14. Disturbances in water-electrolyte balance – dehydration and hyperhydration. Types and complications.

DISTURBANCES IN WATER-ELECTROLYTE BALANCE - DEHYDRATION AND HYPERHYDRATION

• Water-electrolyte imbalance is the loss of balance between the levels of water and levels of electrolytes in the body
• Water makes up ~ 60% of total body weight
• Total body water:
• 2/3 intracellular
• 1/3 extracellular
• The water content of the body remains constant

Electrolytes

Movement of water

• Sodium determines the volume of water that is outside the cells
• Na+ retention causes volume to expand
• Na+ loss causes volume to decrease
• Water moves freely within the intracellular and extracellular compartments keeping osmolality equal
• There are 3 types of homeostasis involved:

1. Fluid balance
2. Electrolyte balance
3. Acid-base balance

• The following systems are involved in the regulation of exchange of water between the ICF and ECF

1. Renal
2. Endocrine
3. GI system
4. Cardiovascular
5. Respiratory
6. Nervous

Regulation of ECF

1) Kidneys

1. a) Hypovolemia
2. b) Renin production increases
3. c) Initiates activation of angiotensinogen to angiotensin
4. d) Constricts blood vessels
5. e) Causes aldosterone to be secreted from adrenal glands
6. f) Increased water and Na+ retention by the kidneys

2) Brain

1. a) Hypothalamus responds to decrease in water content or decrease in Na+ concentration in the blood
2. b) Stimulates pituitary gland to release ADH (vasopressin)
3. c) ADH stimulates increased Na+ and water retention

3) Heart

1. a) When blood volume is abnormally high → atrial natriuretic peptide (ANP) is released from cardiomyocytes in the right atrium
2. b) ANP increases GFR and inhibits reabsorption of water and Na+
3. c) This results in increased excretion of water (diuresis) and sodium (natriuresis) → reduces circulating blood volume and pressure