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SPLEEN

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This detailed overview discusses the development, anatomy, and histology of the spleen in human anatomy. Beginning with the differentiation of mesenchymal cells in the dorsal mesogastrium during the fifth week of development, it details the formation of lymphoblasts and other blood-forming cells. The anatomy highlights key features such as size, shape, and peritoneal connections, while also covering the microstructure including white and red pulp. The document further addresses congenital anomalies and accessory spleens, providing a comprehensive understanding of this vital organ.

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SPLEEN

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  1. SPLEEN ROY GEORGE SHARON

  2. DEVELOPMENT • Collection of mesenchymal cells in the dorsal mesogastrium- 5th week • Differentiate into lymphoblasts and other blood forming cells • Mass projects to left, covered by peritoneum • Dorsal mesogastriumgastrosplenic lig.  lienorenal lig.

  3. Contd. • Fusion of lienorenal lig to post.abdominal wall • Change in orientation of stomach • Spleen lies on left side  forms the left boundary of the lesser sac of peritoneum

  4. ANATOMY

  5. Large encapsulated mass of vascular and lymphoid tissue • SITUATION • Upper Lt. quadrant of the abdomen b/n the fundus of stomach and diaphragm • SHAPE • Slightly curved wedge to ‘domed’ tetrahedron

  6. SIZE • 12cm long , 7cm broad , 3-4 cm wide • WEIGHT • 150 gm (80gm -250gm)

  7. Relations of spleen • SURFACES • Superolateral • Inferomedial • BORDERS • Superior • Inferior • POLES • Anterior • Posterior

  8. SURFACES • DIAPHRAGMATIC • Smooth, convex • Faces superiorly and laterally • related to abd. surface of: • Lt. dome of diaphragm • lower lobe Lt. lung • 9-11 ribs

  9. VISCERAL SURFACE • irregular,faces inferomedially • marked by renal,gastric,pancreatic & colic impressions

  10. Gastric impression • Faces anterolaterally • Broad and concave • Sep. from stomach by peritoneal recess

  11. Renal impression • Concave • Sep. from gastric impression by a raised strip of splenic tissue • Related to: ant. Surface of Lt. kidney superior pole of Lt. suprarenal gland

  12. Colic impression • Inferior pole of spleen • Rel. to splenic flexure of colon & phrenicocolic lig.

  13. Pancreatic impression • Lies b/n colic impression and lateral part of hilum • Rel. to tail of pancreas which lies in the splenorenal lig.

  14. HILUM OF SPLEEN • Lies on visceral surface • A long fissure pierced by several apertures  br. of splenic A & V, nerves and lymphatics pass

  15. BORDERS OF SPLEEN

  16. SUPERIOR BORDER • Sep. diaphragmatic surface from gastric impression • Usually convex • 1-2 notches near the anterior extremity

  17. INFERIOR BORDER • Seperates renal impression from diaphragmatic surface • More blunt and rounded • Corresponds to 11th rib

  18. ANTERIOR POLE • Larger, less angulated • Connects lateral ends of superior & inferior borders • Lies adjacent to splenic flexure and phrenicocolic lig.

  19. POSTERIOR POLE • Angulated • Faces the rounded vertebral column

  20. PERITONEAL CONNECTIONS • Almost entirely covered by peritoneum • Connected to: posterior abd. wallsplenorenal lig. anterolateral abd.wallphrenicocolic lig stomach  gastrosplenic lig.

  21. SPLENORENAL LIG • Two layers of peritoneum • Ant. Layer  peritoneum of post.wall of lesser sac • Post. Layer -->peritoneum over inf. surface of diaphragm • CONTENTS • Splenic vessels • Tail of pancreas

  22. GASTROSPLENIC LIG. • 2 layers • Ant. Layer from peritoneum lifted of gastric impression • Post. Layer peritoneum over post. aspect of stomach • CONTENTS • Short gastric A. • Lt. gastroepiploic br. of splenic A.

