blood vessels

Question 1

Arteries

Answer 1

• Thick artery walls
• Walls consist of thick layers of:
• elastic tissue (can expand and contract to absorb some of the shock forces against the wall)
• smooth muscle (controls diameter and keeps artery open)
• encased in a thick outer layer of collagen (withstand forces and makes arteries strong)
• inner layer (endothelium) is folded, allowing the artery to expand and maintain the high pressure

Question 2

Arterioles

Answer 2

• similar structure to arteries but
• smaller
• have relatively thinner muscle and elastic layers because blood pressure is decreasing
• contraction of the smooth muscle constricts the arteriole and is used to control the flow of blood through the body (important in directing flow of blood to important organs e.g. during exercise)

Question 3

Capillaries

Answer 3

• Smallest of the blood vessels
• Very thin walls- only one-cell thick endothelium
• No smooth muscle, elastic tissue etc
• Lumen is very narrow (for a short diffusion distance) and can squeeze red blood cells against the endothelium to improve transfer of oxygen
• Increased resistance greatly slows the flow of blood in the capillary beds (and the pressure drops too) which reduces damages to the wall
• Walls are very leaky to allow blood plasma and dissolved substances to leave the blood

Question 4

Venules

Answer 4

• Very thin walls that contain some muscle cells
• Thin layers of muscle and elastic tissue outside the endothelium
• Thin outer layer of collagen
• NO VALVES

Question 5

Veins

Answer 5

• Vein walls are not thick
• Lumen is very wide to maximise blood flow
• Have valves to ensure that the low pressure blood only flows in the right direction
• Thinner layers of collagen, smooth muscle and elastic tissue as they do not need to stretch and recoil
• Movement of skeletal muscles compresses the veins and pushes the blood along

Question 6

What is the only artery that carries deoxygenated blood?

Answer 6

pulmonary arteries

Question 7

What blood vessel carries blood away from the heart at high pressure?

Answer 7

arteries

Question 8

What blood vessel carries blood towards the heart at low pressure?

Answer 8

veins

Question 9

How is tissue fluid formed?

Answer 9

• Capillaries have small gaps in the walls so liquid and small molecules can be forced out
• The arterial end has HIGHER HYDROSTATIC PRESSURE inside the capillaries compared to the hydrostatic pressure in the tissue fluid
• This forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid
• Known as ULTRAFILTRATION
• As fluid leaves, hydrostatic pressure reduces so this is much lower at the venule end
• Large molecules (plasma proteins) remain in the capillaries which creates a lowered water potential
• At the venule end, there is HIGH ONCOTIC PRESSURE
• Water potential in capillaries is lower than the water potential in the tissue fluid so water re-enters the capillaries by OSMOSIS from the tissue fluid at the venule end of the capillaries

Question 10

What is tissue fluid?

Answer 10

A liquid that surrounds/bathes cells in tissues, made from substances that leave the blood plasma e.g. water, glucose, amino acids fatty acids, ions and oxygen

Question 11

What is lymph?

Answer 11

tissue fluid in the lymph vessels

Question 12

What is the lymphatic system?

Answer 12

a drainage system made up of lymph vessels
-where excess tissue fluid that is not reabsorbed in the capillaries ends up

Question 13

How is lymph returned to the blood?

Answer 13

• Smallest lymph vessels are the lymph capillaries
• Valves in the lymph vessels stop the lymph going backwards
• Lymph gradually moves towards the main lymph vessels in the thorax (chest cavity) where it is returned to the blood near the heart