General Embryology

Sanjaya AdikariDepartment of Anatomy

Lecture I

Our life begins as one cell formed by the

union of the maternal and paternal germ

cells

Diploid(46/23 pairs)

Diploid(46/23 pairs)

Diploid

Haploid(23)

Haploid(23)

Homologous pairHuman chromosomes

Mitosis

Meiosis

Gametogenesis

Female

Ovary(primodial germ cells)

Ovum/oocyteOogenesis

Male

Testis(spermatogonia)

SpermatidSpermatogenesis Spermiogenesis

Sperm

Ovarian cycle

Uterine cycle

Hormonal cycle

Development of the fetus

Development of the placenta

Ovarian cycle

Fertilization

Zygote

FSH & LH

OestrogenProgesteron

0 14 28

FSH

LH

Uterus

hCG

Fetus

Dating of pregnancy & the age of fetus

/POA

General Embryology

Sanjaya AdikariDepartment of Anatomy

Lecture II

Early development of embryo

Cleavage

Blastocyst

Day 05 After 1 wk

Inner cell mass(embryoblast)

Outer cell mass(trophoblast)

Amniotic cavity

Blastocyst cavity

embryonic plate

Bilaminar disc (2 weeks)

Amniotic cavity

Blastocyst cavity

Epiblast

Hypoblast

Syncytiotrophoblast

Cytotrophoblast

embryonic pole

abembryonic pole

exocoelomic membrane

exocoelomic cavity(primitive yolk sac)

Bilaminar disc….cont.

/Epiblast

/Hypoblast

Extra-embryonic mesoderm

Amniotic cavity

Secondary yolk sac

Extra-embryonic coelom(chorionic cavity)

Connecting stalk

Gastrulation

Trilaminar disc (3 weeks)

Ectoderm

Intra-embryonic mesoderm

Endoderm

Notochord

Neural crest

Neural fold

Notochord

Neural tube

Neural crest cells

Neural tube & neural crest cells

Starts in the 3rd week

This is the earliest system to start developing

Folding of the embryo

Ventral mesentary

Paraxial mesoderm

Intermediate mesoderm

Derivatives of germ layers

Ectoderm

CNS including neural crest cells

Peripheral nervous system

Sensory epithelium of ear, eye and nose

Skin (epidermis) and its appendages (hair, nails, sebaceous

glands and sweat glands)

Secretory component and ducts of mammary gland

Pituitary gland

Secretory acini and ducts of parotid salivary gland

Enamal of teeth

Lens of the eye

Endoderm

Lining epithelium of the gastrointestinal tract

Secretory acini and ducts of submandibular and sublingual salivary glands

Alveolar parenchyma and the lining epithelium of the respiratory tract

Liver parenchyma

Epithelium of the gall bladder

Exocrine pancreas

Epithelium of the urinary bladder and urethra

Parenchyma of the thyroid and parathyroid glands

Epithelial lining of the tympanic cavity and auditory tube

Epithelium of the palatine tonsil

Hassel’s corpuscles of thymus

Mesoderm Paraxial mesoderm

SclerotomeMyotomeDermatome 

Intermediate mesoderm  Lateral plate mesoderm Somatic mesodermSplanchnic mesoderm

Branchial mesoderm

Somites

Limb bud

Twins

identical

Totipotent Pluripotent Unipotent

Ovuma/oocytes

10015 fail to get fertilized

15 fail to get implanted

70 get implanted

7042 survive by the time of first

missed menstruation

Number of cases get aborted in coming weeks

General Embryology

Sanjaya AdikariDepartment of Anatomy

Lecture III

Placenta and the umbilical cord

Blastocyst cavitySyncytiotrophoblast

Cytotrophoblast

Primary villus

Secondary villus

Tertiary villus

2 1

Placental barrier

Chorionic villi

Lacunar/intervillous spaces

Cotyledon (15-20)

Chorionic plate

Decidual plate

Macroscopic appearance of placenta

Placenta – fetal surface

Placenta – maternal surface

Umbilical cord

umbilical arteries umbilical vein

Wharton’s jelly

References

• Medical embryology by Jan Langman

• Human embryology and developmental

biology by Bruce M. Carlson

• Human embryology by Malkanthi S.

Chandrasekera