Spleen Anatomy

#boundingbox

The spleen is an important lymphoid organ. Let’s look at its structure.

Key components include the Capsule, Trabecula, Red pulp (RBCs), Sinusoid, Reticular fibrous framework, and areas of circulation. Within the white pulp, we find the Germinal center, Mantle zone, Marginal zone, Follicle (B cells), and the Periarteriolar lymphatic sheath (T cells).

Spleen Location and Dysfunction

The spleen is located in the left upper quadrant of the abdomen, anterolateral to the left kidney, and is protected by the 9th to 11th ribs.

Splenic dysfunction, which can occur after a splenectomy or in conditions like sickle cell disease autosplenectomy, leads to several immunological impairments. Specifically, there’s a decrease in IgM, reduced complement activation, and a drop in C3b opsonization. These changes result in an increased susceptibility to infections by encapsulated organisms.

Postsplenectomy Findings and Management

After a splenectomy, several characteristic findings may be observed in the blood. These include Howell-Jolly bodies, which are nuclear remnants, and target cells. Patients may also experience thrombocytosis due to the loss of platelet sequestration and removal, and lymphocytosis, indicating a loss of lymphocyte sequestration.

It is crucial to vaccinate patients undergoing splenectomy or those with splenic dysfunction against encapsulated organisms, such as pneumococci, Haemophilus influenzae type b (Hib), and meningococci, to prevent severe infections.

Spleen White Pulp Components

Let’s delve into the specific cellular components of the spleen’s white pulp.

Thymus Anatomy and Development

#boundingbox

The thymus is located in the anterosuperior mediastinum and is the primary site for T-cell differentiation and maturation. It is an encapsulated organ. The thymus epithelium is derived from the third pharyngeal pouch, which is endodermal in origin, while thymic lymphocytes are of mesodermal origin.

The cortex of the thymus is dense with immature T cells, and the medulla is paler, containing mature T cells and Hassall corpuscles with epithelial reticular cells. A normal neonatal thymus appears “sail-shaped” on a chest X-ray, as indicated by the asterisks in the image, but it typically involutes by age 3 years.

Thymus Clinical Aspects

Regarding cell types, T cells mature in the thymus, while B cells originate in the bone marrow.

An absent thymic shadow or a hypoplastic thymus can be indicative of certain immunodeficiencies, such as Severe Combined Immunodeficiency (SCID) or DiGeorge syndrome.

Thymoma is a neoplasm of the thymus. It is often associated with various paraneoplastic syndromes, including myasthenia gravis, superior vena cava syndrome, pure red cell aplasia, and Good syndrome.

Topics Covered:

• Spleen Structure Overview
• Splenic Dysfunction and Immunity
• Post-Splenectomy Care
• Spleen White Pulp Microanatomy
• Thymus Structure and Development
• Thymus-Related Conditions