Veterinary Physiology-III

OVARY

• Reproduction in birds is characterized by ovoviviparity where the embryonic development occurs for a very short period in the mother’s body and complete development occurs outside the mother’s body. To meet the needs of the developing embryo and fetal growth, the avian egg contains nutrient materials in the yolk, albumin and shell.

Ovary

• Consists of outer cortex containing follicles and inner medulla having connective tissue, blood vessels and nerves
• In domestic birds, only the left ovary and the left oviduct are functional; it is attached to the dorsal wall anterior to the left kidney posterior to the left lung
• The ovary has distinct follicles protruding from the surface. The largest of the follicles is the most mature and is called F1, the next most mature F2 and so on down to F5. This arrangement of group of follicles is known as follicular hierarchy; each follicle differs from the adjacent by about 1 day growth.
• The ovary also contains intermediate sized follicles and many other small follicles which are microscopic.
• The immature follicles consist of an oocyte surrounded by follicular cells. The oocyte contains nucleus, cell organelles and surrounded by a membrane. As the follicles mature, yolk material is added to the ovum and the yolk is surrounded by perivitalline (vitalline) membrane secreted by follicular cells. The mature follicles consist of an oocyte and several layers of tissue – vitalline membrane and zona radiate (innermost layers), perivitalline layer, granulosa layer, theca interna and theca externa, connective tissue and epithelium (outermost)
• The thecal layers are well vascularized and the thecal and granulosa layers are steroidogenic. The stigma is avascular and ovulation occurs through the stigma. After ovulation, the remnants of the follicles remain for a short time but no CL is formed.

Click here for ovary of hen