Introduction to embryology course for biomedical sciences students

1. KILIMANJARO CHRISTIAN MMEDICAL UNIVERSITY COLLEGE
Faculty of Nursing and Rehabilitation Medicine
Department of Anatomy and Neuroscience
EMBRYOLOGY LECTURE (L9,10,11)
INTRODUCTION TO EMBRYOLOGY (SESSION 13))
Date: November 25th 2022, from 8:00 am, GF 01 MD1 Classroom.
Lecturer: J. S. Kauki, BSc, MSc, on PhD, Email: jskauki@gmail.com.
Office ext. 69 IPH Block, 3RD Floor, Anatomy dept.

2. General Course Objectives
• An understanding of human embryology provides a rational basis for comprehending
gross anatomy and the variations and/or abnormalities that a physician encountered in
the physical examination, radiology, surgery or other invasive and non-invasive
diagnostic procedures.
• An understanding of development is of great value in understanding congenital
malformations, whether these be inherited or acquired in utero. Surgical approaches
for treating these malformations require an understanding of embryology.
• An understanding of embryonic and fetal development is obviously essential for anyone
entering the field of Health sciences
• Future therapeutics employing genetic or molecular medicine may necessitate in utero
approaches.

3. Cleft lip and palate
Amelia
We need to know the cause and management of these and many other conditions that occurs during development

4. Discussion
• What causes Congenital anomalies / Birth defects?

6. Recent History
• 1965 - Neural Crest Research Nicole Le Douarin.
• 1977 - Thalidomide and its affects on development. Thalidomide
• 1978 - First IVF baby born. In Vitro Fertilization
• 1986 Discoveries of growth factors
• 1995 Genetic control of early embryonic development
• 1996 - "Dolly the sheep" First adult somatic cell cloning using the process of
nuclear transfer.
• 2002 Cell cycle
• 2002 Cell death
• 2007 Embryonic stem cells
• 2010 Development of in vitro fertilization (More? Assisted Reproductive
Technology)
• 2000 - Human Genome Complete Human Genome
• 2001 Talk given by Robert Winston "Engineering Reproduction: Will We Still Be
Human At The End of the 21st Century".
• 2009 - Induced pluripotent stem (iPS) Stem Cells
• 2011 - First Successful Transplantation of a Synthetic Tissue Engineered Windpipe
Karolinska Institute | University College London
Louise Brown, the first IVF
baby as an adult.

7. In Vitro Fertilization (IVF)

8. The ten most frequently reported birth defects in USA
between 2003-2004
1. Hypospadias
2. Obstructive Defects of the Renal Pelvis or Obstructive Genitourinary
Defects
3. Ventricular Septal Defect
4. Congenital Dislocated Hip
5. Trisomy 21 or Down syndrome
6. Hydrocephalus
7. Cleft Palate
8. Trisomy 18 or Edward Syndrome
9. Renal Agenesis/Dysgenesis
10. Cleft Lip and Palate - occur with another defect in 33.7% of cases.
(Cases for TZ and Ethiopia)

9. Patterns of Congenital anomalies compared
RANKS
Major Congenital anomaly USA EthiopiaTanzania
Genital urinary 1 6 8
Cardiovascular 2 5 6
Musculoskeletal 3 3 2
Neural tube defects 4 1 1
Ear, Nose, Head and Neck 5 7 4
Orofacial defects 6 2 -
Syndrome defects (Down,
Patau) 7 4 7
Gastrointestinal - - 3
Multiple congenital anomalies - - 5
Others 8 8 9
0
1
2
3
4
5
6
7
8
9
10
GU CVS MSS NT E,N,H&N OFD SD GIT MCA O
Patterns of Congenital anomalies compared between
countries
USA Ethiopia Tanzania
Between 3% to 4% of all live born children will be diagnosed with significant birth defects within their first two years

10. Causes congenital anomalies / Birth defects?
• Approximately 50% of congenital anomalies cannot be linked to
a specific cause.
• However, known causes include single gene defects,
chromosomal disorders, multifactorial inheritance,
environmental teratogens and micronutrient deficiencies.
• Genetic causes can be traced to inherited genes or from
mutations.

12. Common terms encountered
Oocyte = female germ cell produced in the ovary
Sperm (spermatozoon) = male germ cell
Zygote = cell resulting from union of sperm and ovum
Cleavage = series of mitotic divisions of the zygote forming early embryonic cells (blastomeres)
Blastomeres = individual cells of the cleavage stage embryo.
Morula = round cluster of ~16 blastomeres (from Latin meaning mulberry).
Compaction = process during which tight and gap junctions form between blastomeres evidenced by a
smoothing of the morula surface.
Blastocyst = ~58 cell stage at which fluid accumulation occurs within the embryo forming the blastocoel cavity.
Trophoblast = the cell layer that gives rise only to extraembryonic tissue.
Inner cell mass = tissue in blastula that gives rise to the embryo proper and some extraembryonic tissues.
Zona pellucida = glycoprotein rich layer surrounding ovum, zygote, morula and blastula which is shed just prior
to implantation (around day 6 of development).
Implantation = penetration of the uterine wall by the embryo at ~days 6-8.

13. Developmental periods
• Human development is a continuous process that begins with a fertilization of an
ovum by a sperm in the female reproductive system.
• The resulting zygote (conceptus) is transformed into a human being through cell
division, cell migration, programmed cell death (Apoptosis), differentiation, growth
and cell rearrangement.
• Embryonic period: First eight weeks of development.
• Period in which all major organ systems form but only the cardiovascular system truly functions
and is essential for subsequent development.
• Period of greatest susceptibility to teratogens.
• Teratogen is any agent that can disturb development of an embryo/ fetus thus causing a birth defect in the
child or halt the pregnancy outright.
• Fetal period: Ninth week through birth.
• Period in which the major tissues and organ systems complete differentiation, enlarge &
begin functioning.

