Unit 1 BIOL273 - Introduction to Physiology PDF

INTRODUCTION A. What is Physiology? Question: What is Physiology? Answer: Study of the normal functioning of a living organism and its component parts Understanding physiology requires a large vocabulary of new terms \- Learning physiology is like learning a new language B. Key Concepts/Themes...

INTRODUCTION A. What is Physiology? Question: What is Physiology? Answer: Study of the normal functioning of a living organism and its component parts Understanding physiology requires a large vocabulary of new terms \- Learning physiology is like learning a new language B. Key Concepts/Themes in Physiology - There are several key concepts or themes that are important in understanding physiology - Structure & Function - Biological energy - Information flow - Homeostasis \* LEVELS OF ORGANIZATION A. Organizational Levels \- Living organism have several levels or organization A. Chemical - atoms & molecules B. Cellular - neuron, lymphocyte C. Tissue - collection of cells (e.g. connective) D. Organ - structural unit made of tissues (e.g. heart) E. Organ system - integrated group of organs Organism - individual form of life (G. Community, Ecosystem, Biosphere) B. Physiology is an Integrative Science - Physiology considers many different levels of organization (see above) - Most questions at the organ level are already answered - Therefore, most current research focuses on the molecular and cellular level - Researchers attempt to understand how events within a single cell influence neighbouring cells, tissues, organs & organ systems C. Tissue Types \- Cells in the body assemble into larger units called tissues - Cells are held together by cell junctions → anchoring junctions, gap junctions, tight junctions - In between the cells is the extracellular matrix → synthesized and secreted by cells in the tissue - There are four primary tissue types in the human body Epithelial, connective, muscle and neural 1\. Epithelial - Epithelia protect the internal environment of the individual - Regulate exchange of material between the external environment and internal environment → any material that moves between these two environments must cross an epithelium - Epithelia consist of one or more layers of cells connected to one another and to a basal lamina (basement membrane)
Five types of epithelia: F. Exchange - rapid exchange of material G. Ciliated - line airways & female reproductive tract H. Secretory - synthesize & release products into the external environment/blood I. Transporting - selective transport of material J. Protective - found on surface of the body
 2\. Connective \- Connective tissue provides structural support and barriers → has an extensive extracellular matrix (ECM) that contains proteoglycans, collagen, elastin, and fibronectin Five types of connective tissue: - Loose - elastic tissue (e.g. tissue underlying the skin) - Dense - strength is the primary function (e.g. tendons) - Adipose - contains adipocytes (e.g. white fat and brown fat) - Blood - watery matrix lacking insoluble protein fibers - Supporting - dense substances (e.g. cartilage and bone) 3\. Muscle \- Ability to contract to produce force and movement Three types of muscle: K. Skeletal → responsible for gross body movement L. Smooth → responsible for influencing the movement of substances into/out of/within the body Cardiac → found only in the heart, contraction moves blood through the body 4\. Neural - Carry information from one part of the body to another - There is very little ECM in neural tissue
Two types of cells in neural tissue: M. Neurons → carry information as electrical or chemical signals Glial cells → supporting cells for neurons FUNCTION AND MECHANISM - Function and mechanism are two interrelated concepts in physiology
Function: the function of a system is the \"why\" - Why does the system exist? Mechanism: the process of a system is the \"how\" \- How does the system work? Physiologists study mechanism to understand function → how cellular and molecular changes affect the organism as a whole \* HOMEOSTASIS N. Homeostasis is a central organizing principle of physiology
Question: What is homeostasis?
Answer: It is the maintenance of a relatively stable internal environment O. Homeostasis involves a series of automatic control mechanisms P. Maintains a similar condition for all the cells of the body Q. Achieved through the effects of different organ systems working together R. Result of homeostatic control is oscillation around a set-point S. Setpoints can change with time
Acclimatization: Environmentally induced change in physiological function with no genetic change - e.g. acclimatization to altitude Failure to maintain homeostasis will disrupt function and may result in a disease state CELL-TO-CELL COMMUNICATION A. Four Basic Mechanisms of Cell-to-cell Communication \- There are four basic mechanisms of how cells communicate in the body via: 1\. Gap junctions - known as direct cell-to-cell communication - Communication between cells occurs via protein channels (connexons) between adjacent cells - Gap junctions are capable of opening and closing - They are found in many cell types → e.g. heart 2\. Contact-dependent signal T. This type of communication is from the interaction between membrane molecules on two cells U. Found in immune cells (see Unit \#6) & during development 3\. Local communication - communication with neighbouring cells - Occurs via paracine and autocrine signals - Chemicals secreted by cells which act on neighbouring cells are known as paracrine signals - Act on immediate vicinity - Autocrines are chemicals that act on the cell that produces them - Histamine is an example of a paracrine signalling molecule → vasodilator 4\. Long-distance communication - Responsibility of the nervous and endocrine systems - Nervous system uses combinations of chemical and electrical signals - e.g. neurohormones, neurotransmitters Endocrine system uses chemical signals → these signals are known as hormones B. Specificity of Chemical Signals Question: Why do some cells respond to a chemical signal and others do not? Answer: 1. Target cells have various receptor proteins 2\. Only respond to a chemical signal if they have the appropriate receptor 1\. Receptors - Are usually trans-membrane proteins (or glycoproteins) - Receptors are usually found in plasma membrane but can be intracellular (cytosolic or nuclear) - Membrane spanning receptors have three main domains (regions): а. Extracellular domain - involved in binding the ligand (chemical signal) b\. Trans-membrane domain - hydrophobic c\. Intracellular (cytoplasmic) domain - involved in activating the cellular 2\. Receptors vs. chemical signals \- It is the receptor NOT just the signal that determines the type of response \- ANY molecule that can bind with the receptor and induce activity will elicit the response 3\. Responses to chemical signals i\. Signalling molecule binds to the receptor ii\. Activated receptor interacts with molecules inside the cell to start a signal iii.Signal is carried to appropriate place inside the cell (e.g. nucleus) → signal transduction iv\. Response occurs CONTROL AND INTEGRATION A. Local or Long-Distance Control \- Homeostasis may be maintained by local or long-distance pathways 1\. Local control - The effects are exerted on neighbouring cells - e.g. paracrine control of blood vessel diameter in response to low O2 2\. Reflex control \- The reaction in one or more organs controlled from elsewhere in the body \- Can be any long-distance path of the nervous and/or endocrine systems) \- Some points to remember on homeostatic control systems: - Stability is result of balance between input and output - Negative feedback returns variable to original condition - Homeostatic systems maintain similarity NOT constancy - Set points can be reset - Some variables are controlled more closely than others - Most control systems require communication between cells B. Types of Reflex Control - Response loops start with a stimulus and result in a response - Feedback pathways control the response loop - There are three types of feedback/control systems to regulate the response loops a\. Negative Feedback \- Negative feedback results in a change that opposes or removes the signal thus returning the variable to its original value  Allows for homeostatic control - Negative feedback keeps a system near or at set-point \- Results in oscillation around the set-point \- e.g. blood pressure b\. Positive Feedback - Response sends a signal → reinforces stimulus, sending the variable further from the set point until and external signal turns the response off - NOT homeostatic → response reinforces the stimulus - Sends system temporarily out of control - e.g. labour c\. Feedforward Control V. Anticipatory control: predicts that change is about to happen, starts the response loop → prevent change e.g. sight, smell or thought of food