Red pulp

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Red pulp
Illu spleen.jpg
Spleen
Details
Identifiers
Latin pulpa splenica
TA98 A13.2.01.005
TA2 5175
FMA 15844
Anatomical terminology

The red pulp of the spleen is composed of connective tissue known also as the cords of Billroth and many splenic sinusoids that are engorged with blood, giving it a red color. [1] [2] Its primary function is to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells. [3]

Contents

The spleen is made of red pulp and white pulp, separated by the marginal zone; 76–79% of a normal spleen is red pulp. [4] Unlike white pulp, which mainly contains lymphocytes such as T cells, red pulp is made up of several different types of blood cells, including platelets, granulocytes, red blood cells, and plasma. [1]

The red pulp also acts as a large reservoir for monocytes. These monocytes are found in clusters in the Billroth's cords (red pulp cords). The population of monocytes in this reservoir is greater than the total number of monocytes present in circulation. They can be rapidly mobilised to leave the spleen and assist in tackling ongoing infections. [5]

Sinusoids

The splenic sinusoids, are wide vessels that drain into pulp veins which themselves drain into trabecular veins. Gaps in the endothelium lining the sinusoids mechanically filter blood cells as they enter the spleen. Worn-out or abnormal red cells attempting to squeeze through the narrow intercellular spaces become badly damaged, and are subsequently devoured by macrophages in the red pulp. [6] In addition to clearing aged red blood cells, the sinusoids also filter out cellular debris, particles that could clutter up the bloodstream.

Cells found in red pulp

Red pulp consists of a dense network of fine reticular fiber, continuous with those of the splenic trabeculae, to which are applied flat, branching cells. The meshes of the reticulum are filled with blood:

Red pulp macrophages

Macrophages are highly diverse mononuclear phagocytes that are present throughout the body, including the spleen. Those located in the red pulp are known as red pulp macrophages (RPMs). They are necessary for maintaining blood homeostasis by performing phagocytosis upon injured and senescent erythrocytes and blood-borne particulates. Evidence suggests that RPMs are mainly produced during embryogenesis and are maintained during adult life.

Additionally, there are a number of cell-intrinsic and cell-extrinsic factors that regulate the development and survival of RPMs, these factors being: Spi-C, IRF8/4, heme oxygenase-1 and M-CSF.

RPM's are capable of inducing the differentiation of regulatory T cells by the expression of transforming growth factor-β. They can also secrete type-1 interferons during parasitic infections. [7]

Blood in the arteries end in the Billroth's cords (red pulp cords). These cords are made up of fibroblasts and reticular fibres which form an open blood system without an endothelial lining, and it is within these cords that F4/80+ macrophages are found, which are associated with the reticular cells of these areas and are collectively known as red pulp macrophages. From the Billroth's cords, the blood passes into the venous sinuses of the red pulp, which are lined with discontinuous endothelium as well as stress fibres extending under the basal plasma membrane, parallel to the cellular axis. This arrangement of the stress fibres combined with the parallel arrangement of the sinus endothelial cells forces the blood in the red pulp through slits that are formed by the stress fibres. However, this passage can become difficult for ageing red blood cells due to their less flexible membranes and therefore they get stuck in the cords and they will be subsequently phagocytosed by the red pulp macrophages. This process is known as erythrophagocytosis, which is important for the turnover of red blood cells and the recycling of iron, which is a major function of the red pulp macrophages and is made possible by this special structure of the red pulp.

The iron from the red blood cells is either released by the red pulp macrophages or stored in the erythrocyte itself in the form of ferritin. Also, the erythrocyte can store larger amounts of iron in the form of hemosiderin (an insoluble complex of partially degraded ferritin), and large deposits of this can be seen in the red pulp macrophages. The red pulp macrophages also obtain iron by scavenging a complex of haemoglobin (released from erythrocytes destroyed intravascularly throughout the body) and haptoglobin, via endocytosis through CD163. The iron stored in the splenic macrophages is released in accordance with the requirements of the bone marrow. [5]

Diseases

In lymphoid leukemia, the white pulp of the spleen hypertrophies and the red pulp shrinks. [4] In some cases the white pulp can swell to 50% of the total volume of the spleen. [8] In myeloid leukemia, the white pulp atrophies and the red pulp expands. [4]

Related Research Articles

<span class="mw-page-title-main">Haematopoiesis</span> Formation of blood cellular components

Haematopoiesis is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult human, roughly ten billion to a hundred billion new blood cells are produced per day, in order to maintain steady state levels in the peripheral circulation.

