C APILLARY F LUID E XCHANGE

C APILLARIES Nearly every tissue of the body is within 0.1 mm of a capillary. Materials that move into and out of the capillaries include: Oxygen Carbon Dioxide Glucose Urea Hormones Minerals

M OVEMENT OF M OLECULES Molecules can move across the membrane through: Diffusion Filtration / Absorption

D IFFUSION

Oxygen and carbon dioxide diffuse through the capillary Other larger molecules move via exocytosis or endocytosis

F ILTRATION / A BSORPTION Depends on two forces: Fluid pressure due to ventricular contractions (filtration) Osmotic pressure due to water concentrations (absorption)

F ILTRATION - F LUID P RESSURE The force that the blood exerts on the walls of the capillaries. Causes fluid to leave capillaries. Pressure is higher at arteriole end of capillary compared to venule end.

F ILTRATION - F LUID P RESSURE More pressure in capillary forces fluids from high pressure (in the capillary) to low pressure (in extracellular fluid)

A BSORPTION - O SMOTIC P RESSURE Blood is hypertonic therefore water is always trying to enter (high number of plasma proteins). Constant throughout the entire capillary bed.

N ET P ROCESS Net Absorption 10 mmHg in Net Filtration 10 mmHg out

N ET P ROCESS

H EMORRHAGE ( EXCESSIVE BLEEDING ) Low fluid pressure; normal osmotic pressure. Proteins and fluids are lost; but the concentration of proteins has not changed. The force that drives the fluid from the capillaries is diminished, but the force that drive it into the capillaries is not altered (force differential). This movement into the capillaries provides a homeostatic adjustment. Restores fluid volume.

S TARVATION Normal fluid pressure; low osmotic pressure. Swelling or edema. Plasma proteins are used as a last source of energy. Decreases capillary absorption (lower osmotic pressure). More water enters the tissues than is pulled back= swelling. Same with inflammation

D ISORDERS OF THE C APILLARY F LUID E XCHANGE Edema Plasma proteins are used as an energy source Fewer proteins in blood = less osmotic pressure Lower osmotic pressure = fluid build up in tissues Fluid build up = swelling

L YMPHATIC S YSTEM Lymph system also transports proteins that slowly leak from capillaries back to the blood

T HE L YMPHATIC S YSTEM The lymphatic system returns proteins from the ECF to the circulator system. Lymph  is a fluid (like blood) found in lymph vessels (similar to veins) that contain some proteins that have leaved through capillary walls. The proteins are returned through slow muscle contractions against vessels.