L11- Introduction to Embryology and Gametogenesis 2023 PDF

Introduction to embryology and gametogenesis Dr Nurul Hannim binti Zaidun MBBS, Msc (Medicine) Dept of Anatomy, Faculty of Medicine UiTM  Learning outcomes 1. Developmental periods in embryology 2. Describe gametogenesis 3. Describe spermatog...

Introduction to embryology and gametogenesis Dr Nurul Hannim binti Zaidun MBBS, Msc (Medicine) Dept of Anatomy, Faculty of Medicine UiTM  Learning outcomes 1. Developmental periods in embryology 2. Describe gametogenesis 3. Describe spermatogenesis and spermiogenesis 4. Describe oogenesis 2  LO1: Developmental periods in embryology 1. Division in developmental period 2. Stages in embryonic development 3. Significance of learning developmental period 3  Developmental periods in embryology Most developmental changes Embryonic occur during the embryonic Prenatal and fetal periods. Fetal Human development is divided into prenatal (before birth) and postnatal (after Human birth) periods. Infancy development The embryonic: The most visible advances occur during Childhood the 3rd – 8th week. Postnatal The fetal period: Puberty Differentiation and growth of tissues and organs occur, and the rate of body growth Adulthood increases. 4  Stages of Embryonic Development It has Stage 1 (fertilization) until stage 23 (D56) A trimester is a period of 3 months, one third of the 9-month period of gestation. The most critical stages of development occur during the first trimester (13 weeks), when embryonic and early fetal development is occurring. 5 6 7 8  Postnatal Period Period Definition Changes Infancy The period of extrauterine The body grows rapidly during infancy. life (the 1st year after birth). Total length increases by approximately one half, and weight is usually tripled. By 1 year, most infants have six to eight teeth. Neonate 1 month or younger (newborn). Childhood The period between infancy The primary (deciduous) teeth continue to appear and are later replaced by the and puberty. secondary (permanent) teeth. Active ossification (formation of bone) with higher rate of growth at early childhood. Just before puberty, growth accelerates back—the prepubertal growth spurt. Puberty The period when humans In females: the first signs of puberty may be after age 8 become functionally capable In males: puberty commonly begins at age 9. of procreation (reproduction) Adulthood Full growth and maturity 18 and 21 years. attained Ossification and growth are virtually completed during early adulthood (21 to 25 years). Brain development continues into early adulthood, including changes in gray- matter volume. 9  Significance of Embryology Bridges the gap between prenatal development and medicine. Develops knowledge concerning the beginnings of life and the changes occurring during prenatal development Understand the basis of variations in human structure Illuminates clinically oriented anatomy Explains how normal and abnormal relations develop Supports the research and application of stem cells for the treatment of certain chronic diseases 10  LO 2: Describe gametogenesis 1. Definition 2. The process 3. The differences between male and female gametogenesis 4. Meiotic division in gametogenesis 11  Gametogenesis Gametogenesis is the process of production of mature gamete cells (oocytes/sperms) from bipotential primordial germ cells (PGC) in the gonads. When male and female gamete met during fertilization, it forms zygote and mark the development into neonate. 12  Gametogenesis The gametes form in the epiblast in the 2nd week primitive streak during gastrulation the wall of yolk sac corresponding developing gonads (4th week) In preparation of fertilization, the germ cells undergo mitosis and meiosis. Function of the meiosis is to reduce the number of chromosomes and cytodifferentiation to complete maturation 13  Normal gametogenesis Production of gametes from spermatogonia (spermatogenesis) and oogonia (oogenesis) from primordial germ cells. The number of chromosome number is reduced by half and the shape of the cells is altered. 