L23 - Renal Function 2: Filtration & Clearance

Question 1

Why is inulin the ideal substance for determining glomerular filtration rate?

Answer 1

it is not reabsorbed, it is not secreted, it is exogenous and it is not metabolised

Question 2

If there are 4 units of inulin in 100 mL of plasma and 4 units per minute are appearing in the urine, how much plasma is being filtered every minute?

Answer 2

100 mL of plasma is being filtered every minute

Question 3

What is renal clearance?

Answer 3

rate of urinary excretion of a substance, relative to its plasma concentration

Question 4

If plasma concentration of urea was 4/100 mL, GFR was 100 mL/min and 50% of the urea was reabsorbed, then urea clearance would be:

Answer 4

50 mL/min

Question 5

If the clearance of X is less than GFR, then (X is being secreted by the nephron / X is being reabsorbed by the nephron, more X is being secreted than reabsorbed / non of the above)

Answer 5

X is being reabsorbed by the nephron

Question 6

What normally happens to GFR if mean arterial pressure increases from 90 to 110 mmHg?

Answer 6

it doesn’t change

Question 7

Why doesn’t GFR change when arterial pressure increases from 90 to 110 mmHg?

Answer 7

autoregulation maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mmHg

Question 8

Which components are involved in autoregulation of GFR?

Answer 8

myogenic response and tubuloglomerular feedback

Question 9

How does the Macula densa respond to increased GFR?

Answer 9

releases a paracrine that results in constriction of the afferent arteriole

Question 10

What is the Macula densa?

Answer 10

structure found in the nephron through which the afferent arteriole travels before reaching the glomerulus

Question 11

What is tubuloglomerular feedback and how does it respond to GFR?

Answer 11

response of the Macula densa to increased GFR
results in release of a paracrine which constricts the afferent arteriole and decreases hydrostatic pressure in the glomerulus

Question 12

What can renal excretion be altered by?

Answer 12

renin-angiotensin system, sympathetic nervous system, atrial natriuretic peptide and vasopressin

Question 13

Is the sympathetic nervous system activated when blood pressure increases or decreases?

Answer 13

when blood pressure decreases

Question 14

Will the renin-angiotensin system and the sympathetic nervous system be used to excrete or reabsorb sodium?

Answer 14

reabsorb sodium

Question 15

Will atrial natriuretic peptide be used to excrete or reabsorb sodium?

Answer 15

excrete sodium

Question 16

When is the renin-angiotensin-aldosterone system activated?

Answer 16

when there is a drop in blood pressure

Question 17

What happens when renin is released from granular cells?

Answer 17

renin travels around the body until it comes into contact with the liver which releases angiotensinogen -> angiotensin I is formed which comes into contact with the lungs and is converted by ACE into angiotensin II

Question 18

What does angiotensin II do to arterioles?

Answer 18

constricts arterioles to increase blood pressure

Question 19

What happens when angiotensin II interacts with the adrenal gland?

Answer 19

adrenal gland releases aldosterone which assists in regulating sodium balance

Question 20

Where does aldosterone act on the nephron?

Answer 20

aldosterone acts on the collecting duct which results in increased sodium reabsorption

Question 21

Will angiotensin II receptors most likely be located in the afferent or efferent arteriole of the nephron in order to maintain GFR?

Answer 21

efferent arteriole as angiotensin II will result in constriction and therefore regulation of GFR

Question 22

How does noradrenaline affect the afferent arteriole?

Answer 22

constricts the afferent arteriole to reduce renal blood flow which decreases GFR

Question 23

How is GFR maintained during exercise?

Answer 23

RAAS is activated and angiotensin II constricts the efferent arteriole + effect of all other regulation systems

Question 24

Is renal function a priority of the sympathetic nervous system?

Answer 24

no