External Structure and Topography
The spleen is located in the abdominal cavity. Its long axis runs almost parallel to the lower ribs. When viewed in projection along the midaxillary line, it lies precisely between the 9th and 11th left ribs.
The organ has two extremities:
- Posterior extremity (extremitas posterior) — directed upward and backward, approaching the vertebral column, but falling short of it by about 4–5 cm.
- Anterior extremity (extremitas anterior) — faces downward and forward, reaching the left costal margin (projected along the anterior axillary line).
In shape, the spleen resembles a coffee bean. It has two surfaces that converge at the margins of the organ. The diaphragmatic surface (facies diaphragmatica) is convex, smooth, and closely adheres to the diaphragm. The visceral surface (facies visceralis) is concave and faces the internal organs.
These surfaces are separated by borders. The superior border (margo superior) is sharp, directed forward and upward, and usually shows 2–3 characteristic notches. The inferior border (margo inferior) is blunt, facing backward and downward.
Hilum of the spleen and organ impressions
On the visceral surface, occupying approximately the middle third, lies the hilum of the spleen (hilum splenicum). This is a strategic depression through which nerves enter the parenchyma, arteries pass, and veins emerge. The hilum visually divides this surface into lateral (upper) and medial halves.
Adjacent structures closely adhere to the spleen, leaving distinct impressions on it:
- Gastric surface (facies gastrica) — located lateral (superior) to the hilum. It is related to the posterior wall of the body, fundus, and greater curvature of the stomach.
- Renal surface (facies renalis) — occupies the medial half. This is the zone of contact with the left kidney and left suprarenal gland.
- Colic surface (facies colica) — situated near the anterior extremity of the organ, where the left colic flexure approaches it.
The organ is covered almost entirely by visceral peritoneum (except for the hilar region). Two important ligaments, which are derivatives of the dorsal mesogastrium, extend from the hilum:
- Gastrosplenic ligament (lig. gastrosplenicum) — extends to the stomach. Within its thickness, the tail of the pancreas approaches the hilum, and a small accessory spleen (splen accessorius) is sometimes found there.
- Splenorenal ligament (lig. splenorenale) — serves as a continuation of the previous ligament and anchors the organ to the left kidney.
Internal structure: capsule and pulp
Externally, the spleen is covered by a serous membrane (tunica serosa). Beneath it lies a dense fibrous membrane (tunica fibrosa), from which connective tissue cords — trabeculae (trabeculae splenicae) — extend deep into the organ. They form a sturdy internal framework.
All the free space between the trabeculae is filled with functional tissue — the pulp. It is heterogeneous and divided into two types:
- White pulp (pulpa alba) — represented by lymphoid follicles composed of lymphoid tissue.
- Red pulp (pulpa rubra) — formed by reticular tissue whose meshes are filled with erythrocytes, macrophages, and leukocytes. A dense network of blood vessels is also located here.
Blood supply, innervation, and functions
The main blood supply to the organ is the splenic artery (a. splenica), branching off the celiac trunk. A periarterial nerve plexus (plexus splenicus) runs along its course, providing innervation.
The intrasplenic vascular bed has a unique hierarchy:
- The artery divides into trabecular arteries (aa. trabeculares) running within the partitions.
- They give off splenic branches (rr. splenici) to the follicles.
- Within the white pulp, the vessels continue as central arteries (aa. centrales).
- Inside the follicle, they branch into capillaries, forming penicilli (penicilli).
- Arteries transition into expanded venous capillaries — splenic sinuses (sinus splenicus), giving rise to the venous system.
Due to this structure, the spleen performs a number of critically important functions:
- Participates in systemic immune responses.
- Enriches the blood with newly developing leukocytes.
- Performs phagocytosis: macrophages remove microorganisms and foreign particles.
- Acts as an "erythrocyte graveyard," ruthlessly destroying old and damaged red blood cells.
Briefly: answers to topical questions
Which ligaments anchor the spleen in the abdominal cavity?
The spleen is anchored by two peritoneal ligaments extending from its hilum:
- Gastrosplenic ligament (lig. gastrosplenicum) — connects the spleen to the stomach.
- Splenorenal ligament (lig. splenorenale) — connects the spleen to the left kidney; also referred to as the phrenicosplenic ligament.
The anterior extremity of the spleen rests on a portion of peritoneum connecting the left colic flexure to the parietal peritoneum of the diaphragm — the phrenicocolic ligament.
What passes within the thickness of the gastrosplenic ligament?
Passing within the thickness of the gastrosplenic ligament are:
- Short gastric arteries (aa. gastricae breves) — branches of the splenic artery heading toward the gastric fundus.
- Tail of the pancreas — approaches the splenic hilum as part of this ligament.
An accessory spleen (splen accessorius) may occasionally be located in the region of the gastrosplenic ligament.
Where does venous blood drain from the spleen?
Venous blood from the spleen drains into the splenic vein (v. splenica / v. lienalis), which is formed at the splenic hilum by numerous parenchymal veins. The splenic vein runs to the right and joins the superior mesenteric vein to form the hepatic portal vein (v. portae hepatis). Inside the spleen, blood enters the splenic sinuses (sinus splenicus), which mark the beginning of its venous system.
What structures form the white pulp of the spleen?
The white pulp of the spleen is formed by lymphoid tissue organized around arterial vessels into several structural zones.
- Periarterial lymphatic sheaths (periarterial cuffs) — aggregates of T lymphocytes forming a "cuff" around the pulp arteries.
- Lymphoid nodules (noduli lymphoidei splenici) — follicles with germinal centers surrounding the central arteries and consisting predominantly of B cells.
- Intermediate zone — the area surrounding the sheath containing T and B lymphocytes.
- Marginal zone — located at the border between the white and red pulp.
What passes through the hilum of the spleen?
Passing through the hilum of the spleen, located on its visceral surface, are the main blood vessels, lymphatic vessels, and nerves of the organ.
- Splenic artery (a. splenica) — enters the hilum and divides into terminal segmental branches.
- Splenic vein (v. splenica / v. lienalis) emerges from the hilum, formed by the veins of the parenchyma.
- Lymphatic vessels converge in the region of the hilum and exit the organ.
- Nerves enter the organ to provide its innervation (periarterial plexus splenicus).
To remember the skeletotopy of the spleen, use the numbers 9 and 11. The organ is projected onto the thoracic cage precisely between the 9th and 11th ribs. You can associate this with the "911" emergency service—the spleen functions as a safety filter, rapidly destroying bacteria and aged erythrocytes.
Class and exam questions
What is the difference between white and red pulp?
White pulp consists of lymphoid tissue and is responsible for the immune response. Red pulp is formed by reticular tissue; its meshes accumulate erythrocytes, leukocytes, and macrophages that filter the blood.
What passes through the hilum of the spleen?
Nerves enter the organ, arteries pass through, and venous vessels exit via the hilum. The hilum itself is not covered by peritoneum.
Where can an accessory spleen be located?
An accessory spleen (splen accessorius) is most commonly located within the gastrosplenic ligament, close to the hilum of the main organ.
What else to study on this topic
- Intrasplenic circulation: the pathway of blood from trabecular arteries to venous sinuses
- The ligamentous apparatus of the spleen as a derivative of the dorsal mesogastrium
- Topography of the tail of the pancreas relative to the splenic hilum
- Visceral surface organ impressions: boundaries and relations
- Histological differences of the white pulp lymphoid follicles
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