Animal Transport systems notes


Notes on blood vessels




The contents of the vessels are pumped round the system



The vessels link to form a circulatory system



The vessels form a major transport system



Some of the vessels are living and some are dead




Why the pressure drops as blood moves away from the heart

·         This is because when the vessels subdivide into smaller vessels (eg capillaries) they have a larger cross sectional area as they have smaller but more lumens, this means that the pressure is more spread out.

·         The artery can sustain a higher blood pressure due to its smooth muscle and elastic fibres which allow it to stretch and recoil maintaining the pressure whereas smaller vessels such as capillaries cannot because they do not have as much so cannot sustain the high pressure so it lowers.

·         The further away from the heart the more fluids and nutrients are removed from the blood, (eg blood plasma into the kidneys) this means that there is less pressure as the volume is lower. The artery walls are less permeable than capillary walls so more can be removed in the capillaries (to the respiring cells).

How arteries can withstand pressure

·         The endothelium is folded allowing it to become flat when the muscle and elastic fibres stretch to become bigger, this means that the endothelium does not break and snap, so the artery is not damaged.

·         The walls of the artery is thick, containing collagen, smooth muscle and elastic fibres, this means that it is very strong and resistant to pressure as it will not easily break or get damaged.

How arteries can maintain pressure

·         When the walls of the artery stretch (smooth muscle and elastic fibres) they must recoil to maintain the shape and pressure of the arteries this increases it keeping it flowing.

·         The smooth muscle constricts the lumen of the artery meaning that the pressure is maintained as the pressure is not lowered by great increase in lumen size.

When measuring the drop in systolic pressure measure from one peak to the next and then take the first value from the second.

How blood in the veins is returned to the heart

·         They contain valves to prevent backflow of the blood because of the low pressure, they close as the blood starts to flow backwards through sections with low pressure not allowing the return of the blood.

·         Contraction of the surrounding body skeletal muscles help increase the pressure as it constricts the lumen squeezing the artery forcing the blood towards the heart and increasing movement.

·         Breathing movements of the chest act as a pump. The changes of pressure and the squeezing actions move the blood in the veins of the chest and abdomen towards the heart.

·         Gravity can also play a part in increasing the movement of the blood if


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