Structure and function of lymph node and spleen 2 Flashcards
Describe the normal anatomical location of the spleen and the structures closely related to it
- It is located high in the L upper quadrant of abdomen
- It is not normally palpable unless substantially enlarged
- It has a close anatomical relationship with the diaphragm, Left Kidney, gastric fundus, tail of pancreas, splenic flexure of colon.
- Posteriorly protected by ribs 9-11
Describe the arterial supply and drainage of the spleen
- Supplied by splenic artery (branch of coeliac axis)
- Drained by splenic vein (with SMV forms portal vein)
It is highly vascular with all the blood in the body being filtered by it hence trauma to the spleen can be catastrophic
What are the functions of the spleen ?
Removing old red blood cells, breaking down waste products of red blood cells, recycling iron for use in new red blood cells, and holding a reserve of red blood cells and immune cells which the body can use in case of emergencies.
- Detect, retain and eliminate unwanted, foreign or damaged material -
- Facilitate immune responses to blood borne antigens
Describe the structure of the spleen
- An encapsulated organ.
- Its Parenchyma (tissue) includes red pulp and white pulp
Describe the structure of the red pulp
Red pulp:
Contains blood filled sinusoids and splenic cords.
Sinusoids are
- fenestrated - bigger gaps to allow cells between the endothelial cells
- lined by endothelial cells
- supported by hoops of reticulin.
Cords contain macrophages and some fibroblasts and cells in transit (RBC, WBC, PC and some CD8+ T cells)
Describe the structure of the white pulp
- The white pulp forms periarteriolar lymphatic sheaths (PALS) and lymphatic nodules around around the central arteries entering the spleen.
- PALS are populated by T cells (CD4+ cells)
- Antigen reaches white pulp via the blood.
- APCs in the white pulp present antigen to immune reactive cells
- When stimulated by antigen, T and B cell responses may occur
Describe the circulation within the spleen
- Blood flows into the spleen via the splenic artery which then branches into trabecular arteries.
- As an individual trabecular artery emerges from the connective tissue, it is then known as the artery of the white pulp (central artery) which is surrounded by the PALS.
- The blood vessel continues into a lymphatic nodule as the nodular artery. The nodular artery becomes smaller and terminates in the marginal zone or forms a vascular tuft (penicillus) in the red pulp.
- Blood vessels from the white pulp, known as pulp arterioles, continue in the red pulp as sheathed capillaries. The sheathed capillaries are surrounded by macrophages and a network of reticular cells and fibers.
- As blood passes through splenic sinuses, the endothelium of the sinuses traps defective erythrocytes and prevents their reentry into the blood. - Mechanical filtration
- Biological filtration occurs as macrophages recognize non-functional blood cells and remove them from the splenic circulation
What are the features suggestive of splenomegaly ?
- Dragging sensation in LUQ
- Discomfort with eating
- Pain if infarction
Define hypersplenism and list the triad which is characterisitc of it
Hypersplenism is an overactive spleen.
Triad:
- splenomegaly
- fall in one or more cellular components of blood
- correction of cytopenias by splenectomy
Cytopenia is a reduction in the number of mature blood cells. It takes a number of forms: Low red blood cell count: resulting in anemia. Low white blood cell count: leukopenia or neutropenia.
List potential causes of splenomegaly
Infection:
- Wide range: EBV, Malaria, TB, Typhoid, Brucellosis, Leishmaniasis, Trypanosomiasis,
Congestion
- Portal (Hepatic cirrhosis, portal/splenic vein thrombosis, cardiac failure)
Haematological diseases
- Lymphoma/leukaemia, haemolytic anaemia, ITP, Myeloproliferative disorders
Inflammatory conditions
- Rheumatoid arthritis, SLE
Storage diseases
- Gaucher’s, Niemann-Pick disease
Miscellaneous - Amyloid, Tumours (primary and metastatic), cysts
What are some of the causes of hyposplenism and red blood cell feature on blood film indicates it
Most commonly from splenectomy
Need for immunisation after splenectomy as increased risk of infection
Other causes e.g.
- Coeliac disease
- Sickle cell disease
- Sarcoidosis
- Iatrogenic – non-surgical
Features mainly from reduced red pulp function
- Howell-Jolly bodies seen on blood film
Appreciate these key points to remember:
Secondary lymphoid tissues:
Important in immune function
- Lymph nodes respond to antigens filtered in lymph fluid
- Spleen responds to antigens in blood
Other important functions:
- Lymphatic system and fluid homeostasis
Spleen:
- Phagocytosis
- Haematopoiesis - Normal in foetus, Site of extramedullary haematopoiesis in marrow disease
- (Erythrocyte storage)
