Renal - Hormonal control Flashcards
What hormone controls the end of the convoluted distal tubule/collecting duct? What substance does this influence?
ADH (antidiuretic hormone)/Vasopressin (they are the same thing) controls the water balance of the body
What does ADH interact with in the kidney?
It binds to principal cells
What does the activation of the principal cells do?
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)
What do the aquaporin-2 vesicles do when attached to the apical membrane of the collecting duct? What does this allow?
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
Why does increasing the permeability of the collecting duct increase water re-absorption?
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
Label the diagram
What determines if ADH is released?
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)
What is the process of ADH production and release?
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
How do osmoreceptors measure changes in osmolarity/Na+ concentration?
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
Other than an increase of osmolarity/[Na+], how can ADH production be stimulated?
By a decrease in blood pressure/volume
How is a decrease in blood pressure/volume measured?
Pressure = baroreceptors
Volume = stretch receptors on the heart
What is used to control [Na+]? What else is this hormone sensitive to?
The Renin-Angiotensin-Aldosterone system also responds to low blood pressure and low blood volume
How does the Renin-Angiotensin-Aldosterone system get activated?
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
What are the triggers for the release of Renin from juxtaglomerular cells?
- 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)
What is the role of renin?
It is an enzyme that converts the pre-cursor angiotensinogen into angiotensin I
What is the hormone that controls the adrenal glands to influence [Na+] in the body? What is the pathway for it?
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
What are the relative amounts of the substrates and enzymes in the pathway for Angiotensin II production? What is the rate limiting step?
Angiotensinogen, Angiotensin I & II and ACE are in excess amounts
Renin: production controlled by the juxtaglomerular cells and is the RATE LIMITING STEP
What is the hormone that directly affect the kidney to alter [Na+]?
Aldosterone
How is aldosterone amounts controlled?
It is released from the adrenal cortex in response to angiotensin II
What does aldosterone do to control [Na+]?
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
Other than controlling the adrenal gland for aldosterone production, what else does angiotensin II do?
It is a potent vasoconstrictor and in the presence of it, it decreases glomerular filtration by constricting the afferent arterioles
What is the pathway for how the body reacts to eating salty food
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
During heart failure, what hormone is elevated? Why?
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
During BLOOD LOSS what are the main triggers for what renal systems? Why?
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
What hormone is released in response to the increase stretch of the arteries? What does this increase stretch mean for blood volume?
Atrial Natriuretic Peptide (ANP) is released when there is increased blood volume
What is the function of ANP?
Reduces renin and ADH and aldosterone release resulting in increased glomerular filtration rate to cause reduced Na+ and water reabsorption
For the bodies response to blood pressure, how does the time scale of blood pressure change affect response?
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
