Nerves, Hormones & Homeostasis

Assessment StatementsObj State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that carry rapid electrical impulses Draw and label a diagram of the structure of a motor neuron State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons Define resting potential and action potential (depolarisation and repolarisation) Explain how a nerve impulse passes along a non-myelinated neuron Explain the principles of synaptic transmission State that the endocrine system consists of glands that release hormones that are transported in the blood State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms Explain the control of body temperature, including the transfer of heat in the blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering Explain the control of blood glucose concentration, including the roles of insulin, glucagon and α and β cells Distinguish between type I and type II diabetes. 2 Assessment statements from: Online IB Biology Subject GuideOnline IB Biology Subject GuideCommand terms:

Diagram from: The Motor Neuron nerve impulse

From McGraw Hill:

Insulin and Glucagon: Control of Blood Glucose Two types of cells in the pancreas – Secrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis Glucagon – Is produced by alpha cells Insulin – Is produced by beta cells

Maintenance of glucose homeostasis Beta cells of pancreas are stimulated to release insulin into the blood. Insulin Liver takes up glucose and stores it as glycogen. Body cells take up more glucose. Blood glucose level declines to set point; stimulus for insulin release diminishes. STIMULUS: Rising blood glucose level (for instance, after eating a carbohydrate- rich meal) Homeostasis: Blood glucose level (about 90 mg/100 mL ) Blood glucose level rises to set point; stimulus for glucagon release diminishes. STIMULUS: Dropping blood glucose level (for instance, after skipping a meal) Alpha cells of pancreas are stimulated to release glucagon into the blood. Liver breaks down glycogen and releases glucose into blood. Glucagon Figure 45.12

High blood glucose levels Low blood glucose levels 1. pancreas (beta) produces insulin 2. Insulin stimulates muscle and liver to take glucose from blood and convert to glycogen. 3. resulting in lowering the glucose level in the blood. 1. pancreas (alpha) produces glucagon 2. Glucagon stimulates liver to convert glycogen back into glucose. 3. releasing of glucose into blood

Diabetes mellitus, perhaps the best-known endocrine disorder – Caused by a deficiency of insulin or a decreased response to insulin in target tissues – Is marked by elevated blood glucose levels Type I diabetes mellitus (insulin-dependent diabetes) – Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas – Juvenile Type II diabetes mellitus (non-insulin-dependent diabetes) – Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors – Adults – Body produces insulin, pancreas either cant produce enough or body cant use it adequately (glucose cant get into cells so there is a build up of glucose in blood)