The pituitary gland descends from the hypothalamus at the base of the brain, and acts in close association with it. The pituitary is often referred to as the “master gland” because its messenger hormones control
104 Chapter 3 | Biopsychology
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all the other glands in the endocrine system, although it mostly carries out instructions from the hypothalamus. In addition to messenger hormones, the pituitary also secretes growth hormone, endorphins for pain relief, and a number of key hormones that regulate fluid levels in the body.
Located in the neck, the thyroid gland releases hormones that regulate growth, metabolism, and appetite. In hyperthyroidism, or Grave’s disease, the thyroid secretes too much of the hormone thyroxine, causing agitation, bulging eyes, and weight loss. In hypothyroidism, reduced hormone levels cause sufferers to experience tiredness, and they often complain of feeling cold. Fortunately, thyroid disorders are often treatable with medications that help reestablish a balance in the hormones secreted by the thyroid.
The adrenal glands sit atop our kidneys and secrete hormones involved in the stress response, such as epinephrine (adrenaline) and norepinephrine (noradrenaline). The pancreas is an internal organ that secretes hormones that regulate blood sugar levels: insulin and glucagon. These pancreatic hormones are essential for maintaining stable levels of blood sugar throughout the day by lowering blood glucose levels (insulin) or raising them (glucagon). People who suffer from diabetes do not produce enough insulin; therefore, they must take medications that stimulate or replace insulin production, and they must closely control the amount of sugars and carbohydrates they consume.
The gonads secrete sexual hormones, which are important in reproduction, and mediate both sexual motivation and behavior. The female gonads are the ovaries; the male gonads are the testes. Ovaries secrete estrogens and progesterone, and the testes secrete androgens, such as testosterone.
Major Endocrine Glands and Associated Hormone Functions
Associated Hormones Function
Hypothalamus Releasing and inhibiting hormones, such as oxytocin
Regulate hormone release from pituitary gland
Pituitary Growth hormone, releasing and inhibiting hormones (such as thyroid stimulating hormone)
Regulate growth, regulate hormone release
Thyroid Thyroxine, triiodothyronine Regulate metabolism and appetite
Pineal Melatonin Regulate some biological rhythms such as sleep cycles
Adrenal Epinephrine, norepinephrine Stress response, increase metabolic activities
Pancreas Insulin, glucagon Regulate blood sugar levels
Ovaries Estrogen, progesterone Mediate sexual motivation and behavior, reproduction
Testes Androgens, such as testosterone Mediate sexual motivation and behavior, reproduction
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