Introduction To Physiology

INTRODUCTION TO PHYSIOLOGY

Dr. Hoe See Ziau Department of Physiology Faculty of Medicine University of Malaya

Your eyes convert the images into electrical signals that will transmit the information to your brain for processing

Your heart will beat 70 times, pumping 5L of blood to your lungs and another 5L to the rest of your body

More than 1L of blood flow through your kidneys, which will act on the blood to conserve the “wanted” materials and eliminate the “unwanted” materials in the urine. Your kidneys will produce 1ml of urine.

Your digestive system will be processing your last meal for transfer into your bloodstream for delivery to your cells

Besides receiving and processing information, your brain will also provide output to your muscle to help maintain your posture, move your eyes across the screen as you read. Chemicals messengers will carry signals between your nerves and muscles to trigger appropriate muscle contraction.

You will breath in and out about 12 times, exchanging 6L of air between the atmosphere and your lungs

You cells will consume 250ml of O2 and produce 200ml of CO2 You will use about 2 calories of energy derived from food to support your body’s “cost of living” and your contracting muscle will burn additional calories

PHYSIOLOGY The study of the functions of the body  Focuses on mechanisms of action  “Why do I shiver when I am cold?” 

PHYSIOLOGY 

A physiologist’s mechanistic explanation of shivering: Feel cold

Shivering

LEVELS OF ORGANISATION IN THE BODY 

Consists of 6 levels:    

 

Chemicals Cell Tissue Organ System Organism

LEVELS OF ORGANISATION IN THE BODY

CHEMICAL LEVEL Various atoms and molecules  Most common atoms: oxygen, carbon, hydrogen and nitrogen - ~ 96% of total body chemistry  Molecules: e.g: proteins, carbohydrates, fats and nucleic acids.  Inanimate raw materials from which all living things arise 

CELLULAR LEVEL Cells are the basic structural and functional units of life  The smallest units capable of carrying out the processes associated with life  They perform 

 

Basic functions – essential for survival of the cell Specialised functions – essential for the survival of the whole body

CELLULAR LEVEL Cell differentiation results in many different specialised types of cells



Cells make up tissues and organs in the body

TISSUE LEVEL Groups of cells with of similar specialisation  Four primary types: 

   

Muscle tissue Nervous tissue Epithelial tissue Connective tissue

TISSUE LEVEL 

Muscle tissue 

Specialised for contraction and force generation



Three types:  Skeletal

muscle: accomplishes movement of the skeleton  Cardiac muscle: responsible for pumping blood out of the heart  Smooth muscle: encloses and controls movement of contents through hollow tubes and organ

TISSUE LEVEL 

Nervous tissue 

Cells specialised for initiating and transmitting electrical impulses

TISSUE LEVEL 

Epithelial tissue  

Cells specialised for the exchange of materials between cell an its environment Glands: epithelial tissues specialised for secreting  

Exocrine glands: secrete through ducts to the outside of the body Endocrine glands: ductless glands that produce hormones which are released into the blood

TISSUE LEVEL 

Connective tissue 

Connects, supports and anchors various body parts

ORGAN LEVEL A unit made up of several tissue types  Organised together to perform a particular function or functions  Examples: stomach, heart, liver, lung, kidneys, brain, etc… 

BODY SYSTEM LEVEL A collection of organs that perform related functions and interact to accomplish a common activity  Human body has 11 systems 

BODY SYSTEM LEVEL

BODY SYSTEM LEVEL

ORGANISM LEVEL 

The body systems are packed together into a functional whole body

ORGANISM LEVEL The body systems do not act in isolation  Many processes depend on the interplay among multiple systems  E.g.: Regulation of blood pressure depends on coordinated responses among the circulatory, urinary, nervous and endocrine systems 

INTERNAL ENVIRONMENT  

About 60% of adult human body is fluid The body fluid is divided into: 

Intracellular fluid (ICF) 



Extracellular fluid (ECF)  





Fluid contained within the cells

Fluid outside the cells 2 components:  plasma – fluid portion of blood  Interstitial fluid – surrounds and bathes the cells Internal environment

Internal environment - the body fluid environment with which the cells are in direct contact and make lifesustaining exchanges

INTERNAL ENVIRONMENT Extracellular Fluid (internal environment)

Intracellular fluid

(Plasma)

Interstitial fluid

INTERNAL ENVIRONMENT A French physiologist, Claude Bernard (1813-1878), made this observation. He noticed that body cells survive in a healthy condition only when the temperature, pressure, and chemical composition of their environment remained relatively constant.

An American physiologist, Walter B. Cannon (18711945), suggested the name homeostasis for the relatively constant states maintained by the body. This term “homeostasis” has been adopted today to mean the natural ability of the body to maintain health and internal balance, in other words - cell health!

HOMEOSTASIS Maintenance of a nearly constant conditions in the internal environment – homeostasis  Essential for survival and normal functioning of all the cells  Contributed by the functions performed by each body system 

HOMEOSTATIC CONTROL SYSTEM 

A functionally interconnected network of body components that operate to maintain a given chemical or physical state in the internal environment relatively constant around an optimal set level

HOMEOSTATIC CONTROL SYSTEM  1.

2.

Can be grouped into two classes: Intrinsic (local) controls  Inherent compensatory responses of an organ to a change Extrinsic controls  Responses of an organ that are triggered by factors externally to the organ  Accomplished by nervous and endocrine systems  Permit coordinated regulation of several organs toward a common goal

HOMEOSTATIC CONTROL SYSTEM  1.

The control system consists of Detector 

2.

Integrator 

3.

Detects the deviations from normal (change in the internal environment, stimulus)

Receives information from the detector and integrate it with other relevant information and send out impulses to the effector

Effector 

Make appropriate adjustments to reduce the deviation to its desired value

HOMEOSTATIC CONTROL SYSTEM

HOMEOSTATIC MECHANISM Primarily operate on the principle of negative feedback  Negative feedback 



A change in a homeostatically controlled variable triggers a response that drives the variable in the opposite direction of the initial change, thus opposing the change



A control system’s output is regulated to resist change, so that the controlled variable is maintained at a set point

NEGATIVE FEEDBACK

NEGATIVE FEEDBACK

NEGATIVE FEEDBACK

NEGATIVE FEEDBACK

POSITIVE FEEDBACK 

A change in a controlled variable triggers a response that drives the variable in the same direction as the initial change, thus amplifying the change



Positive feedback loop are not homeostatic

POSITIVE FEEDBACK

POSITIVE FEEDBACK Oxytocin stimulates and enhances labor contractions

Baby moves toward the vagina (birth canal)

Stretching of the cervix triggers the brain to produce more oxytocin This positive-feedback cycle does not ease until the baby is finally born

POSITIVE FEEDBACK 

Can sometimes cause vicious cycles and death Loss 2 L of Blood ↓ blood volume ↓ blood available for the heart to pump effectively ↓ BP ↓ blood flow to the heart muscle through coronary vessels

Weakening of the heart ↓ pumping effectiveness of the heart

Positive feedback (vicious cycle)

HOMEOSTATIC DISRUPTION 

When one or more of the body systems fail to function properly,   



Homeostasis is disrupted An optimal internal environment can not be maintained Lead to various pathophysiological states May lead to death