BIOLOGY FORM 5 CHAPTER 4 - 4.1E FERTILISATION & DEVELOPMENT

1. Fertilisation
Embryo Development
Human Reproduction

2. SSeexxuuaall RReepprroodduuccttiioonn
iinn HHuummaann testis
sperms
ovary
eggs (ova)
meiosis meiosis
fertilization
zygote
embryo
foetus
baby

3. Female sex cells – egg
nucleus
containing DNA
– controls cell
division
cell membrane
cytoplasm –
provides
nutrients for
embryo
jelly coat – makes sure
that only 1 sperm can
fertilise the egg

4. Secondary oocyte
released from the follicle
during ovulation
on 14th day of the menstrual cycle.

5. Journey of the Sperm
• Ejaculation - 5 ml of
semen contains 450
million sperm.
• Sperm must pass
through a plug of
mucus in the cervix,
which becomes thin at
the time of ovulation.

6. Journey of the Sperm
• Vagina cervix uterus Fallopian tube
This takes 10 hours of constant swimming!
• Many sperm die during the journey, only the
strongest survive.

8. WWhhaatt iiss ffeerrttiilliissaattiioonn??
When the
sperm and
the egg
FUSE
together.

9. Fertilization: Four Major Steps
1. Sperm contacts the egg
2. Sperm or its nucleus enters the egg
3. Egg becomes activated.
4. Sperm and egg nuclei fuse
Fertilization occurs in the
Fallopian tube

10. Fertilisation
• Sperm must meet the egg in
the Fallopian tube.
• Sperm swim up the female
reproductive tract, aided by
muscular contractions of the
uterus stimulated by
prostaglandins in the semen.
• The oocyte secretes a
chemical that attracts sperm

11. Conception
• This gives a three day “window” for
intercourse to result in fertilization: two days
before to one day after ovulation

12. Fertilisation
Although
thousands of sperm
may reach an egg,
only one enters it.

14. It requires the combined action of many
sperms to allow one sperm to penetrate the
oocyte.

15. ACROSOME

17. Fertilisation

18. Fertilisation
• The tail of the
sperm remains
outside as the
head travels
through the egg
cytoplasm to the
nucleus.

20. Fertilisation
• The secondary oocyte completes the
second meiotic division after sperm
entry to form ovum.

21. Fertilisation
• Fertilisation occurs
when the sperm
nucleus fuses with
the egg nucleus to
form a zygote.
• This is the moment
of conception.

22. Pronuclear fusion
• The male
nucleus expands
to form the male
pronucleus
• The female and
male pronuclei
fuse and then
the first division
occurs

23. The fertilized egg now has 23
PAIR, or 46 chromosomes.
Immediately the cell begins to
duplicate, taking
approximately 30 hours to
complete the first cell
division.

25. Embryo:
• a multicellular organism in the early stages of
development
2 four cell stage embryos
Eight cell stage embryo

26. The Fertilized Egg & Cleavage
• Morula~solid ball of
cells (after 32 cell
stage)
• Blastocyst~hollow
ball stage of
development (at 4.5-5
days) It is at this stage
that it enters the
uterus.

27. Development of Embryo

28. WWhhiicchh iiss mmoorruullaa // bbllaassttooccyysstt??
fertilized egg 2-cell stage a ball of cells
outer cell
layer
uterine lining
cavity
inner cell
mass
yolk sac
uterine lining
future
embryo
amnion

30. REPRODUCTIVE CYCLE VIDEO

33. Implantation
• The embryo implants in the wall of the uterus on about the 7th day of
development
• Trophoblast secretes enzymes that erode the uterine wall

35. ECTOPIC PREGNANCY
• Implantation can also occur in Fallopian tube,
cervix, or abdominal cavity.
• Implantation anywhere outside the uterus is called
an ectopic pregnancy.
(It is possible for fetus to grow in the abdominal
cavity, but growth inside the Fallopian tube causes
the tube to rupture, resulting in severe bleeding.)

36. Ectopic Pregnancy

37. ECTOPIC PREGNANCY

39. Pregnancy – this is when a baby grows inside a woman.
The baby grows inside
the womb (the uterus).
It is protected by a bag
of water, and gets food
from the woman
through the placenta.

