Long term control of BP Flashcards
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
What does renin do?
Converts angiotensinogen into angiotensin 1
What is angiotensin 1 converted to and by what?
Angiotensin 2 by angiotensin converting enzyme
What is angiotensin 2?
The active hormone
What does angiotensin 2 do?
- Stimulates release of aldosterone from adrenal cortex
- Increases release of ADH from pituitary gland
- Is a vasoconstrictor
What is aldosterone and what does it do?
A steroid hormone
- Increases Na reabsorption in the loop of Henle, giving a bigger osmotic gradient
- Recues diuresis and increases plasma volume
What does increasing the release of ADH do?
Reduces diuresis and increases plasma volume
- Increase water permeability of the collecting duct
- Also increases sense of thirst
What effect does angiotensin being a vasocontrictor have?
Increases TPR and thus increases MAP
What type of system is angiotensin and why?
A negative feedback system
- Multiple mechanisms detect any decrease in MAP
- Stimulate release of renin
- This evokes multiple mechanisms which increase MAP
What does ADH mean?
Antidiuretic hormone
Where is ADH synthesised?
Hypothalamus
Where is ADH released?
Posterior pituitary gland into the blood stream
What triggers ADH release?
Decrease in blood volume
Increase in osmolarity if ISF
Circulating angiotensin 2
What does ADH do?
Increases permeability of collecting duct to water reducing diuresis and increasing plasma volume and MAP
Causes vasoconstriction and therefore increases MAP
What type of system is ADH?
Negative feedback system
- Multiple mechanisms detect any decrease in MAP
- Stimulate release of ADH
- This evokes multiple mechanisms which increase MAP
What do ANP and BNP stand for?
ANP = atrial natriuretic peptide
BNP = brain natriuretic peptide
Where are ANP and BNP produced and released?
ANP = myocardial cells
BNP = ventricles
What triggers the release of ANP/BNP?
Increased distension of the atria and ventricles (a sign of increased MAP)
What do ANP and BNP do?
- Increase excretion of Na (natriuresis)
- Inhibit the release of renin
- Act on medullary CV centres to reduce MAP
*All tend to reduce MAP
What type of system are ANP and BNP?
Negative feedback system but decreasing MAP
- A mechanism detects any increase in MAP
- Stimulates release of ANP and BNP
- This evokes multiple mechanisms which reduce MAP
What proportion of hypertension cases are primary/secondary?
Primary = 95-90%
Secondary = 5-10%
What are some types of drug that can be used for hypertension? (5)
- Ca2+ channel antagonists
- B-adrenoreceptor antagonists
- Thiazide diuretics
- Angiotensin converting enzyme inhibitors
- Angiotensin 2 antagonists
