S3: haemopoiesis, the spleen + bone marrow & blood counts + films Flashcards
Define haemopoiesis
Production of blood cells that occurs in the bone marrow
Bone marrow extensive throughout the skeleton in infant -> remain in the axial skeleton as we get older
Describe the functions of the main blood cell types
RBC = deliver oxygen to tissues, carry haemoglobin, maintain haemoglobin in its reduced state, maintain osmotic equilibrium, generate energy
Neutrophil = first-responder phagocyte, most common WBC, essential part of innate immune system, live for 1-4 days
Monocyte = circulate for ~1-3 days before turning into macrophages, phagocytose microorganism and remove cellular debris, antigen presenting role, defence against chronic bacterial infections
Eosinophils = immune response against multicellular parasites, mediator of allergic responses, granular
Basophils = large dense granules containing histamine + heparin, active in allergic reactions and inflammatory conditions
Lymphocytes = B cells, T cells, natural killer cells
Important hormones = erythropoietin + thrombopoietin
Name the 4 main roles of the spleen
1) sequestration and phagocytosis = old RBCs removed
2) blood pooling = RBCs + platelets can be rapidly mobilised
3) extramedullary haemopoiesis
4) immunological function
Describe causes of splenomegaly
Back pressure - portal hypertension in liver disease
Over work
Extramedullary haemopoiesis
Expanding as infiltrated with cells
Expanding as infiltrated with other material
NEVER NORMAL FOR ENLARGED SPLEEN
Describe causes of hyposplenism
Lack of functioning splenic tissue
Splenectomy
Sickle cell disease
GI diseases eg. coeliac, chron’s, ulcerative colitis
Autoimmune disorders eg. hashimoto’s disease, systemic lupus
Explain what is meant by the normal range and why it changes
Normal range = 95% of healthy population
Changes with age, sex, ethnicity + co-morbidities
Explain the significance of the reticulocyte count
Measurement of the number of young erythrocytes
Increased: haemolytic anaemia, recent blood loss, response to iron, vit B12, folate replacement
Decreased: bone marrow failure, haematinic deficiency
Explain the meaning of the terms that are frequently used to describe abnormalities in a blood count or film
Microcytic = small
Macrocytic = large
Hypochromic = pale, less Hb
Hyperchromic = dense, more Hb in given volume
Howell-jolly bodies = DNA/nuclear fragments in RBC
Heinz bodies = denatured Hb
Describe how a FBC is analysed
Spectrophotometry = amount of light absorbed by sample proportional to amount of absorbent compound within it (used to measure Hb)
Flow cytometry = single file line of cells, pass through light beam, forward scatter: more scatter = bigger cell; side scatter, myeloperoxidase activity
Explain what is meant by packed cell volume
Proportion of blood that is made up of RBC
Used to assess anaemia but more often polycythemia
Explain what is meant by red cell count
Number of RBC in a given volume of blood
Used for assessment of anaemia and erythrocytosis
Explain what is meant by mean cell volume
Mean size of RBC
Most important parameter used to screen the cause of anaemia
Explain what is meant by mean cell Hb concentration
Mean concentration of Hb in RBC
Increased in spherocytosis
Explain what is meant by red cell distribution width
Variation in size of RBC
Used to help assess cause of anaemia
Describe the clinical significance of splenomegaly
Risk of rupture if spleen is enlarged and no longer protected by rib cage
Avoid contact sports and vigorous activity
