Gametogenesis 2023 PDF

Developmental Anatomy (Embryology) Def: science deals with origin and development of the mammalian organism from fertilization to the end of life The whole development al events ( ontogenesis ) of the organism includes Intra uterine 1. Embryogenesis 2. Fetogenesis 1. Extr...

Developmental Anatomy (Embryology) Def: science deals with origin and development of the mammalian organism from fertilization to the end of life The whole development al events ( ontogenesis ) of the organism includes Intra uterine 1. Embryogenesis 2. Fetogenesis 1. Extra uterine 1. Infancy 2. Child hoods. 3. Adolescence 4. Maturity 5. Old age (senility) Prof. Ahmed Saber El Fayoumy  Classification of embryology General Embryology : general principles of the development from zygote to embryo. Special Embryology : Deals with the differentiation and formation of the special organs or system Comparative embryology: Deals with the comparative of the structural features of the organisms of various stages in all mammals Experimental Embryology : Deals with the factors and agents which activate or regulate the development. Or study the effects of agents or factors on the development of organism  Aim of thesis course Understanding the complexity of anatomical structures Understanding comparative anatomy Understanding the phylogony of organsium (historic development) Understanding the teratology and congenital anomalies Important of gynacology and obestetrics  Stages of development Progenesis: Gametogenesis, sexual cycle and fertilization Blastogenesis: cleavage, morula then formation of blastula Gastrulation: formation of the three-germ layers ( ectoderm, mesoderm and endoderm) Fetal membrane: formation of amnion, chorion, allantois and yolk sac Placentation: formation of placenta Organogenesis : formation of organs  Gametogenesis Def: It is the process of the formation & maturation of both male gametes (spermatozoa) and female gamete (ovum) It is called in the male Spermatogenesis and in the female it is called Oogenesis Prof. Ahmed Saber El Fayoumy  The gametogenesis includes both of nuclear and cytoplasmic events Include three period 1. Proliferation (mitosis division) 2. Growth 3. Maturation (nuclear changes or miosis devision) The male and female gametes are derived from premordial germ cell (pgc) from endoderm of yolk sac (gut) Primordial germ cell At the 4th week the primordial germ cell migrates from the endoderm of the yolk sac to genital ridge (future testis or ovary according to sex) In male primordial germ cells will be spermatogonia In female will be oogonia Primordial germ cells (PGCs) precursor germ cells or gonocytes  Time of gametogenesis In male: the three period starts from puberty till death In female: – it starts in fetal ovary and in most species progresses to the primary oocyte stage (proliferation) – Birth to puberty (growth) – maturation present after puberty at ovulation (first miosis) and fertilization (second miosis) – finally stop at senility (menopause)  SPERMATOGENESIS The sperm formation involves two steps : A. Spermatocytogenesis is the first step: where the spermatogonia forms rounded cells called spermatids B. Spermiogenesis is the second step where the spermatids differentiate into specialized motile cells known as spermatozoa (sperm).  Site and time of spermatogenesis Within seminiferous tubules of testis Begin at puberty  Spermatocytogenesis At puberty perimordial germ cell proliferate by mitosis and form spermatogonium After several proliferation spermatogonia differentiate into type- A and type- B. type-B spermatogonia, rested and grow and are called primary spermatocytes. type A spermatogonia act as stem cells where it divided into type A&B again and so on  Maturation: The primary spermatocytes divided by first meiotic division into 2 haploid secondary spermatocytes (N) Each secondary spermatocytes rapidly divided by second meiotic division into 2 spermatides  The spermatocytogeneses 1-Period of proliferation: primordial germ cells( 2 N) (At puberty) Spermatogonia (2N) Mitotic division Spermatogonia type( B) 2N Spermatogonia type (A) (Resting cell) II- period of growth Growth Primary spermatocyte (2 N XY) III-Period of maturation maturation (1st meiosis) secondary spermatocyte secondary spermatocyte (1N X) (1N Y) ( 2nd meiosis) Spermatid spermatid spermatid spermatid  Spermiogenesis definition: