8.3 - Blood, tissue fluid, and lymph

Question 1

Blood

Answer 1

• Blood consists of a yellow liquid - plasma - which carries a wide variety of other components including dissolved glucose and amino acids, mineral ions, hormones, and the large plasma proteins including albumin, fibrinogen and globulins.
• Plasma also transports red blood cells and many types of white blood cells
• It also carries platelets. Platelets are fragments of large cells called megakaryocytes found in the red bone marrow, and they are involved in the clotting mechanism of the blood
• Plasma makes up 55% of the blood by volume - and much of that volume is water
• Only the plasma and the red blood cells are involved in the transport functions of the blood.

Question 2

Functions of the blood

Answer 2

• oxygen to carbon dioxide from the respiring cells
• digested food from the small intestine
• nitrogenous waste products from the cells to the excretory organs
• Chemical messages (hormones)
• food molecules from storage compounds to the cells that need them
• platelets to damaged areas
• cells and antibodies involved in the immune response

Question 3

Tissue fluid

Answer 3

• The substances dissolved in plasma can pass through the fenestrations in the capillary walls, with the exception of the large plasma proteins.
• The plasma proteins, particularly albumin have an osmotic effect
• They give the blood in the capillaries a relatively high solute potential compare with the surrounding fluid.
• As a result, water has a tendency to move into the blood in the capillaries from the surrounding fluid by osmosis.
• However, as blood flows through the arterioles into the capillaries, it is still under pressure from the surge of blood that occurs every time the heart contracts.
• This hydrostatic pressure
• At the arterial end of the capillary, the hydrostatic pressure forcing the fluid out of the capillaries is relatively high at about 4.6kPa
• It is higher than the oncotic pressure attracting water in by osmosis, so fluid is squeezed out of the capillaries.
• As the blood moves through the capillaries towards the venous system, the balance of forces changes.
• The hydrostatic pressure falls to around 2.3 kPa in the vessels as fluid has moved out and the pulse is completely lost. The oncotic pressure is still -3.3 kPa, so it ia noq atronger

Question 4

Lymph

Answer 4

• Some of the tissue fluid does not return to the capillaries.
• 10% of the liquid that leaves the blood vessels drains into a system of blind-ended tubes called lymph capillaries, where it is known as lymph. Lymph is similar in composition to plasma and tissue fluid but has less oxygen and fewer nutrients
• It also contains fatty acids, which have been absorbed into the lymph from the vili of the small intestine
• The lymph capillaries join up to form larger vessels.
• The fluid is transported through them by squeezing the body muscles.
• One-way valves like those in veins prevent the backflow of lymph.
• Eventually, the lymph returns to the blood, flowing into the right and left subclavian veins.
• Along the lymph vessels are the lymph nodes.