the circulatory system Flashcards
1
Q
describe and explain 4 ways in which the structure of a capillary is adapted for exchange between blood and surrounding tissue (4 MARKS)
A
- single cell thick walls reduces diffusion distance
- flattened endothelial cells reduces diffusion distance
- narrow lumen reduces flow rate giving more time for diffusion
- small diameter gives a short diffusion distance
2
Q
explain how tissue fluid is formed and how it may be returned to the circulatory system (6 MARKS)
A
- hydrostatic pressure of blood is high at arterial end of capillary
- water passes out
- proteins remain in capillary
- this lowers water potential
- water moves back into venous end of capillary by osmosis
- lymphatic system collects excess tissue fluid which returns to blood
3
Q
explain how an arteriole can reduce the blood flow into the capillaries (2 MARKS)
A
- muscles contract
- narrows lumen
4
Q
arteries
A
- arteries carry blood AWAY from the heart under HIGH PRESSURE
- elastic tissue in wall to recoil and stretch
- thick muscle layer
- narrow lumen
- folded endothelium to allow artery to stretch
5
Q
veins
A
- veins carry blood BACK to the heart under LOW PRESSURE
- thin muscle wall
- large lumen
- very little elastic or muscle tissue
- valves in veins to stop backflow
- blood flow through the veins is helped by contraction of body muscles surrounding them
6
Q
arterioles
A
- arteries divide into arterioles
- arterioles form a network throughout the body (large surface area)
- blood is directed to different areas of demand in the body by muscles inside the arterioles which contract to restrict the blood flow or relax to allow full blood flow
7
Q
how are capillaries adapted for efficient diffusion
A
- theyre always found very near cells in exchange tissues - short diffusion pathway
- one cell thick walls - short diffusion pathway
- large number of capillaries - increase surface area for exchange
CAPILLARY BEDS ARE NETWORKS OF CAPILLARIES IN TISSUES
