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Foot process
This schematic illustrates the four different types of glial cells, all of which possess cellular processes: ependymal cells (light pink), astrocytes (green), microglia (red), and oligodendrocytes (light blue). Cell bodies of neurons are in yellow (Their axons are surrounded by myelin, produced by oligodendrocytes).
An illustration of podocytes, which surround the glomerular capillaries with their cell bodies, primary processes and interdigitating foot processes (FPs).

Foot processes (may also be known as footplates or endfeet) are specialized protrusive cellular extensions that may exhibit a pyramidal or finger-like morphology.[1][2] They are most evident in mural cells, that are associated with and ensheath walls of blood capillaries, such as pericytes, podocytes and astrocytes.[3]

Despite not being exclusive, the term foot process is commonly associated with podocytes,[4] the term perivascular or pericapillary endfeet is commonly associated with astrocytes,[5] and the term footplate commonly refers to the base of stapes.[1] In podocytes, terminal foot processess are also named pedicels (from Latin pedīculus, "little foot").[6]

Foot processes are also present in Müller cells (modified astrocytes of the retina),[6] pancreatic stellate cells,[7] dendritic cells,[8] oligodendrocytes,[9] and others. Microglia, which are notably smaller than other macroglial cells, can also extend their foot processes to contact areas of capillaries that are devoid of astrocyte endfeet, and thereby contribute to the formation of the glia limitans.[10] The term foot process may also apply to the basal infoldings, which are indentations found in the basal surface of certain epithelial cells, such as the retinal pigment epithelium and the amniotic epithelium.[11].

  1. ^ a b Dorland's illustrated medical dictionary (33rd ed.). Philadelphia, PA: Elsevier Saunders. 2020. ISBN 9781455756438.
  2. ^ Zhang, XA; Huang, C (September 2012). "Tetraspanins and cell membrane tubular structures". Cellular and molecular life sciences : CMLS. 69 (17): 2843–52. doi:10.1007/s00018-012-0954-0. PMC 10438980. PMID 22450717.
  3. ^ Goddard, LM; Iruela-Arispe, ML (March 2013). "Cellular and molecular regulation of vascular permeability". Thrombosis and haemostasis. 109 (3): 407–15. doi:10.1160/TH12-09-0678. PMC 3786592. PMID 23389236.
  4. ^ Martin, CE; Phippen, NJ; Keyvani Chahi, A; Tilak, M; Banerjee, SL; Lu, P; New, LA; Williamson, CR; Platt, MJ; Simpson, JA; Krendel, M; Bisson, N; Gingras, AC; Jones, N (August 2022). "Complementary Nck1/2 Signaling in Podocytes Controls α Actinin-4-Mediated Actin Organization, Adhesion, and Basement Membrane Composition". Journal of the American Society of Nephrology : JASN. 33 (8): 1546–1567. doi:10.1681/ASN.2021101343. PMC 9342632. PMID 35906089. Foot processes are actin-rich terminal projections that interdigitate to encapsulate the glomerular vasculature.
  5. ^ Gordon, GRJ; Mulligan, SJ; MacVicar, BA (September 2007). "Astrocyte control of the cerebrovasculature". Glia. 55 (12): 1214–1221. doi:10.1002/glia.20543. PMID 17659528. Endfeet are enlarged astrocytic compartments that appear to be specialized for the direct interaction with vessels.
  6. ^ a b Mescher, Anthony L. (2023). Junqueira's Basic Histology: Text and Atlas (17th ed.). McGraw-Hill Education. ISBN 978-1264930395.
  7. ^ Li, J; Chen, B; Fellows, GF; Goodyer, CG; Wang, R (2021). "Activation of Pancreatic Stellate Cells Is Beneficial for Exocrine but Not Endocrine Cell Differentiation in the Developing Human Pancreas". Frontiers in cell and developmental biology. 9: 694276. doi:10.3389/fcell.2021.694276. PMID 34490247. Based on their star ("stellate-like") shape with foot-like processes, PaSCs were found to surround cell clusters, ductal cells and newly formed islets, making complex cell-cell dendritic-like contacts.
  8. ^ Lindquist, JA; Bernhardt, A; Reichardt, C; Sauter, E; Brandt, S; Rana, R; Lindenmeyer, MT; Philipsen, L; Isermann, B; Zhu, C; Mertens, PR (19 May 2023). "Cold Shock Domain Protein DbpA Orchestrates Tubular Cell Damage and Interstitial Fibrosis in Inflammatory Kidney Disease". Cells. 12 (10). doi:10.3390/cells12101426. PMID 37408260. In this context, dendritic cells within the renal interstitium are ideally positioned for immune surveillance, as their foot processes extend into the tubules, allowing them to take up antigens.
  9. ^ Warren, AM; Grossmann, M; Christ-Crain, M; Russell, N (15 September 2023). "Syndrome of Inappropriate Antidiuresis: From Pathophysiology to Management". Endocrine reviews. 44 (5): 819–861. doi:10.1210/endrev/bnad010. PMC 10502587. PMID 36974717. The myelin sheath that protects axons is composed of foot processes of oligodendrocytes, supported by astrocytes that maintain homeostasis and form the blood-brain barrier.
  10. ^ Barkaway, A; Attwell, D; Korte, N (July 2022). "Immune-vascular mural cell interactions: consequences for immune cell trafficking, cerebral blood flow, and the blood-brain barrier". Neurophotonics. 9 (3): 031914. doi:10.1117/1.NPh.9.3.031914. PMC 9107322. PMID 35581998.
  11. ^ Hoyes, AD (January 1972). "Fine structure of human amniotic epithelium following short-term preservation in vitro". Journal of anatomy. 111 (Pt 1): 43–54. PMC 1271113. PMID 5016950. Well developed hemidesmosomes were present on the basal plasma membrane, and this was also often folded to form the basal or foot processes ...