Ovary - Anatomy & Physiology

()Map REPRODUCTIVE SYSTEM (Map) FEMALE REPRODUCTIVE TRACT

Introduction

The ovary is the female Gonad homologous to the male Testes. It is ususally a paired organ in domestic species, but in the bird only the left Ovary is present. The structures found within the ovary are undergoing constant changes throughout the oestrus cycle from the Follicles containing Oocytes, to the formation of Corpus Haemorrhagicum,Corpus Luteum, and finally Corpus Albicans. Ovaries are ellipsoidal in shape with an irregular surface due to the projection of dominant follicles and corpora lutea. These irregularities are absent in the mare due to the cortex and medulla being reversed, but are greatest in Polytocous animals such as the sow due to many dominant follicles, and so corpora lutea, developing at once.

Structure

Histological Section of a Rabbit Ovary under Low Power- Courtesy of J.Bredl, Copyright RVC 2008

Outer Tunica Albuginea

• Connective tissue layer covering the ovarian cortex.
• Overlying this structure is a single layered Germinal epithelium.

Ovarian Cortex

• This is where follicles in various stages of development are found, as well as Corpus Haemorrhagicum, Corpus Luteum and Corpus Albicans

Ovarian Medulla

• The Medulla is made up of dense connective tissue. This is where all of the lymphatics, nerves and vasculature of the Ovary are found.

Function

It has two main functions:

• Producing the female gametes oocytes via Gametogenesis.
• Producing the reproductive hormones Oestrogens and Progesterone, an endocrine function.

Anatomical Location

• In most domestic species the ovaries lie just caudal to the kidneys and close to the tips of the uterine horns. In Ruminants the ovaries are found more caudally, close to the pelvic inlet.
• The ovaries are suspended in the abdominal cavity by the Mesovarium of the Broad Ligament.

Histology

Stroma

• The body of the ovary (ovarian stroma) consists of:
  • spindle-shaped cells
  • fine collagen fibres
  • ground substance
• Stromal cells resemble fibroblasts, but some contain lipid droplets.
• Budles of smooth muscle cells are scattered throughout the stroma.

Cortex

• Follicles containing oocytes in various stages of development.
• Atretic Follicles
• Corpora lutea
• Corpora albicantes
• The superficial cortex is more fibrotic than the deep, and is called the tunica albuginea.
• On the surface of the ovary is the germinal epithelium. This is a continuation of the peritoneum.

Medulla

• Highly vascular
• Contains hilus cells, which are similar to the Leydig cells of the testes.

Vasculature

Arterial Supply

• The ovarian artery (a branch of the Aorta) and ovarian branches of the Uterine artery form anastomoses in the mesovarium and the broad ligament.
• From this arterial plexus ~10 coiled Helicine arteries enter the hilus of the ovary.
• Smaller branches form a plexus at the corticomedullary junction, giving rise to straight Cortical arterioles, which radiate into the cortex.
• Here they branch and anastomose to form vascular arcades, which give rise to a rich capillary network around follicles.

Venous Drainage

• Venous drainage follows the course of the arterial system.
• Medullary veins are large and tortuous.

• The Ovarian Artery - a direct branch off the Aorta
• The Ovarian Artery is closely associated with the Uterine Vein. This is important for the transfer of luteolytic PGF2α from the Uterus to the Ovary.