption in distal tubule:
~…. of filtered Na+ is reabsorbed in the distal
tubule and collecting ducts
12%
The osmolarity of the tubular fluid decreases further as …. is impermeable to water ….
the apical membrane
~100 mOsmL-1
In the later part of the distal tubule and collecting ducts further Na+ reabsorption is linked to …
K+ secretion in principal cells (P cells)
N a+ enters (ENaC) and K+ leaves P cells via
channels in …
Na+ is pumped out into the intercellular space
and K+ enters P cells by the action of the Na+/K+ ATPase in ….
the apical membrane
the basolateral membrane
The capacity of P cells to reabsorb Na+ is regulated by … secreted from the….
aldosterone
adrenal cortex
Explain how does aldosterone work on P cells:
Aldosterone binds intracellular receptors
and the hormone-receptor migrates to the
nucleus where it stimulates the synthesis
of more:
- Na+ (ENaC) channels that become
inserted into the apical membranes - Na+/K+ ATPase that are inserted into
the basolateral membrane
The action of aldosterone is not immediate because it requires the
synthesis of new protein
As a result the effect is delayed by about an hour and can take anything
up to 5 days to reach maximum
How is the release of aldosterone from the adrenal cortex in response to low plasma [Na+] regulated?
The renin-angiotensin system
w dół [Na+]…………?………… w górę aldosterone
w dół [Na+]…………?………… w górę aldosterone
Juxtaglomerular apparatus - the production of ….
Explain it:
renin
When [Na+] in the distal tubule is low cells of the macula densa cause
the juxtaglomerular cells (modified smooth muscle cells) of the afferent
arteriole to secrete the proteolytic enzyme renin into the blood
Rozwiń skrót: (ANP)
Atrial naturetic peptide
When plasma volume is expanded sufficiently by the increase in total body Na+ the secretion of renin is …. by ….
inhibited
atrial naturetic peptide (ANP)
Atrial myocytes release ANP (28 aa) when … (acting as … )
they are stretched as in plasma volume expansion
acting as baroreceptors
ANP Promotes Na+ excretion (Natriuresis) by: (4)
- Inhibition of the renin aldosterone secretion
- At high doses causes afferent arteriolar vasodilation, increasing GFR
- Direct inhibition of Na+ reabsorption in the medullary collecting duct
- Decreased ADH secretion
Drinking water - osmolarity of the body fluid (plasma)….. and to …. the body needs to excrete ….
falls
rectify this
water
Drinking isotonic saline - the osmolarity of the body fluid (plasma) is …, total volume of the extracellular fluid (ECF) is …. . To rectify this the
body needs to excrete ….
unchanged
increased.
excess water and salts
Na+ is the …. ion in the ECF so is…. of the total body water
most abundant
the principal determinant
When the ECV falls the kidneys increase Na+ reabsorption via activation of …… .As angiotensin II stimulates ….., water intake
is …. and the ECV is ….
the renin-angiotensin
thirst
also increased
restored
When the ECV increases excretion of Na+ in the kidneys ….. This is brought about by … filtered load of Na+ and a …. in tubular absorption
increases
increased
decrease
!!! Osmolarity of body fluids is regulated by ….
osmoreceptors/ADH
ECF volume (ECV) is regulated by …
renin - angiotensin
Przypomnienie:
renin - angiotensin and osmoreceptors/ADH are regulated independently of each other !!!!
…% HCO3 - is reabsorbed in proximal tubule and loop of Henle
80-90
Intercalated cells of the distal tubule
1-2
How do Intercalated cells of the distal tubule (I cells) work?
1. H+ actively secreted by an ATP dependent pump into tubular fluid 2. pH of tubular fluid falls to 4-4.5 3. Conversion of HCO3 - to CO2 and water 4. CO2 diffuses into cell down concentration gradient 5. CA catalyses reformation of carbonic acid which dissociates into H+ and HCO3 - 6. HCO3 - transported into interstitial fluid by an HCO3 - /Clexchanger (apical membrane has a low permeability to H+)
Active secretion of H+ in the distal tubule can result in urine with a pH as low as …
4-4.5
If the average volume of urine produced per day is ….and pH 4 = 0.1 mM, then only …. mmol of free H+ can be excreted daily
This is not enough…
- 5 l
0. 15
How is the additional metabolic acid excreted?
The body normally produces about 15 mols of CO2 and 50 mmol of nonvolatile acid (remember dissolved CO2 in body fluid forms H+)
To maintain plasma [H+ ] within normal range CO2 is removed in the lungs and non-volatile acid via the kidneys
As mentioned before the total free H+ secreted by the tubules his very small, so the non-volatile acid is normally removed by buffering it with “urinary buffers” mainly phosphate or secreting ammonium ions.
Phosphate is derived from the diet, whilst ammonium salts are derived from the metabolism of glutamine in the proximal tubule (see earlier slide)
Summary of the renin-angiotensin (-aldosterone) system:
- When plasma [Na+] is low in distal tubule, macula densa cells cause granular cells of the afferent arteriole to secrete renin
- Renin converts the plasma peptide angiotensinogen (452 aa) into angiotensin I (12 aa)
- Angiotensin I is converted to angiotensin II (10 aa) by a converting enzyme found on the capillary endothelium of the lungs and other
vascular beds. - Angiotensin II acts of zona glomerulosa of the adrenal cortex causing the secretion of the hormone aldosterone in to the blood.
- Aldosterone has numerous effects including increasing reabsorption of Na+ by the distal tubule.
LO: The transport mechanisms in the distal tubule
.
LO: The renin-angiotensin system in the regulation of Na+ balance
.
LO: The importance of Na+ balance in the control of extracellular fluid volume
.
LO: The mechanism of acid secretion
.
LO: Acid-base balance and the maintenance of plasma pH
.
You are expected to read:
Pocock, Richards and Richards, Human Physiology:
2nd edition: pp405-407, 614-618 & 635-638
3rd edition: pp364-367, 549-553 & 568-571
4th edition: pp526-529, 543-548 & 565-570
.
