L19 Gene Models And Nephron Functions 3

Question 1

What are the two cell types within the late DT and CCD?

Answer 1

Principal and intercalated cells

Question 2

Intercalated cells within the late DT and CCD are divided into sub divisions. What are they?

Answer 2

Alpha intercalated cells (IC)
Beta intercalated cells

Question 3

What is the main function for alpha and beta IC?

Answer 3

H+ secretion and HCO3- reabsorption

Question 4

What does Late distal, connecting tubules and cortical collecting duct do?

Answer 4

1. Controls concentration of urine
2. Reabsorbs Na+ and water
3. Secretes K+ and H+

Question 5

What are the functions of each cell type within the CCD and late DT?

Answer 5

1.Principal - Na+ and water reabsorption, K+ and H+ secretion
2.Intercalated - H+ secretion and HCO3 reabsortion in alpha cells and vice versa in beta cells.

Question 6

What does ENaC stand for?

Answer 6

Epithelial sodium channel

Question 7

Explain how ions are moved out within the Principal cell

Answer 7

• ENaC, located on the apical membrane, allows Na+ ions to enter the cell from the tubular fluid.
• Sodium- potassium pumps 3 Na+ out and 2K+ into the cell
• ROMK and Kir2.3 pumps potassium ions out

Question 8

What does Amiloride do?

Answer 8

Amiloride block ENaC in the collecting duct and late distal tubule leading to reduced reabsorption of sodium ions which increases urine excretion.

Question 9

How does Amiloride treat for high blood pressure?

Answer 9

• Amiloride blocks the ENaCs in the late distal convoluted tubule and collectind duct.
• This reduces the reabsorption of sodium and therefore water from the kidney into the bloodstream
• As a result, more sodium and water are excreted in the urine, leading to a decrease in blood volume and pressure

Question 10

What is Liddle’s syndrome?

Answer 10

Rare genetic disorder that causes the body to retain too much sodium.
Leads to excess high blood pressure (hypertension) and lod blood potassium levels (hypokalemia)

Question 11

How do diuretics help with high blood pressure?

Answer 11

1) Diuretics work by causing the kidneys to release more sodium and water into the urine
2) Reduces volume in the bloodstream
3) This lowers the blood pressure because of the reduction in the workload

Question 12

What forms the Epithelial Na+ channels (ENaC)?

Answer 12

It is formed of 3 subunits which are:
Alpha
Beta
Gamma

Question 13

How does Liddle’s syndrome lead to hypertension ?

Answer 13

Increased sodium reabsorption which leads to water retention causing hypertension.

Question 14

How does the conc of reabsorption of sodium ions directly affect the amount of potassium ions diffuse out?

Answer 14

Sodium ions is reabsorbed causing an increase, this increase causes an electrochemical gradient to pump out sodium ions through NaK pump, to mainatin the gradient K+ ions is simulataneously diffused out.

Question 15

What is hypokalaemia?

Answer 15

Low potassium levels in the blood.

Question 16

What is hypertension?

Answer 16

High blood pressure where the force of the blood pushes against the walls of your blood vessels too much

Question 17

Explain how excessive Na+ transport in the principal cell leads to hypertension

Answer 17

1) ENac channels reabsorb too much sodium and water which leads to increase fluid volume
2) This puts additional pressure on the walls of the blood vessels, leading to elevated blood pressure (hypertension)

Question 18

Explain how excessive Na+ transport leads to increased K+ secretion in principal cells

Answer 18

1) ENac reabsorbs Na+ which creates an electrical gradient
2) Negative electrical potential within the cell drives the movement of positively charged K+ ions out of the cell via K+ channels
3) This leads to increase K+ secretion into the cell via Na+/K+ ATPase

Question 19

What does AE1 carrier do in alpha IC cell?

Answer 19

1) H+ is actively pumped out of the cell into the urine via a H+ ATPase
2) This allows HCO3- to exchange with Cl- (HCO3- leaves cell and reabsorbs back into the bloodstream, Cl- ion enters the cell)

Question 20

What happens to chlorine in the alpha IC cell ?

Answer 20

Chloride ions enter alpha intercalated cell through AE1 in exchange for HCO3-
Chloride ions exit cell via chloride channels

Entry of chloride is essential for the reabsorption of bicarbonate back into the blood

Question 21

What’s the difference in terms of positions of the transport proteins in alpha and beta IC cells?

Answer 21

Alpha cells - AE1 located on the basolateral membrane (facing blood) and H+/ATPase located on the apical membrane (facing the urine)
Beta cells is flipped

Question 22

What is the difference in their primary responsibilities between alpha and beta IC cells?

Answer 22

Alpha IC: Acid secretion. Secrete H+ ions into the urine and reabsorb HCO3- into the bloodstream

Beta IC: Base secretion. Secrete HCO3- into the urine and reabsorb H+ ions into the bloodstream

Alpha: removes H+ from the body via urina hence why its acid secretion

Question 23

Give me two features of the Medullary collecting duct

Answer 23

• Low sodium permeability
• High water and urea permeability in the presence of antidiuretic hormone (ADH)

Question 24

What is acute renal failure?

Answer 24

• Fall in gomerular filtration rate over hrs/days
• Impaired fluid and electrolyte homeostasis