Control of Blood Pressure

Question 1

What is the goal of the kidney?

Answer 1

Homeostatic control of blood volume and blood pressure

Question 2

Changes in blood pressure signal the release of which hormones?

Answer 2

ADH: increases fluid reabsorption
ANP: increases fluid excretion

Question 3

How do kidneys measure blood pressure?

Answer 3

Kidneys measure GFR as a proxy for systemic blood pressure

Question 4

How does the glomerular filtration rate (GFR) provide a proxy measure for systemic BP?

Answer 4

Increase in blood pressure -> increase in GFR

Decrease in blood pressure -> decrease in GFR

Question 5

What is GFR?

Answer 5

Glomerular Filtration Rate: the rate at which blood is filtered through the glomerulus an into the Bowman’s capsule

Question 6

What is the function of the juxta-glomerular apparatus?

Answer 6

Connects the DCT with the glomerulus

Measures and responds to changes in Na+ concentration in the filtrate

Question 7

Where are macula densa cells located?

Answer 7

DCT

Question 8

What are the 3 components of the juxta-glomerular apparatus?

Answer 8

1. Macula densa cells
2. Juxtaglomerular cells
3. Mesangial cells

Question 9

What do macula densa cells do?

Answer 9

Detect sodium concentration

Question 10

What do juxtaglomerular cells do?

Answer 10

Adjust the diameter of the afferent arteriole

Question 11

What are mesangial cells?

Answer 11

Supporting cells

Question 12

Describe the juxta-glomerular apparatus during homeostasis

Answer 12

Macula densa cells detect Na+ is within ‘allowed’ limits - sends no signal to juxtaglomerular cells
Afferent arteriole has larger diameter than efferent arteriole
Glomerular pressure is maintained

Question 13

Describe tubulo-glomerular feedback when there is an increase in BP

Answer 13

Glomerular hydrostatic pressure increases -> GFR increases -> Na+ concentration in DCT increases
This is sensed by the macula densa cells
Na+ flows into macula densa cells and water follows. Macula densa cells swell and release adenosine
Adenosine signals juxtaglomerular cells -> constricts afferent arteriole, decreases glomerular hydrostatic pressure
Local effect on kidney -> no effect on systemic BP

Question 14

Describe how tubulo-glomerular feedback regulates systemic BP

Answer 14

Glomerular hydrostatic pressure falls -> GFR decreases -> Na+ concentration in DCT decreases
This is sensed by the macula densa cells
Not enough Na+ flows into macula densa cells -> they shrivel up and release prostaglandins
Prostaglandins tell juxtaglomerular cells to vasodilate afferent arterioles
Renin is released
Activation of the renin-angiotensin-aldosterone system (RAAS)

Question 15

Where is angiotensinogen produced?

Answer 15

In the liver

Question 16

Describe the renin-angiotensin-aldosterone system (RAAS)

Answer 16

Activated in response to fall in BP
Antiotensinogen is released into circulation, cleaved by renin into angiotensin I
Angiotensin I converted into angiotensin II by ACE (angiotensin-converting enzyme)
Angiotensin II rapidly increases BP (it is a potent vasoconstrictor)

Question 17

What effect does angiotensin II have on BP?

Answer 17

Increase BP through vasoconstriction

Question 18

What effects does angiotensin II have on blood volume?

Answer 18

Restores blood volume by binding target receptors on:
1. Arterioles: vasoconstriction
2. Hypothalamus: thirst
3. Pituitary gland: release of ADH
4. Adrenal cortex: release of aldosterone
Restores blood volume via increased fluid and salt retention

Question 19

Where is ANP produced and what effect does it have on RAAS?

Answer 19

Endothelial cells lining the atrial walls of the heart
Baroreceptors located here
Increase in BP detected by endothelial cells -> release ANP
Counteracts the effects of ADH, aldosterone and renin

Question 20

What are some of the causes of Chronic Kidney Disease (CKD)?

Answer 20

Hypertension, diabetes, kidney infections, glomerulonephritis, polycystic kidney disease, kidney stones, long-term use of NSAIDs

Question 21

What are the symptoms of chronic kidney disease (CKD)?

Answer 21

Hypertension, nausea, oedema (ankles, feet, lungs), blood/protein in urine, anaemia, weak painful bones

Question 22

What is furosemide?

Answer 22

A diuretic

Rid the body of extra fluid or salt

Question 23

What are the consequences of CKD?

Answer 23

Inadequate removal of fluid and waste products of metabolism

Inappropriate activation of RAAS

Question 24

How is chronic kidney disease treated?

Answer 24

• Diet (reduce salt intake)/weight loss
• Often a combination of antihypertensive treatments required
• Diuretics (furosemide)
• ACE inhibitors/angiotensin receptor blockers (ARBs)
• Aldosterone agonists (nuclear receptors or sodium channels)

Question 25

What does furosemide target?

Answer 25

NKCC2 co-transpoter on the apical membrane of the thick ascending limb
(blocks sodium reabsorption)

Question 26

Describe kidney failure

Answer 26

End stage renal disease
Less than 15% kidney function
Dialysis and/or kidney transplant required

Question 27

What are the 2 types of dialysis for kidney failure?

Answer 27

Haemodialysis

Peritoneal dialysis

Question 28

What is the purpose of dialysis?

Answer 28

Artificial removal of waste, solutes, water and toxins from blood

Question 29

Describe haemodialysis

Answer 29

Blood is diverted through machine, processed, cleaned and returned to the body
Patients require 3 treatments a week

Question 30

Describe peritoneal dialysis

Answer 30

Dialysis fluid is pumped into the peritoneal cavity and the peritoneum acts as a filter