Long term control of blood pressure Flashcards
State 5 functions of the kidney
Waste excretion Ion balance maintenance pH regulation Osmolarity regulation Plasma volume regulation
What is the purpose of plasma volume regulation?
MAP control
State the function of Counter Current System of the kidney
The counter current system creates high osmolarity outside the collecting duct.
What determines the size of the osmotic gradient generated by the Counter Current System?
Na+ transport
What determines whether or not water follows the osmotic gradient generated by the Counter Current System or not?
Control over permeability of collecting duct to sodium determines whether water follows osmotic gradient or not.
This allows control over how much water is lost in urine and how much is reabsorbed into blood
What are the effects of a very permeable collecting duct?
Reabsorb lots of water
Small volume of hyperosmotic urine produced
Conserve plasma volume
What are the effects of an impermeable collecting duct?
Excrete lots of water in a
Large volume of hypo-osmotic urine
Reduce plasma volume
State the three mechanisms of long term BP control
Renin-Angiotensin-Aldosterone System
ADH (vasopressin)
ANP
What cells release renin in the Renin-Angiotensin-Aldosterone System?
Juxtaglomerular granule cells
What triggers juxtaglomerular granule cells to release renin?
Signals of reduced MAP to juxtaglomerular granule cells
- Macula densa detects reduced NaCl delivery
- Afferent arterioles have reduced distension
- Sympathetic system innervation
What is the function of renin?
Converts angiotensinogen to angiotensin I
What converts Angiotensin I to Angiotensin II
ACE (angiotensin converting enzyme)
What two hormones does Angiotensin II stimulate the release of?
Aldosterone
ADH
Where is aldosterone released from?
What is its function?
Released from adrenal cortex
Function: increases Na+ reabsorption at Loop of Henle -> reduced diuresis and increased plasma volume
Where is ADH released from?
What are its two functions?
Released from pituitary gland
Functions:
- increases water reabsorption at collecting duct reading to reduced diuresis and increased plasma volume
- Vasoconstrictor so increases TPR
Summarise the renin-angiotensin-aldosterone system
Reduced MAP signalled to juxtaglomerular granule cells by reduced NaCl in macula densa, reduced distension of afferent arteriolar cells and sympathetic system innervation
Juxtaglomerular granule cells release renin which converts angiotensinogen -> angiotensin I
ACE converts Angiotensin I to angiotensin II
Angiotensin II stimulates aldosterone release from the adrenal cortex which increases sodium reabsorption at the Loop of Henle -> reduced diuresis and increased plasma volume
Angiotensin to stimulates ADH release from pituitary gland which increases water permeability of the collecting duct -> reduced diuresis and increased plasma volume. It is also a vasoconstrictor thus increasing TPR
Where is ADH synthesised?
Hypothalamus
Where is ADH released?
Posterior pituitary gland
What triggers ADH release?
- Reduced blood volume detected by cardiopulmonary baroreceptors and relayed to medullary cardiovascular centres
- increased Osmolarity of ISF as sensed by osmoreceptors of hypothalamus
- circulating angiotensin II
What are the two actions of ADH?
Increased permeability of collecting duct to H2O leading to reduced diuresis and increased plasma volume
Vasoconstrictor -> increased TPR and thus increased MAP
What is another name for ADH?
Vasopressin
How are the renin-angiotensin-aldosterone system and ADH negative feedback mechanisms?
Multiple mechanisms detect reduced MAP and bring about multiple mechanisms to bring about increased MAP.
Where is Atrial Natriuretic Peptide (ANP) produced and released?
Myocardial cells of the atria
What triggers the release of ANP?
Distension of the atria and ventricles leading to increased MAP
What are the actions of ANP?
- increases Na+ excretion
- inhibits renin release, thus reducing MAP
Where does BNP act on?
Medullary cardiovascular centres to reduced MAP
How is the release of ANP a negative feedback system?
Increased MAP stimulates ANP release which evokes multiple mechanisms to reduced MAP
What percentage of hypertension cases have a known cause (are secondary)?
5-10%
List the rational bases of drug treatment for primary hypertension
Ca2+ channel antagonists Beta blockers Thiazide diuretics ACE inhibitors ARBs
