Control of Blood Volume Flashcards
Describe the relation between arterial pressure and urine production?
When arterial pressure increases then the urine production increases. When pressure decreased then the urine production decreases.
What are the two primary determinants of long term regulation of blood pressure.
The renal output curve for salt and water, and the level of salt and water intake. Only long term way of changing BP is by changing one of these!
What are the four mechanisms the antidiuretic hormone (ADH, arginine vasopressin) are released?
- Increase in osmotic pressure which is sensed by hypothalamic osmoreceptors.
- Hypovolemia. Atrial baroreceptors normally inhibit ADH release but decrease in volume leads to decrease firing rate and ADH release.
- Hypotension. A decrease in atrial baroreceptor firing, increases sympathetic activity and increases ADH release.
Angiotesin 2
Describe how the antidiuretic hormone increases blood volume
It increases water permeability in renal collecting ducts which increases water reabsorption and decreases urine production
What occurs to the levels of ADH in hypovolemic show and what does this do?
ADH release is high and this causes vasoconstriction which increases total peripheral resistance in a means to maintain MABP.
What is Renin and what is it released in response too?
Proteolytic enzyme released by kidneys in response too;
- sympathetic nerve innervation 9mediated by baroreceptor feedback),
- Renal artery hypotension (independent of baroreceptors)
- Decreased sodium in kidney distal tubules.
Describe the Renin-angiotensin-aldosterone system (RAAS) pathway
Decreased arterial pressure triggers renin release, its then converted into renin substrate which is then converted into angiotesin 1. Angiotesin 1 is converted by converting enzymes in the lung to angiotesin 2. This causes either renal retention of water and sodium or vasoconstriction which increases arterial pressure
Where is renin released from?
Juxtoglomerular cells
What are the functions of angiotesin 2?
- Acts on resistance vessels to increase total peripheral resistance.
- It acts on the kidneys to constrict renal arteries which decreases blood flow via the kidneys.
- It causes release of aldosterone from renal glands which increases sodium and water reabsorbtion.
- Stimulates release of ADH from pituitary.
what is the function of Atrial natriuretic hormone and when is it released?
Released in response to the stretch of the atria and it helps oppose the effects of the RAAS system, may help counteract volume overload.
What occurs in hypovolaemia?
A loss in blood volume, this can be a decrease in whole blood, plasma or sodium. This will result in a decrease in blood pressure
Describe the classification of hypovolaemic shock
Class 1 - 10-15% blood loss (BL).
Class 2 - 15-30% BL.
Class 3 - 30-40% BL.
Class 4 - >40% BL
What is the imediate response to hypovolemia?
Baroreceptor reflex. The dree of volume loss affects how successful this is.
Describe the later response to hypovolaemia
Arteriole constriction. The decrease in hydrostatic pressure in capillaries favours fluid reabsorption which increases the blood volume
What occurs if there is severe hypovolemia?
There will be tamage to tissue or organs and the heart may fail
