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OVERVIEW OF REPRODUCTION

OVERVIEW OF REPRODUCTION. M.A.Kai-Kai. Learning Objectives. Understanding: the anatomy of the male and female reproductive systems the gonad as a cytogenic and endocrine organ.

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OVERVIEW OF REPRODUCTION

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  1. OVERVIEW OF REPRODUCTION M.A.Kai-Kai

  2. Learning Objectives. Understanding: • the anatomy of the male and female reproductive systems • the gonad as a cytogenic and endocrine organ. • the sequence of reproduction from gametogenesis in the testis and ovary to germ cells transported and fertilised in the female uterine tube formation of zygote. • the processes of folliculogenesis and formation of the female gamete. • spermatogenesis. • fertilisation.

  3. OVERVIEW The Gonads • Male and female reproductive are homologoussimilar embryologic origin, structure and functions. • Consists of gonads(testis and ovary) and genital tubes/ducts. • Paired gonads are cytogenic(gametogenesis) and endocrine(hormones) • Gametogenesis • Genital tubes transport gametes. • Fertilisation and development of embryo occurs in female tubes. 1.Developing follicles 2.Mature follicle 3.Mesovarium 4.Uterine horn 5.Blood vessels

  4. OVERVIEW. The female Reproductive tract of bitch Suspensory ligament Ovary Uterine tube Uterine horn 1.Different parts of the female reproductive system each with specific functions. • Paired ovary is cytogenic and endocrine • Paired uterine tubesinfundibulum, ampulla and isthmustransport oocytes,sperm and embryo, • Uterusuterine horn,body and cervix. • Vagina, Vestibule • External genitalia Vulva,clotoris 2.Transient seasonal changes in structure and function. 3Functional sequence of the femalegametogenesis/ Folliculogenesisovulation Fertilisationdevelopment. 4. Age changes in structure Suspensory Lig. Intercornual Lig. Uterine tube Ureter Mesosalpinx Bladder Uterine horn Body of uterus Mesometrium Cervical canal Cervix Vagina Urethral opening Vestibular bulb Vestibule Ischiourethralis and ischiocavernous muscle Constrictor Vestibuli muscle Clitoris Labium Fossa clitoridis

  5. Descriptive Terms Female animals can be: • Reproductive cycleanoestrus, proestrus,oestrus, metoestrus, and dioestrus • Ovulation(overt, cyclic) • Monoestrus. • Polyoestrus • Nulliparous • Parous • Monocotous • Polycotous

  6. Structure Of Ovary

  7. GAMETOGENESIS Femaleoogenesis and folliculogenesis Malespermatogenesis Two phases: • Hormone-independent phase in foetal gonad and before puberty --gonocytes undergo mitosis --primordial and primary follicles form in ovary --prespermatogonia form in testis. • Hormone-dependent phase> --begins at puberty -- in ovary folliculogenesis and oogenesis form hierarchy of folliclesovulation. --testisspermatogenesis

  8. Gametogenesis • Gametogenesis --meiotic/reductiondivision • First meiotic divisioncrossing • over at prophase 1 between paternal and maternal chromosomesgenetic variability2 haploid germ cells • Second meiotic divisionnormal mitosis4 haploid germ cells. --male germ cell undergo morphogenesischange in cell morphology. • Germ cells from primordial cellstwo processes --Oogenesis in femaleova --Spermatogenesis in malespermatozoa • Meiosis2 divisions • Diploid number restored at fertilisation.

  9. FOLLICULOGENESISFollicular Hierarchy Dependent on: 1.Dimensional criteria. Size 2.Morphological criteria --thickness of the theca and granulosa layer --degree of vascularisation --position of antral cavities --degree of vascularisation --quantity of muscle fibres and interstitial tissue. 3.Normal functional follicles e.g. corpus luteum 4.Atretic follicles

  10. Follicular Hierarchy • Primordial follicles • Follicular growth controlled Follicle Stimulating hormone(FSH) and estrogen • Early Primary folliclelayer follicular cells. --eostrogen is mitogenic cells proliferate. • Late Primary follicle. --stratified Granulosa --theca cells and zona pellucida(ZP) form. • Secondary Follicle, --more FSH,oestrogen receptors --formation of Corona radiata --granulosa cells secrete follicular fluid into intercellular clefts • Graafian/preovulatory follicledominant follicles with more FSH receptors --intercellular spaces coalesce into single antrum --follicular liquorcontains nutrients and hormones. --granulosa cells distributed into peripheral parietal layer,corona radiata and cumulus oophorus . --the CR support and accompany the oocyte at ovulation.Ovum devoid of CR do not fertilise.

  11. The Oocyte • Formation and development of ova and occurs in two stages. 1. Foetal gonad, gonocytes undergo mitosis and induced into meiosis(MIF). --meiosis I arrested in prophase I, forms primary oocyte. 2.Puberty-->FSH,LH,secretion leads to follicular development and oocyte maturation. --hormonal influence-->growth, meiosis I and meiosis II in oocyteforms secondary oocyte. • folliculostatin/inhibinsynchronises events in ovulation. --co-ordinates growth and maturation of oocyte and granulosa cells.

