BGDB Sexual Differentiation - Late Embryo: Difference between revisions
From Embryology
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'''Male Human Embryo''' (week 8, stage 22) | '''Male Human Embryo''' (week 8, stage 22) | ||
Detail from cross-section showing mesonephros, mesonephric duct, paramesonephric duct and developing testis. | Detail from cross-section showing mesonephros, mesonephric duct, paramesonephric duct and developing testis. | ||
| Until the end of the 6th week the male and female genital systems are indistinguishable. Sex differentiation is based upon the presence of specific sex chromosomes. | | Until the end of the 6th week the male and female genital systems are indistinguishable. Sex differentiation is based upon the presence of the specific sex chromosomes. | ||
* week 5 - the primordial germ cells migrate to the region of the future gonads. Cells from the coelomic epithelium and the mesonephros proliferate, forming genital ridges medial to the mesonephros. | |||
* week 6 - these cells surround the germ cells, together forming the primitive sex cords. They contain distinct cortical and medullary regions. | * '''week 5''' - the primordial germ cells migrate to the region of the future gonads. Cells from the coelomic epithelium and the mesonephros proliferate, forming genital ridges medial to the mesonephros. | ||
* '''week 6''' - these cells surround the germ cells, together forming the primitive sex cords. They contain distinct cortical and medullary regions. | |||
** Also in the 6th week, the paramesonephric or Müllerian ducts form, lateral to the mesonephric ducts. | ** Also in the 6th week, the paramesonephric or Müllerian ducts form, lateral to the mesonephric ducts. | ||
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===Male=== | ===Male=== | ||
* week 8 - males Sertoli cells secrete anti müllerian hormone (AMH), which causes regression of the paramesonephric ducts between the 8th and 10th weeks. | * '''week 8''' - males Sertoli cells secrete anti müllerian hormone (AMH), which causes regression of the paramesonephric ducts between the 8th and 10th weeks. | ||
* week 9 to 10 - gonadal cells begin to produce testosterone, which maintains the mesonephric ducts. | * '''week 9 to 10''' - gonadal cells begin to produce testosterone, which maintains the mesonephric ducts. | ||
* mesonephric ducts go on to form the internal genital tract: | * mesonephric ducts go on to form the internal genital tract: | ||
** rete testis | ** rete testis | ||
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===Female=== | ===Female=== | ||
* the opposite occurs. | * during the same time course as above, the opposite occurs. | ||
* The sex cords degenerate and the genital ridge forms secondary cortical sex cords. | * The sex cords degenerate and the genital ridge forms secondary cortical sex cords. | ||
* These induce the primordial germ cells to form the ovarian follicles. | * These induce the primordial germ cells to form the ovarian follicles. |
Revision as of 16:50, 29 May 2011
Practical 12: Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | 2011 Audio |
Week 8
<wikiflv width="560" height="588" autoplay="true" position="left">Stage22_urogenlarge.flv|File:Stage22-UG-icon.jpg</wikiflv> (Carnegie stage 22, male) |
Begin by observing the internal structure of the embryo at the end of week 8.
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Embryo (week 8, Stage 22) Renal
Urinary System Development
- The adult kidneys (the metanephroi) form from day 35, from a portion of the intermediate mesoderm called the metanephric blastema (or metanephric mesenchyme).
- They are induced to form by the ureteric buds, outgrowths from the end of the mesonephric ducts, which come into contact with the metanephric blastema.
- Upon contact, they begin to lengthen and bifurcate rapidly in the metanephric blastema – these branches differentiate into the collecting ducts.
- Both the ureteric buds and the metanephric blastema begin to differentiate; interestingly each induces differentiation in the other structure.
- The ureteric bud is induced by the metanephric blastema to form the collecting tubules, renal pelvis and ureters.
- The metanephric blastema is induced to form the nephrons.
Development of the Kidney
File:Renal blood 01 icon.jpg</wikiflv> |
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Development of the Urinary Bladder
File:Urogenital_septum_001 icon.jpg</wikiflv> | Division of the Cloaca
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Development of the Urethra
- Further development of the urinary system varies depending on the sex of the embryo.
- Males - the pelvic urethra forms the membranous urethra, the prostatic urethra and penile urethra. (The sex of the above animation and sections is male)
- Females - the pelvic urethra forms the membranous urethra and the vestibule of the vagina.
Genital System Development
Male
- week 8 - males Sertoli cells secrete anti müllerian hormone (AMH), which causes regression of the paramesonephric ducts between the 8th and 10th weeks.
- week 9 to 10 - gonadal cells begin to produce testosterone, which maintains the mesonephric ducts.
- mesonephric ducts go on to form the internal genital tract:
- rete testis
- ductuli efferentes
- vas deferens
Female
- during the same time course as above, the opposite occurs.
- The sex cords degenerate and the genital ridge forms secondary cortical sex cords.
- These induce the primordial germ cells to form the ovarian follicles.
- Due to the lack of AMH and testosterone, the mesonephric ducts degenerate
- paramesonephric ducts go on to form the internal genital tract:
- uterine (fallopian) tubes
- uterus body
- vagina
In both sexes, the external genitalia appear similar until the 12th week.
Trigone
Practical 12: Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | 2011 Audio |
References
BGDB: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, April 27) Embryology BGDB Sexual Differentiation - Late Embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Sexual_Differentiation_-_Late_Embryo
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G