Embryogenesis begins with fertilization where a sperm fuses with an egg to form a zygote. The zygote undergoes rapid cell division through cleavage and develops into a blastocyst which implants in the uterus. The cells then differentiate and organize into the three primary germ layers through gastrulation. The embryo continues to grow and develop organs over the next few weeks. Around 8 weeks, external genitalia form and the embryo becomes a fetus. The fetus continues growing and developing until birth. Lactation begins during pregnancy in preparation for feeding the infant. Prolactin and oxytocin play important roles in milk production and ejection. Breast milk provides ideal nutrition for an infant's growth and development

1. Embryogenesis
• It is the development of a fertilized egg that occurs early on
in pregnancy.
• After a sperm fuses with an egg, many changes occur in a
specific order.
• The cells divide, reorganize and form layers of tissue that
will eventually develop into specific organs.
• Embryogenesis happens very early, even before the baby is
a true fetus.
• During embryogenesis, we're just dividing up the cells that
will become specific parts of the fetus later on.

2. Fertilization
• The first step to embryogenesis is fertilization, where
a sperm fuses with an egg, which occurs in
the fallopian tubes of the female reproductive tract.
• Hours after the two cells join together, the cell
begins dividing and moves into the next stage. Below
is a real picture of a sperm fertilizing an egg.
Sperm cell fertilizing an egg

3. Fertilization
 The egg is viable for 12 to 24 hours after ovulation
 Sperm are viable for 12 to 48 hours after ejaculation
 Sperm cells must make their way to the uterine tube for
fertilization to be possible

4. ZYGOTE
1. The sperm and egg join to form a zygote: the first
cell of a new individual.
2. Zygote results of the fusion of DNA from sperm and
egg.
2. Fertilization occurs in the Fallopian Tubes.
3. The zygote begins rapid mitotic cell division
4. Beginning of human development

5. ZYGOTE
1. Still rapidly dividing
2. The zygote floats down from the fallopian tube
and towards the uterus
Only thirty hours after conception
Size: no larger than the head of a pin

6. Cleavage
Cleavage is the mitotic division of cells in the early embryo

7. About 96 hours after fertilization.
This picture shows a MORULA, a solid
ball of 32 cells that resembles a raspberry.
MORULA
Cleavage

8. 1. A ball of more that 64 cells surrounding a fluid-filled
cavity (the blastocele)
1. Blastula is produced by the repeated mitotic division of a
zygote
BLASTULA
Cleavage
Five days after fertilization

9. Cleavage
Implantation
1. The fastening of the embryo to the wall of the uterus
is called implantation
2. Implantation occurs seven days after fertilization
3. Implantation takes places in the uterus.
BLASTOCYST

10. The Embryo
 The embryo is the developmental stage from the
start of cleavage until the ninth week
 The embryo first undergoes division without growth
 The embryo enters the uterus at the 16-cell state
 The embryo floats free in the uterus temporarily
 Uterine secretions are used for nourishment

11. Gastrulation involves a series of cell migrations to positions where
they will form the three primary cell layers.
•Ectoderm forms the outer layer. Ectoderm forms skin, hair,
sweat glands, epithelium, brain and nervous system.
•Endoderm forms the inner layer. The endoderm forms
digestive, respiratory systems, liver, pancreas, all bladder, and
endocrine glands such as thyroid and parathyroid glands.
•Mesoderm forms the middle layer. The mesoderm forms
body muscles, cartilage, bone, blood, reproductive system
organs and kidneys
Differentiation
Gastrulation

12. Development from Ovulation to
Implantation

13. EMBRYO
0.5 cms
20 days after fertilization
•Embryo begins to form organs during the third
week.
•Cannot tell if it is human or other vertebrate. Tall
visible.
Differentiation

14. EMBRYO
1 months
0.6 cms
• Ears, nose and eyes not visible
• Small arm and leg buds, backbone seen
• Heart beats.
Differentiation

15. FETUS
2 months
3 cms
• During the second month most of the major
organ systems form, limb buds develop.
• Limbs distinct with fingers and toes bones
begin to form, eyes far apart.
• The embryo becomes a fetus by the seventh
week.
Differentiation

16. Differentiation
 All organ systems are
formed by the end of the
eighth week
 Activities of the fetus are
growth and organ
specialization
 A stage of tremendous
growth and change in
appearance
Fetus at nine weeks
3 cm

17. FETUS
2 months
3 cms
Differentiation
•Beginning the eighth week, the sexually
neutral fetus activates gene pathways for
sex determination, forming testes in XY
fetuses and ovaries in XX fetuses.
•External genitalia develop.

