What is Spleen?

• The spleen is a vital organ located on the left side of the body, beneath the diaphragm. It is a large, bean-shaped organ enclosed in a protective covering. Unlike lymph nodes, the spleen does not have lymphatic drainage and instead contains a substantial number of red blood cells.
• Present in most vertebrates, the spleen serves as a blood filter and closely resembles a large lymph node in structure. Its name originates from the Greek word “splḗn.” This organ plays crucial roles in relation to red blood cells and the immune system.
• One of the primary functions of the spleen is to remove old or damaged red blood cells and store a reserve of blood. This reserve becomes valuable in cases of hemorrhagic shock. Additionally, the spleen recycles iron and metabolizes hemoglobin from senescent red blood cells. Hemoglobin is broken down into amino acids, while the heme portion is processed into bilirubin and eventually eliminated by the liver.
• The spleen’s white pulp houses lymphocytes responsible for producing antibodies, while its monocytes aid in removing bacteria and antibody-coated blood cells by circulating through the bloodstream and lymph nodes. Injured tissue prompts these monocytes to transform into dendritic cells and macrophages, promoting tissue healing. The spleen is a significant component of the mononuclear phagocyte system, akin to a large lymph node. Its absence can lead to an increased susceptibility to certain infections.
• In humans, the spleen is located in the upper left quadrant of the abdomen and has a purple hue. It is relatively small in size and located behind the ribcage and stomach. As the largest organ in the lymphatic system, the spleen plays a vital role in immune function, blood filtration, and blood volume regulation.
• The lymphatic system comprises ducts and lymph nodes found beneath the skin. It allows white blood cells to travel outside the bloodstream and acts as a receptacle for bacteria, dead cells, debris, and excess fluid.
• The spleen carries out several essential functions, including antibody production, bacterial removal, elimination of old red blood cells, breakdown of red blood cell waste products, iron recycling for new red blood cells, and storage of reserve red blood cells and immune cells for emergencies.
• The production of antibodies occurs in the spleen’s white pulp, while its red pulp contains a reservoir of immune cells that combat infections and support tissue healing, which can be released when needed.
• While the spleen is beneficial to the body, it is not vital for survival. If necessary, other organs can take over some of its functions. However, certain functions of the spleen are crucial in emergencies but not required for survival in most situations.
• In cases of injury or infection, the spleen may need to be surgically removed if it poses a greater risk than benefit to the body.
• Sickle cell disease can also damage the spleen by obstructing blood flow. Consequently, individuals with sickle cell disease are advised to receive additional immunizations.
• People who lack a spleen can generally lead normal and healthy lives. However, they are recommended to undergo regular immunizations to protect against infections.
• Interestingly, approximately 10% of individuals possess an “accessory spleen,” which is a small extra spleen. This additional spleen typically causes no issues or symptoms, and its presence is often discovered incidentally during imaging scans conducted for other reasons.

Definition of Spleen

The spleen is a large organ located on the left side of the body, below the diaphragm. It acts as a blood filter and plays important roles in immune function, removing old red blood cells, recycling iron, and storing a reserve of blood cells. It is part of the lymphatic system and contributes to the body’s defense against infections.

Anatomical Position – Spleen Location

• The spleen is located in the upper left quadrant of the abdomen and is protected by the diaphragm and ribs. Except when it is enlarged, its location precludes direct palpation during clinical examinations. With the exception of the splenic hilum, the spleen is an intraperitoneal organ, enclosed within the peritoneum.
• Certain portions of the greater omentum, a double fold of peritoneum originating from the stomach, join it to the stomach and kidney. In front of the splenic hilum, the gastrosplenic ligament connects the spleen to the greater curvature of the stomach. Behind the splenic hilum, the splenorenal ligament connects the splenic hilum to the left kidney. This ligament contains the splenic vessels and the pancreatic tail.
• Typically, the spleen is located below the left rib cage, next to the stomach. Due to its small size, approximately the size of a fist, and location behind the stomach, it is typically not detectable or palpable.
• Despite being well-protected by its location, the spleen is susceptible to injury from chest or side impacts, which can occur during sports or automobile accidents.
• A ruptured spleen poses a serious danger to the body. Due to the spleen’s abundant blood supply, a rupture can result in rapid and substantial blood loss. In cases where there is concern about the possibility of rupture, the spleen may be removed surgically.
• During an examination, physicians may be able to feel an abnormally enlarged spleen caused by conditions such as mononucleosis, blood cancers, or other diseases. By examining the abdomen, doctors can identify signs of a splenic enlargement and investigate potential underlying conditions.

