The Endocrine System

1. The Endocrine System

2. Endocrine System • Remember: Your nervous system senses impulses over a system of wire-like neurons that carry messages from one cell to another • The term endocrine comes from Greek because endon = within and krinein = to secrete • The endocrine system is made up of glands that release their products into the blood stream. These products broadcast messages throughout the body.

3. Hormones • Hormones = “Chemical messengers” • Hormones travel through the bloodstream and affect the activities of other cells by binding to specific chemical receptors on those cells • Cells that have receptors for a particular hormone = target cells • If a cell does not have the specific receptors for a hormone, that hormone will have no effect on that cell • Responses to hormones are slower and last longer than responses to nerve impulses

4. Glands • Gland = organ that produces and releases a substance or a secretion • Exocrine glands = release their secretions through tube-like structures called ducts (sweat, tears, and digestive juices) • Endocrine glands = release their secretions (hormones) directly into the bloodstream

5. ENDOCRINE VS. EXOCRINE GLAND

6. Hormone Action Section 39-1 Nonsteroid hormone (first messenger) Steroid Hormone Receptor Target cell membrane Target cell membrane Receptor cAMP (second messenger) Hormone-receptor complex Altered cellular function Nucleus Enzyme activities DNA Altered cellular function Protein synthesis Nucleus Cytoplasm Cytoplasm mRNA

7. Control of the Endocrine System • Hormones must be closely monitored to keep the functions of different organs in balance, because the endocrine system is one of the master regulators of the body. • The endocrine system is regulated by feedback mechanisms that function to maintain homeostasis.

8. Feedback Inhibition • When there is an increase in a substance, that “feedback” inhibits or stops the process producing that substance. • For example: temperature controlled by thermostats

9. Figure 39–10 Actions of Insulin and Glucagon Beta cells release insulin into the blood Body cells absorb glucose Blood glucose level increases Blood glucose level decreases Liver converts glycogen to glucose Homeostasis: Normal blood glucose level Blood glucose level increases Blood glucose level decreases Liver converts glycogen to glucose Alpha cells release glucagon into blood Section 39-2

10. Human Endocrine Glands • Pituitary gland • Hypothalamus • Thyroid gland • Parathyroid glands • Adrenal glands • Pancreas • Reproductive glands

11. Figure 39–2 The Endocrine Glands Section 39-1 Pineal gland The pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles. Hypothalamus The hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland. Thyroid The thyroid produces thyroxine, which regulates metabolism. Pituitary gland The pituitary gland produces hormones that regulate many of the other endocrine glands. Pancreas The pancreas produces insulin and glucagon, which regulate the level of glucose in the blood. Parathyroid glands These four glands release parathyroid hormone, which regulate the level of calcium in the blood. Ovary The ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg. Thymus During childhood, the thymus releases thymosin, which stimulates Tcell development. Testis The testes produce testosterone, which is responsible for sperm production and the development of male secondary sex characteristics Adrenal glands The adrenal glands release epinephrine and nonepinephrine, which help the body deal with stress.

12. Pituitary gland • Bean-sized structure that dangles on tissue at the base of the skull within the brain • The pituitary gland is divided into two parts: anterior pituitary and posterior pituitary • “Master gland” because secretes nine hormones that directly regulate many body functions and controls the actions of several other endocrine glands • Growth hormone (GH) • Thyroid-stimulating hormone (TSH) • Luteinizing hormone (LH) • Follicle-stimulating hormone (FSH)

13. Hypothalamus • Part of the brain above and attached to the pituitary gland • Controls the secretions of the pituitary gland • Connects nervous system and endocrine system

14. Thyroid gland • At the base of the neck and wraps around the upper part of the trachea • Regulates the body’s metabolism • Produce thyroxine, which affects cellular respiration rates producing energy • Hyperthyroidism = too much thyroxine (increased temperature, increased heart and metabolic rates, increased blood pressure, and weight loss) • Hypothyroidism = too little thyroxine (low temperature, low metabolic rates, lack of energy, weight gain and sometimes goiter) • Needs enough iodine to produce normal amounts of thyroxine

15. Parathyroid gland • Four glands found on the back of the thyroid • Maintain homeostasis in blood calcium levels • Secrete parathyroid hormone (PTH), which regulates calcium levels in the blood

16. Adrenal glands • Two pyramid-shaped structures that sit on top of the kidneys (one gland on each kidney) • Help the body prepare for and deal with stress by secreting adrenaline • Has two parts: • Adrenal cortex: outer part secretes over 24 hormones (corticosteroids, aldosterone, corisol) • Adrenal medulla: inner part secretes epinephrine and norepinephrine producing the “fight or flight” response to stress by increasing heart rate, blood pressure and blood flow

17. Pancreas • Right side of the body behind the stomach • Remember: the pancreas secretes enzymes through a duct to help break down food = exocrine gland • Different cells in the pancreas release hormones into the blood = endocrine gland • Clusters of cells that resemble islands = islets of Langerhans that secrete insulin and glucagon that help keep the level of glucose in the blood stable • Insulin stimulates cells in liver and muscles to remove sugar from the blood and store sugar as glycogen or fat • Glucagon stimulates the liver to break down glycogen and release glucose back into the blood • Diabetes mellitus = too little insulin (high blood glucose levels) • Type I = commonly develops before age 15 and there’s little or no insulin secreted, so take daily insulin injections and restricted diet • Type II = commonly develops in adults after age 40 and there is low to normal amounts of insulin, but cells don’t properly respond to the hormone, so adjust diet and exercise

18. Reproductive glands • Gonads • Female = ovaries, which produce eggs (ova) and secrete estrogen • Male = testes, which produce sperm and secrete testosterone • Produce gametes and secrete sex hormones responsible for secondary sex characteristics

19. http://www.teachersdomain.org/resource/envh10.sci.life.eco.endodisrupt/http://www.teachersdomain.org/resource/envh10.sci.life.eco.endodisrupt/