9.3 fertilization and foetal development & parturition€¦ · human reproductive system...

9.3 Fertilization and Foetal Development

9.4 Roles of Hormones during Pregnancy

& Parturition

Human

Reproductive

System

Embryogenesis

FOETAL

DEVELOPMENT

ROLE OF HORMONES

FERTILIZATION

Stages in fertilization

Capacitation

Cortical reaction

Acrosomal reaction

Fusion of sperm head membrane

& secondary oocyte membrane

Pregnancy

Parturition

Cleavage

Gastrulation

Organogenesis

9.3 FERTILIZATION AND

FOETAL DEVELOPMENT

Learning outcomes:• Explain stages that lead to fertilization : capacitation, acrosomal

reaction, fusion of sperm head membrane & oocyte and cortical reaction. [C2]

• Define embryogenesis [C1]

• State developmental stages from zygote to the formation of morula, blastocyst and gastrula through cleavage. [C1]

• Define organogenesis [C1]

. • State organ formed from each germ layers during organogenesis.

[C1]

At the end of the lesson, students should be able to:

9.4 ROLES OF HORMONES DURING

PREGNANCY AND PARTURITION

Learning outcomes:At the end of the lesson, students should be able to:

• Explain the roles of hormones during pregnancy [C2]

• i. Progesterone

• ii. Estrogen

• iii. Human chorionic gonadotropin (hCG)

• Explain the roles of hormones during parturition/birth process [C2]

• i. Progesterone

• ii. Estrogen

• iii. Oxytocin

• iv. Prostaglandin

9.3 Fertilization And

Foetal Development

Fertilization

Fusion of sperm and ovum

• Occurs in the Fallopian tube

• Sperms can live up to

72 hours

• Secondary oocytes will

live up to 24 hours after

ovulation

Fertilization

1. Capacitation

2. Acrosomal reaction

3. Fusion of sperm head membrane and oocyte

4. Cortical reaction

Occurs in 4 stages:

Stages of Fertilization

1. Capacitation 2. Acrosomal reaction


4. Cortical reaction3. Fusion of sperm

head membrane and oocyte

Stages of Fertilization1. Capacitation

2. Acrosomal

reaction

3. Fusion of sperm

head membrane

and oocyte4. Cortical

reaction


Basal body(centriole)

Spermplasmamembrane

Spermnucleus

Spermhead

Acrosome

Jelly coat

Sperm-bindingreceptors

Fertilizationenvelope

Corticalgranule

Fusedplasmamembranes

Hydrolytic enzymesVitelline layer

Egg plasma membrane

Perivitellinespace

EGG CYTOPLASM

Actinfilament

Acrosomalprocess

23

46

4623

23

2323

23 46

Primary

spermatocyte

Primary oocyte

sperms produced

by meiosis

fertilizationsingle-celled

zygote

ova produced by meiosis but only

one develops to maturity

embryogenesis

spermatogenesis

oogenesis

Embryogenesis and Foetal Development

• Embryonic development involves three stages:

Cleavage Gastrulation Organogenesis

Embryogenesis

Definition:Process of formation and

development of embryo until birthOccurs during pregnancy in human

– The condition of carrying one or

more developing embryos in the

uterus.

– Starts with conception and ends with

birth.

– Averages 266 days (38 weeks) from

conception.

– Consist of 3 stages: cleavage,

gastrulation and organogenesis.

Cleavage

Cleavage

The succession of rapid cell divisions without

significant growth during early embryonic development

that converts the zygote into a solid ball of cells called morula.

Each cell is called as blastomere.

Cleavage

Cleavage

Spherical mass of cells

Hollow, fluid-filled

ball of cells

Implantation - occurs around

7 days after fertilization

Cells in morula continue dividing to form blastocyst.

Blastocyst is a sphere of cells with fluid-filled space

(blastocoel) with inner mass cell and trophoblast layer.

Cleavage

GastrulationFormation of gastrula from blastocyst after implantation

occurs, characterized by migration of cells inward to form a

three germ-layered embryo.

Gastrulation

Neurulation

NeurulationThe initial stage of organogenesis to form nervous system

by which neural plate develops into a neural tube. Neural

tube will develop into brain and spinal cord.

.

Organogenesis

OrganogenesisThe process by which organ rudiments develop from

the three embryonic germ layers after gastrulation

Trophoblast, the outer layer of blastocyst developes into four

extraembryonic membranes that surround the gastrula

The extraembryonic membranes provide protection and nutrition

to the embryo

They are not part of the embryo (discard at birth)

They consist of:

i. Chorion

ii. Amnion

iii. Allantois

iv. Yolk sac

Development of embryo

9.4 Roles of Hormones during

Pregnancy & Parturition

GESTATION PERIOD OR PREGNANCY

PLACENTA: SOURCE OF HORMONES DURING PREGNANCY AND

PARTURITION

myometrium

Roles of Hormones During Pregnancy

Hormone Secreted by Function

Estrogen

Follicle cells :

follicle development

before fertilization

Corpus luteum :

from conception until

1st trimester

Placenta : from 2nd

trimester onwards

• Stimulates the develop-ment of the uterine wall

• Growth of mammary glands

• Inhibits LH and FSH• Inhibits prolactin release• Increase sensitivity ofmyometrium to oxytocin



Progesterone

Corpus luteum :

from conception until 1st

trimester

Placenta :

from 2nd trimester

onwards

• Inhibits myometrium

contraction

• Stimulates uterus enlargement

• Stimulates the growth of the

mammary glands and breast

enlargement

• Inhibits LH and FSH

• Inhibits prolactin release

•Maintain the pregnancy



Human

Chorionic

Gonadotropin

(hCG)

Trophoblast / chorion /

embryo

• Stimulates the corpus luteum

to maintain the secretion of

estrogen and progesterone

up to 3 months of pregnancy

• Produced in large quantities

• Some is secreted in the

urine

• Detected during

pregnancy test

Parturition or birth process

• Parturition or birth is brought about by a series of

strong rhythmic uterine contractions

• Involves positive feedback

mechanism

• Occurs in 3 stages:

Cervix dilation

Expulsion: baby delivery

Placental delivery

Parturition or birth process

Roles of Hormones During Parturition



Progesterone Placenta - level drops off at the end of pregnancy stimulates the beginning of contraction that will lead to birth

Estrogen Placenta

- Triggers the formation of

oxytocin receptors on the

myometrium



Oxytocin Fetus and mother’s

Posterior pituitary

- Stimulates powerful contractions by the smooth muscle of the uterus

- Stimulates the placenta to secrete prostaglandin

Prostaglandin Placenta - Enhance contractions of smooth muscle of the uterus

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