Changes in Plasma Osmolarity, Distribution of ECF and Oedema

Increase in blood osmolarity

Hypothalamic osmoreceptors detect increased blood osmolarity, adh released from posterior pituitary, adh acts on nephrons to reabsorb water into blood, urine becomes more concentrated, blood becomes more dilute

Fluid movement between compartments

Ion flux between interstitial fluid and icf is restricted, nutrients, gases and wastes typically move in a single direction via diffusion

Filtration of ecf

Hydrostatic pressure forces protein-free plasma from blood into interstitial fluid

Reasborbtion into blood

fluid is reabsorbed from interstitial fluid into blood via oncotic or colloid osmotic pressure

Capillary hydrostatic pressure

Pressure exerted by blood on the walls of the capillaries, primarily responsible for forcing fluid out of the capillaries and into interstitial fluid via filtration

Interstitial fluid hydrostatic pressure

Pressure exerted by interstitial fluid surrounding cells

Plasma oncotic osmotic pressure

Osmotic pressure exerted by large proteins present in plasma, particularly albumin, proteins too large to pass through capillary walls and therefore remain in blood vessels

Interstitial fluid oncotic osmotic pressure

Oncotic pressure exerted by proteins present in interstitial fluid

Oedema

Fluid accumulation inside tissues, caused by increased hydrostatic pressure, decreased oncotic pressure, lymphatic obstruction or increased vascular permeability

Increased hydrostatic pressure and oedema

Water retention due to kidney failure, heart failure and vessel obstruction causes blood pooling and hypertension, cardiac related oedema usually present in lower extremities

Decreased oncotic pressure and oedema

Decreased plasma proteins due to liver failure, malnutrition or nephrotic syndrome, proteins may escape from blood into glomerulus if there is a problem with the nephron

Lymphatic obstruction and oedema

Neoplastic obstruction or inflammatory obstruction

Increased vascular permeability and oedema

Injury triggers inflammatory response, histamine released causes increased capillary permeability, fluid and protein can pass into interstitial fluid which reduces oncotic pressure and volume