Body control systems. Body control systems. Endocrine System. Why do hormones only affect certain cells? Classes of hormones.

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1 Body control systems Nervous system Controls body activities thru nerve impulses and neurotransmitters Quick Sends message directly to target organ Endocrine System Endocrine glands release hormones into bloodstream Hormones are carried to all cells of the body, but only affect certain cells Regulate the metabolism of target cells Body control systems Endocrine system Controls body activities by releasing hormones Slower responses Broader influence Hormones are carried by the blood to target cells Endocrine cell Membraneenclosed sacs Target cell Receptor Adrenal glands (type of endocrine gland), which sit atop the kidneys Why do hormones only affect certain cells? Hormones only affect target cells, cells that have receptors for that specific hormone Figure 25.1 Classes of hormones Peptide hormones Target cell Receptor Blood vessel Hormone molecules Short chains of amino acids Most common type of hormone Water soluble, circulate in a free form (not attached to plasma s) Steroid hormones Lipid-soluble, can diffuse thru cell s Bind to transport s in blood

2 Action of steroid hormones Action of peptide hormones Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Hormone binds to a receptor in the plasma. Hormone binds to a plasma receptor Activates a signal transduction pathway in the cell Alters cell functions peptide hormone (first messenger) 1. activated receptor enzyme Binding leads to activation of an enzyme that changes ATP to camp. plasma ATP 3. camp (second messenger) 3. camp activatesan enzyme cascade. 4. Many molecules of glycogen are broken down to glucose, which enters the bloodstream. glucose (leaves cell and goes to blood) glycogen steroid hormone 1. Hormone diffuses through plasma because it is lipid soluble. capillary 4. Diffuse thru Bind to receptors inside target cells plasma cytoplasm nucleus 2. Hormone binds to receptor inside nucleus. The hormone-receptor complex binds to the DNA and alters gene expression New s are made changes the cell s activity receptor DNA mrna 3. Hormone-receptor complex activates gene and synthesis of a specific mrna molecule follows. Action of epinephrine on muscle Mechanism of action: estrogen Estrogen stimulates cell growth in the breast and other parts of the body Binds to estrogen receptors inside the cell Switches on/off gene transcription ribosome mrna 4. mrna moves to ribosomes, and synthesis occurs. Master endocrine glands: the hypothalamus and Hypothalamus major link between nervous and endocrine system Hypothalamus secretes 9 hormones, the secretes 7. Together these hormones regulate all aspects of growth, development, metabolism, and homeostasis The Hypothalamus Is the main control center of the endocrine system. Integrates nervous and endocrine control Receives information from the nervous system Secretes hormones It controls secretion of hormones by the gland Pituitary Gland The gland is located in the sphenoid bone Two lobes Anterior Posterior

3 Infundibulum (stalk) The posterior Posterior Anterior Is actually an extension of the hypothalamus It stores and secretes hormones made in the hypothalamus Such as ADH Infundibulum (stalk) The anterior Posterior Anterior Synthesizes and secretes several hormones directly into the blood FSH, LH, and prolactin Secretion regulated by Hormones from the hypothalamus Negative feedback Control of Hormone Secretion Human growth hormone Most hormones are released in short bursts Hormone secretion is controlled by 1. Signals from the nervous system 2. Chemical changes in the blood 3. Other hormones Most hormone secretion is regulated by negative feedback TSH Has a broad effect on the body Causes cells in liver, muscles, bones and other tissues to grow and multiply Increase breakdown of fat in adipose tissue Releases fatty acids for ATP production Pituitary gland disorders Pituitary gland disorders Disorders of hgh secretion Overproduction of hgh during childhood Giantism Overproduction of hgh during adulthood results in acromegaly Enlarged bones in hands, feet and face Disorders of hgh secretion Underproduction of hgh during childhood Dwarfism

