Hormone Classification and Mechanisms · Physiology

Which of the following is true regarding the 'Free Hormone' hypothesis?

  1. Only hormones bound to proteins can enter target cells.
  2. Only the unbound fraction of a hormone is biologically active.
  3. Free hormones are protected from renal excretion.
  4. The concentration of free hormone is always higher than bound hormone.
Show answer and explanation

Correct answer: Only the unbound fraction of a hormone is biologically active.

Carrier proteins act as a reservoir, but only the 'free' or unbound hormone can diffuse across membranes or bind to cell surface receptors to exert physiological effects. This free fraction is usually less than 1-10% of the total hormone concentration.

Difficulty: Medium Question 37 of 40

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