42. Gestation period
• Period from conception till birth
- 9 months
• Divided into three trimesters.
• 1st trimester – formation – Month 1 - 3
• 2nd trimester – growth – Month 4 - 6
• 3rd trimester – growth – Month 7 - 9

43. Diary of human development
Week 0
• Egg is fertilised in the
fallopian tube.

44. Diary of human development
Week 1
• Embryo becomes
attached to the lining
of the uterus (womb).

45. 12-day Human Embryo

46. Diary of human development
Week 2
.
Week 4
.

48. Embryonic Development

50. Diary of human development
Week 10
• Foetus fingers and
toes grow. It can move
its arms and legs a
little – it can swallow
and frown.

51. First Trimester
• Third month - completion
of development
• now referred to as foetus
• nervous system and
sense organs develop
• all major organs
established

52. During this first
trimester period of
“formation”, many
things can go wrong.
Sometimes the
woman’s body will
self-abort. This is
called a miscarriage.
THIS IS THE END OF
THE FIRST TRIMESTER,
WHEN THE MAIN TASK
WAS FORMATION!

53. ULTRASOUND IMAGING
Head
Body
Head
Body

54. 5 weeks 6 weeks 7 weeks
8 weeks 9 weeks 12 weeks

55. PLASENTA
FORMATION
• After ~ 3 months, the corpus luteum degrades and
the placenta takes over nourishment of the embryo
• Uterine tissues begin to form the placenta
• The placenta itself secretes oestrogen and
progesterone

56. 2nd Trimester
Diary of human development
Week 14
• It is possible to
determine the foetus’s
sex.

57. By now, the fetus has grown large enough that
the movements can sometimes be felt by the
mother. Often felt like a flutter or a "flip-flop",
these first movements that can be felt by the
mother is called quickening.

58. Diary of human development
Week 18
• Foetus has hair,
eyebrows. Doctors can
hear the heartbeat.
Mother begins to feel
its kicks.

59. WEEK 20

60. THIS IS THE END OF THE
SECOND TRIMESTER,
WHEN THE MAIN TASK
WAS FUNCTIONING!

61. 14 weeks 16 weeks 18 weeks
20 weeks 24 weeks

63. 3rd Trimester
Diary of human development
Week 26
• Foetus opens its
eyes.

64. Diary of human development
Week 30
• If born now, the baby
could live with special
care.

65. Diary of human development
Week 34
• Baby has grown a lot
of fat in the last 4
weeks, to keep it warm
when it is born.

66. At the end of the fourth month, white, downy hair
called lanugo (lu- noo- go) covers the entire body
of the fetus. It provides warmth, since the fetus
has no layer of fat beneath the skin yet.
At some point later, a white waxy, cheese-like substance also forms over the
entire surface of the skin. This is called vernix caseosa. The vernix is a perfect
skin lotion, which along with the lanugo, protects he skin from the constant
exposure to amniotic fluid. It is also believed that it serves as a sort of skin
cleanser and antibacterial substance. The lanugo and vernix caseosa diminishes
in amount during the last weeks of the gestation period and usually rubs off
during delivery. The presence of a great deal of vernix or lanugo at the time of
birth, therefore, is often a sign of prematurity.

67. During this last month of the gestation
period, baby continues to grow… at a
rate of ½ to 1 pound per week. Baby
will turn around in the womb, to a head-down
position. The lungs are maturing,
preparing for that first breath.
THIS IS THE END OF THE THIRD TRIMESTER, WHEN
THE MAIN TASK WAS GROWTH!

68. POSITION OF HEAD TURNS
DOWNWARDS BEFORE DELIVERY

69. Diary of human development
Week 38
• Baby is born.

73. DDeevveellooppmmeenntt ooff
HHuummaann FFooeettuuss
uterus
foetus
placenta
umbilical cord
amnion
amniotic fluid

74. How ddooeess tthhee ffooeettuuss ggeett ooxxyyggeenn??
Any
ideas?

80. The placenta
• Harmful substances
such as nicotine,
alcohol, drugs and
virus can also pass
across the placenta
from the mother to
the foetus.

