Male Endocrinology and Reproductive Hormones

Comprehensive practice flashcards covering male endocrinology, including hormone synthesis, mechanisms of action, and clinical topics like anabolic steroid abuse and aging.

GnRH Neurons

Neurosecretory cells located in the hypothalamus that release hormones into blood vessels to act on the anterior pituitary.

Anterior Pituitary Endocrine Cells

Cells that produce and release pituitary hormones such as FSH and LH in response to releasing hormones from the hypothalamus.

Testis Steroid Hormones

Hormones produced by the testis including testosterone (androgen) and estradiol-17$\beta$ (estrogen).

Testis Protein Hormones 1

Proteins produced by the testis, specifically inhibin and activin.

Steroid Hormone Mechanism of Action

Steroids diffuse through the plasma membrane, cytoplasm, and nuclear membrane to bind to nuclear receptors, which act as transcription factors to trigger mRNA production and protein synthesis.

Sex Steroid Binding Globulin (SSBG)

A large, water-soluble protein that binds to steroids to allow their transport in the water-based solution of blood.

Albumin

One of the two primary water-soluble proteins used to transport steroids in the blood.

Protein Hormone Mechanism of Action

Hormones like LH and FSH bind to plasma membrane receptors, activate G proteins and adenylate cyclase to produce cAMP, which then activates Protein Kinase A to facilitate gene transcription.

Sertoli Cells

Cells in the testis that produce inhibin and androgen binding protein; they support developing germ cells and are regulated by FSH.

Leydig Cells

Cells in the testis that produce testosterone in response to LH stimulation.

5$ext{\alpha}$-reductase

The enzyme responsible for converting testosterone into Dihydrotestosterone (DHT) inside target cells.

Aromatase

The enzyme that converts testosterone into estradiol.

Inhibin

A protein produced by Sertoli cells that exerts negative feedback on the anterior lobe of the pituitary to suppress FSH.

Interstitial Cell Stimulating Hormone (ICSH)

A historical name for LH used before it was discovered that the same hormone exists and functions in both males and females.

Dihydrotestosterone (DHT)

A potent androgen responsible for the differentiation of male external genitalia and adult secondary sex characteristics.

Estradiol (in males)

Produced from testosterone via aromatase; it mediates hypothalamus differentiation, negative feedback, and the closure of epiphyseal plates in long bones.

Endocrine Regulation Arm 1

The regulatory pathway involving Hypothalamus (GnRH), Anterior Pituitary (FSH), and Sertoli cells (Inhibin) which provides negative feedback.

Endocrine Regulation Arm 2

The regulatory pathway involving Hypothalamus (GnRH), Anterior Pituitary (LH), and Leydig cells (Testosterone) which provides negative feedback.

Steroid Breakdown

The process occurring primarily in the liver where enzymes chemically modify steroids by adding glucuronic acid and sulfate to inactivate them.

Andropause

A gradual long-term drop in testosterone (by $50-65\%$ from age 20s to 70s) associated with aging, leading to decreased sex drive, muscle loss, and mood changes.

Klinefelters Syndrome

A genetic condition (XXY) that can cause low testosterone levels.

Anabolic Steroids

Synthetic substances related to testosterone that 'build up' organs and tissues; they are androgenic and can cause shrunken testes and low endogenous testosterone in boys.

Prohormone Abuse

The use of steroid precursors like Androstenedione ('Andro') or DHEA that the body converts into anabolic steroids or estrogens.

Dehydroepiandrosterone (DHEA)

A steroid precursor often found in 'nutritional supplements' that is not FDA regulated and can have the same side effects as anabolic steroids.