This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
The main source of menstrual blood during menstruation is: 
Select and explain. 
A. Aerial, B. Venous, C. Both, D. Cavernous
A: Aerial
Answer: A: Aerial 
Explanation: Menstrual bleeding is from both systems, but aerial bleeding is appreciably greater than venous. Endometrial bleeding appears to follow rupture of an aeriole of a coiled aery, with consequent hematoma formation. With a hematoma, the superficial endometrium is distended and ruptures. Hemorrhage stops with aeriolar constriction. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 3. Implantation, Embryogenesis, and Placental Development. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.