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Chapter 13 Hormonal Regula3on of Homeostasis Chapter 13 Hormonal Regula3on of Homeostasis 13.1 The Glands and Hormones of the Endocrine System 13.2 Hormonal Regula3on of Growth, Development, and Metabolism 13.3 Hormonal Regula3on of the Stress Response 13.4 Hormonal Regula3on of Blood Sugar Chapter 13 Hormonal Regula3on of Homeostasis In Sec3on 1, you will learn that: • The endocrine system func3ons with the nervous system to regulate other body systems and maintain homeostasis. • The endocrine glands secrete hormones directly into the bloodstream. • Hormone secre3on is regulated by the nervous system, other hormones, or nega3ve feedback mechanisms. The Glands and Hormones of the Endocrine System • The nervous and endocrine systems are self‐regula3ng, and help regulate other body systems, thereby maintaining homeostasis. The Glands and Hormones of the Endocrine System • The nervous system rapidly affects specific 3ssues, to which it is directly connected by neurons. The endocrine system relies on chemical messengers called hormones, which circulate in the blood and have broad, long‐las3ng effects. Over 200 human hormones have been iden3fied! The Glands and Hormones of the Endocrine System • The endocrine glands have no ducts, and secrete hormones directly into the bloodstream. These hormones then bind to receptor proteins on their target cell membranes. The pancreas is an endocrine gland that secretes the hormone insulin into the bloodstream. Pancreas tissue The Glands and Hormones of the Endocrine System • Hormones trigger changes in their target cells when they bind to receptor proteins on or within the cells. A model of a hormone (A) bound to its protein receptor (B). Each hormone of the endocrine system has a unique molecular shape, which fits into a specific receptor protein on its target cells. LIPID‐SOLUBLE AND WATER‐SOLUBLE HORMONES • LIPID‐SOLUBLE • WATER‐SOLUBLE • Can diffuse easily across cell membranes • Cannot diffuse across the cell membrane • Bind to receptor proteins inside the cell • Combine with receptor proteins on the surface of the target cell • Ac3vate specific genes which cause changes in the cell • Starts a series of reac3ons inside the cell • E.g. testosterone, estrogen, cor3sol • E.g. epinephrine, GH, thyroxine, insulin The Glands and Hormones of the Endocrine System • Many hormones are regulated by nega3ve feedback mechanisms (the response acts in opposi3on to the s3mulus). For example, ADH is released when the blood plasma concentra3on is high (and blood pressure is low). ADH s3mulates the kidneys to absorb more water, which dilutes the blood plasma (and increases blood pressure). See Fig.13.9 p.441 The Glands and Hormones of the Endocrine System • Many hormones from the hypothalamus and pituitary are called tropic hormones (s3mulate endocrine glands to produce other hormones). The generalized regulatory pathway of tropic hormones. Chapter 13 Hormonal Regula3on of Homeostasis In Sec3on 2, you will learn that: • The hypothalamus regulates the pituitary gland, which secretes tropic hormones that affect various endocrine glands. • Human growth hormone mainly affects bone and muscle growth. The thyroid hormones s3mulate metabolism. Hormonal Regula3on of Growth, Development, and Metabolism • The hypothalamus controls the pituitary gland. The pituitary gland has two lobes (and is about the size of a pea!) that store and release tropic hormones, which are regulated by nega3ve feedback mechanisms. Hormonal Regula3on of Growth, Development, and Metabolism • The anterior pituitary gland releases human growth hormone (hGH), which s3mulates fat metabolism, and targets the liver to release hormones that s3mulate protein synthesis, and muscle and bone growth. HUMAN GROWTH HORMONE • Too much hGH during childhood can result in gigan3sm • Too li\le hGH during childhood can result in pituitary dwarfsim • Too much hGH in adulthood can result in acromegaly • Advances in gene3c engineering have allowed for produc3on of synthe3c hGH using bacteria THE ANTERIOR PITUITARY • Other hormones released by the anterior pituitary include: 1) Prolac3n (PRL) ‐ s3mulates milk produc3on in the breast 3ssue a^er birth 2) Thyroid‐s3mula3ng hormone (TSH) – s3mulates the thyroid to produce its hormes ‐ thyroxine (T4) and calcitonin 3) Adrenocor3cotropic hormone (ACTH) – s3mulates the adrenal cortex to produce cor3sol 4) Follicle s3mula3ng hormone (FSH) – s3mulates follicle development in the ovaries and sperm development in the testes 5) Leutenizing hormone (LH) – plays a role in the male and female reproduc3ve systems THE POSTERIOR PITUITARY • Stores hormones released by the hypothalamus: 1) Oxytocin – s3mulates uterine contrac3ons and contrac3ons in the breast 3ssue to help release milk from the milk ducts 2) Ani3diure3c hormone (ADH) – makes the distal tubules of the kidneys more permeable to water (more water retained by the body) THE THYROID GLAND • secretes hormones that regulate cell metabolism, growth, and development • controls the rate at which the body metabolizes fats, proteins and