15.2 Applications and skills

15.2.5 Applications of hormones and metabolism (HL)

Application: Some athletes take growth hormones to build muscles

  • Human growth hormone (HGH), or somatotropin, is a peptide hormone secreted by the anterior pituitary gland.
  • Natural secretion of HGH declines with age, but synthetic HGH is often used by athletes in order to build muscle mass, strengthen connective tissue and increase bone mineralisation.
  • HGH is banned by most sporting authorities, but it is difficult to detect in anti-doping tests.
  • HGH works directly on some tissues, but also targets cells of the liver to stimulate the production of another anabolic hormone, called insulin-like growth factor (IGF-1).
  • IGF-1 is also a banned substance, but it is detectable by anti-doping tests.

HGHFigure 15.2.5a – HGH stimulates production of IGF-1

  • The scientific evidence for HGH as a performance-enhancing drug is mixed:
    • HGH may allow athletes to train harder by speeding recovery of tired muscles.
    • Increases in mass of muscle and connective tissue do not always correlate with increased strength or power.
    • Side-effects of HGH use in athletes include muscle and joint pain, and high cholesterol levels in the blood.

Application: Control of milk secretion by oxytocin and prolactin

  • Lactation depends on the action of two peptide hormones, oxytocin and prolactin.

production and ejection of milkFigure 15.2.5b – Overview of the production and ejection of milk




Produced in …


Anterior pituitary

Secreted by …

Posterior pituitary

Anterior pituitary

Inhibited by …

Estrogen and progesterone (during pregnancy)

Target tissue

Mammary glands

Mammary glands

Stimulated by …

Suckling (mechanoreceptors)

Suckling (mechanoreceptors)


Contraction of gland cells to release milk into nipple

Promotes milk production in cells of the mammary glands


Activity: Control of lactation

hormone levels of lactationFigure 15.2.5c – Hormone levels during pregnancy and lactation

Analyse Figure 15.2.5c, and answer the following questions:

  1. Describe the significance of the peak in oxytocin i) at birth ii) during breastfeeding.
  2. Explain why the peaks in prolactin occur between breastfeeding times.
  3. The hormones above are shown in relative, not absolute concentration. The average concentration of prolactin of a post-partum woman is 70ng/ml. Estimate the peak concentration of oxytocin during lactation.
  4. Determine whether the interaction of oxytocin and prolactin is an example of positive or negative feedback.

Nature of Science: Combating iodine deficiency

  • Iodine is necessary for the proper working of the thyroid hormone, thyroxine, which regulates metabolic rate.
  • Dietary sources normally come from the sea (e.g. fish, kelp), so people who live inland or at high altitudes may be at risk for developing iodine deficiency disorders.
  • The international council for the control of iodine deficiency disorders (ICCIDD) is a part of a group of nutritional scientists who work to eliminate the effects of iodine deficiency worldwide.
  • One of the most successful programmes has been to advocate for the iodisation of table salt. Over the past forty years, the number of people who have access to iodised table salt has increased by 70%.
  • This is an example of cooperation and collaboration between groups of scientists. The salt iodisation programme requires nutritional scientists, food scientists and engineers to work together.

protropinFigure 15.2.5d – Protropin
Synthetic HGH is banned from sport, but is available by prescription for therapeutic use.

Food for thought

For which of the following conditions might HGH therapy be suitable:

HIV/AIDS, diabetes, coronary heart disease (CHD), chronic kidney disease, low birthweight?

Discuss your thoughts with a partner.

Language tool

Anabolic hormones promote the growth of cells. Testosterone, insulin and HGH are examples.

goiterFigure 15.2.5e – Goitre
An enlarged thyroid gland, called goitre, is a symptom of iodine deficiency.

epoFigure 15.1.6f – EPO
Erythropoietin, EPO, is a hormone that controls red blood cell production. Recent scandals involving high-profile endurance athletes who used synthetic EPO for ‘blood doping’ have shone a spotlight on the issue of fairness in sport.

Science and social responsibility (Aim 8)

Is the use of performance-enhancing drugs acceptable in terms of fairness as long as all athletes have equal access to them?

Course link

Synthetic HGH is produced in the laboratory using recombinant DNA technology. This is an example of ‘biopharming’. You may choose to learn more about it in Option B: Biotechnology and bioinformatics. See 13.1.4.


Activity answers