LAB 4.5 Reproductive system - hen


hen reproductive system

1. Ovary (only one, derived from left side). The ova at  varying stages of development to egg yolks are seen in the image below.

2. Ostium (catches egg yolk)

The ova in the most advanced state of development appear as almost full-sized egg yolks. Each ovum is present in the hen chick when she hatches, but development from a very small ovum to a complete hen's egg takes two weeks. Growth of the yolk accelerates ten days before ovulation when the yolk is released into the oviduct.  A large infundibulum (ostium) leads to a thick glandular region of the oviduct where egg albumen is formed, then to a narrower isthmus where shell membranes are added, and finally to a wide uterus where a calcareous shell is formed. In the image below is the glandular region, with the oviduct slit open and laid out flat. The vagina opens into the cloaca and forms mucus to facilitate egg-laying.

4. Isthmus (deposits shell membranes)
5. Uterus (deposits calcareous shell)
6. Urodaeum of cloaca

Study hint: There is more information on eggs and their formation coming up in LAB 11.