TEAS SCIENCE
(Systems)
Body systems
Our bodies consist of a number of biological systems that carry out specific functions
necessary for everyday living.
The Circulatory System
The circulatory system, also known as the cardiovascular system, is a vast network of
organs and blood vessels that acts both as a delivery and waste removal system for the
body. Nutrients, oxygen and hormones are delivered to every cell and as these
necessities are provided, waste products such as carbon dioxide are removed.
Not only does the circulatory system keep our cells healthy, but it also keeps us alive.
The heart constantly receives signals from the rest of the body that direct how hard it
needs to pump to properly supply the body with what it needs, according to Nemours.
For example, when asleep, the body sends electrical signals to the heart that tell it to
slow down. When participating in heavy exercise, the heart receives the message to
pump harder to deliver extra oxygen to the muscles.
How the Circulatory System Works
The heart lies at the center of the circulatory system and pumps blood through the
rest of the network. This hollow muscle is made up of four chambers: The left and right
atriums make up the two chambers at the top and the left and right ventricles form the
two chambers at the bottom. The chambers are separated by one-way valves to ensure
that blood flows in the correct direction.
The rest of the circulatory system is made up of two independent networks that work
together: The pulmonary and systemic systems.
The pulmonary system is responsible for providing fresh oxygen to the blood and
removing carbon dioxide. Oxygen-poor blood arrives from veins leading to the right
atrium of the heart. The blood is then pumped through the right ventricle, then through
the pulmonary artery, which splits off into two and divides into increasingly smaller
arteries and capillaries before entering the lungs. The tiny capillaries form a network
within the lungs that facilitate the exchange of carbon dioxide and oxygen. From the
lungs, the oxygen-rich blood flows back toward the heart.
Next, the systemic system of arteries, veins and capillaries takes over. Arteries and
veins are not the same, although they are both types of blood vessels. Arteries carry
oxygen- and nutrient-rich blood from the heart to all parts of your body. Veins carry the
oxygen- and nutrient-poor blood back to the heart. The capillaries are the smallest type
of blood vessel, and provide the bridge between the arteries and veins.
As the oxygen-rich blood arrives from the lungs, it enters the left atrium and then
travels through to the left ventricle before being pumped throughout the body. The
blood gets pumped through the aorta artery (the largest artery in the body) before
entering the smaller arteries that carry the blood to every part of the body. As the blood
delivers nutrients and oxygen to each cell, carbon dioxide and other waste products are
picked up as the blood flows through the capillaries and into the veins.
The contraction and relaxation of the heart – the heartbeat – is controlled by the
sinus node, which is a cluster of cells situated at the top of the right atrium. The sinus
node sends electrical signals through the electrical conduction system of the heart that
direct the muscle to contract or relax.
The heartbeat is divided into two phases: the systole and diastole phases. In the first,
the ventricles contract and push blood out into the pulmonary artery or the aorta. At the
same time, the valves separating the atria and ventricles snap shut to prevent blood
from flowing backwards. In the diastole phase, the valves connecting to the atrium
open, and the ventricles relax and fill with blood. The sinus node controls the pace of
these two phases.
Circulatory System Diseases
Heart disease is the leading cause of death for both men and women in the United
States, claiming 610,000 people per year, according to the Centers for Disease Control
and Prevention.
Heart disease is a broad term that covers a wide range of diseases and disorders,
including stroke (the blockage of blood to the brain), heart attack (the flow of blood to
the heart is blocked), hypertension (high blood pressure causing the heart to work
harder), arteriosclerosis (the arteries become thick and stiff) and aneurysm (a damaged
blood vessel that can lead to internal bleeding).
Nervous System
The nervous system is a complex collection of nerves and specialized cells known
as neurons that transmit signals between different parts of the body. It is essentially the
body's electrical wiring.
Structurally, the nervous system has two components:

Central nervous system: made up of the brain, spinal cord and nerves. Is the
integration and command center of the body.

Peripheral nervous system: consists of sensory neurons, ganglia (clusters of
neurons) and nerves that connect to one another and to the central nervous
system.
Two main subdivisions of nervous system:

The somatic system consists of nerves that connect the brain and spinal cord with
muscles and sensory receptors in the skin.

The autonomic nervous system regulates certain body processes, such as blood
pressure and the rate of breathing that; work without conscious effort.
Description of the Nervous System
Nerves are cylindrical bundles of fibers that start at the brain and central cord and
branch out to every other part of the body.
Neurons send signals to other cells through thin fibers called axons, which cause
chemicals known as neurotransmitters to be released at junctions called synapses, the
NIH noted. There are over 100 trillion neural connections in the average human brain,
though the number and location can vary.

Neurons (also called neurones or nerve cells) are the fundamental units of the
brain and nervous system, the cells responsible for receiving sensory input from
the external world, for sending motor commands to our muscles, and for
transforming and relaying the electrical signals at every step in between.
A synapse gives a command to the cell and the entire communication process typically
takes only a fraction of a millisecond. Signals travel along an alpha motor neuron in the
spinal cord 268 mph (431 km/h); the fastest transmission in the human body.

Sensory neurons react to physical stimuli such as light, sound and touch and send
feedback to the central nervous system about the body's surrounding
environment.

Motor neurons, located in the central nervous system or in peripheral ganglia,
transmit signals to activate the muscles or glands.

