hematopoiesis

Human stem cell ( Hematopoietic stem cell)

foundation of the adult hematopoietic system.

hematopoiesis

Continuous regulated process of blood cell production

three types of human stem cell

Totipotential stem cells, Pluripotential stem cell, Multipotential stem cell

Totipotential stem cell

Ovum is fertilized most versatile stem cell, can develop into any human cell type including development from embryo into fetus

Pluripotential stem cell

These cells are present several days after fertilization , “ they cannot developed into a fetus.”

Multi potential stem cell

these cells are dervide from pluripotent stem cells, they can be found in adult, they are limited to specific types of cells to form tissues.

Monophyletic theory

suggest that all blood cells are derived from a single progenitor stem cell called pluripotent hematopoietic stem cells. the monophyletic theory is the most widely used theory

Polyphyletic theory

Suggest that eah of the blood cell lineages is dervide from its own unique stem cell.

Hematopoeitic microenvironment

it is an ideal environment of HSC is the allowance for: self renewal, proliferation and differentitation, apoptosis

it is trhe 4 process of cell maturation

CELL RENEWAL, PROLIFERATION, DIFFERENTATION, AND MATURATION

stromal cells

Genral term for specialized cells within the BM(Bone marrow) that provide protecitve and nourisihing environment to the HSCs.

Example of stromal cells

Reticular adventitial cells or fibroblast, adiopocytes, lymphocytes, endothelial cellsm monocyte/macrophages, osteoclast and osteoblast, glial cells, perivascular

THREE STAGES OF HEMATOPOIETIC DEVELOPMENT

MESOBLAST/YOLK SACK PHASE, HEPATIC PHASE, MEDULLARY PHASE (MYLEOID)

Mesoblastic or yolk sac phase

• begins around 19th day of embryonic development after fertilization.

• early in embryonic development, cells from the mesoderm migrate to the yolk sac.

• these primitive but trnasient yolk sac erythroblast are important in early embryogenesis to produce hemoglobin (Grower-1, Grower-2, nad portland

Hepatic phase

• the hepatic phase of hematopoiesis begins at 5th to 7th week of gestation

• characterized by recognizeable clusters of developing erythroblast, granulocytes, and monocyutes colonizing the fetal liver, thymus, spleen, placenta and ultimatley the bone marrow space in the final medullary phase.

• production of megakaryocytes also begins during th hepatic phase.

• hematopoiesis during the phase occurs extrabascularly, with the liver remaining the major site of hematopoiesis during second trimester of fetal life.

• hemoglobin (Hb F) is the predominant hemoglobin, but detectable levels of adult hemoglobin (HbA) may be present.

• stage for the beginning of definitive hematopoiesis with a decline primitive hematopoiesis in the yolk sac.

Medullary(myeloid) phase

• Prior to the fifth month of fetal development, hematopoiesis

• by the end of the 24 weeks gestation the bone marrow becomes the promary site of hematopoiesis.

  • Measurable levels of erythropoietin (EPO), granulocyte colony stimulating factor (G-CSF), granulocytemacrophage colony stimulating factor (GM-CSF), and hemoglobins F and A can be detected
    in adult hematopoiesis, the red marrow is found only in the:
    Ribs, sternum, shoulder blade, skull (CHILDREN),vertebrea, pelvic bone, proximal end of long bones.

site of adult hematopoietic tissue

Bone marrow(MAJOR SITE), lymph nodes, spleen, liver, and thymus

Reference ranve for normal adult Hgb is

Hgb is 95- 97 %Hb A, 2 to 3%Hb A2, and ≤1% Hb

Bone marrow

ne of the largest organs in the body, is the tissue located within the cavities of the cortical bones