where does red blood cell production occur in adults
Red blood cell In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a plasma membrane as the sack. Approximately 2.4 million new erythrocytes are produced per second in human adults.[2] The cells develop in the bone marrow and circulate for about 100â€“120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds (one minute).[3] Approximately a quarter of the cells in the human body are red blood cells.[4][5] Nearly half of the blood's volume (40% to 45%) is red blood cells.
Bone marrow The composition of marrow is dynamic, as the mixture of cellular and non-cellular components (connective tissue) shifts with age and in response to systemic factors. In humans, marrow is colloquially characterized as "red" or "yellow" marrow (Latin: medulla ossium rubra, Latin: medulla ossium flava, respectively) depending on the prevalence of hematopoetic cells vs fat cells. While the precise mechanisms underlying marrow regulation are not understood,[6] compositional changes occur according to stereotypical patterns.[9] For example, a newborn baby's bones exclusively contain hematopoietically active "red" marrow, and there is a progressive conversion towards "yellow" marrow with age. In adults, red marrow is found mainly in the central skeleton, such as the pelvis, sternum, cranium, ribs, vertebrae and scapulae, and variably found in the proximal epiphyseal ends of long bones such as the femur and humerus. In circumstances of chronic hypoxia, the body can convert yellow marrow back to red marrow to increase blood cell production.[10]