Download The Body`s Systems

Our Bodies and Their Systems
A Model for Society
Our Bodies and Their Systems
In our divided society, we are called to be healers. As healers, we need to envision society in a new way with
systems that work together in harmony. Our own human bodies provide an insightful model of how natural
systems can function with each other in proper ways.
We contend that the systems of society— health care, education, judicial, political, economic, transportation,
communication, and all the others—should interact with each other in the same way that the systems of a
healthy body operate. In healthy individuals, all of their organ systems operate in harmony with each other.
They should serve as the model for a healthy society.
The Cell – the Fundamental Unit of Life
Systems thinking is holistic thinking. Consideration of biological systems starts with the cell, the fundamental
unit of life. A microcosm of the whole organism, each cell contains specialized parts called organelles that
work together to carry out all the fundamental tasks of life for each particular cell. Each organelle carries out a
unique function: some parts help generate the energy required to power the cell; others transport vital
substances from one part of the cell to another; still other organelles function like manufacturing plants,
churning out the raw materials needed for a cell to work properly; certain other parts of the cell assemble and
customize these raw materials so that they are best suited to carry out their tasks; other parts help defend the
cell and maintain a proper internal environment. The cell, then, is very much like a miniature city—a society
that functions in concert to carry out the specialized tasks the cell is designed to do. Helping to orchestrate and
coordinate all of the dynamic functions of the cell is the main information bank of the cell, the nucleus. Here, in
the center of the cell, is stored the DNA of the cell.
DNA—deoxyribonucleic acid— is the material that encodes all the genetic information for the cell and for the
whole body. Each of the 3 trillion cells in the human body, except for the specialized sex cells, contains an
identical set of DNA. The genetic material in the nucleus of a cell is organized into long and twisted strings
called chromosomes. The typical human cell has 46 chromosomes in it. Each chromosome is a long string of
DNA organized into thousands of genes. A gene is a section of the string of DNA that encodes a particular bit
of genetic information. There are about 30,000 genes in a human being. The Human Genome Project has
been working on deciphering the massive amount of information contained in the DNA of human cells.
DNA is a blueprint. Each gene is a set of directions for assembling a certain protein. Proteins are the building
blocks that cells use for constructing its constituent parts and carrying out its intended functions. Not all of the
genes in a person’s DNA are active in every cell. The particular combination of genes used by a cell
determines the cell’s purpose.
The Process of Development – from Conception to Baby
The sperm and egg are cells of the body that each only contains half of the genetic material that other body
cells do—they have 23 chromosomes. When the sperm and egg are united together in the process of
fertilization, the full suite of genetic material—46 chromosomes—is restored.
Fertilization occurs after sperm—about 3 million of them—are deposited in the woman’s cervix, the opening of
the womb. Of these millions of sperm, usually only one of them will reach an egg that has been released from
the ovary. When more than one arrives simultaneously, twins can develop. The sperm penetrates the outer
layers of the egg and fuses with the egg, joining their genetic material. The new cell, created by the union of
the sperm and egg, then begins an intricate process of development, culminating in the creation of a new
baby.
The first step in the process of development is cellular division: one cell becomes two; two becomes four, and
so on, resulting in the formation of a clump of cells. These early cells are stem cells. Each one has the
potential to give rise to any cell type in the body. As development proceeds, the growing cells each become
more and more specialized, and less able to change its type of cell. Cells multiply in at least 260 varieties, and
there are billions of cells in a human body.
A complex set of instructions, relayed by chemical signals inside and around the growing cell, directs the
future development of an individual cell. These instructions guide the cell to turn on and off different genes,
which encode specific proteins that allow the cell to grow more and more specialized. Other chemical
messages serve as a road map for the subsequent development of the cell’s offspring. Two basic messages
are told to the cell and its descendants: what to grow into, and where to go in the developing organism. In this
way, many different kinds of cells grow together to create a body with a unique form, that of the human body.
