Unit 4
Table of Contents
Biology in the News
Chapter 14
The Digestive System Brings Nutrients into the Body
The Mouth Processes Food for Swallowing
The Pharynx and Esophagus Deliver food to the Stomach
The Stomach Stores Food, Digests Proteins, and
Regulates Delivery
The Small Intestine Digests Food and Absorbs Nutrients and
Water
Accessory Organs aid Digestion and Absorption
The Large Intestine Absorbs Nutrients and Eliminates Wastes
How Nutrients are absorbed
Endocrine and Nervous Systems Regulate Digestion
Nutrition: You are what you eat
Weight Control: Energy Consumed Versus Energy Spent
Disorders of the Digestive System
Eating Disorders: Anorexia Nervosa and Bulimia
Chapter 11
The Nervous System has Two Principal Parts
Neurons are the Communication Cells of the Nervous System
Neurons Initiate Action Potentials
Neurological Cells Support and Protect Neurons
Information is transferred from a Neuron to its Target
Chapter 12
Receptors Receive and Convert Stimuli
Somatic Sensations arise from Receptors throughout the Body
Vision: Detecting and Interpreting Visual Stimuli
Disorders of Sensory Mechanisms
Chapter 24
Pollutants Impair Air Quality
Pollution Jeopardizes Scarce Water Supplies
Pollution and Overuse Damage the Land
Energy: Many Options, many Choices
Humans are created a Biodiversity Crisis
Sustainable Development Supports Future Economic Needs
Biology in the News
An article titled Low
Oxygen Levels Could Drive Cancer Growth, Research Suggests that was posted in ScienceDaily (May 3, 2012)states that
low oxygen levels not only have some contribution to certain cancers but that
it is actually the main cause. The
researcher, Ying Xu from the University of Georgia has spent a lot of time
studying and gathering data. A study was
published in the Journal of Molecular Cell Biology stating the lack of oxygen
actually increases cancer growth.
When someone has
cancer the drugs designed to stop it usually stop working 3-6 months after the
first treatment. Drugs also meant to
stop cancer at a molecular level are usually dodged making researchers believe
that the genetic mutation isn’t the powerhouse of cancer. On a study done on seven different types of
cancer in all of them the oxygen levels were very low. When cancer cells don’t have enough oxygen to
make enough energy the cells begin making their own energy through ATP. To make ATP (energy) cancer cells have to
find lots more food to stay alive. So
cancer cells make a new blood vessel in order to find more food which is bad
for someone who has cancer because of further growth. This new blood provides oxygen the cancer
cells crave. The oxygen actually slows
down the cancer growth but it doesn’t last long and the hunt for food
continues.
Ying Xu stresses the
importance of finding a way to keep cancer cells oxygenated. This way the growth is less and the need to
make more blood vessels isn’t there.
Ying Xu says this new method for cancer treatment “could result in a sea
change in cancer treatment”.
Chapter 14
The Digestive System Brings Nutrients into the Body
The job of the digestive system is to bring nutrients to the
body. The digestive system organs all
share that goal including the mouth, pharynx, esophagus, stomach, small
intestine, large intestine, rectum, and anus.
The hollow tube formed by these organs is called the GI or
gastrointestinal tract. There are four
accessory organs also aiding in digestion called the salivary glands, liver,
gallbladder, and pancreas.
Nutrients found in food are absorbed by the body using five
different processes of chewing, secretions, digestion, absorption, and
elimination. There are also tow aids
that help with the digestion process.
One is peristalsis that propels food forward and happens in every part
of the GI tract. Peristalsis is
prevalent in the esophagus and transports food to the stomach quickly. The other aid is segmentation that mixes the
food. Particles of food are then pressed
against the mucosa where the body can absorb nutrients. Segmentation happens mostly in the small
intestine.
The Mouth Processes Food for Swallowing
A person’s mouth starts the process of digestion by first
chewing food into very small pieces. Our
teeth are created in a way that gives us great chewing abilities. We have sharp edged incisors (front teeth)
with pointed canine teeth that helps slice food. Then we also have molars in the back of our
mouths used to grind food up with.
Most adults have 32 permanent teeth by the time we are 25
years old. Inside our mouths are very
high amounts of bacteria that thrive on the food trapped between our
teeth. The bacteria can then release
acids that dissolve enamel causing cavities.
Without our tongue chewing would be highly useless. The tongue is made up of a skeletal muscle
that is then enclosed by a mucus membrane.
The skeletal muscle of the tongue makes it so we have control over its
movements. The tongue allows us to taste
and is necessary for talking and making sounds.
Salivary glands are also important for digesting food because it
produces saliva that moistens the food.
Saliva makes it easier to chew and swallow made up of four ingredients. One ingredient is mucin that holds food
particles together to be swallowed. The
second ingredient is salivary amylase that starts the process of digestion
carbohydrates. The third ingredient in
saliva is bicarbonate that keeps the mouths pH level between 6.5-7.5. The last ingredient is lysozyme that prevents
bacterial growth.
The Pharynx and Esophagus Deliver food to the Stomach
After food has been chewed up the tongue pushes it into the
throat (pharynx) for swallowing. When
swallowing occurs we briefly stop breathing.
The process starts with the tongue pushing the food (bolus) into the
pharynx. With the presence of food,
receptors in the pharynx begin the swallowing reflex. The tongue also helps by further pushing food
back past the epiglottis and esophagus.
Once the act of swallowing has started it can’t be stopped and is now
involuntary from that point on. Just past
the pharynx is the esophagus. The lining
of the esophagus is lined with mucus to help food slide down easily with the
help of gravity. At the base of the
esophagus is the esophageal sphincter that opens and closes momentarily
allowing food into the stomach. The
sphincter prevents stomach contents backflow into the esophagus. When the sphincter malfunctions stomach acid
can go back into the esophagus called acid reflux or heart burn.
