Embed Size (px)
Citation preview
• Define the concept of the “internal environment” and state itsphysiologic importance.
• Differentiate between the external and internal environments.
• Define and discuss the concept of homeostasis and itsimportance to the living organism.
• Discuss the physiologic control mechanisms that enablemaintenance of the normal steady state of the body.
• Define a feedback mechanism and describe its components.
• Differentiate between positive and negative feedbackmechanisms and give examples for each in the body.
Objectives
Study source for this lecture:(Guyton & Hall Textbook of Medical Physiology, 13th ed, Chapter 1)
• All the cells in the body arecontinuously bathing in fluid.
• Because this fluid is outsidethe cell, it is calledextracellular fluid (ECF).
• It is from the ECF that cells getthe ions and nutrients neededto maintain life.
The Internal Environment“Milieu Intérieur”
(Guyton and Hall Textbook of Medical Physiology. 13th ed. Ch-1)
Because,ØAll body cells live in the same environment (i.e. ECF).ØThe composition of ECF is almost similar between the different species.
It was named the “internal environment” by the French physiologist ClaudeBernard.
Energy (ATP) Work
GlucoseOxygen
Chemicalreactions enzymes
pHTemperature
wasteCO2Urea
Ions
Fatty acidsAmino acids
In order for the cell to function properly,
ECF(Mr. Ford’s class-Introduction to anatomy and physiology-youtube)
The internal environment need tohave the right amount/level ofthese substances/variables.(not too much and not too little)
5
External vs Internalenvironment
• ECF = theinternalenvironment.
• The skinseparates thisenvironmentfrom the outsideworld whichknown as theexternalenvironment.
“Internal environment”
In Multicellular organisms
“External environment”
External vs Internalenvironment
In Unicellular organisms
Internal environment = External environment
External vs Internalenvironment
8
Homeostasis• The internal environment must be keptconstant in the face of an ever changingexternal environment.
• The internal environment of the body (ECF)isin a dynamic state of equilibrium
• The process by which the body keeps the internalenvironment constant despite changes in theexternal environment is known as“Homeostasis”.
• Homeostasis means:– Homeo- : sameness, similarity– -stasis: standing
• Essentially all the functions of the body organsand tissues aim at keeping the internalenvironment at a nearly constant state.
“Homeostasis”
(Guyton and Hall Textbook of Medical Physiology. 13th ed. Ch-1)
Internalenvironment
O2
CO2
ProtectionSkin
Immune system
Control systems
Nervoussystem
Endocrinesystems
Body constituents are normally regulated within a range rather than afixed value;
12
Control Mechanisms• The body has thousands of control systems.
• They function to restore balance when it is lost.
• Control systems operate;– Within the organ itself– Throughout the body→ to control interrelations between organs.
Feedback Mechanisms
What is meant byfeedback?ØA loop system inwhich the systemresponds toperturbation eitherin the same direction(positive feedback)or in the oppositedirection (negativefeedback).
What are the components of afeedbackmechanism?
The Thermostat Analogy
Negative feedbackThe effector response of thesystem is in the oppositedirection to the stimulus thatinitiated the response.
E.g;• A high level of in CO2 in the
ECF will increase pulmonaryventilation, increasing theamount of CO2 expiredwhich will bring the level ofCO2 in ECF down.
• Most of the control systemsof the body act by negativefeedback.
Types of Feedback Mechanisms
Positive feedbackThe effector response is in thesame direction of the stimulusthat initiated the response.
E.g;• In nerve signaling, entry of a
small amount of Na+ intothe cell will open more Na+channels causing more Na+to enter the cell.
• Only few systems displaypositive feedbackmechanisms..WHY?
(Guyton and Hall Textbook of Medical Physiology. 13th ed. Ch-1)
Examples of Negative FeedbackMechanismsBody temperature control
Blood pressure control
Examples of Positive FeedbackMechanisms
Childbirth
Can you find otherexamples for a positivefeedback mechanism in
the body?
Disease is a state of disturbedhomeostasis
