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The spleen is the largest lymphoid organ in the body (strictly speaking a hemolymphoid organ). The main functions of the spleen are:
- To filter blood by removing worn-out RBCs and microbial agents from the circulation.
- To manufacture RBCs in fetal life and lymphocytes after birth.
- To provide immunity to the body by producing immunoglobulin M (IgM) by plasma cells.
- To store RBCs and release them in circulation when required. LOCATION The spleen is located in the left hypochondrium between the fundus of the stomach and the diaphragm, behind the midaxillary line opposite the 9th, 10th, and 11th ribs. Its long axis lies parallel to the long axis of the 10th rib. It moves a bit in living during respiration.
Size, Shape, and Colour
The spleen is a wedge-shaped soft organ with purple colour. The
size of the spleen roughly corresponds to the fist of the subject.
Measurement
Measurements of the spleen are:
Thickness: 1 inch
Breadth: 3 inch
Length: 5 inch
Weight: 7 oz
Surface Projection The spleen is marked on the surface on the left side of the back of the trunk. Its long axis corresponds to that of the 10th rib. Its upper border corresponds to the upper border of the 9th rib, and its lower border corresponds to the lower border of the 11th rib. Its medial end lies about 5 cm from the posterior midline of the body at the level of spine of T10 vertebra and lateral end at the midaxillary line
Borders
Superior Border
The superior border is thin and convex. It separates the
visceral surface (gastric impression) from the diaphragmatic
surface. It characteristically presents one or two notches
near its anterior end. These notches indicate that the spleen
develops by the fusion of separate masses of lymphoid tissue
(lobulated development).
Inferior Border
The inferior border separates the visceral surface (renal
impression) from the diaphragmatic surface. It is rounded and
corresponds to the lower border of the 11th rib
Intermediate Order
The intermediate border is rounded and separates the
gastric impression from the renal impression on the visceral
surface.
Surfaces
Diaphragmatic surface
The diaphragmatic surface is smooth, convex, and directed
upward, backward, and to the left.
Visceral Surface The visceral surface is concave and irregular. It presents four impressions: gastric, renal, colic, and pancreatic. *The gastric impression is produced by the fundus of the stomach. It is the largest impression and lies between the superior and intermediate borders. The hilum of spleen is located in the lower part of this impression. *The renal impression is produced by the left kidney and lies below and behind the gastric impression between the intermediate and inferior borders. *The colic impression is produced by the left colic flexure. It is triangular in shape and situated in front of the lateral end. *The pancreatic impression (occasional) is produced by the tail of the pancreas. It is located between the hilum and the colic impression. RELATIONS Peritoneal Relations The spleen is completely enclosed in the peritoneum except at its hilum, from where two peritoneal folds extend — one to the stomach and one to the left kidney, called gastrosplenic and lienorenal ligaments, respectively.
- Gastrosplenic ligament extends from the hilum of the spleen to the upper one-third of the greater curvature of the stomach. It contains short gastric vessels.
ARTERIAL SUPPLY.
The spleen is supplied by the splenic artery, the largest branch of the coeliac trunk (Fig. 7.23). It traverses through the lienorenal ligament to reach near the hilum of the spleen, where it divides into five or more branches, which enter the spleen through its hilum to supply it. The splenic artery is remarkably tortuous to allow movements of the spleen following distension of the stomach and movements of diaphragm, without obstruction to the blood flow. N.B. The spleen is classified into two types, diffuse and compact, depending upon the branching pattern of the terminal branches of the splenic artery, which enter the hilum. (a) Diffuse type of spleen, if the terminal branches are long and arise far away from the hilum. (b) Compact type of spleen, if the terminal branches are small and arise close to the hilum.
VENOUS DRAINAGE The venous blood from the spleen is drained by the splenic vein, which is formed at the hilum by the union of five or more tributaries which emerge from the splenic substance. The splenic vein runs a straight course from left to right behind the body of pancreas. Behind the neck of pancreas it joins the superior mesenteric vein to form the portal vein. Its tributaries are:
- Short gastric veins.
- Left gastroepiploic vein.
- Pancreatic veins.
- Inferior mesenteric vein. LYMPHATIC DRAINAGE The splenic tissue proper has no lymphatics. The tissue fluid formed in the spleen freely enters the venous sinusoids. The splenic lymphatics are confined to its trabeculae, capsule, and visceral peritoneum. They drain along the splenic vessels into the pancreaticolienal lymph nodes. NERVE SUPPLY The spleen is supplied by the sympathetic fibres derived from the coeliac plexus. They supply blood vessels (vasomotor) and smooth muscle fibres present in the trabeculae and capsule. SEGMENTS OF THE SPLEEN The splenic artery within the spleen usually gives two branches—superior and inferior. These branches usually do not anastomose and each branch supplies its own territory (segment). Thus, an avascular zone exists between these two territories. Thus, the spleen presents two segments, superior and inferior, separated by an avascular plane passing perpendicular to the long axis of the spleen (Fig. 7.25). The knowledge of these vascular segments is essential for segmental resection of the spleen to preserve the splenic tissue if required. N.B. The branches of the splenic artery within the spleen are segmental in distribution whereas the tributaries of the splenic vein within the spleen are intersegmental.
The very large (massive) spleen projects downward and medially toward the right iliac fossa in the direction of the axis of the 10th rib. The enlarged spleen may be differentiated from the enlarged kidney by the presence of one or more notches on its superior border
- Splenectomy: The splenectomy (surgical removal of the spleen) is sometimes performed when the spleen is ruptured or inadvertently nicked at operation. It is also performed in the treatment of certain blood diseases. If the accessory spleens are located in the splenic pedicle they should also be removed. The removal of spleen does not impair the immune response seriously. N.B. Rupture of spleen: Although well protected by 9th, 10th, and 11th ribs, the spleen is the most frequently ruptured organ in the abdomen following severe external blow. The pain is referred to the left shoulder due to irritation of the left dome of diaphragm by the splenic blood. It is called ‘Kehr’s sign’
