HPG Axis and Early Follicle Growth - Vocabulary Flashcards

Vocabulary flashcards covering key terms and definitions from the notes on the HPG axis, follicle formation and growth, oocyte development, and steroid/protein lipid hormone actions.

Hormone

A chemical produced by endocrine glands that travels in the blood to distant target organs, producing effects at very low concentrations.

Target organ

An organ that responds to a specific hormone with a physiological effect.

Protein hormone

A hormone made from amino acids, synthesized in the endoplasmic reticulum, packaged in secretory vesicles, and released into the bloodstream; hydrophilic and binds to transmembrane receptors.

GnRH (Gonadotropin-Releasing Hormone)

Hormone produced by the hypothalamus that stimulates the pituitary to secrete FSH and LH.

FSH (Follicle-Stimulating Hormone)

Pituitary gonadotropin that promotes ovarian follicle growth and estradiol production.

LH (Luteinizing Hormone)

Pituitary gonadotropin that triggers ovulation and progesterone production.

Hydrophilic

Water-soluble; a property of protein hormones enabling blood transport and membrane receptor binding.

Secretory vesicle

A vesicle that stores and releases protein hormones from the cell.

Endoplasmic reticulum (ER)

Organelle where protein hormones are synthesized and packaged for secretion.

Transmembrane receptor

Receptor located in the cell membrane that binds hydrophilic hormones to initiate signaling.

Steroid hormone

Hormones derived from cholesterol; lipophilic, diffuse through membranes, and usually act via intracellular receptors.

Estrogen

Class of steroid hormones; the main one in humans is estradiol.

Estradiol

The primary estrogen produced by the ovaries; regulates the reproductive cycle and reproductive tissues.

Estriol

Estrogen produced mainly by the placenta during pregnancy.

Estrone

Estrogen produced in the body, particularly around menopause.

Progestin

A class of progestational hormones; natural progestogen is progesterone.

Progesterone

Main natural progestin; maintains pregnancy and regulates the menstrual cycle.

Dihydroprogesterone

A progesterone-related compound present in some species (noted in pregnancy contexts such as mares).

MGA (melengestrol acetate)

A synthetic progestin used to maintain pregnancy or influence ovulation in livestock.

Norethindrone

A synthetic progestin used in hormonal therapies.

Hypothalamic-Pituitary-Ovarian Axis

The hormonal axis where GnRH from the hypothalamus stimulates the pituitary to release FSH/LH, which regulate ovarian estrogen and progesterone production.

Negative feedback

Regulation in which estradiol and progesterone inhibit GnRH (and thus FSH/LH) secretion.

Ovarian hormones

Estrogens (like estradiol) and progesterone produced by the ovaries that regulate the reproductive cycle.

Primordial germ cell (PGC)

Diploid precursor cells to oocytes and sperm; originate from the yolk sac and migrate to the gonads.

Yolk sac

Extraembryonic membrane from which PGCs originate.

Genital ridge

The embryonic gonadal region where PGCs migrate to form the gonads.

Meiosis

Cell division that produces haploid gametes from diploid cells; includes Meiosis I and Meiosis II.

Meiosis I

First meiotic division; homologous chromosomes separate.

Meiosis II

Second meiotic division; sister chromatids separate to form haploid gametes.

Oocyte

Immature egg cell; results from meiosis and becomes the mature oocyte at ovulation.

Polar body

Small cell produced during meiosis that receives excess chromosomes and usually degenerates.

Primordial follicle

Earliest ovarian follicle; oocyte with a single layer of surrounding pre-granulosa cells.

Pre-granulosa cells

Cells that surround the oocyte and become granulosa cells to form primordial follicles.

Antral follicle

Follicle containing an antrum (fluid-filled cavity) and dependent on gonadotropins for growth.

Primary follicle

Early growing follicle with proliferating granulosa cells around the oocyte.

Secondary follicle

Follicle with multiple layers of granulosa cells and theca cells; precursor to the antral stage.

Dominant follicle

The follicle selected to continue growth, often secreting large amounts of estradiol and suppressing others.

Graafian follicle

Mature, pre-ovulatory follicle ready to rupture and release the oocyte.

Atresia

Degeneration and death of ovarian follicles that do not ovulate.

Gonadotropin-independent growth

Follicle growth that occurs without FSH/LH signaling in early stages.

Gonadotropin-dependent growth

Follicle growth that requires FSH/LH signaling, especially after the primordial stage.

2-cell, 2-gonadotropin theory

Model: Theca cells (LH) produce androgens; granulosa cells (FSH) convert androgens to estradiol via aromatase.

Theca cell

Ovarian cells stimulated by LH to produce androgens.

Granulosa cell

Ovarian cells stimulated by FSH to convert androgens to estradiol via aromatase.

Inhibin

Hormone from granulosa cells that inhibits FSH secretion by the pituitary.

Activin

Hormone that stimulates FSH production; interacts with inhibin.

Cohort of follicles

Group of follicles recruited to grow in response to rising FSH, from which a dominant follicle may emerge.

Estradiol (repeated term for emphasis)

Primary estrogen produced by developing follicles; supports reproductive tract and regulates the cycle.

Estrus

Period of sexual receptivity and mating readiness in species where estradiol-driven signals peak.

LH surge

Rapid rise in LH that triggers ovulation and corpus luteum formation.

Carrier protein

Plasma proteins that bind and transport lipophilic hormones in the blood.

Intracellular receptor

Receptor inside the cell that binds lipophilic hormones and regulates gene expression.

Prostaglandin F2α

A lipid hormone derived from fatty acids; acts as a local reproductive signal.

Prostaglandin

Group of lipid hormones derived from fatty acids with diverse physiological roles.

Aromatase

Enzyme in granulosa cells that converts androgens to estrogens (essential in the 2-cell theory).