MEH session 6 Flashcards
Where is the spleen located?
Left upper quadrant of the abdomen
What is red pulp?
Sinuses lined by endothelial macrophages and cords
Red cells preferentially pass through here
Role:
Removed old red cells
Metabolises haemoglobin
What is white pulp?
Similar structure to lymphoid follicles
White cells and plasma preferentially pass through here
Role:
Synthesises antibodies
Removes antibody coated bacteria and blood cells
How does blood enter the spleen?
Splenic artery
How does blood leave the spleen?
Portal vein
What is the role of the spleen?
- old/abnormal red cells and platelets are removed by RES macrophages
- platelets and red blood cells can be rapidly mobilised during bleeding
- puriplotential stem cells proliferate during haematological stress or if marrow fails (myelofibrosis)
- Immunological - 25% of T cells here, 15% of B cells here. Important defence against encapsulated bacteria.
What is splenomegaly?
Enlargement of the spleen
Why might someone with splenomegaly experience a loss of appetite and weight loss?
The enlarged spleen impinges upon the stomach. The stomach cannot expand when food enters so they cannot eat as much.
Can the spleen be palpated under normal conditions?
No, it is never normal to palpate the spleen below the costal margin.
Where do you start to palpate the spleen?
Right iliac fossa
Where is the splenic notch?
Medial side of the spleen
How is an enlarged spleen measured?
Measure in cm from costal margin in mid-clavicular line
What causes splenomegaly?
- overworking red pulp eg. Haemolytic anaemia
- overworking white pulp eg. Infection with encapsulated bacteria
- back pressure - portal hypertension in liver disease
- extramedullary haemopoiesis - during haemotological stress/when marrow fails
- expansion due to infiltration of cells that shouldn’t be there
Eg. Leukaemia and lymphomas - expansion due to accumulation of waste products of metabolism
Eg. Gauchers disease, sarcoidosis
What is Gaucher’s disease?
A defect in the beta glucosidase enzyme which catakayses the breakdown of glucocerebroside (a constituent of red and white cell membranes) so cases glucocerebroside to accumulate in fibrils)
What are the consequences of splenomegaly?
Hypersplenism
Pancytopenia or thrombocytopenia can occur due to pooling of blood in the enlarged spleen
Risk of rupture if enlarged and no longer protected by rib cage. It is very vascular so this can cause excessive bleeding which may be fatal.
What can a ruptured spleen lead to?
- Haematoma formation which may lead to:
Anaemia
Hypertension in splenic artery - Infarction of spleen
Splenic artery is an end artery
What is hyposplenism and what does hyposplenism increase the risk of?
Reduced splenic function
Increased risk of overwhelming sepsis
What are the causes of hyposplenism?
Sickle cell disease - multiple infarcts and then fibrosis
Splenectomy - to prevent spleen from rupturing/tumour present
-coeliac disease
How does hyposplenism present on a blood film?
Howell-Jolly bodies - basophilic nuclear remnants (clusters of DNA) in circulating erythrocytes.
Normally during erythropoiesis, erythroblasts expel their nuclei but in some cases a small portion of DNA remains. Normally such cells would be removed by the spleen.
Which organisms are patients with hyposplenism particularly at risk of developing an overwhelming sepsis from?
Encapsulated organisms
- pneumococcus
- haemophilus influenzae
- meningococcus
What does cytopenia mean?
Reduction in number of blood cells
What does the suffix cytosis or philia describe?
An increase in the number of blood cells
Which leucocytes can be described as being a
Myeloid granulocyte
Basophils
Neutrophils
Eosinophils
Which leucocyte can be described as being an agranulocyte and myeloid?
Monocyte
Which leucocyte can be described as been an agranulocyte and lymphoid?
Lymphocytes
A neutrophil usually has 2-5 lobes in their nucleus. What are multiple lobules a sign of?
Vitamin B12 deficiency
Which is the most abundant leucocyte?
