HOMEOSTASIS

1 EJC H2 Biology T2W2 Homeostasis Homeostasis 1. Introduction In multicellular organisms, different parts of the body perform different functions. Communication is of utmost importance to ensure that bodily functions can be coordinated and carried out efficiently. Communication ensures that there is coordination between organs so that the organisms can function as a whole in responses to changes. In particular, the composition of the internal environment must be maintained at a narrow, optimum range to support the proper functioning of the body cells. In this segment, we will be learning about the concept of homeostasis to appreciate how such optimum conditions of the internal environment may be maintained, so that cells can function in a state of maximum efficiency. In particular, we will focus on insulin and glucagon regulation of the blood glucose concentration in the body. 2. Learning Outcomes 3 (p) Outline how insulin and glucagon regulate the concentration of blood glucose through the respective tyrosine kinase receptor and G-protein linked receptor. (The outline should be limited to describing how the ligand induces a conformational change in a membrane-bound receptor to trigger downstream signaling pathways that elicit physiological changes in blood glucose concentration. Details of different second messengers and specific kinases activated in the pathway are not required.) Students should be able to use the knowledge gained in this section in new situations or to solve related problems. 3. References  Campbell, N.A. and Reece, J.B. (2008). Biology, 8th edition. Pearson.  Sherwood, Fundamental of Human Physiology, 4th edition  Brooker et al., Biology, McGraw-Hill  Ho YK (2003) A-level course in Biology – Core syllabus, Longman

2 EJC H2 Biology T2W2 Homeostasis 4. Organisation of Lecture Content 1. Introduction 1 2. Learning Outcomes 1 3. References 1 4. Organisation of Lecture Content 2 5. Overview of Homeostasis 3 A. Definition: What is Homeostasis 3 B. The Importance of Homeostasis 4 C. The Principles of Homeostasis 4 6. Communication Systems 6 A. Hormonal Control: The Endocrine System 6 B. Hormones 7 C. Mechanisms of Hormone Action 7 D. The Pancreas: Islets of Langerhans 8 E. Blood Glucose Regulation by Insulin and Glucagon 9 I. Role of Insulin – decrease blood glucose concentration 11 II. Role of Glucagon – Increase blood glucose concentration 12

3 EJC H2 Biology T2W2 Homeostasis 5. Overview of Homeostasis A Definition: What is Homeostasis? o Homeostasis is the maintenance of a constant internal cellular environment of an organism, providing it with a degree of independence from its external environment. o It involves self-regulating and negative feedback mechanisms to control the level of substances that are to be maintained. Note: The concept of ‘self-regulating and negative feedback’ will be detailed later.  Th