Stress and the brain

Your stress response: the details

There are three main parts of you that control your stress response – your hypothalamus, your pituitary (in your brain) and your adrenal glands above your kidneys.

Together, these are called the hypothalamo-pituitary-adrenal (HPA) axis.

What’s so special about your hypothalamus?

For such a tiny piece of brain, your hypothalamus is spectacularly important. A tiny injury in the hypothalamus can produce dramatic and often fatal disruptions of widely dispersed bodily actions.

Not only does your hypothalamus control your stress hormones, it is involved in sex, eating and drinking.

By a variety of mechanisms, your remarkable hypothalamus also keeps your blood volume, pressure, salinity, acidity, blood oxygen levels and glucose concentrations stable – even when you’re doing vigorous exercise. One part of your hypothalamus even receives direct input from your retina – and regulates your sleep-wake cycles.

Your hypothalamus also controls your body temperature. So whether you’re strolling naked through the snow or enjoying a Swedish sauna – your hypothalamus keeps your core body temperature at a steady 37 degrees (the optimum temperature for your cells’ enzymes to work).

Your pituitary gland

When a human brain is removed from its skull, the pituitary gland appears to dangle from the base of the brain. However in your living brain the pituitary is gently held in a cradle of bone at the base of your skull, just above the roof of your mouth.

It deserves this special protection because it is the ‘mouthpiece’ through which your remarkable hypothalamus speaks to the rest of your body. Your hypothalamus tells your pituitary what to release and when.

In the 1930’s Ernst and Berta Scharrer working in Germany proposed the radical idea that neurons of the hypothalamus extend axons into the pituitary - and these neurons actually release hormones. They were right! The neurons in your hypothalamus act like a gland releasing hormones.

How are your adrenal glands involved?

Just above each of your kidneys, are your adrenal glands. These have two parts: the outer part called your adrenal cortex and the inner part – your adrenal medulla. Both parts play a huge role in your stress response.

How does your brain affect glands near your kidneys?

Your hypothalamus releases the hormone corticotrophin-releasing hormone (CRH). This travels to the pituitary gland and triggers the release of adrenocorticotropic hormone (ACTH). This hormone travels in your blood to your adrenal glands, instructing them to release a third hormone, cortisol.

What’s in a word?

Cortex	Means ‘bark’ in latin – ie the outer layer
Medulla	Latin for ‘middle’ (from medi)
Hypo	Latin for ‘under’
Thalamus	Part of the brain above hypothalamus
Renal	Related to the kidneys
Epinephrine	The American term for Adrenalin
Hormone	Means ‘to excite’ in Greek (from hormaein)

A new anti-stress pill

Stafford Lightman’s group at Bristol university are involved in an intensive program to develop an anti-stress pill.

The target for the pills is Corticotropin-releasing hormone (CRH). This hormone is released by the hypothalamus and eventually leads to the release of cortisol. So the pill blocks the entire stress pathway starting at the top.

The pill is likely to be extremely important in treating depression associated with severe stress.

Stress in people caring for loved ones

A recent study looked at people caring for loved ones with Alzheimer’s disease. The extra strain these care-givers are under indeed causes increased levels of cortisol in their blood. In addition, investigation of the carers’ immune response showed it was impaired. Other studies have showed that chronic stress can decrease your ability to heal wounds.

For more information on stress, explore the work of two leading neuro-endocrinologists:

Stafford Lightman in Bristol

Joe Herbert in Cambridge