Long term control of BP Flashcards
(45 cards)
What are the functions of the kidneys?
Excretion of waste products
Maintenance of ion balance
Regulation of pH
Regulation of osmolarity
Regulation of plasma volume
How is regulation of plasma volume important?
Controlling plasma volume is used to regulate MAP:
- If trying to squeeze big plasma volume through CVS = high MAP
- If trying to squeeze low plasma volume through CVS = low MAP
How do the kidneys regulate plasma volume? (vauge)
Control how much water is lost as urine and how much is retained
What does the renal counter-current system create?
A very high osmolarity outside the collecting duct
What determines how big the osmotic gradient outside the collecting duct is?
Control over Na transport
What determines if water flows along the osmotic gradient?
Control over permeability of the collecting duct to water
What is the efferent arteriole and what does it do?
Flows close to the loop of Henle and collecting duct and as things move along they can be reabsorbed or secreted
(move form blood to filtrate or back)
How is transfer between blood and filtrate done?
- Done by kidney building up a big Na gradient in the extracellular fluid in the loop of Henle.
- Water comes into the collecting duct, by controlling permeability, you can either allow water to follow that osmotic gradient or not.
Where does filtrate start and with what osmolarity?
Bowman’s capsule
Osmolarity of 200 milliosmoles (same as blood so no osmotic gradient)
What happens to osmotic gradient as filtrate passes through loop of Henle and why?
As it comes down the loop of Henle, Na is transported out which builds up osmotic gradient.
What is osmolarity of filtrate by the time it reaches collecting duct?
50 miliosmoles
What modulates the amount of water retained/reabsorbed?
Modulating Na transport
Making collecting duct very permeable to water
Making collecting duct impermeable
How can modulating Na transport affect the amount of water retained?
Will affect how big the osmotic gradient is in the first place
What happens when you make the collecting duct highly permeable to water? (fate of MAP)
Will result in lots of water reabsorption, little urine and conserve plasma volume
- Increase MAP
What happens when you make the collecting duct impermeable to water? (fate of MAP)
§ Little water reabsorbed an lots ending up in urine
- Large volume of very dilute urine
- Diuresis
Leads to decrease in plasma volume and decrease in MAP
What hormone system regulates sensing of plasma volume?
Renin-angiotensin-aldosterone system (RAAS)
What is RAAS?
Feedback system that senses disturbances in plasma volume and MAP.
Produces hormones to produce appropriate response.
What hormones does RAAS produce?
Renin
Where is renin produced?
Juxtaglomerular of the kidney
What triggers renin production?
Activation of sympathetic nerves to the juxtaglomerular apparatus.
Decreased distension of afferent arterioles (the renal baroreflex).
Decreased delivery of Na/Cl through the tubule.
How does activation of sympathetic nerves lead to renin production?
Sympathetic activation when BP is low.
Increases contractility of heart and HR.
Increases SV, CO and MAP.
Activates juxtaglomerular cells and releases renin.
How does decreased distension of afferent arterioles lead to renin production?
Signalling a reduction in MAP
- If lower MAP then arterioles are less stretched/distended
How does decreased distension of Na/Cl through the tubules lead to renin production?
If BP is higher = more filtration
- More Na/cl going out of proximal tube
- More Na/Cl delivered to macula densa
If BP is low = less filtration
- Less delivery of Na/Cl
Reduction in MAP and triggers release of renin
What is the path of filtrate?
- Blood comes into Bowman’s capsule from the afferent arteriole
- Its filtered under high pressure
- Filtrate comes out proximal tubule
- Down descending limb of loop of Henle, off the ascending limb
- Back down past Bowman’s capsule
- Juxtaglomerular cells are here