18. Growth
FETUS
4 months
18 cms
•Head enlarged, face has human feature.
•The fetus increases in size during this
trimester, and bony parts of the skeleton
begin to form.
•Fetal movements can be felt by the mother..

19. FETUS
7 months
About 40 cms
Growth
 During this trimester the fetus increases in size.
 Circulatory and respiratory systems mature in
preparation for air breathing.
 Fetal growth during this time uses large parts of
its mother's protein and calcium intake.
 Maternal antibodies pass to the fetus during the
last month, conferring temporary immunity.

20. FETUS
About 50 cms
9 months
• Fat under skin, smooth wrinkles.
• Nails on fingers and toes completely formed.
• Baby at term.
Growth

21. Fertilization Cleavage Differentiation Growth
Zygote Gastrula EmbryoMorula Blastocyst
NeuralizationImplantationFertilization Mitosis
Uterine
Wall
Fallopian
tubes
VaginaFallopian
tubes
Uterine
Wall
Uterine
Wall
Uterine
Wall
FetusFetus
Childbirth

23. Childbirth (Partition)
 Labor – the series of events that expel
the infant from the uterus
 Initiation of labor
Estrogen levels rise
Uterine contractions begin
The placenta releases prostaglandins
Oxytocin is released by the pituitary
Combination of these hormones produces
contractions

24. • Lactation happens when the mammary glands in the breasts of
a mother, produce milk for her infant.
• All female mammals have mammary glands to feed their
young. The word “mammary" is derived from the Latin word
“mammae", which is a sound similar to the sound made when
a baby is rooting/searching for the breast.
Lactation

25. Different Stages in Lactation
Stage 1
~
Mammogenesis
• The first stage of lactation is called Mammogenesis, which occurs when the breasts are
developed, right from birth, through to puberty and then the process is completed during
pregnancy.
• This stage of lactation, starts in a woman when she is still in her own mother’s womb, as a
small embryo. At 12 weeks gestation, the breasts have developed nipples, areolae, alveoli
(milk producing cells) and mammary buds.

26. • Sex hormones will then further develop the breasts, until she
is born.
• During puberty, Estrogen and pituitary growth factors will
cause the breasts to grow. New breast tissue is accumulated
with every monthly ovulation cycle, up until the age of 35.
• A woman’s breasts, are only ready to produce milk once she
has become pregnant, this is when the final changes in the
breasts occur to enable her to produce milk.
• The hormones responsible for these changes during pregnancy
include: Prolactin, Placental lactogen, Estrogen, Progesterone,
and the Adrenocorticotropic hormone.

27. Mammogenesis
• The inactive breast is mainly made up of adipose tissue; however, the lactating
breast has a greater proportion of glandular tissue.
• During pregnancy the breasts enlarge; the nipple pigment darkens; the skin
becomes thinner and the veins in the breast become more prominent.
• In mammogenesis the ductal system grows and branches; the amount of connective
tissue and supporting cells increases and fat is laid down in the breast. This is
stimulated by the estrogens, growth hormone, prolactin, insulin and the adrenal
corticoids.
• Progesterone is involved in the last stages of mammogenesis after the ductal system
has grown. It acts with the other hormones to develop the breast lobules and
alveoli, and adapts the alveoli to have secretory properties.

28. The difference between an inactive breast and a
lactating breast

29. Lactogenesis
There are two main stages of lactogenesis:
Lactogenesis I: the ability of the mammary glands to secrete milk from mid-
pregnancy to late pregnancy.
Lactogenesis I starts from mid-pregnancy till 2 days after birth. It involves the
differentiation of alveolar epithelial cells and the stimulation of milk synthesis by
prolactin.
Lactogenesis II: the formation of large amounts of milk after parturition.
Lactogenesis II starts from day 3 postpartum to day 8. It is triggered by the
reduction of progesterone. The breast become full and warm and produce large
amounts of milk.

