8.3. BLOOD, TISSUE FLUID, LYMPH

Question 1

what is blood made up of?

Answer 1

• consists of a yellow liquid plasma (55% of blood by volume, much of this is water)
• red blood cells
• white blood cells

Question 2

what does plasma carry?

Answer 2

• wide variety of other components incl. dissolved glucose, amino acids, hormones, large plasma proteins (i.e. albumin, fibrinogen, and globulins)
• platelets
• red blood cells and white blood cells are also transported by plasma

Question 3

what is the function of albumin?

Answer 3

• important for maintaining the osmotic potential of the blood

Question 4

what is the function of fibrinogen?

Answer 4

• important in blood clotting

Question 5

what is the function of globulin?

Answer 5

• involved in transport and the immune system

Question 6

what are platelets?

Answer 6

• fragments of large cells called megakaryocytes found in the red bone marrow
• involved in the clotting mechanism of blood

Question 7

what does the blood transport?

Answer 7

• oxygen to, and 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 8

what does blood also contribute to?

Answer 8

• maintenance of a steady body temperature and acts as a buffer, minimising pH changes

Question 9

what substances in plasma cannot pass through the fenestrations in the capillary walls?

Answer 9

• large plasma proteins

Question 10

why does the blood in the capillaries have a relatively high solute potential, and a low water potential compared to surrounding fluid?

Answer 10

• as the plasma proteins, particularly albumin which has an osmotic effect, cannot pass through the capillary walls
• as a result, water moves into the blood in the capillaries from the surrounding tissue by osmosis (oncotic pressure of about -3.3kPa)

Question 11

what is hydrostatic pressure in the blood?

Answer 11

• 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
• at the arterial end of the capillary, hydrostatic pressure forcing fluid out of the capillaries is higher (4.6kPa) than the oncotic pressure attracting water in by osmosis

Question 12

at the arterial end of the capillary, hydrostatic pressure forcing fluid out of the capillaries is higher (4.6kPa) than the oncotic pressure attracting water in by osmosis, what does this lead to?

Answer 12

• fluid is squeezed out of the capillaries
• it fills the spaces between the cells and is called tissue fluid

Question 13

what is the composition of tissue fluid?

Answer 13

• same as plasma, without the red blood cells and the plasma proteins

Question 14

where does diffusion take place?

Answer 14

• between the blood and the cells through the tissue fluid

Question 15

how does the balance of force change as blood moves through the capillaries towards the venous system?

Answer 15

• hydrostatic pressure falls to around 2.3kPa in the vessels as fluid has moved out and the pulse is completely lost
• oncotic pressure is still -3.3kPa, it is now stronger than the hydrostatic pressure, so water moves back into the capillaries by osmosis as it approaches the venous end of the capillaries
• by the time blood returns to the veins, 90% of the tissue fluid is back inside the blood vessels

Question 16

how do you calculate filtration pressure?

Answer 16

hydrostatic pressure - oncotic pressure

Question 17

what is lymph?

Answer 17

• not all of the tissue fluid returns to the capillaries, 10% of it drains into a system of blind-ended tubes called lymph capillaries
• the lymph capillaries join up to form larger vessels

Question 18

what is the composition of lymph?

Answer 18

• similar to plasma and tissue fluid, but has less oxygen and fewer nutrients
• also contains fatty acids, which have been absorbed into the lymph from the villi of the small intestine

Question 19

how is the fluid transported to the larger vessels that form from lymph capillaries?

Answer 19

• by the squeezing of body muscles
• one way valves like those in veins prevent the back flow of lymph
• eventually the lymph returns to the blood, flowing into the right and left subclavian veins (under the clavicle, or collar bone)

Question 20

what are along the lymph vessels?

Answer 20

• lymph nodes
• lymphocytes build up the lymph node when necessary and produce antibodies, which are then passed into the blood

Question 21

what do lymph nodes also do?

Answer 21

• intercept bacteria and other debris from the lymph, which are ingested by phagocytes found in the nodes
• the lymphatic system plays a major role in the defence mechanisms of the body

Question 22

why do we sometimes get enlarged lymph nodes?

Answer 22

• as a sign the body is fighting off an invading pathogen
• this is why doctors examine the neck, armpits, stomach or groin of their patients (sites of major lymph nodes AKA lymph glands)