  23. CONGENITAL ANOMALIES • SPLENIC AGENESIS Rare 10% children with heart d/s • POLYSPLENIA Failure of splenic fusion

  24. ACCESSORY SPLEEN(SPLENICULI) Single/multiple 10-30% of population • SITES 50% - Hilum 30% - splenic vessels/behind tail of pancreas remainder – mesocolon/splenic ligaments

  25. ACCESSORY SPLEEN

  26. NON PARASITIC SPLENIC CYST - rare • TRUE CYST -From embryonal rests 1. dermoid cyst 2.mesenchymal inclusion cyst • FALSE CYST – Trauma - severe pancreatitis - contain serous & haemorrhagic fluid

  27. SPLENIC CYST

  28. SPLENIC MICROSTRUCTURE • Fibrous framework • White pulp • Red pulp

  29. FIBROUS FRAMEWORK • Tissue capsule • Trabeculae

  30. CAPSULE • Continuous layer, 1.5mm thick • abundant type 1 collagen & elastin • TRABECULAE extend downwards into substance of spleen branch within it supporting framework • Largest enter the hilum • Provide a conduit for splenic A&V,n

  31. WHITE PULP • 0.25-1mm in diameter • White semi- opaque dots on cut section • Aggregations of T lymphocytes  terminations of splenic arteriolar adventitia periarteriolar lymphatic sheath ( PALS )

  32. PALS enlarged by aggregation of B lymphocytes LYMPHOID FOLLICLES (MALPIGHIAN BODIES) • Centres of lymphocyte proliferation and differentiation antigenically stimulated  GERMINAL CENTRES • Within follicles, splenic arterioles branch to form a series of parallel terminal arterioles PENICILLI

  33. RED PULP • 75% of total splenic volume • Contain VENOUS SINUSES splenic veins • Sep. by fibrocellular network RETICULUM  fibroblasts (reticular cells) & collagen(splenic macrophages)

  34. VENOUS SINUSES • Elongated ovoid vessels 50microm. • Lined by incomplete endothelium aligned along long axis (stave cells) attached by intercellular junctions (blood passes from splenic cords to sinus lumen) luminal &external surface bears short irregular microvilli Supported circumferential &longitudinal reticular fibres

  35. MARGINAL ZONE • At interface of red pulp and white pulp • Region where the blood is delivered to the red pulp • Lymphocytes leave the circulation to migrate to T and B lymphocyte areas of the white pulp • Aggregation of macrophages surround arteriolar ends- periarteriolar macrophage sheath (Schweigger-Seidel)

  36. SURFACE ANATOMY • Spleen is marked on Lt. side of back with long axis along line of 10th rib • Upper border upper border of 9th rib • Lower border lower border of 11th rib • Ant. extends to mid –axillary line • Post.  4cm lateral to 10th thoracic spine

  37. VASCULAR SUPPLY • ARTERIAL SUPPLY • Splenic A. – large,tortuous • Divides in lienorenal lig. into 2-3 main branches4-5 segmental br. • In each segment ,ramifies within trabeculae to supply parenchyma and capsule

  38. VENOUS SUPPLY • Minor veins pass from red pulp segmental veinsdrain into main splenic V. in lienorenal lig. • LYMPHATIC SUPPLY • Drain along trabeculae • Pancreaticosplenic and coeliac nodes

  39. Splenic venous circulation

  40. SPLENIC MICROCIRCULATION • OPEN CIRCULATION • Arteriolar blood reticular spaces in splenic cords enter sinuses through minute slits • CLOSED CIRCULATION • Arteriolar blood venous sinuses

  41. NERVE SUPPLY • Arise from coeliac sympathetic plexus • Mainly adrenergic vasomotor • Regulate of blood flow through spleen

  42. PHYSIOLOGY • As plasma rich blood pass through sinuses: 1.filtered 2.particles phagocytosed sinus splenic pulp pressure reflects pressure throughout the portal system90% blood course through OPEN circulation

  43. CONTD. • ERYTHROCYTE CLEARANCE • Abnormal, aged  cleared • Approx. 20 ml red cells removed/day • Factors: • change in biophysical properties • hypoxic, acidotic, glucose deprived environment

  44. fall in cellular ATP levels • loss of ATP dependent functions • sodium and calcium efflux • loss of membrane integrity

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