Regulation of GFR, potassium and blood pressure

Question 1

What is GFR?

Answer 1

Glomerular filtration rate

- Volume of fluid filtered from the glomerular capillaries into Bowman’s space per minute.

Question 2

What happens if GFR is too high or too low?

Answer 2

• Too high - Too much filtrate, and increased urine production. Needed substances pass too quickly through tubules, insufficient reabsorption lost in urine
• Too low - Too little filtrate. Reduced flow of filtrate. Certain waste substances may not be excreted

Question 3

How does GFR change by changing the resistance of the afferent arteriole?

Answer 3

• GFR decreases when afferent arteriole constricts

* GFR increases when afferent arteriole dilates

Question 4

By which two mechanism do changes in the resistance of the afferent arteriole occur?

Answer 4

1) Tubuloglomerular feedback

2) Myogenic response

Question 5

Which cells detect flow of filtration rate?

Answer 5

Macula densa cells

Question 6

Name the signal caused by macula densa cells leading to changes in GFR

Answer 6

Paracrine signal - increase or decrease GFR (not vasoconstriction or vasodilation)

Question 7

What happens in the myogenic response when there is an increase in blood pressure of the afferent arteriole?

Answer 7

• Increased GFR

- Vasoconstriction to decrease GFR

Question 8

How are potassium levels regulated?

Answer 8

• 100% of potassium is filtered and ALL of this is reabsorbed via PCT and LOH

Question 9

Which hormone regulates potassium?

Answer 9

Aldosterone released from the adrenal gland

Question 10

What is released in response from a decrease in blood pressure and from where?

Answer 10

Renin from juxtaglomerular cells

Question 11

What are the functions of aldosterone?

Answer 11

• Stimulates principle cells to secrete more potassium
• More water is reabsorbed as more sodium and chlorine are reabsorbed
• Blood volume increases
• Increased venous return and stroke volume

Question 12

What stimulates aldosterone release?

Answer 12

Decreased blood pressure and increased potassium

Question 13

What are the systemic vasoconstriction effects of GFR?

Answer 13

• constriction of afferent arteriole decreases GFR

Question 14

Describe the mechanism of how decreased blood pressure affects renin secretion

Answer 14

• decrease GFR
• increased sympathetic activity from the CV centre
• macula densa and juxtaglomerular cells cause renin release

Question 15

How does constriction of the efferent arteriole stop there being a large fall in GFR when the afferent arteriole if constricted?

Answer 15

• reduces blood flow to glomerular capillaries
• increased hydrostatic pressure, helps preserve GFR
• relatively small decrease in GFR

Question 16

What are the systemic effects of ANGII release in response to a decrease in blood pressure?

Answer 16

• arterioles vasoconstrict
• adrenal cortex secretes aldosterone
• Hypothalamus ADH secretion & increased thirst
• Medulla oblongata reflexes to blood pressure

Question 17

What are the effects on GFR of ANGII release in response to a decrease in blood pressure?

Answer 17

• Overall decrease as decreases blood flow in afferent arteriole and GFR
• GFR preserved to a degree because constriction of efferent arteriole helps preserve hydrostatic pressure