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In postnatal birds and mammals (including humans), this usually occurs within the red bone marrow. [2] In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac. By the third or fourth month, erythropoiesis moves to the liver. [3] After seven months, erythropoiesis occurs in the bone marrow.
Human red blood cells are produced through a process named erythropoiesis, developing from committed stem cells to mature red blood cells in about 7 days. When matured, in a healthy individual these cells live in blood circulation for about 100 to 120 days (and 80 to 90 days in a full term infant ). [ 62 ]
Red blood cells are circular, biconcave, disk-shaped and deformable to allow them to squeeze through narrow capillaries. They do not have a nucleus. Red blood cells are much smaller than most other human cells. RBCs are formed in the red bone marrow from hematopoietic stem cells in a process known as erythropoiesis. In adults, about 2.4 million ...
Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form the single cell zygote and the germinal stage of development commences. Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages.
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These hematopoietic stem cells are further closely associated with endothelial cells throughout human life. Later, they migrate to the fetal liver where the majority of physiologic EMH (extra-medullary hematopoiesis) takes place. They can also migrate to the spleen and lymph nodes where hematopoiesis can occur, but to a lesser degree.
This diagram shows the hematopoiesis as it occurs in humans. It may look incomplete when rendered directly from WikiMedia. Reference list is found at: File:Hematopoiesis (human) diagram.png. The morphological characteristics of the hematopoietic cells are shown as seen in a Wright’s stain, May-Giemsa stain or May-Grünwald-Giemsa stain.
Almost all vertebrate organisms have hemoglobin-containing cells in their blood, and with the exception of mammals, all of these red blood cells are nucleated. [1] In mammals, NRBCs occur in normal development as precursors to mature red blood cells in erythropoiesis, the process by which the body produces red blood cells.