Transcript GAMETOGENESIS - University of Edinburgh

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.
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.
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 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.
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
Intercornual
Lig.
Mesosalpinx
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,oestrus,
metoestrus, and dioestrus
► Ovulation(overt, cyclic)
► Monoestrus.
► Polyoestrus
► Nulliparous
► Parous
► Monocotous
► Polycotous
Structure Of Ovary
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 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
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
►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
Ovulation
Mechanisms
--hormonal surge 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 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 PG2a.
►
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 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.
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metamorpho
genesis
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
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
4. The cortical reaction
fusion of plasma
membranes
of sperm and egg
5. Sperm nucleus enters
oocyte, forms pronucleus,
meiosis II complete.
Examples of sexual dimorphism in mammalian gametogenesis
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.
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.
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.