Long term control of BP Flashcards
What is the primary difference between long term & short term control of Blood pressure?
Short term revolves primarily around the baroreceptor reflex
Long term control probably does not involve this reflex
What is the basic idea of long term blood pressure control?
Based mainly on the volume of plasma in the blood
Controlled by the kidney, using at least 3 hormone systems
What hormone systems are utilised to control long term blood pressure?
Renin-angiotensin-aldosterone system
Antidiuretic factor (ADH, vasopressin)
Atrial natriuretic peptide
What are the functions of the kidneys?
Excretion, and regulation
Excrete waste products Maintain ion balance Regulate pH Regulate osmolarity Regulate plasma volume
How can kidneys alter Mean arterial pressure?
By altering plasma volume
In the kidneys, exchange of fluid with capillaries takes place at several stages/areas
Describe the different stages/types of fluid exchange
Filtration:
- Takes place in the Glomerulus , in the Bowman’s capsule
- Moves OUT of blood, into lumen - LOSS
Secretion:
- Peritubular capillaries into proximal tube
- Capillaries into Distal tube
- Capillaries into Collecting duct
- LOSS
Reabsorption:
- Proximal tube into peritubular capillaries
- Loop of Henle into capillaries
- Distal tube into capillaries
- Collecting duct into capillaries
- GAIN
How does the kidney control the amount of water lost in urine?
Collecting duct generates a very high osmolarity outside of it
How?
- Controlling Na+ transport
- It can hence vary osmolarity ∴ vary the size of the osmotic gradient
It can also control the permeability of the collecting duct to water ∴ determines if water will follow the osmotic gradient or not
Describe how the kidneys would conserve water
By making the collecting duct VERY permeable to water
∴ very easy for water to move out the CD, down osmolarity gradient
This will cause lots of reabsorption ∴ extracts lots of water from kidney ∴ less leaves the end to be excreted
Describe how the kidneys would excrete more water
By reducing the permeability of the collecting duct to water
Lower permeability = less reabsorption ∴ more water in the collecting duct
∴ more water excreted as urine
∴ Diuresis
What effect will increased permeability of the collecting duct to water have on blood volume?
- Increased volume of blood -
Higher permeability ∴ high reabsorption ∴ more water LEAVES the CD/kidney ∴ increase Plasma volume
What will the urine be like if the collecting duct is very permeable?
Small volume of hyper-osmotic pish
Hyper-osmotic = very concentrated
What can trigger the Renin-angiotensin-aldosterone system?
1) Sympathetic neurones, activated by the CVCC when blood pressure drops, link directly to granular cells
2) Granular cells in the kidneys are directly sensitive to BP ∴ respond to low pressure in renal afferent arterioles
3) Paracrine feedback from Maculla densa in the distal tubule. Reduced delivery of Na+/Cl- signals drop in MAP
What is the effect of triggering the Renin-angiotensin-aldosterone system?
Renin production
From juxtaglomerular (granular) cells of the kidney
Describe the how a drop in blood pressure causes renin production via the paracrine route (Na+/Cl-)
The Macula densa communicates with granular cells based on how much fluid flows through the distal tubule
When fluid volume is high, the Na+/Cl- delivery is high, so the MD releases paracrine signals that inhibit renin release
When low, the amount of Na+/Cl- delivery is reduced, so the MD releases other paracrine signals to stimulate renin production & release
Where exactly is the Macula densa?
Loop of Henle ascending limb
In the distal tubule of the kidney
What does renin do?
Converts inactive Angiotensinogen into Angiotensin I (ANG I)
Describe the pathway of the reactions involving Angiotensin proteins that is kicked off by Renin
Angiotensinogen (an inactive plasma protein, constantly produced by the liver) is turned to ANG I by Renin
Angiotensin I (ANG I) encounters the ACE enzyme in the blood into ANG II
What does Angiotensin II do?
Stimulates release of Aldosterone from the adrenal cortex
Increases the synthesis of ADH (vasopressin) in the Hypothalamus & release from the posterior pituitary gland
Causes vasoconstriction of arterioles
ALSO:
- CVVC - triggers Cardiovascular response to increase BP
ANG II stimulates release of Aldosterone from the AC
What does aldosterone do?
Increases Na+ reabsorption in the Loop of Henle
∴ reduces diuresis & increases plasma volume
ANG II stimulates release of ADH from the pituitary gland
What does ADH do?
Increases water permeability of the collecting duct
∴ reduces diuresis & increases plasma volume
It is also involved in triggering the sensation of thirst
What type of system is the R-A-A system?
Negative feedback system
Multiple mechanisms detect a drop in BP
Stimulates release of renin
Renin release decreases as BP becomes more normal
What is ADH?
Anti-diuretic hormone
AKA vasopressin
What triggers the release of ADH?
Decreased blood volume - cardiopulmonary baroreceptors relay this info to medullary CVCs
Increased osmolarity of interstitial fluid - measured by osmoreceptors in the hypothalamus
ANG II in blood
What does ADH do?
Increases permeability of collecting duct to water
Vasoconstriction
(another -ve feedback system)
What is ANP?
Atrial natriuretic peptide
Produced in & released from myocardial cells in the atria, triggered by increased atrial distension
Increased Atrial distension = increased MAP
∴ ANP produces in response to increased BP
What does ANP do?
Increases excretion of Na+ - Natriuresis
Inhibits release of Renin
Acts of medullary CV centres to reduce MAP
So what is the primary difference between the RAA system & the ANP system?
RAA - increases BP
ANP - decreases BP
