blood vessels and tissue fluid

Question 1

1. Explain the role of the heart in the
   production of tissue fluid.

Answer 1

Contraction of left ventricle produces high blood pressure; This forces water and some dissolved substances out of blood capillaries; through pores, to surround cells.

Question 2

2. Describe how tissue fluid is formed and how it is
   returned to the circulatory system.

Answer 2

Formation: High blood pressure at the arterial end of capillary bed; Forces water and small molecules such as ions and glucose out; Large proteins remain in capillary; Return: Low water potential in capillary at venous end of capillary bed; Due to proteins; Water enters capillary; By osmosis; Any excess fluid drains into the lymph;

Question 3

3. The water potential of the blood plasma is more
   negative at the venule end of the capillary than at
   the arteriole end of the capillary. Explain why.

Answer 3

Water has left the capillary; Proteins in blood are too large to leave capillary; This increases the concentration of blood proteins and makes the water potential more negative.

Question 4

4. Explain four ways in which the structure of the
   aorta is related to its function.

Answer 4

Elastic tissue to allow stretching to accommodate surges in blood flow and recoil to smooth out the flow of blood and maintains pressure during diastole; Muscle withstands high pressures; Thick collagen outer coat withstands pressure and stop bursting; Smooth endothelium reduces friction with blood cells; Semi-lunar valve prevents backflow into the left atrium.

Question 5

5. Describe and explain the structure of capillaries.

Answer 5

Capillaries are very narrow tubes made of endothelial tissue that is one cell thick. The cells are also flattened and have pores between them. This means the red blood cells have to slow down and squeeze up to the wall so there is a short diffusion pathway and time for the exchange of oxygen to take place. Capillaries also have a large surface area for exchange of substances via diffusion/osmosis.

Question 6

6. An arteriole/venule/artery/vein is described as an organ. Explain why.

Answer 6

They are made of different tissues.

Question 7

7. An arteriole contains muscle tissue. Explain how these muscle fibres reduce blood flow to capillaries.

Answer 7

The muscle contracts; this reduces the size of the lumen to constrict blood flow.

Question 8

8. The thickness of the aorta/artery wall changes all
   the time during each cardiac cycle. Explain why.

Answer 8

Aorta wall stretches because ventricle contracts and pressure increases; Aorta wall recoils because ventricle relaxes and pressure falls; This maintains a smooth flow of blood

Question 9

9. Capillaries have a much smaller cross-sectional area than arteries, but pressure falls from arteries to capillaries. Explain why.

Answer 9

There are many more capillaries than arteries, so total cross-sectional area (or volume) increases, giving a lower blood pressure.

Question 10

11 In which type of blood vessel is the pressure lowest

Answer 10

veins

Question 11

10. Describe and explain the adaptations of veins.

Answer 11

Veins have valves to ensure blood does not backflow as blood pressure is low. This also means they need less muscle, and elastic tissue.