OVERVIEW OF REPRODUCTION M A KaiKai Learning Objectives

OVERVIEW OF REPRODUCTION M. A. Kai-Kai

Learning Objectives. Understanding: Anatomy of the male and female reproductive systems Structure of the gonad as a cytogenic and endocrine organ. 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.

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

OVERVIEW. The female 1. Different parts of the female reproductive system each with specific functions. ►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. 3 Functional sequence of the female gametogenesis/ Folliculogenesis ovulation Fertilisation development. 4. Age changes in structure Reproductive tract of bitch Suspensory ligament Ovary Uterine tube Uterine horn Suspensory Lig. Uterine Ureter tube Mesosalpinx Intercornual Lig. Bladder Uterine horn Body of uterus Mesometrium Cervical canal Cervix Vagina Vestibular bulb Ischiourethralis and ischiocavernous muscle Labium Urethral opening Vestibule Constrictor Vestibuli muscle Clitoris Fossa clitoridis

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

Structure Of Ovary

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.

Gross structure of testis ►Gross structure 1. Testis parenchyma 2. Mediastinum(M) and rete testis. ►Pampiniform plexus blood vessels.

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

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.

FOLLICULOGENESIS Follicular Hierarchy Dependent on: 1. Dimensional criteria. Size 2. Morphological criteria --thickness of 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

►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/inhibin synchronises events in ovulation. --co-ordinates growth and maturation of oocyte and granulosa cells. The Oocyte

follicles Follicular ►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. ►Primordial Hierarchy

Ovulation Mechanisms --hormonal surge leads to increase in enzyme activity(collagenase) --increased intrafollicular pressure. --neural ► Ovulation; rupture of ovarian wall and follicle releasing gamete. ► Gamete transported and fertilised in uterine tube. ► Granulosa cells and theca interna become luteinised form corpus luteum(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 PG 2 a. ►

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: 1. Spermatocytogenesis mitosis of stem cell spermatogonia A. 2. Meiosis reduction division 3. Spermiogenesis metamorphogenesis

Spermiogenesis ►A process of morphogenesis, changing typical cell into spermatozoa with flagella ►Consists of: Golgi phase golgi membrane forms cap over nucleus. (1, 2). Acrosome phase formation of Acrosome from Golgi. (3) 3. Spermiogenesis. (4, 5) 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 M i d d l e p i e c e axoneme

Hierarchy Of Spermatocytes

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 1 4 4 ovum sperm 2

Fertilisation Capacitation Fertilisation consists of: 1. Binding of sperm to zona pellucida 2. Acrosome reaction: 3. Penetration of Zona Pellucida The cortical reaction 4. Fusion of plasma membranes of sperm and egg 5. Sperm nucleus enters oocyte, forms pronucleus, meiosis II complete.

Differences in mammalian gametogenesis Female oogenesis 1. Female born with definite number of post mitotic follicles and gametes needed in life. 2. Meiosis begins in the fetal ovary, is arrested at prophase I and is resumed at puberty. 3. Meiosis imitated once in a definite group of cells 4. Differentiation of gametes occurs while diploid in the first meiotic prophase 5. Gamete has typical cellular structure. 6. There are more variations in the mechanisms oogenesis according to patterns of reproduction Male Spermatogenesis 1. Male gametes undergo mitosis throughout life, but Sertoli cells are post mitotic 2. Meiosis starts at puberty. 3. Meiosis initiated continuously in a mitotically dividing stem cell population. 4. Differentiation of gametes occurs while haploid after meiosis ends. 5. The spermatozoa has atypical structure. 6 There is less variation in the mechanisms of spermatogenesis.

References 1. Alberts, B; Johnson, A; Lewis, J; Martin, R; Roberts, K; & Walter, P(2002). The Molecular Biology of the Cell. 4 th. Edition. Garland Science Chapter 20. 2. Dyce, K; M. , Sack, W; O, & Wensing, C; J; G. (2006). 3 rd. Edition. Textbook of Veterianry Anatomy. Pages 183 – 202, 435 -453 3. Neill, J; D. (editor-in-Chief). Physiology of Reproduction. 3 rd. Edition. Elsevier. London. Volume 1. Page 3 -113.