Organisms Exchange Substances with their Environment: Mass Transport in Animals - Tissue Fluid

Question 1

What is tissue fluid?

Answer 1

• Tissue fluid is the fluid that surrounds cells in tissues
• It is made up of water and dissolved substances that leave the blood (oxygen, amino acids, nutrients)
• Cells take in oxygen and nutrients from tissue fluid and release metabolic waste (CO2, urea) into it

Question 2

What is hydrostatic pressure?

Answer 2

• Hydrostatic pressure is the pressure exerted by a liquid

Question 3

How is tissue fluid formed?

Answer 3

• As blood is pumped through increasingly small vessels (arterial end of capillary), a large hydrostatic force pushes blood fluid out of the capillaries
• Only small substances that fit through gaps in capillaries can escape - these are the components that make up tissue fluid

Question 4

What forces act against the hydrostatic pressure of fluid in capillaries?

Answer 4

• Hydrostatic pressure of tissue fluid outside capillaries
• Osmotic pressure
• At venule end, water potential of the blood is lower
• Due to large plasma proteins that stay in blood

Question 5

Explain how hydrostatic pressure and osmotic pressure changes across a capillary affect the movement of tissue fluid

Answer 5

• Arterial end - closer to artery

• Higher hydrostatic pressure inside capillary, pushing fluid out
• Smaller osmotic pressure outside of capillary

• Venule end - closer to vein

• Higher hydrostatic pressure outside of capillary, pushing fluid in capillary
• Loss of water from capillaries reduces hydrostatic pressure
• Larger osmotic pressure outside capillary, due to big proteins in blood
• Water and dissolved metabolic waste moves into capillary by osmosis

Question 6

What happens to the tissue fluid that is not pushed back into the capillaries?

Answer 6

• Drained by the lymphatic system
• Hydrostatic pressure is higher outside lymph vessel, pushing tissue fluid in lymph vessel
• Body muscles contract and squeeze lymph vessels - valves ensure lymph moves in right direction (back towards circulatory system)

Question 7

Why is pressure highest at arterial end of capillary?

Answer 7

• Caused by left ventricle contracting and sending blood out of heart, through arteries and arterioles, at high pressure

Question 8

What term is used to describe the movement of molecules out of capillaries due to hydrostatic pressure?

Answer 8

• Pressure filtration

Question 9

What is lymph fluid?

Answer 9

• Carried by lymph vessels
• Carries waste products
• Contains water, nutrients, oxygen, white blood cells, chylomicrons
• Does not contain red blood cells or big protein molecules - too big