L20 Flashcards
Na+ Excretion =
Filtered Na - Tubular reabsorption of Na+
The kidneys try to adjust excretion to match ingestion of Na+
There is no Na being activly secreted therefore the amount of Na being filtered out of the body depends on the filtered load and tubular reabsorption
what factors affect tubular reabsorption of Na
theres 6 (5 and a 1/2)
• changes in Starling forces
– hydrostatic and oncotic pressures can alter GFR
- renin-angiotensin-aldosterone system
- renal nerve activity
• prostaglandins - PGE2 inhibits tubular Na+
reabsorption (blocks ENaC)
• atrial natriuretic peptide, plus other inhibitors of Na+/K+-ATPase - reduces Na+ reabsorption
what is an example of how renal nerve activity effects tubular reabsorption
sympathetic nerve stimulation to increase constriction of the afferent arteriole results in reduced GFR, therefore increased proximal and distal Na+ reabsorption
what is the equation for net glomerular filtration pressure
Starling forces
PUF = PGC - PBS - pGC
PGC = glomerular capillary hydrostatic pressure
πGC = glomerular capillary oncotic pressure
PBS = Bowmann’s space hydrostatic pressure
Relationship between selective changes in the resistance of either the afferent arteriole and efferent arteriole on renal blood flow (RBF) or GFR.
when and where would you get Constriction vs Dilation
Low Na diet and to want to increase the amount of Na maintained then you constrict the afferent arteriol to decrease the GFR
High Na then you constrict the efferent arterioles, this increases GFR
This constriction is done by nervous input
Increase in PGC = increase in GFR
when is ANP released and what does it do
when high BP - released from cardiac atria
reduces Na+ reabsorption by
increasing cGMP in the collecting ducts which
reduces Na+/K+-ATPase activity…decrease Na+
transport across the CD cells.
Which of the following statements is TRUE?
A. If the afferent arterioles are constricted the GFR will increase.
B. Atrial naturetic peptide decreases the tubular reabsorption of Na +.
C. If the efferent arterioles are constricted the GFR will decrease.
D. Na+ can be actively secreted by the cells of the collecting ducts
A. GFR will decrease
C. increase
D. Na is NOT actively secreted
B is correct
the juxtaglomerular apparatus has 2 cell types. what are they
Macula densa of
thick ascending limb
Granular (Juxtaglomerular)
cells
the macular dencer cells have what kind of function
Macula densa of
thick ascending limb
- osmoreceptor function
where/what are the Granular (Juxtaglomerular)
cells
they are the smooth muscle of the afferent arteriole
what is the function of the Granular (Juxtaglomerular)
cells
- baroreceptor function
- produces renin and
angiotensin II
what produces renin
• renin is produced and released from the granular (juxtaglomerular) cells of the juxtaglomerular apparatus
what produces aldosterone
produced by the adrenal cortex (zona glomerulosa cells); stimulated by angiotensin II
what is aldosterone
• aldosterone - mineralocorticoid hormone
what stimulates aldosterone to be produced
zona glomerulosa cells of adrenal cortex are stimulated by angiotensin II
where does aldosterone act and what does it do
• aldosterone increases Na+ reabsorption at the level of the late distal tubule and collecting duct
HOWEVER
ENaC is also in other areas of the body therefore Na is reabsorbed/absorption eg sweat glands, salivary glands which are all affected by aldosterone and therefore play a role in Na ballance
what secretes angiotensinogen
angiotensinogen is always in the blood and it is secreted by the liver
when renin is secreted from granular juxtaglomerular cells it acts as an enzyme. what does it do
converts angiotensinogen to ANG1
what convertes ANG1 to ANG2
ANG1 is converted to ANG2 by angiotensin converting enzyme which is secreted by the lungs
what causes aldosterone to be secreted
ANG2 has many effects and causes aldosterone to be secreted
where is angiotensin converting enzyme secreted from
secreted by the lungs
what happens when aldosterone binds to its receptor
altering gene expression causing upregulation of quiescent Na+ channels
• de novo synthesis of Na+ channels, Na+/
K+-ATPases and other induced proteins
(genomic effects)
• possible non-genomic effects
where is aldosterones receptor
Rone = steroid hormone therefore lipophilic
Crosses the basolateral membrane to bind to the mineralocorticoid receptor in the cytoplasm
what does SGK mean
SGK – serum
glucocorticoid
simulating kinase
what are the 3 phases of action of aldosterone
• Phase 1 – ‘latent’ period 0.5 - 1 hr -
de novo protein synthesis; induce
proteins (SGK)
• Phase 2 – ‘early response’ 1.5 - 3 hr -
activation of pre-existing Na+ channels and Na+/K+-ATPases (the channels that were quiescent)
• Phase 3 – ‘late response’ 6 - 24 hr -
induction of ‘new’ Na+ channels and
Na+/K+-ATPases
describe phase 1 of the of action of aldosterone
• Phase 1 – ‘latent’ period 0.5 - 1 hr -
de novo (new) protein synthesis; induce
proteins (SGK)
describe phase 2 of the of action of aldosterone
• Phase 2 – ‘early response’ 1.5 - 3 hr -
activation of pre-existing Na+ channels and Na+/K+-ATPases (the channels that were quiescent)
describe phase 3 of the of action of aldosterone
• Phase 3 – ‘late response’ 6 - 24 hr -
induction of ‘new’ Na+ channels and
Na+/K+-ATPases
what is Nedd42
Na channeles are not always in the membrane
Nedd42 is a regulation enzymes and leads to channels being removed from the membrane (cause ubiculatin)
what does SGK do
Low na causes aldosterone to be released which upregulates SGK which phosphorylates Nedd42 so that it can’t take ENaC out of the membrane
what upregulates SGK
aldosterone
Which of the following statements is TRUE?
A. The macula densa cells function as baroreceptors.
B. Aldosterone is a steroid hormone and binds to a receptor on the basolateral membrane of Late Distal Tubule and Collecting Duct cells.
C. Angiotensin II is cleaved by renin to produce Angiotensin I.
D. Renin is released from the granular (juxtaglomerular) cells of the afferent arteriole.
A. osmoreceptors
B. aldosterone acts of the late distal tubule and collecting duct BUT the receptor is in the cytoplasm
C. angiotensinogen is cleaved by renin to make ANG1
D is correct
