Accessory Organs - Spleen Flashcards
What is the spleen?
It is an organ that is located in the left hypochondium, and is roughly the size of a clenched fist. In the adult, the spleen functions mainly as a blood filter, removing old red blood cells. It also plays a role in both cell-mediated and humoral immune responses.
Anatomical position?
Located in the left hypochondriac region, under the cover of the diaphragm and the ribcage - it cannot be palpated normally on clinical examination (except when enlarged).
It is an intraperitoneal organ, covered entirely by peritoneum (except at the splenic hilum).
The spleen is connected to the stomach and the kidney by parts of the greater omentum - a double fold of peritoneum that originates from the stomach:
1) Gastrosplenic ligament - anterior to the splenic hilum, connects the spleen to the greater curvature of the stomach.
2) Splenorenal ligament - posterior to the splenic hilum, connects the hilum of the spleen to the left kidney. The splenic vessels and tail of the pancreas lie within the ligament.
Between these two ligaments is the lesser sac.
Structure?
The spleen has a slight oval shape. It is covered by a weak capsule that protects the organ whilst allowing it to expand in size.
The outer surface of the spleen can be anatomically divided into two:
1) Diaphragmatic surface - in contact with diaphragm and ribcage.
2) Visceral surface - in contact with the other abdominal viscera.
It has anterior, superior, posteromedial and inferior borders. The posteromedial and inferior boders are smooth, whilst the anterior and superior borders contain notches.
In enlargement of the spleen (known as splenomegaly), the superior border moves inferomedially, and its notches can be palpated.
Anatomical relations?
It lies in close proximity to other structures in the abdomen.
Anteriorly - stomach
Posteriorly - diaphragm, left lung and ribs 9-11.
Inferiorly - left colic flexure
Medially - Left kidney, pancreas
Vasculature?
The spleen is a highly vascular organ. It receives most its supply from the splenic artery. This vessel arises from the coeliac trunk, running laterally along the superior aspect of the pancreas, within the splenorenal ligament. As the artery reaches the spleen, it branches into five vessels - each supplying a different part of the organ.
These arterial branches do not anastomose with each other - giving rise to vascular segments of the spleen. This enables a surgeron to remove on of these segments, without affecting the others (a procedure known as a subtotal splenectomy).
Venous drainage occurs through the splenic vein. It combines with superior mesenteric vein to form the hepatic portal vein.
Innervation?
The nerve supply to the spleen is from the coeliac plexus.
Lymphatics?
The lymph vessels of the spleen follow the splenic vessels mentioned above and drain into the pancreaticosplenic lymph nodesm, and ultimately the coliac nodes.
Clinical relevance - rupture of the spleen?
The spleen is an abdominal organ with the highest incidence of injury. A splenic rupture occurs when there is a break in its fibroelastic capsule, disrupting the underlying parenchyma.
Rupture is caused by blunt or penetrating trauma. It is often associated with left rib fractures, with a bony fragment easily tearing the capsule.
As the spleen is a highly vascular organ, its rupture results in profuse bleeding into the peritoneal cavity. Splenectomy is indicated when injury to the spleen and subsequent haemorrhage are life threatening. This may be done as a sub total (partial) splenectom - recall that there are no arterial anastomoses in the spleen - or as a total splenectomy.
The liver and bone marrow take over some of the functions of the spleen, however, an individual who has no spleen is more susceptible to some bacterial infections and as such, requires life long antibiotics.
Further indications for splenectomy include haematological conditions such as a haemolytic anaemia, idiopathic thrombocytopenic purpura, thrombotic thrombocytopenic purpura, hypersplenism and proliferative disorders such as myelofibrosis of lymphoma.
