12. SPLEEN

SPLEEN:

  • The spleen is formed by reticular and lymphatic tissue and is the largest lymph organ.
  • It lies in the left hypochondriac region of the abdominal cavity between the fundus of the stomach and the diaphragm.
  • It is purplish in colour and varies in size in different individuals, but is usually about 12 cm long, 7 cm wide, and 2.5 cm thick. It weighs about 200g.

ORGANS ASSOCIATED WITH THE SPLEEN:

  • Superiorly and posteriorly — diaphragm
  • Inferiorly — left colic flexure of the large intestine
  • Anteriorly — fundus of the stomach
  • Medially — pancreas and the left kidney
  • Laterally — separated from the 9th, 10th, and 11th ribs and the intercostal muscles by the diaphragm

STRUCTURE:

  • The spleen is slightly oval in shape with the hilum on the lower medial border.
  • The anterior surface is covered with peritoneum. It is enclosed in a fibroelastic capsule that dips into the organ, forming trabeculae.
  • The cellular material, consisting of lymphocytes and macrophages, is called splenic pulp, and it lies between the trabeculae.
  • Red pulp is the part suffused with blood and white pulp consists of areas of lymphatic tissue where there are sleeves of lymphocytes and macrophages around blood vessels.
  • Structures entering and leaving at the hilum:
    • Splenic artery (branch of the coeliac artery)
    • Splenic vein (branch of the portal vein)
    • Lymph vessels (efferent only)
    • Nerves
  • Blood flows through sinuses with distinct pores allowing close contact with splenic pulp.

FUNCTIONS:

  1. PHAGOCYTOSIS:
    • Old and abnormal erythrocytes are destroyed and bilirubin and iron are sent to the liver.
    • Leukocytes, platelets, and microbes are phagocytosed.
  2. STORAGE OF BLOOD:
    • Can store up to 350ml of blood and release it during hemorrhage.
  3. IMMUNE RESPONSE:
    • Contains T- and B-lymphocytes activated by antigens.
    • Lymphocyte proliferation during infection can cause splenomegaly.
  4. ERYTHROPOIESIS:
    • Important for fetal blood production; can also produce blood cells in adults under stress.

DISORDERS OF THE SPLEEN:

SPLENOMEGALY (ENLARGEMENT):

  • Usually secondary to infections, circulatory disorders, blood diseases, or malignant neoplasms.

INFECTIONS:

  • Red pulp congestion occurs with blood-borne microbes or local infection.
  • Chronic infections causing splenomegaly:
    • Tuberculosis
    • Typhoid fever
    • Malaria
    • Brucellosis (undulant fever)
    • Infectious mononucleosis

CIRCULATORY DISORDERS:

  • Caused by congestion when liver blood flow is impeded, e.g., fibrosis, portal venous congestion, right-sided heart failure.

BLOOD DISEASES:

  • Splenomegaly may result from haemolytic and macrocytic anaemia, polycythaemia, chronic myeloid leukaemia.
  • Enlarged spleen can cause anaemia, leukopenia, and thrombocytopenia due to excessive haemolysis and phagocytosis.

TUMOURS:

  • Rare benign and primary malignant spleen tumors; metastases from blood-spread tumor fragments are more common.
  • Associated with chronic leukaemia, Hodgkin’s disease, and non-Hodgkin lymphoma.

Detailed Notes:
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PATH: PHARMD/ PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ HUMAN ANATOMY AND PHYSIOLOGY/ SPLEEN.

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