Topics: Blood, Heart, Artery Pages: 11 (2908 words) Published: January 7, 2013
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Transport In Humans

Transport In Humans
The human transport system is a system of tubes with a pump and valves to ensure one way blood flow. We need a transport system to deliver oxygen, nutrients and other substances to all our body cells, and take away waste products from them. The oxygenated blood (high in oxygen, red in color) comes to the heart from the lungs in the pulmonary vein; the heart pumps it to the aorta (an artery) to the rest of the body. The deoxygenated blood returns to the heart from the body in the vena cava (a vein), the heart pumps is to the lungs to get rid of the carbon dioxide. Oxygenated Blood: Red color, high oxygen low Carbon dioxide. Deoxygenated Blood: Blue color, low oxygen high Carbon dioxide. Did you notice that during one circulation, the blood went through the heart twice, this is why we call it double circulation. When the blood is flowing away from the heart, it has a very high pressure, when it is flowing towards the heart it has a lower pressure.

The Blood:
The blood is a fluid consisting of several types of cells floating in a liquid called plasma.

Red Blood Cells:
These are one of the smallest cells in your body, they are round with a dent in the middle, we call this shape a Biconcave disc. The function of the red blood cells is to transport oxygen from the lungs to the body cells. A red protein called Haemoglobin, when the blood reaches the lungs, oxygen diffuses from the alveoli to the red blood cells and combines with haemoglobin forming an unstable compound called oxyhaemoglobin. When the blood reaches the body cells, the oxyhaemoglobin is easily split into oxygen and haemoglobin again, the oxygen diffuses through the blood plasma to the cells.

Red blood cells are fully adapted to their function by the following characteristics: Biconcave disc shape gives it large surface area to carry more oxygen Haemoglobin to combine with oxygen www.xtremepapers.com/revision/gcse/biology/transport_in_humans.php 1/8

No nucleus that takes up space.

White Blood Cells:
White blood cells are one of the substances floating in the blood plasma. They are completely different in function than red blood cells. White blood cells are part of the Immune System, they play a big role in protecting the body by killing bacteria which cause disease, also known as pathogens. White blood cells can be distinguished from red blood cells easily because they are much bigger, with a nucleus, and present in fewer amounts.

Types Of White Blood Cells:

They kill bacteria by engulfing them, taking them in the cell then kill them by digesting them using enzymes, this process is called phagocytosis. Most white blood cells are the phagocyte type.

Unlike phagocytes, lymphocytes have a large nucleus. They are produced in the lymph nodes (in the lymphatic system). Lymphocytes kill bacteria by secreting antibodies and antitoxins which kill the pathogens directly or make them easier to kill. Each pathogen could be killed by a certain type of antibody

The Platelets:
Platelets are tiny cell fragments that prevent bleeding when the skin is cut, and stops bacteria from entering our systems through the wound. This works by blood clotting, when the skin is cut, some reactions take place that results in platelets producing a protein, this protein will change the fibrinogen (another soluble protein in the plasma) to insoluble fibrin. The fibrin forms long fibres that clot together blocking the cut, thus preventing any bleeding, this is called blood clotting.

Blood Plasma:
This makes up most of the blood. It is mostly water with some substances dissolved in it, these include carbon dioxide, hormones, food...
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