Glial cells, derived from the Greek word for "glue," are specialized cells that
support, protect or nourish nerve cells.
The branch of medicine that studies and treats the nervous system is called neurology,
and doctors who practice in this field of medicine are called neurologists.
What Are the Parts of the Nervous System?
The nervous system is made up of the central nervous system and the peripheral
nervous system:
The Brain and the Spinal Cord are the Central Nervous System.
The nerves that go through the whole body make up the peripheral nervous system.
The human brain is incredibly compact, weighing just 3 pounds. It has many folds and
grooves, though. These give it the added surface area needed for storing the body's
important information.
The spinal cord is a long bundle of nerve tissue about 18 inches long and 1/2-inch
thick. It extends from the lower part of the brain down through spine. Along the way,
nerves branch out to the entire body.
Both the brain and the spinal cord are protected by bone: the brain by the bones of
the skull, and the spinal cord by a set of ring-shaped bones called vertebrae. They're
both cushioned by layers of membranes called meninges and a special fluid called
cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove
waste products.
What Are the Parts of the Brain?
The brain is made up of three main sections: the forebrain, the midbrain, and the
hindbrain.
The Forebrain
The forebrain is the largest and most complex part of the brain. It consists of the
cerebrum — the area with all the folds and grooves typically seen in pictures of the
brain — as well as some other structures under it.
The cerebrum contains the information that essentially makes us who we are: our
intelligence, memory, personality, emotion, speech, and ability to feel and move. Specific
areas of the cerebrum are in charge of processing these different types of information.
These are called lobes, and there are four of them: the frontal, parietal, temporal, and
occipital lobes.
The cerebrum has right and left halves, called hemispheres. They're connected in
the middle by a band of nerve fibers (the corpus callosum) that lets them communicate.
These halves may look like mirror images of each other, but many scientists believe they
have different functions:

The left side is considered the logical, analytical, objective side.

The right side is thought to be more intuitive, creative, and subjective.
So when you're balancing your checkbook, you're using the left side. When you're
listening to music, you're using the right side. It's believed that some people are more
"right-brained" or "left-brained" while others are more "whole-brained," meaning they
use both halves of their brain to the same degree.
The outer layer of the cerebrum is called the cortex (also known as "gray matter").
Information collected by the five senses comes into the brain to the cortex. This
information is then directed to other parts of the nervous system for further processing.
For example, when you touch the hot stove, not only does a message go out to move
your hand but one also goes to another part of the brain to help you remember not to
do that again.
In the inner part of the forebrain sits the thalamus, hypothalamus, and pituitary gland:

The thalamus carries messages from the sensory organs like the eyes, ears, nose,
and fingers to the cortex.

The hypothalamus controls the pulse, thirst, appetite, sleep patterns, and other
processes in our bodies that happen automatically.

The hypothalamus also controls the pituitary gland, which makes the hormones
that control growth, metabolism, water and mineral balance, sexual maturity, and
response to stress.
The Midbrain
The midbrain, underneath the middle of the forebrain, acts as a master coordinator
for all the messages going in and out of the brain to the spinal cord.
The Hindbrain
The hindbrain sits underneath the back end of the cerebrum. It consists of the
cerebellum, pons, and medulla. The cerebellum — also called the "little brain" because it
looks like a small version of the cerebrum — is responsible for balance, movement, and
coordination.
The pons and the medulla, along with the midbrain, are often called the brainstem.
The brainstem takes in, sends out, and coordinates the brain's messages. It also controls
many of the body's automatic functions, like breathing, heart rate, blood pressure,
swallowing, digestion, and blinking.
How Does the Nervous System Work?
The basic workings of the nervous system depend a lot on tiny cells called neurons.
The brain has billions of them, and they have many specialized jobs. For example,
sensory neurons send information from the eyes, ears, nose, tongue, and skin to the
brain. Motor neurons carry messages away from the brain to the rest of the body.
All neurons, however, relay information to each other through a complex
electrochemical process, making connections that affect the way we think, learn, move,
and behave.
Intelligence, learning, and memory. As we grow and learn, messages travel from one
neuron to another over and over, creating connections, or pathways, in the brain. It's
why driving takes so much concentration when someone first learns it, but later is
second nature: The pathway became established.
In young children, the brain is highly adaptable. In fact, when one part of a young
child's brain is injured, another part often can learn to take over some of the lost
function. But as we age, the brain has to work harder to make new neural pathways,
making it harder to master new tasks or change set behavior patterns. That's why many
scientists believe it's important to keep challenging the brain to learn new things and
make new connections — it helps keeps the brain active over the course of a lifetime.
1. Memory is another complex function of the brain. The things we've done,
learned, and seen are first processed in the cortex. Then, if we sense that this
information is important enough to remember permanently, it's passed inward
to other regions of the brain (such as the hippocampus and amygdala) for longterm storage and retrieval. As these messages travel through the brain, they too
create pathways that serve as the basis of memory.
2. Movement. Different parts of the cerebrum move different body parts. The left
side of the brain controls the movements of the right side of the body, and the
right side of the brain controls the movements of the left side of the body. When
you press your car's accelerator with your right foot, for example, it's the left side
of your brain that sends the message allowing you to do it.
3.
Basic body functions. A part of the peripheral nervous system called the
autonomic nervous system controls many of the body processes we almost
never need to think about, like breathing, digestion, sweating, and shivering. The
autonomic nervous system has two parts: the sympathetic nervous system and
the parasympathetic nervous system.
The sympathetic nervous system prepares the body for sudden stress, like if you
witness a robbery. When something frightening happens, the sympathetic nervous
system makes the heart beat faster so that it sends blood quickly to the different body
parts that might need it. It also causes the adrenal glands at the top of the kidneys to
release adrenaline, a hormone that helps give extra power to the muscles for a quick
getaway. This process is known as the body's "fight or flight" response.
The parasympathetic nervous system does the exact opposite: It prepares the
body for rest. It also helps the digestive tract move along so our bodies can efficiently
take in nutrients from the food we eat.
The Senses
I.
Sight. Sight probably tells us more about the world than any other sense. Light
entering the eye forms an upside-down image on the retina. The retina
transforms the light into nerve signals for the brain. The brain then turns the
image right-side up and tells us what we are seeing.
II.
Hearing. Every sound we hear is the results of sound waves entering our ears and
making our eardrums vibrate. These vibrations then move along the tiny bones of
the middle ear and turned into nerve signals. The cortex processes these signals,
telling us what we're hearing.
III.
Taste. The tongue contains small groups of sensory cells called taste buds that
react to chemicals in foods. Taste buds react to sweet, sour, salty, bitter, and
savory. The taste buds send messages to the areas in the cortex responsible for
processing taste.
IV.
Smell. Olfactory cells in the mucous membranes lining each nostril react to
chemicals we breathe in and send messages along specific nerves to the brain.
V.
Touch. The skin contains millions of sensory receptors that gather information
related to touch, pressure, temperature, and pain and send it to the brain for
processing and reaction.
Digestive System
What is the Digestive System?
The digestive system is made up of the gastrointestinal tract—also called the GI tract or
digestive tract—and the liver, pancreas, and gallbladder. The GI tract is a series of hollow
organs joined in a long, twisting tube from the mouth to the anus. The hollow organs
that make up the GI tract are the mouth, esophagus, stomach, small intestine, large
intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the
digestive system.
The small intestine has three parts. The first part is called the duodenum. The jejunum is
in the middle and the ileum is at the end. The large intestine includes the appendix,
cecum, colon, and rectum. The appendix is a finger-shaped pouch attached to the
cecum. The cecum is the first part of the large intestine. The colon is next. The rectum is
the end of the large intestine.
Bacteria in your GI tract, also called gut flora or microbiome, help with digestion. Parts
of your nervous and circulatory NIH external link systems also help. Working together,
nerves, hormones, bacteria, blood, and the organs of your digestive system digest the
foods and liquids you eat or drink each day.