The Stomach Stores Food, Digests Proteins, and Regulates
Delivery
The stomach is a muscular sac that can expand along the
digestive tract. The stomach has three
important functions of storing food, digestion, and the rate in which food goes
to the small intestine. There are four
walls that make up the stomach called the mucosa, submucosa, muscularis, and
serosa. The mucosa layer has millions of
tiny openings called gastric pits. The
stomach makes 1-2 liters of gastric juice daily usually after someone has
eaten. The pH level of stomach acid is
about 2. Next food and gastric juices
are carried to the small intestine called chyme.
Muscle contractions keep your stomach small when it is
empty.
As you begin to eat your stomach
relaxes and stretches as needed.
This
triggers peristalsis to increase propelling about a tablespoon of chyme into
the small intestine before the pyloric sphincter closes.
Peristalsis is defined as a wavelike muscular
contractions of the alimentary canal or other tubular structures by which
contents are forced onward toward the opening (
http://education.yahoo.com/reference/dictionary/entry/peristalsis,
accessed 3 May 2012).
After eating
peristaltic contractions occur every 15-25 seconds.
This usually takes between 2-6 hours for the
stomach to empty after a meal.
Chyme
combined with either high acid or fat stimulates hormones to slow down peristaltic
enabling the small intestine to absorb more nutrients.
Besides alcohol and aspirin all nutrients
can’t be absorbed by the stomach.
This
is because the stomach lacks necessary cellular transport and is lined with
mucus.
The Small Intestine Digests Food and Absorbs Nutrients
and Water
In the small intestine digestion continues. The small intestine is made up of three
sections. First, the duodenum is where
most of the digestion takes place but is only 10 inches in length. The next two sections are the jejunum and
ileum where almost all the rest of digestion takes place. The way the small intestine is made makes it
great for absorption. In the small
intestine there are large folds covered in villa, microscopic projections. On the villa are epithelial cells that have
even more smaller projections called microvilla. Last the folds, villa, and microvilla
increase the small intestine surface area by more than 500 times. This makes the small intestine perfect for
absorbing nutrients.
Accessory Organs aid Digestion and Absorption
There are accessory organs that help with digestion as
well. The salivary glands, pancreas,
gallbladder, and liver are all helpful accessory organs.
The pancreas is an organ positioned behind the stomach. The pancreas has both endocrine and exocrine
functions making it very valuable. This
organ secretes and produces digestive enzymes and sodium bicarbonate that
neutralizes stomach acid. There are two
pancreatic ducts that deliver these juices to the duodenum where they help with
digestion.
The liver is located in the upper right abdominal
cavity. The liver helps with the
digestion and absorption of lipids by producing watery liquid called bile. Bile also contains electrolytes, cholesterol,
salt, phospholipids, and pigments all aiding with digestion. The liver is in a great location to start
handling and storing nutrients. This way
the body can access these nutrients as soon as the process of digestion and
absorption has taken place. The liver
also helps to maintain homeostasis throughout the body.
Liver
The gallbladder receives bile that was produced by the liver
via ducts. The gallbladder removes the
water and stores the concentrated bile until the next meal.
The Large Intestine Absorbs Nutrients and Eliminates
Wastes
Digestion then continues to the large intestine where by now
most of the water and nutrients have been removed. The nutrients and remaining water are
absorbed by the large intestine. The
large intestine is larger in diameter than the small intestine but isn’t al
long or efficient at absorbing nutrients.
The three regions within the large intestine are referred to as the
colon. An interesting fact I learned is
that feces isn’t only food the body couldn’t digest but also 5% of feces is
actually bacteria.
How Nutrients are absorbed
Depending on the type of nutrient determines how it is absorbed. Carbohydrates and proteins are absorbed by
active transport. In the small
intestine there are enzymes produced by the pancreas, stomach, and small
intestine that breakdown proteins into amino acids. Carbohydrates actually begin digestion in the
mouth by polysaccharides to disaccharides.
Carbohydrates are completely broken down into simple sugars by the small
intestine. Lipids are digested into
fatty acids and monglycerides. This
happens because they are non-polar so the fatty acids and monglycerides
dissolve into micelles. Micelles are
small bile, salt, lecithin droplets that have a polar surface and a non-polar
interior. The next process is that once
inside a cell the fatty acid and monglyceride combine into a triglyceride. The triglycerides are then coated with proteins
called chylomicrons. The chylomicrons
are too big to directly enter capillaries so they travel via lymph.
As the small intestine absorbs nutrients the water
concentration in the intestinal lumen becomes higher than in blood or other
intestinal cells. This is due to
diffusion and the ability for the small intestine to absorb water is almost
limitless. Although most water is
absorbed in the small intestine a limited amount of water is also absorbed by
the large intestine. When someone has diarrhea they are usually suffering from
a bacterial infection in the small intestine.
The opposite effect is constipation that occurs when feces stays in the
large intestine for too long. Too much
water is absorbed making the feces dry and hard. Constipation can be painful and can result
from factors such as stress, lack of exercise, and lack of dietary fiber.
Depending if a vitamin is fat or water soluble will
determine how the body absorbs it. Fat
soluble vitamins dissolve and diffuse across the lipid membrane. Vitamins that are water soluble are either
diffused through channels or pores or they are absorbed using active
transport. Almost mine liters of gastric
juices, pancreatic juices, digestive enzymes, and bile are produced and
reabsorbed every day. In addition to
the nutrients we eat our bodies also reabsorb some digestive secretions.
Endocrine and Nervous Systems Regulate Digestion
When we digest our bodies actually go through a temporary
change because of all the nutrients entering the bold stream. The digestive system is the most active when
we eat food or when there is chyme and not active when these items aren’t
there. Once the body absorbs all the
nutrients then the body has to use or store them. The body regulates all the interactions
between organs and makes sure they get the nutrients they need. Nutrients that can’t be used right away are
stores away to be used at a later date.
If the reserves keep building without being used then that person’s body
weight will increase. But when we eat
fewer nutrients then the body uses nutrients from reserves. When this happens on a normal basis body
weight then decreases.
Nutrition: You are what you eat
Nutrition is the key to keeping our bodies healthy and
working correctly. They saying “you are
what eat” is a very true statement.
