Gametogenesis and Anomalies - 2025

Gametogenesis & Anomalies ONANUGA I.O. (PhD)  What you need to know Introduction Concept of chromosome Mitosis or meiosis? Spermatogenesis Oogenesis Congenital anomalies 2025-02-06 2  An introduction to gametogene...

Gametogenesis & Anomalies ONANUGA I.O. (PhD)  What you need to know Introduction Concept of chromosome Mitosis or meiosis? Spermatogenesis Oogenesis Congenital anomalies 2025-02-06 2  An introduction to gametogenesis Gametogenesis is the formation of gametes (sex cells). The creation of highly specialized sex cells through a process called MEIOSIS. It occurs in the gonads (testis and ovary). There are two types of gametogenesis: (1) Spermatogenesis: formation of sperm in male. (2) Oogenesis: formation of egg in female. 2025-02-06 3 2025-02-06 4  Somatic and Germ-line cells Development of a fertilized egg into an adult results in two distinct types of cells – Somatic cells These create all tissues and organs of the adult except for cells destined to become sperm or egg They can only undergo mitosis – Germline cells The final differentiated form of these cells are mature gametes: the sperm and egg These cells undergo mitosis until gametogenesis – They then undergo meiosis 2025-02-06 5  CELLS These are precursor cells that give rise to gametes. They are formed in the epiblast during the second week of embryonic development. PGCs migrate from the epiblast to the wall of the yolk sac through the allantois. PGCs number increase mitotically as they migrate from the yolk sac to the developing gonads during the 4th week. There number continue to increase mitotically in the developing gonad where they arrived by the end of 2025-02-06 6 MEIOSIS AND MITOSIS  Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere 2025-02-06 8  REPLICATION OF CHROMOSOMES Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere. 2025-02-06 9  Karyotype A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male 2025-02-06 10  Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome 2025-02-06 11  Cell cycle and cell division Mitosis DNA Copied Cells prepare Meiosis Cells for Mature Division Mitosis is for growth and repair. Meiosis is for formation of gametes (sexual reproduction). 2025-02-06 12  MITOSIS 2025-02-06 13  Eukaryotic Cell Division  Used for growth and repair  Produce two new cells identical to the original cell  Cells are diploid (2n) Chromosomes during Metaphase of mitosis Anaphase Cytokinesis Prophase Metaphase Telophase 2025-02-06 14  MEIOSIS  Preceded by interphase  Daughter cells contain half which includes chromosome the number of chromosomes replication as the original cell  Two meiotic divisions-  Produces gametes (eggs & Meiosis I and Meiosis II sperm)  Called Reduction- division  Occurs in the testes in males  Original cell is diploid (2n)  Four daughter cells (Spermatogenesis)  Occurs in the ovaries in produced that are monoploid (1n) females (Oogenesis). 2025-02-06 15  MEIOSIS 2025-02-06 16  SIS Stages Diploid e separat gs Homolo Start with 46 double stranded Meiosis chromosomes (2n) I After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded separate chromatids Sister chromosomes (n) II Meiosis  Occurs in our germ cells that produce gametes Haploid 2025-02-06 17  SPERMATOGENESIS Is the series of events that occur in the seminiferous tubule of the testes that leads to the production of sperm or spermatozoa. Duration/Onset: It begins during puberty, around the age of 14 years and continues. About 250 - 400 million sperm per day. The PGCs that migrated to the developing gonad (testes) differentiated into spermatogonia. 2025-02-06 18  Before puberty... Before puberty: at birth, the germ cells in the male gonad (testes) are in the sex cord as large, pale cells surrounded with supporting cells called sustentacular cells or sertoli cells. Shortly before puberty: sex cord acquires lumen and become the seminiferous tubules. At the same time, the PGCs differentiated to spermatogonial stem cells (spermatogonia). 2025-02-06 19 SSCs divide mitotically until puberty. The daughter cells becomes spermatogonia.  At puberty!!! Spermatogenesis begins. Each spematogonium divide mitotically to form distinct daughter cells type A and B. Type A: remains at the basement membrane to maintain the germ cell line. 2025-02-06 20 Type B: gets pushed towards the lumen, where it becomes a primary  Spermatogenesis Each primary spermatocyte generated undergoes meiosis to produce 4 spermatozoa. During meiosis I, the prophase is long (22 days). This is follow by rapid completion of meiosis I. Each primary spermatocytes forms 2 haploid secondary spermatocytes. During meiosis II, secondary spermatocytes form 4 haploid spermatids. 