Internal Transport in the Body- AS Level, Biology, Edexcel

Notes on the Internal Transport in the Body section of Unit 1 for AS Level. Mainly for the Edexcel spec.

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Internal Transport in the Body
-Internal transport systems at work are examples of mass flow
-Mass flow= fluid moves in a response to a pressure gradient, flowing from a region of high pressure
to regions of low pressure
Transport in mammals
-Mammals have a closed circulation- blood is pumped by heart- circulated in a continuous system of
tubes (arteries, veins and capillaries) under pressure
-The heart has four chambers and is divided into right and left sides- blood flows from the right side
of the heart to the lungs where it is oxygenated and then back to the left side of the heart- from
here it is pumped round the rest of the body and back to the right side of the heart
-Blood passes twice through heart in each circulation so = double circulation
-Advantages of mammalian circulation:
Oxygenated blood is delivered at high pressure to all regions of the body simultaneously
Oxygenated blood reaches the respiring tissues undiluted by deoxygenated blood
The transport medium ­ the blood
-Blood is a special tissue of a liquid medium called plasma in which are suspended red cells
(erythrocytes), white cells (leucocytes) and the platelets
-Plasma= medium for exchange of substances between cells and tissues- red cells= involved in
transport of respiratory gases- white cells= adapted to combat infection
The plumbing of the circulatory system- arteries, veins and capillaries
arteries -carry blood away from the heart
-strong, elastic walls
-have the thickest walls
veins -carry blood back to the heart
-strong, elastic walls
-low pressure (possibility of backflow)
-have valves at intervals to prevent back flow
capillaries - are the fine networks of tiny tubes linking
arteries and veins
-walls consist of endothelium only (e= the
innermost lining layer of arteries and veins)
-walls are very thin
-branch profusely and bring the blood circulation
close to the cells- no cell is far from one
-Blood leaving the heart is under high pressure, and travels in waves/ pulses- by the times it's
reached the capillaries it is under very much lower pressure, without a pulse
-The arteries, veins and capillaries serving the lungs are known as the pulmonary circulation
-Those that the heart pumps the blood through, serving the body are known as the systematic

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The blood clotting mechanism
-In the event of a break in our closed blood system, blood clots prevent the loss of blood
-A clot both stops the outflow of blood+ reduces invasion opportunities for pathogens+ allows for
repair of the damaged tissue to get under way
-Initial conditions at the wound trigger a cascade of events by which a blood clot is formed:
- Firstly, platelets collect at the site
- Platelets stick to the damaged tissues and clump together
- The collecting platelets release…read more

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Walls of the heart are supplied with oxygenated blood + nutrients via coronary arteries- vital for
maintenance of the pumping action
-Valves of the heart prevent backflow- maintain direction of flow
atrio-ventricular valves -large valves
-prevent backflow from ventricles to atria
-edges are supported by tendons anchored to
the muscle walls of the ventricles below
semilunar valves -separate the ventricles from pulmonary artery
(right side) and aorta (left side)
-rather similar to the valves in veins
-cut out backflow from aorta and pulmonary
artery into…read more

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Blood pressure and its measurement
-Blood pressure= pressure of blood flowing through arteries
-Initially, flow is a surge or pulse, but pressure falls as blood flows on through the smaller arteries,
arterioles and capillaries to the veins- pulsation has entirely disappeared by the time the capillaries
have been reached
-Resistance of the blood= what slows down the flow and causes the blood pressure to fall
(peripheral resistance)…read more

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Blood pressure= quoted as two values (typically, one over the other)- the high pressure is produced
by ventricular systole (systolic pressure), and is followed by low pressure at the end of the
ventricular diastole (diastolic pressure)- normally, systolic and diastolic pressures are about 15.8 and
10.5 kPa respectively
-Sphygmomanometer is used with a stethoscope to measure these 2 values:
1.…read more


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