There are many different food guides available, one of them is called
mypyramid. In mypyramid food is divided
into six different food groups that recommend what people should eat. This program gives options to make a
personalized food/nutrition plan.
Dietary guidelines for Americans by the USDA and the department of
health give the recommended calorie intake.
Most nutritionists believe that the information given by mypyramid is
healthy and accurate. Diets full of
fresh fruits and vegetables are best. A
main source of energy is through eating carbohydrates. Many nutritionists recommend a person’s diet
should contain between 45-65% of carbohydrates.
There are two categories of carbohydrates, either simple or
complex. Simple carbohydrates are found
naturally in fruits and honey. Complex
carbohydrates are made up of many sugar units connected together. The USDA estimates that the average person on
North America ingests at least 142 pounds of sweeteners and/or refined sugars
every year.
Lipids and fats are necessary for cell health. Phospholipids and cholesterol are very
important because they make up most of the cell membrane. Fat is essential for health because it stores
energy, cushions organs, gives skin an insulated layer, and helps to store many
different vitamins. Depending on the
ration of hydrogen and carbon atoms in their fatty acids determines the type of
fat. Saturated fats have two hydrogen
atoms for every carbon atom in the fatty tail.
Saturated fats are typically found in meats, dairy products, and coconut
oil. This type of fat raises bad
cholesterol that can cause many cardiovascular problems including heart disease. Unsaturated fat is oils that stay liquid at
room temperature. They are also missing one
or more pairs of hydrogen atom in there fatty tails. Unsaturated fats are healthier because they
lower bad cholesterol. Examples of
unsaturated fats are olive oil and salmon.
The last type of fat is trans fats that are used to lengthen the time a
product stays good for. Trans fats also
increase bad cholesterol and is found in margarine and shore shelf cookies to
name a couple. So of all the fats out
there unsaturated fats are best.
Nutritionists recommend that lipids should only account for 20-30% of
calories we eat every day.
Protein is vital for every cell because it serves as a
receptor, transports molecules, and is in muscle fibers. Proteins are made up 20 different amino
acids. Our bodies can make 12 amino
acids but relies on the remaining 8 amino acids to come from the foods we
eat. A complete protein has all the
necessary 20 amino acids in one food.
Some meats and soybeans are complete proteins. If you eat a balanced diet then you most
likely will obtain all the required amino acids. People who eat a vegetarian diet have to be
careful to eat a balanced diet because most plants lack one or more amino
acids. Approximately 15% of calories are
recommended to come from protein.
Sometimes during pregnancy or childhood protein deficiencies can come up
causing poor physical and mental performance or can even stunt growth.
A minimum group of 13 chemicals are crucial for us to
properly function. Our bodies produce
some vitamins but most other vitamins we have to get from food and other
sources. Minerals are also crucial for our bodies. They are important for our muscles and
nerves. There are 21 minerals that are
considered essential for maintaining health.
Although we need vitamins and minerals it is also harmful to take too
many at one time.
Fiber is in many fruits, veggies, and grains. It helps to make our feces regular although
our bodies can’t digest fiber. When
people eat a diet that is low in fiber they can suffer from constipation and
are at higher risk for developing colon cancer.
Weight Control: Energy Consumed Versus Energy Spent
The food we eat is converted into energy. This energy is then measured by
calories. To keep a healthy body weight
we have to eat the amount of calories we use.
Researchers use a formula called BMR or basal metabolic rate that tells
you the amount of calories needed for organ function. Some factors that determine someone’s BMR are
gender, age, health, stress level, food intake, genetics, and how much muscle
someone has.
When we consistently eat more calories than we use the
energy is stored in the form of fat. The
amount of fat cells is determined by the time someone is an adult. Researchers believe this might by why some
people have a hard time losing weight.
People who are overweight have 2-3 times more fat cells than someone who
isn’t overweight. When people diet their
fat cells feel like they are starving and send the body into koas making it
hard to lose weight. Instead exercise
will actually change the amount of calories needed each day. To lose a pound of fat a person has to burn
or use up to 3,500 calories. The way
nutritionists recommend the best way to lose weight is by increasing physical
activity and to also reduce the amount of calories consumed. An astounding 80 billion dollars is spent
yearly on medical expenses and lost productivity due to nutrition/health
problems. There have been studies done
that connect obesity and the occurrence of heart disease, diabetes, cancer,
arthritis, and many other health problems.
Disorders of the Digestive System
There are digestive problems that can occur that aren’t necessarily
life threatening. One of the most common
digestive problems is food poisoning caused by bacteria or toxic
substances. Food allergies cause an
allergic response throughout the body causing diarrhea and throwing up. When someone is lactose intolerant they have
a hard time digesting milk. Some
symptoms include gas, bloating, diarrhea, and stomach cramps. Another digestive problem is peptic ulcers
that are sores in the stomach. They are
very painful due to erosion of the mucosal lining of the stomach or
duodenum. The ulcers are usually caused
by bacteria that love acidic environments called helicobacter pylori. Another cause of ulcers is using too much
aspirin or anti-inflammatory drugs. Some
people are intolerant to gluten called celiac disease. Someone who shouldn’t eat gluten experiences
a wide range of symptoms along with how sensitive someone is. A person’s immune system with celiac disease
responds by damaging or destroying villa in the small intestine. Diverticulosis is a condition where the large
intestines wall is weak. People with
this condition don’t usually feel pain but have inflammation or
infections. Noncancerous growths in the
colon are called colon polyps that form in many different places in the body. Hepatitis is inflammation of the liver caused
by toxic products or viruses. Researchers
have found five different viruses that cause hepatitis. The most common forms of hepatitis are hepatitis
A, B, and C.
Malnutrition is caused by an unbalances or unhealthy
diet. The United Nations has estimated
that 800 million people are undernourished.
That is about 13% of the world’s population that doesn’t have correct
nutrition. Sadly about 20 million people
die from starvation every year.
