corpus luteum

{{Short description|Temporary endocrine structure in ovaries}}

{{Infobox microanatomy

| Name = Corpus luteum

| Latin= corpus luteum

| Image =

| Caption = x

| Image2 = Gray1163.png

| Caption2 = Section of the ovary. 1. Outer covering. 1’. Attached border. 2. Central stroma. 3. Peripheral stroma. 4. Bloodvessels. 5. Vesicular follicles in their earliest stage. 6, 7, 8. More advanced follicles. 9. An almost mature follicle. 9’. Follicle from which the ovum has escaped. 10. Corpus luteum.

| Width = 300

| System = Reproductive system

| Location = Ovary

}}

The corpus luteum (Latin for "yellow body"; {{plural form}}: corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A.{{cite web |url=http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab19_ovary.html |title=Histology Laboratory Manual |website=www.columbia.edu|access-date=3 May 2018 |url-status=live |archive-url=https://web.archive.org/web/20170506050216/http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab19_ovary.html |archive-date=6 May 2017}}{{Cite book |title=Inquiry Into Biology |publisher=McGraw-Hill Ryerson |year=2007 |isbn=978-0-07-096052-7|pages=497 |type=Textbook}} It is the remains of the ovarian follicle that has released a mature ovum during a previous ovulation.{{sfn|Karch|2017|page=657}}

The corpus luteum is colored as a result of concentrating carotenoids (including lutein) from the diet and secretes a moderate amount of estrogen that inhibits further release of gonadotropin-releasing hormone (GnRH) and thus secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). A new corpus luteum develops with each menstrual cycle.

==Development and structure==

The corpus luteum develops from an ovarian follicle during the luteal phase of the menstrual cycle or oestrous cycle, following the release of a secondary oocyte from the follicle during ovulation. The follicle first forms a corpus hemorrhagicum before it becomes a corpus luteum, but the term refers to the visible collection of blood, left after rupture of the follicle, that secretes progesterone. While the oocyte (later the zygote if fertilization occurs) traverses the fallopian tube into the uterus, the corpus luteum remains in the ovary.{{cn|date=September 2023}}

The corpus luteum is typically very large relative to the size of the ovary; in humans, the size of the structure ranges from under 2 cm to 5 cm in diameter.{{cite web |url=http://www.rbmonline.com/Article/2155 |title=FSH and follucogenesis: from physiology to ovarian stimulation |work=Reproductive biomedicine Online |vauthors=Vegetti W, Alagna F |year=2006 |access-date=2009-05-26 |url-status=live |archive-url=https://web.archive.org/web/20110715155817/http://www.rbmonline.com/Article/2155 |archive-date=2011-07-15 }}

Its cells develop from the follicular cells surrounding the ovarian follicle.{{sfn|Boron|2005|page=1300}} The follicular theca cells luteinize into small luteal cells (thecal-lutein cells) and follicular granulosa cells luteinize into large luteal cells (granulosal-lutein cells) forming the corpus luteum. Progesterone is synthesized from cholesterol by both the large and small luteal cells upon luteal maturation. Cholesterol-LDL complexes bind to receptors on the plasma membrane of luteal cells and are internalized. Cholesterol is released and stored within the cell as cholesterol ester. LDL is recycled for further cholesterol transport. Large luteal cells produce more progesterone due to uninhibited/basal levels of protein kinase A (PKA) activity within the cell. Small luteal cells have LH receptors that regulate PKA activity within the cell. PKA actively phosphorylates steroidogenic acute regulatory protein (StAR) and translocator protein to transport cholesterol from the outer mitochondrial membrane to the inner mitochondrial membrane.{{cite journal | author = Niswender GD | title = Molecular control of luteal secretion of progesterone | journal = Reproduction | volume = 123 | issue = 3 | pages = 333–9 |date=March 2002 | pmid = 11882010 | doi = 10.1530/rep.0.1230333 | doi-access = free }}

