Long Term Control of Blood Pressure Flashcards
What is long term control probably nor mediated by?
Arterial baroreflex
What does long term control revolve around?
Control of plasma volume by the kidney
What are the 3 hormone systems involved in the long term control?
- Renin-angiotension-aldosterone system
- Antidiuretic factor (ADH/ vasopressin)
- Atrial natriuretic peptide
What are the functions of the kidney?
- Excretion of waste products
- Maintenance of ion balance
- Regulation of pH
- Regulation of osmolarity
- Regulation of plasma volume
What is controlling plasma volume used to regulate?
MAP
What is the main site of reabsorption in the kidney?
Loop of Henle
What is created by the renal counter current system?
A very high osmolarity outside the collecting duct
What does control over Na transport determine?
The size of the osmotic gradient
What does control over the permeability of the collecting duct to water determine?
If th water follows the osmotic gradient or not
What is reabsorbed from the filtrate?
Na
What does the reabsorption of Na cause?
A progressive increase in the Na concentration outside of the collecting duct
What will making the collecting duct very permeable to water result in?
- Lots of water reabsorption
- Little urine
- Conservation of plasma volume
What will making the collecting duct very impermeable to water result in?
- Little reabsorption
- Lots of urine
- Reduction in plasma volume
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
- Decreased delivery of Na/Cl through the tubule
What are the triggers of renin production all signs of?
Low MAP
What does renin do?
- Converts inactive angiotensinogen to angiotensin I
- Angiotensin I is then converted by angiotensin converting enzyme to angiotensin II
What does angiotensin II do?
- Stimulates release of aldosterone from the adrenal cortex
- Increases release of ADH from the pituitary
- Is a vasoconstrictor
What does stimulation of the release of aldosterone from the adrenal cortex do?
- Increases Na reabsorption in the loop of Henle
- Therefore reduced diuresis and increases plasma volume
What does an increase in the release of ADH from the pituitary do?
- Increases water permeability of the collecting duct
- Therefore reduces diuresis and increases plasma volume
- And increases sense of thirst
What does vasoconstriction cause?
Increase in TPR
Why can the renin-angiotensin-aldosterone system be considered a negative feedback system?
- Multiple mechanism detect any decrease in MAP
- Stimulates release of renin
- This evokes multiple mechanisms which increase MAP
Where is ADH produced?
- Synthesised in the hypothalamus
- Released from the posterior pituitary gland
What triggers ADH release?
- A decrease in blood volume (as sensed by cardiopulmonary baroreceptors and relayed via medullary CV centres)
- An increase in osmolarity of interstitial fluid (as sensed by osmoreceptors in the hypothalamus)
- Circulating angiotensin II (triggered by the renin-angiotensin -aldosterone system)
What are the trigger of the release of ADH all signs of?
Low plasma volume and/or low MAP
What does ADH do?
- Increases the permeability of the collecting duct to H2O, therefore reduces diuresis and increases plasma volume- increases MAP
- Causes vasoconstriction, therefore increasing Map
Why can the release of ADH be considered a negative feedback system?
- Multiple mechanism detect any decrease in MAP
- Stimulates release of ADH
- This evokes multiple mechanisms which increase MAP
Where are ANP and BNP produced?
Produced in and released from myocardial cells in the atria and ventricles respectively
What triggers ANP and BNP release?
Increased distension of the atrium
What do ANP and BNP do?
- increases excretion of Na
- Inhibits the release of renin
- Acts on medullary CV centres to reduce MAP
Why can the release of ANP/BNP be considered a negative feedback system?
- A mechanism that detects any increase in MAP
- Stimulates release of ANP and BNP
- This evokes multiple mechanisms which reduce MAP
What is increased distension of the atrium a sign of?
Increased MAP
What does the release of ANP/BNP tend to do?
Decrease MAP
What are the 2 classes of causes of hypertension?
- Primary, of unknown cause
- Secondary, known cause
What types of drugs are used in the long term treatment of hypertension?
- Ca channel antagonists
- B-adrenoreceptor antagonists
- Thiazide diuretics
- Angiotensin converting enzyme inhibitors