Neutrophils
How long do neutrophils usually live for?
1-4 days
How is neutrophil function controlled?
The glycoprotein, Granulocyte colony stimulating factor (G-CSF) which:
• Increases their production in bone marrow
• Decreases their maturation time
• Enhances chemotaxis and phagocytosis
When would you administer recombinant GCSF to a patient?
When they require more neutrophils
Severe neutropenia and sepsis
What are the common haematological causes of neutrophilia?
Myeloproliferative diseases - disease in which bone marrow makes too many blood cells
G-CSF in excess
What health behaviour can cause neutrophilia?
Smoking
What response mechanisms can cause neutrophilia?
(Bacterial) infection
Acute inflammation
Acute haemorrhage
Give an example of a drug that can cause neutrophilia?
Prednisone
What are the causes of neutropenia due to increased removal?
- immune destruction
- septic infection so neutrophils used
- splenic pooling
What are the causes of neutropenia due to reduced production?
- B12/folate deficiency
- infiltration by malignancy or fibrosis
- aplastic anaemia (empty bone marrow)
- drugs eg. Chemotherapy, antibiotics, anti-epileptics…
- viral infection - very common to have neutropenia following a viral infection (this is normal and not a bad thing)
- congenital disorders eg. Cyclic neutropenia
What are the consequences of neutropenia?
Life threatening bacterial or fungal infection
Mucosal ulceration - painful mouth ulcers
Which is the largest type of leucocyte?
Monocytes
Where is approximately half of the monocyte population stored?
Red pulp of spleen
What are the causes of monocytosis?
Chronic inflammatory conditions:
- rheumatoid arthritis
- lupus (SLE)
- crohn’s disease
- ulcerative colitis
Chronic infections:
- TB
- myeloproliferative disorders
- malignancies eg. Hodgkins disease, certain leukaemias
When do eosinophils play an important role?
• Important role in the immune response to multicellular parasites ◦ Helminths ◦ Roundworm ◦ Flukes • Important role in skin diseases: ◦ Bulbous pemphigold • Inappropriately activated in allergic diseases ◦ asthma ◦ Eczema ◦ Hayfever ◦ Urticaria ◦ Aspergillosis Hodgkins lymphoma
Therefore, usually these conditions cause eosinophilia
How do eosinophils work?
• Release of their granular contents which contains:
◦ enzymes such as elastase
◦ Reactive oxygen species
◦ Various leukotrienes and cytokines
Describe the function of basophils.
- Granules contain the vasodilator histamine and anticoagulant heparin
- These are released following binding of IgE to surface receptors
- Play an important role in parasitic and allergic reactions
What are the causes of lymphocytosis?
Viral infections Bacterial infections especially whooping cough Stress related- MI/cardiac arrest Post splenectomy Smoking Lymphoproliferative malignancies
Why would splenectomy cause lymphocytosis?
Lymphocytes not stored in spleen
What are the symptoms of pancytopenia?
• Anaemia ◦ Fatigue ◦ Dizziness ◦ Chest pain ◦ Shortness of breath • Thrombocytopenia ◦ Bleeding ◦ Bruising • Neutropenia ◦ Infection ◦ Ulcers fever
What are the causes of pancytopenia due to reduced production of blood cells in bone marrow?
B12/folate deficiency Malignancy or fibrosis Idiopathic immune aplastic anaemia Drugs Viruses Congenital bone marrow failure
Describe the composition of healthy bone marrow.
50% fat
50% haemopoietic cells
What is aplastic anaemia?
Pancytopenia with a hypocellular bone marrow in the absence of an abnormal infiltrate and with no increase in reticulin (fibrosis)
What are the different sources of haemopoietic stem cells?
- aspiration of bone marrow
- GCSF mobilised stem cells in the peripheral blood (collected by leucopheresis) eg. If donating stem cells to a sibling for a transplant or voluntary donor
- umbilical cord
What is used to match people for haemopoietic stem cells?
HLA type