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Lauralee Sherwood Hillar Klandorf Paul Yancey Chapter 1 Homeostasis and Integration: The Foundations of Physiology Kip McGilliard • Eastern Illinois University 1.1 Introduction Characteristics of living things • Organize themselves using energy and raw materials from their surroundings (metabolism) • Maintain integrity in the face of disturbances (homeostasis) • Reproduce 1.1 Introduction Explanation of biological adaptations • Mechanistic (proximate) explanation • Emphasizes mechanisms • Cause-and-effect sequences • Evolutionary (ultimate) explanation • Variation and natural selection • Species must cope with selective pressures • Adaptations -- beneficial features that enhance overall survival of the species 1.1 Introduction Adaptations reflect evolutionary history including cost-benefit trade-offs • Example: Shivering in mammals • Cost -- requires energy • Benefit -- maintains body temperature in the cold 1.1 Introduction Physiology is an integrative discipline • Closely interrelated with anatomy, physics, chemistry, biochemistry, molecular biology, and genetics Physiology is a comparative discipline • Comparing physiological features in different types of organisms • Krogh principle -- for every adaptation, there will be a particular species in which it is most conveniently studied 1.2 Methods in Physiology Scientific method 1. Ask a question about nature 2. Propose alternative hypotheses to explain the phenomenon • • • Hypothesis = Tentative explanation about some aspect of nature Induction = Taking specific information and creating a general explanation Hypotheses must be testable and falsifiable 1.2 Methods in Physiology Scientific method 3. Design experiments that test the hypothesis by making testable predictions • Deduction = Making specific predictions based on a hypothesis and testing those predictions 4. Conduct experiments 5. Refine earlier questions and hypotheses, and design new tests 1.2 Methods in Physiology Scientific method • When a hypothesis has been consistently supported and all alternative hypotheses have been falsified, a hypothesis may be elevated to a scientific theory. 1.3 Levels of Organization in Organisms Basic functions essential for survival of the cell • Self-organization • Self-regulation • Self-support and movement • Self-replication 1.3 Levels of Organization in Organisms Examples of specialized functions of some cells • Gland cells secrete digestive enzymes. • Neurons generate and transmit electrical impulses. • Kidney cells selectively retain needed substances while eliminating unwanted substances in the urine. • Muscle cells produce movement. 1.3 Levels of Organization in Organisms (a) Chemical level: a molecule in the membrane that encloses a cell (b) Cellular level: a cell in the stomach lining (c) Tissue level: layers of tissue in the stomach wall (d) Organ level: the stomach (e) Body system level: the digestive system (f) Organism level: the whole body Figure 1-2 p8 1.3 Levels of Organization in Organisms Levels of organization • Cell = Smallest unit capable of carrying out the processes associated with life • Tissue = Group of cells with similar structures and functions 1.3 Levels of Organization in Organisms Four primary tissue types • Epithelial tissue • Exchange of materials • Connective tissue • Connects, supports, and anchors various body parts • Muscular tissue • Contraction and force generation • Nervous tissue • Initiation and transmission of electrical impulses 1.3 Levels of Organization in Organisms Organ: Body structure that integrates different tissues and carries out a specific function Stomach Epithelial tissue: Protection, secretion, and absorption Connective tissue: Structural support Muscle tissue: Movement Nervous tissue: Communication, coordination, and control Figure 1-3a p9 Figure 1-3b p9 INTERACTION: Differences between cell and tissue types To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 1.3 Levels of Organization in Organisms Levels of organization • Cell = Smallest unit capable of carrying out the processes associated with life • Tissue = Group of cells with similar structures and functions • Organ = Two or more tissues organized to perform a particular function • Organ system = Collection of organs that interact to accomplish a common activity 1.4 Size and Scale among Organisms Organisms range in size from unicellular prokaryotes to large multicellular eukaryotes over a scale of 1020 Scaling = Study of the effects of size on anatomy and physiology 1.4 Size and Scale among Organisms Volume grows along three dimensions Surface area grows along two dimensions Bandicoot Elephant Figure 1-4 p11 1.4 Size and Scale among Organisms Larger organisms have smaller surfacearea-to-volume ratios • Surface area is related to the square of the radius • Volume is related to the cube of the radius • Advantage of smaller surface-area-to-volume ratio (larger animals) -- better retention of heat • Disadvantage -- reduced ability to obtain enough nutrients to meet the needs of the larger volume 1.5 Homeostasis: Basic Mechanisms and Enhancements Claude Bernard documented the ability of mammals to maintain a relatively constant state of the internal environment (milieu interieur). Walter B. Cannon coined the term “homeostasis” Homeostasis = Maintenance of a consistent internal state Homeostasis is not a fixed state, but a dynamic steady state. 