Changes in blood volume and pressure

hypervolaemia

An increase in blood volume that increases cardiac filling, stroke work, cardiac output, and blood pressure.

What organ is central to blood volume control and how?

The kidney, by regulating Na⁺ (and thus water) excretion.

What happens to GFR if blood volume falls too low?

Glomerular Filtration Rate (GFR) stops.

What initiates renin release in the kidney?

Low blood pressure, Na⁺ deficiency, dehydration, or haemorrhage.

What is the function of renin?

Converts angiotensinogen into angiotensin I, which is then converted to angiotensin II.

What does angiotensin II do?

Causes vasoconstriction and stimulates aldosterone release to increase blood pressure and volume.

What stimulates aldosterone secretion

Angiotensin II and elevated K⁺ levels.

What does aldosterone do in the kidneys?

Increases Na⁺ reabsorption, leading to water reabsorption and increased blood volume.

Where are arterial baroreceptors located?

In the carotid sinus and aortic arch.

What is the role of baroreceptors in blood volume control?

Sense blood pressure changes and adjust sympathetic output to regulate renal function and GFR.

What role does the macula densa play in tubuloglomerular feedback?

Detects NaCl concentration and signals juxtaglomerular cells to adjust renin release.

How does sympathetic activity affect the kidney during low blood pressure?

Increases constriction of renal arterioles and enhances renin release.

What does increased NaCl intake trigger?

Raises osmolarity → stimulates vasopressin and thirst → increases water intake and reabsorption.