13. Osmolality of all three compartments
13
Osmolality of all three compartments is the
same, because water is able to move freely
among all three compartments
15. Movement of water – Starling’s Forces
15
The amount of water in each body compartment is
dependent on:
1- osmotic pressure
2- hydrostatic pressure (filtration)
+ 3- Membrane characteristics
16. Osmolality
is the number of particles (mmol) contained in
one liter of water, so measured in mmol/L.
i.e. it is the concentration by number
32. Volume Regulation
General Concept: 2- Signaling
32
• Renin-angiotensin II-aldosterone and sympathetic activity are the primary
signals of volume regulation; these signals are activated together.
• ADH is only employed when volume is extremely low i.e. secondary line.
• If ADH is active, then renin-angiotensin II-aldosterone and sympathetic
activation are already engaged.
36. Volume Regulation
General Concept: 3- Action at Targets – Angiotensin II
36
Angiotensin II is the most potent vasoconstrictor in the body
37. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
37
The effect of aldosterone on sodium reabsorption is so powerful that it
can reduce the urine sodium concentration to as low as 1 mEq/L
38. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
38
39. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
39
Aldosterone Overview
•An increase in the plasma potassium concentration of 0.1 mEq/L is enough to stimulate
the release of aldosterone.
• Although aldosterone release is not affected by acid-base disorders, aldosterone plays
an important role in the generation and maintenance of many acid-base disorders.
•Increased aldosterone activity results in metabolic alkalosis and decreased activity
results in metabolic acidosis (type 4 RTA).
41. Volume Regulation
General Concept: 3- Action at Targets – ADH
41
•ADH is only released when a substantial (10-15 mmHg) fall in blood pressure occurs.
•Although it is an emergency defense, ADH is not a very effective defense against
hypovolemia. Because water distributes among all three body water compartments,
water resorption at the collecting tubules causes only a minimal rise in plasma volume.
•The primary function of ADH is the regulation of plasma osmolality.
42. Volume Regulation
General Concept: Atrial natriuretic peptide
42
Atrial natriuretic peptide is the only volume regulatory hormone that decreases
effective volume
•The physiologic significance of ANP is uncertain.
•Although congestive heart failure is associated with volume overload and elevated
levels of ANP, the kidney still excretes minimal amounts of sodium. This contradiction is
explained by the theory that ANP activity requires a normal blood pressure.
•Since CHF is typically associated with a lower than normal blood pressure, the effect
of ANP is blocked.