2010 BGD Practical 3 - Gametogenesis: Difference between revisions

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== Terms ==
 
* '''antral follicle''' -  the stage following preantral in the decription of the sequence ovarian follicle development.
* '''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.
* '''atretic follicle''' - An ovarian follicle that fails to mature and degenerates. Also called "atresia" refering to the process of degeneration of the ovarian follicle. This process can occur at any stage of follicle development (folliculogenesis).
* '''clomiphene citrate''' - drug taken orally to promote the process of follicle/egg maturation.
* '''corona radiata''' - Layer of follicle cells of cumulus oophorus remaining attached to zona pellucida of oocyte after ovulation. Also called granulosa cells.
* '''corpus albicans''' - (L. ''corpus'' = body, L. ''albicans ''<nowiki>= whitish); a degenerating corpus luteum in ovary. </nowiki>
* '''corpus luteum''' - (L. ''corpus'' = body, L. ''luteum'' = yellow) The remains of ovarian follicle after ovulation that acts as an endocrine organ supporting pregnancy and preventing menstruation (loss of the endometrial lining). de Graaf first observed it in the ovary of a cow as a yellow structure.
* '''cortical''' - (L. ''corticalis'') at the outside (like the bark of a tree), usually combined with medulla meaning the core.
* '''cumulus oophorus''' - (L. ''cumulus ''<nowiki>= a little mound G. </nowiki>''oon'' = egg + phorus = bearing); part of the wall of an ovarian follicle surrounding and carrying the ovum (oocyte).
* '''follicle''' - (L. ''folliculus'' = little bag,dim. of L. ''follis''). A structure which develops in the ovary and contains a developing egg (oocyte).
* '''follicular fluid''' - the fluid found in the antrum of a secondary follicle. Secreted by cells in the wall of the follicle. This fluid is released along with the oocyte at ovulation.
* '''germinal epithelium''' - cellular component covering surface of ovary, it is continuous with mesothelium covering mesovarium. Note that it is a historical misnomer, as it is not the actual site of germ cell formation.
* '''Graafian follicle''' - named after Regnier de Graaf (1641-1673), an historic Dutch physician embryologist who studied pregnancy using rabbits.
* '''granulosa cells''' - the supporting cells that surround the developing egg within the follicle thecal layers.
* '''mesovarium''' - mesentry of the ovary formed from a fold of the broad ligament that attaches the ovary
* '''medullary''' - (L. ''medius'' = in the middle) relating to the medulla; pith, marrow, inner portion of an organ. Usually combined with cortex (cortical) meaning the outer layer.
* '''ovulation''' - release of the oocyte from the mature follicle. In humans generally a single oocyte is released from a cohort of several maturing follicles.
* '''preantral follicle''' -  the stage following primordial in the description of the sequence ovarian follicle development.
* '''primary follicle''' -  the stage following primordial in the description of the sequence ovarian follicle development.
* '''primordial follicle''' - the first stage in the description of the sequence ovarian follicle development. Present in the ovary from birth, located in the stroma of the ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.
* '''primordial germ cell''' - oocyte present in the primordial follicle ovary from birth, located in the stroma of the ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.
* '''secondary follicles''' - the stage following primary in the description of the sequence ovarian follicle development.
* '''stromal cells''' - in the ovary, cells surrounding the developing follicle that form a connective tissue sheath (theca folliculi). This layer then differentiates into 2 layers (theca interna, theca externa). This region is richly vascularized and involved in hormone secretion.
* '''superovulation therapy''' - a fertility drug treatement (oral clomiphene citrate and/or injectable FSH with or without LH) aimed at stimulating development/release of more than one follicle during a single menstrual cycle.
* '''tertiary follicle''' - the stage following secondary in the description of the sequence ovarian follicle development.
* '''theca folliculi''' - stromal cells in the ovary, cells surrounding the developing follicle that form a connective tissue sheath. This layer then differentiates into 2 layers (theca interna, theca externa). This region is vascularized and involved in hormone secretion.
* '''theca externa''' - stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle. Consisting of connective tissue cells, smooth muscle and collagen fibers.
* '''theca interna''' - stromal cells forming the inner layer of the theca folliculi surrounding the developing follicle. This vascularized layer of cells respond to LH (leutenizing hormone) synthesizing and secreting androgens which are processed into estrogen.
* '''tunica albuginea''' - dense connective tissue layer lying between germinal epithelium and cortical region of ovary.
* '''uterus''' - site of embryo implantation and development. Uterine wall has 3 major layers: endometrium, myometrium, and perimetrium. Endometrium can be further divided into the functional layer (shed/lost during menstruation) and basal layer (not lost during menstruation).
* '''zona pellucida''' - extracellular layer lying directly around the oocyte underneath follicular cells. Has an important role in egg development, fertilization and blastocyst development. This thick extracellular matrix consists of glcosaminoglycans and 3 glycoproteins (ZP1, ZP2, ZP3).