It is the transformation of the spermatid into motile spermatozoa by changes in the cytoplasm & nucleus Sperm (spermatozoa) is formed of Head contains nucleus and acrosome (contain enzymes) Mid piece contains mitochondria Tail Golgi apparatus forms acrosomal cap around anterior part of nucleus. Contains proteolytic enzymes Nucleus is condensed and become smaller directed to one pole Centrioles and Microtubules: make collar around neck and form the tail (flagellum)  Mitochondria: arrange around neck or mid piece Excess cytoplasm: is lost as residual body Cytoplasmic bridges : that connect the newly formed sperm is breakdown then sperms release from Sertoli cells to lie free in lumen of seminiferous tubules. About 64 -74 days are required to go from a spermatogonium to a sperm  Oogenesis It is the formation and maturation of female gamete (ovum) within the ovary Unlike male gamete the formation and maturation of the ovum take very long time – from early embryonic period till birth (proliferation period) and – from birth till puberty (growth period) and – after puberty during ovulation and fertilization (maturation period). Oogenesis  Primordial germ cells Stage of proliferation Mitotic before birth oogonium Growth From birth to puberty Primary oocytes (2N) 1st meiotic Maturation after puberty at ovulation Secondary oocytes (1N) 1st polar body 2nd meiotic At fertilization Ovum + second polar body 2 polar body  female has fixed number of primary oocytes After puberty the primary oocytes either – Complete the maturtaion phase and become ovum – Or degenerates (die) – During oogenesis the oocytes become surrounded by follicular or granulosa cells of ovary by processes called folliculogenesis to form (primary follicle then secondary follicle and finally tertiary or mature follicle or Graffian follicle to be ovulated – Become surround by zona pellucida (glycoprotein layer) formed by ovum and granulosa cells  folliculgenesis Formation and maturation of graaffian follicle around the oocyte it passes by several stages Ovulation is the rupture of the mature graafian follicle and release of the secondary oocyte under the effect of – LH hormone and increase intrafollicular pressure At ovulation only – secondary oocyte released – surrounded by zona pellucida and – cuboidal granulosa layer (corona radiata) and few gnaulosa cells – while the rest of follicle will form corpus luteum Release of secondary oocyte (1N) surrounded by follicle cells (2N)  Structure of ovulated oocyte Secondary oocyte – cytoplasm) – Nucleus – cytoplasmic membrane (Vitelline membrane ) Previtelline space 1st polor body Zona pellucida Corona radiata  Spermatogenesis Oogenesis 1-occurrence In the testes In the ovary 2-Time & result of After puberty Only in fetal period multiplication It gives two types Gives only one type of cells(A&B) of cells 3-The growth Limited &short Very long & slow 4-First meiosis Occur at any time Occur only just after puberty before ovulation 5-Second meiosis At any time after Occur only after puberty fertilization 6-The end result Four equal One ovum & spermatid cells 3polar body  Membranes of ovum Primary membrane: cell membrane or cytoplasmic membrane or oolemma. Secondary membrane: – the zona pellucida formed by the oocyte and follicular cells in mammals ( gylcoprotein). – Albumin material surround the ova in frog ans fish. Tertiary membrane: Albumen, shell membrane and shell of the egg of hens (it is an additional layers formed by oviduct )  Type of ova The ovum classified according to the amount of yolk contain or according to the distribution of yolk within the ovum A- according to the amount of yolk Microlecithal or oligolecithal: have small amount of yolk, such as amphioxus or mammals Mesolecithal or mediolecithal: have a moderate amount of yolk such as amphibians (frog) and fish Macrolecithal or polylecithal: have large amount of yolk such birds and reptile  B-According to distribution of yolk A- Iso-lecithal; The yolk uniformly distributed in the cytoplasm (e.g. Amphioxus and Mammals). B- Anisolecithal 1. telo-lecithal : The yolk present in the vegetal pole and the cytoplasm and nucleus in the animal pole (e.g. Amphibia (frog) fish, reptile and birds.) 1. microtelolecithal incomplete separation as in frog and fish 2. Macrotelolecithal complet separation as reptiles and birds 2- Centro-lecithal: the yolk present centrally insects