Cells don’t develop by themselves. Millions of cells follow similar trajectories in their lives. Similar cells then
become tissues; tissues develop into organs; organs function together in systems of the body. From the
earliest stages of cells dividing in the newly formed embryo, body systems are beginning to develop.
With each passing week of gestation, the fetus becomes more and more developed, and what originates as a
clump of dividing cells begins to look distinctively human. By the end of the first trimester, all of the organs of
the body have been roughly formed, and throughout the remainder of the pregnancy, systems of organs begin
to interact with each other: blood cells begin to form and are pumped through the developing circulatory
system; the brain and nervous system begin to control certain body functions; the musculoskeletal system
begins to allow the fetus to move around in the uterus.
When gestation comes to an end and the baby is born, the systems of the body continue to develop. The
central nervous system, in particular, continues to develop in profound ways after the individual is born, and is
influenced by both genetics and the surrounding environment. Early experiences affect the development of the
brain and lay the foundation for intelligence, emotional health, and moral development. Healthy early
development of the brain is vitally dependent on nurturing and dependable relationships.
The Wisdom of the Body
Knowing structure and functions of the body’s organs isn't enough. They are connected to each other as organ
systems which must work in harmony with each other to maintain a steady internal environment in which the
body's 75 to 100 trillion cells can thrive.
Our bodies are surrounded by the external environment, but they also have an internal environment, which
was described in the late 19th century by the French physiologist Claude Bernard (1813-1878). He noted that
body cells remained healthy only when the temperature, pressure, and chemical composition of the internal
environment of the body remained relatively constant. The American physiologist, Walter B. Cannon (18711945), coined the term "homeostasis" to describe this phenomenon. From the two Greek words, "homeo"
meaning the same, and "stasis," meaning standing, homeostasis describes the tendency of the body to
maintain a certain balance or equilibrium. As Cannon emphasized, homeostasis does not mean something
fixed and unchanging that remains the same all the time, but rather "a condition that may vary, but which is
relatively constant." He called this "The Wisdom of the Body."
In health, all of the body’s systems are aligned, constantly interacting to maintain an optimal internal
environment for all of the body’s individual cells, regardless of the hostility of the external environment. There
is no such thing as winners and losers among the body’s organ systems. In the healthy body, ALL of its
components thrive, not just some of them.
This, indeed, is the wisdom of the body.
The Body’s Systems
There are many systems in the body, and together they can seem somewhat overwhelming. What follows is a
brief introduction to each of the major systems of the body, including a description of their primary components
and functions. Understanding the many systems of the body can help us envision how the systems of society
should function together.
Nervous system
The nervous system is the body's primary control system. Composed of the brain, the spinal cord, and nerves,
it sends, receives, and processes nerve impulses throughout the body. Sensory experiences—gathered by the
eyes, ears, skin, and other specialized structures—are transmitted by nerves to the brain and spinal cord.
There, millions of bits of information are integrated and processed, and the brain generates appropriate nerve
impulses to respond to the incoming stimuli. These nerve impulses tell muscles and organs what to do and
how to adapt to the environment. There are three parts of the nervous system that work together: the central
nervous system, the peripheral nervous system, and the autonomic nervous system.
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The central nervous system consists of the brain and spinal cord. It sends out nerve impulses and
analyzes information from the sense organs, which inform the brain about things you see, hear, smell,
taste and feel.
The peripheral nervous system includes the nerves that branch off from the brain and the spinal cord.
It carries the nerve impulses from the central nervous system throughout the body to the muscles and
glands.
The autonomic nervous system regulates involuntary action, such as heartbeat and digestion.