carbohydrates DISORDERS OF THE THYROID GLAND • Cre3nism can occur if the thyroid doesn’t develop properly during childhood • This can cause hypothyroidism • Adults with hypothyroidism tend to feel 3red, have a slow heart rate, have puffy skin, and experience hair loss and weight gain • Overproduc3on of thyroxine is called hyperthyroidism • Symptoms include anxiety, insomnia, heat intolerance, irregular heartbeat and weight loss • A condi3on called Graves’ disease occurs when the body’s own immune system a\acks the thyroid – it is an extreme form of hyperthyroidism • Symptoms include swelling around the eyes that makes them appear to protrude (and interferes with vision) Hormonal Regula3on of Growth, Development, and Metabolism • Thyroxine (T4) is required for healthy mental and physical development during childhood, and an ac3ve metabolism throughout life. Thyroxine contains iodine, and thus people require iodine in the diet. Iodine is added to table salt to prevent hypothyroidism, a condition in which the thyroid gland does not produce enough thyroxine. Hormonal Regula3on of Growth, Development, and Metabolism • Thyroxine secre3on is regulated by the release of thyroid‐s3mula3ng hormone (TSH) from the anterior pituitary. TSH is regulated by nega3ve feedback by thyroxine on the hypothalamus and pituitary. 1. Releasing hormone from hypothalamus stimulates anterior pituitary 2. Anterior pituitary releases TSH into bloodstream 3. TSH targets thyroid 4. Thyroid secretes thyroxine into bloodstream 5. High levels of thyroxine cause negative feedback, shutting down production of TSH Hormonal Regula3on of Growth, Development, and Metabolism • The thyroid gland also produces calcitonin, which helps lower blood calcium levels (by s3mula3ng uptake of calcium by the bones) • The parathyroid glands secrete parathyroid hormone (PTH), which raises blood calcium levels (by s3mula3ng bone cells to release calcium) Chapter 13 Hormonal Regula3on of Homeostasis In Sec3on 3, you will learn that: • The hormones of the adrenal glands regulate the short‐term and long‐term stress responses. 13.3 Hormonal Regula3on of the Stress Response • The adrenal glands release several hormones involved in the body’s response to stress. 13.3 Hormonal Regula3on of the Stress Response • Each adrenal gland is composed of an outer layer called the adrenal cortex, and an inner part called the adrenal medulla. The adrenal medulla is s3mulated by neurons from the hypothalamus. 13.3 Hormonal Regula3on of the Stress Response • In the short‐term stress response, also called the fight‐or‐flight response, the adrenal medulla is s3mulated to release epinephrine and norepinephrine. These hormones increase the body’s metabolism, breathing rate, and heart rate. This provides more energy for the body to respond to danger. 13.3 Hormonal Regula3on of the Stress Response • When the body is under stress, the hypothalamus secretes a releasing hormone. The releasing hormone s3mulates the anterior pituitary to release adrenocor3cotropic hormone (ACTH), which s3mulates the adrenal cortex to release cor3sol, a steroid hormone. 13.3 Hormonal Regula3on of the Stress Response • Cor3sol triggers the metabolism of proteins and fats to produce glucose. Cor3sol also suppresses the immune system, which is probably one reason that chronic stress is unhealthy. • Cor3sol secre3on is suppressed by nega3ve feedback to the hypothalamus and anterior pituitary. 13.3 Hormonal Regula3on of the Stress Response • The adrenal cortex also secretes aldosterone, which s3mulates the kidneys to absorb sodium and thus water. This increases the blood pressure. When homeostasis is reached, nega3ve feedback shuts off the secre3on of aldosterone. • Low aldosterone causes low blood pressure, an imbalance of electrolytes (sodium and potassium ions) in the blood, and unhealthy weight loss, which are symptoms of Addison’s disease. Chapter 13 Hormonal Regula3on of Homeostasis In Sec3on 4, you will learn that: • The hormones of the pancreas act antagonis3cally to maintain blood glucose levels within a narrow range. Diabetes results from improper regula3on of blood glucose. 13.4 Hormonal Regula3on of Blood Sugar • Blood glucose levels must stay within a narrow range for the body to maintain homeostasis. 13.4 Hormonal Regula3on of Blood Sugar • The islets of Langerhans in the pancreas contain beta cells, which secrete insulin in response to high levels of blood glucose. • The islets of Langerhans also contain alpha cells, which secrete glucagon in response to low levels of blood glucose. 13.4 Hormonal Regula3on of Blood Sugar • Insulin s3mulates the cells of the liver to take up and store glucose. • Other cells respond to insulin by taking up more glucose for cellular respira3on. 13.4 Hormonal Regula3on of Blood Sugar • Glucagon s3mulates the liver cells to break down glycogen, which releases glucose. 13.4 Hormonal Regula3on of Blood Sugar • If the beta cells are destroyed, Type 1 diabetes results. Type 2 diabetes develops when the insulin receptors on the cells do not respond properly to insulin. Pancreatic cells from someone with type 1 diabetes