<span class="mw-page-title-main">Spleen</span> Organ recycling old red blood cells and also housing lymphocytes

The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes from Ancient Greek σπλήν (splḗn).

<span class="mw-page-title-main">Lymphatic system</span> Organ system in vertebrates complementary to the circulatory system

The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphoid organs, lymphatic tissue and lymph. Lymph is a clear fluid carried by the lymphatic vessels back to the heart for re-circulation. The Latin word for lymph, lympha, refers to the deity of fresh water, "Lympha".

<span class="mw-page-title-main">Lymph node</span> Organ of the lymphatic system

A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that include B and T cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles including cancer cells, but have no detoxification function.

<span class="mw-page-title-main">Splenectomy</span> Surgical removal of the spleen

A splenectomy is the surgical procedure that partially or completely removes the spleen. The spleen is an important organ in regard to immunological function due to its ability to efficiently destroy encapsulated bacteria. Therefore, removal of the spleen runs the risk of overwhelming post-splenectomy infection, a medical emergency and rapidly fatal disease caused by the inability of the body's immune system to properly fight infection following splenectomy or asplenia.

<span class="mw-page-title-main">Hereditary spherocytosis</span> Medical condition

Hereditary spherocytosis (HS) is a congenital hemolytic disorder wherein a genetic mutation coding for a structural membrane protein phenotype causes the red blood cells to be sphere-shaped (spherocytosis), rather than the normal biconcave disk shape. This abnormal shape interferes with the cells' ability to flex during blood circulation, and also makes them more prone to rupture under osmotic stress, mechanical stress, or both. Cells with the dysfunctional proteins are degraded in the spleen, which leads to a shortage of erythrocytes and results in hemolytic anemia.

<span class="mw-page-title-main">Renal corpuscle</span> Blood-filtering component of the nephron of the kidney

A renal corpuscle is the blood-filtering component of the nephron of the kidney. It consists of a glomerulus - a tuft of capillaries composed of endothelial cells, and a glomerular capsule known as Bowman's capsule.

In immunology, the mononuclear phagocyte system or mononuclear phagocytic system (MPS) also known as the macrophage system is a part of the immune system that consists of the phagocytic cells located in reticular connective tissue. The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS. The mononuclear phagocyte system and the monocyte macrophage system refer to two different entities, often mistakenly understood as one.

There are at least two anatomical structures called a Malpighian corpuscle. They are also known as:

A splenocyte is a white blood cell that resides in the spleen and are involved in functions of the spleen, like filtering blood and the immune response.

An autosplenectomy is a negative outcome of disease and occurs when a disease damages the spleen to such an extent that it becomes shrunken and non-functional. The spleen is an important immunological organ that acts as a filter for red blood cells, triggers phagocytosis of invaders, and mounts an immunological response when necessary. Lack of a spleen, called asplenia, can occur by autosplenectomy or the surgical counterpart, splenectomy. Asplenia can increase susceptibility to infection. Autosplenectomy can occur in cases of sickle-cell disease where the misshapen cells block blood flow to the spleen, causing scarring and eventual atrophy of the organ. Autosplenectomy is a rare condition that is linked to certain diseases but is not a common occurrence. It is also seen in systemic lupus erythematosus (SLE).

The cords of Billroth are found in the red pulp of the spleen between the sinusoids, consisting of fibrils and connective tissue cells with a large population of monocytes and macrophages. These cords contain half of the mouse body's monocytes as a reserve so that after tissue injury these monocytes can move in and aid locally sourced monocytes in wound healing.

<span class="mw-page-title-main">Howell–Jolly body</span> Cluster of DNA in red blood cells

A Howell–Jolly body is a cytopathological finding of basophilic nuclear remnants in circulating erythrocytes. During maturation in the bone marrow, late erythroblasts normally expel their nuclei; but, in some cases, a small portion of DNA remains. The presence of Howell–Jolly bodies usually signifies a damaged or absent spleen, because a healthy spleen would normally filter such erythrocytes.

