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Luteinizing hormone
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Chorionic gonadotropin alpha
Identifiers
Symbol
CGA
Alt. symbols
HCG, GPHa, GPHA1
Entrez
1081
HUGO
1885
OMIM
118850
RefSeq
NM_000735
UniProt
P01215
Other data
Locus
Chr. 6 q14-q21
Luteinizing hormone beta polypeptide
Identifiers
Symbol
LHB
Entrez
3972
HUGO
6584
OMIM
152780
RefSeq
NM_000894
UniProt
P01229
Other data
Locus
Chr. 19 q13.3
Luteinizing hormone (LH, also known as lutropin and sometimes lutrophin[1]) is a hormone produced by gonadotropic cells in the anterior pituitary gland. In females, an acute rise of LH ("LH surge") triggers ovulation[2] and development of the corpus luteum. In males, where LH had also been called interstitial cell–stimulating hormone (ICSH),[3] it stimulates Leydig cell production of testosterone.[2] It acts synergistically with FSH.
Contents
[hide]
1 Structure
2 Genes
3 Function
3.1 Effects in females
3.2 Effects in males
4 Normal levels
5 Predicting ovulation
6 Disease states
6.1 Excess
6.2 Deficiency
7 As a medication
8 References
9 External links
Structure[edit]
LH is a heterodimeric glycoprotein. Each monomeric unit is a glycoprotein molecule; one alpha and one beta subunit make the full, functional protein.
Its structure is similar to that of the other glycoprotein hormones, follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG). The protein dimer contains 2 glycopeptidic subunits, labeled alpha and beta subunits, that are non-covalently associated (i.e., without any disulfide bridge linking them):[4]
The alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino acids in human but 96 amino acids in almost all other vertebrate species (glycoprotein hormones do not exist in invertebrates).
The beta subunits vary. LH has a beta subunit of 120 amino acids (LHB) that confers its specific biologic action and is responsible for the specificity of the interaction with the LH receptor. This beta subunit contains an amino acid sequence that exhibits large homologies with that of the beta subunit of hCG and both stimulate the same receptor. However, the hCG beta subunit contains an additional 24 amino acids, and the two hormones differ in the composition of their sugar moieties.
The different composition of these oligosaccharides affects bioactivity and speed of degradation. The biologic half-life of LH is 20 minutes, shorter than that of FSH (3–4 hours) and hCG (24 hours).[citation needed]
Genes[edit]
The gene for the alpha subunit is located on chromosome 6q12.21.
The luteinizing hormone beta subunit gene is localized in the LHB/CGB gene cluster on chromosome 19q13.32. In contrast to the alpha gene activity, beta LH subunit gene activity is restricted to the pituitary gonadotropic cells. It is regulated by the gonadotropin-releasing hormone from the hypothalamus. Inhibin, activin, and sex hormones do not affect genetic activity for the beta subunit production of LH.
Function[edit]
Effects of LH on the body
In females: ovulation, maintaining of corpus luteum and secretion of progesterone.
In males: testosterone secretion.
Effects in females[edit]
LH supports theca cells in the ovaries that provide androgens and hormonal precursors for estradiol production. At the time of menstruation, FSH initiates follicular growth, specifically affecting granulosa cells.[5] With the rise in estrogens, LH receptors are also expressed on the maturing follicle, which causes it to produce more estradiol. Eventually, when the follicle has fully matured, a spike in 17α-hydroxyprogesterone production by the follicle inhibits the production of estrogens, leading to a decrease in estrogen-mediated negative feedback of GnRH in the hypothalamus, which then stimulates the release of LH from the anterior pituitary.[6] However another theory of the LH peak is a positive feedback mechanism from estradiol. The levels keep rising through the follicular phase and when they reach an unknown threshold, this results in the peak of the LH.[7] This effect is opposite from the usual negative feedback mechanism presented at lower levels. In other words, the mechanism(s) are not yet clear. The increase in LH production only lasts for 24 to 48 hours. This "LH surge" triggers ovulation, thereby not only releasing the egg from the follicle, but also initiating the conversion of the residual follicle into a corpus luteum that, in turn, produces progesterone to prepare the endometrium for a possible implantation. LH is necessary to maintain luteal function for the second two weeks of the menstrual cycle. If pregnancy occurs, LH levels will decrease, and luteal function will instead be maintained by the action of hCG (human chorionic gonadotropin), a hormone very similar to LH but secreted from the new placenta.
Gonadal steroids (estrogens and androgens) generally have negative feedback effects on GnRH-1 release at the level of the hypothalamus and at the gonadotropes, reducing their sensitivity to GnRH. Positive feedback by estrogens also occurs in the gonadal axis of female mammals and is responsible for the midcycle surge of LH that stimulates ovulation. Although estrogens inhibit kisspeptin (Kp) release from kiss1 neurons in the ARC, estrogens stimulate Kp release from the Kp neurons in the AVPV. As estrogens' levels gradually increase the positive effect predominates, leading to the LH surge. GABA-secreting neurons that innervate GnRH-1 neurons also can stimulate GnRH-1 release. These GABA neurons also possess ERs and may be responsible for the GnRH-1 surge. Part of the inhibitory action of endorphins on GnRH-1 release is through inhibition of these GABA neurons. Rupture of the ovarian follicle at ovulation causes a drastic reduction in estrogen synthesis and a marked increase in secretion of progesterone by the corpus luteum in the ovary, reinstating a predominantly negative feedback on hypothalamic secretion of GnRH-1.[8]
Effects in males[edit]
LH acts upon the Leydig cells of the testis and is regulated by gonadotropin-releasing hormone (GnRH).[9] The Leydig cells produce testosterone (T) under the control of LH, which regulates the expression of the enzyme 17β-hydroxysteroid dehydrogenase that is used to convert androstenedione, the hormone produced by the testes, to testosterone,[10] an androgen that exerts both endocrine activity and intratesticular activity on spermatogenesis.
