Follicular histology

Structural organization and development of follicles

The female gonads (ovarium) are paired structures located in the pelvic cavity. Their parenchyma is divided into two main layers: the medulla and the cortex. The cortex is precisely where follicles at various stages of development, as well as transitory endocrine structures, are concentrated.

In childhood, the ovaries contain a substantial reserve of primordial follicles. Their growth and natural atresia occur long before the onset of puberty. However, a complete cycle of folliculogenesis culminating in ovulation is activated exclusively during puberty. This process is under the strict control of gonadotropic stimulation by the hypothalamic-pituitary system.

Cellular composition and hormonal activity

From a histological standpoint, the follicular cells (granulosa) surrounding the developing germ cell belong to epithelial tissue. Meanwhile, the cells of the internal theca layer of the follicles are formed by connective tissue.

The functional specialization of these cells ensures the synthesis of essential sex hormones:

• Estrogens (estradiol, estrone, estriol) are synthesized predominantly by the follicular cells of maturing follicles.
• Androgens are produced by the theca cells.

Locally, estrogens stimulate the proliferation of granulosa cells, induce the synthesis of follicle-stimulating hormone receptors, and prevent the death (atresia) of the dominant follicle.

Physiological effects of estrogens

Hormones produced by the follicular apparatus exert multilevel effects on the body:

1. Reproductive system: they ensure the maturation of female reproductive organs, stimulate the development of the mammary gland duct system, and regulate the proliferative phase of the menstrual cycle in the uterus.
2. Systemic effects: they shape the female phenotype (fat distribution), affect lipid metabolism, blood clotting, and calcium ion metabolism.
3. Bone system: they initiate the closure of epiphyseal growth plates, halting linear bone growth in length.

Clinical aspects and pathologies

Disruptions in follicular development can lead to the formation of cystic structures. Simple ovarian cysts are essentially large follicles.

• In newborns: large follicles can be detected as a palpable abdominal mass.
• In adolescent girls: cysts arise due to continuous follicular growth following failed ovulation or due to a lack of their regression (involution).

Most follicular cysts ranging from 3 to 10 cm in diameter are asymptomatic, but when complicated (hemorrhage, rupture, or torsion), they can cause an "acute abdomen" presentation.

Class and exam questions

What else to study on this topic

• Morphology of the ovarian medulla and cortex
• Structure and functions of the corpus luteum
• Processes of follicular atresia in childhood
• Ultrasound and histological signs of ovarian torsion
• Features of the blood supply and endocrine regulation of the gonads

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