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Transport in Animals
The Circulatory System
Multicellular organisms need a transport system as they cannot use direct diffusion
and have a large number of cells that all respire quickly so need a constant supply of
glucose and oxygen.
Single/Double circulatory system Blood passes through the heart once/twice for
each complete circuit of the body.
An advantage of a double circulatory system is it gives blood an extra push so blood
travels faster, so oxygen is delivered to tissue more quickly.
Closed circulatory system The blood is enclosed inside blood vessels.
Open circulatory system Blood isn't enclosed in blood vessels all the time. Instead
it flows freely through the body cavity.
Valves only open one way, if there is a higher pressure behind a valve its forced open, a
higher pressure in front it is forced shut.
The heart is mainly cardiac muscle, when it contracts it creates high pressure.
The left ventricle is more muscular (8-15mm) than the right (4-5mm) as it needs to
contract powerfully to pump blood all around the body.
The cardiac cycle...
o Ventricles relax, atria contracts: Ventricles relax atria fill with blood volume
decrease and pressure increase high pressure opens AV valves blood
flows into ventricles atria contract (increasing pressure) forcing out remaining
o Ventricles contract, atria relax: Pressure is higher in the ventricles than atria AV valves close high pressure
opens semi-lunar valves blood forced into pulmonary artery and aorta.
o Ventricles relax, atria relax: Increased volume and low pressure high pressure in the pulmonary artery and
aorta semi-lunar valves close atria fill with blood due to high pressure in the vena cava and pulmonary vein.
Electrical Activity of the Heart
Cardiac muscle is myogenic it can contract and relax without receiving signals from nerves.
Sino-atrial node (SAN) sets the rhythm of the heart beat by sending electrical waves over the atrial walls so the right and
left contract together. A band of non-conducting collagen tissue prevents the wave directly passing to the ventricles.
Atrioventricular node (AVN) passes the wave down the bundle of His so there is a slight delay and the Purkyne tissue
causes the ventricles to contract bottoms up.
o P wave contraction of the atria.
o QRS contraction of the ventricles.
o T wave relaxation of the ventricles.
Heart rate (bpm) = 60 ÷ time taken for one heart beat (e.g. P wave to the next P wave).
Arteries Carry blood from the heart to the rest of the body. Carries oxygenated blood except for the pulmonary arteries
which take deoxygenated blood to the lungs.
o Walls are thick and muscular with elastic tissue (to cope with high pressure from the heartbeat).
o Inner endothelium is folded allowing arteries to expand and cope with high pressure.
Capillaries Arteries branch into capillaries and capillaries connect to veins.
o Substances like glucose and oxygen are exchanged between cells and capillaries.
Veins Take blood back to the heart under low pressure. Carries deoxygenated blood except from the pulmonary veins
which takes oxygenated blood to the heart from the lungs.
o Wider than arteries with little elastic or muscle tissue.
o Veins contain valves to stop backflow and blood is helped by contracting surrounding muscles to flow.
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Tissue fluid This surrounds cells, it is made from substances that leave the blood (e.g. oxygen, nutrients or water). Cells
take in oxygen and nutrients from tissue fluid and release metabolic waste into.…read more