2.01 - Introduction to Haematology Flashcards
What is haematopoiesis?
Production of mature blood cells from stem cells in the bone marrow:
- red blood cells
- platelets
- white blood cells
Distribution of haematopoiesis in
a) fetal
b) children
c) adults
a) liver and spleen
b) throughout the skeleton
c) axial skeleton
What cell does haematopoiesis begin from?
Multipotent haematopoietic stem cell (HPSC) - haemocytoblast.
Structure of erythrocytes.
- biconcave structure
- enucleated
Structure of haemoglobin.
Globular tetramer protein:
- 2 alpha chains
- 2 beta chains
- 4 haem groups
Deoxyhaemoglobin exists in low affinity (T) state or high affinity (R) state - when oxygen binds, it converts from T to the R state.
Lifespan of erythrocytes.
120 days
Process of erythropoiesis.
- Interstitial peritubular cells in the kidney detect hypoxia.
- Kidney produces EPO in response to hypoxia.
- Common myeloid progenitor (CMP) differentiates, releasing reticulocytes.
- Reticulocytes mature into erythrocytes (RBCs).
- Number of RBCs and Hb increases, allowing more O2 to be delivered to tissues.
How long does it take for reticulocytes to mature into erythrocytes?
2 days.
Process of thrombopoiesis.
- Liver produces TPO in response to thrombocytopenia.
- CMP cells differentiate into megakaryocytes.
- Platelets bud off from the membrane of megakaryocytes.
Process of monocytosis.
- Inflammation (acute or chronic).
- CMP cells differentiate into myeloblast.
- Myeloblast differentiates into monocyte.
- Monocyte leaves the blood circulation after 20 hours, and become tissue macrophages.
Function of
a) monocyte
b) macrophage
a) phagocytosis in the blood
b) phagocytosis in the tissue
Products of granulopoiesis.
- basophils
- neutrophils
- eosinophils
Process of granulopoiesis.
- Microbial infection triggers release of G-CSF.
- CMP cells differentiate into myeloblast.
- Myeloblast differentiates into granulocytes.
Function of:
a) neutrophils
b) eosinophils
c) basophils
a) phagocytose any foreign organisms by releasing reactive oxygen species.
b) actions against parasitic infection; raised in anaphylaxis.
c) release histamine as part of the immune response.
Process of lymphopoiesis.
Common lymphoid progenitor (CLP) cells differentiate into:
- natural killer cells
- B lymphocytes
- T lymphocytes
What organs are part of the reticuloendothelial system?
- kidney
- liver
- spleen
- lymph nodes
- bone marrow
What is the function of the spleen?
White pulp: forms antibodies and removes any bacteria or erythrocytes coated in antibodies; particularly effective against encapsulated bacteria.
Red pulp: removes old RBCs and metabolises haemoglobin.
Role of the spleen in haemorrhage.
In response to bleeding, platelets and RBCs are pooled in the spleen to minimise blood loss.
What are the encapsulated bacteria?
Some Have Pretty Nice Capsules:
Streptococcus pneumoniae
Haemophilus influenzae
Pseudomonas aeruginosa
Neisseria meningitidis
Cryptococcus
Causes of splenomegaly.
- overworking red or white pulp
- backpressure 2° to portal hypertension
- leukaemia
- infection
- accumulation of waste products of metabolism
Infective causes of splenomegaly.
- malaria
- Schistosomiasis
- HIV
- EBV
Causes of hyposplenism.
- splenectomy
- sickle cell disease
- coeliac disease
Indications for splenectomy.
- splenic rupture
- cancer
- hereditary spherocytosis
- ITP
Management of asplenic patients.
- vaccinations
- prophylactic antibiotics
- carry a card notifying medical staff of their condition
Blood film typical of hyposplenic patients.
RBCs with Howell-Jolly bodies (defective).
Normal functioning spleen would remove defective cells as they were filtered through.
Specimen collection errors that may result in abnormal blood results.
- wrong blood in the tube
- wrong bottle used for the test
- pooling of different samples
- poor technique or heavy handling
Delivery of specimen errors that may result in abnormal blood results.
