BGDA Practical 3 - Week 1 Summary: Difference between revisions

From Embryology
Line 42: Line 42:
===X chromosome===
===X chromosome===
{|
{|
| [[File:Human idiogram-chromosome X.jpg|thumb|X]]
| [[File:Human idiogram-chromosome X.jpg|Human idiogram-chromosome X.jpg]]
|
|
* 155 million base pairs  
* 155 million base pairs  

Revision as of 14:27, 9 May 2011

BGDsmall.jpg
Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3

Week 1

Overview of development of the 1-chambered conceptus (blastocyst)

Week1 summary.jpg

Ovulation is the initial release of oocyte.

Follicular fluid and fimbriae together aid oocyte movement into infundibulum then the ampulla of the uterine tube.

Sperm deposited in the vagina then enter the uterus, mature (capacitation), then actively migrate along the uterine tube.

Fertilization generally occurs in the ampulla region of the tube.

Following fertilization, repeated rounds of cell division occur without growth forming initially a solid ball of cells (morula), which cavitates to form the 1-chambered conceptus (blastocyst). Liberation of the blastocyst from the zona pellucida the allows attachment (adplantation) to the uterine wall.

Following ovulation the empty follicle within the ovary now forms the corpus luteum.

Note - the day timings shown above for the first week are approximate and may vary by several days for events following fertilization.


Blastocyst (right) hatching from zona pellucida (left)

CSt3.jpg Human carnegie stage 3 label.jpg

Sex Determination

Mammalian sex determination is regulated by chromosomes.

  • Females have two X chromosomes. (XX)
  • Males have a single X and a small Y. (XY)
  • The X and Y chromosome are morphologically and functionally different from each other.
  • Evolutionary studies have shown that the Y was once the homologous pair for X.
  • It is only in the last 5 years that we have some idea about how these two types of chromosomes may be regulated and genes of importance located upon them.


In females - the main scientific problem was understanding gene dosage, only one copy of X chromosome is needed to be genetically active the other copy is inactivated (More? X Inactivation.

In males - the main scientific problem was understanding what on the Y chromosome determined "maleness", and how this is done.

X chromosome

Human idiogram-chromosome X.jpg
  • 155 million base pairs
  • In contrast to the Y chromosome, the X chromosome contains about 5% of the haploid genome and encodes house-keeping and specialized functions.
  • Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development
  • An early discovery (1961) was that in order to have correct levels of X chromosome gene/protein expression (gene dosage), females must "inactivate" a single copy of the X chromosome in each and every cell. The initiator of the X inactivation process was discovered (1991) to be regulated by a region on the inactivating X chromosome encoding an X inactive specific transcript (XIST), that acts as RNA and does not encode a protein.
  • The genetic content of the X chromosome has been strongly conserved between species because these genes have become adapted to working as a single dose - Ohno's law
  • X inactivation occurs randomly throughout the embryo, generating a mosaic of maternal and paternally derived X chromosome activity in all tissues and organs. This can be seen in the fur colour of tortoiseshell cats.

Y chromosome

Y Chromosome

  • Y chromosome - 59 million base pairs, hypervariable in length, mostly non-functional repeats
  • Current known protein-coding genes = 48 including SRY
  • SRY encodes a 204 amino acid protein that is a member of the HMG (High mobility group) box class of DNA-binding proteins. Transcription factors bind to specific sites of DNA and regulates the transcription (expression) of other genes.



--Mark Hill 13:21, 9 May 2011 (EST) These concepts will be covered later in detail with BGDB - Sexual Differentiation.

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


BGDsmall.jpg

Practical 3: Oogenesis and Ovulation | Gametogenesis | Fertilization | Early Cell Division | Week 1 | Implantation | Week 2 | Extraembryonic Spaces | Gastrulation | Notochord | Week 3 | Quiz


Additional Information

Terms

  • adplantation - Initial adhesion of blastocyst (released from zona pellucida) to uterine wall. Adplantation is followed by implantation.
  • ampulla - longest segment (approximately 2/3 of overall length) of uterine tube (oviduct or Fallopian tube). Medial segment forming the remainder of the tube is called the isthmus.
  • antrum- (L. a cave), cavity; a nearly-closed cavity or bulge. In the ovary this refers to the follicular fluid-filled space within the follicle.
  • blastocyst - the developmental stage following morula, as this stage matures, the zona pellucia is lost allowing the coceptus to adplant and then implant into the uterine wall.
  • capacitation the process by which sperm become capable of fertilizing an egg, requires membrane changes, removal of surface glycoproteins and increased motility.
  • cavitates - to form a space within a solid object.
  • conceptus the product of conception, that is all the structures derived from the zygote. This includes not only the embryo, but also the placental and membrane components formed from the conceptus.
  • fertilization The penetration of the egg by the sperm and the resulting combining of genetic material that develops into an embryo. The union of two haploid gametes to form a diploid cell or zygote.
  • fimbriae (Latin, fimbria = a fringe) finger-like projections at the ovarian end of uterine tube. At ovulation they sit over the ovary to aid egg movement into the uterine tube.
  • follicular fluid - the fluid found in the antrum of an antral follicle (secondary follicle). Secreted by cells in the wall of the follicle, this fluid is released along with the oocyte at ovulation.
  • infundibulum - funnel-shaped initial segment of uterine tube (oviduct or Fallopian tube) opening into peritoneal cavity and connected to the ampulla. The peritoneal opening sitting over the ovary.
  • morula (Latin, morula = mulberry) early stage in development (week 1) where the cells have divided to produce a solid mass of cells (12-15 cells) with a "mulberry" appearance. This stage is followed by formation of a cavity in the mass (blastocyst stage).
  • oocyte - (egg or ovum) female germ cell.
  • ovulation- release of the oocyte from the mature follicle.
  • triploidy - in humans, three sets of 23 chromosomes instead of 2 (diploid) combine to form the embryo. This occurs mainly by fertilization of a single egg by two sperm and less frequently by a diploid egg or sperm. Most human triploids abort spontaneously, with very rare survival to term.
  • tetraploidy - in humans, four sets of 23 chromosomes instead of 2 (diploid) due to a failure of the first mitotic division after fertilization, these fertilization events do not development.
  • uterine tube - (also called oviduct or Fallopian tube) the laterally paired tubes that connect the ovary to the uterus. Is the site for oocyte fertilization and initial development of the conceptus.
  • uterine wall - the site of normal blastocyst implantation.
  • zona pellucida- glycoprotein shell that surrounds the oocyte through to blastula stage of development
  • uterus- site of embryo implantation and development. Uterine wall has 3 layers; endometrium, myometrium, and perimetrium.
  • zona pellucida- extracellular layer lying directly around the oocyte underneath follicular cells. Consists of glcosaminoglycans and glycoproteins (ZP1, ZP2, ZP3).



BGDsmall.jpg

BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | 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, March 29) Embryology BGDA Practical 3 - Week 1 Summary. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_3_-_Week_1_Summary

What Links Here?
© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G