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

Table 3.

Differentiation of tunics and histogenesis -superior 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 −	Collagen appreciable, mesenchymal cells & fibroblasts present	Collagen present, mesenchymal cells exceed mature fibroblasts, musculature prominent in media	Mesenchymal cells & collagen appreciable, pseudo-discontinuous musculature in media
2^nd Trimester	TI +, TM −, TA −capillary-sized vasa vasorum	TI +, TM −, TA − capillarysized vasa vasorum	TI ++, TM ++, TA ++ vasa vasorum capillary-sized	Collagen increased in amount, mesenchymal cells & fibroblasts present	Mesenchymal cells exceed mature fibroblasts, musculature prominent in media	Pseudo-discontinuous musculature in media, cardiac musculature seen
3^rd Trimester	TI ++, TM ++, TA ++	TI ++, TM ++, TA ++	TI +++, TM +++, TA +++	Collagen arranged orderly, mesenchymal cells & muscle fibres present in media	Collagen appreciable, mature fibroblasts exceed mesenchymal cells, cardiac musculature appreciated, smooth muscle present in adventitia	Media showed mature & continuous musculature
Adult	TI ++, TM ++, TA +++	TI +++, TM +++, TA +++	TI +++, TM +++, TA +++	Well-defined musculature in media	Prominent musculature in media as well as adventitia	Myocytes abundant, cardiac musculature seen, adventitia showed musculature