1.5 Homeostasis: Basic Mechanisms and Enhancements Majority of cells in a multicellular organism are not in direct contact with the external environment. The internal environment consists of the extracellular fluid. • Plasma • Interstitial fluid Extracellular fluid Cell Interstitial fluid Plasma Blood vessel Intracellular fluid Figure 1-5 p12 1.5 Homeostasis: Basic Mechanisms and Enhancements Homeostasis is essential for proper cell function, and most cells, as a part of an organized system, contribute to homeostasis Maintain Body systems Homeostasis Is essential For survival of Make up Cells Stepped Art Fig. 1-6, p.12 1.5 Homeostasis: Basic Mechanisms and Enhancements Homeostatically regulated factors of the internal environment • • • • • Concentration of energy-rich molecules Concentration of O2 and CO2 Concentration of waste products pH Concentration of water, salt, and other electrolytes • Volume and pressure • Temperature • Social parameters 1.5 Homeostasis: Basic Mechanisms and Enhancements Animals vary in their homeostatic abilities (e.g. thermoregulation) • Regulators • Use internal mechanisms to defend a relatively constant state • Conformers • Internal state varies with that of the environment • Avoiders • Minimize internal variations by avoiding environmental disturbances 1.5 Homeostasis: Basic Mechanisms and Enhancements Figure 1-7a p14 Figure 1-7b p14 Figure 1-7c p14 1.5 Homeostasis: Basic Mechanisms and Enhancements Negative feedback is the main regulatory mechanism for homeostasis • Negative feedback occurs when a change in a controlled variable triggers a response that opposes the change. 1.5 Homeostasis: Basic Mechanisms and Enhancements Components of a negative feedback system • Sensor -- Measures the variable being regulated • Integrator -- Compares the sensed information with a set point • Effector -- Makes the corrective response Examples • Control of room temperature • Mammalian thermoregulation 1.5 Homeostasis: Basic Mechanisms and Enhancements Deviation in controlled variable (detected by) * relieves - Sensor (informs) Set Point Integrator (sends instructions to) Effector(s) (brings about) Compensatory response * (results in) Controlled variable restored to normal (leads to) Negative feedback to shut off the system responsible for the response Fig. 1-8a, p.13 Fall in room temperature below set point * Relieves Thermometer + Set Point Thermostat + Furnace Heat output Fall in room temperature below set point * (negative feedback) Fig. 1-8b, p.13 Fall in body temperature below set point * Relieves Temperature-monitoring nerve cells + Temperature control center Set Point + Skeletal muscles (and other effectors) Heat production through shivering and other means Fall in body temperature below set point (negative feedback) Fig. 1-8c, p.13 ANIMATION: Negative feedback system To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 1.5 Homeostasis: Basic Mechanisms and Enhancements Additional design features of negative feedback systems • Antagonistic control • Two effectors with opposite effects • Behaviors as effectors (e.g. avoiders) • Anticipation or feed forward system • Predicts an oncoming disturbance before a regulated state is changed • Acclimatization systems • Alter existing feedback and other components over time to work better in a new situation 1.5 Homeostasis: Basic Mechanisms and Enhancements Controlled variable Sensor Integrator Set point Effector to decrease variable Effector to increase variable e.g., furnace e.g., air conditioner (a) Antagonistic effectors Stepped Art Fig. 1-9a, p.16 Controlled variable Oncoming disturbance Sensor Sensor Integrator Anticipator Effector Activates corrective response before the variable is disturbed (b) Anticipation or feedforward control Stepped Art Fig. 1-9b, p.16 ANIMATION: Feedback control of temperature To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 1.6 Regulated Change Some internal processes are not always homeostatic • • • • • • • Dormancy Locomotion Growth and development Neural signaling On-demand regulation (e.g. digestion of food) Reset systems -- change set point Positive feedback systems 1.6 Regulated Change Positive feedback systems • Output is continually enhanced so that the controlled variable continues to move in the direction of the initial change. • Create rapid change • Example: Oxytocin release and uterine contractions during mammalian birth 1.6 Regulated Change Controlled variable Higher regulator Sensor Integrator Set point Effector (a) Reset control of negative feedback by a higher system or clock Stepped Art Fig. 1-10a, p.18 Deviation in controlled variable (May use a Sensor) Integrator or regulatory process Accentuates the change Output (may use an effector) Stepped Art (b) Positive feedback Fig. 1-10b, p.18 Signal from mature fetus Uterus begins contractions Stretch sensors Contractions enhanced Mother’s hypothalamus Pituitary gland Oxytocin secreted (c) Example of positive feedback: birth of a mammal Stepped Art Fig. 1-10c, p.18 1.6 Regulated Change Disruptions in regulation can lead to illness and death. • Pathophysiology -- altered physiology of organisms associated with disease • Example: Congestive heart failure is a positive feedback cycle leading to death 1.7 Organization of Regulatory and Organ Systems Homeostasis and other regulation is hierarchically distributed. • Regulation at the cellular level • Intrinsic controls • Regulation by a tissue or organ for its own benefit • Extrinsic controls • Regulatory mechanisms initiated outside an organ to alter its activity • Coordinated regulation of several organs toward a common goal 1.7 Organization of Regulatory and Organ Systems Organ systems can be grouped according to their contributions to the organism. • Whole-body control systems • Nervous system • Endocrine system • Support and movement systems • Skeletal system • Muscular system 1.7 Organization of Regulatory and Organ Systems Organ systems can be grouped according to their contributions to the organism. • Maintenance systems • • • • • • Circulatory system Immune system Respiratory system Excretory system Digestive system Integumentary system • Reproductive system 1.7 Organization of Regulatory and Organ Systems BODY SYSTEMS Information from the external environment relayed through the nervous system NERVOUS SYSTEM Regulates ENDOCRINE SYSTEM INTEGUMENTARY RESPIRATORY SYSTEM SYSTEM Urine containing wastes and excess water and electrolytes Nutrients, water, electrolytes Feces containing undigested food residue EXCRETORY SYSTEM IMMUNE SYSTEM DIGESTIVE SYSTEM Sperm leave male REPRODUCTIVE Sperm enter SYSTEM female Exchanges with all other systems. EXTERNAL ENVIRONMENT MUSCULAR AND SKELETAL SYSTEMS Exchanges with all other systems. Keeps internal fluids in Keeps foreign material out Protects against foreign invaders Enables the body to interact with the external environment CIRCULATORY SYSTEM Figure 1-11 p20