Endocrine System
Along with the nervous system, the endocrine system is one of the body’s vital communication and control
systems. The endocrine system acts to regulate body processes that go on for relatively long periods of time,
including: sexual development; growth; mobilizing the body against stress; maintaining nutrient, electrolyte and
water balance in the blood; and regulation of cellular metabolism. This system is made up of a group of glands
spread throughout the body, including the pituitary gland, thyroid gland, parathyroid glands, adrenal glands,
thymus gland, pineal body, pancreas, ovaries, and testes. The glands produce hormones, releasing them
directly into the bloodstream. Hormones are the body's long-distance messengers, chemicals that operate in
feedback loops to directly change the activity of cells. These hormones are transported to specific organs and
tissues throughout the body and help organs adapt to changing internal and external environments. They also
help orchestrate the interactions of different body systems.
Circulatory System
The cardiovascular or circulatory system is the body's transport system. It is made up of a group of organs that
transport blood throughout the body. The heart pumps the blood through blood vessels, including arteries and
veins, transporting it to all the cells and tissues of the body. Oxygen-rich blood leaves the left side of the heart
and enters the biggest artery, called the aorta. The aorta branches into smaller arteries, which branch further
into even smaller vessels that travel all over the body. The smallest blood vessels are called capillaries and
are found in body tissues. Within capillaries, a vital exchange takes place: blood brings nutrients and oxygen
to the cells and removes carbon dioxide, water, and other waste products of metabolism. The blood, which no
longer contains oxygen and nutrients, then goes back to the heart through veins. Veins carry waste products
away from cells and bring blood back to the right side of the heart. From the right heart, blood is pumped to the
lungs, where a reverse exchange occurs: the waste product carbon dioxide is eliminated, and the blood
becomes restored with oxygen.
As the body’s transport system, the cardiovascular system needs to be responsive to the changing metabolic
needs of the body. To meet the increased physiologic demands placed on the body by exercise, for example,
complex control mechanisms are put into action. As a result, the heart beats faster and more forcefully, and
certain blood vessels constrict while others expand, preferentially shunting nutrient-rich blood to areas of high
demand like the muscles.
Respiratory System
The respiratory system ensures that the body is supplied with oxygen and that carbon dioxide is expelled from
the body. Oxygen is critical to the basic processes of cellular metabolism that sustain life, while carbon dioxide
is a waste product of metabolism. The respiratory system includes the nose, trachea, and lungs. When signals
from the respiratory center of the brain instruct the diaphragm to activate, inspired air enters through the nose
or mouth, traveling down a long tube called the trachea. The trachea branches into two bronchial tubes, or
primary bronchi, which direct air to the lungs. The primary bronchi branch off into even smaller bronchial tubes,
or bronchioles. The bronchioles branch further, ultimately ending in the alveoli, or air sacs. Air follows this path
to the alveoli, where gas exchange occurs: oxygen passes through the walls of the air sacs and blood vessels
into the blood stream while carbon dioxide passes back into the lungs and is exhaled.
Digestive System
The gastrointestinal or digestive system helps provide the body with energy necessary for life. It comprises
organs that break down food into protein, vitamins, minerals, carbohydrates, and fats, which the body needs
for energy, growth, and repair. After food is chewed and swallowed, it goes down the esophagus and enters
the stomach, where powerful stomach acids further break it down. From the stomach the food travels into the
small intestine. Chemicals secreted into the small intestine from the liver and pancreas help continue to break
down the food into nutrients that can enter the bloodstream. Tiny hair-like projections in the walls of the
intestines help transport the nutrients into the blood vessels surrounding the walls. The excess food that the
body doesn't need or can't digest is turned into waste and is eliminated from the body. The liver, which plays
an important role in digesting food, also helps store energy acquired from digested food, build important
proteins for the body, and metabolize various substances in the bloodstream.
Urinary System
The urinary system eliminates waste from the body, in the form of urine. The kidneys remove waste from the
blood, combining the waste with water to form urine. From the kidneys, urine travels down two thin tubes
called ureters to the bladder. When the bladder is full, urine is discharged through the urethra.