Many people are slightly to extremely overweight. The world health organization has declared
obesity to be a world epidemic. Obesity
has greatly increased from 12.6 to 34% in only 16 years. Even in remote places like Papua New Guinea
where people were never overweight are now showing some obesity. Even though there is lots of interest in fat
genes but we can’t blame these genes for the entire world being
overweight. I know here in the United
States nothing is done in moderation.
Everything is supersized and “diet” making people believe something is
healthy when it really isn’t.
Eating Disorders: Anorexia Nervosa and Bulimia
Both men and women suffer from eating disorders. Most eating disorders are common in
industrialized western civilizations.
Two eating disorders are anorexia and bulimia. Anorexia is where a person either stops
eating or obsessively diets. They do
this to the point of starvation or even death.
Bulimia is where someone eats then throws up or takes other measures to
reduce calorie intake. Both of these
conditions hurt the body and mind of the person. Although it is unsure what causes eating
disorders many people who have an eating disorder also suffer with depression
and anxiety.
Chapter 11
The Nervous System has Two Principal Parts
The nervous system is always receiving information and
sorting through information in our brains memory bank. The nervous system deciphers and makes sense
of information very fast making the body able to act quickly. There are four characteristics of the nervous
system. One characteristic is the ability to receive information from many
different senses at the same time.
Another characteristic if the nervous system is the ability to take
information from many different places and put it together to make sense. The third characteristic is the nervous systems
ability to process things fast and produce a response in little as one tenth of
a second. The last characteristic of the
nervous system is the ability to initiate muscle response, glandular
secretions, and conscious thought and emotion.
The nervous system works closely with the endocrine system to maintain
homeostasis.
The nervous system includes the central nervous system (CNS)
and the peripheral nervous system (PNS).
The CNS is made up of the brain and spinal cord. The CNS receives, processes, and stores
information. The PNS carries information
to the brain and spinal cord.
Neurons are the Communication Cells of the Nervous System
Neurons are the communication cells in the nervous
system. Neurons generate and conduct electrical
impulses from one part of the body to another are called action
potentials. Single celled neurons can
range all the way from the spinal cord to the toes. There are three types of neurons in the
nervous system. Sensory neurons of the
PNS respond to light or pressure stimuli.
They transmit information to the CNS though electrical pulses. Interneurons in the CNS receive and disperse information
from sensory neurons. Motor neurons in
the PNS transmit impulses away from the CNS to the body’s tissues and
organs.
All neurons are made up of a cell body, one or more
dendrites, and one axon.
The nucleus
contains DNA that is in the cell body with the mitochondria and the cells other
organelles.
Dendrites are defined as one
of the threadlike extensions of the cytoplasm of a neuron; dendrites branch
into treelike processes and compose most of the receptive surface of a neuron (
http://medical-dictionary.thefreedictionary.com/dendrite,
accessed 26 Apr 2012).
Interneurons and
motor neurons have many dendrites that extend in all directions from the cell
body.
An axon is a long and thin tube that
is part of the cell membrane.
Axons
specialize in guiding electrical impulses.
Usually the motor neurons or interneurons get the information from other
neurons through its dendrites.
Neurons Initiate Action Potentials
The sodium potassium pump is important in controlling cell
volume and is done by removing sodium ions from the cell. The sodium potassium pump is necessary for
developing and maintaining electrical charges across the cell membrane. Neurons that are resting are called resting
membrane potential. The resting membrane
potential of a neuron is -70 millivolts (mV).
This means the inside is negatively charged in comparison to the outside
of the cell. The sodium concentration is
the interstitial fluid is much higher than the sodium concentration in the
cytoplasm. Sodium is always seeping into
the cell and potassium is always diffusing out of the cell. Active transport balances the rate of seepage
of sodium and potassium through pumps working in opposite directions. When a resting neuron gets an impulse from
another neuron it goes through changes. Depending
on the signal the change might depolarize the membrane making the voltage
closer to zero. The change has the possibility to
hyperpolarize it making it making it even more negative. A neuron can receive hundreds of impulses
from other neurons. This results in many
action potentials at the same time. An
action potential is a sudden reverse in voltage that occurs across the cell
membrane. An action potential is the
only form that information is transmitted over long distances by the nervous
system. An action potential happens
because the axon membrane has voltage sensitive ion channels that open and
close when a threshold has been reached.
When an action potential is happening an axon can’t create another
action potential called the refraction period.
This guarantees the impulses can only travel in one direction at a
time. An action potential is a
phenomenon that either happens or it doesn’t happen. The number of action potentials range from as
little as zero to hundreds in only a second.
Stronger stimuli don’t generate faster or bigger action potentials but
rather produces more action potentials.
Then depending on the neuron the action potential can range in speed
from 5-250 mph. Action potential speed
is better with the larger diameter of the axon.
It doesn’t matter if neurons are generating action potentials the sodium
potassium pump always keeps normal concentrations to maintain homeostasis.
Neurological Cells Support and Protect Neurons active
transport
Of all the cells that make up the nervous system only 20% of
the cells are neurons. The rest of the
cells are neuroglia cells that provide physical support and also protects neurons
ensuring healthy concentrations of the chemicals around them. Neurons axons are protected by neuroglia
cells in the peripheral nervous system are called Schwann cells. The Schwann cells produce a fatty insulation
layer called myelin. During the
development of Schwann cells a shiny white shielding layer is around the axon
is formed called the myelin sheath. The
gaps between Schwann cells are called the nodes of Ranvier. The myelin sheath is important because it
helps to insulate the neuron saving it energy.
It also speeds up the impulse transmissions and helps to regenerate
damaged or cut axons in the PNS. Some
axons take anywhere from a few weeks to a year to revive depending on the
length of the axon.
Neurons in the CNS don’t revive after an injury has occurred. This explains why spinal injuries and
disorders like multiple sclerosis result in permanent loss of function. With multiple sclerosis the myelin sheath in
the brain and spinal cord slowly form hard scar tissue. Neurons become no longer insulated and hinder
the impulse transmission. This disorder
usually appears in people between the ages of 20 and 40.
