SOMITE FORMATION AND HEART FORMATION

1. DEVELOPMENTAL
BIOLOGY
SOMITES AND HEART FORMATION
SUBMITTED BY:
S.DHASARADHA BAI
18PBI803

2. SOMITE FORMATION - INTRODUCTION
• The variety of organs in a vertebrate body is formed from the
mesoderm
• Mesoderm becomes partitioned at the neurala stage into 4 sub –
divisions:
Axial mesoderm
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
• Paraxial mesoderm gives rise to somites from which connective
tissues develop which includes bone, muscle, dermis and cartilage

3. DEVELOPMENT OF SOMITES
• This happens after gastrulation and early neuralation
• Thick bands of paraxial mesodermal cells are arranged on either sides
of neural tube called segmental plates
• The plates separate into somites where specification is done by the
expression of Noggin proteins
• A clock and wave mechanism controls somite formation
• Somites will be formed in every 90 minutes
• Formation is specific – ie., 50 in chick, 65 in mouse

4. FATE OF A SOMITE
• Cells of ventro – medial portion of somite becomes sclerotome on
commitment
• Large number of cells move away from somite and surround the
notochord and neural tube
• These cells form cartilage and replace the notochord
• The remaining epithelial portion of somite is called
DERMAMYOTOME
• EPAXIAL MYOTOME and HYPAXIAL MYOTOME unite to
form myotome from which muscles are formed

5. [ CONTINUED]
• Remaining cells of dermamyotome becomes mesenchymal cells called
DERMATOME to form dermis

7. HEART FORMATION - INTRODUCTION
• Heart is the central pumping organ in vertebrates that functions first in
the embryo
• In humans, heart rudiment starts beating in the 23rd day foetus

8. CARDIAC TUBE
• When the head of the chick embryo is lifted off the blastoderm and
foregut begins to form, cardiogenic tissue move anteriorly towards the
middle of the embryo
• The 2 groups of cells remain in close contact with folding endoderm
and forms 2 ENDOCARDIAL TUBES
• Bilateral origin of heart primordia is a striking phenomenon in cardiac
development
• The heart forming cells begins to differentiate into 2 cardiac
primordials

9. [CONTINUED]
• Some cells form pericardium and the other cells form endocardium
• The endocardium is surrounded by cardiac jelly
• The remaining cells form myocardium
• The posterior portion of endocardium receives vitelline veins
• On the opposite site of heart tube, TRUNCUS ARTERIOSUS gives
rise to aorta
• The contraction of heart is due to Na – Ca exchange pump
• The beating of heart is controlled by pacemaker

10. LOOPING OF HEART CHAMBER
• Rapid elongation of heart tube and looping into S – shape results in the
formation of atrial and ventricular chambers
• The thin – walled caudal chamber is sinus venosus
• Atrial region is cephalic to sinus venosus
• The narrow portion which connects ventricle to truncus is conus

11. STRUCTURES

14. REFERENCES
• An Introduction to Developmental Biology – S.Chattopadhyay
• Developmental Biology – Scott.F.Gilbert – Eighth Edition
• https://www.slideshare.net/LawrenceJames/development-of-heart
• https://www.slideshare.net/VharshaHaran/somite-differentiation-
and-neural-crest?qid=c49bc772-5acf-412b-aeb2-
0e3580dddbb9&v=&b=&from_search=1

15. THANK YOU