4 Hormones regulate the rate of metabolism Thyroxine (T3/T4) Thyroid Gland Secreted by the thyroid gland Increases the metabolic rate hgh Insulin Located in the neck Thyroid follicles produce thyroid hormones T4 = Thyroxine T3 = Triiodothyronine Both increase BMR, stimulate cell metabolism T3 and T4 production Low blood T3/T4 or low metabolic rate Release of TRH Release of TSH Actions of T3/T4 1 Low blood levels of T3 and T 3 or low metabolic rate stimulate release of Hypothalamus TRH by hypophyseal portal veins to anterior, stimulates release of TSH by thyrotrophs 3 TSH released into blood stimulates thyroid follicular cells Synthesis of T3 and T4 by thyroid gland Negative feedback 5 Elevated T3inhibits release of TRH and TSH (negative feedback) Too little thyroid hormone Results from dietary deficiency of iodine or from a defective thyroid gland Sx: Goiter enlargement of the thyroid gland Congenital hypothyroidism during fetal life or infancy severe mental retardation (cretinism) have receptors for thyroid hormones Increase basal metabolic rate (BMR) increase body temperature Growth and development released into blood by follicular cells Thyroid Gland Disorders: hypothyroidism Anterior 4 T3 and T4 Thyroid follicle Affect most body cells 2 TRH, carried TSH Stimulate synthesis Increase use of glucose and fatty acids for ATP production Why does the thyroid gland enlarge? X X

5 Hyperthyroidism Excess thyroid hormones The most common form of hyperthyroidism is Graves disease an autoimmune disease. Produce antibodies that mimic the action of TSH and continually stimulate the thyroid gland Sx: enlarged thyroid, protruding eyes (exophthalmos) Hormones and homeostasis Control of blood glucose Insulin Glucagon Calcium homeostasis Calcitonin Parathyroid hormone (PTH) Vitamin D (calcitriol) Pancreas Produces two antagonistic hormones that regulate the body s energy supplies: Insulin blood sugar levels Glucagon blood sugar levels Body cells Insulin take up more glucose Pancreas releases insulin into the blood Liver takes Blood glucose level up glucose falls to a set point; and stores it as stimulus for insulin Stimulus: Rising blood glucose glycogen release diminishes level (for example, after Glucose eating a carbohydrate-rich level meal) Homeostasis: Normal blood glucose level Stimulus: Declining blood Glucose glucose level level (for example, after skipping a meal) Blood glucose level rises to set point; Pancreas releases stimulus for glucagon glucagon into the blood release diminishes Liver breaks down glycogen and releases glucose Glucagon to the blood Figure How insulin stimulates glucose uptake In the absence of insulin, the glucose transporters reside within the cell Insulin binds to its receptor Glucose transporters are moved to plasma They are inserted in the, and glucose transport is activated Pancreatic Disorders Diabetes Mellitus Most common endocrine disorder Caused by an inability to produce or use insulin Sx: high blood glucose, glucose spills into urine Type 1 diabetes (insulin-dependent diabetes) Insulin level is low because the person s immune system destroys the pancreatic Beta cells Type 2 diabetes Target cells are less sensitive to insulin due to lower # of insulin receptors Gestational diabetes

6 Type I Diabetes Autoimmune disease Occurs most often in children and young adults Without insulin, cells use fatty acids for energy Complications: damage to blood vessels in retina and kidneys Rx: insulin injections Insulin and type 1 diabetes (4:03) Type 2 diabetes Most common form 90% of diabetics 55% are obese Insulin resistance body tissues more resistant to the actions of insulin Lower uptake of glucose Can be controlled by diet, exercise and weight loss Gestational diabetes Pregnant women who have never had diabetes before but who have high blood glucose levels during pregnancy Affects about 4% of all pregnant women It may precede development of type 2 diabetes Calcium homeostasis Calcitonin Parathyroid hormone Calcitriol (vitamin D) Why is calcium important? Bone formation Muscle contraction Cardiac muscle action potential Blood clotting Neurotransmitter release Calcium Homeostasis Three hormones regulate blood calcium levels Calcitonin Parathyroid hormone (PTH) Calcitriol (vitamin D) Calcitriol (vitamin D)