Transport of male and female

gametes, Fertilization,

Implantation

Dr. Vikash Kumar Kajla

Both the male and female gametes must be transported in a

viable condition to the site of fertilization for the successful

reproduction

The gametes are transported in the opposite direction –

oocytes from ovary to infundibulum to ampulla-isthmus

junction and spermatozoa from vagina to cervix to uterus to

ampulla-isthmus junction

Sperm must be in the oviduct when the oocyte reaches the

site of fertilization – the ampulla-isthmus junction

Transport of gametes,fertilisation and implantation

1.Ova ovulated from ovary, transported through uterine Tube.

2.Sperm deposited in vaginatransportedcapacitation,

acrosomecapacity to fertilise.

3.Fertilisation at ampulla-isthmic junction.

4.Zygote transportedimplantated in endometrium.

1.Ova ovulated from ovary, transported through uterine

Tube.

2.Sperm deposited in vaginatransportedcapacitation, acrosomecapacity to fertilise.

3.Fertilisation at ampulla-isthmic junction.

4.Zygote transportedimplantated in endometrium.

Fertilisation at

Ampulla-isthmic junction

1

2

3 44

ovum

sperm

Sperm Transport in male duct statem

The testicular spermatozoa are transported

7 days in bulls, 12 days in boar and 16 days in

ram.

Sperm Immotile & Incapable of fertilization.

Maturation of spermatozoa between rete testis &

cauda epididyamis.

Migrate in epididymis, they develop motility

and potential fertilizing capacity.

Cauda and vas deferens serve as store space for

mature spermatozoa.

Sperm Transport

In cattle, sheep semen is deposited in the vagina.

Swine- cervix, horse- uterus.

Sperm transport in the female genitalia in two phases – rapid and sustained

Rapid phase - within minutes after insemination, non-motile uncapacitatedspermatozoa are rapidly transported to oviducts

The copulation-induced peristalsis of the female tract

oxytocin released by cervical stimulation during copulation.

Both dead and live but uncapacitated sperm are transported and they leave the oviduct through infundibulum into the peritoneal cavity

Cervix is the greatest barrier to the transport of sperms

cervical mucus is thin and watery during estrus.

dead and abnormal sperms are removed and most of the live sperms are trapped in the cervical crypts

most of the seminal plasma are removed in the cervix (semial plasma inhibits capacitation)

Mucosal folds of the cervical crypts and uterotubal junction act as sperm reservoirs

This helps the slow, sustained phase of sperm release.

In pigs, uterotubal junction acts as the reservoir.

Utero-tubal junction also is a barrier to sperm movement and weak sperms are filtered

In FT Sperm transport depends on the motility of cilia and segmental contractions of FT

Under normal condition, spermatozoa reach the site of fertilisation some hours before ova.

Barriers to sperm transport:

Cervical mucus (filtration and selection),

endometrial glands,

Uterotubal junction.

In uterus enormous no. of sperm are phagocytosed by macrophages(WBC).

Many are lost due to retrograde flow.

Sperm retain their fertilizing capacity in the female tract 24-48 h;

In cow, ewe 30-48h; sow -72h,bitch-90h and 72-120h in mare.

The cervix is an ideal site for survival of the spermatozoa

(In vaginal passage, sperm do not survive more than 1 to 2 h).

Normally, only one spermatozoon is necessary for fertilization,

but without a total optimum concentration (10-million

sperm/ml in artificial insemination) the conception rate declines.

Goat reproductive system

Capacitation of Spermatozoa

Removal of adherent Seminal plasma.

1.5h in sheep, 3-6h in pigs

Capacitation begins in the uterus and is

completed in the oviduct.

Then reach to the ampulla of oviduct and

become hyperactive due to Ca2+ influx.

In the presence of oocytes, spermatozoon

membranes undergo change.

