The document summarizes key aspects of embryonic development from weeks 3-8. It defines the embryonic period as the time of organogenesis from the three germ layers. Ectoderm forms skin and nervous system. Mesoderm forms muscles, bones, blood vessels and urogenital systems. Endoderm lines the gut and forms organs like liver and pancreas. It describes events like neural tube formation and development of limbs. The fetal period follows from week 9 to birth involving further growth and maturation. Common embryonic disorders are also listed.

1. Unit 2.1
Embryonic Development

3. General Objective
At the end of the session,all participants will be
able to explain about embryonic development.

4. Specific Objectives
At the end of this session, all participants will be
able to:
define embryonic period
state derivatives of germ layers
explain various events during embryonic period
define fetal period
define embryonic disorders
list the embryonic disorders

5. Embryonic Period
Definition:
It is the period of organogenesis which
occurs from 3rd to 8th weeks of development of
product of conception during which each of the
three germ layers give rise to its own tissues and
organ systems.

6. Germ Layer Derivatives
Ectoderm derivatives
1. Surface Ectoderm: gives rise to
 Skin
 Hair
 Nails
 Enamel of teeth
 Oral epithelium including cheeks, lips, gums
 Lens of eyes

7. Epithelium of conjunctiva,cornea, ciliary body,
iris
Exocrine glands: Sweat,
sebaceous,mammary,lacrimal glands

8. 2. Neuro-ectoderm:
 Central nervous system
Retina and optic nerve
Pineal gland
Glial cells of CNS like astrocytes,
oligodendrocytes,ependymal cells.

9. 3. Neural crest:
 Peripheral Nervous System
Adrenal medulla
Melanocytes
Cranial nerves
Ganglions such as sensory,cranial,autonomic

11. Mesoderm derivatives
Intermediate mesoderm
 develops between paraxial and lateral plate
mesoderm.
 Gives rise to urogenital and reproductive system
such as kidneys,testis, ovaries,genital
ducts,accessory sex glands.

12.  Paraxial mesoderm
 It is the area of mesoderm which forms
simultaneously with the neural tube.
 Gives somitomeres which further forms somites.
 Usually appears towards the end of 3rd
gestational week

13.  Somites further gives rise to:
a. Myotome:muscle tissue
b. Sclerotome:bones and cartilage
c. Dermatome:dermis of skin
d. Duramater

14.  Lateral plate mesoderm:
 Located lateral to the intermediate mesoderm.
 Forms:
a. Splanchnic mesoderm:
I. Heart and visceral layer of serous pericardium and blood
vessels

15. II. Smooth muscle and connective tissues of respiratory and digestive
organs.
b. Somatic mesoderm
I. Bones, ligaments
II. Blood vessels and connective tissue of limbs

16. It also gives rise to pulmonary system
components, lymphatic system,adipose tissue,
etc.

17. Endoderm derivatives
 Epithelial lining of:
 GI tract
 Respiratory tract
 Urinary bladder
 Parenchyma of:
 Thyroid, parathyroid
 Liver, Pancreas

18. Key Events During Embryonic Period
Day 14-15
 Appearance of primitive streak

19. Day 16-18
 Notochordal process appears

20. Notochord Formation

21. Day 19-20
 Primitive streak
continues to develop
 Umbilical vessels and
cranial neural folds
begin to form

22. Day 20-21
 Cranial neural folds
elevated
 Deep neural groove is
established
 Embryo begins to bend

23. Day 22-23
 Fusion of neural folds begin in cervical region
Caudal neuropores open widely
Heart tube begins to fold
Beginning of neurulation occurs

24. Neurulation

25. Dorsal view of neural tube

26. Day 24-25
 Cranial neuropore is closed
Optical vessels are formed

27. Day 26-27
 Upper limb buds appear

28. Day 28-30
 Hind limb buds appear

29. Day 31-35
 Nasal pits are formed
 Embryo becomes tightly
C-shaped

30. Day 36-42
 Brain vesicles become prominent
External auricle is formed
Umbilical herniation is initiated

31. Day 43-49
 Pigmentation of retina
occurs
 Eyelids are formed
 Upper limbs are formed

32. Day 50-56
 Limbs long,
 Bent at elbows, knees,
fingers, toes free, face
more human-like,
 Umbilical herniation
persists to end of third
month

33. Fetal Period
It is the period from beginning of 9th week to
birth in which maturation of organs, tissues and
rapid growth of body occurs.

34. Embryonic Disorders
Definition
It is defined as the
deformity or defect which
arises or exists at or before
birth during the process of
development which may be
the result of genetic or
environmental factors.

35. Embryonic Disorders
1. Neural tube defects
2. Congenital Heart defect
3. Cleft lip/cleft palate
4. Chromosomal abnormalities
5. Esophageal atresia
6. Renal agenesis
7. Undescended testis
8. Syndactyly ,Polydactyly

36. SUMMARY

37. Post- test
Fill in the blanks using appropriate words:
• Mesoderm between paraxial and lateral plate
is called…………..
• Neural crest gives rise to………….
• …………..is the process of formation of neural
tube from neural plate.

38. Write “T”for true and “F” for false: (1*3=3)
• Neuro ectoderm gives rise to Peripheral
Nervous system ( )
• Notogenesis is the process of formation of
neural tube ( )
• Fetal period is the period from 9th week to
birth ( )

39. Answer the following question: (5*1=5)
What are the derivatives of ectodermal layer?

41. References:
• 1. T.W.saddler ,langman’s textbook of embryology
, 12th edition,Lippincott Williams and wilkins,
south asian edition published by wolters kluwer.
• 2. D.C. Dutta, textbook of obstetrics, 5th edition,
new central book agency Pvt ltd, India.

42. • Subedi durga , Gautam saraswoti, midwifery
nuring part-1, 2nd edition, medhabi publication.
• Indrani T.K(2003) Textbook of midwifery, New
Delhi:Jaypee brothers,medical publishers(P).ltd
• Jacob.A(2005) A Comprehensive Textbook of
Midwifery, Jaypee Brothers , New Delhi

43. • BennettV.R, Brown L.k(2003)Myles textbook for
midwives, 14th edition,churchill,livingstone.
• http:/www.embryology.med.unsw.edu.aw
• 6. Tuitui roshani, manual of midwifery A,
vidyarthi pustak bhandar, Kathmandu.