Fertilization occurs when an ovum fuses with a sperm, leading to the development of an embryo. Sperm must travel through the female reproductive tract, confronting barriers like cervical mucus, before reaching the ampulla where fertilization occurs. Capacitation and the acrosome reaction prepare the sperm for fertilization. Gamete fusion results in the formation of a zygote containing male and female pronuclei. The zygote undergoes cleavage and develops into a blastocyst that implants in the uterus, initiating pregnancy. Pregnancy can be detected through urine or blood tests that detect human chorionic gonadotropin, a hormone produced by the developing placenta.

1. 1

2. Conception
 Fertilisation (also known as conception,
fecundation and syngamy), is the fusion of gametes
to produce a new organism. In animals, the process
involves the fusion of an ovum with a sperm, which
eventually leads to the development of an embryo.
Depending on the animal species, the process can
occur within the body of the female in internal
fertilisation, or outside in the case of external
fertilisation.
2

3. 3

4. 4

5. Sperm transport
 Semen is ejaculated into vagina, cervical and may
reach cervical canal
 Semen coagulate by coagulating enzymes from
prostate gland which interacts with fibrinogenous
substrate from seminal vesicles
 Coagulum protects spermatozoa from vaginal
acidity and prevent loss of spermatozoa
 Coagulum liquefies after 15 to 20 minutes
 Liquefaction time is one criteria for semen quality
 Sperm may live up to 48 – 72 hours in female
reproductive tract.
5

6. Barriers (1)
 Spermatozoa have to confront three barriers before
reaching ampulla, the site for fertilization
 First barrier – cervical mucus
 Mucus will filter and choose spermatoza – dead and
immotile spermatozoa are discarded, normal
spermatozoa are stored in the cervical crypts (first
reservoir)
 Filtered spermatozoa discarded in the vaginal
secretion post-coital
 Consistency of cervical mucus assist in sperm motility
upwards
 Mucus thick, sperm could not penetrate
 Mucus thin and more stringy, sperm is assisted in
motility by swimming in channels form by the mucus

7. Barriers (2)
 Endometrial glands – second barrier
 Will choose and filter spermatozoa
 Chosen spermatozoa are stored here (second
reservoir)
 Here, capacitation occurs due to prostaglandins
from endometrium

8. Barriers (3)
 Third barrier – utero-tubal junction
 Chosen spermatozoa are finally stored in the
isthmus (third reservoir) to wait for the ovum
to travel down
 Ovulated ovum will be caught by infundibulum
when fimbriae comes close to ovary
 Ovum will travel down the infundibulum to
the ampulla by oviductal contraction and
presence of cilia

9. 9

11. Capacitation (1)
 A time dependent phenomenon which is species-
specific
 Takes more than 24 hours in human
 Reversible process (if capacitated spermatozoa are
placed in epididymal fluid or seminal plasma, will be
decapacitated – contains decapacitating factor) only in
vitro
 Must occur to enable acrosome reaction to occur
 Substances like cholesterol, glycosaminoglycans and
glycoproteins are stripped from plasma membrane of
sperm head

12. Capacitation (2)
 Two elements in this process:
t Hyperactivated motility – sperm starts to
show whiplashing movement to enable
sperm to move forward faster
r Change to membrane surface –
membrane stability decreases. More
permeable to calcium ions. Tyrosine
kinase activity increases. Adenyl cyclase
activity in spermatozoa heightens and causes
protein phosphorylation which are cAMP
dependent

13. Acrosome reaction
 Occurs right after capacitation
 Totally dependent on calcium uptake into
cells and increase in intracellular pH (pH 7.1
to pH 7.5)
 The acrosome swells and the outer acrosomal
membrane fuses with the overlying plasma
membrane
 Vesiculation occurs and pores are formed
 Acrosomal contents (hyaluronidase, acrosin
etc) are released

14. Acrosome reaction
 Two types:
 True acrosome reaction – reaction occurs at
zona pellucida
 False acrosome reaction – degeneration of
sperm due to death (enzymes from acrosome
will self-desctruct sperm)

15. Initiators of the acrosome
reaction (1)
 High calcium influx
 ZP3 (zona pellucida glycoprotein 3)
 Progesterone etc
 ZP3 in ovum will bind to sperm binding
protein (receptor) on sperm plasma membrane
 This binding site may contain galactosyl
transferase activity
 When binding occurs, G protein involvement
will stimulate calcium influx and the rise in
pH initiates the acrosome reaction

16. Initiators of the acrosome reaction
(2)
 Progesterone will also stimulate calcium
influx which then stimulates adenyl cyclase
and cAMP
 Progesterone can stimulate acrosomal
leakage to release hyaluronidase
 Hyaluronidase will digest hyaluronic acid
which binds cumulus cells
 When these cells breaks apart, spermatozoa
can bind to zona pellucida
 Progesterone has been reported to initiate
capacitation also