The development of the corpus luteum is accompanied by an increase in the level of the steroidogenic enzyme P450scc that converts cholesterol to pregnenolone in the mitochondria.{{cite journal | vauthors = Rapoport R, Sklan D, Wolfenson D, Shaham-Albalancy A, Hanukoglu I | title = Antioxidant capacity is correlated with steroidogenic status of the corpus luteum during the bovine estrous cycle | journal = Biochim. Biophys. Acta | volume = 1380 | issue = 1 | pages = 133–40 |date=March 1998 | pmid = 9545562 | doi = 10.1016/S0304-4165(97)00136-0 | url = https://zenodo.org/record/890705 }} Pregnenolone is then converted to progesterone that is secreted out of the cell and into the blood stream. During the bovine estrous cycle, plasma levels of progesterone increase in parallel to the levels of P450scc and its electron donor adrenodoxin, indicating that progesterone secretion is a result of enhanced expression of P450scc in the corpus luteum.

The mitochondrial P450 system electron transport chain including adrenodoxin reductase and adrenodoxin has been shown to leak electrons leading to the formation of superoxide radical.{{cite journal | vauthors = Hanukoglu I, Rapoport R, Weiner L, Sklan D | title = Electron leakage from the mitochondrial NADPH-adrenodoxin reductase-adrenodoxin-P450scc (cholesterol side chain cleavage) system | journal = Arch. Biochem. Biophys. | volume = 305 | issue = 2 | pages = 489–98 |date=September 1993 | pmid = 8396893 | doi = 10.1006/abbi.1993.1452 | url = https://zenodo.org/record/890721 }}{{cite journal | vauthors = Rapoport R, Sklan D, Hanukoglu I | title = Electron leakage from the adrenal cortex mitochondrial P450scc and P450c11 systems: NADPH and steroid dependence | journal = Arch. Biochem. Biophys. | volume = 317 | issue = 2 | pages = 412–6 |date=March 1995 | pmid = 7893157 | doi = 10.1006/abbi.1995.1182 | url = https://zenodo.org/record/890751 }} Apparently to cope with the radicals produced by this system and by enhanced mitochondrial metabolism, the levels of antioxidant enzymes catalase and superoxide dismutase also increase in parallel with the enhanced steroidogenesis in the corpus luteum.

class="wikitable" ! Follicular structure	Luteal structure	Secretion
Theca cells	Theca lutein cells	androgens, progesterone
Granulosa cells	Granulosa lutein cells	progesterone,{{sfn|Boron|2005|page=1300}} estrogen(majority),{{sfn|Boron|2005|page=1300}} and inhibin A{{sfn|Boron|2005|page=1300}}[http://www.bioeng.auckland.ac.nz/physiome/ontologies/female_repro_system/cells.php The IUPS Physiome Project --> Female Reproductive System – Cells] {{webarchive|url=https://web.archive.org/web/20091210133027/http://www.bioeng.auckland.ac.nz/physiome/ontologies/female_repro_system/cells.php |date=2009-12-10 }} Retrieved on Nov 9, 2009

File:Steroidogenesis.svg, with progesterone in yellow field at upper center.{{cite journal|last2=Richfield|first2=David|year=2014|title=Diagram of the pathways of human steroidogenesis|journal=WikiJournal of Medicine|volume=1|issue=1|doi=10.15347/wjm/2014.005|issn=2002-4436|last1=Häggström|first1=Mikael|doi-access=free}} The androgens are shown in blue field, and aromatase at lower center – the enzyme present in granulosa lutein cells that convert androgens into estrogens (shown in pink triangle).]]

Like the previous theca cells, the theca lutein cells lack the aromatase enzyme that is necessary to produce estrogen, so they can only perform steroidogenesis until formation of androgens. The granulosa lutein cells do have aromatase, and use it to produce estrogens, using the androgens previously synthesized by the theca lutein cells, as the granulosa lutein cells in themselves do not have the 17α-hydroxylase or 17,20 lyase to produce androgens.{{sfn|Boron|2005|page=1300}}

Once the corpus luteum regresses the remnant is known as corpus albicans.{{cite book | last = Marieb | first = Elaine | title = Anatomy & physiology | publisher = Benjamin-Cummings | page= 915 | year = 2013 | isbn = 9780321887603 }}