B3.2.11 (HL)—Tissue fluid in capillaries

Tissue fluid forms when capillary hydrostatic pressure forces plasma out, while plasma proteins help draw fluid back near venule ends.

Tissue fluid is formed when hydrostatic pressure at the arteriole end of a capillary forces some plasma out through the capillary wall.

Small solutes and water leave, but cells and most plasma proteins remain in the blood. As pressure falls and osmotic effects change along the capillary, some fluid is reabsorbed.

Compare hydrostatic and osmotic forces along the capillary; state why filtration changes with position.

Higher blood pressure at the arterial end favors filtration, while lower pressure toward the venous end favors return of fluid.

Tissue fluid is not whole blood: red cells and large proteins normally stay inside the capillary.

HL transport adds pressure and route systems. Tissue fluid forms by capillary pressure and returns by osmotic pull or lymph. Double circulation separates pulmonary and systemic routes. The heart creates directional pressure with chambers, septum, valves, and cycle timing. Plants add root pressure and phloem pressure-flow translocation.

Tissue fluid: hydrostatic pressure out, osmotic pull back, lymph drains excess.
Heart: double circulation, one-way valves, thick left ventricle, cardiac cycle sequence.
Plant HL: root pressure by active ion loading and osmosis; phloem by source-to-sink pressure flow.

Concept essentials

Hydrostatic pressure at arteriole ends forces plasma fluid out of capillaries.
Plasma proteins remain in blood and create osmotic pull back into capillaries.
Lower pressure near venule ends allows most tissue fluid to re-enter blood.
Excess tissue fluid is drained into the lymphatic system.

B3.2.11 (HL)—Tissue fluid in capillaries

Tissue Fluid Forms at High Capillary Pressure

Pressure, Heart, Lymph, And Phloem

Concept essentials