17. Sperm binding properties to zona
 Outer acrosomal membrane has receptor to ZP3
 Inner acrosomal membranes has receptor to ZP2
 Equatorial segment and post-acrosomal region
is the part of the spermatozoon that enters the
ovum
 Tail and midpiece left outside ovum

22. Gamete fusion
 Sperm penetration of the zona takes between 5-20
minutes
 Sperm lies tangent at the ovum surface between the
zona pellucida and oolemma at the perivitelline
space
 Microvilli at the oocyte surface will engulf the sperm
head
 The equatorial segment and the post-acrosomal
region of the sperm fuses with the ovum
 After fusion, zygote forms and male and female
pronuclei
 Syngamy occurs when both male and female
chromosomes combines and then form 2-cell
conceptus

23. Formation of male and female
pronuclei

24. Embryonic development (1)
 Germinal period (movement of zygote and
implantation in uterus) lasts two weeks
 Cleavage occurs - 1 cell to 2 daughter cells after 36
hours post fertilization
 Daughter cells called blastomeres
 Zygote still covered by ZP
 ZP inhibits blastomeres from falling apart
 If this happens, two possibilities occur
7. Monozygotic twins
8. Chimaeras
Chimaeras is the fusion of two different zygotes
from two fertilized ovum – two sets of two
different genotype

25. Fertilized egg 2 cell stage
4 cell stage 8 cell stage

26. Embryonic development (2)
 Blastomeres becomes morula on day 3
 Progesterone from functioning CL will
stimulate the release of glycogen from
endometrium for energy to developing
embryo (histiotropic nutrition)
 High levels of progesterone also inhibit
oviductal constriction to enable morula to
move towards the uterus by peristaltic
contraction and cilia movement
 Becomes blastocyst on day 4 - 5

27. Embryonic development (3)
 Blastocysyt has fluid-filled cavity
(blastocoele)
 Has inner cell mass (ICM) surrounded by
trophodectum (trophoblast)
 ICM will form extra embryonic membranes
(amnion, yolk sac etc) and fetus
 Trophoblast forms chorion
 Blastocyst floats in uterine cavity for 1 – 2 days
 Prior to implantation, will shed ZP by
enzymatic digestion

28. Implantation (1)
 A nutritional and physical contact between fetus and
mother
 Blastocyst surface becomes sticky
 Trophoblastic cells (cytotrophoblast) releases
enzymes to digest proteins on endometrium
 Syncytiotrophoblast enters endometrium to suck up
metabolic fuel and nutrients
 Deep invasion into endometrium occurs
 Change to endometrium occurs (stromal
reaction/primary decidualization reaction)
 Endometrium releases prostaglandins to stimulate
vascularization causing edema and increasing
nutrient stores

29. Implantation (2)
 The invaded part of the endometrium is called
decidua
 2 –3 days post invasion, decidua enlarges to
become secondary decidua
 Blastocyst enters this decidua
 After entry, a layer of endometrial cells will
cover and bury the blastocyst
 Syncytiotrophoblast on the other hand keep
on digesting endometrial cells to get
nutrients until the placenta is formed

31. 31

32. 32

33. Multiple pregnancy
 Multiple pregnancy is a pregnancy with two or more fetuses. Twins -
2 fetuses, Triplets - 3 fetuses, Quadruplets - 4 fetuses, Quintuplets -
5 fetuses, Sextuplets - 6 fetuses and Septuplets - 7 fetuses
 Naturally occurring factors causing multiple pregnancy are:
 heredity
A family history of multiple pregnancy increases the chances of
having twins
 older age
Women over 30 have a greater chance of multiple conception.
 high parity
Having one or more previous pregnancies, especially a multiple
pregnancy, increases the chances of having multiples.
 race
African-American women are more likely to have twins than any
other race. Asian and Native Americans have the lowest twinning
rates. Caucasian women, especially those over age 35, have the
highest rate of higher-order multiple births (triplets or more).

34. How to detect pregnancy?
 Urine test – detect hCG
 Blood test – detect hCG
 Ultrasound
 Milk test – P4
 Blood test - PMSG

35. •The hCG Urine Pregnancy Test
Strip is a test kit based on a visual,
qualitative principle for the
determination of hCG (Human
Chorionic Gonadotropin) a
glycoprotein hormone secreted by
the developing placenta after
fertilization in urine specimens.
• Pregnancy Test Strips are over
99% accurate and are capable of
detecting hCG, at levels of just
20mIU/ml/hCG. Can test accurately
6 to 8 days after conceiving - and 7
days after missed period.
•The appearance of hCG soon after
conception and its subsequent rise
in concentration during early
gestational growth make it an
excellent marker for the early
detection of pregnancy

36. hCG
 The developing placenta begins releasing hCG into blood as early
as 6 days after implantation.Some hCG also gets passed in the
urine.
 HCG helps to maintain pregnancy and affects the development of
fetus.
 Levels of hCG increase steadily in the first 14 to 16 weeks following
last menstrual period (LMP), peak around the 14th week following
LMP, and then decrease gradually.
 The amount that hCG increases early in pregnancy can give
information about pregnancy and the health of the baby. Shortly
after delivery, hCG can no longer be found blood.
 More hCG is released in a multiple pregnancy, such as twins or
triplets, than in a single pregnancy.
 Less hCG is released if the fertilized egg implants in a place other
than the uterus, such as in a fallopian tube. This is called an
ectopic pregnancy.