30. Galactopoiesis
• Galactopoiesis starts around 9 days after birth and finishes at the
beginning of involution. It is the maintenance of milk secretion.
• Controlled by hormones. Breast size starts to diminish between 6 to 9
months after birth. The rate of milk formation normally decreases after
7-9 months; however milk production can continue for years if the child
continues to suckle.

31. Involution
• Involution is the loss of secretory function of milk, due to the accumulation
of inhibiting peptides. It normally starts 40 days after the last breastfeed.
• The epithelial cells no longer require their secretory properties so they are
removed by the process of apoptosis and replaced by adipocytes.

33. The importance of prolactin in
lactation
• Prolactin secretion starts in the 5th week of pregnancy.
• The levels of serum prolactin gradually increases until parturition; afterwards
quantity of prolactin returns to the non-pregnant level.
• It is secreted by the anterior pituitary gland, cells in the breast and the
decidua of the uterus.
• It is transported via the blood to the breasts, where it acts on cells in the
alveoli.
Control of Prolactin:
• Prolactin secretion is inhibited by prolactin-inhibitory factor produced by the
hypothalamus.
• Angiotensin II, vasopressin and gonadotrophin-releasing hormone (GnRH)
control the release of prolactin.

34. Functions of prolactin:
Prolactin is involved in mammogenesis
• Prolactin causes the mammary ducts and alveoli to mature; increases breast size and
initiates the final stage of cell differentiation in the alveoli cells.
• The epithelial cells in the alveoli differentiate to become secretory cells; however the
cells need to have come in contact with cortisol and insulin before prolactin can
complete its role.
Prolactin stimulates milk secretion
• Normally, when a new mother nurses her baby, hears her baby or plays with her
baby, nervous signals are sent from the nipples to the hypothalamus.
• This causes a surge in the levels of prolactin released, which lasts for about a hour.
Prolactin makes the mammary glands secrete milk into the alveoli.
• If the surge is absent or blocked as a result of hypothalamus or pituitary gland
damage, or if nursing does not continue; the breasts start to lose their ability to
produce milk in about a week or two.

35. Pituitary hormones
Several pituitary hormones seem to be involved in the formation of
milk, so that it is customary to speak of a lactogenic (“milk-
producing”) complex of hormones.
To some degree, the role of the pituitary
hormones adrenocorticotropin, thyrotropin, and growth hormone in
supporting lactation in women is inferred from the results of studies
done on animals and from clinical observations that are in agreement
with the results of animal studies.
Prolactin, growth hormone, and adrenal hormone seem of greatest
value in restoring lactation after removal of the pituitary, although the
precise response varies from species to species.

36. The importance of oxytocin in
breastfeeding
Ejection ("Let down") process in milk secretion
• Milk is continuously secreted into the alveoli of the breast, however
to get the milk from the alveoli and into the ducts it needs to be
ejected.
• Ejection is a neuronal and hormonal reflex involving oxytocin.

37. Composition of breast milk
Composition
Water
Fat
Lactose
Casein
Lactalbumin and other milk proteins
Ash (calcium and minerals)
Percentage (%)
88.5
3.3
6.8
0.9
0.4
0.2
Growth hormone, cortisol, parathyroid hormone and insulin provide the
amino acids, fatty acids, glucose and calcium needed for milk formation.

38. Composition and properties of milk
• Milk can be regarded as an emulsion of fat globules in a colloidal
solution of protein together with other substances in true solution.
• Two constituents of milk, the protein casein and milk sugar, or lactose,
are not found elsewhere in the body.
• Maternal breast milk provides vitamins, minerals, protein, and anti-
infectious factors; antibodies that protect the infant’s gastrointestinal
tract are supplied, resulting in a lower rate of enteric infection in breast-
fed than in bottle-fed babies.
• The bonding that is established through breast-feeding is
advantageous to building the parent-child relationship.