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histological diagram of ovary

histological diagram of ovary

Each ovary is an oval slightly flattened organ encapsulated in a thin fibrous connective tissue layer called tunica albuginea. A single layer of cuboldal epithelial cells (germinal epithelium) covers the surface of ovary, which becomes continuous with mesothelial lining (simple squamous epithelium) of peritoneal cavity. In old age, it changes into simple squamous type.
The ovary is formed of stroma and parenchyma (ovarian follicles & interstitial cells).
 STROMA: The supporting framework of the ovary consists of spindle-shaped fibroblasts (stromal cells), reticular fibers and ground substance, which together constitute the ovarian stroma. The stroma is divisible into two contrasting zones.
       The extreme peripheral part of cortical stroma (subgermlnal layer) is formed of dense C.T. called tunica albugenla, which is responsible for the whitish color of the ovary. The rest of stroma of cortical region contains ovarian follicles. This stroma of C.T. is rich in spindle shaped fibroblasts that respond grossly to the hormonal stimuli (theca reaction), in the peripheral zone of stroma (cortex) are present the numerous preovulatory follicles which contain female gametes in various stages of development. In addition, there may also be postovulatory follicles of various kinds like corpora lutea, corpora albicantes and atretic follicles.
       The central zone or ovarian medulla contains loose cellular C.T. with many elastic fibres, smooth muscles, convoluted veins and spiral or halicine arteries.

  PARENCHYMA: OVARIAN FOLLICLES: In cortex of mature ovary, follicles are present in various stages of development. Each follicle consists of a germ cell or ovum surrounded by follicular granulosa cells. 
The follicles are of following types.
Primary Follicle: It consists of a single layer of cuboidal follicular cells (simple cuboldal epithelium) containing primary oocyte, which is surrounded by zona pellucida. Zona pellucida is an acidophilic homogenous membrane, which is rich in glycoproteins.
Secondary or Vesicular Follicle: It is also a growing follicle with many layers of follicular cells (stratified cuboldal epithelium). With further growth, a small cavity (antrum) appears in the follicle due to secretions of follicular cells as well as debris of degenerated follicular cells.
         Grafflan/Tertlary/Mature Follicle: A mature follicle is about 1 cm in diameter. This is a mature form containing a large crescent-shaped cavity within follicular cells (central antrum). Due to enlarging follicle, the immediately surrounding stromal C.T. cells enlarge, become polyhedral and rich in mitochondria and lipid droplets. These are called theca cells. The highly vascularized C.T. becomes differentiated into outer or theca externa and inner or theca interna layers. Theca folliculi forms a vascular C.T. capsule for the mature follicle. From without inwards the follicle has following layers
The outermost fibrous layer is theca externa. Its cells secrete prostaglandins, which help in ovulation.
The inner fibrous layer is theca Interna. Its cells secrete massive amount of androstenedlone.
A clear basement membrane.
  Stratum granulosum secretes massive amounts of estrogens. This stratum consists of 5-6 layers of follicular cells surrounding the antrum.
  Antrum containing liquor folliculi
. Cumulus Oophorous (Discus Prolegerus), which is a group of few layers of follicular cells surrounding the oocyte. The innermost layer of cumulus oophorous (i.e.. the single layer of columnar follicular cells immediately surrounding the zona pellucida and oocyte) is known as corona radlata due to its radiating appearance (like the spokes of a wheel or like the spines of a crown), vll. Zona Pellucida, which is an acellular resistant membrane of polysaccharides.
vlll. Primary Oocyte (117-143 nm) consists of an eccentric large nucleus with prominent nucleolus and surrounded by a cytoplasm rich in yolk. The primary oocyte, 36-48 hours before ovulation, leaves the dictiyotene stage and completes the first meiotic division (by an unequal cytokinesis) to give rise to: (a) secondary oocyte with maximum cytoplasm and; (b) first polar body which is present between secondary oocyte with minimum cytoplasm and zona pellucida. The nucleus of secondary oocyte is rounded and eccentric in position. Primary, secondary and tertiary follicles are the three stages of growing or maturing follicle.
  Corpus Luteum: Following ovulation, the ruptured follicle collapses and fills with blood. The follicular walls become reorganized to form a temporary endocrine gland corpus luteum. which secretes estrogen and progesterone. The blood clot, theca lutea and granulosa luteal layers are invaded by capillaries from theca externa to form rich vascular network. It is known as corpus luteum because it has a yellow color due to the presence of a yellow lutein pigments in its lutein cells.

Types and Fate of Corpora Lutea: It depends upon the fertilization.
  Corpus Luteum of Menstruation or Menstrual Yellow Body: if fertilization does not occur, the corpus luteum persists functioning during the second half of the menstrual cycle (for only 10-14 days) and secretes progesterone. Then it degenerates and is transformed into corpus albicans.
 Corpus Luteum of Pregnancy or Gravidic Yellow Body: If fertilization and implantation occur (pregnancy continues), the corpus luteum persists functioning for about 10 weeks.
 Corpus Albicans: After involution of the corpora lutea (either of menstruation or of pregnancy) they are transformed Into scar of dense collagenous connective tissue appearing as white bodies in the stroma of the ovary. These are gradually absorbed by macrophages of the stroma.


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