Introduction & Homeostasis 2023 PDF

‫بسم هللا الرحمن الرحيم‬ Introduction to Physiology Prof. Amal Youssef Physiology Dept. FOM - SCU  Objectives of the lecture  Definition of physiology  Define the basic living unit of the body.  Identify the basic characteristics of the cells.  List the structure and functio...

‫بسم هللا الرحمن الرحيم‬ Introduction to Physiology Prof. Amal Youssef Physiology Dept. FOM - SCU  Objectives of the lecture  Definition of physiology  Define the basic living unit of the body.  Identify the basic characteristics of the cells.  List the structure and function of the cell and its organelles.  Recognize the levels of organizarion.  Identify the body organ systems and describe their function in general.  Explain the internal environment of the body and its 3 composition. Prof. Amal Youssef  What is the science concerned with the life of the human being and how the body works???. Physiology (fiz-e-OL-o-je) is the term for the study of how the body functions, and is based on a Latin term Physis = nature or origin. 4 Ology = science. Prof. Amal Youssef  What Is The Basic Structure Of The Body? The cell The cell is the structural, functional, and biological units of all living beings 5 Prof. Amal Youssef  Although cells perform different functions; they have some basic characters. 6 Prof. Amal Youssef  Characteristics of Cells Cells provide structure and support to the body. The cell interior is organised into different organelles surrounded by a separate membrane. The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth. 7 Prof. Amal Youssef  Characteristics of Cells (cont.) Mitochondria is mainly responsible for the energy transactions vital for the survival of the cell. Lysosomes digest unwanted materials in the cell. Endoplasmic reticulum plays a significant role in the internal organisation of the cell. 8 Prof. Amal Youssef Cell Structure and Function 9 Prof. Amal Youssef  Cellular Components: Structure and Function Prof. Amal Youssef 10  Levels of organization 11 Prof. Amal Youssef   Each organ is an aggregate of many different cells held together by intercellular supporting structures.  Each type of cell is specially adapted to perform one or a few particular functions. 12 Prof. Amal Youssef  12 Body Systems 13 Prof. Amal Youssef HUMAN SYSTEMS WORK TOGETHER Prof. Amal Youssef 14 HUMAN SYSTEMS WORK TOGETHER Prof. Amal Youssef 15 HUMAN SYSTEMS WORK TOGETHER Prof. Amal Youssef 16  External Environment 17 Prof. Amal Youssef  The “Internal Environment” All cells live in essentially the same environment. For this reason. The Extracellular Fluid is ALSO called the….. Volume and composition of ECF fluid should be maintained constant (within narrow limits) in spite of changes in external environment for the normal function 18 Prof. Amal Youssef (optimal function) of cells. Prof. Amal Youssef  Composition of ECF is same all over the body because of constant mixing of interstitial fluid & blood and also because of circulation of blood. Chemical, thermal, and neural factors interact to maintain homeostasis. Extreme dysfunction leads to death, but moderate dysfunction leads to sickness. 20 Prof. Amal Youssef  Control of body functions Two biological systems Neural Hormonal Rapid & small Slow & long duration duration 21 Prof. Amal Youssef  Control of body functions Controls and Secreting hormones coordinates bodily from endocrine activities that require glands regulate rapid responses activities that require Detects and initiates duration rather than reactions to changes speed in external e.g., parathyroid environment hormone regulating e.g., regulation of calcium levels blood pressure upon rising Nervous Endocrine system 22 system Prof. Amal Youssef Prof. Amal Youssef 23  Cells are the basic unit structure of the body necessary for survival. Basic characters for different cells 24 Prof. Amal Youssef HOMEOSTASIS Prof. Amal Youssef Physiology Dept. FOM - SCU  Learning Objectives Define homeostasis and the components of a homeostatic system. Recognize each of the components in representative systems. Explain the internal environment of the body and its composition. Define negative feedback. Explain how homeostatic mechanisms regulated by negative feedback detect and respond to environmental changes. Define positive feedback. Describe the actions of a positive feedback loop. Define feedforward feedback with examples. 26 Prof. Amal Youssef  Home Stasis 27 Prof. Amal Youssef Definition – Maintenance of a constant internal environment to sustain life. Internal environment – milieu interieur - extracellular fluid which includes interstitial fluid.  Homeostasis “The Essence of Life”: Dynamic Constancy Homeostasis For optimal cell function in human several conditions (important variables) in the internal environment (extracellular fluid) must be maintained within narrow limits, These include: - Body Temperature - Blood pressure - Blood pH - O2 and CO2 concentration - Osmoregulation-Water balance - Blood glucose Changes in the external environment can cause these variables 29 to change. Prof. Amal Youssef  If a system is in homeostasis, it is in its normal, or resting, state. If disturbances disrupt the normal state, the system will act to restore the normal state. For example, a person who is standing still has a normal resting respiratory rate. If that person runs as fast as he/she can for 30 seconds, his/her respiratory rate will increase to meet the body’s demand for oxygen. Furthermore, when the person returns to a resting state, the respiratory rate eventually will return to a normal rate because of the decreased30 demand for oxygen. Prof. Amal Youssef 31 Prof. Amal Youssef  Body systems Essentially all organs and tissues of the body perform functions that help maintain these constant conditions. Examples: 1- Cardiovascular system – blood flow and temp regulation 2-The lungs provide oxygen to the ECF to replenish the oxygen used by the cells, 3-The kidneys maintain constant ion concentrations, 4- The gastrointestinal system 32 provides nutrients. Prof. Amal Youssef  Nervous and endocrine systems regulate the 33 function of the other systems Prof. Amal Youssef Components of Homeostatic Systems Sensor that detects changes in a Receptor variable, the stimulus e.g., a change in temperature Receives and interprets a message Control (input) from the receptor Initiates changes through the (Coordinating) effector center A part of the nervous system (brain or spinal cord). Carries out the response initiated by the coordinating center to correct Effector the disturbance (stimulus) Most body Prof. Amal Youssef structures. 