1. Embryology is the study of the development of organisms from fertilization to birth. It involves periods of prenatal development from fertilization to birth and postnatal development until age 25. 2. The prenatal period is divided into three parts - the embryonic period from weeks 3-8 where germ layers differentiate into organs, the fetal period from week 9 to birth involving tremendous growth, and the pre-embryonic period from fertilization to week 2 involving fertilization and implantation. 3. Recent advances in embryology include prenatal diagnosis of congenital anomalies, in vitro fertilization, gene and stem cell therapy which may help treat diseases.

1. Embryology
[Pre-fertilization Events]
© 2020. Dr. Joseph K. Choge, PhD

2. Embryology
Zm- Overview
Lecture 1
Embryology
[Pre-fertilization Events]

3. Pre-Fertilization Events
Embryology Definition/Description - 1
 Embryology is:
1. The science of the origin and development of the
individual from fertilization of an oocyte to the end of
the eighth week of development and, by extension,
during any stage of prenatal development*
2. The branch of biology that deals with the formation, early
growth, and development of living organisms*
3. The embryonic structure or development of an
organism*
4. The study of the origin, growth, development, and
function of an organism from fertilization to birth*
• Embryology involves periods of Prenatal and Postnatal
Development
• Prenatal Development:
Period from fertilization to birth
• Post-natal Development:
Development continuation upto
age of 25 years.

4. Pre-Fertilization Events
Branches (Sub-divisions) of Embryology - 2
1. General Embryology: 0-8wks
after fertilization
2. Systemic Embryology: functional
maturation of various
organs/systems
3. Descriptive Embryology:
Structure & development stages
of organs
4. Comparative Embryology:
Various animal species
comparisons
5. Experimental Embryology:
Results from embyos of lower
animal experiments
6. Chemical Embryology:
Biochemical aspects of prenatal
development
7. Teratology: Abnormal embryonic
and fetal development; deals with
congenital anomalies or birth
defects.

5. Pre-Fertilization Events
Prenatal Development - 3
• Pre-natal Development
Begins with zygote (fertilized
ovum)
Ends with birth of newborn
Involves morphogenesis
Morphogenesis includes: Cell
Division; Transformation or
Specialization, Migration;
Apoptosis
• Congenital Anomalies:
may occur during morphogenesis
may be due to genetic factors or
environmental factors
Embrology helps us understand factors
causing congenital anomalies
Embryology also helps us understand
rationale of structure & functions of
body systems
Useful in treatment & prevention of
congenital anomalies

6. Some of the Causes of Embryological Defects
(Pathophysiology Inborn Errors of Metabolism)
Where the Problems Lie in Each Disease
= genetic defect
1. Acid maltase deficiency
2. Muscle phosphorylase deficiency
3. Debrancher enzyme deficiency
4. Phosphofructokinase deficiency
5. Phosphoglycerate kinase deficiency
6. Phosphoglycerate mutase deficiency
7. Lactate dehydrogenase deficiency
8. Carnitine palymityl transferase deficiency
9. Carnitine deficiency
10. Myoadenylate deaminase deficiency
Skeletal muscles normally depend on energy from carbohydrates and
fats. These fuels can be stored in the muscle (glycogen) or imported
directly from the bloodstream (glucose and fatty acids).
When a genetic defect interferes with the processing of specific fuels,
energy shortages can occur and toxic byproducts may build up.
Some people may be able to bypass their defects by adjusting diet or
exercise to draw energy more efficiently from unaffected pathways.

7. Pre-Fertilization Events
Divisions of Prenatal Development Period - 4a
• Prenatal period divided into three
parts:
1. Embryonic period: from fertilization
to end of Wk8 of embryogenesis
[further sub-divided into pre-
embryonic and embryonic (proper)
period]
2. Foetal Period: From 3rd month to
birth
3. Foetal Period: From Wk9 to birth;
tremendous growth & specialization
of body structures occurs;
• Pre-embryonic Period:
from fertilization to end of Wk2 of IUL.
Morphogenic events: Fertilization,
Transportation, Cleavage, Implantation,
Primordial embryonic tissue formation
• Embryonic Period:
From Wk3 to 8 of IUL
Differentiation of germ layers into
specific body organs
Placenta, Umbilical cord and Extra-
embryonic membrane formation

8. Pre-fertilization Events
Stages of development before birth – 4b*
Time Period Stage Main Events
Conception to
week 2
Pre-embryonic
period
Fertilized ovum undergoes mitosis.
Formation of morula; appearance of
blastocyst; blastocyst implanted.
2nd to 8th week Embryonic
period
Germ layers and placenta develop.
Main body systems form.
9th week to birth Fetal period Further growth and development of organs.
Locomotor system becomes functional.