Information is transferred from a Neuron to its Target
Information is transferred from a neuron to the place it
needs to go called a synaptic transmission.
When a synaptic transmission takes place the cell membrane of the neuron
sends messages. The order in which synaptic
transmissions occur is in a particular pattern.
After a synaptic transmission takes place several factors control the
response to the neurotransmitters.
Scientists have identified more than 50 chemicals that can function as neurotransmitters
that are stored in the axon bulb and then released in reply to a potential
action. Neurotransmitters are classified
as either excitatory, inhibitory, or both.
Excitatory neurotransmitters depolarize a postsynaptic cell and
encourage new impulses. Inhibitory neurotransmitters
cause the postsynaptic cell to hyperpolarize meaning the inside of the cell
becomes more negative. Hyperpolarization
makes it harder for a threshold to be reached.
Some neurotransmitters can be excitatory or inhibitory depending on their
receptor type. The effects of
neurotransmitters are short lived and when the signal stops the transmission
stops as fast as it started. The dialogue
between the action potential to the neurotransmitter allows the postsynaptic
cell to process lots of information.
Chapter 12
Receptors Receive and Convert Stimuli
A human’s sensory mechanisms are constantly providing the
brain with information about the outside and inside world. The sensory information is received and
converted into nerve impulses. The nerve
impulses are then transmitted to the brain where everything is made sense
of. Sensory input that cause changes
either outside or inside the body are called stimuli. The stimuli are in the form of heat,
pressure, sound, or even chemicals.
Receptors are specialized to receive stimuli and convert its energy into
another form. Some receptors have
dendritic structures of sensory neurons and are powerful enough to start an
impulse. We feel a sensation when the
central nervous system gets an impulse and we are consciously aware it
happened. When we understand what a
specific sensation means this is called perception.
By determining the type of stimulus energy receptors are
classified by how they convert the energy.
Mechanoreceptors respond to sound waves, fluid pressure, physical touch,
and gravity. Thermoreceptors respond to
hot and cold. Pain receptors respond to
chemicals and photoreceptors respond to light.
There are only a few receptors that we aren’t consciously
aware of their actions. They are trying
to maintain homeostasis and monitor blood pressure and fluid volumes. They also regulate the chemicals within our
internal environment.
Nerve impulses are transmitted from receptors to specific
areas in the brain. An impulse that
generates stimuli for vision goes to the exact spot in the brain designated for
vision. An interesting fact is that when
you are punched in the eye it can fell like you saw stars. This is because the eye triggers impulses in
the visual sensory neurons that interpret it as light. The central nervous system gets the
information it needs from knowing where the impulse came from and also by how
often they receive an impulse. The central nervous system also has the
ability to pick what sensation it wants to concentrate on. Receptors that are in the skin adapt very
fast to light tough or pressure. The
central nervous system knows what’s going on without overloading the senses
with information. When someone has
persistent sensations like pain the body is trying to alert us of an injury,
illness, or tissue damage so appropriate action can be taken.
Somatic sensations include temperature, touch, vibration,
pressure, and pain. The five senses of
taste, touch, smell, hearing, and balance have specific receptors linking them
to the particular part of the body.
Somatic Sensations arise from Receptors throughout the
Body
We feel somatic sensations from many different receptors in
the body. Some of the somatic sensations
we experience are pleasurable because the receptors that detect somatic
sensations are in the skin, joints, tendons, skeletal muscles, and internal
organs. In places where you have more
sensitivity you have more neurons and vice versa. The place where all the information goes is
called the somatosensory area in the primary motor area in the frontal lobe of
the brain. The receptors that sense
touch, pressure, and vibration are called mechanoreceptors. All mechanoreceptors have altered dendric
endings of sensory neurons. Although
there are receptors in many different places in the body an impulse requires
intense stimulation. One of the most
popular mechanoreceptors is muscle spindles.
A muscle spindle is a small bundle of skeletal muscle cells located in
skeletal muscles. A muscle spindle
monitors muscle length which usually also determines how a joint is positioned
due to how it is attacked to the bone.
Near the skins surface are thermoreceptors that use the
information they gather determining hot and cold. Thermoreceptors are able to adapt fast and adjust
sensory input so the feelings are too intense.
An example of this is getting into a hot bath. At first the bath is very hot but after a
minute it doesn’t feel as hot. Other
thermoreceptors in the abdominal and thoracic organs monitor the temperature
within our bodies. These receptors don’t
adapt to maintain homeostasis.
Most of us avoid doing things that cause us pain. The body’s ability to feel pain is actually
important in our survival. Pain warns us
of injuries and unsafe stimuli. Some
pain is fast and sharp occurring in only 1/10th of a second after
the stimuli. A good example of fast pain
is when you go to the dentist to get a tooth drilled. Other pain is slower to feel taking seconds
to hours to experience after an injury has occurred induced by a chemical
release. A good example is when you work
out it isn’t until many hours later that you feel the uneasy muscle pain. There is also a phenomenon called referred
pain in which the body doesn’t know where the pain is coming from. The body then randomly assigns a place to tell
the body where the pain is coming from.
Referred pain is very common and an example of this is a heart
attack. When someone is having a heart
attack they sometimes feel pain in the left shoulder or arm. To keep us safe pain receptors don’t usually
adapt.
Vision: Detecting and Interpreting Visual Stimuli
Light travels in wave form at 186,000 miles per second. Our eyes then let us receive and process the
light. To do this the light must be
focused on specialized cells in our eyes called photoreceptors. The white part of our eye is called sclera
and is a tough outer layer. This layer
is continuous with a clear cornea. Light
passes through the cornea and the agueus humor that is a space filled with
fluid that serves as a cushion for the cornea and eye lens. The light either passes through the pupil or
hits the colored part of the eye, the iris.
The iris is a muscle that controls how much light enters the eye. After light passes through the pupil it hits the
lens of the eye. The lens is flexible
and attached by connective tissue to smooth muscle called ciliary muscle. After passing through the pupil it hits the
lens of the eye. The lens in flexible
and attached by connective tissue to smooth muscle called the ciliary
muscle. After passing through the
vitreous humor, light meets the back and side layers of the retina. The retina is made up of photoreceptor cells,
neurons, and some blood vessels. In the
center of the retina is the macula where photoreceptor density is the
highest. When we look and focus directly
on something this is done with the macula.
