Did You Know?
The spleen is the largest lymphatic organ in the human body.
The word 'spleen' is derived from the Greek word 'splḗn'. In most animals, this organ has a purple and gray color, whereas in humans, it is brownish in color. It plays a very important role in the immune system. It primarily helps in the filtration of blood by removing old and senescent red blood cells from the bloodstream. It also holds a reserve of fresh blood, which is invaluable in cases of a hemorrhagic shock. The spleen also functions to recycle iron in the body. It is also responsible for antibody production.
Despite its essential functions, it is possible to surgically remove the spleen without endangering the life of the animal or person. This procedure is called a splenectomy, and is usually carried out due to the clinical malfunctioning of the spleen, which gives rise to health disorders such as splenomegaly, asplenia, and hyposplenia. It may also be removed in case of severe tissue damage or due to the development of cancerous conditions.
Location of the Spleen
Location of the spleen with respect to the pancreas
In humans, the spleen is located in the left upper quadrant of the abdomen. It is a fist-sized organ, that is present adjacent to the stomach and pancreas. Its size is between 7 to 14 cm in length, and it weighs about 150 - 200 g. It is located between the 9th
rib. Because of the presence of the ribcage, and like many other internal organs, one is unable to feel the presence of the spleen. Its presence is felt only in cases where the organ, due to some reason, gets abnormally enlarged. This could be due to bacterial or viral infections, diseases like malaria, tissue damage, etc. The size of this organ also increases during the process of digestion.
Structure of the Spleen
Histology of the spleen
The spleen is attached to the greater curvature of the stomach with the help of the gastroplenic ligament. The organ itself shows a membranous encapsulation, which is composed of fibrous and elastic tissue. This external tissue extends into the parenchyma of the organ, and the projections are called trabeculae. The parenchymous tissue of the spleen is structurally supported by a fine mesh of reticular fibers, which helps divide the parenchyma into two types of tissue. These tissues are called the red and white pulp, and are separated from each other by the presence of the marginal sinus (the amount of red pulp is more than that of white pulp).
The red pulp
is made up of a network of cell cords in conjugation with vascular sinuses. These cords contain macrophages, plasma cells, granulocytes, lymphocytes, erythrocytes, etc. The vascular sinuses are wide channels that have an internal lining of endothelial cells. The presence of fenestration in the walls of these sinuses allows the passage of blood and other lymphatic fluids in and out of the spleen.
The white pulp
is present around the arterioles, such that the lymphoid tissue surrounds a central arteriole. This tissue is made up of various layers of specialized cells. The layer or sheath directly enclosing the arteriole consists of T cells, and is called the periarteriolar lymphoid sheath (PALS). This layer is surrounded by a marginal sinus. The sinus is covered with a thick layer composed of B cells and macrophages. The marginal sinuses are linked to the sinuses found in the red pulp.
Spleen Shape in Different Species
Elongated and dumb-bell shaped in carnivorous animals╬
Flat and oblong in case of ruminating animals╬
Equine spleen is dorsally broad and ventrally narrow╬
Elongated and strap-like in case of pigs╬
Spherical shape in chickens╬
Triangular in ducks╬
Oval shape in pigeons
Function of the Spleen
It produces lymphocytes, and is a site for their activation, which initiates antibody production.❒
It filters the blood to eliminate aging erythrocytes, antigens, foreign cells, cell debris, etc.❒
White pulp acts as a secondary lymphoid organ.❒
It acts as a reservoir for erythrocytes and platelets.❒
It produces blood (hematopoiesis) in the fetal stage of an animal (later carried out by bone marrow).
Although the spleen is protected by the ribcage, it is susceptible to injury. One of the most common causes of injury is a direct hit, like in the case of an accident. In some cases, injury to the spleen can also be caused due to fractured ribs on the left side. The less common causes include playing contact sports like ice hockey, football, etc. If the impact of the injury is severe, it can result in a ruptured spleen, causing a massive amount of blood loss in the abdominal area. Such a situation can be life-threatening, and should be considered a medical emergency. Due to the location of the spleen, it is also prone to disease and infection. Diseases like tuberculosis, malaria, leukemia, liver diseases like hepatitis, etc., can affect it. Although removal is possible, it is seen that if the spleen is removed, the person is at a greater risk of infection. Therefore, it is recommended that at the first sign of an infection, or health issues such as severe sore throat, unexplained cough, severe pain in the abdomen, headache, etc., the person should get in touch with a health care professional.