Ovary Anatomy: A Look at Structure and Function
Learn how the physical structure of the ovaries, from their cellular makeup to their dynamic changes, provides the anatomical foundation for their vital functions.
Ovaries are components of the female reproductive system, functioning as glands that produce eggs and hormones. They are integral to the processes of menstruation and pregnancy. The development of these organs begins in the embryonic stage, and they undergo significant changes throughout a person’s life.
Position and General Appearance of Ovaries
The ovaries are a pair of small, oval-shaped glands situated in the lower abdomen on either side of the uterus. They reside in a shallow depression known as the ovarian fossa, which is bordered by major blood vessels and the ureter. An adult ovary measures about 4 cm in length, 2 cm in width, and 1.5 cm in thickness, comparable to the size of a large almond. Their external surface appears whitish and can be somewhat uneven.
Ligaments hold the ovaries in place within the pelvic cavity. The ovarian ligament connects each ovary to the side of the uterus, while the suspensory ligament attaches the ovary to the pelvic wall. Another structure, the mesovarium, connects the ovary to the broad ligament, a wide sheet of tissue that supports the uterus and other reproductive organs. These connections keep the ovaries close to the fallopian tubes which transport eggs to the uterus.
Detailed Internal Ovarian Structures
Internally, the ovary is divided into two regions: the outer cortex and the central medulla. The cortex is the larger, more active part, containing the ovarian follicles. These follicles are small sacs that house and nurture developing egg cells, known as oocytes. The cortex consists of a dense connective tissue called the stroma, which contains cells that respond to hormonal signals.
Surrounding the cortex is a layer of dense connective tissue called the tunica albuginea, covered by a single layer of cuboidal cells known as the germinal epithelium. Within the cortex, follicles exist in various stages of development, from primordial follicles to mature Graafian follicles. After an egg is released, the remnant of the follicle transforms into a structure called the corpus luteum, which degenerates into a scar-like tissue known as the corpus albicans if pregnancy does not occur. The inner medulla is composed of looser connective tissue.
Vascularization and Innervation of the Ovaries
The primary blood supply comes from the ovarian artery, which branches from the abdominal aorta, just below the renal arteries. Additional blood flow is provided by the ovarian branch of the uterine artery. These vessels enter the ovary through a region on its surface called the hilum, located where the mesovarium attaches.
Blood drains from the ovaries through a network of veins called the pampiniform plexus, which consolidates to form the ovarian vein. The drainage path differs on each side; the right ovarian vein drains directly into the inferior vena cava, while the left ovarian vein drains into the left renal vein. The ovaries are also supplied by autonomic nerves from the ovarian plexus, which regulate blood flow and transmit sensory information. Lymphatic vessels follow a similar path, draining fluid from the tissues.
Functional Roles Tied to Ovarian Anatomy
The process of egg development, or oogenesis, occurs within the follicles of the ovarian cortex. Each month, hormonal signals prompt a group of follicles to grow and mature. One follicle becomes dominant and develops into a mature Graafian follicle, while the others degenerate. This maturation culminates in ovulation, where the follicle ruptures and releases a mature oocyte.
The cells within developing follicles, specifically the granulosa and theca cells, produce estrogen. After ovulation, the cells of the corpus luteum secrete large amounts of progesterone and some estrogen. These hormones prepare the uterus for a potential pregnancy and regulate the reproductive cycle through complex feedback loops.
Anatomical Transformations Over a Lifetime
At birth, the ovaries contain the maximum number of primordial follicles they will ever have, estimated to be around one to two million. During childhood, the ovaries are relatively inactive, and many of these follicles degenerate. By the time of puberty, about 300,000 to 400,000 follicles remain.
With the onset of puberty, the ovaries increase in size and begin their cyclical function. Throughout the reproductive years, the ovarian cortex contains follicles in various stages of development and regression, including mature follicles and corpora lutea. As a person approaches menopause, the follicle reserve depletes, reducing ovarian size and making the tissue more fibrous.
Following menopause, this atrophy continues, thinning the cortex and leaving it largely without follicles. The surface of the postmenopausal ovary is often smoother due to the end of cyclical follicular rupture. This anatomical shift marks the end of the ovaries’ reproductive capacity.