LH is released from the pituitary gland, and is controlled by pulses of gonadotropin-releasing hormone. When T levels are low, GnRH is released by the hypothalamus, stimulating the pituitary gland to release LH.[9] As the levels of T increase, it will act on the hypothalamus and pituitary through a negative feedback loop and inhibit the release of GnRH and LH consequently.[10] Androgens (T, DHT) inhibit monoamine oxidase (MAO) in pineal, leading to increased melatonin and reduced LH and FSH by melatonin-induced increase of GnIH synthesis and secretion. T can also be aromatized into estradiol (E2) to inhibit LH. E2 decreases pulse amplitude and responsiveness to GnRH from the hypothalamus onto the pituitary.[11]
Changes in LH and testosterone (T) blood levels and pulse secretions are induced by changes in sexual arousal in human males.[12]
Normal levels[edit]
Reference ranges for the blood content of luteinizing hormone (LH) during the menstrual cycle.[13]
The ranges denoted By biological stage may be used in closely monitored menstrual cycles in regard to other markers of its biological progression, with the time scale being compressed or stretched to how much faster or slower, respectively, the cycle progresses compared to an average cycle.
The ranges denoted Inter-cycle variability are more appropriate to use in non-monitored cycles with only the beginning of menstruation known, but where the woman accurately knows her average cycle lengths and time of ovulation, and that they are somewhat averagely regular, with the time scale being compressed or stretched to how much a woman's average cycle length is shorter or longer, respectively, than the average of the population.
The ranges denoted Inter-woman variability are more appropriate to use when the average cycle lengths and time of ovulation are unknown, but only the beginning of menstruation is given.
LH levels are normally low during childhood and, in women, high after menopause. As LH is secreted as pulses, it is necessary to follow its concentration over a sufficient period of time to get proper information about its blood level.
During the reproductive years, typical levels are between 1–20 IU/L. Physiologic high LH levels are seen during the LH surge (v.s.); typically they last 48 hours.
In males over 18 years of age, reference ranges have been estimated to be 1.8–8.6 IU/L.[14]
LH is measured in international units (IU). When quantifying the amount of LH in a sample in IUs, it is important to know which international standard your lot of LH was calibrated against, as they can vary broadly from year to year. For human urinary LH, one IU is most recently defined as 1/189th of an ampule denoted 96/602 and distributed by the NIBSC, corresponding to approximately 0.04656µg of LH protein for a single IU, but older standard versions are still widely in use.[15][16]
Predicting ovulation[edit]
Chance of fertilization by menstrual cycle day relative to ovulation.[17]
The detection of a surge in release of luteinizing hormone indicates impending ovulation. LH can be detected by urinary ovulation predictor kits (OPK, also LH-kit) that are performed, typically daily, around the time ovulation may be expected.[18] A conversion from a negative to a positive reading would suggest that ovulation is about to occur within 24–48 hours, giving women two days to engage in sexual intercourse or artificial insemination with the intention of conceiving.[19]
The recommended testing frequency differs between manufacturers. For example, the Clearblue test is taken daily, and an increased frequency does not decrease the risk of missing an LH surge.[20] On the other hand, the Chinese company Nantong Egens Biotechnology recommends using their test twice per day.[21] If testing once per day, no significant difference has been found between testing LH in the morning versus in the evening, in relation to conception rates,[22] and recommendations of what time in the day to take the test varies between manufacturers and healthcare workers.[23] Tests may be read manually using a colour-change paper strip, or digitally with the assistance of reading electronics.
Tests for luteinising hormone may be combined with testing for estradiol in tests such as the Clearblue fertility monitor.[24]
The sensitivity of LH tests are measured in milli international unit, with tests commonly available in the range 10–40 m.i.u. (the lower the number, the higher the sensitivity).[citation needed]
As sperm can stay viable in the woman for several days, LH tests are not recommended for contraceptive practices, as the LH surge typically occurs after the beginning of the fertile window.
Disease states[edit]
Excess[edit]
In children with precocious puberty of pituitary or central origin, LH and FSH levels may be in the reproductive range instead of the low levels typical for their age.
During the reproductive years, relatively elevated LH is frequently seen in patients with polycystic ovary syndrome; however, it would be unusual for them to have LH levels outside of the normal reproductive range.
Persistently high LH levels are indicative of situations where the normal restricting feedback from the gonad is absent, leading to a pituitary production of both LH and FSH. While this is typical in menopause, it is abnormal in the reproductive years. There it may be a sign of:
Premature menopause
Gonadal dysgenesis, Turner syndrome
Castration
Swyer syndrome
Polycystic ovary syndrome
Certain forms of congenital adrenal hyperplasia
Testicular failure
Pregnancy - BetaHCG can mimic LH so tests may show elevated LH
Note: A medical drug for inhibiting luteinizing hormone secretion is Butinazocine.[25]
Deficiency[edit]
Diminished secretion of LH can result in failure of gonadal function (hypogonadism). This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, amenorrhea is commonly observed. Conditions with very low LH secretions include:
Pasqualini syndrome[26][27][28]
Kallmann syndrome
Hypothalamic suppression
Hypopituitarism
Eating disorder
Female athlete triad
Hyperprolactinemia
Hypogonadism
Gonadal suppression therapy
GnRH antagonist
GnRH agonist (inducing an initial stimulation (flare up) followed by permanent blockage of the GnRH pituitary receptor)
As a medication[edit]
LH is available mixed with FSH in the form of menotropin, and other forms of urinary gonadotropins. More purified forms of urinary gonadotropins may reduce the LH portion in relation to FSH. Recombinant LH is available as lutropin alfa (Luveris).[29] All these medications have to be given parenterally. They are commonly used in infertility therapy to stimulate follicular development, the notable one being in IVF therapy.
Often, HCG medication is used as an LH substitute because it activates the same receptor. Medically used hCG is derived from urine of pregnant women, is less costly, and has a longer half-life than LH.
