WhatsApp Image 2025-01-06 at 7.51.04 PM.jpeg

# SECTION 2 Communication The spleen is an organ containing lymphocytes and macrophages. It's divided into splenic pulp (red and white). **Red pulp:** Blood-filled tissue. **White pulp:** Lymphatic tissue with lymphocytes and macrophages surrounding blood vessels. The spleen is connected to the...

# SECTION 2 Communication The spleen is an organ containing lymphocytes and macrophages. It's divided into splenic pulp (red and white). **Red pulp:** Blood-filled tissue. **White pulp:** Lymphatic tissue with lymphocytes and macrophages surrounding blood vessels. The spleen is connected to the following structures at its hilum: * Splenic artery (branch of the coeliac artery) * Splenic vein (branch of the portal vein) * Lymph vessels (efferent only) * Nerves Blood flows through the spleen in sinusoids, which have pores allowing close contact with splenic pulp. This facilitates removal of aged or damaged cells from the bloodstream. ## Functions **Phagocytosis:** The spleen destroys old/abnormal red blood cells and breaks down products like bilirubin and iron, transporting them to the liver via splenic and portal veins. It also phagocytoses other cellular material (leukocytes, platelets, bacteria). Unlike lymph nodes, the spleen doesn't have afferent lymphatics, making it resistant to diseases spread through lymph. **Storage of blood:** The spleen can store up to 350 mL of blood. In response to sympathetic stimulation, it can rapidly return blood to circulation, particularly in hemorrhaging situations. **Immune response:** The spleen contains T- and B-lymphocytes that get activated by antigens (e.g., infections). Proliferation of lymphocytes during serious infections may enlarge the spleen (splenomegaly). **Erythropoiesis:** The spleen, alongside the liver, is involved in fetal blood cell production. It can also produce blood cells in adults when necessary. ## Thymus Gland * The thymus gland is located in the mediastinum, behind the sternum, and extends into the neck. * Its size increases until puberty, when it begins to atrophy. * Weight at birth, around 10-15g, and maximum weight at puberty is between 30-40g. * By middle age, it returns to its weight at birth. **Figure 6.8:** Shows a cross-section of the spleen, highlighting spleen pulp, splenic vein, and artery, and lymph vessels. **Figure 6.9:** Shows the thymus gland in the adult body, in relation to other structures (e.g. trachea, thyroid gland, and major blood vessels).