Steroid Hormones and Chemical Signaling

Vocabulary flashcards for reviewing steroid hormones, their functions, and related concepts.

Hormones

Messenger molecules that enable communication between cells and cause a physiological response. Classes include steroid hormones, peptide hormones, and amino acid derivatives. Secretion is regulated by feedback loops involving the hypothalamus, pituitary gland, and target organs.

Steroid Hormones

Derived from cholesterol and are lipid soluble, able to permeate membranes freely; involved in carbohydrate regulation, mineral balance, and reproduction. They bind to intracellular receptors to influence gene transcription.

Glucocorticoids

Primarily regulate carbohydrate metabolism and have anti-inflammatory and immunosuppressive effects. Act by binding to glucocorticoid receptors in target cells.

Mineralocorticoids

Primarily regulate electrolyte balance, particularly sodium and potassium levels, and fluid balance in the body. Aldosterone is a key mineralocorticoid.

Androgens

Male sex hormones responsible for development and maintenance of male reproductive tissues and secondary sexual characteristics. Testosterone and dihydrotestosterone (DHT) are major androgens.

Estrogens

Female sex hormones responsible for development and regulation of the female reproductive system and secondary sexual characteristics. Estradiol is the primary estrogen.

Progestogens

Hormones involved in regulating the menstrual cycle, supporting pregnancy, and maintaining the uterine lining. Progesterone is the main progestogen.

Steroid Hormone Receptors and Transport

Steroid hormones are hydrophobic molecules that are complexed with carrier molecules such as globulin or bind proteins for transport in the bloodstream. Receptors are intracellular and act as transcription factors upon hormone binding. Zinc fingers in the receptor bind to specific DNA sequences.

Zinc Fingers

Binds to cysteine/histidine residues to lock the conformation of steroid receptors, enabling them to interact with DNA.

Cholesterol

The main precursor to all/most steroid hormones. Synthesized de novo or obtained from LDL.

LDL (Low-Density Lipoprotein)

A carrier for cholesterol in the bloodstream, delivering cholesterol to cells for steroid hormone synthesis.

Cholesterol Side-Chain Cleavage

The conversion of cholesterol to pregnenolone, the first committed step in steroid hormone biosynthesis, catalyzed by the CYP11A1 enzyme in mitochondria.

Androgen Synthesis and Importance

Important for the development and maintenance of the male reproductive system and secondary sex characteristics. Synthesized in Leydig cells of the testes.

Leydig cells

Cells that respond to LH and synthesize testosterone. Located in the testes.

Sertoli cells

Facilitate germ cell progression to spermatozoa in the seminiferous tubules and regulated by FSH and testosterone. Support spermatogenesis.

5-alpha reductase

Enzyme that converts testosterone into 5-alpha-dihydrotestosterone, a more potent androgen.

Androgen and Anti-androgen Relationships

Androgens like testosterone promote male characteristics. Anti-androgens are antagonists of the androgen receptor used for treating androgen-dependent conditions such as prostate cancer and hirsutism. Structural modifications alter binding affinity.

Anti-androgen

Antagonists of the androgen receptor used for treating androgen-dependent conditions. Examples include cyproterone acetate and flutamide.

CYP19 mediated aromatase

Enzyme that converts testosterone to estradiol, primarily in ovaries, adipose tissue, and brain.

Estrogen

Promotes endometrium cell proliferation and lactation, and regulates gonadotrophin-releasing hormone and CNS effects. Three major estrogens: estrone, estradiol, and estriol.

Estrogen Receptor Activation

Estrogen receptor activation leads to receptor dimerization, phosphorylation, and increased transcription. ERα and ERβ are the two main subtypes with different tissue distribution and functions.

Estrogens in Disease and Therapy

Hormone receptor-positive breast cancer can be targeted by estrogen receptor antagonists such as tamoxifen. Estrogen replacement therapy is used to manage menopausal symptoms.

Hormone-Dependent Breast Cancer

Hormone receptor-positive breast cancer can be targeted by estrogen receptor antagonists such as tamoxifen.

Aromatase inhibitors

Block testosterone conversion to estradiol and are used in post-menopausal women with hormone receptor-positive breast cancer. Examples include anastrozole and letrozole.

Oral Contraceptives

Contain synthetic estrogens and progestins to prevent ovulation. Ethinylestradiol and levonorgestrel are commonly used.