BLOOD is a special tissue of the body. Yes, it is the fabric, though, and liquid. After all, what is the fabric? This is a collection of cells and intercellular substance that performs a specific function in the body and are United by a common origin and structure. Let's examine these three characteristics of blood.
1. Functions of blood
The blood is the carrier of life. Because it's circulating through the vessels, supplies all cells of the body the nutrients and oxygen needed for breathing. She takes the cell waste products, waste and carbon dioxide, which is formed during processing of nutrients into energy. And, finally, the third important function of the blood - protective. Blood cells destroy trapped in the body of pathogenic microorganisms.
2. The composition of the blood
Blood is approximately 1/14 of the weight of the body. In men it is about 5 liters, women a little less.
If you take fresh blood, place it in a test tube and let it stand, it will split into 2 layers. The top layer will be transparent yellowish liquid - plasma. And below is the residue from the cells of the blood - corpuscles. Plasma makes up about 60% of blood volume (3 l), and it consists of 90% water. The other 10% is a variety of substances: proteins, fats, carbohydrates, salts, hormones, enzymes, gases, vitamins, etc.
The formed elements of blood are three types of cells: red blood cells - red blood cells, white blood cells - leukocytes and platelets - platelets.
Erythrocytes are the most numerous among the formed elements in blood 4-5 million per 1 mm3 1 mm3 corresponds to one drop of blood)! Exactly erythrocytes determine red blood, because they contain red iron - containing pigment called hemoglobin. Erythrocytes are responsible for the transport of gases and primarily oxygen. Hemoglobin is a special protein that is able to capture oxygen from the lungs. He is painted in light red color. Blood oxygen is carried to all cells of the body. Giving oxygen, the hemoglobin of the red becomes dark red or purple. Then, taking from cells carbon dioxide, hemoglobin delivers it to the lungs and from the lungs the carbon dioxide is excreted during exhalation.
Red blood cells live for 3-4 months. Every second dies about 5 million red blood cells!
Leukocytes are part of the human immune system, they are the main weapons of the body in disease control. In any case of injury or infection, they immediately rush to the site of lesion, surrounded by pathogenic organisms and devour them. In addition, leukocytes are involved in the immune (protective) reactions that produce antibodies. Antibodies are special proteins (immunoglobulins)that are produced when ingested foreign substances (antigens). Antibodies have the ability to bind to antigens, after which it is excreted from the body. 1 mm3 of blood contains 10 thousand leukocytes.
Thrombocytes (blood platelets) are responsible for the clotting of blood. For example, if the damaged blood vessel, the blood begins to flow from it. In order to avoid blood loss because it is dangerous for life - the body includes a protective mechanism - formation of a blood clot that stops bleeding. Platelets rush to the rupture of the vessel and stick to its walls and to each other, forming a tube. When the platelets release chemicals that trigger coagulation: they activate a plasma protein fibrinogen, and it forms a water-insoluble strands of the protein fibrin. Fibrin strands entangle blood cells at the injury site, and it turns semi-solid mass - clot.
Hematopoiesis (hemopoiesis) in mammals carry hematopoietic cells, which are located in the red bone marrow. In addition, some lymphocytes are formed in the lymph nodes, the thymus gland (thymus and spleen. Together with red bone marrow, they constitute a system blood-forming organs.
The bone marrow.
The child red (active) bone marrow is located in all bones of the skeleton,
as an adult red bone marrow is
in the cancellous bone of the skeleton and the epiphyses of tubular bones.