Endocrine System

• The ability to detect change and to respond is called sensitivity.
• The endocrine system is a group of specialised tissues (glands) that produce chemicals called hormones.
• Hormones are chemical ‘messengers’, produced in​ specialized glands, and transported in the blood to a​ target organ.
• The endocrine glands are often called ductless glands.
• Exocrine glands have ducts to carry their secretions e.g. salivary glands.
• Most hormone activity is controlled directly or indirectly by the hypothalamus and pituitary gland.
• The pineal gland is located within the brain and produces the hormone melatonin.
• The pituitary gland produces ADH to stimulate water reabsorption in the kidneys, TSH which stimulates the thyroid gland to release thyroxine, and FSH which controls the functions of the reproductive organs. 
• The thyroid gland, in the neck, produces thyroxine, which stimulates metabolism. 
• The parathyroid produces parathyroid hormone, which increases blood calcium levels.
• The thymus produces the hormone thymosin which causes lymphocytes to mature.
• The pancreas is an endocrine gland because it releases the hormone Insulin into the blood.​ The pancreas is also an exocrine gland as it releases enzymes into the pancreatic duct into the small intestine.
• The Islets of Langerhans produce insulin while the rest of the pancreas  produces enzymes for digestion.
• The adrenal gland produces adrenaline, which helps the body cope with emergencies —the ‘flight or fight’ hormone.
• The ovary produces oestrogen and progesterone to prepare the female for pregnancy. The testes produce testosterone which triggers sperm production and growth in the male.
• Low insulin levels result in diabetes. This can be treated with injections of insulin.
• An example of a hormone supplement is anabolic steroids. These are a drug that builds up protein and strengthens muscles.
• Feedback occurs when the level of hormone in the blood controls the production of another hormone or itself.
• The regulation of thyroid hormone secretion depends on a negative feedback loop between the pituitary and the thyroid gland. A high thyroxine concentration inhibits the pituitary gland, which sends out less TSH, leading to less thyroxine, so the level drops.
• TSH stands for thyroid stimulating hormone.