Tubular Function

Question 1

What does excess fluid cause

Answer 1

elevated blood volume, which leads to elevated blood pressure

Question 2

What is Glomerular Filtration Rate

Answer 2

the rate at which blood is filtered through the glomerulus into the Bowman’s capsule

Question 3

What is the juxta-glomerular apparatus and what does it do

Answer 3

it is a specialised structure formed by the distal convoluted tubule and the glomerular afferent arteriole. It functions to regulate blood pressure and the filtration rate of the glomerulus. It measures the Na conc of the filtrate and adjusts the diameter of the afferent arteriole accordingly.

Question 4

What do macula densa cells do

Answer 4

detect sodium concentration

Question 5

what do juxtaglomerular cells do

Answer 5

adjust the diameter of the afferent arteriole

Question 6

What happens under normal homeostatic blood pressure

Answer 6

• GFR is within normal limits as is the concentration of sodium as it enters the distal convoluted tubule.
• the macula densa detect that sodium is within normal limits and do not signal the juxtaglomerular cells
• therefore, juxtaglomerular cells maintain the large diameter of the afferent arteriole and hence GFR is maintained

Question 7

What happens when there is an elevated systemic blood pressure?

Answer 7

• elevated systemic blood pressure leads to an elevated glomerular hydrostatic pressure and an elevated GFR.
• elevated GFR means concentration of sodium in distal convoluted tubule is also elevated.
• detected by macula densa cells, which signal to the juxtaglomerular cells by releasing adenosine
• adenosine causes the juxtaglomerular cells to constrict, reducing the flow of blood into the glomerulus and decreasing GFR

Question 8

What happens if there is a decreased systemic blood pressure

Answer 8

• causes a decrease in glomerular hydrostatic pressure which causes a decrease in GFR
• more time for sodium to be reabsorbed from filtrate, so concentration of sodium is below normal as it enters DCT
• Macula densa cells release prostaglandins
• This causes the juxtaglomerular cells to dilate
• Renin is released from the juxtaglomerular cells as well

Question 9

How does the renin angiotensinogen system restore blood pressure

Answer 9

• angiotensinogen is released into circulation
• renin converts angiotensiongen to angiotensin I
  Angiotensiongen converting enzyme converts angiotensin I into angiotensin II
  Angiotensin II is a potent vasoconstrictor and rapidly increases blood pressure