Gastrointestinal tract: A series of hollow organs joined in a long, twisting tube
from your mouth to the anus. The organs that make up your gastrointestinal tract
are the mouth, esophagus, stomach, and small intestine, large intestine, which
includes the colon and rectum, and anus. Also called the GI tract, alimentary
canal, or digestive tract.

Esophagus: The muscular tube that carries food and liquids from your mouth to
your stomach.

Hormones: A chemical one part of your body makes and releases into your blood
to help trigger or control functions in another part of your body.
Why is Digestion Important?
Digestion is important because your body needs nutrients from food and drink to work
properly and stay healthy. Proteins, fats, carbohydrates, vitamins NIH external link,
minerals NIH external link, and water are nutrients. Your digestive system breaks
nutrients into parts small enough for your body to absorb and use for energy, growth,
and cell repair.
-Proteins break into amino acids
-Fats break into fatty acids and glycerol
-Carbohydrates break into simple sugars

Amino Acids: The building blocks of proteins. Your body produces many amino
acids, and others come from food. Your blood absorbs amino acids through the
small intestine and carries them throughout your body.

Sugars: A class of carbohydrates with a sweet taste. Glucose, fructose, and
sucrose are all types of sugars.
How Does My Digestive System Work?
Each part of your digestive system helps to move food and liquid through your GI tract,
break food and liquid into smaller parts, or both. Once foods are broken into small
enough parts, your body can absorb and move the nutrients to where they are needed.
Your large intestine absorbs water, and the waste products of digestion become stool.
Nerves and hormones help control the digestive process.
The Digestive Process
Organ
Mouth
Esophagus
Stomach
Small
intestine
Pancreas
Liver
Large
intestine

Movement
Chewing
Peristalsis
Upper muscle in stomach relaxes to let food enter, and lower muscle mixes food with
digestive juice
Peristalsis
None
None
Peristalsis
Peristalsis: The movement of organ walls in the gastrointestinal tract. Peristalsis
moves food and liquid through the gastrointestinal tract and mixes the contents
within each organ.
How Does Food Move Through the GI Tract?
Food moves through your GI tract by a process called peristalsis. The large, hollow
organs of your GI tract contain a layer of muscle that enables their walls to move. The
movement pushes food and liquid through your GI tract and mixes the contents within
each organ. The muscle behind the food contracts and squeezes the food forward, while
the muscle in front of the food relaxes to allow the food to move.
I.
Mouth. Food starts to move through your GI tract when you eat. When you
swallow, your tongue pushes the food into your throat. A small flap of tissue,
called the epiglottis, folds over your windpipe to prevent choking and the food
passes into your esophagus.
II.
Esophagus. Once you begin swallowing, the process becomes automatic. Your
brain signals the muscles of the esophagus and peristalsis begins.
III.
Lower esophageal sphincter. When food reaches the end of your esophagus, a
ring like muscle—called the lower esophageal sphincter —relaxes and lets food
pass into your stomach. This sphincter usually stays closed to keep what’s in your
stomach from flowing back into your esophagus.
IV.
Stomach. After food enters your stomach, the stomach muscles mix the food and
liquid with digestive juices. The stomach slowly empties its contents, called
chyme, into your small intestine.
V.
Small intestine. The muscles of the small intestine mix food with digestive juices
from the pancreas, liver, and intestine, and push the mixture forward for further
digestion. The walls of the small intestine absorb water and the digested
nutrients into your bloodstream. As peristalsis continues, the waste products of
the digestive process move into the large intestine.
VI.
Large intestine. Waste products from the digestive process include undigested
parts of food, fluid, and older cells from the lining of your GI tract. The large
intestine absorbs water and changes the waste from liquid into stool. Peristalsis
helps move the stool into your rectum.
VII.
Rectum. The lower end of your large intestine, the rectum, and stores stool until it
pushes stool out of your anus during a bowel movement.

