Lecture 5 Flashcards
What is haematopoiesis?
The process of blood cell formation occurring in the bone marrow.
Where does haematopoiesis initially begin during embryonic development?
In the yolk sac around 3 weeks of human development.
What type of cells does the yolk sac contain that contribute to early haematopoiesis?
Mesoderm-derived cells known as haemangioblasts.
What do haemangioblasts differentiate into?
Nucleated red blood cells and endothelial cells.
When does haematopoiesis transition to the liver during development?
At a later stage of embryogenesis.
Where does haematopoiesis occur after birth?
Primarily in the bone marrow.
What are the two main types of cells in the bone marrow?
Haematopoietic cells (form blood cells) and stromal cells (provide support).
What is the function of stromal cells in the bone marrow?
They provide a specialized environment necessary for haematopoiesis.
What types of cells are osteoblasts and osteoclasts?
Cells concerned with bone formation and resorption.
What is the composition of compact bone?
About 70% hydroxyapatite (hydrated calcium phosphate).
What type of tissue is bone considered?
A specialized form of connective tissue.
What are Haversian canals?
Microscopic tubes in the compact bone that contain blood vessels and nerves.
What is the main cause of death after exposure to ionizing radiation?
Haematological failure.
What discovery confirmed the importance of bone marrow in haematopoiesis?
Transplantation of bone marrow cells could save animals exposed to radiation.
What is a haematopoietic stem cell (HSC)?
A stem cell capable of generating all blood cell types and capable of self-renewal.
What limits the self-renewal capability of HSCs?
The ‘Hayflick limit’ and telomere shortening due to the end replication problem.
What is a stem cell niche?
A microenvironment in the bone marrow that supports stem cells.
Where are haematopoietic stem cells found within the bone marrow?
In the endosteum and perivascular regions.
What is the role of growth factors in haematopoiesis?
They drive growth and differentiation of progenitor cells.
What growth factor is essential for erythropoiesis?
Erythropoietin (EPO), produced mainly by the kidneys.
What stimulates the production of erythropoietin (EPO)?
Low oxygen levels in the blood.
What is thrombopoiesis?
The process of platelet formation.
What hormone regulates thrombopoiesis?
Thrombopoietin (TPO), primarily produced by the liver.
How do platelets regulate thrombopoietin levels?
Platelets have TPO receptors and remove TPO from circulation via negative feedback.
What triggers increased TPO production during inflammation?
Cytokine IL-6.
What is the common precursor for erythrocytes and platelets?
The megakaryocyte/erythrocyte precursor (MEP).
What is the function of granulocyte-monocyte colony-stimulating factor (GM-CSF)?
It stimulates the growth of granulocytes and monocytes.
What type of fashion do growth factors act in haematopoiesis?
Paracrine and juxtacrine fashion.
What is the role of interleukin-3 (IL-3)?
It stimulates the growth of most haematopoietic cell types.
How does infection affect haematopoiesis?
It increases growth factor production due to leukocyte activation, enhancing haematopoiesis.
What is a progenitor cell?
A cell derived from a stem cell that is on a committed pathway to differentiate into specific blood cells.
What is the Hayflick limit?
The number of times a normal cell population will divide before stopping due to telomere shortening.
What is a colony in the context of in vitro bone marrow culture?
A visible cluster of cells derived from a single progenitor cell.
What is semi-solid media used for in cell culture?
To support the growth of progenitor cells, allowing colony formation.
Which growth factor stimulates platelet production and is produced by liver cells?
Thrombopoietin (TPO).
How are the early stages of erythrocyte and platelet production connected?
Both share a common pathway through the megakaryocyte/erythrocyte precursor (MEP).
What type of tissue origin do bones have?
Mesodermal/mesenchymal origin.
What characterizes cancellous bone?
A less dense, spongy structure compared to compact bone.
What is the significance of the endosteum in haematopoiesis?
It is a niche location for haematopoietic stem cells within the bone marrow.
What happens to HSCs during serial transplantation?
Their capacity for self-renewal eventually declines.
What are the roles of osteoblasts and osteoclasts?
Osteoblasts build bone, while osteoclasts resorb bone.
What component comprises most of the rigid structure of bone?
Hydroxyapatite, a form of hydrated calcium phosphate.
What does paracrine signaling entail?
The diffusion of signals from a producer cell to a responder cell nearby.
What does juxtacrine signaling involve?
Direct contact between the signaling cell and the responder cell.
What cytokine is associated with increasing liver TPO production during inflammation?
IL-6.
What are examples of growth factors with broad activity in haematopoiesis?
Interleukin-3 (IL-3).
What historical evidence supports bone marrow’s role in blood formation?
Animal studies showing that transfusion of bone marrow, but not blood or lymphoid tissue, saves animals after radiation exposure.
What do progenitor cells require to grow and differentiate in vitro?
Specific growth factors and cytokines.
Why is erythropoiesis important at high altitudes?
To increase red blood cell production due to lower oxygen availability.
