Stress, metabolism, and endocrine disorders
When hormone systems produce too much or too little, the effects can reach every part of the body.
The stress response
Short-term stress triggers the sympathetic nervous system and adrenaline: faster heart rate, raised blood glucose, and alertness. Long-term stress activates the hypothalamus-pituitary-adrenal (HPA) axis: CRH from the hypothalamus triggers ACTH, which triggers cortisol. Chronic high cortisol can suppress immunity, raise blood pressure, and disrupt sleep.
Diabetes mellitus
Diabetes is persistently high blood glucose. Type 1 diabetes is autoimmune destruction of beta cells, so little or no insulin is made; it needs insulin treatment. Type 2 diabetes, far more common, involves insulin resistance and is linked to weight, inactivity, and genetics; it is managed with lifestyle change, medicines, and sometimes insulin. Untreated, both damage blood vessels, nerves, kidneys, and eyes.
Thyroid disorders
Hypothyroidism (too little thyroid hormone) causes tiredness, weight gain, feeling cold, and slow heart rate; a common cause is autoimmune Hashimoto's thyroiditis. Hyperthyroidism (too much) causes weight loss, anxiety, heat intolerance, and rapid heart rate; Graves' disease is a common autoimmune cause, sometimes with bulging eyes.
Adrenal disorders
Cushing's syndrome results from excess cortisol, often from long-term steroid medication, causing weight gain in the trunk and face, thin skin, and high blood glucose. Addison's disease is adrenal cortex failure, causing low cortisol and aldosterone, with fatigue, low blood pressure, and darkened skin.
Growth disorders
Too much growth hormone in childhood causes gigantism; in adults, after growth plates close, it causes acromegaly, with enlarged hands, feet, and facial bones. Too little GH in childhood causes short stature, which can be treated with synthetic GH.
Hormones and metabolism
Metabolic rate is set mainly by thyroid hormones, with insulin, glucagon, cortisol, and adrenaline shifting how fuels are stored or used. After a meal, insulin promotes storage of glucose as glycogen and fat. During fasting, glucagon and cortisol release stored glucose and break down fat. Leptin from fat cells signals energy stores to the brain.
Endocrine disruptors
Some chemicals in the environment, such as certain pesticides and plastic additives, can mimic or block hormones. Research has linked some to effects on development and reproduction, and regulators have restricted several. How much risk typical exposures pose is still being studied.
Worked example
A patient has fatigue, weight gain, and feels cold. Blood tests show low T4 and high TSH. The high TSH indicates the pituitary is trying hard to stimulate an underactive thyroid: primary hypothyroidism. Treatment with synthetic thyroid hormone restores normal levels, and TSH falls through negative feedback.
Key takeaways
Short-term stress uses adrenaline; long-term stress uses the HPA axis and cortisol. Type 1 diabetes is lack of insulin; type 2 is insulin resistance. Hypothyroidism slows metabolism; hyperthyroidism speeds it. Cushing's is excess cortisol; Addison's is adrenal failure. Excess GH causes gigantism or acromegaly. Hormones coordinate fuel storage and use.
Flashcard
Hypothalamus-pituitary-adrenal stress pathway
Check your understanding
A blood test shows high TSH and low thyroid hormone. What does this suggest?