81. • keeps the mother's &
baby’s blood saparate
– forms a barrier

82. Substances that can
diffuse across the placenta
From mother to
fetus
(Umbilical vein)
From fetus to
mother blood
(Umbilical artery)
Oxygen
Amino Acid
Glucose
Fatty acid and glycerol
Vitamin
Antibody
Any virus, drugs, alchohol
Carbon dioxide
Uric acid
Urea

84. Placenta abnormal position

86. Draw a line between the parts and their
function
Amniotic sac
Umbilical cord
Foetus
Develops into the baby
Protects the unborn
baby
Attaches the unborn
baby to the placents

90. The uterine muscle is stimulated to contract
Involuntary contractions lead toward labor, when contractions
are ~ 10-15 minutes apart
The fetus moves toward the cervix, head down.

91. The cervix dilates (opens) to a maximum diameter of 10 cm.
The amnion (the fetal sac) ruptures.
Fluid flows from the vagina (‘breaking water’)

92. The fetus is delivered by powerful
contractions of the uterine muscle

93. The umbilicul cord is cut/tied off by the physician
Mother injected with oxytocin to cause powerful contractions of
the uterus to expel the placenta, or merely pull the placental
membranes out

95. CHILDBIRTH
VIDEOS

96. PARENTAL CARE

104. LACTATION
• Lactation depends on the action of the two hormones:
prolactin and oxytocin. (produced in the pituitary gland)
• Progesterone inhibits the release of prolactin.
• Prolactin promotes milk production in the mammary glands.
• Oxytocin stimulates the ejection of milk from the nipples.
• Every time a baby suckles prolactin levels increase.

105. END 0F
DEVELOPMENT (CONT)

106. TWINS
• 2 babies born at the same time

107. Identical twins are pprroodduucceedd wwhheenn tthhee ttwwoo
cceellll ssttaaggee sspplliittss,, ffoorrmmiinngg ttwwoo sseeppaarraattee cceellllss..
TThheenn tthhee cceellllss ccoonnttiinnuuee ttoo ddiivviiddee sseeppaarraatteellyy
ffoorrmmiinngg ttwwoo eemmbbrryyooss..
Two cell stage

109. • Identical Twins
• 1 ovum fertilized by 1
sperm to form 1 zygote
which splits into 2
identical replicas
• Share same placenta.
• Same sex / same DNA
• Fraternal Twins
• 2 ovum fertilized by 2
different sperms to form 2
zygotes
• genetically no closer than
brothers and sisters
• Different placenta.
• Same/different sex & DNA
Identical
twins
Fraternal
twins
Same
sex only
Same or
opposite sex

111. Fraternal or Identical Twins ?

112. Fraternal or Identical Twins ?

113. IIddeennttiiccaall TTwwiinnss
IIddeennttiiccaall
cchhrroommoossoommeess
((DDNNAA))
IIddeennttiiccaall
pprrootteeiinnss
VVeerryy ssiimmiillaarr
aappppeeaarraanncceess
Identical twins have identical DNA, but different fingerprints!

114. FORMATION
OF
CONJOINED
TWINS /
SIAMESE
TWINS

115. Siamese Twins
Conjoined twins joined
at the head, abdomen
etc.
Inner cell masses
subdivide but do not
separate completely,
forming conjoined twins

116. CONJOINED
TWINS

117. THE END

119. The placenta
• The embryo
develops into a
foetus attached to
the placenta by the
umbilical cord.
Umbilical cord
Placenta
Amniotic sac
filled with
amniotic fluid
Mucous
Plug

120. • Blood from the embryo
– Travels to the placenta through arteries of the
umbilical cord and returns via the umbilical vein

121. The placenta
• The foetus blood
system IS NOT
DIRECTLY
CONNECTED to
the blood system of
the mother.

122. The placenta
• The exchange of
oxygen, food and
wastes between the
mother and foetus
depends on
diffusion across the
thin wall of the
placenta.

123. LLaabbeell tthhee ddiiaaggrraamm
Placenta Amniotic fluid Foetus (baby) Umbilical cord Amniotic sac

124. Foetus (baby)
Placenta
Umbilical cord
Amniotic sac
Amniotic fluid
AAnnsswweerrss