Increases the metabolic activities of the sperm

cells by increasing the rate of glycolysis

Acrosome reaction:

The acrosome reaction involves breakdown and fusion of outer

acrosome membrane with the plasma membrane of the sperm.

formation of vesicles and release of enzymes needed for sperm to

penetrate the cumulus oophorus and corona radiata as well as zona

pellucida .

Fuse with vitalline membrane of oocytes during fertilization.

Ovum Transport

The fimbriated end of the infundibulum picks up the ovum

Ovum transported down the uterine tube towards the uterus

combined actions of the cilia (beat towards uterus) and peristaltic contractions of uterine tube.

ratio of hormones, oestrogens and progesterone (high oestrogen level increase contractions) ,levels of prostaglandins

following ovulation, the ovum with the vitelline membrane is surrounded by a thin zona pellucida and granulosa cells – cumulus oophorus.

The ovum remains viable in the uterine tube 12 to 24 hrs

Bitch 4 to 8 days; cattle 20-24h; horse 6-8h; sheep 16-24h, swine 8-10h

In bitch, the ova enter the oviduct as primary oocyte and then mature in the uterine tube.

In the cow, ewe and sow the ovum is released as secondary oocyte.

speciesSite of semen

deposition

Volume of

ejaculate (ml)

Sperm

concentration

(billion/ml)

No. of sperm reaching

site of fertilization

Cow Vagina 4 1 4200-27500

Sheep Vagina 1 2 600-5000

SwineCervix and

uterus125 0.200 Few

Human Vagina 3.5 0.120 Few

species Time of ovulation

Cow 10-12 hours after end of estrous phase

Sheep Late of estrous phase

Goat Few hours after end of estrous phase

Swine Mid-estrous phase

HumanDay(14) after initiation of menstrual

cycle

Species

Time of

formation

of zygote

(hours)

Entry to

uterus

(days)

Cow 0-24 3-4

Sheep 0-38 2-4

Goat 0-30 4

Swine 0-15 2-4

Human 0-24 3

Sperm attachment

The attachment of sperm head to the zona pellucida is regulated by

receptor sites on the zona surface.

A glycoprotein ZP3 – synthesised by the mature oocyte functions

as the sperm receptor to which the sperm with intact acrosome

can bind.

Presence of glycosyl transferase, proteinases and glycosidases on

the plasma membrane covering help the sperm head to bind with

ZP3.

Ruptured follicle will transformed into the corpus luteum, that

produce large amount of progesterone that helps to prepare the

uterus for implantation of fertilized egg

In absence of fertilization corpus luteum degenerates.

FERTILISATION

Fertilisation is fusion of male and female gametes to form one single cell,

the zygote

at ampullary-isthmic junction of the oviduct.

Sperm-oocyte encounter

Fertilization requires three critical events:

a. Sperm migration between cummulus cells

b. Sperm attachment and migration through the zona pellucida

c. Fusion of sperm and ovum plasma membranes

Cumulus penetration

Oviductal secretions cause hyperactivity if not all of cumulus cells are

removed by mechanical means as ovum travels through the oviduct.

cattle cumulus absent 3-4 hours after fertilization

Hydrolytic enzymes in the acrosome aids in penetration of cumulus cells

by the sperm.

Sperm Attachment

ZP3 sperm receptor "lock and key" mechanism starts

Sperm Penetration

5 to 15 minutes after sperm attachment.

the sperm acrosome in penetration of zona - at least 9 enzymes released

Acrosin is major zona lysin

Sperm motility is also required

Only one spermatozoan

Gamete Fusion

Zona is penetrated; the sperm interacts with the vitelline membrane;

Stimulates second meiosis in the ovum to form the second polar body.

Sperm head undergoes decondensation and forms male pronucleus

Chromosomes of ovum form the female pronucleus.

fuse sperm and egg chromosomes into a single cell,2n. This process is known as “syngamy”.

Block to Polyspermy

Immediately following fertilisation, the ovum surface changes and

prevent entry of additional spermatozoa.

Block to polyspermy occurs at the zona pellucida (e.g., sheep, swine)

Release of enzymes to harden the zona pellucida and inactivates

sperm receptor ZP3.

Polysperm fertilized embryos are unable to develop normally and

dies or the embryo development is abnormal

Occurs in 1-2% of mammalian fertilizations; increased by delayed

insemination-pigs and sheep

In some species of mammals, such as swine, several ova are produced and fertilized during a single cycle resulting in multiple births.

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.

EMBRYO DEVELOPMENT

The zygote is a large cell having low nuclear : cytoplasmic ratio

(small nucleus and more cytoplasm)

Within few minutes after formation by mitotic division the zygote

becomes a two-celled embryo, the blastomere

By series of mitotic division, 4-celled, 8- celled, 16-celled embryo.

Finally a solid ball of cells called the morula

Most species form a morula at approximately 16 to 32 cells stage

(in about 5 days after fertilization).

Each cell up to 8-16 cell stage of embryo is totipotent i.e. diff.

tissus

Morula leads to formation of a fluid filled cavity called blastocoele

The zygote remains in the oviduct for 3- 4 days after fertilisation

(dogs 10 days)

Twinning

Dizygotic develop from two separate eggs that are fertilized by two

separate

Species differences – sheep and goat- ~<75% twins; cattle-1-3.5%

twins; horses-1-2% twins

Older animals more prone to produce twins

Induced twinning – by superovulation and immunization against

inhibin

Monozygotic-twins develop from one zygote that splits and forms two

embryos

Rare in domestic animals - cattle <10% of twins born. Identical

twinning can be artificially achieved by microsurgery of two

totipotent blastomeres

IMPLANTATION

Following fertilisation, the new embryo reaches the uterus 4 days

post-oestrus in cows and ewes. slightly sooner in sows and slightly

latter in bitches.

The rate of transport through oviduct is controlled by the

oestrogen and progesterone ratio.

After entrying into the uterus the embryo remains free-floating in

the uterine fluid and derives its nutrients from the endometrial

secretions.

The embryo continues to grow by mitotic division

The cells become arranged to one side (known as compaction) and

fluid accumulates in the central cavity known as blastocoele and the

conceptus is called blastocyst

The blastocyst has two cell types –

(1) trophoblast(outer) which later forms the placenta

(2) Inner cell mass (ICM) Group of cells surrounded by trophoblast

which develops into foetus

When the blastocyst reaches the uterus, it is still covered by zona

pellucida.

In 6-11 days after fertilization, “zona hatching”. (Zona pluceda break)

Zona hatching – cattle 9-11 days, horse-8; sheep-7-8 and swine in 6

days after fertilization

Blastocyst elongation occurs in cows, sheep, and pigs, but not in

horses

Concurrent with blastocyst elongation, gastrulation (ICM

differentiate into three distinct layers – ectoderm, mesoderm and

endoderm) occurs in the embryo

After fertilisation, implantation occurs about

14-20 days in sow,

15 days in bitch,

15-18 days in ewe,

30-35 days in cow and mare

20-25 days in doe,

13 days in queen

6-8 days in primates.

Hypoblast

Hormonal Requirement of Implantation

The ratio between progesterone and oestrogen is important

progesterone alone in determining the preimplantation changes in the

uterus.

During the progestational period the muscular activity and tone of the

uterus are considerably decreased which helps to retain the blastocyst in

the uterine lumen.

Progesterone is also needed for the growth and secretion of endometrial

glands

in pigs, embryonic estrogen promotes uterine secretions

Changes in Reproductive Organs

Vulva - swollen

Vagina - pale and dry –in early pregnancy

swollen and pliable during late pregnancy

Cervix - tightly closed by viscid mucous Plug

Uterus – enlarges by growth and stretching

proliferation of all the layers of uterus; myometrium is quiescent

without any contractions

Ovary – contains corpus luteum (verum);

this ovarian CL regress by 7th month in horse; some follicle activity

occur during early gestation

Pelvic ligaments and pubic symphysis relax during late pregnancy

under the influence of estrogen and relaxin