9. Pre-Fertilization Events
Postnatal Development - 5
• Postnatal Development period:
from birth to about 25 years
Sub-divided into 5 developmental
parts:
1. Infancy: 0- 1 years
2. Childhood: 2-12 years
3. Puberty: 13-16 years
4. Adolescence: 17- 18 years
5. Adulthood: 19-25 years
Participatory Activity 1.1
1. Differentiate between 'infant'
and 'neonate'.
2. What do you understand by
'neonatology'.
3. Describe 'Perinatal', 'Prenatal',
'Postnatal' periods.
4. Describe key events that occur
during postnatal development
period (the 5 parts opposite).

10. Pre-Fertilization Events
Clinical Relevance - 6
1. Offspring of Older Women: The incidence of
Down’s syndroms (Trisomy 21) increases with
the age of the mother*
2. Offspring of Older Men: An increased incidence
of achondroplasia (a congenital skeletal
anomaly characterized by retarded bone
growth) and Marfan’s syndrome is associated
with advanced paternal age*
3. Male Fertility: This depends on the number and
motility of sperm*
Participatory Activity 1.2: (i) Define infertility
(in medical terms), (ii) outline its common causes
and (iii) principles of and challenges during
management.
4. Hormonal contraception*
Participatory Activity 1.3:
i. Synthesize (summarize in your own words)
the concept of contraception and the
consequent use of various contraceptives.
ii. Tabulate the following important
information:
Name/Type of Contraceptive
Route of administration
Mode and Length of action before expiry
Side Effects/Adverse Effects
Contraindications

11. Pre-Fertilization Events
Clinical Relevance - 7
5. Primordial Germ Cells (PGCs) and Teratomas
 Teratomas are tumors of disputed origin that
often contain a variety of tissues*
Examples of tissues with teratomas:
1. Muscle
2. Gut epithelia,
3. Bone
4. Hair
5. Others
• It is thought that these tumors arise from a
pluripotent stem cell that can differentiate into any
of the three germ layers or their derivatives
6. Challenges of Cultural beliefs
versus scientific Embryological facts.
 Participatory Activity 1.4
As an embyrologist, how do you
handle myths vis-a-vis embryological
facts (such as a belief that viewing a
'shocking event' may lead to birth of a
'shocking' baby)? (e.g. reading 'Double
Trouble', Three Masketeers', Alibaba
and 40 Thieves'.

12. Pre-Fertilization Events
Clinical Relevance - 8
7. Birth Defects and Spontaneous
Abortions: Chromosomal and
Genetic Factors*
• Numerical Abnormalities:
Haploid*
Diploid*
Euploid*
Aneuploid*
Trisomy*
Monosomy*
Participatory Activity 1.5:
1. Define ‘Abortion’
2. Classify the types of abortions
3. Which type(s) is/are attributable
to embryological defects?
4. What are the dangers and
related effects of abortion?
5. Outline the management and
challenges of abortion.

13. Embryology
Recent Advances of Embryology – 9
1. Prenatal Diagnosis: to detect
congenital anomalies before birth: (i)
Amniocentesis, (ii) Chorionic villous
sampling, (iii) Ultrasonography, (iv)
Fetoscopy, (v) Maternal serum
screening, (vi) MRI, (vii) Others
2. In vitro fertilization (test tube
babies);
3. Gene Therapy: Replacing
defective genes (to treat
conditions e.g. Progeria)
4. Cloning: Advances in molecular
biology, to produce living organisms by
genetic manipulation.
5. Stem Cell Therapy: Genetic
manipulation to replace defective stem
cells (e.g. possible cancer cure by
replacing malignant cells, Treating
degenerative and genetic diseases).

14. Embryology
History and Advances of Embryology – 10
 Participatory Activity 1.6:
1. Summarize the contributions made
by various embryology scientists *
2. What are some of the advances in
medical-related embryology ever
since?*
3. Comment about progeria in relation
to advances in embryology.*
Premature aging: Amy, a child with progeria, at age 16.