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O-level Biology: Transport in Humans

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O-level Biology: Transport in Humans
« on: September 08, 2014, 09:47:36 AM »
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
  • 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:
Phagocytes: 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.
Lymphocytes: 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 nutrients, urea and other waste products. The blood  plasma transports substances from one place to another.
 Functions of the blood:
  • Transportation of R.B.Cís, W.B.Cís, oxygen,  food nutrients, hormones, and waste products.
  • Defence against disease, by white blood  cells phagocytosis and production of antibodies.
  • Supplying cells with glucose to respire and  keep a constant temperature.
Blood Vessels (Vascular System):  This is a number tubes carrying blood away  from and to the heart and other organs. The main types are Arteries, Veins and Capillaries.
Arteries: Their function is to transport blood away from the heart to the lungs or other body organs.
The blood in the arteries always has a high pressure. The heart pumps the  blood quickly into the arteries, resulting in the pressure, each time the ventricle of the heart contracts, the pressure in  arteries increase, when the ventricle relaxes, the pressure falls. The lumen of  arteries is also very narrow, adding to the pressure.
The structure is simple, beside the narrow  lumen, the arteries have a strong thick wall to withstand the pressure. Their  walls are also elastic and stretchable.
Brief description of characteristics of  arteries:
  • Transporting blood away from the heart
  • Always in a high pressure
  • Strong but stretchable walls
  • Narrow lumen.
Veins: Their function is  to transport blood to the heart from the body.
The veins always always have a low blood pressure because by the time the  blood with high pressure reaches the veins, it loses most of the pressure. This  means that blood flows very slowly in veins, to help this, veins lie between  muscles so that the blood is squeezed when the muscles contract.
They have a simple structure. Because they  have a low pressure, they donít need strong, thick walls like the artery,  instead they have thin less elastic walls. Their lumen is much wider too. Veins  have a unique feature, that is valves. Because blood in veins flows slowly with a low pressure, there is a risk of a backflow, specially in veins that move  blood upwards against gravity, like the ones in the leg. The valves ensure that  the blood is always flowing in the direction of the heart. When the muscles  squeeze the blood, the valves are open the let blood through, when muscles  relax, valves close to prevent a backflow.
Brief description of characteristics of  veins:
  • They carry blood to the heart
  • Always in a low pressure
  • Thin less elastic  walls
  • Wide lumen
  • Valves present.
Blood  Capillaries:  Blood capillaries are very we
Blood capillaries are the smallest blood vessels in our systems. Their function is to get blood from the arteries
 as close as possible to the  tissues in order to exchange materials with the cells, and to link arteries  with veins.
When arteries come near and organ or a  tissue, it divides into arterioles, these arterioles divide more into several  blood capillaries that go through the tissue, this is when the exchange of oxygen and food nutrients with carbon dioxide and waste products such as urea  take place by diffusion.
ll adapted to their jobs. They are one cell thick to reduce the diffusion distance of materials for faster diffusion.  They also have pores in their walls between the  cells, to allow the plasma to get out of the blood and become tissue fluid.
 The Heart: The heart is a pumping organ that is responsible for the movement of blood around the body. The function of the heart is to give the blood a push, keeping it flowing around the body all the time. That is why the heart is constantly working, if it stops for a minute, the other organs will not receive  any oxygen or nutrients, thus the body fails and the person dies. The heart is  located in the chest, the thoriac cavity between both lungs.
Structure: The heart is hollow, it has 4 chambers. Two of them are atria and  two are ventricles. One of each of these on each side. When looking at the  diagram of a heart, notice that your right is the left side of the heart, and  your left is the heartís right, as if you are looking at your own heart on a  mirror.
The sides of the heart are separated by a  wall called septum. Each side contains an atrium (at the top) and a ventricle  (at the bottom), there is a valve between the atrium and the ventricle in each  side, it is called bicuspid valve in the left side and tricuspid valve in the  right side. There are several blood vessels associated with the heart, these are:
  • The Pulmonary vein, it transports  oxygenated blood from the lungs to the right atrium.
  • The Aorta, which is the biggest artery in  the body, it transports oxygenated blood from the heart to the rest of the  body.
  • The Vena Cava, the biggest vein in the  body, it transports deoxygenated blood from the whole body to the heart.
  • The pulmonary artery, it transports  deoxygenated blood from the heart to the lungs.
  Note that blood vessels entering the heart  are veins, and the ones leaving the heart are arteries. The left side of the  heart always contains oxygenated blood because it receives blood fresh from the lungs and pumps it to the body, the right side always contains deoxygenated  blood because it receives is from the body. You can memorise this by the word LORD:
Left Oxygenated Ė Right Deoxygenated
The heart receives blood from  the lungs at the left atrium and pumps it to the body  from the left ventricle, then it receives it  again from the body at the right atrium and pumps it to the lungs from the  right ventricle. The red shows oxygenated blood and the blue shows deoxygenated  blood.