The kidneys also play an integral role in maintaining the delicate balance of fluids and electrolytes that allow
cells to function properly. As blood is pumped through the kidneys, the composition of various electrolytes is
adjusted, with extra salts and water being excreted in the urine. By altering the amount of water and solutes in
the bloodstream, the kidneys also are critical in maintaining appropriate blood pressure throughout the body.
Immune System
The immune system is the body's primary defense system, protecting it against infections and diseases. This
system is a complex network of specialized organs, tissues, and cells that work together to respond to external
threats, including viruses, bacteria, fungi and other harmful substances that may enter the body from the
environment. One of its primary functions is to distinguish between molecules inside the body that are native to
the body or foreign invaders, called pathogens. The immune system protects the body in three overlapping
ways:
1. Innate Immunity: Innate defenses act immediately in a non-specific way to deter the incursion of
pathogens. General defenses include physical barriers (such as skin and cilia in mucous membranes)
to prevent entry of threatening substances. Tears, nasal secretions and saliva contain bacteriadestroying enzymes.
2. The inflammatory system: When the general defenses are breached, special cells migrate to infected
areas to engulf pathogens in an inflammatory response. This response helps detect and eliminate the
invader before it can establish a foothold and begin reproducing.
3. The immune response: If an invading pathogen escapes the innate defenses, the body can launch an
adaptive, or specific response against one type of antigen. White blood cells help orchestrate this
process, in which different cell types secrete antibodies and other chemicals to fight disease.
Lymphatic System
The lymphatic system is also a defense system for the body. Consisting of a network of vessels, nodes and a
few specialized organs, it has several key functions:
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filters out organisms that cause disease
produces white blood cells
generates disease-fighting antibodies
distributes fluids and nutrients in the body
drains excess fluids and protein so that tissues do not swell
The lymphatic vessels are closely linked with the circulatory system, and help transport body fluids. These
vessels carry excess fluid away from the spaces between tissues and organs and return it to the bloodstream.
Lymph, the fluid inside these vessels, contains white blood cells that are transported in and out of the
bloodstream as necessary.
Reproductive System
The reproductive system helps to maintain the continuity of life, allowing humans to produce children. Sperm
from the male fertilizes the female's egg, or ovum, in the fallopian tube. The fertilized egg travels from the
fallopian tube to the uterus, where the fetus develops over a period of nine months.
Integumentary System
The integumentary system provides the body's primary contact with the external environment. Comprising the
skin (the largest organ of the body), the subcutaneous tissues and subcutaneous fat, this system serves
several key roles:
 insulates the body, enabling it to maintain a normal core temperature in spite of variation of
temperature of the external environment
 serves as a protective barrier for the body
 supports the removal of waste through dead skin cells and sweat
 maintains proper tissue moisture
 holds receptors for stimuli response
Skeletal System
The skeletal system provides much of the body’s infrastructure. Made up of bones, ligaments and tendons, the
skeleton shapes the body and protects organs. The skeletal system works with the muscular system to help
the body move. A less obvious function of the skeletal system is to serve as a production factory for valuable
cellular material. Bone marrow is a soft, fatty tissue that is found inside bones where red blood cells, many
white blood cells, and other immune system cells are produced and released into the bloodstream.
Muscular System
The muscular system is made up of tissues that work with the skeletal system to enable the body to move.
While all muscles are under the control of the nervous system, some muscles are voluntary, meaning that you
decide when to move them. Others are involuntary, meaning that they are controlled automatically by the
nervous system and hormones without the input of conscious thought. Muscles function by contracting and
expanding, thus allowing the body to move and function.
There are three types of muscle tissue in the body:
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Skeletal muscles, which are voluntary, help the body move. These include muscles of the arms and
legs, the face and head, and the trunk.
Smooth muscles, which are involuntary, are located inside organs, such as the stomach and
intestines.
Cardiac muscle is found only in the heart. Its motion is involuntary.