The Lymphatic System

Question 1

How is lymph moved?

Answer 1

• hydrostatic pressure.
• contraction of body muscles aided by the valves in the lymph vessels.

NOT:
- by the heart beating.

Question 2

The lymphatic system?

Answer 2

Not all the tissue fluid returns to the capillaries, excess drains into the lymphatic system where it forms lymph. Lymph is a colourless/pale yellow fluid similar to tissue fluid but containing more lipids. The lymphatic system drains into the circulatory system near the vena cava via the thoracic duct.

Question 3

Tissue fluid?

Answer 3

Tissue fluid is the fluid which allows the exchange of substances between the blood and cells. It is composed of blood plasma.

Question 4

What substances are exchanged via tissue fluid?

Answer 4

Delivered:

• glucose
• amino acids
• fatty acids
• salt
• oxygen

Removes:

• carbon dioxide
• waste products

Question 5

How is tissue fluid formed?

Answer 5

At the arterial end by hydrostatic pressure, capillaries are narrower than the arterioles hence pressure builds up which forces tissue fluid out of the blood. It is resisted by:

• pressure of the tissue fluid on the capillaries from the outside
• the lower water potential of the blood caused by plasma proteins too large to leave the blood
• however the pressure pushes the tissue fluid and small molecules out of the capillary leaving cells and large proteins this is ultrafiltration.

At the venous end by osmotic pressure. Most tissue fluid is returned to the blood plasma via the capillaries. This is resisted by:

• osmotic pressure resulting from the proteins in the plasma lowering the WP, pull water back into the capillaries
• hydrostatic pressure at the venule end of the capillary is higher outside and tissue fluid is forced in.
• remaining tissue fluid enters the lymph vessels and drains back into veins close to the heart.