B3.2 Transport
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adaptations of capillaries
The wall of a capillary is made from a single layer of endothelial cells- reduces the diffusion distance for oxygen and carbon dioxide between the blood and the tissues of the body
how is tissue fluid formed
thin endothelium cells of some capillaries have gaps between them called fenestrations which allow blood plasma to leak out and form tissue fluid
what does tissue fluid do
surrounds the cells, enabling exchange of substances such as oxygen, glucose, and carbon dioxide it contains oxygen, glucose and other small molecules from the blood plasma
what is the capillary bed
when capillaries form branches between the cellsp they INCREASE SA for diffusion of substances to and from cells
how is the rate of diffuion increases in capillaries
narrow lumen(small diameter) and walls that are one cell thick to increase the rate of diffusion between the blood and cells
what do arteries do
transport blood away from the heart at high pressure from ventricles to tissues of the body
arteries walls have 3 layers
the innermost layer is an endothelial layer-very smooth and reduces friction for free blood flow middle layer- contains smooth muscle cells and a thick layer of elastic tissue(to withstand high pressure and control diameter of lumen to regulate blood pressure) outer layer-mostly made up of collagen and elastic fibres
what happens during vasoconstriction of circular muscles
increase blood pressure by decreasing the diameter of the lumen
Vasodilation of the circular muscles
causes blood pressure to decrease by increasing the diameter of the lumen
what do veins do
transport blood to the heart at low pressure
what do veins have
a wide lumen-maximises the volume of blood that can flow at any one time thin flexible walls
what can be used to measure the pulse rate
the radial or cartoid artery
how can arteries be blocked
Atherosclerosis - when there is damage to the walls of the arteries due to high blood pressure
what does the damage of the wall of arteries lead to
build-up of fatty deposits known as atheromas under the endothelium- narrow lumen of artery- reducing space for blood flow
what can repair damage to artery wall
Fibrous tissue- not elastic so elasticity of walls reduced
how can blood clotting form
when the smooth lining of the arteries break down creating plaques
what are clots formed within a blood vessel wall called
thrombus and when circulated- embolus
how does atherosclerosis lead to coronary heart disease
because it leads to the narrowing of arteries from build of plaque- blood clots-dont receive required level of oxygen and nutrients-parts of heart muscle die
how is water lost by leaf during transpiration
more water is drawn from the nearest xylem vessels to replace the water lost by evaporation
what does the transpiration pull allow for
allows water to be moved upwards through the plant, against the force of gravity
what is capillary action
movement of water that occurs due to adhesion to the walls of a narrow tube
what is the transpiration pull
The loss of water from the xylem vessels generates tension in xylem- moves into cells in leaves creating pulling force via choesion between water molecules
why is transpiration important
helps plant cool- evaporative helpful in uptake of mineral ions
how are mature xylem vessels formed
cell walls between the connected cells degrade and the cell contents are broken down so they become long continuous hollow tubes