Control of NaCl Balance (Wed 8/11/17) Flashcards
LO: Describe the concept of “effective circulating volume” and be able to predict the effects of positive and negative sodium balance
The more sodium reabsorbed into blood, osmolality of blood increases, more water absorbed, more blood volume, so greater blood pressure. Thus increase in ECV can lead to hypertension.
We have sensors for blood pressure across the vasculature. They detect stretch in the vasculature. Grouped as barrow? receptors.
In the high pressure circuit:
- Aortic Arch
- Carotid Sinus
- Juxta Glomerular Apparatus
In the low pressure circuit:
- Atria
- Pulmonary Vasculature
- Hepatic Vasculature
Na Balance is Achieved by Changes in Distal Na Handling
This takes time. If input of sodium increases, the body will take a few days to balance the output and get back to steady-state. This is because the collecting duct can only take in/release a small amount of sodium per day. Blood pressure remains constant due to short term control of blood pressure over these couple of days.
If you have too much sodium in your diet, and try to get the collecting duct to remove it, it will become overloaded, so the proximal tubule needs to reabsorb it. Increase in amount of sodium, the GFR will increase, we increase the amount of Na & H2O absorbed to match increase in GFR. This keeps distal delivery of Na constant.
If the blood volume increases very quickly, glomerular tubular balance can be over-ridden. Blood pressure increases, the return of blood to right atria increases, causing stretch, so atrial naturetic peptide is released increases GFR and decrease colloid osmotic pressure in peritubular capillaries, so there is decreased reabsorption. This means the collecting tubule will be overloaded and a lot of sodium will be lost very fast. This decreases blood volume.
When blood volume decreases very rapidly, sympathetic activity decreases. and less sodium is excreted. This decreases GFR and stimulates proximal tubule Na+ re-absorption.
LO: Describe the important controls of renal sodium excretion including, glomerular filtration rate (GFR), glomerular tubular balance, the renin-angiotensin-aldosterone system, sympathetic nerves, atrial natriuretic peptide
Distal Tubule Control of Na+ Absorption:
When blood volume goes down, less sodium, renin goes up.
Angiotensin Converting Enzyme: ACE inhibitors mean no angiotensin 2, means no vasoconstriction, no aldosterone.
*see slide 15
LO: Describe the effect of derangement in renal sodium excretion and understand the impact of inhibiting the renin-angiotensin-aldosterone system
LO:
