Physiology of ReproductionPhysiology of Reproduction(II)(II)

Teng Yincheng M.D., Ph.D., Professor

Department Of Obstetrics & Gynecology

Renji Hospital Affiliated to SJTU School of Medicine

Pregnancy occurs when a mature liberated ovum

is fertilized by a mature capacitated spermatozoon

Pregnancy is defined as the course of embryo and fetal growth and development in uterine

It begain at the fertilization and end the delivery of the fetal and it’s attachment

The Sperm:The Sperm:• The spermatozoa leave

the testis carrying 23 chromosomes but not yet capable of fertilization.

• Their maturation is completed through their journey in the 6 meters of the epididymis and when mixed with the seminal plasma from the epididymis, seminal vesicle and prostate gland.

After semen is ejaculated, the sperms reach the cervix by

their own motility within seconds leaving behind

the seminal plasma in the

vagina

The Sperm:The Sperm:

At time of ovulation, the cervical mucous is in the most favourable condition for sperm

penetration and capacitation as:1. It becomes more copious, less viscous and

its macromolecules arrange in parallel chains providing channels for sperms passage.

2. Its contents from glucose and chloride are increased.

The Sperm:The Sperm:

• The sperms ascent through the uterine cavity and Fallopian tubes to reach the site of fertilization in the ampulla by:

1. Its own motility, and by2. Uterine and tubal peristalsis which is

aggravated by the prostaglandins in the seminal plasma.

The Sperm:The Sperm:

• The sperms reach the tube within 30-40 minutes

• But they are capable of fertilization after 2-6 hours. • This period is needed for sperm

capacitation.

The Sperm:The Sperm:

• Is the process after which the sperm becomes able to penetrate the zona pellucida,that surrounding the ovum and fertilize it.

• The cervical and tubal secretions are mainly responsible for this capacitation.

Capacitation of spermsCapacitation of sperms

• Capacitation is believed to be due to :1.Increase in the DNA concentration in

the nucleus,2.Increase permeability of the coat of

sperm head to allow more release of hyaluronidase.

Capacitation of spermsCapacitation of sperms

The ovum:The ovum:The ovum leaves the ovary after

rupture of the Graafian follicle, carrying 23 chromosomes and surrounded by the zona pellucida and corona radiata.

The ovum is picked up by the fimbrial end of the Fallopian

tubes and moved towards the ampulla by the :

1. Ciliary movement of the cells and 2. Rhythmic peristalsis of the tube.

The ovum:The ovum:

Fertilization:Fertilization:• Millions of sperms

ejaculated in the vagina, but only hundreds of thousands reach the outer portion of the tubes.

• Only few succeed to penetrate the zona pellucida, and only one spermatozoon enters the ovum transversing the perivitelline space.

Fertilization:Fertilization:• After penetration of the ovum by a

sperm, the zona pellucida resists penetration by another sperms due to alteration of its electrical potential.

• The pronucleus of both ovum and sperm unite together to form the zygote (46 chromosomes).

ZygoteZygote

Sex Determination:Sex Determination:* The * The mature ovummature ovum carries carries 22 autosomes22 autosomes and and

one X chromosomeone X chromosome, while the , while the mature mature spermsperm carries carries 22 autosomes22 autosomes and either an and either an X or Y chromosome. X or Y chromosome.

* If the fertilizing sperm is carrying * If the fertilizing sperm is carrying X X chromosome the baby will be achromosome the baby will be a female female (46 (46 XX),XX), if it is carrying if it is carrying Y Y chromosome the chromosome the baby will be a baby will be a male (46 XY).male (46 XY).

Cleavage and blastocyst Cleavage and blastocyst formation:formation:

On its way to the uterine On its way to the uterine cavity, the fertilized ovum cavity, the fertilized ovum (zygote)(zygote) divides into divides into 2,4,8 2,4,8

then 16 cells then 16 cells (blastomeres(blastomeres). ).

• This This cleavagecleavage starts starts within within 24 hours of 24 hours of fertilizationfertilization and occurs and occurs nearly nearly every 12 hoursevery 12 hours repeatedly repeatedly

• The resultant The resultant 16 cells 16 cells massmass is called is called morulamorula which reaches the which reaches the uterine cavity after uterine cavity after about about 4 days4 days from from fertilization. fertilization.

Cleavage and blastocyst Cleavage and blastocyst formation:formation:

• A cavity appears within the morula converting it into a cystic structure called blastocyst.

• The cells become arranged into an :1. Inner mass (embryoblast) which will form

all the tissues of the embryo, and an 2. Outer layer called trophoblast which

invade the uterine wall.

Cleavage and blastocyst formation:Cleavage and blastocyst formation:

The blastocyst remains free in the uterine cavity for 3-4 days, during which it is nourished by

the secretion of the endometrium (uterine milk).

Cleavage and blastocyst Cleavage and blastocyst formation:formation:

Implantation Implantation (nidation) :(nidation) :

The necessary conditions of imbed

Disapearing of

the pellucid zone Syntrophoblast

formed from the blast Synchronizing development of blast

and the endometriun P Secretory enough

The stage of egg imbedThe stage of egg imbed

Apposition

Adhesion

Penetration

The deciduaThe decidua::• It is the thickened

vascular endometrium of the pregnant uterus.

• The glands become enlarged, tortuous and filled with secretion.

• The stromal cells become large with small nuclei and clear cytoplasm, these are called decidual cells.

The decidua, like The decidua, like secretory secretory

endometrium, endometrium, consists of three consists of three

layers:layers:1.1. The superficial The superficial

compact layer,compact layer,2.2. The intermediate The intermediate

spongy layer,spongy layer,3.3. The thin basal The thin basal

layer.layer.

The trophoblast of the blastocyst invades the

decidua to be implanted in:

-The posterior surface of the upper uterine segment in about 2/3 of cases,

-The anterior surface of the upper uterine segment in about 1/3 of cases.

The deciduaThe decidua

After implantation the decidua becomes

differentiated into: 1. Decidua basalis; under

the site of implantation.2. Decidua capsularis;

covering the ovum.3. Decidua parietalis or

vera; lining the rest of the uterine cavity.

The deciduaThe decidua

As the conceptus enlarges and fills the uterine cavity the decidua capsularis fuses with the decidua parietalis

This occurs nearly at the end of 12 weeks

The decidua has the following functions:

1.It is the site of implantation. 2.It resists more invasion of the trophoblast. 3.It nourishes the early implanted ovum by

its glycogen and lipid contents.4.It shares in the formation of the placenta.

The deciduaThe decidua

Chorion:Chorion:After implantation, the trophoblast differentiates After implantation, the trophoblast differentiates

into 2 layers:into 2 layers: a. An outer one called syncytium

(syncytiotrophoblast) which is multinucleated cells without cell boundaries,

b. An inner one called Langhan’s layer (Cytotrophoblast) with simple cytoplasm.

• A third layer of mesoderm appears inner to the cytotrophoblast.

• The trophoblast and the lining mesoderm together form the chorion.

• Mesodermal tissue ( connecting stalk) connects the inner cell mass to the chorion and will form the umbilical cord later on.

Chorion:Chorion:

• Spaces (lacunae) appear in the syncytium, increase in size and fuse together to form the " chorio-decidual space" or " intervillus space".

• Erosion of the decidual blood vessels by the trophoblast allows blood to circulate in this space.

Chorion:Chorion:

• The outer syncytium and inner Langhan’s cells form buds surrounding the developing ovum called primary villi.

• When the mesoderm invades the center of the primary villi they are called secondary villi.

• When blood vessels (branches from the umbilical vessels) develop inside the mesodermal core, they are called tertiary villi.

Chorion:Chorion:

Primary villous Secondary villousSecondary villous

Transverse section of tertiary villous

• At first, the chorionic villi surround the developing ovum.

• After the 12th week, the villi opposite the decidua capsularis atrophy leaving the chorion laeve which forms the outer layer of the foetal membrane and is attached to the margin of the placenta.

Chorion:Chorion:

• The villi opposite the decidua basalis grow and branch to form the chorion frondosum and together with the decidua basalis will form the placenta.

• Some of these villi attach to the decidua basalis ( the basal plate) called the "anchoring villi", other hang freely in the intervillus spaces called "absorbing villi"

Amnion:Amnion:After implantation, 2 cavities appear in the inner cell mass; the amniotic

cavity and yolk sac and in between these 2 cavities the

mesoderm develops.

Development of embryo and fetus

3 weeks 4 weeks 6 weeks 8 weeks

Attachment of the fetalAttachment of the fetal

1.Placenta

2.Fetal membranes

3.Umbilical cord

4.Amniotic fluid

1.PlacentaIt’s an exchange organ between maternal and fetal Amniotic membrane

chorion frondosum

Basal decidua

Round

Weight:450-650g

Diameter:16-20cm

Thickness:1-3cm

thick in center and thin

in margin

The functions of placenta

Gas exchangeSuply of nutritionDepletion of fetal product of metabolisnDefense functionHormone synthesisHuman chorionic gonadotropin(HCG)

Human placental lactogen(HPL)

Pregnancy specific -glycoprotein(PS 1G)

Human chorionic thyrotropin(HCT)

Estrogen, P, Oxytocinase, heat stable alkaline

phosphatase(HSAP)

2.Fetal membrane Chorion

Amnion

3.Umbilical cord Length:30-70cm average:50cm

Consist of 2 artery and 1 vein

4.Amniotic fluid

Source: early from serum dialysis

late from fetal urine

Absorse: by fetal membrane, fetal

swallowing(500ml/day)

Amniotic exchange: between maternal

and fetal 400ml/h

Status of amniotic fluid

pH:7.20

Density:1.007-1.025

Contained: water(98-99%)

inorganic substance

organic substance(1-2%)

Volume of amniotic fluid

8 weeks:5-10ml

10 weeks:30ml

20 weeks:400ml

38 weeks:1000ml

The function of amniotic fluid Protect maternal and fetal

Maternal changes during pregnancy

Isthmus: be dialated and become soft from 1cm

pre-pregnancy a portion of the uterus

after 12 gestational weeks

Cervix: be soft and coloration or stain

secrete amount of mucus avoiding the

uterus cavity suffer from infection

Changes of ovary

Stop ovulation

Corpus luteum formation and maintains for

10 weeks

And the function of corpus luteum is

substituted by the placenta

Corpus luteum atretic gradually after 3-4

months gestation.

2.Changes of the circulationHeart border: become enlargement

Heart rate: increased 10-15 beat per min at the

late pregnancy Heart volume: increased 10% at the late

pregnancy

Cardiac output

Very important for fetal growth and development

Incrased begain 10 weeks and upto the peak at 32 weeks

80ml/bp and keeps the level to the term pregancyChanges of blood system

Volume: increased (30-45% ) begain 6- 8 weeks

and up to the peak at 32-34 weeks

increased about 1500ml including

plasma 1000ml and red cell 500ml

Changes of blood component

Red cell: reticulocyte increased

red cell decreased 3.6×1012(4.2×1012)

Hb decreased 110g/L(130g/L)

WBC: neutrophilic granulocyte increased

lymphocyte mild increased

no change in orther blood cells Coagulation

Hypercoagulability

Factor increasedⅱⅴⅶ ⅷ Ⅸ ⅹESR increased significantly upto 100mm/h

Plasma protein

albumin decreased

THANKS FOR YOUR ATTENTION

Teng YinchengTeng Yincheng

M.D., Ph.D., ProfessorM.D., Ph.D., Professor

Dep. of Obstet. & Gynecol.Dep. of Obstet. & Gynecol.

Renji Hospital Affiliated to SJTU School of MedicineRenji Hospital Affiliated to SJTU School of Medicine