Notice that the walls around the left  ventricle are much thicker than the ones in the right ventricle. The reason for  this is that because the left ventricle pumps blood to the whole body, so blood will travel a long distance, so it needs lots of muscles to contract and pump  the blood more strongly.
However, the right ventricle pumps blood the lungs  which are very close to heart, the blood does not need to be pumped very strongly.
Mechanism of the  heart:  When the heart is being filled with blood  (whether from the body or the lungs), this is called the diastole. When the  heart is pumping the blood out of it (whether to the body or to the lungs), it is called the systole.
During diastole, the heart is getting  filled with blood, the blood enters the atria first, the atria contract to  force blood into the ventricles, both tricuspid and bicuspid valves are open to  allow blood into the ventricles and the semilunar valves are shut. Once the ventricles get filled with blood, it is systole, the bicuspid and tricuspid  valves get shut and semilunar valves are open, the ventricles contract strongly  forcing the blood into the Aorta or pulmonary artery.
During diastole the  semilunar valves are shut to keep the blood out of the arteries. During systole  the tricuspid and bicuspid valves are closed, to prevent blood from flowing  back into the atria when it is pumped. The tricuspid and bicuspid valves are kept  fixed by fibres called tendons, they prevent the valves from opening in the  opposite direction, allowing backflow.
The tendons also control the opening and  closing of the cuspid valves, when the tendons are loose, the valves are open.  When the tendons are tightened the valves close.
Ventricles:Relax Contract
Cuspid Valves:OpenClose
Semilunar Valves:CloseOpen
If you listen to your heartbeat, you will  hear two sounds, one low and one high. These are results of the systole and  diastole. They are the sounds of the cardiac valves opening and shutting.
 Coronary  Heart Disease (CHD):
The heart, like any other organ, needs a  supply of blood containing oxygen and   nutrients. In fact, the heart needs a higher amount of blood supply than  any other organ because it is working all the time, and contains a lot of  muscles. The coronary arteries are those which supply the heart tissues with  blood, they branch from the aorta. CHD develops when cholesterol layers build  on the walls of the coronary arteries, partially blocking the path of blood,  thus this tissue of the heart is not supplied with oxygen nor nutrients, so it stops working properly. If it is not treated at this age, a blood clot may form  near the partially blocked area, completely blocking the artery, when this  happens, the blood cannot function anymore, a heart attack occurs, which is  extremely fatal.
The  causes of CHD are mostly in the diet. A diet with lots of fats, increases the  chance of cholesterol building up on the walls of the artery, causing CHD, Same  thing with salts. Smoking also increases the rate of fat deposition. It was also said that Causes Of CHD are:
  • Diet full of fats increases the fats level in blood
  • Diet full of salts, salts can be deposited in the artery leading to CHD, same as fats or cholesterol
  • Smoking, carbon monoxides increases fat deposition
  • Stress was also said to contribute to CHD by raising blood pressure
  • Lack of exercise, regular workouts improve the blood flow wearing layers of fats or salts deposited on the walls of  arteries away.
So to protect yourself from CHD you need to  avoid diets full of fats and salts, avoid smoking, try to be less stressed out,  and exercise regularly.
 Tissue Fluid And Lymph:  Tissue fluid is a fluid surrounding the  cells of a tissue. It supplies them with all their needs of oxygen and  nutrients, and takes away all their waste products including carbon dioxide.  Tissue fluid plays a very big role in substance exchange between blood and  cells.
Plasma from the blood capillaries move to  the tissue through gaps in the walls. They become tissue fluid. They exchange  their content of oxygen and nutrients with the cells and take carbon dioxide and waste products. At the end of the capillary bed, the tissue fluid leaks  back into the blood, and becomes plasma again, but not all of it. A little of  it is absorbed by the lymphatic vessel and becomes lymph. The lymphatic vessel  takes the lymph to the blood stream by secreting them in a vein near the heart,  called subclavian vein. The lymph in the lymphatic vessels are moved along by  the squeeze of muscles against the vessel, just like some veins.
The lymphatic system plays a big role in  the protection against disease. It produces the white blood cells lymphocytes.  Which kill any cell with a different antigens than the ones in your body cells.  So if bacteria get into your body, your lymphocytes quickly recognise them as foreigners and will divide and kill them.
Lymphocytes are considered a problem when  it comes to organs transplant. For example if someone (recipient) with renal  failure receives a kidney from another person (the donor), the cells of the kidney will have different antigens than the other cells in the patientís body.  The lymphocytes will consider the cells of the kidney an enemy and start  attacking it, this is called tissue rejection. Organ transplant is perfect in one  case, this is when the donor and the recipient are identical twins, because the  antigens of their cells perfectly match. In other cases the recipient is given immunosuppressant drugs to actually weaken their immune system to prevent  tissue rejection.
Brief Summary Of Functions Of The Lymphatic  System:
  • Production of white blood cells lymphocytes
  • Transport of digested fats from villi to  blood stream
  • Transport of lymph from the tissue fluids  to the blood stream at the subclavian vein.


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