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Mammalian
transport systems
Joanna
George-Johnson, Contributor
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| 'I
believe I can fly' to the next stage of the game at New Generation Camp, located
at Happy Hills, Laughlands, St. Ann. - Contributed | Small
organisms such as amoeba can exchange materials such as food, water and waste
easily between them and their environments by the process of simple diffusion
and osmosis. This is not the case with larger animals as their surface area to
volume ratio is too small for these simple processes to adequately fill their
needs. This is due to the fact that the rate of diffusion and osmosis falls off
quickly, as the distance over which these processes take place increases. The
inner cells of the animal would, therefore, not receive adequate materials if
these processes were used. The need thus arises for the use of specialised transport
systems. The
mammalian transport system is composed of three simple parts: - A
fluid tissue known as blood
- A
muscular organ to pump blood - the heart
- Vessels
through which the blood flows
Blood
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| A
light micrograph of human blood. - Contributed | Blood
is a tissue as it is composed of multiple cells. These include red and white blood
cells (erythrocytes and leucocytes respectively). There are also smaller cell
fragments known as platelets. All of these play various roles in the functioning
of blood as a whole. The cells are suspended in a fluid known as plasma, a solution
of water, amino acids, ions, plasma proteins among other things. Red
blood cells (erythrocytes) These
are the most common blood cells. They are identified by their red pigmentation
as a result of the presence of haemoglobin, and their biconcave disc shape. This
haemoglobin is the pigment responsible for the oxygen-carrying capacity of the
blood. They also lack nuclei. These cells are produced in the liver at a remarkable
rate, as owing to the lack of a nucleus they have a very short life span. Haemoglobin
is the pigment responsible for oxygen transport. White
blood cells (leucocytes) The
purpose of white blood cells is to fight against infections, thus producing immunity
against disease. Unlike red blood cells, these are colourless and have nuclei.
Two types of such cells exist and they differ both in structure and function.
Lymphocytes have large round or bean-shaped nuclei, and cytoplasm without granules.
They act by producing antibodies which cause pathogens to clump together. Conversely,
phagocytes engulf and digest pathogenic agents. They have lobed nuclei, and cytoplasmic
granules. The
following image is a light micrograph of human blood. See if you can identify
the types of blood cell present. Platelets
These
are small fragments of cells, and the endothelium of blood vessels. They aid in
blood clotting. Functions
of blood 1.
The most obvious is that of transport. Many materials are transported including:
- Oxygen.
As outlined before, oxygen is transported as it binds to the iron atoms within
haemoglobin, forming oxyhaemoglobin. This binding is reversible. Oxygen is added
to haemoglobin in areas of high concentration (the lungs) and released in low
concentration (body tissues).
- Carbon
dioxide. A small amount of carbon dioxide is transported bound to haemoglobin.
However, the majority of CO2 transported is in solution as hydrogencarbonate (HCO3-)
ions.
- Food
materials. It is essential that all body cells have a constant supply of glucose,
as it is the body's main respiratory substrate. However, cells also need fatty
acids, amino acids, minerals, water and vitamins, which are absorbed from digested
food in the intestines.
- Waste
materials. Urea is major nitrogenous waste in mammals. Accumulation of urea in
the body would be dangerous to health, thus the blood system takes urea to the
kidneys for excretion.
- Hormones
- Defends
against disease
- Regulates
body temperature.
Joanna
George-Johnson teaches at Ardenne High School.
Email: Masterbio@gmail.com.
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