Testosterone replacement Therapy (TRT)

Hypothalamus: Senses energy status, stress, sleep, and age. Releases GnRH in precise pulses.

 

Pituitary gland: Responds to GnRH by releasing LH and FSH. These are instructions, not testosterone itself.

 

Testes: (Leydig cells) LH signals testosterone production. Levels rise only if the signal is appropriate.

 

Sertoli cells: FSH supports sperm development and releases inhibin, which feeds back to slow the system when output is sufficient.

 

Negative feedback loop: Rising testosterone signals the brain to dial production down. Falling levels remove the brake.

 

Downstream effects: Testosterone influences muscle growth, bone density, red blood cell production, mood, and metabolism — but only within the limits set by this axis.