Chapter 20 Endocrine System The endocrine system consists of glands and tissues that secrete Hormones are chemicals that affect other glands or tissues, many times far away from the site of hormone production Hormones carried in the blood stream to body regions distant from the site of production Exception: Local are not carried in blood but affect neighboring s 1 Endocrine glands Are ductless Secrete into tissues Hormones then diffuse into the bloodstream Exocrine glands Secrete their products through ducts Salivary glands send saliva to the mouth through salivary ducts Pancreas is both endocrine and exocrine gland Endocrine function: secretes insulin and glucagon in surrounding tissue Exocrine function: secretes pancreatic juices into duodenum via pancreatic duct Endocrine system works with the nervous system in regulating body activities Nervous system regulates quick body responses (e.g. breathing, body movements etc) Endocrine system regulates slow body responses (e.g. growth and development) Cooperation between the endocrine and nervous systems is required for Homeostasis. Sometime distinction between Endocrine System and Nervous System is blurred Neurosecretory s are specialized s Conduct nerve signals As well as secrete into the blood Blood vessel Endocrine System Nervous System Secretes into the blood Slower response Transmits nerve impulses Faster response Neurosecretory Target More prolonged response Less prolonged response Hormone molecules 1
A few chemicals serve both as in the endocrine system And as chemical signals in the nervous system e.g. Ephinephrine (adrenaline) The Action of Hormones Hormones act on target s May increase uptake or release of a substance May bring about alteration of structure of target signals Neurotransmitter molecules receptors hormone nontarget capillary Some have a very narrow range of targets and effects Glucagon from pancreas affects only liver and fat s While others have numerous effects on many kinds of target s Sex that promote male and female characteristics affect most tissues of body Growth hormone affects large number of body s target s Two classes of Hormones: Two mechanisms of action Peptide Hormones (Water soluble or Hydrophilic) Can not physically cross the membrane Bind to receptor proteins projecting out from the s plasma membrane Steroid Hormones (Lipid Soluble or Hydrophobic) Diffuse across membrane into the Receptor inside (cytoplasm or nucleus) Both mechanisms involve Three events Reception Binding of hormone to receptor on or inside the Signal Transduction Cellular events triggered by hormone-receptor complex Response Change in s behavior 2
Peptide Hormone Action capillary epinephrine (first messenger) 1. Epinephrine binds to a receptor in the plasma membrane. Steroid Hormone Action 1. Hormone diffuses through plasma membrane because it is lipid soluble. steroid hormone plasma membrane cytoplasm activated enzyme receptor protein nucleus 2. Hormone binds to receptor inside nucleus. 2. Binding leads to activation of an enzyme that changes ATP to camp. camp (second messenger) ATP plasma membrane 3. camp activates an enzyme cascade. glucose (leaves and goes to blood) 4. Many molecules of glycogen are broken down to glucose, glycogen which enters the bloodstream. receptor DNA protein mrna 3. Hormone-receptor complex activates gene and synthesis of a specific mrna molecule. protein ribosome mrna 4. mrna moves to ribosomes, and protein synthesis occurs. The Endocrine System The Endocrine System The endocrine system Consists of more than a dozen glands secreting more than 50 Only the sex organs and the cortex of the adrenal gland produce steroid Most of the endocrine glands produce water-soluble thyroid gland parathyroid glands (posterior surface o f thyroid) adrenal glands pineal gland hypothalamus gland (hypophysis) thymus gland pancreas ovary (female) testis (male) The hypothalamus, closely tied to the, connects the nervous and endocrine systems Production of controlled by: Negative Feedback Action of other Insulin and glucagon data to control center Sensor change of internal conditions stimulus Control center Homeostasis response to stimulus Effect negative feedback and return to normal The hypothalamus in the brain receives information from nerves about the internal condition of the body and about the external environment exerts master control over the endocrine system Uses the gland to relay directives to other glands Brain Posterior Anterior Bone 3