34  3 Control Output: Input: center 4 Information Information sent sent along along efferent afferent pathway to pathway to Effector Receptor (sensor) 2 Change detected Homeostatic Control by receptor Mechanisms 5 Response of effector feeds 1 Stimulus: back to Produces influence change magnitude of in variable Variable (in homeostasis) stimulus and returns variable to homeostasis 35 Prof. Amal Youssef  Homeostatic mechanisms How is dynamic equilibrium maintained? Definition: Feedback control (feedback mechanism) means the control of certain function by the resultant effect of this function Negative Positive Feed forward Most common Less common 36 Prof. Amal Youssef  ↑↓ ↑↓ ↑ ↓ NEGATIVE 37 FEEDBACK Prof. Amal Youssef POSITIVE FEEDBACK 1. 1- Negative feedback mechanism – - most common - the effect of the controlling system is in the opposite direction of change in the parameter (an effect inhibits itself) so that disturbance is minimized. - Variable maintained within a normal level, its set point - If stimulus increases, homeostatic control system activated to cause a decrease in the stimulus and vice versa Prof. Amal Youssef 38 Components of -ve feedback regulation Disturbance Controlled variable at a set point Sensormonitors Sensor monitors current currantvalue value Feedback signals Controller- compares Set point If error environment Stability of internal Output through effectors Effector response Response reverses the 39 initial disturbance in homeostasis Correction  -ve feedback mechanism e.g. regulation of blood pressure by baroreceptors, regulation of hormonal secretion, regulation of PCO2 of ECF. Prof. Amal Youssef 40 Homeostasis of Blood Pressure Baroreceptors in walls of blood vessels detect an increase in BP Brain receives input and signals from blood vessels and heart Blood vessels dilate, HR decreases BP decreases 41 Prof. Amal Youssef 42 Prof. Amal Youssef 43 Prof. Amal Youssef 2- Positive feedback mechanism – A mechanism that brings greater change in the same direction. The effect of regulating system magnifies the error and sets in vicious cycle (an effect stimulates itself) which stops only when the initial stimulus is removed. Prof. Amal Youssef 44  2 lits of blood loss +ve feedback mech. Ineffective heart pump ↓B.P. Instability of environment ↓blood flow to heart muscle internal Weakness of heart muscle ↓heart pump Vicious cycle (death cycle) stops when blood volume is corrected 45 Prof. Amal Youssef  Does positive feedback always lead to instability and lethal effects? Prof. Amal Youssef 46  47 Prof. Amal Youssef  +ve feedback mechanism Examples of useful +ve feedback regulation – for rapid magnification of basic corrective mechanisms (lead to stability of internal environment). 1. Oxytocin secretion during parturition 2. Enzymatic cascade for blood coagulation 3. Lactation Prof. Amal Youssef 48  I. Child birth (Positive Feedback) Positive feedback can some times be useful, i.e., operate in the body to complete certain function e.g., process of parturition (labor): Uterine contraction→ descend of the baby → stretch of uterine cervix → oxytocin release → uterine contraction And so on until labor is complete 49 Prof. Amal Youssef II. Blood Clotting (Positive Feedback) 50 Prof. Amal Youssef IV. Lactation (Positive Feedback) 51 Prof. Amal Youssef  Feedforward Control Feedforward regulation responds to an anticipatory cue prior to a change in the internal environment. A common example of a feedforward mechanism is: 1. Responding to cold weather by shivering. When the thermoreceptors of the skin detect the cold, signals to the body are alerted to be aware of a possible fall in body temperature. The body reacts to this by shivering to produce internal heat before its internal temperature falls due to the cold external environment. 52 Prof. Amal Youssef 2. Increases in heart and respiration rates before race. Prof. Amal Youssef 53 1. A relatively stable environment is essential for life to function. 2. The tendency for life to favor these conditions is called homeostasis. 3. Each functional structure contributes in the maintenance of homeostatic conditions of the ECF, which is called the internal environment. 4. Each cell benefits from homeostasis, and in turn, each cell contributes in the maintenance of homeostasis. 5. Negative feedback mechanism is the most important acting mechanism to achieve stable conditions in the body. 6. Positive feedback mechanism can lead to death and is 54 only useful in certain conditions. Prof. Amal Youssef  Components of a Biological Control System Afferent Efferent 55 Prof. Amal Youssef 56 Prof. Amal Youssef  References  Guyton AC, and Hall JE (2010): Text book of medical physiology, 12th ed., W.B. Saunders Company.  Lauralee Sherwood (2012): Human physiology, from cell to system, 8th ed., Blackwell Press. K Sembulingam and Prema Sembulingam (2012): Essentials of Medical Physiology, Sixth Edition, Jaypee brothers medical publishers (p) ltd. Vander et al. (2001): Human Physiology: The Mechanism of Body Function, Eighth Edition, The McGraw−Hill Companies 57 Prof. Amal Youssef Prof. Amal 58 Youssef