Flashcards in Session 4 - Changes in Plasma Volume (Hormonal control) Deck (72)
Where does medium and long term control of blood pressure stem from?
• Neurohumoral responses
Directed at controlling sodium balance and thus extracellular fluid volume
How does modification of ECF modify BP?
• Blood plasma part of ECF
• Modifying ECF volume modifies volume of blood
What are the four parallel pathways which control BP?
• Renin-angiotensin-aldosterone system
• Sympathetic nervous system
• Antidiuretic hormone (ADH)
• Atrial natriuretic peptide (ANP)
Where is renin released form?
• Granular cells of juxtaglomerular apparatus
What three factors control renin release?
• Reduced NaCl delivery to distal tubule (reduced perfusion, low GFR)
• Reduced perfusion pressure in the kidney causes the release of renin (baroceptors in afferent arteriole cause release from granluar cells of JGA)
• Sympathetic stimulation to JGA increases release of renin
What does the sympathetic system stimulate to cause renin release?
• B adrenergic receptors of granular cells of JGA
How is renin released by JGA as a result of decreased GFR?
• Less NaCl detected by macula densa cells in JGA
• Stimulates granular cells to release prostaglandin PGI2
• PGI2 acts on granular cells to cause renin release
How is renin released by granular cells as a result of reduced perfusion pressure ?
• Decreased pressure decreases wall tension at granular cells, which stimulates renin release
What does renin do?
• Enzyme released by juxtaglomerular granular cells
• converts angiotensinogen to angiotensin 1
• ACE converts angiotensin 1 to angiptensin 2
Where is ACE found?
• On the endothelium of cells, especially in lung
How does angiotensin 2 cause increase in BP?
• Vasoconstriction - arterioles
• Stimulates Na+ reabsorption - kidney
• Sympathetic nervous system - Increased release of NA
• Aldosterone release - adrenal cortex (revise effects) (Na+ reabsorption)
• Releases ADH - Hypothalamus, stimulated by thirst receptors
What two receptors does Ang 2 act on?
• AT1 and AT2
What is the main receptor Ang 2 acts on?
What type of receptors AT1 and AT2
• G protein couples
What five places does angiotensin effect?
• Sympathetic NSAdrenal cortex
Outline what angiotensin 2 does to the following-Arterioles
• Vasoconstricts afferent and efferent arterioles
Outline what angiotensin 2 does to the following
• Stimulates Na+ reabsorption at the kidney
What does angiotension 2 do to the hypothalamus?
• Stimulates ADH release
Outline what angiotensin 2 do in the nephron
• Vasoconstriction of afferent and efferent arterioles
• Enhanced Na+ reabsorption at the PCT in apical membrane
What does aldosterone do?
• Stimulates Na+ and water reabsorption
• Acts on principal cells of collecting duct
• Activates/increases expression apical Na+ channel (ENaC) and apical K+ channel
• Also increases basolateral Na+ extrusion via activation/increased expression Na/K/ATPase
What inhibits aldosterone?
What does ACE do other than its direct effects?
• Breaks down bradykinin -> Peptide fragments
Why do ACE inhibitors cause a cough?
• Reduce breakdown of bradykinin
• More bradykinin, more vasodilation
• Also causes cough in lungs
Give three ways sympathetic nervous system effects BP
• High levels of sympathetic innervation reduces renal blood flow (Decreased GFR/Decreased Na+ excretion)
• Activates apical Na/H-exchanger and basolateral Na/K ATPase in PCT
• Stimulates renin release from Jgcells
○ Leads to increased Ang 2 levels
How does sympathetic stimulation effect the nephron?
• Acts on arterioles to reduce renal blood flow
• Stimulates granular cells of afferent arteriole to release renin
• Stimulates Na+ reabsorption from PCT via renin-ang-aldosterone axis
What is the main role of ADH?
• Formation of concentrated urine by retaining water and controlling plasma osmolarity
What is ADH release triggered by?
• Stimulated by increases in plasma osmolarity or severe hypovolaemia
How does ADH generate concentrated urine?
• Addition of aquaporin to collecting duct
• Stimulates apical Na/K/Cl co-transporters in thick ascending limb, increasing water reabsorption down conc gradient
How does addition of aquaporin by ADH to collecting duct effect blood volume?
• Re-absorption of water
• Forms concentrated urine