8.3 - Blood, Tissue Fluid & Lymph

Question 1

What is blood plasma?

Answer 1

Main component of blood, yellow, carries dissolved substances such as blood cells

Question 2

What does blood plasma consist of?

Answer 2

• dissolved glucose, aas, mineral ions, hormones
  Proteins: albumin (maintains bloods osmotic potential)
  fibrinogen (proteins for blood clotting)
  globulins (involved in transport & immune system)
• erythrocytes and different types of leukocytes
• platelets - part of large cell called megakaryocyte, found in red bone marrow - involved in blood clotting

Question 3

What is the % composition of components of blood?

Answer 3

55% plasma (most of which is water)

45% RBCs, wbc, platelets

Question 4

What are functions of blood?

Answer 4

• transport of O2 and CO2 to and from respiring cells
• transport of digested food from small intestine
• nitrogenous waste products from cells to excretory organs (urea)
• transport hormones
• transport of stored food to necessary locations
• transport of platelets to damaged areas
• blood contributes to the maintenance of body temp (vasodilation/constriction) and is a buffer to minimise pH changes

Question 5

Define hydrostatic pressure.

Answer 5

Pressure due to gravity, increases with depth due to the weight above it
Is also increased by heart surge contraction

Question 6

Define oncotic pressure.

Answer 6

The tendency of water to move out of blood capillaries by osmosis due to the presence of plasma proteins.

Question 7

How does tissue fluid form? (Arterial side)

Answer 7

• Blood flows from arterioles into capillaries, still under hydrostatic pressure (gravity and heart surge contraction)
• at arterial end of capillaries, hydrostatic pressure (4.6) forces fluid out of capillaries as it is larger than oncotic pressure (3.3), net 1.3 pressure out
• fluid squeezed out called tissue fluid
  —this tissue fluid bathes and fills spaces between cells (same composition as blood plasma w/out RBCs or proteins)

Question 8

How does tissue fluid form? (Venous end)

Answer 8

• diffusion takes place between blood and cells through tissue fluid
• hydrostatic pressure falls at the venous end, oncotic pressure remains
  Water moves back into the capillaries as there is a higher solute potential, due to more plasma proteins being present than water (the other solutes move out the tissue fluid), this brings water back into the capillaries
• by the time blood vessels reach veins, 90% of tissue fluid is back into capillaries

Question 9

What happens to the 10% of tissue fluid that doesn’t return to the capillaries?

Answer 9

It drains into blind-ended tubes called lymph capillaries and is known as lymph.

Lymph: similar composition to plasma, less O2 and nutrients as it is taken up by tissue
- contains fatty acids absorbed into lymph from villi of small intestines

Question 10

What are lymph capillaries and what role do they play in fighting infection?

Answer 10

• lymph capillaries form to join larger vessels, they have 1 way valves
• lymph returns to blood flowing into L & R subclavian veins
  Lymph nodes: exist along lymphatic vessels. Within them are lymph nodes
  —they have lymphocytes that build up in lymph nodes where needed to product antibodies and intercept bacteria. They are ingested by phagocytes