References[edit]
Jump up ^ Ujihara M, Yamamoto K, Nomura K, Toyoshima S, Demura H, Nakamura Y, Ohmura K, Osawa T (June 1992). "Subunit-specific sulphation of oligosaccharides relating to charge-heterogeneity in porcine lutrophin isoforms". Glycobiology. 2 (3): 225–31. doi:10.1093/glycob/2.3.225. PMID 1498420.
^ Jump up to: a b Physiology: 5/5ch9/s5ch9_5 - Essentials of Human Physiology
Jump up ^ Louvet JP, Harman SM, Ross GT (May 1975). "Effects of human chorionic gonadotropin, human interstitial cell stimulating hormone and human follicle-stimulating hormone on ovarian weights in estrogen-primed hypophysectomized immature female rats". Endocrinology. 96 (5): 1179–86. doi:10.1210/endo-96-5-1179. PMID 1122882.
Jump up ^ Jiang X, Dias JA, He X (January 2014). "Structural biology of glycoprotein hormones and their receptors: insights to signaling". Molecular and Cellular Endocrinology. 382 (1): 424–51. doi:10.1016/j.mce.2013.08.021. PMID 24001578.
Jump up ^ Bowen, R. (13 May 2004). "Gonadotropins: Luteinizing and Follicle Stimulating Hormones". Colorado State University. Retrieved 12 March 2012.
Jump up ^ Mahesh VB (January 2012). "Hirsutism, virilism, polycystic ovarian disease, and the steroid-gonadotropin-feedback system: a career retrospective". American Journal of Physiology. Endocrinology and Metabolism. 302 (1): E4–E18. doi:10.1152/ajpendo.00488.2011. PMC 3328092  . PMID 22028409.
Jump up ^ Guyton and Hall Textbook of Medical Physiology 2006 page 1021
Jump up ^ Norris DO, Carr JA (2013). Vertebrate Endocrinology. Academic Press. p. 126. ISBN 978-0-12-396465-6.
^ Jump up to: a b "Male Medical Fertility Treatment: HCG + LH + Recombinant FSH To Increase Sperm Count Through Spermatogenisis". Archived from the original on February 19, 2015. Retrieved 6 April 2015. [unreliable medical source?]
^ Jump up to: a b "The onset of puberty is controlled by two major hormones: FSH initiates spermatogenesis and LH signals the release of testosterone". Retrieved 6 April 2015. [unreliable medical source?]
Jump up ^ Pitteloud N, Dwyer AA, DeCruz S, Lee H, Boepple PA, Crowley WF, Hayes FJ (March 2008). "Inhibition of luteinizing hormone secretion by testosterone in men requires aromatization for its pituitary but not its hypothalamic effects: evidence from the tandem study of normal and gonadotropin-releasing hormone-deficient men". The Journal of Clinical Endocrinology and Metabolism. 93 (3): 784–91. doi:10.1210/jc.2007-2156. PMC 2266963  . PMID 18073301.
Jump up ^ Stoléru SG, Ennaji A, Cournot A, Spira A (1993). "LH pulsatile secretion and testosterone blood levels are influenced by sexual arousal in human males". Psychoneuroendocrinology. 18 (3): 205–18. doi:10.1016/0306-4530(93)90005-6. PMID 8516424.
Jump up ^ Häggström, Mikael (2014). "Reference ranges for estradiol, progesterone, luteinizing hormone and follicle-stimulating hormone during the menstrual cycle". WikiJournal of Medicine. 1 (1). doi:10.15347/wjm/2014.001. ISSN 2002-4436.
Jump up ^ Mayo Medical Laboratories - Test ID: LH, Luteinizing Hormone (LH), Serum, retrieved December 2012
Jump up ^ World Health Organization Proposed International Standard for Luteinizing Hormone. WHO Expert Committee on Biological Standardization. World Health Organization. Geneva. 2003.
Jump up ^ WHO International Standard, Luteinizing Hormone, Human, Recombinant. National Institute for Biological Standards and Control.
Jump up ^ Dunson, D.B.; Baird, D.D.; Wilcox, A.J.; Weinberg, C.R. (1999). "Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation". Human Reproduction. 14 (7): 1835–1839. doi:10.1093/humrep/14.7.1835. ISSN 1460-2350.
Jump up ^ Nielsen MS, Barton SD, Hatasaka HH, Stanford JB (August 2001). "Comparison of several one-step home urinary luteinizing hormone detection test kits to OvuQuick". Fertility and Sterility. 76 (2): 384–7. doi:10.1016/S0015-0282(01)01881-7. PMID 11476792.
Jump up ^ "Ovulation Predictor Kit Frequently Asked Questions". Fertility Plus. Archived from the original on March 12, 2012. Retrieved 12 March 2012. [unreliable medical source?]
Jump up ^ "Clear Blue Ovulation Test Instructions". Ovulation Guide. Retrieved 2018-01-19.
Jump up ^ "Advanced Ovulation Test" (PDF). Homehealth-UK. Retrieved 2018-01-19. Version 1.1 02/11/15
Jump up ^ Martinez AR, Bernardus RE, Vermeiden JP, Schoemaker J (1994). "Time schedules of intrauterine insemination after urinary luteinizing hormone surge detection and pregnancy results". Gynecol Endocrinol. 8 (1): 1–5. PMID 8059611.
Jump up ^ Page 67 in: Godwin I. Meniru (2001). Cambridge Guide to Infertility Management and Assisted Reproduction. Cambridge University Press.
Jump up ^ "How to Get Pregnant". OPregnancy.com. 2009. Archived from the original on March 12, 2012. Retrieved 12 March 2012. [unreliable medical source?]
Jump up ^ U.S. Patent 4,406,904
Jump up ^ Weiss J, Axelrod L, Whitcomb RW, Harris PE, Crowley WF, Jameson JL (January 1992). "Hypogonadism caused by a single amino acid substitution in the beta subunit of luteinizing hormone". The New England Journal of Medicine. 326 (3): 179–83. doi:10.1056/NEJM199201163260306. PMID 1727547.