Peristalsis: The movement of organ walls in the gastrointestinal tract. Peristalsis
moves food and liquid through the gastrointestinal tract and mixes the contents
within each organ.

Sphincter: A ring-like muscle that opens and closes to let fluid or other matter
pass into or out of an organ.

Digestive juices: Fluids produced in your gastrointestinal tract to help break down
food.

Chyme: A thick liquid of partially digested food and digestive juices made in your
stomach. Chyme moves from your stomach into your small intestine for further
digestion.

Bowel movement: Stool passed out of your body through the rectum and anus.
How Does My Digestive System Break Food into Small Parts my Body can use?
As food moves through your GI tract, your digestive organs break the food into smaller
parts using:

Motion, such as chewing, squeezing, and mixing

Digestive juices, such as stomach acid, bile, and enzymes
-Mouth. The digestive process starts in your mouth when you chew. Your salivary glands
make saliva, a digestive juice, which moistens food so it moves more easily through your
esophagus into your stomach. Saliva also has an enzyme that begins to break down
starches in your food.
-Esophagus. After you swallow, peristalsis pushes the food down your esophagus into
your stomach.
-Stomach. Glands in your stomach lining make stomach acid and enzymes that break
down food. Muscles of your stomach mix the food with these digestive juices.
-Pancreas. Your pancreas makes a digestive juice that has enzymes that break down
carbohydrates, fats, and proteins. The pancreas delivers the digestive juice to the small
intestine through small tubes called ducts.
-Liver. Your liver makes a digestive juice called bile that helps digest fats and some
vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the
small intestine for use.
-Gallbladder. Your gallbladder stores bile between meals. When you eat, your
gallbladder squeezes bile through the bile ducts into your small intestine.
-Small intestine. Your small intestine makes digestive juice, which mixes with bile and
pancreatic juice to complete the breakdown of proteins, carbohydrates, and fats.
Bacteria in your small intestine make some of the enzymes you need to digest
carbohydrates. Your small intestine moves water from your bloodstream into your GI
tract to help break down food. Your small intestine also absorbs water with other
nutrients.
-Large intestine. In your large intestine, more water moves from your GI tract into your
bloodstream. Bacteria in your large intestine help break down remaining nutrients and
make vitamin K NIH external link. Waste products of digestion, including parts of food
that are still too large, become stool.

Bile: Fluid made by your liver carries toxins and waste products out of your body.
Bile also helps you digest fats and the fat-soluble vitamins A, D, E, and K. Bile is
stored in your gallbladder.

Enzyme: A substance that speeds up chemical reactions in your body.

Saliva: A fluid produced by your salivary glands that moistens food in your mouth
so it moves more easily through the esophagus into your stomach. Saliva also
contains an enzyme that begins to break down the starch in food into molecules
called maltose.
What Happens to the Digested Food?
The small intestine absorbs most of the nutrients in your food, and your circulatory
system passes them on to other parts of your body to store or use. Special cells help
absorbed nutrients cross the intestinal lining into your bloodstream. Your blood carries
simple sugars, amino acids, glycerol, and some vitamins and salts to the liver. Your liver
stores, processes, and delivers nutrients to the rest of your body when needed.
The lymph system NIH external link, a network of vessels that carry white blood cells and
a fluid called lymph throughout your body to fight infection, absorbs fatty acids and
vitamins.
Your body uses sugars, amino acids, fatty acids, and glycerol to build substances you
need for energy, growth, and cell repair.

Lymph system: protect from infection.
How Does My body Control the Digestive Process?
Your hormones and nerves work together to help control the digestive process. Signals
flow within your GI tract and back and forth from your GI tract to your brain.
1. Hormones
Cells lining your stomach and small intestine make and release hormones that control
how your digestive system works. These hormones tell your body when to make
digestive juices and send signals to your brain that you are hungry or full. Your pancreas
also makes hormones that are important to digestion.
2. Nerves
You have nerves that connect your central nervous system—your brain and spinal
cord—to your digestive system and control some digestive functions. For example,
when you see or smell food, your brain sends a signal that causes your salivary glands to
"make your mouth water" to prepare you to eat.
Respiration System
The human respiratory system is a series of organs responsible for taking in
oxygen and expelling carbon dioxide. The primary organs of the respiratory system are
the lungs, which carry out this exchange of gases as we breathe.
The lungs work with the circulatory system to pump oxygen-rich blood to all cells
in the body. The blood then collects carbon dioxide and other waste products and
transports them back to the lungs, where they're pumped out of the body when we
exhale.
Parts of the Respiratory System
As we breathe, oxygen enters the nose or mouth and passes the sinuses, which are
hollow spaces in the skull that help regulate the temperature and humidity of the air we
breathe.
From the sinus, air passes through the trachea, also called the windpipe, and into
the bronchial tubes, which are the two tubes that carry air into each lung (each one is
called a bronchus). The bronchial tubes are lined with tiny hairs called cilia that move
back and forth, carrying mucus up and out. Mucus is a sticky fluid that collects dust,
germs and other matter that has invaded the lungs and is what we expel when we
sneeze and cough.
The bronchial tubes split up again to carry air into the lobes of each lung. The right
lung has three lobes while the left lung has only two, to accommodate room for the
heart. The lobes are filled with small, spongy sacs called alveoli, which is where the
exchange of oxygen and carbon dioxide occurs.
The alveolar walls are extremely thin (about 0.2 micrometers) and are composed
of a single layer of tissues called epithelial cells and tiny blood vessels called pulmonary
capillaries. Blood in the capillaries picks up oxygen and drops off carbon dioxide. The
oxygenated blood then makes its way to the pulmonary vein. This vein carries oxygenrich blood to the left side of the heart, where it is pumped to all parts of the body. The
carbon dioxide the blood left behind moves into the alveoli and gets expelled in our
exhaled breath.
The diaphragm, a dome-shaped muscle at the bottom of the lungs, controls
breathing and separates the chest cavity from the abdominal cavity. When air gets taken
in, the diaphragm tightens and moves downward, making more space for the lungs to
fill with air and expand. During exhalation, the diaphragm expands and compresses the
lungs, forcing air out.
Breathing is the process that brings oxygen in the air into your lungs and moves oxygen
and through your body. Our lungs remove the oxygen and pass it through our
bloodstream, where it's carried off to the tissues and organs that allow us to walk, talk,
and move.
Our lungs also take carbon dioxide from our blood and release it into the air when we
breathe out.

