Blood

Blood is the only liquid tissue in the body. Its volume in an adult is about 5 liters, which is 6–8% of body weight. Blood continuously circulates through a closed system of blood vessels, performing transport, protective, regulatory and homeostatic functions.

Blood composition

Blood consists of plasma (55%) and formed elements (45%).

Plasma is a yellowish liquid containing water (90%), proteins (albumin, globulins, fibrinogen), glucose, electrolytes, hormones and metabolic products. Plasma proteins maintain oncotic pressure, transport substances and participate in coagulation.

Shaped elements

Erythrocytes (red blood cells) are biconcave discs with a diameter of 7–8 microns, lacking a nucleus. There are 4.5–5.5 million erythrocytes in 1 μl of blood. They contain hemoglobin - a protein that binds oxygen in the lungs and distributes it to the tissues. The total surface area of ​​all red blood cells is about 3,800 m².

The lifespan of an erythrocyte is 120 days, after which it is destroyed in the spleen. 2.5 million new red blood cells are born in the bone marrow every second.

Leukocytes (white blood cells) are cells of the immune system. In 1 µl - 4,000–9,000. They are divided into:

• Neutrophils (60–70%) - phagocytose bacteria
• Lymphocytes (25–30%) - T cells, B cells, NK cells
• Monocytes (3–8%) - turn into macrophages in tissues
• Eosinophils and basophils - are involved in allergic reactions

Platelets are fragments of megakaryocytes involved in blood clotting. In 1 µl - 180,000–320,000. When a vessel is damaged, platelets adhere to the site of damage, are activated and form a platelet plug - the first stage of hemostasis.

Blood groups

The ABO system is determined by antigens on the surface of red blood cells:

• Group O (I) - no antigens, universal donor
• Group A (II) - antigen A
• Group B (III) - antigen B
• Group AB (IV) - both antigens, universal recipient

Rh factor (Rh) - the presence or absence of antigen D. 85% of people are Rh positive. Rh incompatibility during pregnancy can lead to hemolytic disease of the newborn.

Blood clotting

The coagulation cascade includes more than 13 factors and ends with the conversion of fibrinogen into fibrin - threads that form a clot network. Violation of any link in the cascade leads to increased bleeding (hemophilia) or, conversely, to thrombus formation.

3D anatomy atlas Humio - study the heart, blood vessels and blood supply to organs in an interactive format will help you consolidate your knowledge about the cardiovascular system.