Jump up ^ Valdes-Socin H, Salvi R, Daly AF, Gaillard RC, Quatresooz P, Tebeu PM, Pralong FP, Beckers A (December 2004). "Hypogonadism in a patient with a mutation in the luteinizing hormone beta-subunit gene". The New England Journal of Medicine. 351 (25): 2619–25. doi:10.1056/NEJMoa040326. PMID 15602022.
Jump up ^ Valdes-Socin H, Daly AF, Beckers A (2017). "Luteinizing Hormone Deficiency: Historical Views and Future Perspectives" (PDF). Austin Andrology. 2 (1): 1015.
Jump up ^ Luveris information[unreliable medical source?] Archived June 18, 2006, at the Wayback Machine.
External links[edit]
Luteinizing Hormone at the US National Library of Medicine Medical Subject Headings (MeSH)

[show]
v
t
e
GnRH and gonadotropins
GnRH modulators
(incl. analogues)
Agonists
Peptide: Azagly-nafarelin
Buserelin
Deslorelin
Fertirelin
Gonadorelin
Goserelin
Histrelin
Lecirelin
Leuprorelin (leuprolide)
Nafarelin
Peforelin
Salmon GnRH
Triptorelin
Antagonists
Peptide: Abarelix
Cetrorelix
Degarelix
Ganirelix
Ozarelix§
Non-peptide: Elagolix†
Linzagolix†
Opigolix§
Relugolix†
Gonadotropins
Preparations
Follicle-stimulating hormone
Human chorionic gonadotropin
Luteinizing hormone
Menotropin
Urofollitropin
Others
(indirect)
Progonadotropins
Sex steroid antagonists (via disinhibition of the HPG axis): Antiandrogens (e.g., flutamide, bicalutamide, enzalutamide)
Antiestrogens/SERMs (e.g., tamoxifen, clomifene, enclomifene)
Aromatase inhibitors (e.g., anastrozole)
GnRH agonists (e.g., GnRH)
Antigonadotropins
Sex steroid agonists (via negative feedback on the HPG axis): Androgens/anabolic steroids (e.g., testosterone, nandrolone esters, oxandrolone)
D2 receptor antagonists (prolactin releasers) (incl., domperidone, metoclopramide, risperidone, haloperidol, chlorpromazine, sulpiride)
Estrogens (incl., bifluranol, estradiol, estradiol esters, ethinylestradiol, diethylstilbestrol, paroxypropione)
Progestogens (incl. progestins, e.g., chlormadinone acetate, cyproterone acetate, hydroxyprogesterone caproate, gestonorone caproate, medroxyprogesterone acetate, megestrol acetate)
Others (mixed or unknown mechanism of action): Danazol
Gestrinone
Metallibure
#WHO-EM
‡Withdrawn from market
Clinical trials:
†Phase III
§Never to phase III
See also
GnRH and gonadotropin receptor modulators
Androgens and antiandrogens
Estrogens and antiestrogens
Progestogens and antiprogestogens
[show]
v
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e
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[show]
v
t
e
GnRH and gonadotropin receptor modulators
GnRH
Agonists: Peptide: Avorelin
Azagly-nafarelin
Buserelin
Deslorelin
Fertirelin
GnRH
Gonadorelin
Goserelin
Histrelin
Leuprorelin (leuprolide)
Lutrelin
Nafarelin
Peforelin
Triptorelin
Zoptarelin doxorubicin
Antagonists: Peptide: Abarelix
Acyline
Cetrorelix
Degarelix
Detirelix
Ganirelix
Iturelix
Ozarelix
Prazarelix
Ramorelix
Teverelix (antarelix); Non-peptide: Elagolix
Linzagolix
Opigolix
Relugolix
Sufugolix
Gonadotropin
LH/hCG
Agonists: Peptide: Choriogonadotropin alfa
Human chorionic gonadotropin
Luteinizing hormone
Lutropin alfa
Menotropin (human menopausal gonadotropin)
FSH
Agonists: Peptide: Corifollitropin alfa
Follicle-stimulating hormone
Follitropin alfa
Follitropin beta
Follitropin epsilon
Menotropin (human menopausal gonadotropin)
Urofollitropin
Varfollitropin alfa
NAMs: Non-peptide: ADX-61623
See also: Receptor/signaling modulators • Signaling peptide/protein receptor modulators • GnRH and gonadotropins
Retrieved from "https://en.wikipedia.org/w/index.php?title=Luteinizing_hormone&oldid=837173899"
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Mark Humphrey (actor)
From Wikipedia, the free encyclopedia
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Mark Humphrey
Born
Mark Adrian Humphrey
(1960-12-27) December 27, 1960 (age 57)
Vancouver, British Columbia, Canada
Nationality
Canadian
Occupation
Actor
Years active
1985–present
Website
http://www.markhumphrey.com/
Mark Adrian Humphrey (born December 27, 1960 in Vancouver, British Columbia) is a Canadian actor best known for the role of Jake Antonelli in the Canadian television series E.N.G.[1][2] In 1988 he made his feature film debut in the film Iron Eagle II [3][4] as Captain Matt Cooper, Doug Masters' (Jason Gedrick) surviving best friend. Humphrey has been featured in other films and in several television movies. In 2005 he starred in Living With the Enemy with Sarah Lancaster. In 2006 he starred in The Wives He Forgot with Molly Ringwald as a handsome amnesiac. In 2007 he appeared in Still Small Voices with Catherine Bell. Humphrey has also appeared in numerous television series.
In 2009 Humphrey appeared in the Canadian dramatic series Paradise Falls,[5] and the television movies Encounter with Danger with Shannen Doherty, and Hostile Makeover with Maggie Lawson. He appeared in the 2010 feature film Summer Eleven. In 2015 Humphrey joined the cast of the Hallmark Channel series When Calls the Heart as mysterious preacher Frank Hogan.[6] [7]
Humphrey appeared in the 2005 independent film Cruel But Necessary with his ex-wife Wendel Meldrum and their son Luke Humphrey.[8]
Biography[edit]
Humphrey was born in Vancouver, British Columbia to parents Jack and Sidney Humphrey. His family relocated to Toronto, Ontario in 1967, where his father, Jack Humphrey, worked as a producer for CBC Radio and Television. After graduating from high school, Humphrey moved to New York City to study acting at the Lee Strasberg Theatre and Film Institute. Humphrey spent five years in New York, later returning to Toronto, and eventually relocating to California.
