Chapter 20. Endocrine System Chemical signals coordinate body functions Chemical signals coordinate body functions. !

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1 26.1 Chemical signals coordinate body functions Chapter 20 Endocrine System! Hormones Chemical signals Secreted by endocrine glands Usually carried in the blood Cause specific changes in target cells Secretory vesicles Endocrine cell Blood vessel Target cell 26.1 Chemical signals coordinate body functions! The endocrine system Consists of all hormone-secreting cells Works with nervous system to regulate body activities Hormone molecules

2 26.1 Chemical signals coordinate body functions! Comparing the endocrine and nervous systems Nervous system reacts faster Uses electrical signals via nerve cells Endocrine system responses last longer Uses hormones via blood 26.2 Hormones affect target cells by two main signaling mechanisms! Hormone signaling involves three key events Reception Signal Transduction Response 26.2 Hormones affect target cells by two main signaling mechanisms! Amino-acid-derived hormones Are water-soluble Include proteins, peptides, and amines Bind to plasma-membrane receptors on target cells Initiate a signal transduction pathway Water-soluble hormone (epinephrine) 1 Target cell Relay molecules 2 3 Receptor protein Plasma membrane Signal transduction pathway Glycogen Glucose Cellular response (in this example, glycogen breakdown) Animation: Water-Soluble Hormone

3 26.2 Hormones affect target cells by two main signaling mechanisms Lipid-soluble hormone (testosterone) 1! Steroid hormones Nonpolar lipids made from cholesterol Target cell 2 Receptor protein Can diffuse through plasma membranes Bind to a receptor protein in the cytoplasm or nucleus Hormone-receptor complex carries out the transduction of the hormonal signal 3 Nucleus DNA 4 mrna Hormonereceptor complex Transcription New protein Animation: Lipid-Soluble Hormone Cellular response: activation of a gene and synthesis of new protein 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands! The vertebrate endocrine system Consists of more than a dozen glands Secretes more than 50 hormones Thyroid gland Parathyroid glands Thymus Adrenal glands (atop kidneys) Pancreas Hypothalamus Pineal gland Pituitary gland Ovary (female) Testes (male)

4 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands! Hormones Some have a very narrow range of targets and effects Some have numerous effects on many kinds of target cells 26.4 The hypothalamus, which is closely tied to the pituitary, connects the nervous and endocrine systems! The hypothalamus Blurs the distinction between endocrine and nervous systems Receives input from nerves about body conditions Responds by sending out appropriate nervous or endocrine signals Uses the pituitary gland to exert master control over the endocrine system

5 26.4 The hypothalamus, which is closely tied to the pituitary, connects the nervous and endocrine systems! The pituitary gland consists of two parts Brain Posterior pituitary Composed of nervous tissue Hypothalamus Stores and secretes oxytocin and ADH Posterior pituitary Anterior pituitary (Bone) Hormone Posterior pituitary Hypothalamus Neurosecretory cell 26.4 The hypothalamus, which is closely tied to the pituitary, connects the nervous and endocrine systems! Anterior pituitary Synthesizes and secretes hormones that control the activity of other glands Oxytocin Blood vessel ADH Anterior pituitary Is controlled by the hypothalamus Releasing hormones stimulate the anterior pituitary Inhibiting hormones inhibit the anterior pituitary Uterine muscles Mammary glands Kidney tubules

6 Blood vessel Releasing hormones from hypothalamus Neurosecretory cell Endocrine cells of the anterior pituitary 26.5 The thyroid regulates development and metabolism! Thyroid gland hormones Thyroxine (T 4 ) and triiodothyronine (T 3 ) Regulate Metabolism Development Pituitary hormones TSH ACTH FSH Prolactin and (PRL) LH Thyroid Adrenal cortex Testes or Mammary ovaries glands (in mammals) Growth hormone (GH) Entire body Endorphins Pain receptors in the brain Negative feedback Maintains homeostatic s of T 4 and T 3 in the blood Hypothalamus TRH Anterior pituitary Thyroid TSH Thyroxine Inhibition Inhibition 26.5 The thyroid regulates development and metabolism! Thyroid imbalance can cause disease Hyperthyroidism Too much T 4 and T 3 in the blood Leads to high blood pressure, loss of weight, overheating, and irritability Produces Graves disease Hypothyroidism Too little T 4 and T 3 in the blood Leads to low blood pressure, overweight, often cold, lethargy