SINUSES are hollow spaces in the bones of your head. Small openings connect
them to the nasal cavity. The sinuses help to regulate the temperature and
humidity of the air you breathe in, as well as to lighten the bone structure of the
head and to give tone to your voice.

The NASAL CAVITY (nose) is the best entrance for outside air into your
respiratory system. The hairs that line the inside wall are part of the air-cleansing
system.

Air can also enter through your ORAL CAVITY (mouth), especially if you have a
mouth-breathing habit or your nasal passages may be temporarily blocked.

The ADENOIDS are overgrown lymph tissues at the top of the throat. When your
adenoids interfere with your breathing, they are sometimes removed. The lymph
system, consisting of nodes (knots of cells) and connecting vessels, carries fluid
throughout the body. This system helps your body resist infection by filtering out
foreign matter, including germs, and producing cells (lymphocytes) to fight them.
The TONSILS are lymph nodes in the wall of your pharynx. Tonsils are not an
important part of the germ-fighting system of the body. If they become infected,
they are sometimes removed.


The PHARYNX (throat) collects incoming air from your nose and passes it
downward to your trachea (windpipe).

The EPIGLOTTIS is a flap of tissue that guards the entrance to your trachea. It
closes when anything is swallowed that should go into the esophagus and
stomach.

The LARYNX (voice box) contains your vocal cords. When moving air is breathed
in and out, it creates voice sounds.

The ESOPHAGUS is the passage leading from your mouth and throat to your
stomach

The TRACHEA (windpipe) is the passage leading from your pharynx to the lungs

The RIBS are bones supporting and protecting your chest cavity. They move a
small amount and help the lungs to expand and contract.

The trachea divides into the two main BRONCHI (tubes), one for each lung. The
bronchi, in turn, subdivide further into bronchioles

The RIGHT LUNG is divided into three LOBES, or sections. The left lung is divided
into two LOBES.

The PLEURA are the two membranes that surround each lobe of your lungs and
separate the lungs from your chest wall.

The bronchial tubes are lined with CILIA (like very small hairs) that have a wavelike motion. This motion carries MUCUS (sticky phlegm or liquid) upward and out
into the throat, where it is either coughed up or swallowed. The mucus catches
and holds much of the dust, germs, and other unwanted matter that has invaded
your lungs. Your lungs get rid of the mucus through coughing.

The DIAPHRAGM is the strong wall of muscle that separates your chest cavity
from your abdominal cavity. By moving downward, it creates suction to draw in
air and expand the lungs.

The smallest sections of the bronchi are called BRONCHIOLES, at the ends of
which are the alveoli (plural of alveolus).

The ALVEOLI are the very small air sacs that are the destination of air that you
breathe in. The CAPILLARIES are blood vessels that are imbedded in the walls of
the alveoli. Blood passes through the capillaries, brought to them by the
PULMONARY ARTERY and taken away by the PULMONARY VEIN. While in the
capillaries, the blood moves carbon dioxide into the alveoli and takes up oxygen
from the air in the alveoli.
Immune System
The immune system is made up of special organs, cells and chemicals that fight
infection (microbes). The main parts of the immune system are: white blood cells,
antibodies, the complement system, the lymphatic system, the spleen, the thymus, and
the bone marrow. These are the parts of your immune system that actively fight
infection.
The Immune System and Microbial Infection
The immune system keeps a record of every microbe it has ever defeated, in types
of white blood cells (B- and T-lymphocytes) known as memory cells. This means it can
recognize and destroy the microbe quickly if it enters the body again, before it can
multiply and make you feel sick.
Some infections, like the flu and the common cold, have to be fought many times
because so many different viruses or strains of the same type of virus can cause these
illnesses. Catching a cold or flu from one virus does not give you immunity against the
others.
Parts of the Immune System
The main parts of the immune system are:

