Gametogenesis Notes PDF

 Cell divisions & Gametogenesis GAD Lecture 2 &3 Presented by : Dr. Shaimaa Alakabawy  Objectives: At the end of this lecture the student will be able to: – Explain the major steps of cell division – Describe the events of both meiosis and mitosis...

 Cell divisions & Gametogenesis GAD Lecture 2 &3 Presented by : Dr. Shaimaa Alakabawy  Objectives: At the end of this lecture the student will be able to: – Explain the major steps of cell division – Describe the events of both meiosis and mitosis – Understand the major differences between types of cell divisions – Describe different steps of spermatogenesis and oogenesis – Describe the major differences between gametogenesis in both sexes  Cell division Difference between meiosis and mitosis  Cell division in germ cell Mitosis: the germ cell(2n=46 chromosomes) divides into 2 cells, each cell contains 46 chromosomes (2n=44 autosomes and 2 sex chromosomes) Meiosis: the germ cell(2n) divides into 2 cells, each cell contains 23 chromosomes (n=22 autosomes and one sex chromosome)  Gametogenesis Definition: Formation of the mature male gametes( spermatogenesis) and the mature female gametes( oogenesis) from immature germ cell inside the gonads. Spermatogenesis  DEFINITION It is the process of formation of sperms(male gametes) in the seminiferous tubules of the testis(male gonads).  AIM: Reduce the number of chromosomes from 46 to 23. Change the shape of the male germ cell to become ready for fertilization.  STAGES: SPERMATO-CYTOGENESIS: SPERMIOGENESIS  SPERMATO-CYTOGENESIS: Stage of proliferation: the spermatogonium divides by mitosis to form 2 daughter spermatogonia. Each cell contains 46 chromosomes Stage of growth: the daughter spermatogonium enlarges to form a primary spermatocyte which contains 46 chromosomes Stage of maturation:2 steps Mieosis: the primary spermatocytes divides by meiosis to form 2 secondary spermatocytes Equational division: each secondary spermatocyte divides equational division (similar to mitosis) to form 2 spermatids.( each contains the same number of chromosomes as the secondary spermatocytes ) 2. SPERMIOGENESIS: Stage of transformation: The spermatid changes into a motile sperm Spermiogenesis  Sperm Head: Neck: Body (middle piece): Tail: Principle piece: Its terminal piece:  Sperm Head: formed of condensed nucleus & acrosomal cap covering its anterior 2/3. 0000 Neck: a constriction behind the head. contains the 2 centrioles.  Sperm Body (middle piece): Plasma membrane. Mitochondrial sheath. no 9 bundles of microfilaments. Tail: Principle piece. Terminal piece.  Sperm Abnormality In form: I Giants (too big). 2 Dwarfs (too small). With two heads (bicephalic). y With two tails (bicaudal).  sperm In number: Azospermia: is absence of sperms in the semen. Oligospermia: is the e presence of few sperms. Few  Dead Necrospermia: is the presence of dead sperms. Abnormal form of sperm Oogenesis Oogenesis  Definition: It is the process of production of a mature ovum in the cortex of the ovary. It starts during fetal life and continues after puberty(during each ovarian cycle), and after fertilization.  Aim: Reduce the number of chromosomes from 46 to 23. Increase the size of the ovum from 30 µ to 120 µ.  1-PRENATAL DEVELOPMENT: Stage of proliferation: During intra-uterine life, the ovary contains only oogonia. The oogonium divides by mitosis to form 2 daughter oogonia, each oogonium contains 46chromosomes(44 autosomes+2x chromosomes) Stage of growth: Then the majority of the oogonia degenerate, while the surviving ones increase in size to form1ry oocytes(46 chromosomes) Each 1ry oocyte is surrounded by a layer of flat epithelial cells called follicular cells. 1ry oocyte, together with the follicular cells, is known as a primordial follicle.  2.POSTNATAL (after puberty) Stage of maturation: 1.Meiosis: each 1ry oocyte (44 + XX) undergoes 1st meiotic division to give rise: – 1st polar body (22+X): a small cell as it receives a little of cytoplasm. – 2ry oocyte (22+X): a large cell as it receives most of the cytoplasm.  Post natal (cont.): 2. Equational division:(similar to mitosis) 2ry oocyte (22 + X) undergoes 2nd meiotic division to give rise: 2nd polar body. Ovum. Growing follicles  1ry follicle The simple flat epithelial cells start to enlarge & become cubical then simple columnar, then they divide forming many layers around the oocyte. The follicular cells then deposit zona pellucida & the follicular cells are now called granulosa cells  2ry follicle Small irregular spaces appear between the granulosa cells, which later join each other to form one large space called the follicular cavity (antrum) Growing follicles  Graffian follicle The follicular cells surrounding the oocyte are called cumulus oophorus. The stroma cells of the cortex of ovary differentiate into: An inner vascular layer called theca interna. An outer fibrous layer called theca externa. Graffian follicle  Graffian follicle 2ry oocyte: (120 µ) Zona pellucida: surrounds the oocyte. Cumulus oophorus: follicular cells surrounding oocyte.  Graffian follicle – Follicular antrum: fills the mature follicle & is lined by stratum granulosa. – The stroma cells of the ovary differentiate into: – An inner vascular layer called theca interna. – An outer fibrous layer called theca externa. After rupture After rupture After rupture After rupture  Reference: The developing Human: Clinically Oriented Embryology