#15 The Circulatory System (English)

The Circulatory System

 

- The heart pumps blood into two main arteries, the pulmonary artery, which takes blood to the lungs, and the aorta, which carries blood to all the other parts of the body.

- The blood from the lungs is returned to the heart in the pulmonary vein. The blood from the body is returned to the heart in the vena cava.

- The blood has to go through the heart twice on one complete journey around the system. The system is therefore said to be a double circulatory system.

- When the blood is in the lungs, it picks up oxygen. When the blood is in other parts of the body, it gives up oxygen to the cells that need it for respiration.

- Blood with a lot of oxygen in it is called oxygenated blood. Blood that contains only a little oxygen is called deoxygenated blood.

 Blood Vessels

Blood travels all over the body in tubes called blood vessels:

Arteries	Veins	Capillaries
- Carry blood away from the heart - Carry oxygenated blood (except for the pulmonary artery). - Blood is always in high pressure. - No valves - Thick muscular walls - Small lumen. - Have a pulse.	- Carry blood towards the heart. - Carry deoxygenated blood (except for the pulmonary vein) - Blood is always at a low pressure. - Valves are present to stop the blood flowing backwards. - Thinner walls. - Large lumen. - Do not have a pulse	- Join arteries and veins. - Present in all organs and tissues. - Site of exchange of substances between blood and tissue fluid. - One cell thick (for faster diffusion. - One cell wide.

Diagram of the heart

What the heart does as blood passes through the heart

1.      All the muscles relax. Blood flows into the left and right atria from the veins.

2.      The muscles in the atria contract so the blood is pushed into the ventricles.

3.      The muscles of the ventricles contract. This forces the atrioventricular valves to shut. The semilunar valves open as the blood is forced into the arteries.

4.      The semilunar valves slam shut when the blood pushes up against them, preventing the blood from flowing backwards.

The heart is made of a special kind of muscle called cardiac muscle. This muscle contracts and relaxes without stopping. To keep up this activity, the cardiac muscle needs a constant supply of nutrients and oxygen. Coronary arteries branch off from the aorta and they supply the heart muscle with glucose, fatty acids and oxygen.

The right and left sides of the heart are separated by a septum.

Coronary Heart Disease (CHD)

CHD is when the coronary arteries that deliver blood to the muscles of the heart get blocked or damaged, so they can no longer supply the heart muscle with all the nutrients and oxygen that is needed.

It is usually caused by damage to the walls of the coronary arteries. This happens when cholesterol builds up in the walls partly blocking the artery.

When part of the cardiac muscle does not get enough blood, it cannot contract normally. If is stops contracting completely; the person has a HEART ATTACK!!!

Factors increasing the risk of CHD:

-          Stress

-          A diet high in saturated fats

-          Too much salt (high blood pressure)

-          Smoking

-          Lack of exercise

-          Obesity

-          Being a male and of an old age

-          High blood cholesterol level.

-          Inherited factors

How to prevent CHD

-          STOP SMOKING

-          EAT HEALTHIER
DO MORE EXERCISE

Blood components

Component	Structure and function
Red Blood Cell	- Contains haemoglobin, the oxygen-carrying molecule. - Transport oxygen and some CO2 - No nucleus - Biconcave shape to increase surface area.
White Blood Cell	- Destroys pathogens (bacteria, viruses and other invaders) that get into the body. - Part of the immune system. - Bigger and fewer than red blood cells. - Always have a nucleus. - 2 types exist: phagocytes and lymphocytes.
Platelets	- Tiny cell fragments that float in the blood plasma. - Do not have a nucleus - Help the blood to clot when a blood vessel is damaged.
Plasma	- Pale yellow liquid - Mostly water but has many other substances dissolved in it like glucose, amino acids, inorganic ions, hormones, carbon dioxide and urea. - Carries these from place to place. - Contains soluble proteins called plasma proteins. These include important proteins needed for blood clotting  (e.g. Fibrinogen) - Part of the immune system.

White Blood Cells

§  PHAGOCYTES

-          Provide a non-specific response to infection.

-          They ingest pathogens (phagocytosis)

-          2 types: monocytes and macrophages

§  LYMPHOCYTES

-          Kill pathogens by secreting chemicals called antibodies.

-          Provide a specific response to infectious diseases.

-          2 types: T-cells and B-cells.

Phagocytosis

1.      White blood cells called macrophages recognize invading bacteria as pathogens.

2.      The cell traps the bacteria by closing around them.

3.      The bacteria are trapped in a vacuole.

4.      Enzymes are secreted into the vacuole, which kill and digest the bacteria.

Antibodies

Antibodies are chemicals produced by lymphocytes. Lymphocytes produced antibodies in response to the presence of pathogens such as bacteria.

All cells have molecules on the outside of them called antigens. Your own lymphocytes know how to recognize the antigens on your won cells. When a cell with different antigens – such as bacteria – gets into your body, your lymphocytes that are able to make an antibody that ‘matches’ the bacterium go into action.

The antibodies make bacteria clump together in preparation for action by phagocytes, or neutralize toxins produced by the bacteria. Once antibodies have been made, they remain in the blood to provide long-term protection. 

Process of blood clotting

1.      A blood vessel gets cut or damaged. Its walls, which are usually smooth, become rough.

2.      Platelets bump into these rough walls.

3.      The damaged cells in the walls and the platelets react to this by producing a protein.

4.      The protein produced by the platelets cause the soluble fibrinogen in the blood plasma to change into an insoluble protein called fibrin.

5.      The fibrin forms long fibers that precipitate out of the blood plasma. The fibers get tangled up with one another, and with the red and white blood cells in the blood. This forms a blood clot and eventually dries to form a scab.

The Lymphatic System

Blood capillaries have tiny holes between the cells in their walls. The blood plasma can leak out through these holes. It seeps between all the cells in the tissue, filling up the spaces between them. It is now called tissue fluid.

Tissue fluid provides a continuous pathway between the blood plasma and the cells in the tissues. 

Some of the fluid that leaks out o blood capillaries returns to the blood in the capillary bed. But some does not. It is collected up and returned to the blood through lymph vessels.

In the tissue, there are tiny blind-ending vessels called lymphatic capillaries. Tissue fluid moves into these. Once it is inside the lymphatic capillaries, it is called lymph.

The lymphatic capillaries gradually join up with each other to form larger lymph vessels. Lymph vessels have valves to prevent the lymph flowing the wrong way. Lymph flows due to the contracting muscles that squeeze into the vessels.  The large lymphatic vessels take the lymph to veins called subclavian cells. The lymph flows into the blood in these veins.  

Transplant rejection

If one of a person’s organs fail, (e.g. heart, liver, lungs, kidneys…), it can be treated by being given the organ taken from someone else. This is called a transplant.

However, the donor has different antigens on their cells from the recipient. So the recipient’s lymphocytes recognize the transplant as foreign and they attack it. This is called transplant rejection.

To try to avoid tissue rejections, surgeons try to find donors who have a very close match between their antigens and those of the recipient. Otherwise, the donor will need to take immunosuppressant drugs that ‘turn down’ the immune system for the rest of their lives.