At the back of the eye is the optic nerve that carries information to
the thalamus. This information is then
sent to the visual cortex. In both eyes
is our optic disk that in each eye has a blind spot. Last are the skeletal muscles that surround
the eye and control movement of the eye.
There are two sets of smooth muscles that the iris controls
the amount of light let into the eye.
When you walk into a room with bright light the two sets of smooth
muscles contract cause the pupil to get smaller. So in unlit places the smooth muscles don’t
contract and the pupil gets larger.
Nerves control the two sets of smooth muscles. When someone is unconscious or has a
concussion, doctors look to see if the pupils are fixed and dilated. They do this to see if the pupils respond to
bright light shined in them. If the pupils
don’t respond this can point to a possible failure of the nervous system.
The ability to focus on objects near and far is done with
the assistance of the ciliary muscle.
When this muscle contracts, the inner radius part of the muscle shrinks
reducing the tightness on the fibers attached to the lens. This action allows the lens to bulge abs we
are then able to focus on a close up object.
As a person gets older the lens has a tendency to stiffen and can’t
bulge in the way it needs to enabling focus.
This results in presbyopia and makes it hard to focus on close up
objects usually appearing after age 40.
Not everyone has the same shape eyeball which makes up unique but can
also affect the way we focus. An
inherited condition called myopia is a condition where the eyeball is longer
than usual. People who have myopia can
easily see near objects but objects in the distance are blurry. A condition where the cornea or lens has an
irregular shape causes blurred vision caused by astigmatism. Astigmatisms can be corrected with special
lenses that help compensate for odd shaped cornea or lens.
The human eye converts light into impulses in the
retina. Our retina makes it so we can
also see color and adapt to different light intensities. There are photoreceptors cells called rods
and cones because of their unique shape.
Rods all have contain the same photopigment as each other called
rhodopsin. Rhodopsin is much more
sensitive to light than the photopigments in cones. This means that in dim light we use rods to
see. Just because humans see in color
doesn’t mean that all animals can see in color too. The reasons why humans can see in color are
because we have three types of cones red, green and blue. Each of these cones contains photopigments
that absorbs red, green, or blue light particles. The brain then understands the light coming
in by the three types of cones. All
three types of cones are stimulated we see white light but when there isn’t any
light we see nothing or black.
Disorders of Sensory Mechanisms
Even though we are meant to see and hear it doesn’t always
work out that way. When someone loses
their hearing they become deaf. Deafness
can occur for many different reasons.
One way someone can have hearing loss is by damaged hair cells. That makes it so sound can’t be translated
into impulses to the sensory nerves called nerve deafness. This can occur from being exposed to loud
sounds. Another type deafness is called
conduction deafness that is caused by damage to the tympanic membrane in the
middle ear. This makes it so sound waves
aren’t relocated to the inner ear. Some
people can benefit from hearing aids or a cochlear implant that converts sound
into electrical signals. Inflammation on
the middle ear is called otitis media.
This is usually the result of a respiratory infection that backs up into
the auditory tubes. A syndrome called
Meniere’s syndrome is an inner ear problem that also impairs a person’s
balance. The cause of this condition is
unknown but symptoms include dizziness, nausea, and progressive hearing
loss.
There are also problems with eyes. When the retina detaches from the choroid,
medical attention is needed. Medical
attention is usually needed when someone receives a blow to the head. The retina tears and peels away from the
choroid. Another eye problem is
cataracts where the eye lens becomes milky.
This creates a normal protein to not be enough creating protein
clumping, making the lens milky. This
can be congenital but can also result from other diseases or disorders. An astonishing 5.5 million people in the
United States have cataracts that impair their vision. When someone has glaucoma, pressure within
the eye rises. This condition occurs
when a drainage vessel becomes blocked. This
creates excess fluid and pressure within the eye and if left untreated can lead
to blindness. Glaucoma develops slowly
over time without symptoms. Macular
degeneration is a disease that is caused by the retina detaching and the
degeneration of photoreceptor cells in the macular portion of the retina. This disease causes visual impairment making
it hard to recognize faces or read. It
is estimated that one out of 155 people are affected by macular
degeneration. This is scary since at
this time there isn’t a cure. It isn’t
that rare to meet someone who has some degree of color blindness. Color blindness is due to a deficiency in one
or more cones. It is rare for someone to
not have all three cones but it does happen.
In this event the person would not see any color at all. Color blindness is usually inherited from the
x chromosome and most commonly effects men.
Chapter 24
Pollutants Impair Air Quality
Humans have been negatively impacting air, water, and
land. The impact is not done just
locally but on a global scale. We
breathe air that is composed of 79% nitrogen, 21% oxygen, 0.03% carbon dioxide,
and other trace amounts of air pollution.
The air pollutants are composed of either CFC’s (chlorofluorocarbons)
used in refrigerators or Halons that are present in fire extinguishers.
Greenhouse gasses are in the upper layer of the atmosphere
or stratosphere. Most greenhouse gas is
water vapor (60%) and the rest is a combination of carbon dioxide, methane,
nitrous oxide, and air pollutants.
Together the greenhouse gases create the greenhouse effect. This allows sunlight to enter earth’s
atmosphere trapping most of the heat which is a natural event. The carbon dioxide part of greenhouse gases
has accumulated over millions of years.
The problem is humans have increases the carbon dioxide levels of the
greenhouse gases. The increase of these
gases rises the average global temperature creating global warming. The main reason is due to burning fossil
fuels for energy which releases carbon into the air. The carbon in fossil fuels is from buried and
decayed plant matter that is preserved in sedimentary process that takes
millions of years. There are some major
types of pollution that directly affect global warming.
