Haemopoiesis Flashcards
What is the function of platelets?
Primary haemostasis
What is the lifespan of red blood cells?
120 days
What is the lifespan of neutrophils?
7-8 hours
What is the lifespan of platelets?
7-10 days
What is the progression of formation of neutrophils?
Myeloblast Promyelocyte Myelocyte Metamyelocyte Band forms Neutrophils
What are blasts?
Nucleated precursor cells
What are megakaryocytes?
Why are they polyploid?
Platelet precursors
They undergo endomitosis, i.e. the nucleus can divide many times without the cytoplasm dividing
What is the immediate red cell precursor?
Reticulocytes
What is the name for the nucleated precursor between neutrophils and blasts?
Myelocytes
Name and describe the 5 events in haemopoiesis?
Self-renewal: a property of stem cells, lost in the descendents.
Proliferation: increase in numbers
Differentiation: Descendents commit to one or more lineages
Maturation: descendents acquire functional properties and may stop proliferating
Apoptosis: descendents undergo cell death
What state are stem cells generally in?
A quiescent state
They divide every few weeks
What gastrulation layer are haemoopoietic stem cells derived from?
The mesoderm
Describe the sites of haemopoiesis in utero
Yolk sac: first site of erythroid activity, stops by week 10
Liver: starts by week 6
Spleen: starts by week 12
Bone marrow: starts by week 16
Where are haemopoietic stem cells located in the steady state?
When might this change?
The bone marrow
They can be mobilised into the circulation for harvesting and transplantation
What are the compartments of the bone marrow?
Cellular (haemopoietic and non-haemopoietic cells)
Vascular elements
Connective tissue matrix
Describe the structure of bone marrow
Haematopoietic and non-haematopoietic cells surrounded by a shell of vascularised and innervated bone
Trabeculae (minute projections of bone) are found throughout the metaphysis so many cells in that region are found close to the bone surface
What is the endosteum?
What is it lined by?
The interface between bone and bone marrow
It is covered by bone-lining cells including osteoblasts and osteoclasts
Describe the blood supply to the bone
Centrally located nutrient arteries terminate within the bone at the periphery of the marrow space
The marrow cavity has a complex network of blood vessels organised into repeating units
Arteries feed into sinusoids.
There is a rich supply of arterioles and sinusoids near the endosteum.
What are sinusoids?
Specialised venules in the marrow that form a reticular network of fenestrated vessels that regulate the passage of cells in and out of the circulation.
How do newly formed blood cells pass into the circulation?
They can pass through fenestrations in endothelial cells of the sinusoids to enter the circulation.
How do neutrophils get into the circulation?
They actively migrate towards the sinusoid
How do platelets get into the circulation?
Megakaryocytes fenestrate the endothelial cell with cytoplasmic processes.
The velocity of flow in the sinusoids fragments the cytoplasmic projections creating platelets which are released into the circulation.
What is the difference in red and yellow marrow?
Red marrow is haemopoietically active
Yellow marrow is fatty and inactive
Why is there a reduction in marrow cellularity with age?
There is an increase in yellow marrow with age.
