6.2 Applications and skills
6.2.6a Therapeutic and clinical uses of hormones
Many health conditions are caused by abnormal hormone function. Hormones are used in a variety of therapies, such as replacement therapies and fertility treatments.
Causes and treatment of Types I and II diabetes
- Diabetes is actually a group of diseases that cause a person to have consistently elevated blood sugar, either because the body doesn’t respond to insulin, or because the body cannot produce insulin.
- Type I diabetes is also called early-onset diabetes.
- Type II diabetes is also called late-onset diabetes.
- There is no cure for diabetes. When left untreated, diabetes will cause blindness, kidney failure, nerve damage, cardiovascular disease and death.
Leptin and obesity
- In a healthy body, leptin released by adipose tissue acts on the hypothalamus to reduce appetite. When the blood plasma concentration of leptin falls, appetite is restored. The amount of adipose tissue remains in homeostasis by this negative feedback mechanism.
- In the 1950s, scientists discovered a strain of mouse with a deficiency in a gene called ‘Ob’. These mice were obese and had insatiable appetites because their body was not producing leptin.
- Scientists hypothesised that they had found a genetic basis for obesity.
- Clinical trials using leptin as a therapy for obesity have shown limited success, because while a small proportion of patients have a deficiency, the majority of patients have abnormally high concentrations of leptin.
- A more current model of the relationship between leptin and obesity is as follows: As more adipose tissue is deposited, more leptin is produced. The hypothalamus is desensitised to high levels of hormone. Appetite is not suppressed, and calorie intake is converted to adipose tissue in a positive feedback loop. Leptin insensitivity could predispose certain individuals to developing obesity.
Figure 6.2.6a.a – Negative vs positive feedback
Appetite and adipose deposition are linked in positive (left) and negative (right) feedback loops. Top: Obese body. Bottom: Healthy body.
Melatonin and jet lag
- The body’s ‘internal clock’ is located in the SCN, or suprachiasmatic nucleus, which is directly connected by neurons to the retina.
- The SCN maintains a circadian rhythm of sleep and wakefulness approximately equal to 24 hours. External stimuli synchronise the clock to the natural day/night cycle.
- Light activates photoreceptors on the retina, which synchronises the SCN to daytime. In the absence of light, the pineal gland produces a hormone, called melatonin, which synchronises the SCN to night.
Figure 6.2.6a.b – Normal melatonin profile in an adult
- Melatonin promotes sleep. Production starts in the evening and peaks at night. The hormone is rapidly removed from the blood by the liver in the morning.
- When you travel across a number of time zones very quickly (i.e. on a jet), circadian rhythms become temporarily desychronised. It can take up to five days for external stimuli to resynchronise the SCN to a new day/night cycle.
- Sleep disturbance, indigestion, fatigue and irritability are all symptoms of ‘jet lag’, or desynchronosis.
- Melatonin supplements may be taken to help normalise sleep patterns.
Did you know?
- A third type of diabetes, called gestational diabetes, may develop in pregnant women during the last trimester of pregnancy. Normally, it subsides four to six weeks after the birth of the baby.
- Type II diabetes is a growing problem all over the world, and the typical patient is getting younger. High fat and sugar diets, and lack of exercise are to blame.
Figure 6.2.6a.d – Fat mice
Leptin deficiency causes obesity in mice.
- A circadian rhythm is any biological process that displays an internal, and trainable, cycle of approximately 24 hours. The best understood example is the sleep–wake cycle, but daily cycles of body temperature and bowel movement are other examples.
- The retina is the photosensitive layer of cells of the eye.
- Circadian, from the Latin circa = approximately and diem = day.
Figure 6.2.6a.e – Adjusting flying east/west
It is easier for the SCN to resynchronise after east-to-west travel than west-to-east travel. Suggest a reason why.
Figure 6.2.6a.f – Sleepy teen
In teenagers, melatonin production starts and peaks later in the night than in adults. There is a reason why you are so sleepy at school!