Importance of vascularity and blood flow in the reproductive system of female birds: a review

The reproductive system of female birds is characterized by a high metabolic rate associated with production of the egg constituents, i.e. the yolk in the ovary, and the albumen and calcified shell in the oviduct. Both organs require a high level of vascularization and intense blood flow, which differs depending on their activity. The increasing expansion of the vascular system and blood flow within the follicle wall as it develops facilitates the rapid delivery of oxygen, hormones, growth factors, nutrients, and egg-yolk precursors to the oocyte. The network of blood vessels is established during angiogenesis, a very complex process involving numerous regulators, the most important, of which are vascular endothelial growth factor and its receptors. Although angiogenesis is an essential process for the normal functioning of the female reproductive system, information about this event in birds is limited. This review aims to provide up-to-date information on the importance of proper vascularization, mechanisms of angiogenesis, and blood flow regulation within the reproductive system of hens.