Ultrastructure of Ovary in mammals

ULTRASTRUCTURE OF OVARY IN MAMMALS

The ovary is a crucial reproductive organ in females responsible for the production of eggs (ova or oocytes) and the secretion of hormones, including estrogen and progesterone. The ultrastructure of the ovary reveals its complex organization, including follicles, ova, and various supporting structures. Here are the key components of the ultrastructure of the ovary in mammals:

1. Ovarian Cortex:

• Ovarian Follicles:
• Primary Follicles:
• Contain primary oocytes surrounded by a single layer of granulosa cells.
• Develop into secondary follicles.
• Secondary Follicles:
• Characterized by the formation of an antrum (fluid-filled cavity).
• Granulosa cells divide into multiple layers.
• Graafian (Mature) Follicles:
• Large, fluid-filled antrum.
• Cumulus oophorus: Mound of granulosa cells that surround the oocyte.
• Theca cells: Surround the follicle and contribute to hormone production.

2. Ovulation:

• Ruptured Follicle (Corpus Hemorrhagicum):
• After ovulation, the remaining follicle collapses and forms a temporary structure.
• Contains blood from the ruptured blood vessels.
• Corpus Luteum:
• Formed from the remnants of the ruptured follicle.
• Secretes progesterone, preparing the uterus for possible implantation.

3. Ovarian Medulla:

• Connective Tissue and Blood Vessels:
• Provide support and nourishment to the ovarian structures.

4. Oogonia and Oocytes:

• Oogonia:
• Undifferentiated germ cells present during fetal development.
• Divide by mitosis to produce primary oocytes.
• Primary Oocytes:
• Arrested in prophase I of meiosis during fetal development.
• Reside in primordial follicles until puberty.
• Secondary Oocytes:
• Result from the completion of meiosis I during ovulation.
• Arrested in metaphase II until fertilization.
• Ovum (Mature Egg):
• Formed after the completion of meiosis II following fertilization.

5. Follicular Cells:

• Granulosa Cells:
• Surround the oocyte in the follicles.
• Contribute to the formation of the antrum and nourish the developing oocyte.
• Theca Cells:
• Found in the theca layer surrounding the follicle.
• Contribute to hormone production.

6. Stroma:

• Supporting Tissue:
• Connective tissue framework supporting the follicles and blood vessels.

7. Hilum:

• Location:
• Depression on the surface of the ovary where blood vessels, lymphatics, and nerves enter and exit.

8. Surface Epithelium:

• Location:
• Covers the outer surface of the ovary.
• A single layer of cuboidal or squamous epithelial cells.

9. Corona Radiata:

• Location:
• The layer of cells that adheres to the oocyte during ovulation.
• Composed of granulosa cells.

The ultrastructure of the ovary reflects its dynamic function in the female reproductive system, including the development and release of eggs, hormonal regulation, and support structures for these processes. The cyclic nature of follicular development, ovulation, and the formation of the corpus luteum is crucial for reproductive success.

Let’s understand this in simple language:

1. Components of Female Reproductive System:
• Consists of ovaries, oviducts, uterus, cervix, vagina, and external genitalia.
• Integrated structurally and functionally to support ovulation, fertilization, pregnancy, birth, and child care.
• Includes a pair of mammary glands.
2. Ovaries:
• Primary female sex organs producing ova and ovarian hormones.
• Located on each side of the lower abdomen.
• Approximately 2 to 4 cm in length, connected to the pelvic wall and uterus by ligaments.
• Covered by thin epithelium enclosing ovarian stroma with peripheral cortex and inner medulla.
3. Female Accessory Ducts:
• Consist of fallopian tubes, uterus, and vagina.
• Fallopian tubes extend from the ovary to the uterus, with an infundibulum, fimbriae for ovum collection, ampulla, and isthmus.
• Uterus, shaped like an inverted pear, is supported by ligaments and opens into the vagina through the cervix.
• Cervical canal, along with the vagina, forms the birth canal.
4. Uterine Structure:
• Uterus has three layers: perimetrium (external), myometrium (middle smooth muscle layer), and endometrium (inner glandular layer).
• Endometrium undergoes cyclical changes during the menstrual cycle, while myometrium contracts during childbirth.
5. Female External Genitalia:
• Includes mons pubis (fatty tissue covered by skin and pubic hair), labia majora (fleshy folds around the vaginal opening), labia minora (paired folds under labia majora).
• Vaginal opening may be partially covered by a membrane called hymen.
• Clitoris is a small finger-like structure at the upper junction of labia minora above the urethral opening.
6. Hymen and Virginity:
• Hymen is often torn during the first intercourse but can also be broken by various activities.
• Presence or absence of hymen is not a reliable indicator of virginity or sexual experience