3B more exchange systems Flashcards
Describe and explain how arterioles control the rate of blood flow to organs?
- contains smooth muscle
- muscle contracts and relaxes
- lumen diameter changes size and shape
- narrowed lumen reduces blood flow
Why are valves present in veins and not in arteries?
Blood in arteries is under higher pressure
High pressure prevents blood flowing backwards
Veins need valves to stop low pressure blood flowing backwards
describe the structure and functions of an artery
They pump blood from the heart to the body.
Thick and muscular walls
Elastic tissue to stretch and recoil as the heart beats, helping maintain high pressure
The inner lining is folded to help the artery stretch
Carries oxygenated blood except the pulmonary artery which carries deoxygenated blood
Explain the roles of the right and left side of the heart…
Right hand side pumps deoxygenated blood to the lungs and the left side pumps oxygenated blood round the whole body
Role of the left ventricle
thick, muscular wall which contracts powerfully and pumps blood around the body.
What are they Atrioventricular valves?
Links the atria to the ventricles and stop blood flowing back into the atria
What are the semi-lunar valves?
Link the ventricles to the pulmonary artery and aorta. Stops blood flowing back into the heart after the ventricles contract
How do the valves open?
When there is high pressure from the heart chambers from behind the valves
How to the valves close?
When the pressure from the heart chambers is from the front
Describe the first stage of the cardiac cycle
Ventricles relax and atria contracts, decreasing the volume of the chambers. This pushes blood into the ventricles and there’s a slight increase in ventricular pressure and chamber volume as the ventricles receive the blood from the atria
Describe the second stage of the cardiac cycle?
The ventricles contract and atria relaxes increasing the ventricles pressure, the pressure becomes higher in ventricles than in the atria forcing the AV valves to close and prevent backflow, and the pressure forces the SL valves to open and blood is forced in.
Describe the third stage of the cardiac cycle
Both the atria and ventricles contract, high pressure in the pulmonary artery and aorta closes the semi-lunar valve. Blood returns to the heart and atria fills again due to higher pressure in the vena cava and pulmonary valve increasing the pressure of the atria
Why does the oxyhaemoglobin curve shift to the right during excersize?
Muscles respire faster
so increased carbon dioxide concentration
Blood pH decreases
Haemoglobins tertiary structre is alteren
Lower affinity for oxygen
So more oxygen released to cells and tissues
What is the equation for cardiac output?
stroke volume x heart rate
Explain the mass flow hypothesis
- Solutes are actively transported from the companion cells to the sieve tubes at the source. Water potential is lowered so water enters sieve tubes by osmosis. A higher pressure forms at the source end
- A pressure gradient forms between the source and the sink end of the phloem so solutes are pushed to along the sieve tubes towards the sink. Once at the sink, the solutes are used for processes such as respiration
- At the sink, solutes are used up and therefore removed from the phloem. This causes the water potential inside the sieve tubes to increase so water leaves by osmosis and lowers the pressure.
