The work of physiologists covers many interesting research areas.
Most of us feel light-headed at altitudes above 5000 m and most of us would lose consciousness at the top of Mount Everest (8800 m). But over a period of days the body adapts in several ways (including elevation of the hormone erythropoietin (EPO) that stimulates the production of red blood cells, increasing the capacity of the blood to transport oxygen from the lungs to the body’s tissues) and our performance at altitude improves.
Some athletes cheat by injecting the hormone and gaining the advantage this produces. The altitude adaptations are retained for a time on return to sea level and so provide an advantage to athletes competing at sea level. For this reason the US Olympic team has a training camp high in the Colorado Rockies.
Early each summer most of feel the heat and fatigue quite easily.
With the progression of summer we ‘get used to’ the heat. That ‘getting used to’ is a phenomenon known as heat acclimatisation and involves several adaptations including developing a larger blood volume (providing more blood to ferry heat to the skin for loss to the environment) and an increase in how much sweat we can produce (which carries heat off the body when it evaporates).
Our sweat glands can become so well “trained” that in extreme cases we can sweat several litres per hour.
Our physical experience of the world around us is mediated by special sensory organs in the body. The cochlea of our ear is specialised for sensitive detection of sound wave energy, but, unfortunately, the delicate cells in the cochlea can be damaged by too much energy.
This means that exposure to sounds that are too loud can damage hearing permanently. For many years the main cause of this damage was the noise from industrial machinery. Nowadays, however, new sources of loud sound such as rock concerts and even by iPods that are turned up too loud, may be damaging hearing.
Don’t be fooled by the decibel scale used to measure sound. This is a logarithmic scale and just a 6 decibel increase in sound is actually 10 times more damaging to your ears!
Fat is a normal and key component of every cell in our body, so it is essential to maintain a certain level of fat in the diet to remain healthy.
How much fat we store in the body depends on how much energy we ingest versus how much we metabolise (or burn). The present ‘obesity epidemic’ in the Western world is often thought to be the result of sedentary lifestyles (machines do all the heavy lifting) combined with an abundance of affordable food.
There are some essential fats (also called essential oils) that we cannot make in the body and so they have to be ingested. They are alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). The problem with eating a lot of fat is that it is very energy-dense (that is – there are more joules of chemical energy per gram than there are in proteins or carbohydrates).
Stores of fat in the body are known as adipose tissue. Until recently adipose tissue was thought of as just a store of energy, a reserve for the lean times. But it is now known to secrete many molecules that affect other body functions, including the immune system.
Adipose tissue actually secretes a hormone called leptin, which appears to signal the brain and to influence appetite and activity. While in some rodent models of obesity the injection of leptin led to drastic reductions in body mass and fat, the injection of leptin reduces adiposity in only a small proportion of people.
A drug called ‘rimonabant’ is now used to inhibit appetite in obese individuals. This drug targets a receptor in the brain that also responds to tetrahydrocannabinol, the active ingredient in marijuana thought to be responsible for ‘the munchies’. Blocking that receptor has been successful in reducing adiposity in humans.