NCM 107
Lesson 1: Process of Conception and Stage of Fetal
Development
LOUISSE MARGARETT S. CALANZA
Lecturer
NCM 107
Let’s get started: MY BIRTH STORY
Before we begin, I want you to share your discovery about your birth story.
Attached a picture of you and write a caption.
Gamete – is the male or female reproductive cell that contains half the genetic material of the
organism.
https://ib.bioninja.com.au/higher-level/topic-11-animal-physiology/114-sexual-reproduction/egg-andsperm.html
Female Gamete: Human Egg (Ovum)
- reproductive cells that is produced in the ovary.
- The largest cell in the female body
- Contains 23 chromosomes
Haploid Nucleus
Contains one copy of each chromosome
Cortical granule
releases enzymes during fertilization that harden the zona
pellucida and digest binding proteins on sperm to prevent
POLYSPERMY** after a sperm cell has entered the ovum.
Corona radiata
An external layer of follicular cells which provide SUPPORT and
NOURISHMENT to the egg cell.
Zona pellucida/ jelly coat
Contains a glycoprotein matrix which acts as a BARRIER to sperm
entry.
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Male Gamete: Human Sperm (Spermatozoa)
- reproductive cells that originate in the testicles
- contains 23 chromosomes
- the smallest cell in the male body
- ejaculation of semen averages 2.5 ml of fluid containing 50 to 200 million spermatozoa per
milliliter or an average of 400 million sperm per ejaculation
Head
Acrosome
Contains HYDROLYTIC ENZYMES which help
PENETRATE the jelly coat.
Nucleus
Contains the PATERNAL DNA (this will combine with maternal
DNA if fertilization is successful).
Centriole
Needed by a zygote to divide
Midpiece
Mitochondria
Provide the ENERGY (ATP) needed FOR THE TAIL TO MOVE.
Tail/Flagellum
Axoneme
A (microtubule structure) which BENDS TO FACILITATE
MOVEMENT.
Conception is also referred to as fertilization or impregnation. It is the union of the sperm and the ovum.
This usually occurs in the outer third of a fallopian tube, termed the ampullar portion.
The period of gestation of the human infant is 38 weeks (about 265 days). These 38 weeks are
divided into three stages of unequal length, identified by specific changes within the developing organism.
Stages of Fetal Development
Sperm and ovum
forming a zygote.
unite,
First
2
weeks,
Pre embryonic
beginning
with The zygote burrows into the
Stage
fertilization
lining of the uterus.
Embryonic
Week 3 through 8
Fetal
From
week
through birth
All the embryo’s organ
systems form during the 6week
period
following
implantation.
8 Growth
and
Organ
refinement.
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THE PROCESS OF CONCEPTION
1. Ovulation
Each month inside your ovaries, a group of eggs
starts to grow in small, fluid-filled sacs called follicles.
Eventually, one mature egg is release from one of the
ovaries, which happens every month.
An ovum is capable of fertilization for only about
24 hours (48 hours at the most). After that time, it
atrophies and becomes nonfunctional. Because the
functional life of a spermatozoon is also about 48 hours,
possibly as long as 72 hours, the total critical time span
during which sexual relations must occur for fertilization
to be successful is about 72 hours (48 hours before ovulation plus 24hours afterward).
2. Hormones Rise
The follicle develops into something called the corpus luteum. The corpus luteum releases a hormone that
helps thicken the lining of your uterus, getting it ready for the egg.
3. The Egg and Sperm Meets at the Fallopian Tube
The released egg (ovum) is propelled into a
nearby fallopian tube through the combination of
peristaltic action of the tube and movements of the cilia
along the length of the tube.
It is fertilized in the fallopian by a single sperm.
If no sperm is around to fertilize the egg, it moves
through the uterus and disintegrates.
In what part of the usually of the fallopian tube
fertilization occurs? _________
What do you call the process during the journey of the sperm in which fluids in the female
reproductive tract prepare the sperm for fertilization? _________________________________ . If they
reach the oocyte before the process is completed they will be unable to penetrate the oocyte’s thick outer
layer of cells.
ACROSOME REACTION
It is the final step undergone by the sperm to penetrate the protective layers of the ovum before
fertilization by releasing enzymes to dissolve the ovum’s membrane (HYALURODINASE – proteolytic
enzyme)
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4. Fertilization
Fertilization completes the genetic makeup of
the baby, including whether it will be a girl or boy.
For fertilization to take place, three events must occur
during the encounter of the spermatozoa and the
oocyte:
-
The sperm cells must migrate between any
present cumulus cells and corona radiate cells.
The sperm cell must attach to and penetrate the
zona pellucida (ZONA REACTION membrane enclosing
the ovum & sperm becomes impenetrable to other sperm)
Finally, the plasma membranes of the ovum and the sperm must fuse.
