Renal System: L39 - Renal control of Composition and Volume of ECF Flashcards
Where are the 3 mains sites of plasma volume detection (which should be proportional to sodium concentration)?
Low-pressure baroreceptors - Right atrium of heart, vena cavae, pulmonary blood vessels.
High-pressure baroreceptors - aortic arch, carotid sinuses.
Intra-renal baroreceptors - afferent arteriole senses blood pressure.
Explain the function of Low-pressure baroreceptors.
Detect high volumes and communicate to cardiovascular centres in the brainstem to secrete more atrial natriuretic peptide (ANP)
Explain the function of High-pressure baroreceptors.
Sense change in pressure and send this information to the cardiovascular centres in the brainstem. Information is integrated and dealt with by changes with ADH and renal nerve activity.
Explain the function of intra-renal baroreceptors.
Afferent arteriole senses change in blood pressure, juxtaglomerular apparatus changes secretion in renin. The macula densa cells of the JGA sense sodium concentration (and hence flow rate) in the distal tubule and also alter renin secretion.
What happens if it is sensed that there is too much blood volume?
When detected that blood volume and distal tubule flow is too high (indicating too much sodium/volume) then mechanisms are activated to enhance secretion of sodium (although inevitably some water is lost with this).
What happens if it is sensed that there is too little blood volume?
When detected too little volume and distal tubular flow are low (indicating too little sodium/volume) then mechanisms are activate to enhance sodium reabsorption to retain water, therefore ECF and blood pressure/volume.
In terms of mechanisms for regulating Na+ and plasma fluid volume, what does the renal sympathetic nerve do?
Nerves are activated in response to low volume (which indicates low Na+) and respond by decreasing filtration of glomerulus (i.e. GFR), increasing reabsorption of Na+ in tubule and increase release of renin. This decreases secretion of sodium and increases sodium in plasma which brings water with it, increasing volume back to normal.
In terms of mechanisms for regulating Na+ and plasma fluid volume, what does the antidiuretic hormone do?
ADH increases permeability of collecting ducts, so water reabsorption increases, which is required when there is a decrease in blood volume.
In terms of mechanisms for regulating Na+ and plasma fluid volume, what does atrial natriuretic peptide do?
This hormone is secreted from the atria of the heart in response to high volume (which indicates high Na+). ANP essentially has opposite effects to renal sympathetic nerves, it increases GFR, decreases Na+ reabsorption in the renal tubules and decreases release of renin.
What are the mechanisms for maintaining blood volume?
- Atrial natriuretic peptide
- Anti diuretic hormone
- Aldosterone
- Renal sympathetic nerves
- Juxtaglomerular apparatus
- Renin-angiotensin
Discuss how renin causes angiotensin II, and the function of angiotensin II.
- Renin-enzyme secreted by JGA.
- Cleaves angiotensinogen into angiotensin I.
- Angiotensin I to angiotensin II by converting enzyme ACE.
- Angiotensin II is active form, it is a potent vasoconstrictor, stimulates tubular Na+ reabsorption, stimulates aldosterone release.
What are the stimuli for renin release by juxtaglomerular apparatus when ECF volume is low?
- Reduced renal perfusion pressure in afferent arteriole.
- Decreased delivery of NaCl to macula densa (if volume decrease, then filter decrease, then decrease in tubules).
- Renal sympathetic nerves (activated by baroreceptors)
What are the effects of RAS to increase volume?
Overall effect is to decrease sodium and water excretion, to preserve/restore blood volume.
- Decrease filtered load of Na+
- Stimulates reabsorption of Na+
- Increases aldosterone secretion which also stimulates Na+ reabsorption
- Powerful vasoconstrictor, increases total peripheral resistance
- Hypothalamus will cause thirst and ADH release.
What is aldosterone and what does it do to increase volume?
Aldosterone is a steroid hormone is secreted from adrenal glands by angiotensin II. Acts on distal tubule and collecting duct to cause increased reabsorption of Na+ (and secretion of K+) also controls 2% of filtered load (necessary).