Deforestation also raises carbon dioxide levels in the
atmosphere because trees absorb carbon dioxide from the air. A large tree can absorb 50 pounds of carbon
dioxide a year. When deforestation is
done by burning there is double the damage done. For one, there are fewer trees to absorb the
huge amounts of carbon dioxide and second, all the carbon originally absorbed
by the tree is immediately released back into the atmosphere.
The ozone is located in two places. It is the layer near the plants surface
(troposphere) and high up in the atmosphere.
The lower layer is pollution and is very toxic to plants and
animals. The upper layer is very
valuable because it keeps cancer causing ultraviolet (UV) rays out. In the 1980’s the upper ozone layer attracted
notice that it was distress due to CFCs.
By 1985 the stratosphere ozone layer was noticeably thin with large
holes developing at certain times of the year.
The United Nations predicted there would be an increase of the
occurrence of skin cancer. Action was taken and by the mid 1990’s the
size of the hole had stabilized. This
hole still remains the same size today because of the efforts made. It is estimated it will take 100-150 years
for the ozone layer to recover.
Acid rain is caused by sulfur dioxide being released into
the air due to burning high sulfur coal and oil for energy. Another component that contributes to acid
rain is exhaust from auto mobiles. Acid
rain corrodes metal, stone, damages forests, and destroys marine
ecosystems. It is most common in Europe,
southern Canada, and the Northeastern United States. Efforts to stop acid rain have been taking
place since the 1970’s. The Obama
administration’s actions are expected to eliminate most remaining sulfur emissions
by the year 2014.
Smog is the brown or grey haze that blankets large
cities. Most smog is caused by coal and
oil being burned. The combination of
burning these fossil fuels and automobile exhaust can cause many health
problems. These problems include chronic
respiratory illnesses. Smog can also
contain oil droplets, wood, coal ash, asbestos, lead, dust, and animal
waste. Smog is when bothersome when a
warm upper layer of air traps a cooler smog ridden air mass beneath it. There are wide spread cleanup efforts and
efforts to reduce pollution emissions that have been very effective. Cities that used to be constantly blanketed
by smog now have clean air due to their efforts.
Pollution Jeopardizes Scarce Water Supplies
Humans have had detrimental effects on the quality and
availability of water. There are three
main reasons why humans have had this effect.
One reason is because we use so much water and don’t think about the
depletion it causes. Another reason is
that when roads and cities are built in natural vegetation it prevents the
ground from soaking up water. The last
reason is that we pollute our water sources.
Water is a renewable resource because of the evaporation of
the oceans and then returning it in the form of rain or snow. Over 97% of water found on earth is on ocean
form. Another 2% of water is in glacier
and polar ice cap form. Lastly only 1%
of all fresh water that humans require is in aquifers and freshwater lakes and
streams. There isn’t an endless supply
of water the way people think there is.
Sadly people who lie in industrialized countries use 10-100 times more
water than those who don’t live in industrialized countries.
When roads and buildings are put up in places where
vegetation once stood the result is problems with storm water run-off. In older cities especially on the east coast
have problems with storm water and sewage overflow into oceans and polluting
freshwater streams. An astonishing 28
billion gallons of sewage overflow caused by storm water runoff flow into New
York Harbor every year. This then causes
many pathogens like gastroenteritis, ear and eye infections, rashes, respiratory
problems, and hepatitis in people who swim or kayak in those areas.
Natural and negligent causes precious freshwater to become
polluted. Things like chemicals from
factories, pesticides, fertilizers, sewage, oil, and rubber have to go
somewhere. There things usually run off
into fresh water. Toxic pollutants can’t
be broken down naturally and remain in the environment for a long time. Some toxic pollutants include oil, gasoline, pesticides,
herbicides, and heavy metals. Another
problem with toxic pollutants is they remain in the animals that eat or drink
food tainted with these chemicals. When
another animal then eats the animal tainted with these chemicals they now
contain a higher concentration of the chemical. This is known as biological
magnification. A great example of how
this happens is with sea animals. Many
worry about mercury levels in the fish they are eating. As animals eat other animals that contain
mercury over time mercury builds up to extremely toxic levels. People
who have consumed food that contains mercury are at risk of problems with
nervous system development in pregnant women and young children. Other water pollutants cause disease causing
organisms, excess nitrogen fertilizers, and even heat pollution. Heat pollution decreases the amount of oxygen
water carries and also makes marine animals require more oxygen than usually
needed. Heat pollution has the ability
to suffocate and kill many types of marine life.
Many chemicals that pollute surface waters also affect
ground water. When ground water is
polluted it can immediately affect humans and once polluted ground water stays
polluted for a long time. The US
Environments Protection Agency estimated 50% of all water systems contain some
pollution. Although the extent of damage
caused by consuming polluted water isn’t known many speculate it causes many
problems. These problems include
miscarriages, skin rashes, nervous disorders, and birth defects. When ground water is contaminated with
radioactive waste the water stays radioactive for thousands of years.
Oil in oceans causes another great threat. In the past several years many million tons
of oil has ended up in oceans.
Approximately 50% of the oil is due to natural causes but the remaining
50% is due from negligence. Oil that is
improperly disposed of on land washes oil into streams and rivers then dumping
into oceans and accounts for 30% of oil in the ocean. The remaining 20% of ocean oil is due to
accidental oil spills. When oil spills
into the ocean approximately ¼ evaporates, ½ is broken down by bacteria, and
the last ¼ sinks to the ocean floor.
This then coats all the living organisms making their ability to
function hard and usually results in their death. Oil that reaches the shoreline effect
breeding grounds and shows signs of damage many years after the spill. With effective human effort ecosystems can
recover faster than they do without human involvement.
Pollution and Overuse Damage the Land
Many believe it isn’t all about how humans destructively
pollute the land and eater. Rather some
blame people believe should also be directed to the amount humans consume. The United States alone consumes 22 tons of
fuel, metal, minerals, food, and forests for every person every year. This number doesn’t include what it took to
build the materials transported to us and the use of natural resources. The real number that one person consumes
yearly is 88 tons. Humans have almost
cleared half of the Earths forests and have changed one third of the Earths
land mass. Half of the people in the
world live in poverty. These people rely
on their local environment have also taken the means necessary to survive. They cut down trees for fuel, shelter, and
overgrazing livestock. This leads to
desertification which changes land to a desert form and makes it impossible to
grow anything in that area for some time.