  12. Ovulation • Mechanisms --hormonalsurge leads to increase in enzyme activity; collagenase --increased intrafollicular pressure. --neural • Ovulationrupture of ovarian wall and folliclereleases gamete. • Gamete transported and fertilised in uterine tube. • Granulosa cells and theca interna become luteinisedform corpusluteum(CL), a transitory endocrine organ. • Luteal phaseprogesterone secretion. • Formation, maintenance and regression of CL under hormonal control. • Life span of CL dependent on luterophic LH and luteolytic PG2a.

  13. Male Reproductive Organs • Paired testis in scrotum • Genital tubesductuli efferensepididymis ductus deferens. • Accessory sex glands, ampulla,vesicular,prostate, Bulbouretral gland. • Penis. • Sequence of reproduction Spermatogenesistransport semenin vaginauterine tube fertilisation at ampulla-isthmic junction.

  14. Gross structure of testis and genital ducts • Gross structure 1.Testis parenchyma 2.Mediastinum(M) and rete testis. • Genital ductsductuli efferentes, Epididymis[head(EH) body and tail(ET)]. • Pampiniform plexusblood vessels.

  15. Spermatogenesis • Functions: 1.Renewal of spermatogenic stem cell 2.Reduction of chromosome to haploid state by meiosis. 3. Metamorphogenesis of a convential cell into a flagella spermatozoa. • Mechanism: • Spermatocytogenesismitosis of stem cell spermatogonia A. • Meiosisreduction division • Spermiogenesismetamorphogenesis

  16. Spermiogenesis • A process of morphogenesis, changing typical cell into spermatozoa with flagella • Consists of 1. Golgi phasegolgi membrane forms cap over nucleus. 2. Acrosome phaseformation of Acrosome from Golgi 3. Spermiogenesis. Formation of flagellum. --organisation of contractile axoneme --organisation of mitochondria in middle piece and principal piece --organisation of dense fibrous sheath. • The spermatozoa structureacrosome, middle piece, the flagellum. AX. Axoneme PC. Posterior centriole DC. Distal centriole axoneme

  17. Hierarchy Of Spermatocytes

  18. Transport of gametes,fertilisation and implantation 1.Ova ovulated from ovary, transported through uterine Tube. 2.Sperm deposited in vaginatransportedcapacitation, acrosomecapacity to fertilise. 3.Fertilisation at ampulla-isthmic junction. 4.Zygote transportedimplantated in endometrium. Fertilisation at Ampulla-isthmic junction 3 4 4 1 ovum sperm 2

  19. Fertilisation • Capacitation • Fertilisationconsists of: • Binding of sperm to zona pellucida • Acrosome reaction: 3. Penetration of Zona Pellucida 4.The cortical reaction fusion of plasma membranes of sperm and egg 5. Sperm nucleus enters oocyte, forms pronucleus, meiosis II complete.

  20. Female born with definite number of post mitotic follicles and gametes needed in life. Meiosis begins in the fetal ovary, is arrested at prophase I and is resumed at puberty. Meiosis imitated once in a definite group of cells Differentiation of gametes occurs while diploid in the first meiotic prophase Gamete has typical cellular structure. As well as forming a haploid nucleus, oogenesis builds up a store of cytoplasmic enzymes, mRNAs, organelles and metabolic substrates. There are more variations in the mechanisms oogenesis according to patterns of reproduction Male gametes undergo mitosis throughout life, but Sertoli cells are post mitotic Meiosis starts at puberty. Meiosis initiated continuously in a mitotically dividing stem cell population. Differentiation of gametes occurs while haploid after meiosis ends. The spermatozoa has atypical structure. The spermatozoa is a motile gamete with little cytoplasmic content. There is less variation in the mechanisms of spermatogenesis. Examples of sexual dimorphism in mammalian gametogenesis

  21. Summary • The reproductive organs consists of paired gonads and genital ducts • The gonads have cytogenic and endocrine functions. Germ cells undergo two meiotic divisions by oogenesis and spermatogenesis. The gametogenic process produces haploid gametes. • The ovum is ovulated from the ovary and sperm is deposited in the female reproductive tract. • The gametes are transported through the genital tubes and fertilisation occurs in the ampulla of the female. Fertilisation is marked by the fusion of the membranes of the male and female gametes. The pronuclei from each parent fuse and the diploid state of chromosome is restored. The Zygote is formed. • The zygote goes through embryogenegsis by the mechanisms of cleavage, blastulation,gastrulation, neurulation and organogenesis.

  22. References 1. Alberts, B; Johnson, A; Lewis, J; Martin, R; Roberts, K; & Walter, P(2002). The Molecular Biology of the Cell. 4th.Edition. Garland Science Chapter 20. 2. Dyce, K; M.,Sack, W;O, & Wensing, C;J;G.(2006). 3rd. Edition. Textbook of Veterianry Anatomy.Pages183 – 202, 435 -453 3. Neill,J;D.(editor-in-Chief). Physiology of Reproduction. 3rd.Edition. Elsevier. London.Volume 1. Page3-113.

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