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15.3C: Onset, Duration, and Half-Life of Hormone Activity

A hormone’s half-life and duration of activity are limited and vary from hormone to hormone.

 

LEARNING OBJECTIVES

 

Distinguish between a hormone’s half-life and its duration of activity

 

KEY TAKEAWAYS

Key Points

 

  • The hormone receptors are dynamic structures that vary in number and sensitivity, that depend on the levels of the stimulating hormone.
  • The blood levels of hormones reflect a balance between secretion and degradation/excretion by the liver and kidneys.
  • The biological half- life of a hormone is the time it takes for the hormone to lose half of its physiological activity.
  • The duration of hormone activity refers to the duration of altered cellular behavior triggered by hormone binding.

 

Key Terms

 

  • hormone receptor: A molecule that binds to a specific hormone that triggers alterations in cell activity.
  • half-life: The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiological, or radiological activity.

 

EXAMPLES

 

Vitamin D is a hormone that has a half-life of one to two months. If one obtains vitamin D solely through sun (UVB) exposure during the summer months, serum vitamin D levels will be critically low by late winter. This is one reason why current recommendations are to take vitamin D supplements in order to maintain serum vitamin D levels throughout the year.

The number of hormone molecules available for complex formation is usually the key factor that determines the level at which signal transduction pathways are activated. The number of hormone molecules that are available is determined by the concentration of circulating hormones.

Half-Life

The blood levels of hormones reflect a balance between synthesis/secretion and degradation/excretion. The liver and kidneys are the major organs that degrade hormones with breakdown products excreted in urine and feces.

A hormone’s half-life and duration of activity are limited and vary from hormone to hormone. For instance, the biological half-life of luteinizing hormone is 20 minutes, which is shorter than that of a follicle-stimulating hormone (three to four hours), and of human chorionic gonadotropin (24 hours).

A biological half-life or elimination half-life is the time it takes for a substance such as a hormone or drug to lose half of its pharmacologic or physiologic activity. In a medical context, half-life may also describe the time it takes for the blood plasma concentration of a substance to halve (plasma half-life) its steady-state.

The relationship between the biological and plasma half-lives of a substance can be complex, due to factors including their accumulation in tissues, active metabolites, and receptor interactions.

Duration

The duration of hormone activity refers to the duration of events that were stimulated by hormone-receptor binding. While typically relatively short and measured in minutes or hours, certain events, such as the onset of puberty, are much longer lasting.

This image depicts the levels of certain hormones during the menstrual cycle, as they correspond to follicular growth and ovulation. Once ovulation starts, the hormone progesterone overtakes the follicle-stimulating hormone, the hormone estrogen, and the luteinizing hormone that were present earlier.

 

Hormone levels during menstrual cycle: This image depicts the levels of certain hormones during the menstrual cycle (B), as they correspond to follicular growth and ovulation (A). 1. Follicle-stimulating hormone 2. Estrogen 3. Luteinizing hormone 4. Progesterone.

 

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