Mass Flow

Question 1

How is tissue fluid formed and returned to circulation (6)

Answer 1

6 from:
High hydrostatic pressure of blood high at arterial end of capillary

Forces fluid out of the capillary

Plasma proteins are too large to leave the capillary and remain

The water potential in the capillary becomes more negative than the surrounding tissue fluid

Water moves back into the capillary at the venous end

By osmosis

Lymph system collects any excess tissue fluid;

Returns the fluid to the circulatory system link at the vena cava/

Question 2

The lymphatic system has three different functions, what are they?

Answer 2

It drains excess tissue fluid
• It absorbs fats from the small intestine, via the lacteals inside each villus.
• It is part of the immune system. There are networks of lymph vessels at various places in the body (such as tonsils and armpits) called lymph nodes where white blood cells develop. These become swollen if more white blood cells are required to fight an infection.

Question 3

There is a net loss of water from a capillary at the arterial end because………

Answer 3

At the arterial end the hydrostatic pressure is greater than pressure of water potential

Question 4

The hydrostatic pressure decreases from the arterial end to the venule end due to……

Answer 4

Frictional force (resistance) of capillary the capillary walls
loss of fluid (not all (filtered) fluid is returned, some drains to lymph)

Question 5

What is tissue fluid?

Answer 5

The solution surrounding cells. It is like plasma, but without the proteins, as these stay in the capillaries.

Question 6

What does lymph have more of than tissue fluid?

Answer 6

Fats from the digestive system

Question 7

Tell me about arteries! (4)

Answer 7

Vessel with the thickest wall, enabling it to carry blood at high pressure / withstand pressure surges;
most elastic tissue, which smooth out flow/maintains pressure; it can distend when ventricles contract and can recoil
most muscle which maintains pressure;
muscle in wall to control blood flow, contracts, vasoconstriction occurs altering blood flow to organs. The proportion of muscle increases in the arterioles and elastics tissue declines

Question 8

The capillary is adapted for the exchange of substances between blood and the surrounding tissue. How? (6)

Answer 8

1. Permeable capillary wall/membrane;
2. Single cell thick/thin walls, reduces diffusion distance;
3. Flattened (endothelial) cells, reduces diffusion distance;
4. Fenestrations, allows large molecules through;
5. Small diameter/ narrow, gives a large surface area to volume/ short diffusion distance;
6. Narrow lumen, reduces flow rate of cells through the capillary giving more time for diffusion;
7. Red blood cells are in close contact with the capillary wall give short diffusion distance

Question 9

Tell me about veins :)

Answer 9

Thin wall does not have to withstand high pressure; so they have less elastic tissue and muscle tissue, but have a larger lumen to reduce friction as blood is under lower pressure
Presence of valves to prevent back flow
Blood flow is a result of skeletal muscle contraction, squeezing it along vessels, residual blood pressure from the heart, negative pressure form the thorax

Question 10

Why do we need mass flow and what do we move by it? (4)

Answer 10

In mass flow a fluid (liquid or gas) moves in a particular direction due to a force. In living organisms this usually means the bulk movement of water (the solvent) together with all its dissolved solutes and
suspended objects. So mass flow is like a river carrying everything with it. Mass flow always requires a source of energy to pump the fluid, but it has the advantage of being much faster than diffusion, especially over large distances. Mass flow is completely independent of concentration difference.
Examples of mass flow include: circulatory systems in animals, xylem and phloem systems in plants, filter feeder currents, and ventilation.

Question 11

How is water transported through plants? Describe xylem vessels. (4)

Answer 11

Water is transported through plants through xylem vessels. Xylem tissue is composed of dead cells joined together to form long empty tubes. Different kinds of cells form wide and narrow tubes, and the end cells
walls are either full of holes, or are absent completely. Before death the cells form thick cell walls containing lignin, which is often laid down in rings or helices, giving these cells a very characteristic appearance under the microscope. Lignin makes the xylem vessels very strong, so that they don’t collapse
under pressure, and they also make woody stems strong.