2- LYMPH NODE
Cortex (outer part)
• It is divided into
Medulla (inner part)
1- Stroma
• Histologically is formed of 2- Parenchyma
3- Sinuses
Histological structure:
The spleen is composed of stroma and parenchyma.
I- Stroma:
a- Capsule:
- Thick fibrous C. T. containing smooth muscle fibres.
- Is not penetrated by afferent lymphatic.
- Is covered by peritoneum.
b- Trabeculae:
- They arise from the hilum of spleen.
- Fibrous C. T. containing smooth muscle fibres.
- Divide the spleen into incomplete intercommunicating splenic lobules.
- The capsule and trabeculae contain blood vessels and nerves.
c- Reticular network:
- Similar to that of lymph node.
II- Parenchyma:
• It is formed of splenic lobules (white pulps and red pulps).
• Each splenic lobule includes:
A- White pulp: (Malpighian corpuscle):
- The malpighian corpuscle is lymphatic follicle (nodule) with central artery of white pulp which is eccentric in position. They scattered all over the spleen.
- The white pulp may contain germinal centre.
- Structure of white pulp. (Is wrote, as previously mentioned)
B- Red pulp:
- The red pulps occupy the areas between the white pulps.
- The red pulp is formed of splenic cords separated by blood sinusoids.
Blood sinusoids:
- They are irregular blood channels.
- Lined with longitudinally arranged endothelial cells which are separated by longitudinal slits (spaces).
- The endothelial cells are surrounded by non-continuous basement membrane.
- Macrophages are associated with the endothelium of the blood sinusoid and are called littoral cells; they are responsible for filtration of blood.
Splenic cords (Billroth cords):
- They are irregular branching and anastomosing masses of diffuse lymphatic tissue mixed with blood cells (RBCs + all types of leucocytes) + macrophages.
- The cords occupy the irregular areas between the blood sinusoids.
The thymus dependent zone:
- It is the peri-arterial lymphatic sheath
- This sheath is formed of reticular fibres rich in T- lymphocytes, and surrounds the central artery of white pulp.
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