The posterior Secretes oxytocin and antidiuretic hormone (ADH) These are made in hypothalamus Hormone Posterior Neurosecretory The hypothalamus exerts control over the anterior by secreting two kinds of releasing inhibiting into short blood vessels that connect the two organs Blood vessel Releasing from hypothalamus Neurosecretory Releasing from Blood vessel Oxytocin Anterior ADH Pituitary TSH ACTH FSH Growth Prolactin and hormone (PRL) LH (GH) Endocrine s of the anterior Endorphins The anterior Secretes TSH, ACTH, FSH and LH, growth hormone, prolactin, and endorphins Uterine muscles contract Mammary glands eject milk Kidney tubules reabsorb water Thyroid Adrenal Testes or Entire Mammary Pain cortex ovaries body glands receptors (in mammals) in the brain Secretion of thyroxine by the thyroid gland Is controlled by a negative-feedback mechanism HORMONES AND HOMEOSTASIS The thyroid regulates development and metabolism TRH Anterior Thyroid TSH Inhibition Inhibition Two from the thyroid gland, T 4 and T 3 Regulate an animal s development and metabolism Maintain blood pressure, heart rate, muscle tone, digestion and reproductive functions Too much or too little of these can result in severe metabolic disorders Thyroxine Iodine deficiency causes Goiter Negative feedback Maintains homeostatic levels of T 4 and T 3 in the blood Anterior TRH No inhibition No inhibition Hormones and Calcium Homeostasis 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 Thyroid TSH No iodine Insufficient T 4 and T 3 produced Thyroid grows to form goiter 4
Blood glucose (mg/100ml) 10/21/2011 Thyroid gland releases calcitonin Rising blood Ca 2+ level (imbalance) Calcium homeostasis Blood Ca 2+ rises Active vitamin D Stimulates Increases Increases Ca 2+ release Ca 2+ uptake Ca 2+ uptake PTH from bones in kidneys in intestines Calcitonin Stimulates Reduces Ca 2+ deposition Ca 2+ uptake in bones in kidneys Blood Ca 2+ falls Homeostasis: Normal blood calcium level (about 10 mg/100ml) Falling blood Ca 2+ level (imbalance) Parathyroid glands release parathyroid hormone (PTH) Parathyroid gland Hormones and Glucose Homeostasis Pancreatic regulate blood glucose levels The pancreas secretes two, insulin and glucagon That control blood glucose Insulin and Glucagon are antagonistic Insulin Signals s to use and store glucose Glucagon Causes s to release stored glucose into the blood Glucose homeostasis Body s Insulin take up more glucose 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 by a test called a glucose tolerance test Beta s of pancreas stimulated to release insulin into the blood High blood glucose level Liver takes up glucose and stores it as glycogen Blood glucose level declines to a set point; stimulus for insulin release diminishes 400 350 Rising blood glucose level (e.g., after eating a carbohydrate-rich meal) Homeostasis: Normal blood glucose level (about 90 mg/100ml) Declining blood glucose level (e.g., after skipping a meal) 300 250 200 Diabetic 150 Blood glucose level rises to set point; stimulus for glucagon release diminishes Liver breaks down glycogen and releases glucose to the blood Glucagon Alpha s of pancreas stimulated to release glucagon into the blood 100 50 0 0 1 2 Normal 1 2 3 4 5 Hours after glucose ingestion Adrenal Glands and Control of Stress Response The adrenal glands mobilize responses to stress Hormones from the adrenal glands Help maintain homeostasis when the body is stressed Short term Stress response signals from the hypothalamus Stimulate the adrenal medulla to secrete epinephrine and norepinephrine, which quickly trigger the fight-orflight responses Long Term Stress response Releasing hormone from causes secretion of ACTH from the» causes the adrenal cortex to secrete glucocorticoids and mineralocorticoids» Boost blood pressure and energy in response to longterm stress 5
How the adrenal glands control our responses to stress Kidney Adrenal gland Adrenal medulla Adrenal cortex Spinal cord (cross section) signals Short-term stress response Adrenal medulla Epinephrine and norepinephrine 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 ACTH Stress Releasing hormone Anterior ACTH Blood vessel Mineralocorticoids Mineralocorticoids (Control salt and water balance) 1. Retention of sodium ions and water by kidneys 2. Increased blood volume and blood pressure Long-term stress response Adrenal cortex Glucocorticoids Glucocorticoids (Mobilize ular fuels) 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose 2. Immune system may be suppressed Steroid Hormones and Sexual Development The gonads secrete sex Estrogens, progestins, and androgens are steroid sex Produced by the gonads in response to signals from the hypothalamus and 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 6