White blood cells

Antibodies

Complement system

Lymphatic system

Spleen

Bone marrow

Thymus.
-White blood cells
White blood cells are the key players in your immune system. They are made in
your bone marrow and are part of the lymphatic system.
White blood cells move through blood and tissue throughout your body, looking
for foreign invaders (microbes) such as bacteria, viruses, parasites and fungi. When they
find them, they launch an immune attack.
White blood cells include lymphocytes (such as B-cells, T-cells and natural killer
cells), and many other types of immune cells.
-Antibodies
Antibodies help the body to fight microbes or the toxins (poisons) they produce.
They do this by recognizing substances called antigens on the surface of the microbe, or
in the chemicals they produce, which mark the microbe or toxin as being foreign. The
antibodies then mark these antigens for destruction. There are many cells, proteins and
chemicals involved in this attack.
-Complement system
The complement system is made up of proteins whose actions complement the
work done by antibodies.
-Lymphatic system
The lymphatic system is a network of delicate tubes throughout the body. The
main roles of the lymphatic system are to:
 Manage the fluid levels in the body
 React to bacteria
 Deal with cancer cells
 Deal with cell products that otherwise would result in disease or disorders
 Absorb some of the fats in our diet from the intestine.
 The lymphatic system is made up of:
 Lymph nodes (also called lymph glands) -- which trap microbes
 Lymph vessels -- tubes that carry lymph, the colourless fluid that bathes your
body's tissues and contains infection-fighting white blood cells
 White blood cells (lymphocytes).
-Spleen
The spleen is a blood-filtering organ that removes microbes and destroys old or
damaged red blood cells. It also makes disease-fighting components of the immune
system (including antibodies and lymphocytes).
-Bone marrow
Bone marrow is the spongy tissue found inside your bones. It produces the red
blood cells our bodies need to carry oxygen, the white blood cells we use to fight
infection, and the platelets we need to help our blood clot.
-Thymus
The thymus filters and monitors your blood content. It produces the white blood
cells called T-lymphocytes.
The Body's Other Defenses Against Microbes
As well as the immune system, the body has several other ways to defend itself
against microbes, including:
 Skin - a waterproof barrier that secretes oil with bacteria-killing properties
 Lungs - mucous in the lungs (phlegm) traps foreign particles, and small hairs
(cilia) wave the mucous upwards so it can be coughed out
 Digestive tract - the mucous lining contains antibodies, and the acid in the
stomach can kill most microbes
 Other defenses - body fluids like skin oil, saliva and tears contain anti-bacterial
enzymes that help reduce the risk of infection. The constant flushing of the
urinary tract and the bowel also helps.
Fever is an Immune System Response
A rise in body temperature, or fever, can happen with some infections. This is
actually an immune system response. A rise in temperature can kill some microbes.
Fever also triggers the body's repair process.
A complex network of specialized cells, tissues, and organs that recognize and
defend the body from foreign substances, primarily disease-causing microorganisms
such as bacteria, viruses, parasites, and fungi. Organs and tissues of the immune system
include the bone marrow, spleen, thymus, tonsils, mucous membranes, and skin.
Granulocytes, macrophages, and T lymphocytes are examples of specialized cells. The
lymphatic vessels of the immune system carry immune cells, which converge in lymph
nodes found throughout the body. A swollen lymph node often indicates an active
immune response to a foreign substance. HIV infection gradually destroys the immune
system.
Skeletal System
The human skeletal system is not quite as simple as the popular children's song
suggests. The "head bone" (actually made up of 22 separate bones) is not connected to
the "neck bone," but rather to a series of small bones that go all the way down the back.
And the "toe bone" is actually made up of several bones that connect to another set of
bones that provide structure for the foot. In total, the human skeleton consists of a
whopping 206 bones.
In addition to all those bones, the human skeletal system includes a network of
tendons, ligaments and cartilage that connect the bones together. The skeletal system
provides the structural support for the human body and protects our organs. Our bones
also serve several other vital functions, including producing blood cells and storing and
releasing fats and minerals.
Development and Structure of the Skeleton
Infants are born with about 300 separate bones, according to Nemours, a
nonprofit children's health provider. As a child grows, some of those bones fuse
together until growth stops, typically by the age of 25, leaving the skeleton with 206
bones.
Our bones are separated into two categories based on the purpose and location
of the bones:

The axial skeleton

The appendicular skeleton
The axial skeleton contains 80 bones, including the skull, spine and rib cage. It
forms the central structure of the skeleton, with the function of protecting the brain,
spinal cord, heart and lungs.
The remaining 126 bones make up the appendicular skeleton; they include the
arms, legs, shoulder girdle and pelvic girdle. The lower portion of the appendicular
skeleton protects the major organs associated with digestion and reproduction and
provides stability when a person is walking or running. The upper portion allows for a
greater range of motion when lifting and carrying objects.
Bones are further classified by their shape: long, short, flat, irregular or sesamoid.

Long bones are found in the arms, legs, fingers and toes. These bones are longer
than they are wide and are cylindrical. They move when the muscles around them
contract, and they are the most mobile parts of the skeleton.

Short bones are found in the wrists and ankles and are about equal in their
length, width and thickness.

Flat bones make up the skull, shoulder blades, sternum and ribs. These curved,
thin bones protect internal organs and provide an anchor for muscles.

Irregular bones are those in the spinal cord and face, which, because of their
unique dimension, don't fit in any of the other shape categories.

