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Summary Transport in mammals
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AS Bio notes Raida 12DTransport in mammals
8.1 transport system in animals
Movement requires energy
This energy comes from glucose and other substances, which are broken down in
respiration inside each individual cell
The most efficient form of respiration which releases the most energy from a given
amount of glucose is aerobic respiration and this requires good supplies of oxygen
Supplying oxygen to respiring tissues is one of the most important functions of an
animal’s transport system
At the same time, waste products such as carbon dioxide can be removed
Very small animals may be able to get enough oxygen to their cells by diffusion,
especially if they are not particularly active
[In a jellyfish, for example, oxygen simply diffuses into its body from the seawater around it, and
then to the respiring cells. Carbon dioxide diffuses in the opposite direction. Because no cell is
very far from the surface, each cell gets an adequate amount of oxygen quickly enough for its
needs]
But in larger animals, diffusion is not sufficient
A transport system is needed to distribute oxygen quickly to all the body cells, and to
remove their waste products
Mammals have greater requirements for oxygen than most other animals because they
use respiration to generate heat inside their bodies to help keep their body temperature
constant
8.2 The mammalian circulatory system
The main transport system of mammals is the Circulatory system
It is made up of a pump (the heart) and a system of interconnecting tubes (the blood
vessels)
The blood always remains within these vessels, and so the system is known as a Closed
blood system
The blood travels twice through the heart on one complete ‘circuit’, this is called a
Double circulation
Blood is pumped out of the left ventricle into the aorta and travels from there to all parts
of the body except the lungs
It returns to the right side of the heart in the vena cava
This is called the Systemic circulation
The blood is then pumped out of the right ventricle into the pulmonary arteries, which
carry it to the lungs
The final part of the journey is along the pulmonary veins, which return it to the left side
of the heart
This is called the Pulmonary circulation
The pressure in the systemic circulation is considerably higher than in the pulmonary
circulation
Systemic circulation: the part of the circulatory system that carries blood from the heart
to all of the body except the gas exchange surface, and then back to the heart
, Pulmonary circulation: the part of the circulatory system that carries blood from the heart
to the gas exchange surface and then back to the heart
8.3 Blood vessels
There are three main types of vessel making up the circulatory system:
1. Vessels carrying blood away from the heart are known as Arteries
2. Carrying blood towards the heart are Veins
3. Linking arterioles and venules, taking blood close to almost every cell in the body are
called Capillaries
Small arteries are called arterioles and small veins are called venules
Artery: vessel with thick, strong walls that carries high-pressure blood away from the
heart
Vein: vessel with relatively thin walls that carries low-pressure blood back to the heart
Capillary: the smallest blood vessel, whose role is to deliver oxygen and nutrients to
body tissues, and to remove their waste products
, Arteries and arterioles
The function of arteries is to transport blood, swiftly and at high pressure to the tissues
Artery walls are very strong and elastic
Blood leaving the heart is at a very high pressure
Blood pressure in the human aorta may be around 120 mmHg/ 16 kPa
The thickness and composition of the artery wall enables it to withstand this pressure
Both arteries and veins have walls made up of 3 layers:
1. An inner layer, which is made up of a layer of endothelium (lining tissue) consisting of a
layer of flat cells (squamous epithelium) fitting together, plus a layer of elastic fibres; the
endothelium is very smooth, minimising friction with the moving blood
2. A middle layer containing smooth muscle, collagen and elastic fibres
3. An outer layer containing collagen fibres and elastic fibres
Endothelium: a tissue that lines the inner surface of a structure such as a blood vessel
Squamous epithelium: one or more layers of thin, flat cells forming the lining of some
hollow structures eg. blood vessels and alveoli
Smooth muscle: a type of muscle that can contract steadily over long periods of time
Arteries have the thickest walls of any blood vessel
The aorta, the largest artery, has an overall diameter of 2.5cm close to the heart, and a
wall thickness of about 2mm
The composition of the wall provides great strength and resilience
The middle layer, which is by far the thickest part of the wall, contains a large amount of
elastic fibres
These allow the wall to stretch as pulses of blood surge through at high pressure
Arteries further away from the heart have fewer elastic fibres in the middle layer but have
more muscle fibres
Arteries that have a lot of elastic tissue in their middle layer - such as the aorta - are
called elastic arteries
The function of an elastic artery is to carry blood from the heart on the first part of its
journey towards its final destination
The elasticity of these artery walls is important in allowing them to stretch, which reduces
the likelihood that they will burst
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