Session 4 - Changes in Plasma Volume (Hormonal control) Flashcards Preview

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Flashcards in Session 4 - Changes in Plasma Volume (Hormonal control) Deck (72)
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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?

• AT1


What type of receptors AT1 and AT2

• G protein couples


What five places does angiotensin effect?

• Arterioles
• Kidney
• Sympathetic NS Adrenal cortex
• Hypothalamus


Outline what angiotensin 2 does to the following-Arterioles

• Vasoconstriction
• 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?

• Spironolactone


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

Increased aldosterone


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


How does stimulation of Na/K/Cl co-transporter in the thick ascending limb increase reabsorption of water?

• Less Na+ moves out into the medulla, reduced osmotic