Sesamoid bones are found in the hands, wrists, feet, ears and knees. These small,
round bones are embedded in tendons and protect them from the great pressure
and force they encounter.
There are some variations between male and female skeletons. For example, the
female pelvis is typically more broad, thin, and round than the male pelvis.
What's Inside your Bones?
Three main types of material make up every bone in your body: compact bone,
spongy bone and bone marrow.
Approximately 80% of every bone is compact bone, which is the hardest and
strongest type of bone and is what allows the body to support its weight. Compact
bone makes up the outer layers of the bone and protects the inner parts of the bones
where many vital functions occur, such as bone marrow production. Compact bone
consists primarily of cells called osteocytes. Microscopic passages in between the cells
to allow nerves and blood vessels to pass through.
About 20% of each bone is spongy bone, which is filled with large holes and
passages. Most often found toward the ends of individual bones, the spongy bone
material is filled with bone marrow, nerves and blood vessels.
Two types of bone marrow fill the pores in spongy bone. Approximately half is red
bone marrow, which is found mainly within flat bones such as shoulder blades and ribs.
This is where all red and white blood cells and platelets (cells that help a cut stop
bleeding) are made. Infant's bones contain all red bone marrow to produce enough
blood cells to keep up with the youngsters' growth.
The other half of marrow is yellow bone marrow, which is found in long bones,
such as thigh bones, and consists primarily of fat. Blood vessels run through both types
of bone marrow to deliver nutrients and remove waste from the bones.
There are four main types of cells within bones:
 Osteoblasts
 Osteocytes,
 Osteoclasts
 Lining cells
-Osteoblasts are cells that create new or repair existing bone material as the bones grow
or break. The cells create a flexible material called osteoid and then fortify it with
minerals to harden and strengthen it. When osteoblasts successfully finish their job, they
retire to become osteocytes or lining cells.
-Osteocytes, found in the compact bone, are responsible for exchanging minerals and
communicating with other cells in the vicinity. They are formed from old osteoblasts
that have gotten stuck in the center of bones.
-Osteoclasts break down existing bone material and reabsorb it. These cells often work
with osteoblasts to heal and reshape bone after a break (the osteoclasts break down the
extra callus formed by the healing process) to make room for new blood vessels and
nerves and to make bones thicker and stronger.
-Lining cells are flat bone cells that completely cover the outside surface of bones. Their
primary function is controlling the movement of minerals, cells and other materials into
and out of the bones.
The skeletal system in an adult body is made up of 206 individual bones. These bones
are arranged into two major divisions: the axial skeleton and the appendicular skeleton.
The axial skeleton runs along the body’s midline axis and is made up of 80 bones in the
following regions:

Skull

Hyoid

Auditory ossicles

Ribs

Sternum

Vertebral column
The appendicular skeleton is made up of 126 bones in the folowing regions:

Upper limbs

Lower limbs

Pelvic girdle

Pectoral (shoulder) girdle
-Skull
The skull is composed of 22 bones that are fused together except for the
mandible. These 21 fused bones are separate in children to allow the skull and brain to
grow, but fuse to give added strength and protection as an adult. The mandible remains
as a movable jaw bone and forms the only movable joint in the skull with the temporal
bone.
The bones of the superior portion of the skull are known as the cranium and
protect the brain from damage. The bones of the inferior and anterior portion of the
skull are known as facial bones and support the eyes, nose, and mouth.
-Hyoid and Auditory Ossicles
The hyoid is a small, U-shaped bone found just inferior to the mandible. The hyoid
is the only bone in the body that does not form a joint with any other bone—it is a
floating bone. The hyoid’s function is to help hold the trachea open and to form a bony
connection for the tongue muscles.
The malleus, incus, and stapes—known collectively as the auditory ossicles—are
the smallest bones in the body. Found in a small cavity inside of the temporal bone, they
serve to transmit and amplify sound from the eardrum to the inner ear.
-Vertebrae
Twenty-six vertebrae form the vertebral column of the human body. They are
named by region:
 Cervical (neck) - 7 vertebrae
 Thoracic (chest) - 12 vertebrae
 Lumbar (lower back) - 5 vertebrae
 Sacrum - 1 vertebra
 Coccyx (tailbone) - 1 vertebra
With the exception of the singular sacrum and coccyx, each vertebra is named for
the first letter of its region and its position along the superior-inferior axis. For example,
the most superior thoracic vertebra is called T1 and the most inferior is called T12.
-Ribs and Sternum
The sternum, or breastbone, is a thin, knife-shaped bone located along the
midline of the anterior side of the thoracic region of the skeleton. The sternum connects
to the ribs by thin bands of cartilage called the costal cartilage.
There are 12 pairs of ribs that together with the sternum form the ribcage of the
thoracic region. The first seven ribs are known as “true ribs” because they connect the
thoracic vertebrae directly to the sternum through their own band of costal cartilage.
Ribs 8, 9, and 10 all connect to the sternum through cartilage that is connected to the
cartilage of the seventh rib, so we consider these to be “false ribs.” Ribs 11 and 12 are
also false ribs, but are also considered to be “floating ribs” because they do not have
any cartilage attachment to the sternum at all.
-Pectoral Girdle and Upper Limb
The pectoral girdle connects the upper limb (arm) bones to the axial skeleton
and consists of the left and right clavicles and left and right scapulae.
The humerus is the bone of the upper arm. It forms the ball and socket joint of
the shoulder with the scapula and forms the elbow joint with the lower arm bones. The
radius and ulna are the two bones of the forearm. The ulna is on the medial side of the
forearm and forms a hinge joint with the humerus at the elbow. The radius allows the
forearm and hand to turn over at the wrist joint.
The lower arm bones form the wrist joint with the carpals, a group of eight small
bones that give added flexibility to the wrist. The carpals are connected to the five
metacarpals that form the bones of the hand and connect to each of the fingers. Each
finger has three bones known as phalanges, except for the thumb, which only has two
phalanges.
-Pelvic Girdle and Lower Limb
Formed by the left and right hip bones, the pelvic girdle connects the lower limb
(leg) bones to the axial skeleton.
The femur is the largest bone in the body and the only bone of the thigh
(femoral) region. The femur forms the ball and socket hip joint with the hip bone and
forms the knee joint with the tibia and patella. Commonly called the kneecap, the patella
is special because it is one of the few bones that are not present at birth. The patella
forms in early childhood to support the knee for walking and crawling.
The tibia and fibula are the bones of the lower leg. The tibia is much larger than
the fibula and bears almost all of the body’s weight. The fibula is mainly a muscle
attachment point and is used to help maintain balance. The tibia and fibula form the
ankle joint with the talus, one of the seven tarsal bones in the foot.
The tarsals are a group of seven small bones that form the posterior end of the
foot and heel. The tarsals form joints with the five long metatarsals of the foot. Then
each of the metatarsals forms a joint with one of the set of phalanges in the toes. Each
toe has three phalanges, except for the big toe, which only has two phalanges.
-Microscopic Structure of Bones
The skeleton makes up about 30-40% of an adult’s body mass. The skeleton’s
mass is made up of nonliving bone matrix and many tiny bone cells. Roughly half of the
bone matrix’s mass is water, while the other half is collagen protein and solid crystals of
calcium carbonate and calcium phosphate.
Living bone cells are found on the edges of bones and in small cavities inside of
the bone matrix. Although these cells make up very little of the total bone mass, they
have several very important roles in the functions of the skeletal system. The bone cells
allow bones to:
 Grow and develop
 Be repaired following an injury or daily wear
 Be broken down to release their stored minerals
Function of the Skeletal System

