L20

Question 1

Na+ Excretion =

Answer 1

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

Question 2

what factors affect tubular reabsorption of Na

theres 6 (5 and a 1/2)

Answer 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

Question 3

what is an example of how renal nerve activity effects tubular reabsorption

Answer 3

sympathetic nerve stimulation to increase constriction of the afferent arteriole results in reduced GFR, therefore increased proximal and distal Na+ reabsorption

Question 4

what is the equation for net glomerular filtration pressure

Answer 4

Starling forces

PUF = PGC - PBS - pGC

PGC = glomerular capillary hydrostatic pressure

πGC = glomerular capillary oncotic pressure

PBS = Bowmann’s space hydrostatic pressure

Question 5

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

Answer 5

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

Question 6

when is ANP released and what does it do

Answer 6

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.

Question 7

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

Answer 7

A. GFR will decrease

C. increase

D. Na is NOT actively secreted

B is correct

Question 8

the juxtaglomerular apparatus has 2 cell types. what are they

Answer 8

Macula densa of
thick ascending limb

Granular (Juxtaglomerular)
cells

Question 9

the macular dencer cells have what kind of function

Answer 9

Macula densa of
thick ascending limb
- osmoreceptor function

Question 10

where/what are the Granular (Juxtaglomerular)

cells

Answer 10

they are the smooth muscle of the afferent arteriole

Question 11

what is the function of the Granular (Juxtaglomerular)

cells

Answer 11

• baroreceptor function
• produces renin and
  angiotensin II

Question 12

what produces renin

Answer 12

• renin is produced and released from the granular (juxtaglomerular) cells of the juxtaglomerular apparatus

Question 13

what produces aldosterone

Answer 13

produced by the adrenal cortex (zona glomerulosa cells); stimulated by angiotensin II

Question 14

what is aldosterone

Answer 14

• aldosterone - mineralocorticoid hormone

Question 15

what stimulates aldosterone to be produced

Answer 15

zona glomerulosa cells of adrenal cortex are stimulated by angiotensin II

Question 16

where does aldosterone act and what does it do

Answer 16

• 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

Question 17

what secretes angiotensinogen

Answer 17

angiotensinogen is always in the blood and it is secreted by the liver

Question 18

when renin is secreted from granular juxtaglomerular cells it acts as an enzyme. what does it do

Answer 18

converts angiotensinogen to ANG1

Question 19

what convertes ANG1 to ANG2

Answer 19

ANG1 is converted to ANG2 by angiotensin converting enzyme which is secreted by the lungs

Question 20

what causes aldosterone to be secreted

Answer 20

ANG2 has many effects and causes aldosterone to be secreted

Question 21

where is angiotensin converting enzyme secreted from

Answer 21

secreted by the lungs

Question 22

what happens when aldosterone binds to its receptor

Answer 22

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

Question 23

where is aldosterones receptor

Answer 23

Rone = steroid hormone therefore lipophilic

Crosses the basolateral membrane to bind to the mineralocorticoid receptor in the cytoplasm

Question 24

what does SGK mean

Answer 24

SGK – serum
glucocorticoid
simulating kinase

Question 25

what are the 3 phases of action of aldosterone

Answer 25

• 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

Question 26

describe phase 1 of the of action of aldosterone

Answer 26

• Phase 1 – ‘latent’ period 0.5 - 1 hr -
de novo (new) protein synthesis; induce
proteins (SGK)

Question 27

describe phase 2 of the of action of aldosterone

Answer 27

• Phase 2 – ‘early response’ 1.5 - 3 hr -

activation of pre-existing Na+ channels and Na+/K+-ATPases (the channels that were quiescent)

Question 28

describe phase 3 of the of action of aldosterone

Answer 28

• Phase 3 – ‘late response’ 6 - 24 hr -
induction of ‘new’ Na+ channels and
Na+/K+-ATPases

Question 29

what is Nedd42

Answer 29

Na channeles are not always in the membrane

Nedd42 is a regulation enzymes and leads to channels being removed from the membrane (cause ubiculatin)

Question 30

what does SGK do

Answer 30

Low na causes aldosterone to be released which upregulates SGK which phosphorylates Nedd42 so that it can’t take ENaC out of the membrane

Question 31

what upregulates SGK

Answer 31

aldosterone

Question 32

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.

Answer 32

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