Humphrey has four siblings. His three brothers, John, Paul, and Andy, are professional musicians. His sister, Lesley, is a former Ford model.
References[edit]
Jump up ^ "E.N.G. Canadian Drama,". Museum.tv. Retrieved 18 October 2014.
Jump up ^ "E.N.G. Cast Photo,". Broadcasting-History.ca. Archived from the original on 23 September 2015. Retrieved 1 October 2014.
Jump up ^ "Iron Eagle II Review". Variety. December 31, 1987. Retrieved 18 October 2014.
Jump up ^ "Iron Eagle II,". MovieStillDB.com. Retrieved 18 October 2014.
Jump up ^ Wild, Diane (August 9, 2007). "Paradise Falls Season 3,". TV-Eh.com. Retrieved 1 October 2014.
Jump up ^ Wang, K.L. Connie (June 9, 2015). "Mark Humphrey: When Calls the Heart's Newest Blessing,". Parade Magazine. Retrieved 13 June 2015.
Jump up ^ "Interview With Actor Mark Humphrey, "When Calls the Heart",". My Devotional Thoughts. February 17, 2017. Retrieved 25 April 2017.
Jump up ^ Schaefer, Glen (September 2007). "Small Project Fed Director's Soul,". The Vancouver Province. Archived from the original on 17 October 2014. Retrieved 1 October 2014.
External links[edit]
Official website
Mark Humphrey on IMDb
E.N.G. Cast Photo Link at the Broadcast History Site
Authority control
WorldCat Identities
VIAF: 268538658
SNAC: w6b03d1g

This article about a Canadian actor or actress is a stub. You can help Wikipedia by expanding it.
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Nucleolus
From Wikipedia, the free encyclopedia
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This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (October 2012) (Learn how and when to remove this template message)
The nucleolus is contained within the cell nucleus.
Images from "The Nucleolus"[1] DIC images
tripartite organization
granular component
The nucleolus (/njuːˈkliːələs/ or /ˌnjuːkliˈoʊləs/, plural nucleoli /njuːˈkliːəˌlaɪ/ or /ˌnjuːkliˈoʊlaɪ/) is the largest structure in the nucleus of eukaryotic cells.[2] It is best known as the site of ribosome biogenesis. Nucleoli also participate in the formation of signal recognition particles and play a role in the cell's response to stress.[3] Nucleoli are made of proteins, DNA and RNA and form around specific chromosomal regions called nucleolar organizing regions. Malfunction of nucleoli can be the cause of several human conditions called "nucleolopathies"[4] and the nucleolus is being investigated as a target for cancer chemotherapy.[5][6]
Contents
[hide]
1 History
2 Structure
3 Function and ribosome assembly
4 Sequestration of proteins
5 See also
6 References
7 External links
History[edit]
The nucleolus was identified by bright-field microscopy during the 1830s.[1] Little was known about the function of the nucleolus until 1964, when a study[7] of nucleoli by John Gurdon and Donald Brown in the African clawed frog Xenopus laevis generated increasing interest in the function and detailed structure of the nucleolus. They found that 25% of the frog eggs had no nucleolus and that such eggs were not capable of life. Half of the eggs had one nucleolus and 25% had two. They concluded that the nucleolus had a function necessary for life. In 1966 Max L. Birnstiel and collaborators showed via nucleic acid hybridization experiments that DNA within nucleoli code for ribosomal RNA.[8][9]
Transcription in the FC, fibrillarin & nucleophosmin[10]
Structure[edit]
Three major components of the nucleolus are recognized: the fibrillar center (FC), the dense fibrillar component (DFC), and the granular component (GC).[2] Transcription of the rDNA occurs in the FC.[10] The DFC contains the protein fibrillarin,[10] which is important in rRNA processing. The GC contains the protein nucleophosmin,[10] (B23 in the external image) which is also involved in ribosome biogenesis.
Structure of the eukaryotic rDNA repeat.[2]
However, it has been proposed that this particular organization is only observed in higher eukaryotes and that it evolved from a bipartite organization with the transition from anamniotes to amniotes. Reflecting the substantial increase in the DNA intergenic region, an original fibrillar component would have separated into the FC and the DFC.[11]
Play media
Nucleus from a cell line. Fibrillarin in red. Transcription regulatory protein CTCFL in green. Nuclear DNA in blue.
Another structure identified within many nucleoli (particularly in plants) is a clear area in the center of the structure referred to as a nucleolar vacuole.[12] Nucleoli of various plant species have been shown to have very high concentrations of iron[13] in contrast to human and animal cell nucleoli.
The nucleolus ultrastructure can be visualized through an electron microscope, while the organization and dynamics can be studied through fluorescent protein tagging and fluorescent recovery after photobleaching (FRAP). Antibodies against the PAF49 protein can also be used as a marker for the nucleolus in immunofluorescence experiments.[14]
Function and ribosome assembly[edit]
Electron micrograph of part of a HeLa cell. The image is a screen capture from this movie, which shows a Z-stack of the cell.