Support and Protection

Movement

Hematopoiesis

Storage

Growth and Development
What Is Anatomy and Physiology?
Anatomy is the study of the structure and relationship between body parts.
Physiology is the study of the function of body parts and the body as a whole. Some
specializations within each of these sciences follow:

Gross (macroscopic) anatomy is the study of body parts visible to the naked eye,
such as the heart or bones.

Histology is the study of tissues at the microscopic level.

Cytology is the study of cells at the microscopic level.

Neurophysiology is the study of how the nervous system functions.
Organizations of living systems
Living systems can be defined from various perspectives, from the broad (looking at the
entire earth) to the minute (individual atoms). Each perspective provides information
about how or why a living system functions:

At the chemical level, atoms, molecules (combinations of atoms), and the
chemical bonds between atoms provide the framework upon which all living
activity is based.


The cell is the smallest unit of life. Organelles within the cell are specialized
bodies performing specific cellular functions. Cells themselves may be specialized.
Thus, there are nerve cells, bone cells, and muscle cells.

A tissue is a group of similar cells performing a common function. Muscle tissue,
for example, consists of muscle cells.

An organ is a group of different kinds of tissues working together to perform a
particular activity. The heart is an organ composed of muscle, nervous,
connective, and epithelial tissues.

An organ system is two or more organs working together to accomplish a
particular task. The digestive system, for example, involves the coordinated
activities of many organs, including the mouth, stomach, small and large
intestines, pancreas, and liver.

An organism is a system possessing the characteristics of living things—the
ability to obtain and process energy, the ability to respond to environmental
changes, and the ability to reproduce.
Homeostasis
A characteristic of all living systems is homeostasis, or the maintenance of stable,
internal conditions within specific limits. In many cases, stable conditions are maintained
by negative feedback.
In negative feedback, a sensing mechanism (a receptor) detects a change in
conditions beyond specific limits. A control center, or integrator (often the brain),
evaluates the change and activates a second mechanism (an effector) to correct the
condition; for example, cells that either remove or add glucose to the blood in an effort
to maintain homeostasis are effectors. Conditions are constantly monitored by receptors
and evaluated by the control center. When the control center determines that
conditions have returned to normal, corrective action is discontinued. Thus, in negative
feedback, the variant condition is canceled, or negated, so that conditions are returned
to normal.
The regulation of glucose concentration in the blood illustrates how homeostasis
is maintained by negative feedback. After a meal, the absorption of glucose (a sugar)
from the digestive tract increases the amount of glucose in the blood. In response,
specialized cells in the pancreas (alpha cells) secrete the hormone insulin, which
circulates through the blood and stimulates liver and muscle cells to absorb the glucose.
Once blood glucose levels return to normal, insulin secretion stops. Later, perhaps after
heavy exercise, blood glucose levels may drop because muscle cells absorb glucose
from the blood and use it as a source of energy for muscle contraction. In response to
falling blood glucose levels, another group of specialized pancreatic cells (beta cells)
secretes a second hormone, glucagon. Glucagon stimulates the liver to release its stored
glucose into the blood. When blood glucose levels return to normal, glucagon secretion
stops.
Compare this with positive feedback, in which an action intensifies a condition so that
it is driven farther beyond normal limits. Such positive feedback is uncommon but does
occur during blood clotting, childbirth (labor contractions), lactation (where milk
production increases in response to an increase in nursing), and sexual orgasm.
Anatomic terminology
In order to accurately identify areas of the body, clearly defined anatomical terms
are used. These terms refer to the body in the anatomical position—standing erect,
facing forward, arms down at the side, with the palms turned forward. In this position,
the following apply:
-Directional terms are used to describe the relative position of one body part to another.
These terms are listed in Table 1.
-Body planes and sections are used to describe how the body or an organ is divided
into two parts:

Sagittal planes divide a body or organ vertically into right and left parts. If the
right and left parts are equal, the plane is a midsagittal plane; if they're unequal,
the plane is a parasagittal plane.

A frontal (coronal) plane divides the body or organ vertically into front (anterior)
and rear (posterior) parts.

A horizontal (transverse) plane divides the body or organ horizontally into top
(superior) and bottom (inferior) parts. This is also known as a cross‐section.
-Body cavities are enclosed areas that house organs. These cavities are organized into
two groups:
-The posterior/dorsal body cavity includes the cranial cavity (which contains the brain)
and the vertebral cavity (which contains the spinal cord).
-The anterior/ventral body cavity includes the thoracic cavity (which contains the lungs,
each in its own pleural cavity, and the heart, in the pericardial cavity) and the
abdominopelvic cavity (which contains the digestive organs in the abdominal cavity and
the bladder and reproductive organs in the pelvic cavity).
-Regional terms identify specific areas of the body. In some cases, a descriptive word is
used to identify the location. For example, the axial region refers to the main axis of the
body—the head, neck, and trunk. The appendicular region refers to the appendages—
the arms and legs. Other regional terms use a body part to identify a particular region of
the body. For example, the nasal region refers to the nose.