What do the terms hydrostatic pressure and oncotic pressure mean in the context of the human circulatory system?

  1. Hydrostatic pressure - pressure exerted by the force of the heart pumping on blood
  2. Oncotic pressure - a form of osmotic pressure exerted by proteins in blood plasma that tends to pull water into the circulatory system

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What is tissue fluid, and how is it formed from plasma in a capillary network?

Tissue fluid is the fluid that surrounds the cells in tissues.


Tissue fluid is formed when high hydrostatic pressure at the arteriole end of a capillary forces plasma out of the capillary and into the interstitial spaces surrounding cells.

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How does tissue fluid return to the circulatory system?

  1. Tissue fluid returns to the circulatory system at the venule end of the capillary where the hydrostatic pressure is lower and oncotic pressure is higher
  2. The lymphatic system collects excess fluid that cannot be absorbed by the capillaries, forming lymph that is eventually returned to the bloodstream

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What are the differences in the composition of blood, tissue fluid, and lymph?

Blood contains red blood cells, white blood cells, platelets, and plasma.


Tissue fluid is like plasma but with fewer proteins, and it does not contain red blood cells but may contain some white blood cells.


Lymph is similar to tissue fluid, but contains less oxygen and nutrients and contains many fatty acids and white blood cells (lymphocytes).

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What are the functions of tissue fluid?

Tissue fluid provides cells with nutrients and oxygen and removes waste products. It also helps fight infection as it forms part of the immune response.

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What is the main component of blood and tissue fluid?

Water is the main component of both blood and tissue fluid.

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What is the role of proteins in the movement of water out of tissue fluid?

Proteins in the blood plasma exert an oncotic pressure that pulls water back into the capillaries from the tissue fluid.

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What is the difference between the arteriole and venule end of a capillary in terms of hydrostatic pressure and the movement of fluid?

The arteriole end of a capillary has high hydrostatic pressure due to the force exerted by the pumping of the heart, forcing fluid out.


The venule end of a capillary has lower hydrostatic pressure, allowing fluid return to the capillaries.

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