Lecture 5: Renal Hormones/Control of Body Water and Salt

Question 1

Explain red blood cell production with low O2 delivery

Answer 1

1. Low O2 delivery: hypoxia or ischemia
2. Leads to an accumulation of hypoxia 1α (↑HIF-1α) in tubular interstitial cells
3. This triggers the synthesis and release of Erythropoietin (Epoetin-α)
4. Epoetin-α goes to bone barrow for RBC production (Erythroid Precursor Cells to normoblasts)

Review Slide 3

Erythropoietin comes from interstitial cells of kidney maturation of erythopoietycytes is controlled by Erythropoietin (Epoetin-α)

Question 2

What is the difference between HIF-1α under normoxia and hypoxia?

Answer 2

• In normoxia: HIF-1α is degraded
• In hypoxia: active HIF dimer is produced and this leads to erythropoiesis (creation of RBC)

Question 3

What does renin regulate?

Answer 3

blood pressure and sodium output

Question 4

What is renin secreted by?

Answer 4

Juxtaglomerular cells (JG cells)

SMC has lots of renin

Question 5

List the 3 mechanisms that trigger renin secretion?

Answer 5

1. ↓ blood pressure activates renal vascular receptor (baroreceptor inside kidney) and ↑ renin release from JG cells
2. ↓ blood pressure also ↓ GFR and delivery of Cl- to Macula Densa in the distal tubule which ↑ renin from JG cells
   3.↓ blood pressure causes a reflex activation of renal sympathetic nerves which ↑ renin release from JG cells.

all mechanisms are triggered by low BP

Question 6

Is Angiotensin 2 a powerful vasodilator or constrictor?

Answer 6

Powerful vassoconstrictor, that’s why BP increases when it’s present

Question 7

When BP decreases explain the effects of the Renin-Angiotension-Aldosterone System on factors listed below

• Renin (kidney)
• Angiotensin I
• Angiotensin II
• ADH & Thrist
• FF
• Aldosterone
• Na+ Reabsorption

Answer 7

• ↑ Renin (kidney)
• ↑ Angiotensin I
• ↑ Angiotensin II (vasoconstriction)
• ↑ ADH & Thirst (water reabsorption)
• ↑ FF (oncotic pressure)
• ↑ Aldosterone
• ↑ Na+ Reabsorption

Question 8

Review Slide 10

Answer 8

Review Slide 10

Question 9

How do renal prostaglandins respond to low blood pressure?

Answer 9

It responds to excessive vasoconstriction, so renal prostaglandins vasodilates

Review Slide 13

Question 10

What two isoforms of prostaglandins are major renal Vasodilators?

Answer 10

PGE2 and PGI2 (in response to ↓ RBF)

Question 11

What is Vioxx?

Answer 11

is a cyclooxygenase-2 (COX-2) inhibitor, and was recalled in 2004 because of increased risk of cardiovascular problems

Question 12

What factors are the body trying to control in order to control body salt and water?

Answer 12

ECF volume and ECF osmolality

Question 13

How can our body control water?

Answer 13

By controlling water intake and by controlling water output (intake=output)

Fluid: primary driver of intake, Urine: primary driver of output

Question 14

Control of water intake is by thirst. What drives thirst? (4)

Stimuli of Thirst

Answer 14

1. Increased Osmolality
2. Decreased Arterial Pressure
3. Decreased Blood Volume
4. Angiotensin II

these all relate to ECF osmolality and ECF volume

Question 15

How do we control water output?

Answer 15

By ADH secretion

Question 16

What triggers ADH secretion? (7)

Stimuli of ADH secretion

Answer 16

1) Increased Osmolality
2) Decreased Arterial Pressure
3) Decreased Blood Volume
4) Angiotensin II
5) Trauma
6) Surgery
7) Drugs eg. opiates and anesthetics.

1-3 are all related to ECF osmolaloty and volume

Question 17

What occurs to Thirst and ADH secretion when there is an increase in plasma osmolality or decrease in BP?

Answer 17

• Leads to an increase in thirst and increase in ADH secretion
• Both leads to an increase in water retention in order to decrease plasma osmolality and increase BP

Question 18

Explain what is occuring in Area 1 and Area 2 in the image below

Answer 18

• Area 1: Area b/w the two curves is sodium retention, Intake is increase but you are not excreting Na+ fast enough. The body is accumlating lots of Na+ and this leads to water reabsoprtion. Water reabsoprtion leads to weight gain
• Area 2: Area b/w the two curves is sodium deficit. Intake is decreased but you are excreting Na+ too fast. The body has little Na+ and you are excreting more H2O. Excretion of H2O leads to weight loss.

Question 19

Regulation of Na+ Excretion

What occurs to the mechanisms listed below with an Increase in NaCl Intake

• Blood Volume
• Atrial Pressure
• Arterial Pressure
• Plasma Protein
• ANP Secretion
• GFR
• Sympathetics
• Renin
• Angiotensin II
• Aldosterone
• Na+ Excretion

Either increases or decreases

HIGH yield

Answer 19

• ↑ Blood Volume
• ↑ Atrial Pressure
• ↑ Arterial Pressure
• ↓ Plasma Protein
• ↑ ANP Secretion
• ↑ GFR
• ↓ Sympathetics
• ↓ Renin
• ↓ Angiotensin II
• ↓ Aldosterone
• ↑ Na+ Excretion (aka ↓ Na+ reabsorption)

Question 20

What occurs to the mechanisms listed below when Hemorrhage occurs

• Blood Volume
• Atrial Pressure
• Arterial Pressure
• ANP Secretion
• GFR
• Sympathetics
• Renin
• Angiotensin II
• Aldosterone
• ADH
• H2O Excretion
• Na+ Excretion

Either increases or decreases

HIGH yield
Hemorrhage-loss of blood

Answer 20

• ↓ Blood Volume
• ↓ Atrial Pressure
• ↓ Arterial Pressure
• ↓ ANP Secretion
• ↓ GFR
• ↑ Sympathetics
• ↑ Renin
• ↑ Angiotensin II
• ↑ Aldosterone
• ↑ ADH
• ↓ H2O Excretion
• ↓ Na+ Excretion (aka ↑ Na+ reabsorption)

Question 21

What does this D-Y graph shift represent?

Answer 21

• Adrenal insufficiency
• (cannot make enough aldosterone so you cannot reabsorb a lot of Na+-> you lose lots of Na+, hence ECF gets smaller)

Question 22

What does this D-Y graph shift represent?

Answer 22

SIADH (syndrome of inappropriate antidiuretic hormone-> lots of ADH so you keep reabsorbing water)

Question 23

What does this D-Y graph shift represent?

Answer 23

Infusion of isotonic NaCl ( Na+ and Cl- both go to the ECF compartment that is why it’s volume is raised)

Question 24

What does this D-Y graph shift represent?

Answer 24

High NaCl Intake