S6) The Spleen, White Blood Cells & Cytopenia Flashcards
Where is the spleen located?
The spleen is located in the left upper quadrant of the abdomen
Describe the contents and structure of the spleen
- Red pulp – sinuses lined by endothelial macrophages and cords
- White pulp – similar structure to lymphoid follicles
Blood enters the spleen via the splenic artery.
Where do the different blood cells go?
- White cells and plasma preferentially passing through the white pulp
- Red cells preferentially passing through the red pulp
Explain how the spleen acts as a blood filter
- The red pulp removes old red cells and metabolises the haemoglobin
- The white pulp synthesises antibodies and removes antibody-coated bacteria and blood cells
Describe four situations where splenomegaly is usually seen
- Increased workload e.g. haemolytic anaemia (increased number of defective red cells)
- Congestion e.g. portal hypertension (increases back pressure)
- Infiltration by leukaemias and lymphomas
- Expansion due to accumulation of metabolic waste products
What is hyposplenism?
Hyposplenism is the term used to describe reduced splenic function and is associated with an increased risk of overwhelming sepsis
What are some causes of hyposplenism?
- Underlying diseases which destroy spleen tissue e.g. sickle-cell disease, coeliac disease
- Splenic rupture from trauma/tumour
A blood film from a patient with hyposplenism will typically reveal which structures?
Howell-Jolly bodies which are basophilic nuclear remnants in circulating erythrocytes
Explain how Howell-Jolly bodies are formed and why they are a good indicator of splenic function
- During erythropoiesis, erythroblasts normally expel their nuclei but in some cases a small portion of DNA remains
- Normally such cells would be removed by the spleen so the presence of Howell-Jolly bodies is a good indicator of reduced splenic function
The term cytopenia is used to describe a reduction in the number of blood cells. It takes a number of forms.
Identify and describe them
- Low red cell count = anaemia
- Low white blood = leucopenia
- Low neutrophil count = neutropenia
- Low platelet count = thrombocytopenia
- Low red cells, white cells, and platelets = pancytopenia
An increase in the number of blood cells is signified by the suffix cytosis or philia. This takes a number of forms.
Identify and describe them
- High red cell count = erythrocytosis
- High white blood = leucocytosis
- High neutrophil count = neutrophilia
- High lymphocyte count = lymphocytosis
- High platelet count = thrombocytosis
Unlike erythrocytes and platelets, all leucocytes have a nucleus.
How can they be classified?
- By their structure (granulocytes and agranulocytes)
- By their cell lineage (myeloid cells and lymphoid cells)
According to their morphological and functional characteristics, these broad categories can be further divided into the five main types of leucocyte.
Identify these
- Basophils (granulocytes and myeloid)
- Neutrophils (granulocytes and myeloid)
- Eosinophils (granulocytes and myeloid)
- Monocytes (agranular and myeloid)
- Lymphocytes (agranular and lymphoid)
Describe the different staining characteristics of granulocytes with H&E
- Basophils stain dark blue
- Eosinophils stain bright red
- Neutrophils stain a neutral pink
What are neutrophils and what do they do?
- Neutrophils are the most abundant type leucocyte and are an essential part of the innate immune system
- They are short-lived and highly mobile cells that can migrate into tissues to destroy pathogens
What are monocytes and what do they do?
- Monocytes are the largest type of leucocyte
- They circulate in the blood for ~1-3 days before moving into tissues and differentiating into tissue resident macrophages or dendritic cells
What are eosinophils?
Eosinophils are leucocytes which have a bi-lobed nucleus and an important role in immune responses to multicellular parasites (helminths)
What are basophils?
Basophils are the least numerous leucocyte and contain large cytoplasmic granules which may obscure the cell nucleus when stained in microscopy
