The Endocrine System- The Second Control System of the Body!
The Endocrine System and Hormone Function
- The Endocrine system helps to coordinate and control the activities of our body’s cells. This system is usually working closely with the Nervous System.
- The endocrine system is not “built for speed” like the nervous system is but is still able to cause major physiological changes and maintain homeostasis within the body.
- The Chemistry of Hormones
- Hormones are the chemical force of the endocrine system. They are the messengers released by glands that cause changes within the body.
Ex. Growth, reproduction, homeostasis and metabolism.
- All hormones can be classified as amino acid based or steroid.
- Amino acid based hormones are proteins, peptides and amines.
- Steroid hormones are made from cholesterol
- Protaglandins are made from lipids
- Mechanisms of Hormone Action
- Hormones affect only certain tissues or organs (target cells or organs)
- Steroid hormones diffuse into the target cell and activate protein synthesis. This explains how birth control patches work, but an insulin patch would not be effective because it is an amino acid hormone.
- Amino Acid hormones bind to a receptor on the target cell and sets off a series of reactions inside the cell.
- Hormones cause one of the four changes: changes in the plasma membrane electrical state, synthesis of proteins, activation or deactivation of enzymes, or stimulation of mitosis.
- Control of Hormone Release
- Hormone levels in the blood are maintained by negative feedback mechanisms. For example: You eat a candy bar at lunch your blood sugar levels rise cells of the pancreas are activated and release insulin into the bloodbody cells are triggered by insulin to take up glucoseblood glucose levels declinepancreas stops releasing insulin.
- There are three ways that endocrine glands can be activated:
- Hormonal- activation from other hormones.
- Humoral- activation by changing blood levels of certain ions (like calcium)
- Neural- activation by nerve impulses.
Major Endocrine Glands and their hormones
- Pituitary gland- hangs by a stalk from the hypothalamus and has two functional lobes- the anterior (glandular tissue) and posterior (nervous tissue)
- Hormones of the anterior pituitary include:
- Growth Hormone- stimulates growth and metabolism
- Prolactin- stimulates milk production
- Follicle Stimulating Hormone (FSH)- stimulates production of egg and sperm
- Leutinizing Hormone (LH)- stimulates ovaries and testes
- Thyroid Stimulating (TSH)- stimulates thyroid gland
- Adrenocorticotropic (ACTH)- stimulates adrenal glands
- Hormones of the posterior pituitary:
- Oxytocin- stimulates contractions of the uterusduring labor
- Antidiuretic- inhibits urine production
- Thyroid Gland- found at the base of the throat,
- Hormones include:
- Thyroid hormone- the major metabolic hormone
- Calcitonin- reduces blood calcium levels by causing its deposition to bone
- Parathyroid glands- tiny masses on the posterior thyroid
- Hormones include:
- Parathyroid hormone- raises blood calcium by stimulating osteoclasts to remove calcium from bone
- Adrenal Glands- sit on top of the kidneys
- Hormones include:
- Epinephrine and Norepinephrine- “Fight or Flight” hormones- increase blood glucose, increase rate of metabolism, constrict certain blood vessels
- Pancreas- the islets of pancreas produce hormones
- Hormones include:
- Insulin- to reduce blood sugar
- Glucagon- to raise blood sugar
- Pineal Gland- found on third ventricle of brain
- Hormones include:
- Melatonin- helps establish the body’s wake and sleep cycles
- Thymus- located posterior to sternum, is largest in infants and children and decreases in size as we age.
- Hormones include:
- Thymosin- matures white blood cells (T cells)
- Testes
- Hormones include:
- Androgens-support sperm formation and male secondary sex characteristics
- Ovaries
- Hormones include:
- Estrogen- stimulate uterine lining growth, development of female secondary sex characteristics
- Progesterone- promotes growth of uterine lining