Structure of Spleen

• The spleen is a distinct organ with a dark purple hue and a distinct structure. It is located in the left hypochondriac region of the abdomen, between the gastric fundus and the diaphragm.
• Spleen size and weight can fluctuate throughout a person’s lifespan. Adults typically possess dimensions of 12 centimeters in length, 8 centimeters in width, and 3 to 4 centimeters in thickness, and weigh approximately 200 grams.
• Two surfaces make up the spleen: the diaphragmatic surface and the visceral surface. The diaphragmatic surface is in direct contact with the diaphragm’s inner surface, whereas the visceral surface confronts the abdominal organs.
• The spleen is surrounded by the peritoneum, which adheres securely to the splenic capsule, an internal fibroelastic coat. This capsule extends into the spleen and forms trabeculae that cross the organ. These trabeculae sustain the structure of the spleen.
• Additionally, the structure of the spleen is distinguished by the white pulp and the crimson pulp. The white substance is composed of lymphatic tissue and is responsible for immune functions, such as the production of antibodies. The red pulp is responsible for filtering and recycling blood components, particularly red blood cells, and contains alveoli.
• Overall, the structure of the spleen reveals its intricate organization and specialized regions, which contribute to its vital body functions.

Red pulp and white pulp are the two varieties of tissue that make up the spleen. These tissues are surrounded by a tissue membrane. The external aspect of the spleen consists of two distinct regions: the diaphragmatic surface and the visceral surface. Here, we will elaborate on each of these essential characteristics.

Diaphragmatic Surface

• The spleen’s diaphragmatic surface is the portion of the organ that is in contact with the diaphragm. It is an upward, outwardly curved surface that presses against the diaphragm.
• The diaphragm is a strong muscle located between the lungs and the stomach. As it contracts and relaxes to facilitate inhalation and exhalation, it plays an essential function in the breathing process. Positioned between the spleen and the lung, the diaphragm separates these organs.
• The proximity of the spleen to the diaphragm and its diaphragmatic surface highlight the anatomical relationship between these two structures. This configuration is essential to comprehending the position and interactions of the spleen within the abdominal cavity.

Visceral Surface

• The visceral surface of the spleen is directed downward, facing the abdominal organs known as the “viscera” or “gut.” It is divided into two distinct regions: the renal region and the gastric region.
• The gastric region, also referred to as the anterior or front surface of the spleen, is positioned at the front and curves inward, resembling the shape of a soup spoon. This curvature allows it to wrap around the stomach, with the stomach nestled within the spleen. At the lowermost part of the gastric region, it comes into contact with the tail of the pancreas.
• On the other hand, the renal region of the visceral surface faces inward toward the central part of the body and downward. It makes contact with the anterior surface of the left kidney and sometimes with the left adrenal gland.
• The differentiation of the visceral surface into the gastric and renal regions provides a clear understanding of the positioning and relationships between the spleen and adjacent abdominal organs, particularly the stomach, pancreas, kidney, and adrenal gland.