- delay or lost
- delivered at wrong temperature
Specimen analysis errors that may result in abnormal blood results.
- specimen mix up
- wrong test requested or performed
- technical error with the analyser
Responsive action errors that may result in abnormal blood results.
- nothing done in response to abnormal result
- reflex tests not conducted
- right result is applied to the wrong patient
How long after a blood sample is taken must it be processed?
Within 2 hours.
Why are blood films fixed with methanol?
Protects the practitioner from from any infectious diseases in the blood.
What are the three key stages where anaemia may occur.
- Abnormalities during production.
- Abnormalities during circulation.
- Abnormalities during removal.
Anaemia - abnormalities during production.
- defective RBC production
- defective Hb production
Anaemia - abnormalities during circulation.
- haemolytic anaemia
- excessive bleeding
Causes of haemolytic anaemia.
- aortic stenosis (MAHA)
- heat damage
- hereditary spherocytosis
- G6PD deficiency
- PKU deficiency
- autoimmune (e.g. SLE, lymphoma, EBV)
Anaemia - abnormalities during removal.
- hypersplenism
Normal reticulocyte count in response to anaemia.
Reticulocytosis should be observed on blood film, demonstrating active bone marrow trying to replace RBCs rapidly.
If reticulocyte count is low / normal, this suggests the bone marrow is not functioning as normal.
Causes of reticulocytosis.
Anaemia with normal bone marrow function:
- excessive bleeding
- splenic sequestration of RBCs
- haemolysis
Causes of microcytic anaemia.
Causes of normocytic anaemia.
Causes of macrocytic anaemia.
Symptoms of anaemia.
- fatigue
- headache
- SOB
- palpitations
- dizziness
- syncope
Signs of anaemia.
- pallor
- bounding pulse
- postural hypotension
- tachycardia
Treatment of anaemia.
Identify the cause and treat that!
What is the role of vitamin B12?
Required for DNA synthesis and essential for the production of reticulocytes.
Storage of vitamin B12.
Stored in the liver that are able to sustain the body for 3 to 5 years - symptoms of deficiency will not present for a long time.
Causes of B12 deficiency.
- insufficient intake (vegan diet)
- lack of intrinsic factor
- disease of the ileum
- use of PPIs
- abuse of nitrous oxide
- methotrexate
What are the causes of lack of intrinsic factor?
Parietal cells of the stomach produce intrinsic factor:
- gastrectomy
- autoimmune destruction (pernicious anaemia) (#1 cause in UK)
Complications of B12 deficiency.
Associated with neurological disease - subacute combined degeneration of the cord
Symptoms of subacute combined degeneration of the cord.
Loss of vibration and proprioception in the hands and feet.
Sensory gait ataxia.
Distal muscle weakness.
Features of dementia.
Function of folate (B9).
DNA synthesis and reticulocyte production.
Causes of folate deficiency.
- insufficient intake
- excessive demand (e.g. pregnancy, increased erythropoiesis)
- Crohn’s disease
Complications of folate deficiency in pregnancy.
Neural tube defects in the unborn fetus.
Dietary sources of iron.
- red meat
- raisins
- oats
- spinach
- fortified cereal
Foods that inhibit iron absorption.
- tannins in tea
- red wine
- phytates in chapattis
Foods that promote iron absorption.
Citrus fruits (ie. orange juice)
Storage of iron.
Macrophages phagocytose erythrocytes:
- return iron to blood via transferrin
- store in the macrophage as ferritin
What protein regulates absorption of iron?
Hepcidin - degrades ferroportin, so prevents iron entering blood.
Hepcidin levels fall to promote erythropoiesis.
Causes of excess iron.
- hereditary haemochromatosis
- transfusion associated haemosiderosis
Pathophysiology of hereditary haemochromatotsis.
Autosomal recessive mutation of HFE protein reduces the affinity of transferrin receptors.
This means more iron is stored in cells, leading to the skin looking tanned and secondary conditions such as cardiomyopathy and diabetes.