In ribosome biogenesis, two of the three eukaryotic RNA polymerases (pol I and III) are required, and these function in a coordinated manner. In an initial stage, the rRNA genes are transcribed as a single unit within the nucleolus by RNA polymerase I. In order for this transcription to occur, several pol I-associated factors and DNA-specific trans-acting factors are required. In yeast, the most important are: UAF (upstream activating factor), TBP (TATA-box binding protein), and CF (core factor), which bind promoter elements and form the preinitiation complex (PIC), which is in turn recognized by RNA pol. In humans, a similar PIC is assembled with SL1, the promoter selectivity factor (composed of TBP and TBP-associated factors, or TAFs), transcription initiation factors, and UBF (upstream binding factor). RNA polymerase I transcribes most rRNA transcripts (28S, 18S, and 5.8S) but the 5S rRNA subunit (component of the 60S ribosomal subunit) is transcribed by RNA polymerase III.[15]
Transcription of rRNA yields a long precursor molecule (45S pre-rRNA) which still contains the ITS and ETS. Further processing is needed to generate the 18S RNA, 5.8S and 28S RNA molecules. In eukaryotes, the RNA-modifying enzymes are brought to their respective recognition sites by interaction with guide RNAs, which bind these specific sequences. These guide RNAs belong to the class of small nucleolar RNAs (snoRNAs) which are complexed with proteins and exist as small-nucleolar-ribonucleoproteins (snoRNPs). Once the rRNA subunits are processed, they are ready to be assembled into larger ribosomal subunits. However, an additional rRNA molecule, the 5S rRNA, is also necessary. In yeast, the 5S rDNA sequence is localized in the intergenic spacer and is transcribed in the nucleolus by RNA pol.
In higher eukaryotes and plants, the situation is more complex, for the 5S DNA sequence lies outside the Nucleolus Organiser Region (NOR) and is transcribed by RNA pol III in the nucleoplasm, after which it finds its way into the nucleolus to participate in the ribosome assembly. This assembly not only involves the rRNA, but ribosomal proteins as well. The genes encoding these r-proteins are transcribed by pol II in the nucleoplasm by a "conventional" pathway of protein synthesis (transcription, pre-mRNA processing, nuclear export of mature mRNA and translation on cytoplasmic ribosomes). The mature r-proteins are then "imported" back into the nucleus and finally the nucleolus. Association and maturation of rRNA and r-proteins result in the formation of the 40S (small) and 60S (large) subunits of the complete ribosome. These are exported through the nuclear pore complexes to the cytoplasm, where they remain free or become associated with the endoplasmic reticulum, forming rough endoplasmic reticulum (RER).[16][17]
In human endometrial cells, a network of nucleolar channels is sometimes formed. The origin and function of this network has not yet been clearly identified.[18]
Sequestration of proteins[edit]
In addition to its role in ribosomal biogenesis, the nucleolus is known to capture and immobilize proteins, a process known as nucleolar detention. Proteins that are detained in the nucleolus are unable to diffuse and to interact with their binding partners. Targets of this post-translational regulatory mechanism include VHL, PML, MDM2, POLD1, RelA, HAND1 and hTERT, among many others. It is now known that long noncoding RNAs originating from intergenic regions of the nucleolus are responsible for this phenomenon.[19]
Cell biology
The animal cell
Components of a typical animal cell:
Nucleolus
Nucleus
Ribosome (little dots)
Vesicle
Rough endoplasmic reticulum
Golgi apparatus (or "Golgi body")
Cytoskeleton
Smooth endoplasmic reticulum
Mitochondrion
Vacuole
Cytosol (fluid that contains organelles, comprising the cytoplasm)
Lysosome
Centrosome
Cell membrane
See also[edit]
Differential interference contrast microscopy
References[edit]
^ Jump up to: a b Pederson T (2011). "The nucleolus". Cold Spring Harbor Perspectives in Biology. 3 (3). PMC 3039934  . PMID 21106648. doi:10.1101/cshperspect.a000638.
^ Jump up to: a b c O'Sullivan JM, Pai DA, Cridge AG, Engelke DR, Ganley AR (2013). "The nucleolus: a raft adrift in the nuclear sea or the keystone in nuclear structure?". Biomolecular Concepts. 4 (3): 277–86. PMC 5100006  . PMID 25436580. doi:10.1515/bmc-2012-0043.
Jump up ^ Olsen, Mark OJ (December 2010). "Nucleolus: Structure and Function". ELS. ISBN 0470016175. doi:10.1002/9780470015902.a0005975.pub2. Retrieved 17 October 2014.
Jump up ^ Hetman M (2014). "Role of the nucleolus in human diseases. Preface". Biochimica et Biophysica Acta. 1842 (6): 757. PMID 24631655. doi:10.1016/j.bbadis.2014.03.004.
Jump up ^ Quin JE, Devlin JR, Cameron D, Hannan KM, Pearson RB, Hannan RD (2014). "Targeting the nucleolus for cancer intervention". Biochimica et Biophysica Acta. 1842 (6): 802–16. PMID 24389329. doi:10.1016/j.bbadis.2013.12.009.
Jump up ^ Woods SJ, Hannan KM, Pearson RB, Hannan RD (2015). "The nucleolus as a fundamental regulator of the p53 response and a new target for cancer therapy". Biochimica et Biophysica Acta. 1849 (7): 821–9. PMID 25464032. doi:10.1016/j.bbagrm.2014.10.007.
Jump up ^ BROWN DD, GURDON JB (1964). "ABSENCE OF RIBOSOMAL RNA SYNTHESIS IN THE ANUCLEOLATE MUTANT OF XENOPUS LAEVIS" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 51: 139–46. PMC 300879  . PMID 14106673.
Jump up ^ Birnstiel ML, Wallace H, Sirlin JL, Fischberg M (1966). "Localization of the ribosomal DNA complements in the nucleolar organizer region of Xenopus laevis". National Cancer Institute Monograph. 23: 431–47. PMID 5963987.
Jump up ^ Wallace H, Birnstiel ML (1966). "Ribosomal cistrons and the nucleolar organizer". Biochimica et Biophysica Acta. 114 (2): 296–310. PMID 5943882.
^ Jump up to: a b c d Sirri V, Urcuqui-Inchima S, Roussel P, Hernandez-Verdun D (2008). "Nucleolus: the fascinating nuclear body". Histochemistry and Cell Biology. 129 (1): 13–31. PMC 2137947  . PMID 18046571. doi:10.1007/s00418-007-0359-6.