<span class="mw-page-title-main">Reticular fiber</span> Type of connective tissue in animals

Reticular fibers, reticular fibres or reticulin is a type of fiber in connective tissue composed of type III collagen secreted by reticular cells. They are mainly composed of reticulin protein and form a network or mesh. Reticular fibers crosslink to form a fine meshwork (reticulin). This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system.

<span class="mw-page-title-main">Hemosiderin</span> Iron-storage complex

Hemosiderin or haemosiderin is an iron-storage complex that is composed of partially digested ferritin and lysosomes. The breakdown of heme gives rise to biliverdin and iron. The body then traps the released iron and stores it as hemosiderin in tissues. Hemosiderin is also generated from the abnormal metabolic pathway of ferritin.

<span class="mw-page-title-main">Marginal zone</span> Part of the spleen

The marginal zone is the region at the interface between the non-lymphoid red pulp and the lymphoid white-pulp of the spleen.

<span class="mw-page-title-main">White pulp</span> Type of tissue in the spleen

White pulp is a histological designation for regions of the spleen, that encompasses approximately 25% of splenic tissue. White pulp consists entirely of lymphoid tissue.

In anatomy and histology, the term wandering cell is used to describe cells that are found in connective tissue, but are not fixed in place. This term is used occasionally and usually refers to blood leukocytes in particular mononuclear phagocytes. Frequently, the term refers to circulating macrophages and has been used also for stationary macrophages fixed in tissues (histiocytes), which are sometimes referred to as "resting wandering cells".

<span class="mw-page-title-main">Trabecular arteries</span>

The trabecular arteries are the name of the branches of the splenic artery after it passes into the trabeculae of the spleen, where it branches. When these arteries then reach the white pulp, and become covered with periarteriolar lymphoid sheaths, the name changes again to central arteries. Branches of the central arteries are given to the red pulp, and these are called penicillar arteries).

<span class="mw-page-title-main">Trabecular veins</span> Veins inside the spleen

The trabecular veins are the largest veins inside the spleen. They drain the blood collected in the sinuses of the pulp.

References

PD-icon.svgThis article incorporates text in the public domain from page 1284 of the 20th edition of Gray's Anatomy (1918)

  1. 1 2 Luiz Carlos Junqueira; José Carneiro (2005). Basic histology: text & atlas. McGraw-Hill Professional. pp. 274–277. ISBN   0-07-144091-7.
  2. ↑ Michael Schuenke; Erik Schulte; Udo Schumacher; Lawrence M. Ross; Edward D. Lamperti (2006). Atlas of anatomy: neck and internal organs. Thieme. p. 219. ISBN   1-58890-360-5.
  3. ↑ Victor P. Eroschenko; Mariano S. H. di Fiore (2008). Di Fiore's atlas of histology with functional correlations. Lippincott Williams & Wilkins. p. 208. ISBN   978-0-7817-7057-6.
  4. 1 2 3 Carl Pochedly; Richard H. Sills; Allen D. Schwartz (1989). Disorders of the spleen: pathophysiology and management. Informa Health Care. pp. 7–15. ISBN   0-8247-7933-9.
  5. 1 2 den Haan, Joke M.M.; Kraal, Georg (2012). "Innate Immune Functions of Macrophage Subpopulations in the Spleen". Journal of Innate Immunity. 4 (5–6): 437–445. doi:10.1159/000335216. ISSN   1662-8128. PMC   6741446 . PMID   22327291.
  6. ↑ Cormack, David H. (2001). Essential histology . Lippincott Williams & Wilkins. pp.  169–170. ISBN   0-7817-1668-3.
  7. ↑ Kurotaki, Daisuke; Uede, Toshimitsu; Tamura, Tomohiko (February 2015). "Functions and development of red pulp macrophages". Microbiology and Immunology. 59 (2): 55–62. doi: 10.1111/1348-0421.12228 . ISSN   0385-5600. PMID   25611090.
  8. ↑ Jan Klein; Václav Hořejší (1997). Immunology. Wiley-Blackwell. p. 30. ISBN   0-632-05468-9.
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