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The blood system (VI. 2) - Coggle Diagram
The blood system (VI. 2)
Blood vessels
Veins
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Blood flow in veins occurs thanks to gravity and by the movement of skeletal muscles that squeeze the veins
In order to prevent backflow, veins contain valves (three cup-shaped flaps of tissue)
Arteries
Their endothelium is permeable and allows blood plasma to diffuse out of the vessel, providing nutrients to the surrounding cells
Tunica externa (tough layer of connective tissue)
Tunica media (thick layer with smooth muscles and elastin)
Tunica intima (smooth endotelium)
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The heartbeat
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Sinoatrial node
The membrane of the heart cell depolarises when it contracts and this prompts the contraction of adjacent cells
The cells in the SA node have extensive membranes, that are the first to depolarise, and therefore initiates the heartbeat
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Changing the heart rate
Low BP, low oxygen concentration and low pH all signal the SA node to speed up the heartbeat
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Signals from one nerve increase the frequency of the heartbeat, the other nerve does the opposite
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The SA node responds to signals from two nerves, both originating from the cardiovascular centre in the brain
The cardiac cycle
0.15- 0.4 seconds
The semilunar valves open and blood enters the arteries, reaching arterial systolic pressure
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0.0 - 0.1 seconds
The atria contract, pumping the blood in the ventricles through the atrioventricular valve
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