The endocrine system consists of all the glands and organs in the body that produce hormones (Figure 50.1). These chemical transmitters bind to the hormone receptors of specific target cells and by working synergistically or antagonistically lead to a variety of physiological reactions. Owing to the existence of complex mechanisms for hormonal regulation, when dysfunction occurs many organs in the body are affected.

The hypothalamic–pituitary axis is important to consider. The hypothalamus, located in the brain just below the thalamus, is the major link between the endocrine and nervous systems and it has many functions. It receives sensory input from other parts of the brain as well as from internal organs, plus it regulates temperature, thirst, hunger, emotional response and sexual behaviour. The hypothalamus also regulates the pituitary gland and together the two structures produce many hormones (Figure 50.2 and Table 50.1). When either of these areas of the brain is affected by disease/injury or their target organs are damaged, hormonal disruption quickly occurs. Acute disorders may be observed in patients with anterior pituitary lobe dysfunction such as adrenal dysfunction.

Adrenal insufficiency can lead to acute deterioration. Adrenocorticotrophic hormone (ACTH) produced by the anterior pituitary, stimulates the adrenal cortex to secrete glucocorticoids such as cortisol (hydrocortisone). This has a major role in catecholamine synthesis and maintenance of blood pressure, glucose regulation and fatty acid metabolism. Should the adrenal glands actually be impaired, the production of aldosterone (a mineralocorticoid responsible for sodium reabsorption and potassium excretion) will also be reduced.

In contrast, excessive corticosteroid production results in Cushing’s syndrome and if hyperaldosteronism is a feature, water retention and potassium loss will also occur.