1. Bill Explain how a nerve impulse passes through a neuron Resting potential creates electrical chemical gradient between external and internal environments of neuron, creating membrane potential Depolarization occurs, where Na and K ions diffuse in and out of membrane channels, creating nerve impulse Self-propagating action, travels down the axon Repolarization occurs, where charges return to resting state Refractory period- when neuron cannot carry another nerve impulse until fully returned to resting potential

2. Topic 6.5 Endocrine System IB Biology II Van Roekel

3. 6.5.7 – 6.5.12 Statements 6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood. 6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms. 6.5.10 Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering. 6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and and cells in the pancreatic islets. 6.5.12 Distinguish between type I and type II diabetes.

4. Endocrine System Nervous System (autonomic nervous system) and endocrine system work closely together in order to maintain homeostasis Endocrine System: consists of all an animal’s hormone secreting cells and glands Endocrine Glands: called ductless glands because they secrete chemical messengers directly into body fluids Hormones: chemical signals formed in specialized cells that travel through body fluids and coordinate various parts of the organism by interacting with target cells

5. Hormones Two types of signaling Hormones penetrate cell membrane and bind to receptor protein inside cell Acts as transcription factor and changes gene expression Lipid-soluble hormone (testosterone) 1 Target cell Nucleus Receptor protein 2 DNA Hormone- receptor complex 3 mRNA Transcription New protein Cellular response: activation of a gene and synthesis of new protein 4

6. Plasma membrane Receptor protein Water-soluble hormone (epinephrine) 2 Signal transduction pathway Relay molecules 1 Target cell Hormone Hormones bind to external protein receptor, triggering a signal-transduction pathway Can result in either change in gene expression or cytoplasmic activity

7. Bill What are the two types of signaling pathways we see used with hormones? Internal- hormones diffuse through cell membrane and bind to intracellular protein receptor. Change gene expression/protein production External signaling- hormones bind to external protein receptor and trigger signal transduction pathway. Can alter cytoplasmic activity or gene expression

10. Homeostasis Human Body has adapted several mechanisms to deal with homeostasis (maintaining balance) Uses negative feedback mechanisms (physiological changes that bring a value back closer to a set point) to maintain homeostasis – so if levels vary too far, a series of steps occurs to return it to normal. Body must control: – blood pH – carbon dioxide concentration – blood glucose concentration – body temperature – water balance within tissues

11. Homeostasis and Negative Feedback

12. Hypothalamus and Pituitary Gland Hypothalamus: region of lower brain that receives info from nerves throughout body and initiates endocrine signals appropriate to environmental conditions (monitors levels of variables) Pituitary Gland: small organ regulated by hypothalamus that stores and/or regulated multiple endocrine secretions (initiates negative feedback mechanisms)

13. Posterior pituitary: Composed of nervous tissue; stores and secretes hormones made by hypothalamus Brain Hypothalamus: Master control center of the endocrine system Anterior pituitary: Composed of endocrine tissue; controlled by hypothalamus; produces and secretes its own hormones

14. Homeostatic Control of Body Temperature Body has thermoreceptors that detect heat and send message to hypothalamus. Hypothalamus (in conjunction with pituitary gland) senses an increase or decrease in body temp Employs mechanisms to return to maintain body temperature

15. Homeostatic control of body temp Cooling Mechanisms Increase activity of sweat glands – Causes heat loss by evaporation of water Vasodilation of blood vessels – Fills capillaries with blood, heat leaves by convection/radiation Heating Mechanisms Constricting skin arterioles so blood is diverted to deeper organs and tissues, less heat loss by convection Stimulates skeletal muscle contractions, aka shivering

17. Control of Blood Glucose Blood glucose level is the concentration of glucose in the blood plasma Cells never cease respiration, therefore you must have a constant (steady) supply of blood glucose available. Negative feedback mechanisms by the body ensure the proper uptake/release of glucose in the blood. Most blood is acted on by Hepatocytes, liver cells directed by insulin and glucagon to regulated blood glucose concentration

18. Control of Blood Glucose High Blood Glucose Levels Beta Cells in Pancreas produce and secrete insulin into blood Insulin signals to cells to open protein channels to allow diffusion of glucose into the cells for cell respiration Stimulates Hepatocytes to convert glucose into glycogen and store it as granules in cytoplasm (same in muscle cells) Lowers Glucose level in blood Low Blood Glucose Levels Alpha Cells in Pancreas produce and secrete glucagon Stimulates hydrolysis of glycogen, in hepatocytes and muscle cells, into glucose Glucose enters bloodstream Increases Glucose concentration in blood

19. Insulin 4 Beta cells of pancreas stimulated to release insulin into the blood Glucose level Homeostasis: Normal blood glucose level (about 90 mg/100 mL) Glucose level Glucagon Low blood glucose level High blood glucose level Body cells take up more glucose Blood glucose level declines to a set point; stimulus for insulin release diminishes Liver takes up glucose and stores it as glycogen Alpha cells of pancreas stimulated to release glucagon into the blood Stimulus: Declining blood glucose level (e.g., after skipping a meal) 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 Liver breaks down glycogen and releases glucose to the blood 7 6 1 2 5 8 3

21. Diabetes Disease characterized by hyperglycemia (high blood sugar) People have plenty of glucose in their blood, but not in their body cells – Type I caused when Beta cells do not produce enough insulin, treated with injection of insulin – Type II caused by body cell receptors that do not respond properly to insulin, controlled by diet

22. Diabetes Mellitus Type I – Autoimmune disorder – Body attacks and destroys beta cells, therefore no insulin is produced. – Blood sugar remains abnormally high as a result. – Less than 10% of diabetics have Type I. – Most often develops in children and young adults Type II – Body cells no longer respond to insulin (insulin resistance) – Body stops creating insulin because it has developed resistance typically caused by constant elevated blood glucose levels. – Most common (90%) – Associated with obesity, lack of exercise, advanced age, and genetics

23. Uncontrolled Diabetes If left untreated – Damage to retina, leading to blindness – Kidney Failure – Nerve damage – Increased risk of Cardiovascular disease – Poor wound healing (possibly gangrene  amputation)