2. What is embryology?
• The study of developmental events that occur during
the prenatal stage.
• The branch of biology and medicine concerned with
the study of embryos and their development.
3. Embryonic period
• Embryonic:
• First 8 weeks development of the three
primary germ layers gives rise to all structures
and basic body plan takes shape.
4. Fetal period
• Fetal period remaining 30 weeks.
• During this period structures and organs
continue to grow and development.
6. Stages of development
1. Fertilization
2. Cleavage
3. Gastrulation
4. Organogenesis
5. Maturation
Cleavage,gastrulation,organogenesis are known as
Embryogenesis, the formation and development of an
embryo.
7.
8. Fertilization
• The process of fusion or union of the
spermatozoon with the mature ovum is
known as conception/fertilization/
impregnantation.
• That produced the fertilized single mono-
nucleated cell called the zygote.
10. Gastrulation
• It is a phase early in the embryonic
development of most animals / human being,
during which the single layered blastula is
recognized into a trilaminar ( three layered)
structure known as gastrula .These three germ
layers are known as the ectoderm ,
mesoderm, and endoderm.
12. How fertilization occurs?
• There are 4 steps of fertilization:
1. Sperm preparation
2. Sperm-egg recognition and binding.
3. Sperm-egg fusion
4. Fusion of sperm and egg nuclei and
activation of the zygote.
13. • Gonad:
Primary organ of reproduction.
Ovaries:
a. In females produce ova (egg).oogenesis.
b. Production controlled by hormones.
c. Estrogen and progesterone.
d. Pituitary gland hormones; FSH and LH.
14. • Testes:
a. In males produce sperm cells ,
spermatogenesis.
b. Production controlled by hormones
c. Testosterone
d. Pituitary gland hormones ; FSH and LH.
15. • Male releases sperm into the female
reproductive tract.
• Sperm have little life span that is three days or
less.
• Egg can be fertilized within a day .
• Sperm produce enzyme to penetrate egg.
16. Growth And Differentiation
Growth – mitotic divisions resulting in a
massive amount of cells.
Differentiation – cells become different in
structure and function (diverse)
Morphogenesis – organization of cells into
tissues and organs.
Controlled by the protein the different cells
produce.
17. Cleavage
• MULTIPLE ROUNDS OF MITOSIS.
• ORIGINAL CELL CLEAVES INTO SMALLER CELLS.
• VOLUME OF CYTOPLASM DOES NOT
INCREASE.
• CLEAVAGE STOPS WHEN CELLS SIZE IS THAT OF
AN ADULT.
• Morula and Blastula.
18. Morula
• An embryo at an early stage of development,
consisting of approximately 4-16 cells.
• The morula is produced by cleavage.
• The morula travels to the uterus where it
implants after 5-7 days.
19.
20. BLASTULA (Blastocyst)
• The fertilized egg changes from a solid mass of
cells (the morula) to a hollow ball of cells
(the blastula).
• The blastula contains a fluid-filled cavity called
the blastocoel.
• Final cleavage stages.
21. Gastrula
1st half of the embryonic stage.
CELLS BEGIN TO GROW AND DIVIDE.
CELLS MOVE --- ESTABLISHES THE SHAPE OF THE
EMBRYO.
GENERALLY FORMS THREE LAYERS:
• Endoderm.
• Mesoderm.
• Ectoderm.
23. Neurulation
NEURULATION – follow gastrulation.
• All body organs formed
• 2nd half of embryonic stage
Ectoderm forms neural folds
Neural folds come together to form neural tube
Neural tube = Brain and spinal cord
Notochord – Present in embryonic stages of
development of chordates.
• Part of the mesoderm
Establishes a direction of development.
Embryo = Neurala.
27. Human Development
• BLASTOCYST
• Stage of embryo development: mass of cells
in mammals resembling a BLASTULA.
• Part of the cells develop into EMBRYO (Inner
mass cells).
• Parts develop into the structures that
SURROUND, PROTECT, and NOURISH the
embryo.(outer ring cells).
28. Continue…
• Amnion: fluid filled sac that surrounds the
embryo…watery environment
• Allantois: sac-like structure that grows out of the
digestive tract of the embryo. Allows for exchange of
gases and waste in the chicken. Gives rise to
umbilical cord in humans.
• Yolk: source of food for embryo(small in humans)
• Chorion: outermost membrane forms embryo part of
the placenta.
29. Gastrula In Humans
3 layered structure that develops from
Blastocyst.
CHORION extends VILLI into the UTERUS to
form PLACENTA.
Embryo is connected to placenta by
UMBILICAL CORD…contains:
• Artery: take waste away from embryo.
• Vein: takes nutrients and oxygen to the embryo.
30. • General notes:
• After 8th week of development, the embryo is now
called a FETUS.
• After 12 weeks of development , the fetus has most
major organs development AND has skeleton.
• After 24 weeks, most growth and maturing of organs
take place. (3rd Trimester).
• Normal pregnancy (period of gestation) is 30 to 40
weeks for a human.
31. • Birth process:
• Hormone OXYTOCIN released by the pituitary
gland begins the periods of birth:
• Labor: fetus born through widened vagina.
• Afterbirth: uterus expels lining, uterus and the
vagina shrink.