Jump up ^ Thiry M, Lafontaine DL (2005). "Birth of a nucleolus: the evolution of nucleolar compartments". Trends Cell Biol. 15 (4): 194–9. PMID 15817375. doi:10.1016/j.tcb.2005.02.007. as PDF
Jump up ^ Beven AF, Lee R, Razaz M, Leader DJ, Brown JW, Shaw PJ (1 June 1996). "The organization of ribosomal RNA processing correlates with the distribution of nucleolar snRNAs". J. Cell. Sci. 109 (6): 1241–51. PMID 8799814.
Jump up ^ Roschzttardtz H, Grillet L, Isaure MP, et al. (2011). "Plant cell nucleolus as a hot spot for iron". J. Biol. Chem. 286 (32): 27863–6. PMC 3151030  . PMID 21719700. doi:10.1074/jbc.C111.269720.
Jump up ^ PAF49 antibody | GeneTex Inc. Genetex.com. Retrieved on 2013-03-03.
Jump up ^ Champe, Pamela C.; Harvey, Richard A.; Ferrier, Denise R. (2005). Lippincott's Illustrated Reviews: Biochemistry. Lippincott Williams & Wilkins. ISBN 978-0-7817-2265-0.
Jump up ^ Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2002). Molecular Biology of the Cell (4th ed.). New York: Garland Science. pp. 331–3. ISBN 0-8153-3218-1.
Jump up ^ Cooper, Geoffrey M.; Hausman, Robert E. (2007). The Cell: A Molecular Approach (4th ed.). Sinauer Associates. pp. 371–9. ISBN 0878932208.
Jump up ^ Wang T, Schneider J; Origin and fate of the nucleolar channel system of normal human endometrium; Cell Res. (1992); 2(2), 97-102
Jump up ^ Audas TE, Jacob MD, Lee S (2012). "Immobilization of proteins in the nucleolus by ribosomal intergenic spacer noncoding RNA". Mol Cell. 45 (2): 147–57. PMID 22284675. doi:10.1016/j.molcel.2011.12.012.
External links[edit]
Wikimedia Commons has media related to Cell nucleolus.
Look up nucleolus in Wiktionary, the free dictionary.
Cooper, Geoffrey M. (2000). "The Nucleolus". The Cell: A Molecular Approach (2nd ed.). Sunderland MA: Sinauer Associates. ISBN 0-87893-106-6.
Nucleolus under electron microscope II at uni-mainz.de
Nuclear Protein Database – search under compartment
Cell Nucleolus at the US National Library of Medicine Medical Subject Headings (MeSH)
Histology image: 20104loa – Histology Learning System at Boston University
[show]
v
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e
Structures of the cell / organelles (TH H1.00.01.2-3)
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see also transcription factors and intracellular receptors
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text:
Muscle tissue
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Muscle tissue
The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. (Same magnification)
A schematic diagram of the different types of muscle cells (same order as above).
Identifiers
MeSH
D009132
Anatomical terminology
[edit on Wikidata]
Muscle tissue is a soft tissue that composes muscles in animal bodies, and gives rise to muscles' ability to contract. This is opposed to other components or tissues in muscle such as tendons or perimysium. It is formed during embryonic development through a process known as myogenesis.[1]
Muscle tissue varies with function and location in the body. In mammals the three types are: skeletal or striated muscle; smooth or non-striated muscle; and cardiac muscle, which is sometimes known as semi-striated. Smooth and cardiac muscle contracts involuntarily, without conscious intervention. These muscle types may be activated both through interaction of the central nervous system as well as by receiving innervation from peripheral plexus or endocrine (hormonal) activation. Striated or skeletal muscle only contracts voluntarily, upon influence of the central nervous system. Reflexes are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cortical structures until after the contraction has occurred.[1]
The different muscle types vary in their response to neurotransmitters and endocrine substances such as acetylcholine, noradrenaline, adrenaline, nitric oxide and among others depending on muscle type and the exact location of the muscle.[1]
Sub-categorization of muscle tissue is also possible, depending on among other things the content of myoglobin, mitochondria, myosin ATPase etc.
Contents
[hide]
1 Structure
1.1 Comparison of types
1.2 Skeletal muscle
1.3 Smooth muscle
1.4 Cardiac muscle
2 Function
2.1 Skeletal muscle
2.2 Smooth muscle
2.3 Cardiac muscle
3 See also
4 References
Structure[edit]
Muscle cells (myocytes) are elongated cells ranging from several millimetres to about 10 centimetres in length and from 10 to 100 micrometres in width.[2] These cells are joined together in tissues that may be either striated or smooth, depending on the presence or absence, respectively, of organized, regularly repeated arrangements of myofibrillar contractile proteins called myofilaments. Striated muscle is further classified as either skeletal or cardiac muscle.[3] Striated muscle is typically subject to conscious control, while smooth muscle is not. Thus, muscle tissue can be described as being one of three different types:
Skeletal muscle, striated in structure and under voluntary control, is anchored by tendons (or by aponeuroses at a few places) to bone and is used to effect skeletal movement such as locomotion and to maintain posture. (Though postural control is generally maintained as an unconscious reflex—see proprioception—the muscles responsible also react to conscious control like non-postural muscles.) An average adult male is made up of 42% of skeletal muscle and an average adult female is made up of 36% (as a percentage of body mass).[4] It also has striations unlike smooth muscle.
Smooth muscle, neither striated in structure nor under voluntary control, is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin (in which it controls erection of body hair).
In vertebrates, there is a third muscle tissue recognized:
Cardiac muscle (myocardium), found only in the heart, is a striated muscle similar in structure to skeletal muscle but not subject to voluntary control.
Cardiac and skeletal muscles are "striated" in that they contain sarcomeres and are packed into highly regular arrangements of bundles; smooth muscle has neither. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles (called intercalated discs). Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions.
