EMBRYOLOGY OF ANTERIOR ABDOMINAL WALL,PORTAL VEIN.FETAL CIRCULATION.

1. 1.DEVELOPMENT OF ANTERIOR
ABDOMINAL WALL,PORTAL VEIN
2.FETAL CIRCULATION
DR.DEEPAK KHEDEKAR
ASSOCIATE PROFESSOR
DEPARTMENT OF ANATOMY
LTMMC&GH SION,MUMBAI-22
NOV 2022

2. Anterior abdominal wall…
• Consist of
• Muscles
External oblique
Internal oblique
Transverse abdominis
Rectus abdominis
• Connective tissue
Rectus sheath

3. Embryology
• Muscular system develops from mesoderm, exception…
 Muscles of the iris, which develop from neuroectoderm,
 Muscles of the esophagus, which are believed to develop by
transdifferentiation from smooth muscle.
• Myoblasts (embryonic muscle cells) are derived from mesenchyme
(embryonic connective tissue).
• Three types of muscle—skeletal, cardiac, and smooth—are formed
during the embryonic period.

4. Myogenic regulatory factors…
• MyoD - a myogenic regulatory factor, activates transcription of
muscle-specific genes.
• MyoD - an important regulatory gene for the induction of myogenic
differentiation.
• Induction of myogenesis in mesenchymal cells by MyoD is dependent
on their degree of mesenchymal cell differentiation.

5. Myogenic precursor cells
• Limb and axial muscles develop by epitheliamesenchymal
transformation from myogenic precursor cells.
• Myogenic precursor cells originate from the somatic mesoderm
(ventral dermomyotome of somites) in response to molecular signals
from nearby tissues .

6. Embryological Events…
• Germ layer formation -
Intraembryonic mesoderm - Paraxial
mesoderm - Somites - epithelization
- central cavity - ball of epithelial
cells - sclerotome & dermatome
• Ventral region of somites -
sclerotorme - Muscle forming areas
- VLL &DML lips - migration of cell
towards dermatome to form
dermamyotome.

7. Myotome…

8. Myogenic precursor cells

9. Myotubes…
• Elongation of the nuclei and
cell bodies of mesenchymal
cells as they differentiate into
myoblasts - 1st indication of
myogenesis.
• Primordial muscle cells fuse to
form elongated,
multinucleated, cylindrical
structures—myotubes.

10. Further events…
• Further growth results from ongoing fusion of myoblasts & myotubes.
• During or after fusion of the myoblasts, myofilaments develop in the
cytoplasm of the myotubes.
• Other organelles such as myofibrils, also form.
• Myotubes slowly becomes invested with external laminae, which
segregate them from the surrounding connective tissue.

11. Connective tissue of the muscle…
• Fibroblasts produce the perimysium and epimysium;
• Endomysium is formed by the external lamina and reticular fibers.
• Most skeletal muscles develop before birth and almost all remaining
ones are formed by the end of the first year.
• Increase in the size of a muscle results from an increase in the
diameter of the fibers because of the formation of more
myofilaments.
• Ultimate size of muscle depends on the amount of exercise that is
performed.
• Many of embryonic fibres fail to establish themselves as necessary
units of the muscle and soon degenerate

12. Myofibrils vs myofilaments…
Myofibril or a muscle fibril - basic rod-like unit of a muscle cell.
• Hundreds of myofibrils running parallel to each other in a muscle cell.
• Myofibrils are composed mainly of actin and myosin proteins.
• Myofibrils comprise of repeating sections of sarcomeres.
• Sarcomeres alternating dark and light bands muscle contractions.
Myofilaments:
• Other types of proteins are also present in myofibrils.
• Organized into thick and thin long filaments
• Thin myofilaments consist primarily of actin protein
• Thick filaments consist of myosin protein.
• Run through the length of the myofibril in sections called sarcomeres.

13. Myotome…
• Each typical myotome part of a somite divides
into a dorsal epaxial division and a ventral
hypaxial division .
• Every developing spinal nerve also divides and
sends a branch to each myotome division;
• Dorsal primary ramus supplies the epaxial
division and the ventral primary ramus, the
hypaxial division.
• Myoblasts that form the skeletal muscles of
the trunk are derived from mesenchyme in
the myotome regions of the somites.