14  Mitosis Process by which one cell divides and gives rise to two daughter cells that are genetically identical. Consists of six phases 1. Interphase 2. Prophase 3. Prometaphase 4. Metaphase 5. Anaphase 6. Telophase 15  Meiosis Cell division in the germ cells in that reduced diploid number of chromosome to haploid in 2 cell divisions – Meiosis I & II 16  1st meiotic cell division Germ cells replicate their DNA Homonogous chromosomes align themselves in pairs - Synapsis X-like structure is formed - Chiasma Homonogous pairs separate into two daughter cells reduce chromosome numbers 2nd meiotic cell division In male, the cell divide into equal four identical spermatozoa in male In females, it yields a single, massive, haploid definitive oocyte and three-minute, non-functional, haploid polar bodies. 17  Functions of meiotic division Genetic variability through 1. Crossover which re-distributes genetic materials 2. Random distribution of homologous chromosomes to the daughter cells 3. Germ cells with haploid number of chromosome 18 LO3:Describe spermatogenesis and spermiogenesis 1. Definition of spermatogenesis 2. The process of spermatogenesis 3. Spermiogenesis 19  Spermatogenesis Definition: The process of formation of sperms in the seminiferous tubules of the testis from spermatogonia Spermatogonia is primitive form of PGC Divided into 3 phases: 1. Multiply (Proliferation and differentiation of spermatogonia) 2. Growth (Meiosis) 3. Differentiate (Spermiogenesis) A. Zini and A. Agarwal (eds.), Sperm Chromatin: Biological and Clinical Applications in Male 19 Infertility and Assisted Reproduction, DOI 10.1007/978-1-4419-6857-9_2, © Springer Science+Business Media, LLC 2011 20  Spermatogenesis Type A spermatogonia Type B spermatogonia 1ry spermatocyte 2ry PGC forms type A spermatogonia spermatocyte (spermatogenesis begin) mitosis type B spermatogonia primary Spermatid spermatocyte meiosis I secondary spermatocyte meiosis II Spermatozoa 21  Assignment 1 Describe the changes undergo by the spermatids to form a mature sperms (spermatozoa) 22  LO4: Describe oogenesis 1. Definition 2. The process 1. The 3 phases 2. Maturity timeline 3. Development of the cells 23  Oogenesis Oogonia differentiate into mature oocyte Maturation of oocytes begins before birth: prenatal and postnatal maturation. Divided into 3 phases: 1. Multiplication (intrauterine) 2. Growth 3. Maturation to secondary oocyte (puberty) 24  Prenatal Maturation of Oocytes Post natal Maturation of Oocytes (puberty) The timeline 25  Prenatal Maturation of Oocytes 3rd month: oogonia arranged in clusters surrounded (differentiate into primary oocyte) by a layer of flat epithelial cells primordial follicle As primordial follicle grows, the flat cells change to cuboidal (follicular cell) primary follicle 5th month: 7 millions (maximum) 7th month: degeneration for most oocytes Near the time of birth: 1. All primary oocytes started prophase of meiosis I 2. Arrested at diplotene stage At birth: 700k to 2mils 26  Maturation of oocytes continues at puberty Puberty: 40,000 oocytes Only 15-20 primary follicles (PF) are selected each month. PF accumulate fluid (antrum) and enter antral/ vesicular stage graafian follicles immediately before ovulation. 27  During puberty Mature follicle induces preovulatory growth phase Completed meiosis I Produce 2 daughter cells of unequal size (each with 23 chromosomes) secondary oocyte and 1st polar body Just before ovulation: Secondary oocyte enters meiosis II but arrests in metaphase 3hrs before ovulation Meiosis II is completed only if fertilization occurs. If no fertilization, the egg degenerates. 28 Development of the primary follicle to mature follicle (graafian follicle) Granulosa cells and the 1ry oocytes secrete a layer of glycoprotein zona pellucida Layer of granulosa form theca folliculi and subdivided into two layers: Theca interna – an inner secretory cells Theca externa – an outer fibrous capsule Granulosa cells form the cumulus oophorus 29  Similarities and differences in the gametogenesis between male and female 30 Clinical significance 31  Assignment 2 What other conditions caused from abnormal chromosomes? 32 Thank you for your time! Email me! [email protected] 33