3.1 Haemopoiesis, The Spleen And The Bone Marrow Flashcards
What is haemopoiesis and where does it occur?
Production of blood cells occurs in the bone marrow
What would a biopsy of the pelvis look like?
Bony trabeculae with fat cells between them
What makes the haemopoietic stem cell (HPSC) so special?
- can differentiate into RBC
- has the greatest power of self renewal compared to any other adult tissue
What are the sources of HPSC?
- bone marrow
- G-CSF (a hormone that controls haemopoiesis) mobilised stem cells
What is the reticuloendothelial system?
- a network in blood and tissues which is part of the immune system containing phagocytic cells.
- cells of the RES can identify and mount an appropriate immune response to foreign antigens
- main organs = the spleen and the liver
What does the spleen consist of and how does this influence blood flow?
Red pulp - sinuses lined by endothelial macrophages and cords. Red cells preferentially pass through here.
White pulp - similar structure to lymphoid follicles. White cells and plasma preferentially pass through here.
What is the role of the portal vein in relation to the spleen?
Takes look to liver from splenic vein
What is the function of the spleen in adults?
- sequestration and phagocytosis of old/abnormal red cells, removed by macrophages
- blood pooling - platelets and red cells rapidly mobilised during bleeding
- extramedullary haemopoiesis - spleen swells and makes blood when bone marrow cant
- immunological function - has some t and B cells
What is splenomegaly and where may it be felt?
Abnormal enlargement of the spleen - never normal to palpate it below the costal margin
Feel in the right iliac fossa
Why would the spleen grow?
- back pressure
- overworking red pulp
- over working white pulp
- reverting to what it use to do (extramedullary haemopoiesis)
- expanding as infiltrated by cells which should e there e.g cancer cells of blood origin such as leukaemia or by other cancer metastasis.
What part of the spleen do cancer cells of blood origin effect?
Expand white pulp
What could possibly be behind - massive - moderate - mild Splenomegaly?
- massive: chronic myeloid leukaemia, myelofibrosis, malaria, schistosomiasis
- moderate: above as well as lymphoma, leukaemia, liver cirrhosis with portal hypertension, infection such as glandular fever
- mild: above as well as infections e.g hepatitis, endocarditis, autoimmune disorders, etc.
Why should you avoid physical activity in cases of splenomegaly?
Rupture of spleen - can lead to a haematoama or infarction.
What is hypersplenism?
Pooling of blood in enlarged spleen(as a result get a low blood count)
What’s a Howell jolly body and where is it found?
Will see in hyposplenism
A cluster of DNA in circulating red blood cells.
How is haemoglobin synthesised?
- on chromosome 11 and 16, switches at different stages in life.
- switch from foetal to adult haemoglobin occurs at 3-6 months of age
- defect in cell membrane components = red cells less deformable and recognised by the spleen as abnormal = shorter life cycle = haemolytic anaemia
How does erythropoietin work in a negative feedback loop?
- patient = anaemic so reduced pO2 detected interstitial cells in kidney
- increased production of erythropoietin by kidney
- erythropoietin stimulates maturation and release of red cells from marrow
- total red cells and so haemoglobin rises
- more oxygen can be delivered = pO2 rises
- as a result erythropoietin production falls
What is cytopenia and what are the 5 main forms?
Cytopenia = reduction in the number of blood cells.
Low red cells = anaemia Low white cells = leukopenia Low neutrophil = neutropenia Low platelet = thrombocytopenia Low red cells, white cella and platelets = pancytopenia
So, ends in -penia, means a reduction
What does it mean when a blood syndrome ends with -cystosis or -philia?
An increase in the number of blood cells. Red cells =erythroytosis White = leucocytosis Neutrophils = neutrophilia Lymphocytes = lymphocytosis High platelet count = thrombocytosis
What is neutrophil maturation controlled by?
Hormone G-CSF
- increases neutrophil production and decreases time to release mature cells from bone marrow
NB: if you need more neutrophils in a patient with severe neutropenia and sepsis after chemotherapy, administer recombinant G-CSF.
What can cause neutrophilia?
- cancer
- acute haemorrhage
- tissue damage
- myeloproliferative disorders (marrow working too hard)
- G -CSF
- smoking
What are the causes of neutropenia?
- b12/folate deficiency
- infiltration f bone marrow by malignancy or fibrosis = no room for production
- aplastic anaemia = empty marrow, no precursors
- radiation = mature cells killed, precursors stunned
- drugs = poison on the marrow
- congenital disorders
What are the consequences of neutropenia?
- bacterial and fungal infections = life threatening
- muscles also ulceration
NB: neutropenic sepsis is a medical emergency. Intravenous antibiotics must be given immediately.
What is the role of monocytes?
- response to inflammation and antigenic stimuli
- migrate to tissue like macrophages
