Histología: Desarrollo folicular

Development of Follicles in the Menstrual Cycle

Introduction to Follicular Development

• The video discusses follicular development during the menstrual cycle, emphasizing hormonal stimulation leading to ovulation.

• An ovocyte is defined as the female germ cell that, upon fertilization by a spermatozoid, can result in pregnancy.

Anatomy of the Ovary

• The ovary consists of an outer cortex and an inner medulla; the medulla contains connective tissue, blood vessels, lymphatics, nerves, and interstitial cells.

• Numerous ovarian follicles at various stages are found in the cortex; typically only one matures fully for release during each cycle.

Stages of Follicle Development

Primordial Follicle Stage

• The primordial follicle stage is hormone-independent and consists of an ovocyte surrounded by a single layer of flat follicular cells.

• As development progresses, these flat cells transform into cuboidal cells forming a primary follicle; this stage also sees secretion of proteins creating a zona pellucida around the ovocyte.

Advanced Primary Follicle Stage

• In this advanced stage (multi-laminar), follicular cells proliferate under activin influence, forming multiple layers known as granulosa cells.

• Surrounding stromal cells form a structure called theca folliculi which has internal (vascularized with angiogenic factors) and external layers.

Hormonal Interactions and Estradiol Synthesis

• Internal theca cells express receptors for luteinizing hormone (LH), crucial for synthesizing androgen precursors to estrogen.

• Granulosa cells convert these androgens into estrogens via aromatase enzyme when stimulated by FSH; estradiol promotes LH receptor formation in granulosa cells.

Secondary and Tertiary Follicles

Secondary Follicle Stage

• Characterized by central cavities filled with antral fluid secreted from granulosa cells containing hyaluronic acid.

Tertiary or Graafian Follicle Stage

Menstrual Cycle and Ovulation Process

Hormonal Changes During the Menstrual Cycle

• Around day 14 of the menstrual cycle, there is a significant increase in estrogen levels which inhibits FSH (Follicle Stimulating Hormone) and stimulates the secretion of LH (Luteinizing Hormone).

• The surge in LH leads to the rupture of the ovarian wall, resulting in the release of an ovum surrounded by a zona pellucida and corona radiata.

Fertilization and Follicular Development

• The released ovum must be captured by the fimbriae of the fallopian tubes for fertilization to occur; otherwise, it will be discarded.

• Following ovulation, the ruptured follicle fills with blood and transforms into a corpus hemorrhagicum.

Role of Corpus Luteum

• The corpus hemorrhagicum evolves into a corpus luteum, which contains lipid inclusions and is responsible for producing estrogen and progesterone.