Only one spermatozoon can penetrate the cell membrane of the ovum. Once it penetrates the
cell, the cell membrane changes composition to become impervious to other spermatozoa. An exception
to this is the formation of gestational trophoblastic disease in which multiple sperm enter an ovum; this
leads to abnormal zygote formation.
https://opentextbc.ca/anatomyandphysiology/chapter/28-1-fertilization/
FACTORS IMPORTANT TO FERTILIZATION
I.
II.
III.
Maturation of the ovum & sperm
Motility of the sperm to reach the ovum
Ability of the sperm to penetrate the zona pellucida & cell membrane of the ovum to achieve
active fertilization
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5. Cell Starts to Divide
Once the egg is fertilized, a rapid process of
division begins. The chromosomal material of the
ovum and spermatozoon fuse to form a _________. If
an X-carrying spermatozoon entered the ovum, the
resulting child will have two X chromosomes and will
be assigned as _____________ (XX). If a Y-carrying
spermatozoon fertilized the ovum, the resulting child
will have an X and a Y chromosome and will be
assigned as ________________.
During this time, mitotic cell division, or cleavage, begins. The first cleavage occurs at about 24
hours; cleavage divisions continue to occur at a rate of about one every 22 hours so by the time the zygote
reaches the body of the uterus; it consists of 16 to 50 cells. Over the next 3 or 4 days, large cells tend to
collect at the periphery of the ball, leaving a fluid space surrounding an inner cell mass. At this stage, the
structure is termed a blastocyst. The cells in the outer ring are trophoblast cells. They are the part of the
structure that will later form the placenta and membranes. The inner cell mass (embryoblast cells) is the
portion of the structure that will form the embryo.
The fertilized egg leaves the Fallopian tube and enters the uterus 3 to 4 days after fertilization.
https://opentextbc.ca/anatomyandphysiology/chapter/28-2-embryonic-development/
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6. Implantation: Moving to the Uterus
It signals the end of the pre-embryonic stage of
development. It is the process by which the fertilized
egg attaches to the endometrium (lining tissues of the
uterus) approximately 8 to 10 days after fertilization.
Some women notice spotting (or slight bleeding)
for 1 or 2 days around the time of implantation. The
lining of the uterus gets thicker and the cervix is sealed
by a plug of mucus. It will stay in place until the baby is
ready to be born.
Implantation usually occurs high in the uterus on the posterior surface. Once implanted, the
zygote is called an embryo.
https://opentextbc.ca/anatomyandphysiology/chapter/28-2-embryonic-development/
TROPHOBLASTIC LAYER OF CELLS: CONTACTS THE ENDOMETRIUM (CHORIONIC VILLI) &
DIFFERENTIATES INTO:
CYTOTROPHOBLAST
( LANGHAN’S LAYER):
protects the growing embryo and fetus from
certain infectious organisms disappears
between the 20th and 24th week.
SYNCYTIOTROPHOBLAST,
OR THE SYNCYTIAL LAYER
production of various placental hormones,
such as hCG, somatomammotropin
(human placental lactogen [hPL]), estrogen,
and progesterone.
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7. Pregnancy Hormones
A hormone called human chorionic gonadotrophin
(HCG) is produced by the cells that will eventually form the
placenta. It can be found in the mother's blood within about
a week of conception and is detected in pregnancy tests
done on blood or urine.
8. Fetal Development
After implantation in the uterus, some of the cells
form the placenta while others form the embryo. The
heartbeat begins during the fifth week of gestation. At the
eighth week the developing embryo is now called a fetus.
The fetus at eight weeks is about ½ inch long and constantly
growing.
Milestones in the Process of Fertilization
A. PRE FERTILIZATION (Transit of Sperm)
i.
Release of the egg during ovulation
ii.
Capacitation
iii.
Acrosome reaction
B. FERTILIZATION (Contact between Sperm & Oocyte)
3 ways of the egg’s response upon sperm’s penetration
I.
Cortical & zona reactions – impenetrability of other sperms
II.
Resumption of 2nd meiotic division – occurs immediately after entry of 1 sperm
III.
Metabolic activation of the egg –post fusion activation; initial cellular & molecular
changes for growth & development associated with embryogenesis
C. POST FERTILIZATION
i.
Sperm’s tail detaches from head & degenerates
ii.
Male & female nuclei lose their nuclear membranes fuse
and intermingle with their chromosomes forming a zygote.
D. PRE-EMBRYONIC PERIOD – 1ST 14 days after conception
CHARACTERISTICS:
i.
Rapid cellular multiplication & differentiation
ii.
Establishment of embryonic membranes
iii.
Development of primary germ cell layers
To have a better understanding about our lesson, please click the attached links below.
1. https://www.youtube.com/watch?v=7ww5T7hCdn4
2. https://www.youtube.com/watch?v=1KL8HAm3uSY
3. https://www.youtube.com/watch?v=dAOWQC-OBv0
4. https://opentextbc.ca/anatomyandphysiology/chapter/28-1-fertilization/
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