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26 Cards in this Set
- Front
- Back
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What is regulation of blood/extracellular fluid equivalent to?
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regulation of body Na+ content
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Why is osmolality normally maintained at the expense of volume?
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Regulation of osmolality is more rapid than that of volume
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How is plasma osmolality regulated?
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1. drinking - driven by thirst
2. excretion of excess water in urine |
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Give the effect of drinking 1.2l of water?
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1.Water rapidly absorbed in the gut
2. Osmoreceptor detect decrease in osmolality 3. Reduce ADH release 4. Inhibits renal reabsorption of water -> rapid increase in production of dilute urine |
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Give the effects of drinking 1.2l of isotonic saline and state what the response is due to?
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1. Does not change plasma osmolality
2. Therefore blood vol. and pressure increase 3. Stimulate slow loss of salt and water - slow prodn. of (normally conc.) urine Response due to increased blood vol/pressure therefore slower increase in ANP inhibition of RAAS thus decreased reabsorption of Na+ and H20, thus increased prodn of urine (more conc. than for just H20) |
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Describe the control of plasma osmolality and ADH?
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1. increased Na+ intake or dehydration
2. Increases plasma osmolality 3. Stimulates receptors in hypothalmus and pituitary 4a. Stimulate increase in ADH 4b. Stimulate thirst 5a. Increase water reabsorption in distal nephron 5b. Increasse water ingestion 6. Decrease plama osmolality |
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Describe ADH
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=anti diuretic hormone/vasopressin
9 a. acids plasma half life ~15 mins Synthesised in hypothalmus Stimulated by increased osmolality, low blood vol/pressure inhibited by alcohol |
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Describe how ADH affects water reabsorption in the distal nephron?
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Principal Cell
ADH binds to V2 receptor cAMP binds to vesicle containing aquaporin Binds to membrane Creating channel for transport of water |
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Describe the limits on urine osmolality?
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-Absence of ADH
No water reabsorption in collecting duct urine osmolality equals that of late distal tubular fluid (60-80mOsm) -max. ADH water reabsorbed until tubular fluid osmolality = medulla interstitium ~1400mOsm |
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What stimulates prodn of ADH
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high plasma osmolality
low BP low blood volume nausea |
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What inhibits prodn of ADH
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alcohol
emotional stress |
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What causes changes in blood volume?
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changes in body [Na+]
as osmorecptors then increase or decrease water to compensate |
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Describe the effects of increased blood volume?
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Increased Blood Vol Causes:
1. Stretch of Atria Therefore increased firing of atrial receptors Release of ANP 2. Increased atrial pressure Increased firing of atrial barorecptors Activation of atrial receptors causes: 1. Decreased SYMPATHETIC outflow to heart and vasculature -> reduction in atrial pressure 2. Inhibition of ADH secretion -> diuresis 3. Decreased stimulation of renal sympathetic nerves reduces renin secretion therefore reduces angiotensin 2 thus reduces aldosterone 4. Increased release of ANP leads to natriuresis Independently of receptors: Pressure natriuresis |
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Describe the effects of RAAS for a fall in vol/pressure?
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1. Fall in pressure/vol
2. Fall in tubular [Na+, Cl-, K+] 3. Activation of sympathetic stim. in afferent arteriole 4. Causes release of renin from granular cells 5. Converts angiotensinogen to angiotensin 1 6. ACE converts angiotensin 1 to angiotensin 2 7. increases aldosterone production |
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Describe the effects of angiotensin II?
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= potent vasoconstrictor
stimulates ADH and thirst stimulates release of aldosterone |
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Where does ACE work?
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Mainly in lungs
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How many amino acids is angiotensin I and II
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I = 10 a. acids
II = 8 a. acids |
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Where is aldosterone secreted from?
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Zona Glomerulosa of adrenal cortex
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What causes aldosterone secretion?
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1. Increased angiotensin II
2. Increased plasma [K+] |
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Describe the action of aldosterone?
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Increases gene transcription of ENaC, ROMK, and Na+ pump
in PRINCIPAL cells in distal tubule and collecting duct |
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How many a. acids in ANP?
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28
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Describe the release of ANP?
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released from atrial muscle
in response to increased blood vol (i.e. stretch) |
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Describe the action of ANP?
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Inhibits ENaC
Dilates afferent - increasing GFR Inhibits renin release and aldosterone production Promotes natriuresis (excretion of NA+ and H20) |
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What effect does increased BP have urine output and Na+ excretion?
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sharply increases it
=prodn vasodilator prostaglandins and NO in renal medulla Increase blood flow thus reduce osmotic gradient in medulla Thus water reabsorption in collecting duct reduced |
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How may hypertension affect the Aterial pressure vs. Vol excreted relative to normal intake?
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Curve may shift to right
so appropriate Na+ and water secretion can only occur at high arterial BP |
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Describe the effects of increased blood volume?
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Look at diagram in notes!
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