14. Risk of Birth defects on teratogen exposure

15. Internal female reproductive structure

16. Gametogenesis
• A process of formation and development
of gametes (sperm and ovum)
• This process involves meiotic cell
division which reduces the number of
chromosomes to half and alters the shape
of cells
• Gametogenesis prepares sex cells for
fertilization

17. Spermatogenesis
• Process by which spermatozoa are produced
from male primordial germ cells
• Begins at puberty (13-16yrs); continues into old age
• Begins with transformation of primitive germ
cells called spermatogonia in the
seminiferous tubules
• Spermatogonia transform into primary
spermatocyte after several mitotic divisions
• Each primary spermatocyte undergoes 1st
meiotic division to form 2 haploid secondary
spermatocytes
• Secondary spermatoctyes undergoes 2nd
meiotic division to form 4 haploid spermatids
• Spermatids are transformed to mature sperms
during spermiogenesis

18. Spermiogenesis
• Transformation of spermatids into
mature sperms
• Involves
• Loss of cytoplasm
• Development of a tail
• Formation of acrosome
• Spermatogenesis (including
spermiogenesis) takes about two
months!
• Produced sperms are viable for 48hrs
• When spermiogenesis is complete,
sperms enter into the lumen of the
seminiferous tubules then
transported into epididymis for
storage
• Sertoli cells lining the seminiferous
tubules Support and nurture the germ
cells
Mature Sperm

20. Maturation of sperms
• Ejaculated sperm must undergo
Capacitation & Acrosome reaction to be
able to fertilize the ovum
• During capacitation
• Capacitation takes place in uterus or uterine
tubes by substances secreted by these parts of
female genital tract
• Glycoprotein coat & seminal proteins are
removed from surface of sperm’s acrosome
• Sperms becomes more active
• Acrosome reaction
• During acrosome reaction, perforations occur
in the acrosome
• Angiotensin converting enzyme in the
acrosome involved in acrosome reaction
• Completed before sperm fuse with oocyte

21. Oogenesis
• Sequence of events by which primitive germ cells
called oogonia in the ovary are transformation into
mature oocytes
• Begins before birth
• Completed after puberty is reached
• The process ultimately produces one mature ovum
every month viable for 24hrs
• Prenatal maturation of oocytes
• Oogonia ploriferates by mitosis to form primary
oocytes before birth
• Connective tissue cells forms follicular cells that
surrounds primary oocyte
• Primary oocytes surrounded by follicular cells is called
primary follicle

22. • Each primary oocytes is surrounded by zona
pelucida
• All primary oocytes begin 1st meiotic div before birth
but completion of prophase of 1st meiotic division
doesn't occur until adolescence
• All primary oocytes remain dormant in suspended
prophase stage of 1st meiotic div in ovarian follicles
until sexual maturity and the menstrual cycles begin
during puberty
Postnatal maturation of oocytes
• Beginning during puberty, usually one follicle
matures each month and ovulation occurs
• Primary oocyte completes the 1st meiotic div
shortly before ovulation to form one secondary
oocyte and first polar body (which degenerates)
• Secondary oocyte begins 2nd meiotic div. at
ovulation but progresses only to metaphase of 2nd
meiotic div. when division is arrested
• If the sperm penetrates the secondary oocyte, the
2nd meiotic division is completed
Oogenesis Cont…
Prenatal
• 1st meiotic div starts during
early fetal life
• 1st Meiotic div arrested at
prophase stage
• Oocyte maturation
inhibitor produced
by follicular cells
Postnatal
• At puberty i.e. Just before
ovulation, primary oocyte
completes 1st meiotic Div
• Starts 2nd meiotic div at
ovulation but is arrested at
Metaphase
• 2nd meiotic div completed after
sperm penetration

23. Follicle Maturation and Ovulation
Oocytes
~2 million at birth
~40,000 at puberty
~400 ovulated over lifetime
Leutinizing Hormone surge
(from pituitary gland)
causes changes in tissues
and within follicle:
• Swelling within follicle due to
increased hyaluronan
• Matrix metalloproteinases
degrade surrounding tissue
causing rupture of follicle
Egg and surrounding cells
(corona radiata) ejected into
peritoneum
Corona radiata provides bulk to
facilitate capture of egg.

24. • Note:
• Long duration of the first meiotic
division (up to 45 yrs) may account for
meiotic errors e.g. Nondisjunction
(failure of chromatids to dissociate) that
occur with increasing maternal age
• Primary oocytes in suspended
prophase are vulnerable to
environmental teratoges such as
radiations
• There are about 2 million primary
oocytes in ovaries of newborn female
infant
• Many regresses and only about 400
become secondary oocytes and are
expelled at ovulation during
reproductive period

25. Human Ovary

26. Abnormal gametogenesis/gametes
• Ideal maternal age for reproduction is 18-35 yrs of age
• Risk of chromosomal abnormalities increases after age
35 yrs
• Nondisjunction e.g. Down syndrome
• Other form of trisomy
• Gene mutation increases with age

27. Textbooks
• Either of the textbooks listed below are recommended for the course
1. Keith L. Moore, T.V.N. Persaud, Mark G. Torchia. (2011). The Developing Human:
clinically oriented embryology (9th ed.). Philadelphia: Saunders. Publisher:
Philadelphia, PA : Saunders/Elsevier, ISBN: 9781437720020
2. Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s
Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone.

28. THANK YOU