Human Endocrine System: Glands, Hormones and Disorders
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Unit 8. Endocrine System
The endocrine system is made up of the endocrine glands and the hormones they produce. Those glands produce hormones, chemical messengers that affect many cell processes (accelerating, delaying, starting, or stopping them). Hormones are transported by blood to all the cells in the body, but they only affect very specific target cells, which have specific receptors for that hormone. The hormone causes changes inside those cells.
Glands release only small quantities of hormones, and once the hormone has carried out its function, it is eliminated from the body.
The hypothalamus, a gland located in the brain, connects the nervous system and the endocrine system. It is one of the most important glands because it controls many of the other glands of the body.
The hormones are controlled by the negative feedback system: when too much hormone is secreted in the blood, the gland itself detects this concentration and stops the secretion.
8.1 Principal glands and types of hormones
Gland | Hormones |
Pituitary | Growth hormone: controls growth |
Prolactin: stimulates breast growth and milk production | |
FSH and LH: act on ovaries and testes | |
Oxytocin: stimulates uterine contractions during childbirth and breast milk production | |
Thyroid | Calcitonin: regulates the level of calcium in the blood |
Parathyroid | Parathyroid hormone: increases the amount of calcium in the blood |
Adrenal glands | Cortisol: produced in stressful situations, increases the production of glucose (for energy) |
Adrenaline: increases heartbeat and muscle strength in situations of alarm ("fight or flight") | |
Pancreas | Insulin: reduces the amount of glucose in the blood |
Glucagon: increases the amount of glucose in the blood | |
Ovaries | Estrogens: stimulates development of secondary sex characteristics |
Progesterone: prepares the uterus for pregnancy | |
Testes | Testosterone: stimulates development of secondary sex characteristics and the production of sperm |
8.2 Diseases of the endocrine system
Hypofunction: one gland produces insufficient hormone.
Hyperfunction: one gland produces too much hormone.
Dwarfism and gigantism: due to a deficiency or excessive production of growth hormone, respectively.
Diabetes: an increase in the amount of glucose in the blood. Type 1 diabetes occurs when the pancreas does not produce enough insulin. Type 2 diabetes occurs when the pancreas produces insulin but the cells do not respond to it.