Chapter 20 Endocrine System Endocrine Glands and Hormones The endocrine system consists of glands and tissues that secrete hormones Hormones are chemicals that affect other glands or tissues, many times far away from the site of hormone production Endocrine glands Secrete hormones into the bloodstream Hormones cause specific changes in target s Birgit Woelker, PhD The Endocrine System pineal gland hypothalamus gland (hypophysis) thyroid gland thymus gland parathyroid glands (posterior surface o f thyroid) adrenal glands pancreas ovary (female) testis (male)
Secretory vesicles Hormones are secreted by endocrine glands and neurosecretory s Blood vessel Blood vessel All hormone-secreting s make up the endocrine system Which works with the nervous system in regulating body activities Target Neurosecretory Target Endocrine Hormone molecules Hormone molecules A few chemicals ( e.g. adrenaline /epinephrine) serve both as hormones in the endocrine system and as chemical signals in the nervous system signals Neurotransmitter molecules Hormones affect target s by two main signaling mechanisms Water-soluble hormones such as proteins and amines Bind to plasmamembrane receptors on target s Water-soluble hormone (epinephrine) Target Relay molecules 1 2 3 Glycogen Receptor protein Plasma membrane Signal transduction pathway Glucose Cellular response (in this example, glycogen breakdown)
Steroid hormones, such as the sex hormones estrogen and testosterone Diffuse through the plasma membrane of target s and bind to intraular receptors Lipid-soluble hormone (testosterone) Target DNA Nucleus mrna 1 2 3 4 Receptor protein Hormonereceptor complex Transcription New protein Cellular response: activation of a gene and synthesis of new protein Some endocrine glands and their functions : Hormones released by the posterior gland and those that regulate the anterior gland Pituitary gland posterior lobe : Oxytocin, Antidiuretic Hormone (ADH), anterior lobe: Growth Hormone (GH), Thyroid stimulating Hormone (TSH), ACTH (Adrenocorticotropic Hormone) Pineal gland: Melatonin Thyroid gland: Thyroxine (T4) and Triiodothyronine (T3) Calcitonin Adrenal gland: Epinephrine (Adrenaline), Norepinephrine Pancreas: Insulin and Glucagon Testes: Androgens (Testosterone) Ovaries: Estrogens The hypothalamus, closely tied to the, connects the nervous and endocrine systems The hypothalamus exerts master control over the endocrine system By using the gland to relay directives to other glands The posterior Secretes oxytocin and antidiuretic hormone (ADH) Hormone Posterior Neurosecretory Brain Blood vessel Anterior Posterior Anterior Bone Oxytocin Uterine muscles Mammary glands ADH Kidney tubules
The anterior Secretes TSH, ACTH, FSH and LH, growth hormone, prolactin, and endorphins Releasing and inhibiting hormones from the hypothalamus Control the secretion of several other hormones Neurosecretory Blood vessel Releasing hormones from hypothalamus TSH for instance controls the secretion of T4 and T3 from the Thyroid gland Endocrine s of the anterior Pituitary hormones TSH ACTH FSH and LH Thyroid Adrenal cortex Growth Prolactin Endorphins hormone (PRL) (GH) Testes or Entire ovaries body Mammary glands (in mammals) Pain receptors in the brain Secretion of thyroxine by the thyroid gland Is controlled by a negative-feedback mechanism Inhibition HORMONES AND HOMEOSTASIS The thyroid regulates development and metabolism Two hormones from the thyroid gland, T 4 and T 3 Regulate an animal s development and metabolism TRH Anterior Inhibition TSH Thyroid Thyroxine
Thyroid imbalance can cause disease like Grave s disease Negative feedback Maintains homeostatic levels of T 4 and T 3 in the blood No inhibition TRH Anterior No inhibition Thyroid TSH No iodine Insufficient T 4 and T 3 produced Marty Feldman Thyroid grows to form goiter Hormones from the thyroid and parathyroids maintain calcium homeostasis Blood calcium level is regulated by a tightly balanced antagonism Between calcitonin from the thyroid and parathyroid hormone from the parathyroid glands Calcium homeostasis Thyroid gland releases calcitonin Stimulus: Rising blood Ca 2+ level (imbalance) Stimulates Ca 2+ release from bones Blood Ca 2+ rises Active vitamin D Increases Ca 2+ uptake in kidneys Calcitonin Homeostasis: Normal blood calcium level (about 10 mg/100ml) Increases Ca 2+ uptake in intestines PTH Stimulates Ca 2+ deposition in bones Reduces Ca 2+ uptake in kidneys Blood Ca 2+ falls Stimulus: Falling blood Ca 2+ level (imbalance) Parathyroid glands release parathyroid hormone (PTH) Parathyroid gland
Pancreatic hormones regulate blood glucose levels The pancreas secretes two hormones, insulin and glucagon that control blood glucose Glucose homeostasis Beta s of pancreas stimulated to release insulin into the blood High blood glucose level Insulin Body s take up more glucose Liver takes up glucose and stores it as glycogen Blood glucose level declines to a set point; stimulus for insulin release diminishes Insulin Signals s to use and store glucose Glucagon Causes s to release stored glucose into the blood Stimulus: Rising blood glucose level (e.g., after eating a carbohydrate-rich meal) Blood glucose level rises to set point; stimulus for glucagon release diminishes Homeostasis: Normal blood glucose level (about 90 mg/100ml) Liver breaks down glycogen and releases glucose to the blood Glucagon Stimulus: Declining blood glucose level (e.g., after skipping a meal) Alpha s of pancreas stimulated to release glucagon into the blood Diabetes is a common endocrine disorder Diabetes mellitus Results from a lack of insulin or a failure of s to respond to it Diabetes can be detected 400 By a test called a glucose tolerance test Blood glucose (mg/100ml) 350 300 250 200 150 Diabetic 100 Normal 50 0 Figure 26.8 0 1 2 1 2 3 4 5 Hours after glucose ingestion
The adrenal glands mobilize responses to stress Hormones from the adrenal glands Help maintain homeostasis when the body is stressed signals from the hypothalamus Stimulate the adrenal medulla to secrete epinephrine and norepinephrine, which quickly trigger the fight-or-flight responses ACTH from the causes the adrenal cortex to secrete glucocorticoids and mineralocorticoids Which boost blood pressure and blood glucose in response to long-term stress How the adrenal glands control our responses to stress Kidney Adrenal gland Adrenal medulla Adrenal cortex Spinal cord (cross section) signals ACTH Stress Releasing hormone Anterior Blood vessel Adrenal medulla ACTH Adrenal cortex Epinephrine and norepinephrine Mineralocorticoids Glucocorticoids Short-term stress response Long-term stress response 1. Glycogen broken down to glucose; increased blood glucose 2. Increased blood pressure 3. Increased breathing rate 4. Increased metabolic rate 5. Change in blood-flow patterns, leading to increased alertness and decreased digestive and kidney activity Mineralocorticoids 1. Retention of sodium ions and water by kidneys 2. Increased blood volume and blood pressure Glucocorticoids 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose 2. Immune system may be suppressed
Glucocorticoids offer relief from pain, but not without serious risks Glucocorticoids relieve inflammation and pain But they can mask injury and suppress immunity The gonads secrete sex hormones Estrogens, progestins, and androgens are steroid sex hormones Produced by the gonads in response to signals from the hypothalamus and Bill Walton Estrogens and progestins stimulate the development of female characteristics and maintain the female reproductive system Androgens, such as testosterone Trigger the development of male characteristics
Establishing links between androgens and human male aggression Has been found to be problematic Does testosterone play a role in aggressive behavior?