topic 10 : red bone marrow

Question 1

Histology of red bone marrow

Answer 1

-jelly like structure found in cavities of bones representing the activite unit of bone marrow (white bone marrow is non-active)

-has a stroma made of: reticular CT and with specialized vessels called sinuosidal capillaries-carry away whay has been formed in here / contain macrophages too- cells that aid hematopoeisis by phagocytosing debris

other cels types:
1.Hematopoietic cells: a.stem cells: can self-renew and replicate to form the different blood cells / b.progenitor cells -cant self renew as wel
2.Macrophages
3.Megakaryoytes : large bone marrow cell with lobular shaped nucleus that forms platelets
4.Reticular cells : made type III collagen fibers that make reticulin needed to support adipoytes & hematopoetic cells
5. Adipocytes: plays a role in storing fat

-endochondral ossification with bony spicules

Question 2

Embryonic/foetal haematopoiesis

Answer 2

Embryonic phase

during weeks 2 to 8: in blood islands off the yolk sac only erythropoeisis is supported , producing nucleated redb blood cells

Fetal phase:
Hematopoietic cells then migrate trough bloodstream to liver & spleen. Hematopoeisid continues with production of erythrocytes & granulocytes.

Finaly hematopoeisis shifts to bone marrow which is the main site after birth. Pre-dominantly produces granulocytes.

Question 3

Haematopoietic
stem cells and their regulation.

Answer 3

Mesodermal Origin: HSCs arise from hemangioblasts during early embryonic development.
Self-Renewal: Capable of self-renewal, ensuring a lifelong supply of stem cells.
Pluripotency: Possess the ability to differentiate into all types of blood cells, including erythrocytes, leukocytes (granulocytes, lymphocytes), and platelets.

location differs with time

regulation:
Microenvironment/Niche: Bone marrow stromal cells provide cytokines and growth factors.

Transcription Factors: Control gene expression for HSC self-renewal and differentiation
e.g GATA-2: Maintains HSC survival and function

Hormonal Regulation: Influences HSC proliferation and differentiation. such as erythropoietin (EPO) and thrombopoietin (TPO)

Question 4

The structure and development of erythrocytes

Answer 4

Erythrocytes (Red Blood Cells):

Origin: Derived from hematopoietic stem cells in the bone marrow.

Maturation:
Proerythroblasts: Early precursor cells.
Erythroblasts: Nucleated cells that synthesize hemoglobin.
Reticulocytes: Ejected from bone marrow into bloodstream; lose nucleus to become mature erythrocytes.

Structure: Biconcave disc shape for efficient gas exchange; packed with hemoglobin for oxygen transport.

Question 5

Structure and Development of Thrombocytes (Platelets):

Answer 5

Origin: Derived from megakaryocytes in the bone marrow.

Maturation:
-Megakaryoblasts: Precursor cells that differentiate into megakaryocytes.
-Megakaryocytes: Large cells that fragment cytoplasm to release platelets.

Function: Essential for blood clotting and wound healing; contain granules with clotting factors and growth factors.