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Revision as of 01:13, 10 May 2010

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


Introduction

Gametes are formed in the gonads; male testis and female ovary by the mechanism of meiotic cell division. The generation of gametes, and their regulation, is substantially different in males and females. After puberty, gonads also synthesis and secrete sex hormones into the bloodstream required for development of the secondary sex characteristics.

Female Gametogenesis

In females, the total number of eggs ever to be produced are present in the newborn female.

  1. All eggs are arrested at an early stage of the first meiotic division as a primary oocyte (primordial follicle). Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis 1 the day before ovulation.
  2. In meiosis 1, a diploid cell becomes 2 haploid (23 chromosomes) daughter cells, each chromosome has two chromatids. One cell becomes the secondary oocyte the other cell forms the first polar body.
  3. The secondary oocyte then commences meiosis 2 which arrests at metaphase and will not continue without fertilization.
  4. At fertilization meiosis 2 completes, forming a second polar body. Note that the first polar body may also undergo this process forming a third polar body.

Female gametogenesis

Female Abnormalities

Meiotic non-disjunction resulting in aneuploidy, most are embryonic lethal and not seen. The potential for genetic abnormalities increase with maternal age.

  • Autosomal chromosome aneuploidy
    • trisomy 21 - Down syndrome
    • trisomy 18 - Edwards syndrome
    • trisomy 13 - Patau syndrome
  • Sex chromosome aneuploidy
    • monosomy X - Turner's Syndrome
    • trisomy X - Triple-X syndrome
    • 47 XXY - Klinefelter's Syndrome

Male Gametogenesis

In males, sperm continues to be generated throughout life from a stem cell population in the testis. Spermatozoa maturation involves two processes meiosis and spermiogenesis Male gametogenesis.jpg

  • Spermatogenesis process of spermatagonia mature into spermatazoa (sperm).
  • Continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes).
  • At puberty spermatagonia activate and proliferate (mitosis).

Spermatozoa animation icon.jpg


Links: Figure 20-22. Highly simplified drawing of a cross-section of a seminiferous tubule in a mammalian testis | Sperm Are Produced Continuously in Many Mammals | Figure 20-23. Cytoplasmic bridges in developing sperm cells and their precursors.

Puberty

  • In humans at puberty, hormonal and morphological changes occur within the gonad and other systems (secondary sex characteristics).
  • Within the testis the immature Sertoli cells cease to proliferate and differentiate.
  • Spermatogonium proliferate and spermatogenesis begins.
  • It takes about 70 days for cells to mature from the diploid spermatogonium to a primary spermatocyte.
  • This maturation occurs in waves along the seminiferous tubules.

Ejeculate

  • release of spermatozoa and accessory gland secretions from the male genital tract (3.5 ml)
  • 200-600 million sperm, by volume less than 10 % spermatozoa
  • Accessory Gland secretions - 60 % seminal vesicle, 30 % prostate and 10 % bulbourethral

Male Abnormalities

Azoospermia - Non-obstructive azoospermia (NOA) and Obstructive azoospermia (OA)
  • Oligospermia - (Low Sperm Count) less than 20 million sperm after 72 hour abstinence from sex
  • Azoospermia - (Absent Sperm) blockage of duct network
  • Immotile Cilia Syndrome - lack of sperm motility

Differences in Mammalian Meioses

Female Oogenesis Male Spermatogenesis
Meiosis initiated once in a finite population of cells continuously in mitotically dividing stem cell population
Gametes produced 1 / meiosis 4 / meiosis
Meiosis completed delayed for months or years completed in days or weeks
Meiosis Arrest arrest at 1st meiotic prophase no arrest differentiation proceed continuously
Chromosome Equivalence All chromosomes exhibit equivalent transcription and recombination during meiotic prophase Sex chromosomes excluded from recombination and transcription during first meiotic prophase
Gamete Differentiation occurs while diploid (in first meiotic prophase) occurs while haploid (after meiosis ends)



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




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2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2024, March 28) Embryology 2010 BGD Practical 3 - Gametogenesis. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_3_-_Gametogenesis

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