White Pulp

• The white substance of the spleen is responsible for the immune functions of the organ. It consists of layered tissues and nodules, each of which plays a unique function in immune system support.
• The periarteriolar lymphoid sheaths (PALS) are a component of the white pulp that serves as a reservoir for T lymphocytes, a form of white blood cell. These T lymphocytes serve as a defense force, comparable to a standing army, ready to defend the body in the event of an attack.
• Within the white pulp are lymph follicles containing B lymphocytes that endure division and multiplication. These B lymphocytes are essential for the production of antibody molecules, which assist the immune system in recognizing and combating disease. If the spleen is removed, other tissues can perform these functions. However, the production of these cells and antibodies lends an additional layer of strength to the immune system.
• The marginal zone of the white pulp contains a unique type of cell known as antigen-presenting cells, making it an essential region. Antigens are bacterial or viral molecules that antibodies and white blood cells can recognize. Antigen-presenting cells play an essential role in the immune response by ingesting invading pathogens and displaying pathogen-derived molecules on their cell surfaces. This process teaches and activates other immune cells so that they can effectively respond to new pathogens.
• Diverse tissues and nodules within the spleen’s white pulp contribute to the immune system’s function, enhancing its capacity to fight off infections and safeguard the body from dangerous pathogens.

Red Pulp

• Red pulp of the spleen serves as a blood-filtering mechanism, as well as a recycling center for red blood cells and a storage site for other vital blood components. It comprises the preponderance of healthy spleen tissue.
• The crimson pulp, composed of connective tissue known as “cords of Billroth,” serves as the blood’s initial filter. It eliminates pathogens and extracts red blood cells at the end of their lifespan. Within the red pulp, immune cells called macrophages degrade and eradicate the non-functional or harmful components of these cells, while preserving the functional components, such as iron, for future red blood cell production.
• In addition, the red pulp functions as a repository for white corpuscles, another type of white blood cell, and contains cells known as “splenic cells.” These cells are responsible for red blood cell storage, digestion, and transport within the spleen. Additionally, platelets, which are essential for blood clotting, are retained in the red pulp.
• In some instances, platelet deficiency may occur if the spleen fails to discharge an adequate number of platelets into the bloodstream after retaining an excessive number of platelets. This condition can result in blood clotting and coagulation complications.
• The red pulp’s functions of filtering blood, recycling red blood cells, and retaining vital blood components highlight its important role within the spleen and its contribution to the health of the circulatory system as a whole.

Functions of Spleen

1. Immune response: The spleen acts as a filter for the blood, trapping bloodborne microbes and initiating an immune response against them. It plays a crucial role in B cell responses to polysaccharide antigens, aiding in the production of antibodies.
2. Lymphocyte production: The spleen contains lymphatic tissue that produces T lymphocytes and B lymphocytes, contributing to the body’s immune system.
3. Antibody and antitoxin production: With the presence of lymphoid reticulo-endothelial tissue, the spleen is involved in the production of antibodies and antitoxins.
4. Haematopoiesis: During fetal development, the spleen acts as an important site for blood cell production.
5. Removal of damaged cells and immune complexes: The spleen eliminates damaged red blood cells and immune complexes from circulation.
6. Reservoir for blood and erythrocytes: The spleen can act as a reservoir for blood, storing emergency reserves of red blood cells that can be released in case of blood loss.
7. Antibody-mediated immunity: Individuals who have had their spleens removed (splenectomized) are more susceptible to infections with encapsulated bacteria and severe malarial infections. This highlights the spleen’s significant role in immune defense.
8. Production of antibodies: The spleen produces antibodies, which are essential for recognizing and fighting infections.
9. Storage of emergency reserves: The spleen stores emergency reserves of both red and white blood cells that can be released to combat infections and promote healing.
10. Waste breakdown and recycling: The spleen breaks down waste products from dead cells and recycles useful components like iron for future red blood cell production.

While the spleen is not necessary for survival, it plays a vital role in immune function and the management of blood components. People without a spleen are advised to take precautions such as vaccinations and antibiotics to mitigate the increased susceptibility to certain infections. In cases of injury or rupture, the spleen may need to be removed due to the risk of life-threatening blood loss. Some research suggests a potential role of the spleen in preventing cardiovascular disease, emphasizing the importance of injury prevention to avoid spleen-related complications.

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