. 2020 May;30(3):387–396. doi: 10.4314/ejhs.v30i3.10

Table 4.

Differentiation of tunics and histogenesis -inferior vena cava (at formation, middle and termination level). TI-Tunica Intima, TM- Tunica Media, TA- Tunica Adventitia. − Undifferentiated, + Differentiated, ++ Defined, +++ Well-defined

Age	Tunics			Cell types, fibre & musculature
	Formation	Middle	Termination	Formation	Middle	Termination
1^st Trimester	TI +++, TM +++, TA +++	TI +, TM +, TA +	TI +, TM +, TA +	Mesenchymal cells & collagen prominent	Mesenchymal cells & fibroblasts present	Primitive musculature in media
2^nd Trimester	TI +++, TM +++, TA +++ capillary-sized vasa vasorum	TI +, TM ++, TA + vasa vasorum capillary-sized	TI +, TM +, TA + vasa vasorum constituted by arterioles & venules	Collagen increased, musculature in media ill-defined, abundant mesenchymal cells & fibroblasts	Mesenchymal cells & fibroblasts present, collagenous stroma prominent	Fibroblast exceeded mesenchymal cells, collagen bundles prominent, primitive musculature in media
3^rd Trimester	TI +++, TM +++, TA +++	TI ++, TM +++, TA ++	TI ++, TM ++, TA ++	Abundant mesenchymal cells & fibroblasts	Fibroblasts exceed mesenchymal cells, musculature prominent in media	Primitive musculature in media, mesenchymal cells & hyalinized collagen bundles also present
Adult	TI +++, TM +++, TA +++	TI +++, TM +++, TA +++	TI +++, TM +++, TA +++	Musculature prominent in media, collagen bundles hyalinized, adventitia showed smooth muscle	Fibroblasts prominent, collagen bundles hyalinized, musculature compact, adventitia showed musculature	Media showed mature musculature & fibroblasts, adventitia showed musculature