Introduction to Human Physiology Abdul Aleem Khan

Le Milieu Intérieur And Homeostasis I and II

STRUCTURE FUNCTION WHAT IT “IS” HOW IT “WORKS”

What is human Physiology A branch of science that deals with the functioning of Human body How does the heart beat ? How do we breathe ? How do we see ? How do we remember ? How do we move ? How do we reproduce?

How cells (like muscle, nerve) function? To answer these global questions it is essential to understand that the functional unit of the body is the cell. How cells (like muscle, nerve) function? And how similar and dis-similar types of cells work together at various organisational levels (integration)  as a whole organism All most all life processes are governed by laws of physics and chemistry

Divisions of Physiology Integumentary Physiology (system) Cardiovascular Physiology (system) Respiratory Physiology (system) Gastrointestinal Physiology (system) Renal Physiology (system) Reproductive Physiology (system) Musculo-skeletal Physiology (system) Neurophysiology Nervous system Endocrine Physiology (system) Immune Physiology (system)

Various levels of structural organization Atoms Molecules Organelles Cells Tissues Organs Systems Organism

Figure 1-1: Levels of Organization and Related Fields of Study

A Cell

Cell theory The cell is the basic structural and functional unit of living organisms The activity of an organism depends on both the individual and collective activity of its cells The biochemical activities of cells are dictated by their specific subcellular structures (principle of complementarity) Continuity of life has a cellular basis (cells come from cells)

Cell Diversity There is really no “typical” cell. Cells have different shapes, different sizes, different functions, different life spans. Stem cells is pluripotent. Examples of Specialized cells: Many different types of blood cells Three different types of muscle cells Fat Storage cells Nerve cells that transmit electrical impulses Cells for reproduction

Cells internal Environoment

“La fixité du milieu intérieur est la condition de la vie libre.” Claude Bernard (1813-1878) “La fixité du milieu intérieur est la condition de la vie libre.” “The fixity of the internal environment is the condition for free life.”

Internal Environment Claude Bernard in 1829 said: The proper functioning of the cells depends on precise regulation of the composition of their surrounding fluid. Surrounding fluid = Internal environment = Le Milieu interier

Internal Environment

Body water Water is main solvent in living cells Hydrophilic molecules dissolve in water Hydrophobic molecules do not dissolve in water Amphiphilic - molecule part hydrophilic/part hydrophobic Body Water Intracellular fluid (inside cells) Extracellular fluid (outside cells) Plasma (inside blood vessels) Interstitial Fluid (outside blood vessels)

Chemical composition of body Major Elements % body wt Oxygen 65% Carbon 18% Hydrogen 10% Nitrogen 3.4% Mineral Elements Sodium 0.17% Potassium 0.28% Chloride 0.16% Calcium 1.5% Magnesium 0.05% Phosphorus 1.2% Sulphur 0.25% Trace Elements Iron 0.007% Zinc 0.002% Water = 60% adult male = 50% adult female Principal organic constituents carbohydrates  sugars fats  fatty acids proteins  amino acids nucleic acids  nuclotides

Organ system Interrelationship Nutrients and oxygen are distributed by the blood Metabolic wastes are eliminated by the urinary and respiratory systems

Co-ordination of Organ System

Maintenance of constancy of the Internal Environment Homeostasis Maintenance of constancy of the Internal Environment Walter Cannon (1929)

Closed Loop Systems (Feedback Systems) Control Systems Open Loop Systems Control center Effector Controlled variable Closed Loop Systems (Feedback Systems) Control center (Set point) Effector Controlled variable Sensor Feedback Systems are of two types: 1. Negative feedback 2. Positive feedback

Maintenance of constancy of the Internal Environment Homeostasis Maintenance of constancy of the Internal Environment

Physiological variables maintained by controlled systems

Homeostasis Process of maintaining the composition of the internal body compartments within fairly strict limits (ion concentrations, pH, osmolarity, temperature etc). Require regulatory mechanisms to defend against changes in external environment and changes due to activity. Cellular homeostasis - intracellular fluid composition Organismal homeostasis - extracellular fluid composition. Control system designed to maintain level of given variable (concentration, temperature, pressure) within defined range following disturbance.

Negative feedback loop requires Sensor (Detector): specific to variable needing to be controlled Comparator (Control system): reference point for sensor to compare against Effector: if sensor  comparator  Error Signal  restore variable to desired level Comparator (reference point) Effector Controlled variable Sensor Disturbance Error signal

Homeostasic Setpoint Homeostatic range -oscillation around setpoint Change in setpoint 1. Acclimatization 2. Biorhythms

Negative feedback System Negative feedback System The response reverses the original stimulus. Example:Blood pressure and blood glucose regulation The response enhances the original stimulus Example child birth Negative feedback System

Maintenance of body temperature Composed of Detector Control system Effector The effector response Decreases or increases the effect of the original stimulus

Negative feedback System Receptors: Baroreceptors Stimulus: change in BP Receptors: Baroreceptors Control Center: Brain Effector: Heart

Negative feedback System

Negative feedback System

Negative feedback System

Limitation of negative feedback Negative feedback control is initiated after variable is disturbed Amount of correction to be applied, is assessed by magnitude of error signal  incomplete correction Overcorrection  oscillations in controlled variable Disadvantages overcome by multiple regulatory mechanisms. Regulation of blood [glucose] Insulin   [glucose]blood Glucagon   [glucose]blood

Positive feedback Negative feedback - error signal  reduces deviation from reference point Positive feedback - error signal  increases deviation from reference point (vicious circle) Error signal controlled variable disturbance effector sensor +

Positive feedback System Stimulus: stretch of the uterus Receptors: stretch receptors (cervix) Control Center: Brain Effector: Uterus

Positive feedback System

Homeostasis Homeostasis is the ability to maintain a relatively stable internal environment in an ever-changing outside world. The internal environment of the body is in a dynamic state of equilibrium. Concepts of homeostasis dynamic. Chemical, thermal, and neural factors interact to maintain homeostasis.