Comparison of types[edit]
smooth muscle cardiac muscle skeletal muscle
Anatomy
Neuromuscular junction none none present
Fibers fusiform, short (<0.4 mm) branching cylindrical, long (<15 cm)
Mitochondria few numerous many to few (by type)
Nuclei 1 1 >1
Sarcomeres none present, max. length 2.6 µm present, max. length 3.7 µm
Syncytium none (independent cells) none (but functional as such) present
Sarcoplasmic reticulum little elaborated moderately elaborated highly elaborated
ATPase little moderate abundant
Physiology
Self-regulation spontaneous action (slow) yes (rapid) none (requires nerve stimulus)
Response to stimulus unresponsive "all-or-nothing" "all-or-nothing"
Action potential yes yes yes
Workspace Force/length curve is variable the increase in the force/length curve at the peak of the force/length curve
Response to stimulus
Skeletal muscle[edit]
Main article: Skeletal muscle
Striated skeletal muscle cells in microscopic view. The myofibers are the straight vertical bands; the horizontal striations (lighter and darker bands) that are visible result from differences in composition and density along the fibrils within the cells. The cigar-like dark patches beside the myofibers are muscle-cell nuclei.
Skeletal muscle is further divided into several subtypes:
Type I, slow oxidative, slow twitch, or "red" muscle is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity.
Type I muscle fiber are sometimes broken down into Type I and Type Ic categories, as a result of recent research.[5]
Type II, fast twitch muscle, has three major kinds that are, in order of increasing contractile speed:[6]
Type IIa, which, like slow muscle, is aerobic, rich in mitochondria and capillaries and appears red when deoxygenated.
Type IIx (also known as type IId), which is less dense in mitochondria and myoglobin. This is the fastest muscle type in humans. It can contract more quickly and with a greater amount of force than oxidative muscle, but can sustain only short, anaerobic bursts of activity before muscle contraction becomes painful (often incorrectly attributed to a build-up of lactic acid). N.B. in some books and articles this muscle in humans was, confusingly, called type IIB.[7]
Type IIb, which is anaerobic, glycolytic, "white" muscle that is even less dense in mitochondria and myoglobin. In small animals like rodents this is the major fast muscle type, explaining the pale color of their flesh.
Smooth muscle[edit]
Main article: Smooth muscle tissue
Smooth muscle is an involuntary non-striated muscle. It is divided into two subgroups: the single-unit (unitary) and multiunit smooth muscle. Within single-unit cells, the whole bundle or sheet contracts as a syncytium (i.e. a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle.
Smooth muscle is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle) such as in the tunica media layer of large (aorta) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder, uterus (termed uterine smooth muscle), male and female reproductive tracts, gastrointestinal tract, respiratory tract, arrector pili of skin, the ciliary muscle, and iris of the eye. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual effects in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells.
Cardiac muscle[edit]
Main article: Cardiac muscle
Cardiac muscle is involuntary, striated muscle that is found in the walls and histological foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle. These three types of muscle all form in the process of myogenesis. The cells that constitute cardiac muscle, called cardiomyocytes or myocardiocytes, predominantly contain only one nucleus, although populations with two to four nuclei do exist.[8][9][page needed] The myocardium is the muscle tissue of the heart, and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer.
Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems. This complex mechanism illustrates systole of the heart.
Cardiac muscle cells, unlike most other tissues in the body, rely on an available blood and electrical supply to deliver oxygen and nutrients and remove waste products such as carbon dioxide. The coronary arteries help fulfill this function.
Function[edit]
This section needs expansion. You can help by adding to it. (March 2014)
Skeletal muscle[edit]
1.They carry out movements of the body.
2.They support the body.
3.They maintain the posture of the body.
Smooth muscle[edit]
It is responsible for the contractility of hollow organs, such as blood vessels, the gastrointestinal tract, the bladder.
Cardiac muscle[edit]
Cardiac muscle is the muscle of the heart. It is self-contracting, autonomically regulated and must continue to contract in rhythmic fashion for the whole life of the organism. Hence it has special features.
See also[edit]
Myocyte
References[edit]
^ Jump up to: a b c "Muscle Tissue TheVisualMD.com". www.thevisualmd.com. Retrieved 2015-12-30.
Jump up ^ Hugh Potter, Summary of muscle tissue Archived 2014-10-21 at the Wayback Machine.
Jump up ^ Pratt, Rebecca. "Muscle Tissue". AnatomyOne. Amirsys, Inc. Archived from the original on 2 February 2017. Retrieved 26 October 2012.
Jump up ^ Marieb, Elaine; Hoehn, Katja (2007). Human Anatomy & Physiology (7th ed.). Pearson Benjamin Cummings. p. 317. ISBN 0-8053-5387-9.
Jump up ^ McCloud, Aaron (30 November 2011). "Build Fast Twitch Muscle Fibers". Complete Strength Training. Retrieved 30 November 2011.
Jump up ^ Larsson, L; Edström, L; Lindegren, B; Gorza, L; Schiaffino, S (July 1991). "MHC composition and enzyme-histochemical and physiological properties of a novel fast-twitch motor unit type". The American Journal of Physiology. 261 (1 pt 1): C93–101. PMID 1858863. Retrieved 2006-06-11.
Jump up ^ Smerdu, V; Karsch-Mizrachi, I; Campione, M; Leinwand, L; Schiaffino, S (December 1994). "Type IIx myosin heavy chain transcripts are expressed in type IIb fibers of human skeletal muscle". The American Journal of Physiology. 267 (6 pt 1): C1723–1728. PMID 7545970. Retrieved 2006-06-11. Note: Access to full text requires subscription; abstract freely available
Jump up ^ Olivetti G, Cigola E, Maestri R, et al. (July 1996). "Aging, cardiac hypertrophy and ischemic cardiomyopathy do not affect the proportion of mononucleated and multinucleated myocytes in the human heart". Journal of Molecular and Cellular Cardiology. 28 (7): 1463–77. doi:10.1006/jmcc.1996.0137. PMID 8841934.
Jump up ^ Pollard, Thomas D. and Earnshaw, William. C., "Cell Biology". Philadelphia: Saunders. 2007.
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