Spleen anatomy and physiology

• The spleen is located in the upper left quadrant of the abdomen, under cover of the diaphragm and the ribcage - and therefore cannot be palpated on clinical examination unless enlarged
• The spleen is an intraperitoneal organ - entirely surrounded by peritoneum
• The spleen is a highly vascular organ - it receuves most of its arterial supply from the splenic artery which arises from the celiac trunk

  The splenic artery runs laterally along the superior aspect of the pancreas within the splenorenal ligament
• Venous drainage occurs through the splenic vein. It combines with the superior mesenteric vein to form the hepatic portal vein
• The spleen is the largest accumulation of lymphoid tissue:

  • Lots of phagocytic cells
  • Removes antigens from blood
  • Removes old red blood cells from blood
  • Produce activated lymphocytes
  • Anterior and superior border of spleen contain notches
• The spleen underlies the left 9th,10th and 11th ribs
• The spleen is closely related to the inferior part of the pleura - possible to puncture the spleen when inserting a chest drain
• The spleen parenchyma contains white pulp and red pulp

  The red pulp makes up roughly 80%
• White pulp of the spleen:

  • Contains lymph-related nodules called malpighian corpuscles
  • Very important role in the normal immune response to infection
  • Antigen presenting cells enter the white pulp which leads to activation of T-lymphocytes
  • Important role in how the body deals with encapsulated bacteria - neisseria meningitidis, haemophilus influenzae and streptococcus pneumoniae
• Red pulp of the spleen:

  • Made primarily made up of tissue known as the cords - rich is macrophages and the venous sinus
  • Old, damaged and dead red blood cells along with antigens and microorganisms are phagocytosed by macrophages
  • Storage of platelets
  • Storage of red blood cells in case of hypovolaemia
  • Prenatally is is haematopoietic until the 5th month of gestation when bone marrow becomes the main site for haematopoiesis
• Portal hypertension is a cause of splenomegaly
• Howell-Jolly bodies is a specific finding on a blood film seen in post splenectomy patient
• The thymus is a primary lymphoid organ that is situated in the superior mediastinum and extends over the great vessels of the heart

  Primary function = maturation of incompetent T cells

  Starts to involute from 12 months - middle age
• Lymph = fluid that flows through the lymphatic channels and intervening lymph

  •Function is to return interstitial fluid to central circulation 

  • lymphatic fluid is transported through lymph nodes where lymphocytes remove substances  before fluid ultimately empties into the subclavian veins where it mixes with central venous blood.
  • Composition is variable - generally similar to blood plasma 
  • Lymph also transports fats from the digestive system (lacteals) via chylomicrons 
• The right lymphatic duct is responsible for draining the lymph from the upper right quadrant of the body. This includes the right side of the head and neck, the right side of the thorax and the right upper limb. The thoracic duct is much larger and drains lymph from the rest of the body. These two ducts then empty into the venous circulation at the subclavian veins