Spleen- Structure and Functions


The spleen is a vital organ that performs various functions related to immunity, blood production and filtration. It is located in the upper left part of the abdomen, under the rib cage, and is surrounded by a protective layer of peritoneum. The spleen is shaped like a flattened oval and has two main surfaces: the diaphragmatic surface, which faces the diaphragm and the chest wall, and the visceral surface, which faces the stomach, pancreas and left kidney. The spleen has two ends: the anterior end, which is broad and rounded, and the posterior end, which is narrow and pointed. The spleen also has two borders: the superior border, which is convex and smooth, and the inferior border, which is concave and notched.

The spleen has an internal structure that consists of a fibrous capsule, trabeculae and pulp. The capsule is a thin layer of connective tissue that covers the spleen and gives it strength and shape. The trabeculae are extensions of the capsule that divide the spleen into lobules and carry blood vessels and nerves into the pulp. The pulp is the soft tissue that fills the lobules and contains two types of cells: white pulp and red pulp. The white pulp is composed of lymphatic tissue that surrounds the branches of the splenic artery and forms nodules called follicles. The white pulp is responsible for producing lymphocytes and antibodies that fight against infections. The red pulp is composed of blood-filled spaces called sinusoids that are separated by cords of cells called splenic cords. The red pulp is responsible for filtering out old or damaged red blood cells and recycling their iron.

The spleen is connected to the circulatory system by two main blood vessels: the splenic artery and the splenic vein. The splenic artery arises from the celiac trunk and enters the spleen at the hilum, which is a depression on the visceral surface. The splenic artery branches into smaller arteries that run along the trabeculae and then into arterioles that enter the white pulp. The arterioles then branch into capillaries that supply blood to the follicles and then drain into small veins called penicillar veins. The penicillar veins join to form larger veins called venous sinuses that run parallel to the splenic cords in the red pulp. The venous sinuses then converge to form larger veins that exit the spleen at the hilum as the splenic vein. The splenic vein joins with the superior mesenteric vein to form the portal vein, which carries blood to the liver.

The spleen is innervated by both sympathetic and parasympathetic nerve fibers that originate from the celiac plexus and travel along the splenic artery. The nerve fibers regulate the contraction of the splenic capsule and trabeculae, as well as the diameter of the blood vessels in the pulp. The nerve fibers also modulate the immune response of the spleen by influencing the activity of lymphocytes and macrophages.

The structure of the spleen reflects its diverse functions in immunity, blood production and filtration. In this article, we will explore these functions in more detail and explain why they are important for our health.