What is physiology ?

What is physiology ?

The goal of physiology is to explain the physical and chemical factors that are responsible for the origin,development and progression of life,from the very simple virus up to the largest tree or to the complicated human being,has its own functional characteristics.  

Human physiology

In human physiology,we attempt to explain the specific characteristics and mechanisms of human body that make it a living being.The very fact that we remain alive is almost beyond our own control,for hunger make us seek for food and fear makes us seek refuge.Sensations of cold make us provide warmth and other forces cause us to seek fellowship and to reproduce.Thus, the human
being is actually an automation, and the fact that we are sensing, feeling,and knowledgeable beings is part of this automatic sequence of life; these special attributes allow us to exit under widely varying conditions.In unicellular organisms, all vital processes occur in a single cell. As the evolution of multicellular organisma has progressed , various cell groups have taken over particular functions.In humans  and other vertebrate animals,the specialized call groups include- a gastrointestinal system to digest and absorb food a respiratory system to take up O2 and eliminate CO2 a urinary system to removes wastes,a cardiovascular system to distribute food,O2,and the products of metabolism,a reproductive system to perpetuate the species;and nervous and endocrine systems to coordinate and integrate the functions of the other systems. This book is concerned with the way each contributes to the functions of the body as hole. This chapter presents general concepts and principles that are basic to the function of all the systems. It also includes a short review of fundamental aspects of cell physiology. Additional aspects of cellular and molecular biology are considered in the relevant chapters on the various organs            

Body works

Body is actually a social order of about 100 trillion cells organized into different functional,structures,some of which are called organs.Each functional structure provides its share in the maintenance of homeostatic conditions in the extracellular fluid, which is called the internal environment.As long as normal conditions are maintained in the internal environment,the calls of the body continue to live and funtion properly.Thus each cell benefits from homeostasis,and in turn each cell contribute its share toward the maintence of homeostasis.The reciprocal interplay provides continuous automaticity of the body until one or more funtional system lose their ability to contribute their share of funtion.When this happens,all the calls of the boby suffer.Extreme dysfunction leads to death,where as moderate dysfunction leads to sickness.The cells that make up the bodies of all but the simplest multicellular animals, both aquatic and terrestrial, exist in an " internal sea " of extracellular fluid enclosed within the integument of the animal. From this fluid, the cells take up O2 and nutrients; into it, they discharge metabolic waste products.The ECF is more dilute than  present day seawater,but its composition closely resembles that of the primordial oceans in which presumably, all life originated. The plasma and the cellular elements of the blood, principally red blood cells, fill the vascular system, and together they constitute                                                                               
the total blood volume.The interstital fluid is that part of the ECF that is out side the vascular system,bathing the cells.About one           
third of the total body water is extracellular; the remaining two thirds are intracellular.In the average 70 kilogram adult human,human the total body water is about 60% of the body weight,or about 42 liters.This percentage can change,depending on age,sex,and degree of obesity.Woman normally have more body fat than man,they contain slightly less water man in propotion to their body weight.Therefore when discussing the average body fluid compartments, we should realize that variations exits, depending on age, sex, and percentage of body fat.   

Control of the body 

1.Within the organs to control functions of the individual parts of the organs.
2.Others operate throughout the intire body to control the interrelations between the organs.
For instance,.
A.The respiratory system,operating in association with the nervous system regulates the concentration of CO2 in the extracellular fluid (ECF).
B. The liver and pancrease regulate the concentration of glucose in the ECF.
C.The kidneys regulate concentration of hydrogen,sodium ,potassium,phosphat and other ions in the ECF.

Even for more importent are the limits beyond which abnormalities can cause death:An incre ase in the body temperature of only11degree F ( 7 degree C ) above normal can often lead to vicious circle of increasing cellular metabolism that literally destroys the cells.Very narrow range for the acid base balance of the body, with a normal pH value of 7.4 and lethal values only about 0.5 on either side of the normal value.Also when the calcium ion concentration falls below about one half normal the person likely to experience tetanic concraction of muscles throughout the body because of spontaneous generation of nerve impulses in the
peripheral nerves. When glucose concentration falls below one half narmal the person frequently develop extreme mental irritability and some times even convulsions.    

Extracellular fluid transport and body
The blood circulatory system : Extracellular fluid transported through all parts of the body in two stages. The first stage is movement of blood through the body in the blood vessels, and the second is movement of fluid between the blood capillaries and the intracellular spaces between the tissue cells. All the blood in the circulation traverses the entire circulatory circuit an average of once each minute when the body is at rest and as many as six times each minute when a person is extremely active.As blood passes through
the blood capillaries continual exchange of extracellular fluid also occurs between the plasma portion of the blood and the interstitial fluid that fills the intercellular spaces. The walls of the capillaries are permeable to most molecules in the plasma of the blood, with the exception of the large plasma protein molecules. Therefore,large amounts of fluid and its dissolved constituents diffuse back and forth between the blood and the tissue spaces. This process of diffusion is caused by kinetic motion of the molecules in both the
plasma and the interstitial fluid. That is, the fluid and dissolved  molecules are continually moving and bouncing in all directions within the plasma and the fluid in the intercellular spaces, and also through the capillary pores. Few cells are located more than 50 micrometers from a capillary to the cell within a few seconds.Thus,the extracellular fluid everywhere in the body-both that of the plasma and that of the interstitial fluid is continually being mixed, thereby maintaining almost complete homogeneity of the extracellular
fluid throughout the body.

Co-transport of glucose and amino acids along with sodium ions : Glucose and many amino acids are transported into most cells against large concentration gradients; the mechanism of this entirely by the co-transport mechanism. The transport carrier protein has two binding sites on its exterior side, one for sodium and one for glucose. Also, the concentration of sodium ions is very high on the out side and very low inside, which provides the energy for the transport. A special property of the transport protein is that the conformational change to allow sodium movement to the enterior will not occur until a glucose molecule also attaches. But when they are both attached,the conformational change takes place automatically, and both the sodium and the glucose are transported to the inside of the cell at the same time. Hence, this is a sodium-glucose co-transport mechanism. Sodium co-transport of the amino acids occurs in the same manner as for glucose,except that it uses a different set of transport proteins. Five amino acid transport proteins have been identified, each of which is responsible for transporting one subject of amino acids with specific mole-
cular characteristics.Sodium co-transport of glucose and amino acids occurs especially in the epithelial cells of the intestinal tract and renal tubules to aid in the absorption of these substances into the blood.