Post on 21-Jan-2021
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
Stages of Fertilization
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
Stages of Fertilization
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
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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
Roles of Hormones During Pregnancy
Hormone Secreted by Function
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
Roles of Hormones During Pregnancy
Hormone Secreted by Function
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
Roles of Hormones During Pregnancy
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
Roles of Hormones During Parturition
Roles of Hormones During Parturition
Hormone Secreted by Function
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
Roles of Hormones During Parturition
Hormone Secreted by Function
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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