Tissue Fluid

Question 1

What is tissue fluid?

Answer 1

• Plasma without proteins and RBCs
• Allows exchange of substances between blood and cells in tissues
• Arterial end of blood supply has highest pO2 and lowest pCO2

Question 2

Arterial end

Answer 2

• Blood under high pressure due to pumping action of the heart
• Hydrostatic pressure forces the fluid/ plasma and small molecules through the capillary walls into interstitial spaces between cells
• Outward flow opposed by reduced solute/ water potential of blood due to plasma proteins
• Hydrostatic pressure greater than osmotic pressure
• Net flow of plasma out of blood

Question 3

Exchange

Answer 3

• Proteins retained as too big
• Fluid contains glucose, amino acids, hormones, fatty acids
• Useful substances diffuse into cells that require them

Question 4

Venous end

Answer 4

• Hydrostatic pressure has decreased due to loss of fluid/ water and friction against capillary wall/ lining
• Retention of proteins so lower water potential inside the capillary (Higher [proteins])
• Osmotic pressure greater than hydrostatic = tissue fluid flows back into capillary by osmosis
• Contains CO2 and other waste products

Question 5

Lymphatic System

Answer 5

• Not all fluid passes back
• Excess tissue fluid drained into lymph vessels of the lymphatic system
• It is now called lymph fluid and contains more lipids and CO2
• Drained back into the circulatory system via thoracic duct in chest
• Empties in subclavian vein (neck)

Question 6

What substances maintain osmotic pressure

Answer 6

Protein/ albumin

Question 7

Low protein diet and Kwashiorkor disease

Answer 7

• Low protein diet = fewer plasma proteins so lower plasma protein levels
• Plasma proteins reduce water potential of blood
• Lower level of protein = increases water potential of plasma
• Decreases water potential gradient
• Less water reabsorbed by osmosis and more remains in tissue fluid

Question 8

High pressure effect

Answer 8

• High blood pressure = higher hydrostatic pressure
• Increases outward pressure at the arteriole end of capillary
• More tissue fluid formed
• Reduces inward pressure at venule end of capillary
• Less tissue fluid reabsorbed by osmosis