AMA 176 - Anatomy & Physiology/Medical Terminology/Pathology 7 Endocrine System
Endocrine System • Function: an information signaling system (like nervous system) that uses blood vessels as information channels (rather than nerves). Glands located all over the body release chemical messengers called hormones which regulate specific bodily functions; e.g. growth, puberty, metabolism, reproduction, etc. Help to maintain homeostasis or balance in the body. • Hormones: work by binding to sites on various tissues that recognize them causing the intended biological effect, somewhat like a lock and key. Each receptor is the lock and the specific hormone that is attracted to that receptor is the key that opens that lock and causes the intended biological effect. (e.g. the pituitary gland secretes growth hormone that opens the “lock” in bones and tissues and causes growth).
Structure of the Endocrine System Two types of glands: • Endocrine: secrete hormones into the bloodstream. (examples: pineal, thymus, thyroid, parathyroid, adrenal, pancreas, pituitary, ovaries, testes) • Exocrine: send chemical substances (tears, sweat, saliva) via ducts to the outside of the body. (examples: sweat, mammary, mucous, salivary, lacrimal (tear) glands)
Pineal & Thymus: • Pineal: located in the brain. Secretes melatonin to regulate the body’s “biological clock”. • Thymus: located behind the sternum. Produces thymosin and T-cells and is responsible for immune responses (more so in childhood, shrinks as we age).
Thyroid: • Located in the neck. • Secretes thyroxine (tetraiodothyronine) (T4) and triiodothyronine (T3). • These are hormones synthesized from iodine from the bloodstream; necessary to maintain metabolism by helping cells take in oxygen.
Parathyroid: • Located on either side of the thyroid in the neck (four small oval bodies). • Parathyroid hormone (PTH) takes calcium from bones and puts it into the bloodstream to help with proper functioning of body tissues, especially the muscles.
Adrenal: • Two small glands on top of each kidney. Composed of two parts; an inner (medulla) and outer (cortex) portion. • Cortex: secretes corticosteroids (complex chemicals made from cholesterol) • Cortisol to regulate glucose, fat and protein metabolism • Aldosterone to regulate electrolytes or salts • Androgens and Estrogens to regulate male and female sex characteristics • Medulla: secretes catecholamines (chemicals made from amino acids). • Epinephrine to increase heart rate and BP, dilate bronchial tubes, release glucose and glycogen for more energy – “flight or fight” • Norepinephrine constricts blood vessels to raise BP)
Pancreas: • Located near stomach • Made of specialized hormone producing cells called the islets of Langerhans that produce insulin and glucagon which regulate blood sugar levels. • Also secretes digestive enzymes into the digestive tract.
Pituitary: • Also called hypophysis; small pea-sized gland located in brain. • The hypothalamus in the brain sends signals to cause the pituitary to release or inhibit many hormones such as growth, thyroid stimulation, pregnancy, etc. • Basically the pituitary hormones tell other glands what to do.
Ovaries & Testes: • Ovaries: located in the lower abdomen in females. Produce eggs (gamete or ovum) as well as hormones responsible for female sex characteristics and regulation of the menstrual cycle. • Testes: located in the inguinal region of the male, suspended in the scrotum. Produce sperm and testosterone responsible for male sex characteristics.