Renal - Hormonal control

Question 1

What hormone controls the end of the convoluted distal tubule/collecting duct? What substance does this influence?

Answer 1

ADH (antidiuretic hormone)/Vasopressin (they are the same thing) controls the water balance of the body

Question 2

What does ADH interact with in the kidney?

Answer 2

It binds to principal cells

Question 3

What does the activation of the principal cells do?

Answer 3

It causes aquaporin-2 containing vesicles to bing to the apical membrane of the collecting duct (i.e. the side that is exposed to the collecting duct/away from capillaries)

Question 4

What do the aquaporin-2 vesicles do when attached to the apical membrane of the collecting duct? What does this allow?

Answer 4

They allow water to move from the tubule into the cell

This allows water to be reabsorbed into the blood stream as the basolateral surface is permeable to water anyway to goes into the capillary

Question 5

Why does increasing the permeability of the collecting duct increase water re-absorption?

Answer 5

The collection duct travels through the medulla of the kidney which has a high osmolarity lower down (i.e. low water concentration) so opening pores allows water to move down its osmotic gradient

Question 6

Label the diagram

Answer 6

Question 7

What determines if ADH is released?

Answer 7

Osmoreceptors detect changes in osmolarity and Na+ concentration and released ADH to maintain homeostasis (i.e. when osmolarity and/or Na+ increases ADH is released)

Question 8

What is the process of ADH production and release?

Answer 8

1 - ADH is synthesis in the hypothalamus

2 - ADH is stored in vesicles in the posterior pituitary

3 - ADH is released from posterior pituitary into the blood

Question 9

How do osmoreceptors measure changes in osmolarity/Na+ concentration?

Answer 9

Osmoreceptors have stretch-inhibited cation channels so that when the osmolarity/[Na+] increases, the cell loses water and becomes smaller which causes the cationic channels to be stretched open. This allows Na+ to enter the cell and triggers and action potential

Question 10

Other than an increase of osmolarity/[Na+], how can ADH production be stimulated?

Answer 10

By a decrease in blood pressure/volume

Question 11

How is a decrease in blood pressure/volume measured?

Answer 11

Pressure = baroreceptors

Volume = stretch receptors on the heart

Question 12

What is used to control [Na+]? What else is this hormone sensitive to?

Answer 12

The Renin-Angiotensin-Aldosterone system also responds to low blood pressure and low blood volume

Question 13

How does the Renin-Angiotensin-Aldosterone system get activated?

Answer 13

1 - Macula Densa cells in the Juxtaglomerular apparatus detect change in NaCl content

2 - Macula Densa cells respond by producing prostaglandins

3 - Granular cells in the afferent arteriole are activated by the prostaglandins and release Renin

Question 14

What are the triggers for the release of Renin from juxtaglomerular cells?

Answer 14

• Low NaCl concentration in the distal tubule (i.e. low NaCl)
• decreased perfusion pressure (i.e. decreased blood pressure)
• increased sympathetic activity (i.e. decreased blood volume)

Question 15

What is the role of renin?

Answer 15

It is an enzyme that converts the pre-cursor angiotensinogen into angiotensin I

Question 16

What is the hormone that controls the adrenal glands to influence [Na+] in the body? What is the pathway for it?

Answer 16

Angiotensinogen, it is converted by Renin into Angiotensin I

Angiotensin I is converted by Angiotensin Converting Enzyme (ACE, FYI this is made in the lungs) into Angiotensin II

Question 17

What are the relative amounts of the substrates and enzymes in the pathway for Angiotensin II production? What is the rate limiting step?

Answer 17

Angiotensinogen, Angiotensin I & II and ACE are in excess amounts

Renin: production controlled by the juxtaglomerular cells and is the RATE LIMITING STEP

Question 18

What is the hormone that directly affect the kidney to alter [Na+]?

Answer 18

Aldosterone

Question 19

How is aldosterone amounts controlled?

Answer 19

It is released from the adrenal cortex in response to angiotensin II

Question 20

What does aldosterone do to control [Na+]?

Answer 20

Increasing aldosterone causes an increase in the transcription of the Na/K ATPase pumps (i.e. they do more work) which increases Na+ reabsorption and K+ excretion

Question 21

Other than controlling the adrenal gland for aldosterone production, what else does angiotensin II do?

Answer 21

It is a potent vasoconstrictor and in the presence of it, it decreases glomerular filtration by constricting the afferent arterioles

Question 22

What is the pathway for how the body reacts to eating salty food

Answer 22

1 - Salt from diet causes an increase in plasma concentration of Na+

2 - The extra salt causes increase osmosis of water from intracellular fluid to the plasma increase blood volume

3 - Increased blood volume causes decreased release of renin by the juxtaglomerular cells resulting in less angiotensin II therefore less aldosterone

4 - Less aldosterone causes less reabsorption of Na+ by the kidneys resulting in more Na+ being removed as urine decreasing blood volume

Question 23

During heart failure, what hormone is elevated? Why?

Answer 23

Angiotensin II because during heart failure there is a decrease in function which means that less blood is getting to the kidneys so the kidneys sense a decrease in blood volume/pressure and counter this with increased renin production resulting in more angiotensin II causing increased blood pressure

Question 24

During BLOOD LOSS what are the main triggers for what renal systems? Why?

Answer 24

Baroreceptors in the kidney (i.e. juxtaglomerular cells) affect antidiuretic II (controlling renin FYI)

Baroreceptors in the heart affect ADH

Losing blood is isosmotic so both water and salt loss are detected

Question 25

What hormone is released in response to the increase stretch of the arteries? What does this increase stretch mean for blood volume?

Answer 25

Atrial Natriuretic Peptide (ANP) is released when there is increased blood volume

Question 26

What is the function of ANP?

Answer 26

Reduces renin and ADH and aldosterone release resulting in increased glomerular filtration rate to cause reduced Na+ and water reabsorption

Question 27

For the bodies response to blood pressure, how does the time scale of blood pressure change affect response?

Answer 27

If blood pressure changes for only a short period of time then the body will try to correct it with hormonal relaxation and vast-control. Over the longer term blood volume and red blood cell count are influenced to more sustainably impact blood pressure