7 Hypothalamus Anterior pituitary Thyroid TRH TSH No inhibition No inhibition No iodine Insufficient T 4 and T 3 produced 26.6 Hormones from the thyroid and parathyroids maintain calcium homeostasis! Blood calcium is regulated by a tightly balanced antagonism between Calcitonin from the thyroid gland Parathyroid hormone (PTH) from the parathyroid glands Thyroid grows to form goiter Ca 2+ 7 Calcitonin 8 Blood Ca 2+ rises 5 Increases Ca 2+ uptake in intestines Active vitamin D 4 Homeostasis: Normal blood calcium (about 10 mg/100 ml) Increases Ca 2+ uptake in kidneys Stimulates Ca 2+ release from bones Ca 2+ 3 Stimulus: Falling blood Ca 2+ (imbalance) PTH 2 1 Parathyroid glands release parathyroid hormone (PTH) Parathyroid gland Thyroid gland releases calcitonin 6 Stimulus: Rising blood Ca 2+ (imbalance) Ca 2+ Homeostasis: Normal blood calcium (about 10 mg/100 ml) Ca 2+ Stimulates Ca 2+ deposition in bones 9 Reduces Ca 2+ uptake in kidneys Blood Ca 2+ falls

8 26.7 Pancreatic hormones regulate blood glucose s! The pancreas secretes two hormones that control blood glucose Insulin signals cells to use and store glucose Glucagon causes cells to release stored glucose into the blood Beta cells of pancreas stimulated to release insulin into the blood 1 2 High blood glucose Insulin 3 Body cells take up more glucose Liver takes up glucose and stores it as glycogen Blood glucose declines to a set point; stimulus for insulin release diminishes 4 Stimulus: Rising blood glucose (e.g., after eating a carbohydrate-rich meal) Glucose Homeostasis: Normal blood glucose (about 90 mg/100 ml) Glucose Blood glucose rises to set point; stimulus for glucagon release diminishes 8 Glucose Homeostasis: Normal blood glucose (about 90 mg/100 ml) Liver breaks down glycogen and releases glucose to the blood 7 Glucose Glucagon Stimulus: Declining blood glucose (e.g., after skipping a meal) 6 Alpha cells of pancreas stimulated to release glucagon into the blood 5 Low blood glucose 26.8 CONNECTION: Diabetes is a common endocrine disorder! Diabetes mellitus Results from A lack of insulin or A failure of cells to respond to it Affects about 21 million Americans

9 26.8 CONNECTION: Diabetes is a common endocrine disorder! Two common types of diabetes mellitus Type 1 (insulin-dependent) 26.9 The adrenal glands mobilize responses to stress! Hormones from the adrenal glands help maintain homeostasis when the body is stressed Autoimmune disease Insulin-producing cells destroyed Type 2 (non-insulin-dependent) Deficiency of insulin More commonly, reduced response to insulin More than 90% of diabetics are type 2 Associated with being overweight and underactive 26.9 The adrenal glands mobilize responses to stress! Nerve signals from the hypothalamus stimulate the adrenal medulla to secrete Epinephrine (Adrenaline) Norepinephrine! These hormones quickly trigger the fight-or-flight responses 26.9 The adrenal glands mobilize responses to stress! Adrenocorticotropic hormone (ACTH) from the pituitary causes the adrenal cortex to secrete Glucocorticoids Mineralocorticoids! These hormones Boost blood pressure Boost energy in response to long-term stress

10 26.10 The gonads secrete sex hormones The gonads secrete sex hormones! Steroid sex hormones Include estrogens, progestins, and androgens Produced by the gonads in response to signals from Hypothalamus! Estrogens and progestins Stimulate the development of female characteristics Maintain the female reproductive system Pituitary The gonads secrete sex hormones! Androgens Such as testosterone Trigger the development of male characteristics EVOLUTION CONNECTION: A single hormone can perform a variety of functions in different animals! Prolactin in humans Stimulates mammary glands to grow and produce milk during late pregnancy Suckling by a newborn stimulates further release of prolactin High prolactin during nursing inhibits ovulation