Physiology

Considers the operation of specific organ systems

Renal – kidney function

Neurophysiology – workings of the nervous system

Cardiovascular – operation of the heart and blood vessels

Focuses on the functions of the body, often at the cellular or molecular level

Physiology

Understanding physiology also requires a knowledge of physics, which explains electrical currents, blood pressure, and the way muscle uses bone for movement

Principle of Complementarity

Function always reflects structure

What a structure can do depends on its specific form

Levels of Structural Organization

Chemical – atoms combined to form molecules

Cellular – cells are made of molecules

Tissue – consists of similar types of cells

Organ – made up of different types of tissues

Organ system – consists of different organs that work closely together

Organismal – made up of the organ systems

Chemical levelAtoms combine to form molecules

1

2

3

4

Cellular levelCells are made up of molecules

Tissue levelTissues consist of similar types of cells

5 Organ system levelOrgan systems consist of different organs that work together closely

Organ levelOrgans are made up of different types of tissues

6 Organismal levelThe human organism is made up of many organ systems

Atoms

Molecules

Smooth muscle cell

Smooth muscle tissue

Connective tissue

Smooth muscle tissue

Epithelial tissue

Blood vessel (organ)

Heart

Blood vessels

Cardiovascular system

Levels of Structural Organization

Figure 1.1

HOME0/STATIS => SAME STAY => SAME STATE

DEFINED AS “DYNAMIC CONSTANCY OF THE INTERNAL ENVIRONMENT”

Claude Bernard — “mileu interieur” = internal environment remains fairly constant with changing external or internal conditions

1893 — experiment with dogs

Question: How is food broken down to supply energy?

It was thought that food (sugar) was completely used up in the body for energy

DEFINED AS “DYNAMIC CONSTANCY OF THE INTERNAL ENVIRONMENT”

Claude Bernard — “mileu interieur” = internal environment remains fairly constant with changing external or internal conditions

EXPERIMENT:

Sugar-fed dog

Meat-fed dog

Sacrificed both – found both had sugar in blood

Bernard later went on through series of experiments to show that sugar was stored in the liver in the form of glycogen

Glucose (in the blood) actually INHIBITS glycogen breakdown

Led to the concept of feedback

From 1929-1932 Walter cannon described and coined the term (term) homeostasis

Logic:

1) All organisms (living systems) are open systems

2) Open systems are subject to disturbances

3) Disturbances are kept within narrow limits

4) By automatic adjustments (feedback)

5) System is NOT in equilibrium

6) But steady state

Organisms are open systems, which are kept in a steady state (homeostasis) by feedback mechanisms

What is a feedback mechanism?

Process or event that causes another event which has an effect on the initial or subsequent event

Simplest: A —— B —— A

Common: A —— B —— C —— A

Two types: positive or negative

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

Chemical, thermal, and neural factors interact to maintain homeostasis

Homeostatic Control Mechanisms

The variable produces a change in the body

The three interdependent components of control mechanisms are:

Receptor – monitors the environments and responds to changes (stimuli)

Control center – determines the set point at which the variable is maintained

Effector – provides the means to respond to the stimulus

Stimulus:Produceschangein variable

1

2

3

Changedetectedby receptor

Input:Informationsent alongafferentpathway to

5 Response ofeffector feedsback to influencemagnitude of stimulus andreturnsvariable tohomeostasis

Variable (in homeostasis)

Imbalance

Imbalance

Receptor (sensor)

Controlcenter 4 Output:

Information sentalong efferentpathway to

Effector

Homeostatic Control Mechanisms

Figure 1.4

Negative Feedback

In negative feedback systems, the output shuts off the original stimulus

Negative Feedback

Figure 1.5

Signalwire turnsheater on

Signalwire turnsheater off

Response;temperaturerises

Response;temperaturedrops

Stimulus: rising roomtemperature

Stimulus: dropping roomtemperature

Balance

Effector(heater)

Effector(heater)

Setpoint

Control center(thermostat)

Heateroff

Setpoint

Receptor-sensor(thermometer inThermostat)

Control center(thermostat)

Heateron

Imbalance

Imbalance

Receptor-sensor(thermometer inThermostat)

Negative Feedback (Regulation of blood glucose levels)

Positive Feedback

In positive feedback systems, the output enhances or exaggerates the original stimulus

Example: Regulation of blood clotting

Figure 1.6

Homeostatic Imbalance

Disturbance of homeostasis or the body’s normal equilibrium

Overwhelming of negative feedback mechanisms allowing destructive positive feedback mechanisms to take over

Organ Systems Interrelationships

Nutrients and oxygen are distributed by the blood

Metabolic wastes are eliminated by the urinary and respiratory systems

Figure 1.2

Necessary Life Functions I

Maintaining boundaries – the internal environment remains distinct from the external

Cellular level – accomplished by plasma membranes

Organismal level – accomplished by the skin

Movement – locomotion, propulsion (peristalsis), and contractility

Responsiveness – ability to sense changes in the environment and respond to them

Digestion – breakdown of ingested foodstuffs

Necessary Life Functions II

Metabolism – all the chemical reactions that occur in the body

Excretion – removal of wastes from the body

Reproduction – cellular and organismal levels

Cellular – an original cell divides and produces two identical daughter cells

Organismal – sperm and egg unite to make a whole new person

Growth – increase in size of a body part or of the organism

Survival Needs

Nutrients – chemical substances used for energy and cell building

Oxygen – needed for metabolic reactions

Water – provides the necessary environment for chemical reactions

Maintaining normal body temperature – necessary for chemical reactions to occur at life-sustaining rates

Atmospheric pressure – required for proper breathing and gas exchange in the lungs