14. Typical myotome…

15. Migration of myoblast…
• Most myoblasts migrate away from the myotome and form
nonsegmented muscles.

16. Fetal circulaton-facts check…
• Fetal cardiovascular system is designed to serve prenatal needs.
• Permit modifications at birth that establish the neonatal circulatory
pattern.
• Normal circulatory changes occurring at birth are very essential, which
result in oxygenation of the blood occurring in the lungs when fetal blood
flow through the placenta ceases.
• Pulmonary vessels are vasoconstricted.
• Three vascular structures most important in the transitional circulation are
the Ductus Venosus, foramen oval, and Ductus Arteriosus
• Placenta is the organ of oxygenation
• Lungs are in dormant state.

17. Fetal circulation- Ductus venosus
• Blood coming from umbilical
veins passes directly into the DV,
a fetal vessel connecting the
umbilical vein to the IVC ,( blood
bypasses the liver).
• Blood flow through the DV is
regulated by a sphincter
mechanism close to the umbilical
vein.
• When the sphincter contracts,
more blood is diverted to the
portal vein and hepatic sinusoids
and less to the DV

18. Fetal circulation-Ductus
arteriosus
• Blood from the IVC is directed by
the crista dividens (inferior border
of the septum secundum), through
the oval foramen into the left
atrium.
• Approximately 10% of pulmonary
blood flow goes to the lungs; most
blood passes through the ductus
arteriosus (DA) into the
descending aorta to the fetal body
and returns to the placenta
through the umbilical arteries.
• DA protects the lungs from
circulatory overloading and allows
the right ventricle to strengthen in
preparation for functioning at full
capacity at birth.

19. Derivatives of Fetal Vessels and Structures…
Umbilical V. –
• Remains patent for a period
• Used for exchange transfusions of
blood during early infancy. (To
prevent complications from
erythroblastosis fetalis)
• Intra-abdominal part of the umbilical
V. becomes the round ligament of
liver (lig.teres) , which passes from
the umbilicus to the porta hepatis;
attached to the left branch of the PV.

20. Ductus Venosus…
• Ductus venosus (DV) becomes the
ligamentum venosum.
• Lig.passes through the liver from the
left br. of the portal v. and attaches
to the IVC.
Umbilical Arteries and Abdominal
Ligaments…
• Intra-abdominal parts of the
umbilical arteries become medial
umbilical ligaments ;
• Proximal parts of these vessels
persist as the superior vesical
arteries.

21. Oval foramen…
• Physiological Closure: At birth.
• Anatomic closure: 3rd month and
results from tissue proliferation and
adhesion of the septum primum to the
left margin of the septum secundum.
• Septum primum : forms the floor of the
oval fossa .
• Septum secundum: Inferior edge forms
a rounded fold, the border of the oval
fossa (limbus fossae ovalis), which
marks the former boundary of the oval
foramen.

22. Ductus Arteriosus (DA)…
• Functional closure : In healthy neonates is completed within the 1st few
days after birth.
• Anatomic closure - & formation of the ligamentum arteriosum normally
occurs by the 12th postnatal week .
• Short, thick lig. arteriosum extends from the left pulmonary artery to
the arch of the aorta

23. PORTAL VEIN – GROSS ANATOMY

24. Developments of venous system…
In 5th wk 3 pairs of major veins can be distinguished the…
 Vitellines veins or omphalomesentric v.
 Umbilical veins
 Cardinal Veins

25. Venous system…

26. Vitellines veins…
• Forms venous plexus around developing duodenum.
• Pass through septum transversum.
• Gives rise to hepatic sinusoids.
• As there is absorption of the left horn of the sinus venosus, blood
from the left side is channeled towards the right side .
• Results in enlargement of the right side vitelline vein.(Right hepato-
cardiac channel) IVC
• Anastomotic channel of the Venous plexus around the duodenum
results in formation of the single vein i.e. Portal Vein.

28. Portal Vein Development…

29. Portal Vein Development…