37. •An ultrasound test is a radiology
technique, which uses high- frequency
sound waves to produce images of the
organs and structures of the body. It
involve no radiation and studies have
not revealed any adverse effects.
•The sound waves are sent through
body tissues with a device called a
transducer placed directly on top of the
skin, which has a gel applied to the
surface.
•The sound waves that are sent by the
transducer through the body are then
reflected by internal structures as
"echoes." which return to the
transducer and are transmitted
electrically onto a viewing monitor.

38. Week Week Week
5 8 11
Twin Twins kicking

39. Fetus formation
 Gene dependant
 Size dependant on nutrition and health of mother,
parity (primiparous mothers have small babies as
compared to multiparous mothers), mother’s size,
pregnant more than one baby and self-damage
caused by smoking, drug addiction, alcoholic etc
 Small sized baby is due to prematurity or even if
full-term, there must be a factor to cause a
retarded growth for the baby

40. Fetal Development
 Heart and brain develop from 3rd week
 Heart starts to pump blood from week 4-5
 Feet and hands starts to develop and tail at coccxy starts
to shrink
 Embryo is less than an inch long at week 5
 Hands and feet is visible and nose also starts to form
 At week eight, it is about an inch long
 By week 9, embryo is called a fetus
 Sexual organs starts to form but sex is not yet determine
 Other organs also starts to form and develop until birth

41.  Rate of fetal growth is slow until week 20 but
accelerate to a maximum at week 30-36
 Peak of growth velocity is on week 8
 Fetal nutrition is from CHO (glucose), amino acids
and lactate. Fatty acids, vitamins and minerals are
also transferred to the fetus via the placenta

42. Factors affecting fetal growth
 Genetic (species, breed, genotype)
 Environmental (nutrition, size, parity, size and blood
circulation of placenta)
 Fetal hormones (thyroid, growth hormone,
somatomedins)

43.  Gestation length: 280 days or 40 weeks or 9 months
and 10 days
 LMP – Last Menstrual Period
 EDD – Estimated Delivery Date (First day of last
menstrual period plus 280 days)
 Trimester – 3 months
 Human – 3 trimesters

44. Factors affecting gestation length
 Maternal factor – age of mother
 Fetal factor – number of fetuses, gender, adrenal and
pituitary function
 Genetic – species, breed, fetal genotype
 Environmental factors – nutrition, temperature,
season

45. Physical changes during pregnancy
 No menstruation
 Nausea in first trimester
 Back and hip pains
 Increase in body weight
 Pigmentation of skin especially in fair-skinned women
(choalasma – mask of pregnancy) especially at the facial region
 ‘Quickening’ or baby movements in uterus – occurs at 5 months
pregnancy onwards
 ‘Braxton-Hicks contraction at 6-7 months pregnancy
 Others eg pica (Pica is a pattern of eating non-food materials
such as dirt or paper and should last at least 1 month to fit the
diagnosis of pica.)

47. Development of embryo and fetus

56. Abnormal pregnancies – Ectopic
pregnancy
 Occurs when a fertilized egg attaches somewhere other than in
the uterus, usually in a fallopian tube (tubal pregnancy).
 Because an ectopic pregnancy can cause life-threatening
complications, the pregnancy must be ended with medicine or
surgery.
 An ectopic pregnancy, especially a tubal pregnancy, can be
dangerous because the fallopian tube does not stretch as the
fertilized egg grows. If a tubal pregnancy is not detected and
treated early, the tube may burst. This can be a life-threatening
situation and requires emergency surgery.
 Pelvic inflammatory disease or tubal surgery increases the risk
of having an ectopic or tubal pregnancy by creating scar tissue
that may block the fallopian tube.

57. Abnormal pregnancies – Molar pregnancy
 A mass of abnormal tissue (hydatidiform mole)
that comes from the placenta inside the uterus,
which triggers symptoms of pregnancy. About 1
out of 1,000 women with early pregnancy
symptoms has a molar pregnancy. There are two
types of molar pregnancy: complete and partial.
 Complete molar pregnancy. In place of a normal
placenta/embryo, the hydatidiform mole is
abnormal placental tissue that grows into a
grapelike cluster that can fill the uterus.
 Partial molar pregnancy. The placenta grows
abnormally into molar tissue. Any fetal tissue that
develops is likely to have severe defects.