Spleen

The spleen is an organ that is present in all vertebrate animals, though the spleen often alludes thought in most people (Steiniger, 2005).  The human spleen is a red color, ovular mass that is roughly the size of a clenched fist located in the Upper Left Quadrant of abdominal peritoneum (Strickland and Lloyd, 2007).  The average spleen weighs around 200g and has an average volume around 215 mL, though this varies in correlation to body height, weight, body mass index, and body surface area (Caglar et al. 2014).  Located in the dorsal region and resting against the diaphragm, the spleen in not able to be palpated in medical examination (Strickland and Lloyd, 2007).  The spleen is a lymphatic organ, which deals with the immune system of the body (Steiniger, 2005).  The function of the spleen is separated into two different anatomical sections, which are the red pulp and the white pulp (Steiniger, 2005).

The red pulp is composed of splenic sinuses, which connect the veins with the arterioles and is not found in all species of vertebrates, and splenic cords, which are composed of loose connective tissue (Steiniger, 2005).  The blood filled splenic sinuses is what the “red pulp” region of the spleen is named for (Mebius and Kraal, 2005).  The red pulp filters the blood through phagocytosis by the macrophages found in this region (Steiniger, 2005).  This filtering of the blood can remove dangers to the body such as microorganisms, leukocytes covered in immune complexes, and old or abnormal red blood cells (Steiniger, 2005).  The blood flows into region through arteries into cords that are composed of fibroblasts and reticular fibers that does not have an endothelial lining, and continues into the venous sinuses that do contain endothelial lining (Mebius and Kraal, 2005).  After the venous sinuses, a structure that contains a series of stress fibers that are connecting the endothelial cells to the part of the extracellular matrix made-up of actin and myosin filaments (Mebius and Kraal, 2005).  This structure that is created allows passage from the venous sinuses only through the spaces between the stress fibers (Mebius and Kraal, 2005).  Active cells are located in these spaces that are set off by foreign substances, especially bacteria, and activate the antibodies to remove them (Strickland and Lloyd, 2007).  This creates difficulty for erythrocytes whose membranes have become stiff with age, and those who are unable to pass through go through phagocytosis (Mebius and Kraal, 2005).  Macrophages in this area can also remove substances from abnormal erythrocytes without effecting them; these substances include leftover pieces of nuclear DNA, altered hemoglobin, and iron (Strickland and Lloyd, 2007).  Stress fibers may also contract preventing the pass of all erythrocytes, creating a reservoir of blood and thus reducing stress and viscosity while the body is at rest (Mebius and Kraal, 2005).

Another function of the red pulp that arises from the removal of old erythrocytes, is to recycle iron with the use of macrophages while working with the macrophages within the liver (Mebius and Kraal, 2005; Strickland and Lloyd, 2007).  The erythrocytes are broken down by a vesicle called a phagolysosome, which is formed from the fusion of a phagosome and a lysosome, this vesicle then releases a compound that contains iron (Mebius and Kraal, 2005).  This compound, called haem, is further broken down into its components of biliverdin, carbon monoxide, and ferrous iron (Mebius and Kraal, 2005).  The iron is originally stored within the macrophages and is later sent to the bone marrow to be used again (Strickland and Lloyd, 2007).

The white pulp in the spleen plays a large role in the immune system (Mebius and Kraal, 2005).  Two compartments within the white pulp store B-cells and T-cells seperately, and these compartment resemble lymph nodes (Mebius and Kraal, 2005).  The B-cells, or B-lymphocytes, serve in the process of filtering the blood when the blood must fit through the space with the stress fibers, and are a location for producing antibodies after the cells are activated in response to a foreign body (Strickland and Lloyd, 2007).  When the T-cells, or T-lymphocytes, leave the white pulp, they go to the red pulp in an area called the periarteriolar lymphatic sheath, where they stay until they exit the spleen and circulate the body (Steiniger, 2005).  Chemokine receptors in the white pulp determine that the T-cells and B-cells are stored in the proper compartments, and also attract plasmablasts that will travel a bridging channel between the T-cell zone of the white pulp into the red pulp where they will become plasma cells (Mebius and Kraal, 2005).

Two main general problems that effects the spleen are the swelling or enlargement of the spleen (splenomegaly) and the rupture of the spleen (Mayo Clinic, 2013b; Al-Kindi et al., 2009).  There are many causes of splenomegaly, which include viral infections (e.g. mononucleosis), bacterial infections (e.g. syphilis or endocarditis), parasites (e.g. malaria), cirrhosis of the liver, several types of hemolytic anemia (early break down of red blood cells), cancers of the blood (e.g. leukemia), disorders of the metabolism, sickle cell disease, pressure or blood clots within the veins of the spleen or liver, or hydatid cysts (Mayo Clinic, 2013b; Oussama et al. 2014).  Splenomegaly may have no symptoms at all in some cases, while others may experience pain or a feeling of being full in Upper Left Quadrant with radiating pain into the left shoulder, a lack of appetite or a smaller appetite than normal, anemia (low iron levels), fatigue, frequent illness or infection, and bleeding easily (Mayo Clinic 2013b).  Diagnosis for splenomegaly may include palpation, blood test that report the complete blood count checking the red blood cells, white blood cells, and platelets, an ultrasound or a computerized tomography (i.e. CT scan) to measure the size of the spleen and its effect on surrounding organs, or a magnetic resonance imaging (i.e. MRI) to follow the blood flow through the organ (Mayo Clinic, 2013b).  Blunt force injuries or non-penetrating injuries can cause the spleen to rupture, and in the causes of these injuries, is the abdominal organ that is most commonly injured (Al-Kindi et al., 2009).  Injuries to cause a spleen rupture occur in cases involving fights, automobile accidents, falls, sports, gunshots, serious cases of mononucleosis, AIDS, malignant growths, peliosis (a vascular disorder), granuloma (masses of granulated tissue), sickle cell disease, a disruption in the blood supply, or hydatid cysts (Mayo Clinic 2013a; Oussama et al. 2014).  Symptoms associated with the rupture of the spleen include pain in the Upper Left Quadrant, tenderness when the Upper Left Quadrant is palpated, feeling light headed or dizzy, and a confused mental state (Mayo Clinic 2013a).  Diagnostic tests to determine a rupture of the spleen include a physical exam while palpating the abdomen, inserting a needle into the abdomen to draw fluids out to check for blood, and a CT scan or other imaging tests (Mayo Clinic 2013a).

Although it holds many risks, a viable option for unalleviated splenomegaly and for a ruptured spleen is splenectomy, and can reduces the rate of reoccurrence that could see reoperation and also reducing the rate of complications in a partial splenectomy or surgery to part of the spleen which could cause hemorrhaging (Oussama 2014).  One of the most common and most serious complications following a splenectomy is the risk for infection (Tanaskovic et al., 2015).  Infection is a higher risk after the removal of the spleen because the function of filtration allowing for detection and removal of antigens is no longer occurring, infection can be prevented through vaccinations, especially for pneumococci (e.g. Prevnar) once before or immediately following surgery and every five years following surgery, an influenza vaccine every year, and meningococci (e.g. Menactra) and Haemophilus influenza (e.g. Hib) before surgery if possible, also a regiment of penicillin for life may be offered (Strickland and Lloyd, 2007; Tanaskovic et al., 2015).  Other complications of splenectomy may include hemorrhage, gastric dilation due to stomach manipulation, pancreatic fistula (i.e. trauma to the pancreas), and a subphrenic abscess, sepsis (caused by Escherichia coli) (Strickland and Lloyd, 2007).

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