Nearly 300 million erythrocytes, 5 million leukocytes and 250 billion platelets are killed in human body every day. However, a healthy personrsquo;s

Hematopoietic system (bone marrow, spleen)

Nearly 300 million erythrocytes, 5 million leukocytes and 250 billion platelets are killed in human body every day. However, a healthy person’s blood remains constant, because these cells renew due to the red bone marrow, spleen and lymph nodes (diagram 51).

Bone marrow

Red bone marrow fills the cavity between the membranes in the heads of long bones, spongy flat bones of the skull, sternum, shoulder blades, vertebrae, ribs, pelvic bones. It consists of primary (embryonal) cells that in the process of maturing become erythrocytes, platelets or leukocytes.

The blood that flows through the bone vessels, constantly takes mature form elements into general bloodstream. Billions of immature cells quickly mobilize and rapidly transforms into mature ones in the case of blood loss. Red blood cells renew the fastest way.

Due to lack of oxygen in the atmosphere for example during a stay in the mountains, bone marrow irritation elicits a greater number of erythrocytes than usual, in addition with the high content of hemoglobin. This gives people the opportunity to live at high altitudes.

Diagram 51. The human hematopoietic system (red dots indicates the location of the bone marrow): 1 — the skull; 2 — sternum; 3 — ribs; 4 — spleen; 5 — the vertebrae; 6 — pelvic bone; 7 — heads of the tubular bones
Diagram 52. Spleen (3); 1 — pancreas; 2 — stomach

Even small doses of radiation and some chemicals that reduce the production of blood cells adversely affect the bone marrow. In cases of severe radiation, viruses or chemical factors, the bone marrow loses its ability to produce mature cells and immature blood cells that are unable to perform their functions get in human blood. High doses of radiation cause radiation sickness, when the red bone marrow may even stop the production of blood cells. Yellow fat is contained in the marrow cavity of long bones and has no hematopoietic function. Taken from http://worldofschool.org

Spleen

The spleen is located in the left hypochondrium below the diaphragm (diagram 51, 52). It produces lymphocytes — the protective blood cells; “sorts” cells (destroys the aged ones, accumulates ferric molecules from old red blood cell molecule for future and then passes them to the bone marrow to form the new ones); filters and neutralizes pathogenic microorganisms and viruses that circulate in the blood. Due to the features of its structure spleen may additionally contain up to 500 ml of blood, that is released when needed (for example, during intensive physical work).

Categories:
Questions:
  • Explain the blood cells formation mechanism.

  • What organs form the blood cells?