2025-02-06 21 Throughout all these events, there is incomplete cytokinesis, therefore, the cells are  Spermatogenesis 1 type A = 16 type B = 64 spermatids Meiosis I Meiosis II 2025-02-06 22  Hormonal regulation of spermatogenesis This involves interactions between the hypothalamus, anterior pituitary gland and testes (HPG axis). The relationship is called brain-testicular axis. The hypothalamus releases gonadotropin releasing hormone GnRH which bind to pituitary gland to release Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). LH binds to the interstitial cells and stimulate them to release testosterone which trigger spermatogenesis. FSH stimulates spermatogenesis indirectly by stimulating sertoli cells to release androgen-binding protein (ABP). ABP 2025-02-06prompts the spermatogenic cells to bind and 23  SPERMIOGEN ESIS Is the series of morphological changes resulting in the transformation of spermatids into spermatozoa. Is a streamlining process. STAGES: Formation of the acrosome that cover half of the nuclear surface. Condensation of the nucleus. Formation of the neck, middle piece, and tail. Shedding of most of the cytoplasm. Note: In human, from spermatogonium to mature 2025-02-06 24 spermatozoon takes 64 to 72  OOGENESIS Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte It takes year to complete. It begins during fetal period. It ends at menopause. 2025-02-06 25  Prenatal Stage Of Oogenesis This is a series of events that Each primary oocyte is leads to formation of mature surrounded by follicular oocyte. cells, and called The PGCs differentiate into primordial follicle. oogonia on getting to the female gonad. The primordial follicle Oogonia multiply rapidly by remain arrested until mitosis , and then enter a puberty is reached. growth phase to form primary The arrest is caused by oocytes. Oocyte Maturation By 3rd month, they are arranged Inhibition (OMI) into clusters each surrounded produced by the follicular by follicular cells. cells (peptide). By 5th month of prenatal development, about 7 million At birth, total primary oogonia are in the ovary. oocyte is about 600,000 By 7th month, majority of to 800,000. oogonia and primary oocytes 2025-02-06 Most of them become 26 become atretic. 2025-02-06 27  PUBERTY… POOL of growing follicles are established. Each month, 15 to 20 are selected for maturation but only one will succeed. They pass through three (3) stages of maturation. - Primary follicle - Secondary/Antral - Preovulatory (Grafian follicle) Primary oocyte begins to grow, the follicular cells becomes cuboidal and become granulosa cells. Primary follicle is formed. Granulosa cells are separated from the stromal cells by theca folliculi. Zona pellucidal (glycoprotein layer) is secreted by the oocyte and granulosa on the oocyte surface. as the growth continues, theca folliculi organise into: - theca 2025-02-06interna (secretory cells) 28  CONT…. Fluid filled space appear within the granulosa and coalese to form the antrum (secondary follicle). The antrum enlarged, and the push the oocyte and granulosa cell around it to the periphery. The granulosa cells surrounding the oocytes form cumulus oophorus. At this stage, the theca internal and externa merge with ovarian stroma. At this stage it is called Secondary follicle. The secondary follicle continues to enlarge until it reaches maturity and produce a swelling on the surface of the ovary. A surge in LH induces the Preovulatory Growth Phase. Meiosis I is completed, resulting in formation of 1 secondary oocyte and first polar body. The first polar body is located between zona pellucida and cell membrane of secondary oocyte (perivitelline space). Then enter meiosis II but arrest at metaphase for about 3 hours before ovulation. Meiosis 2025-02-06 II is not completed until fertilization…. 29 2025-02-06 30  Hormonal regulation of oogenesis Oogenesis is regulated and completed at puberty under the influence of hormones. The hypothalamus releases gonadotropin- releasing hormone (GnRH) which stimulate the pituitary gland to release FSH and LH. FSH stimulate the development of ovarian follicles. Each month it stimulate the growth of 15-20 primary follicles. FSH also stimulate production of estrogen by follicular cells. Luteinizing hormone (LH) serves as the trigger for ovulation (release of secondary oocyte). LH also stimulates follicular and corpus luteum to produce progesterone. 2025-02-06 31  Summary 2025-02-06 32  Female Genital System The Ovary: female sex gland, produce ova. The Uterus: in which the fetus develop. 2025-02-06 33  ASSIGNMENT CELL STRUCTURE & CELL DIVISIONS??? 2025-02-06 34