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By the end of this section, you will be able to:
  • Explain the importance of organization to the function of the human organism
  • Distinguish between metabolism, anabolism, and catabolism
  • Provide at least two examples of human responsiveness and human movement
  • Compare and contrast growth, differentiation, and reproduction

The different organ systems each have different functions and therefore unique roles to perform in physiology. These many functions can be summarized in terms of a few that we might consider definitive of human life: organization, metabolism, responsiveness, homeostasis, adaptation, movement, development, and reproduction.


A human body consists of trillions of cells organized in a way that maintains distinct internal compartments. These compartments keep body cells separated from external environmental threats and keep the cells moist and nourished. They also separate internal body fluids from the countless microorganisms that grow on body surfaces, including the lining of certain tracts, or passageways. The intestinal tract, for example, is home to even more bacteria cells than the total of all human cells in the body, yet these bacteria are outside the body and cannot be allowed to circulate freely inside the body.

Cells, for example, have a cell membrane (also referred to as the plasma membrane) that keeps the intracellular environment—the fluids and organelles—separate from the extracellular environment. Blood vessels keep blood inside a closed circulatory system, and nerves and muscles are wrapped in connective tissue sheaths that separate them from surrounding structures. In the chest and abdomen, a variety of internal membranes keep major organs such as the lungs, heart, and kidneys separate from others.

The body’s largest organ system is the integumentary system, which includes the skin and its associated structures, such as hair and nails. The surface tissue of skin is a barrier that protects internal structures and fluids from potentially harmful microorganisms and other toxins.


The first law of thermodynamics holds that energy can neither be created nor destroyed—it can only change form. Your basic function as an organism is to consume (ingest) molecules in the foods you eat, convert some of it into fuel for movement, sustain your body functions, and build and maintain your body structures. There are two types of reactions that accomplish this: anabolism    and catabolism    .

  • Anabolism is the process whereby smaller, simpler molecules are combined into larger, more complex substances. Your body can assemble, by utilizing energy, the complex chemicals it needs by combining small molecules derived from the foods you eat
  • Catabolism is the process by which larger more complex substances are broken down into smaller simpler molecules. Catabolism releases energy. The complex molecules found in foods are broken down so the body can use their parts to assemble the structures and substances needed for life.

Taken together, these two processes are called metabolism. Metabolism is the sum of all anabolic and catabolic reactions that take place in the body ( [link] ). Both anabolism and catabolism occur simultaneously and continuously to keep you alive.

Questions & Answers

how does hormones produce in our body
Shubham Reply
what is an organelle
Shemia Reply
it is the membranious componet within a cell... eg mitochondrion
what is the Endothelial cell?
Jumana Reply
classification of heart
classification of heart 5 points
wym by classification?
differences between meiosis and mitosi
Daniel Reply
how much function it have
Kerlon Reply
what is a cell membrane
call membrane is outer most part of cell
cell membrane consists from phospholipids and proteins
what is elastic constant in muscle in human of body
which topic you at now
what is chromosome
jeff Reply
a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes
what are the medical application of hooks law experiment in human body
what is the physical reason that make people get fractured in bones or rupture of tissues
Hooke's Law is the Law of Elasticty. In scientific terms, Hooke's Law is the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load
what is DNA
deoxyribonucleic acid, a self-replicating material which is present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.
what is prokaryotic cell
am Modesta
what is deamination
what is defusion
Rashima Reply
diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration through a permeable membrane
and osmosis is the same thing ?
The spreading of something more widely
Osmosis is the movement of water molecules from a region of higher concentration to a region of lower concentration
What is a color of blood before it is exposed to oxygen?
hello there....I have a problem concerning an infection in my feet...so can any one help me?
Ngole Reply
what sort of infection?
is the blood pressure increase? why?
Jumana Reply
what is the reason for cardiac arrest
Oseni Reply
stop the heat suddenly
It's usually triggered when there's a malfunction in the heart which causes arrhythmia..hope u get more clarity online
what is cardiovascular system
cardiovascular system in a lame mans under
what y
the heart
cardiovascular system is a system that circulates blood and lymph through the body, consisting of the heart, blood vessels, blood, lymph, and the lymphatic vessels and glands
thanks dein-aboh perfect
your welcome bro
what is the difference between white blood cells and red blood cells?
Gecious Reply
what is the difference between white blood cell and red blood cells
idk enlightening me... the red is for oxygen the white is for the immune system
what are nephrons and their types
Note Reply
when is the actual time that woman can be pregnant?
Jackson Reply
What symptoms occur during menstruation?

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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