Every year approximately 15 million acres become desert by people
stripping the land. War also causes
damage to environments. In Iraq during
the 1980’s- 1990’s valuable farmland was lost due to war. How people decide to dispose of their garbage
also makes an impact. Recycling any
product you can is very important. Even
after recycling for years I find there are more things I didn’t realize I could
recycle. The other way of disposing of
trash is by landfills that when done correctly is very effective. The best thing to do is to consume less and
recycle everything you can.
Energy: Many Options, many Choices
Everyone uses energy.
If we really looked at the energy we use in a day it would be
astounding. There is a choice in how
much energy we decide to use. Choices
like turning the light off when you leave a room and riding your bike to work
are choices we have. Fossil fuels are
not renewable meaning more can’t be produced.
Fossil fuels took millions of years to make but humans are consuming
them at such a fast rate that they will be gone relatively soon. Focus needs to be on renewable fuels that
might include nuclear energy, biomass fuels, wind, water, geothermal energy,
and solar power.
Nuclear energy creates lots of power with little starting
material. Nuclear energy has to be
safely monitored to ensure the core of the nuclear plant doesn’t overheat
causing a meltdown. If there is a
meltdown the negative is the release of radioactive waste that remains in the
environment for thousands of years.
Biofuels are made using plant material.
Depending if a country is poor or industrialized determines the
pollution outcome. Biofuels require
crops grown well so cold climates aren’t a good place to produce biofuels. In places where water flows, dams can be
installed to provide hydroelectric power plants to produce energy. With kinetic energy water is used to turn
turbines that drive electric generators.
Many dams in the western United States are being taken down because they
have negatively impacted pacific salmon.
Wind energy through wind farms harness the wind and generates
power. Geothermal power uses heat from
underground sources deep within the earth.
The most abundant places are near volcanos. In California 5% of energy is produced by
geothermal sources. Solar power is used
to produce electricity in two ways. One
way is using photovoltaic panels to convert light into energy. The panels absorb photons (light) and release
electrons as a direct current. The other
way is to use mirrors to create steam.
The steam is then used to run turbines to generate electricity on a
large scale. Solar power at this time
isn’t very efficient so it isn’t practical to supply a wide amount of energy
for consumers. Only 30% of solar power
technology is effective at energy saving.
Something interesting I learned was how to position your house in ways
that allows less energy use. Also using
building supplies with high thermal mass are helpful in storing winter heat and
keeping a house cool in the summer.
Humans are created a Biodiversity Crisis
Humans are hurting the biodiversity of the world. Biodiversity is referring to species richness
and the variety of living organisms on Earth.
There have been 1.75 million species that have been unidentified on
Earth. It is estimated that there could
actually be more like 10-80 million different species. It is said that the more diverse a place is
the better ecological health the place is in.
Sadly scientists guess that we might never identify some species because
the extinction rate is 50 times higher that it has been in the past 100,000
years. Some reasons for this include pollution
and overharvesting of Earth’s natural resources. This causes natural habitats to be destroyed
resulting in animal and plant extinction.
Farming directly destroys habitat and alters the variety of plants and
animals within the natural ecosystem.
Farming also causes soil erosion but if done without tilling the land
then soil erosion is minimal. Lots of
rainforests are being destroyed by farmers are alarming rates. Another way natural habitats are being
destroyed is by commercial logging.
Loggers are cutting down 800 year old trees in Africa and shipping them
to other countries to be made into furniture, floors , and much more. Sadly logging has increased to frightening
rates. Africa’s Ivory Coast once has 70
million acres of tropical rain forest and now has been reduced to 5-7 million
acres. People will have to recognize and
possess the drive to do something about the biodiversity being lost so
quickly. Urbanization also directly
effects biodiversity. Cities cover only
3% of the Earth’s surface but produces 78% of carbon emissions, 60% of
residential water usage, and 76% of all wood used. Urbanization also reduces the number of bird
and insect populations thus reducing the biodiversity in that area.
Everything is connected and reliant on each other for the
success of biodiversity. Humans are
reliant on so many other species for food, shelter, clothing, and
medicines. An astonishing 25% of
prescription drugs sold in the United States are made from 50 different species
of plants. There are over 265,000
flowering plants in the world but less than 1% of these plants have been tested
for medical uses. Plants also provide
the nutritious foods humans should eat for the best health.
Sustainable Development Supports Future Economic Needs
People need to come together to make changes and start
creating a sustainable environment. In
1987 the World Commission on Environment and Development, defined sustainable
development by “development that meets the needs of the present without
compromising the ability of future generations to meet their economic
needs”. A strategy that is used to help
us reach a sustainable world is to consume less. By consuming less people will actually gain
more. Everyone should recycle as much as
possible for many reasons. Fewer trees
will be cut down and less natural resources depleted by recycling. By using sustainable agriculture developing
systems will raise crops and livestock by following rules that don’t deplete
the Earth’s resources. Another way to
reach a sustainable world is by having a green roof. A green roof is a vegetated roof system that
increases energy efficiency of buildings.
Green roofs provide a water filtering system and absorb pollution,
nitrogen oxides, and carbon dioxide. An
amazing one square meter of a green roof absorbs the amount of pollution
produces by a vehicle driven 10,000 a yearly.
If the rate in which people are having babies doesn’t stop raising then
eventually the death rate will rise to be equal with the birth rate.
By conserving energy in many ways we can stop depleting our
resources. Simple things like unplugging
items when you’re done with them and switching to florescent light bulbs all
help. By using products that are better
for the environment and contain recycled material help the environment. Protect ecosystems that are important because
when they are destroyed the ecosystem is gone forever. Important foods and medicines will be also
gone forever if an ecosystem is destroyed.
Daily decisions we make will shape what type of future is in store for
humans on Earth.
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