Table of Contents
The
Digestive System and Nutrition
The Digestive System
The GI Tract
The Five Processes for Digestion
Types of Motility
The Mouth
Teeth
The Tongue
Saliva
The Pharynx and The Esophagus
The Stomach
Gastric Juice
Stomach Contractions
Small Intestine
Other Digestive and Absorption Organs
Pancreas
Liver
Gallbladder
Large Intestine
How Nutrients Are Absorbed
Proteins and Carbs
Lipids
Water Absorption
Vitamins and Minerals
Endocrine and Nervous System Regulate
Digestion
Volume and Content of Food
Nutrients
Nutrition
MyPyramid
Carbohydrates
Lipids
Proteins
Vitamins
Minerals
Fiber
Weight Control
BMR
Physical Activity
Digestive System Disorders
GI Tract Disorders
Accessory Organ Disorders
Malnutrition
Eating Disorders
The
Nervous System
The Nervous System Has Two Parts
Neurons
Neuroglial Cells
Transferring
Information
Sensory
Mechanisms
Receptors Receive and Convert Stimuli
How Receptors are Classified
CNS Interprets Nerve
Impulses
Receptors Adapt to
Continuing Stimuli
Somatic Sensations and Special Senses
Somatic Sensations
Mechanoreceptors
Thermoreceptors
Pain Receptors
Vision
Eye Structure
Light and Focusing
Eye Shape
Sensory Disorders
Disorders of the Ears
Disorders of the Eyes
Human
Impact on the Environment
Pollution and Air Quality
Global Warming
Ozone
Acid Precipitation
Smog
Pollution and Water Supplies
Water is Scarce
Water Runoff
Pollution of Fresh Water
Groundwater Pollution
Oil Pollution
Pollution Damages Land
Works Cited
The
Digestive System and Nutrition
The digestive system is the process food goes through
after you eat it so that your cells can get the nutrients they need. Food goes
through a process where it is broken into very small pieces and then is
digested using enzymes and chemicals. It then makes its way through the body.
As it makes its way through the body, nutrients are absorbed where needed.
Whatever is leftover will be eliminated from the body. Eating healthy foods are
necessary for the body to get the nutrition it needs. Not eating a healthy diet
can lead to some diseases and being overweight.
The Digestive System
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| (Learning.Com) |
The digestive system is made up of the mouth, pharynx,
esophagus, stomach, small intestine, large intestine, rectum and anus. They
make up the gastrointestinal tract, which is a hollow tube. One of the jobs
these organs perform is getting the needed nutrients to the body. The salivary
glands, liver, gallbladder and pancreas are also part of the digestive system
and are accessory organs.
The GI Tract
The walls of the GI tract are made from four layers of
tissue. The deepest tissue layer is the mucosa. Every nutrient goes through the
mucosa when it enters the blood. The next layer is sub mucosa, a connective
tissue that has blood vessels, lymph vessels, and nerves in it. The parts of
food that go through the mucosa enter the blood and lymph vessels here. The
third layer is the muscularis. This is made of smooth muscle layers and allows
movement and motility. The outside layer is the serosa. It protects the other
layers and fastens the GI tract to the wall of the body cavity. A circular
muscle referred to as sphincters separates some of the organs in the GI tract y
closing off the passage way between the organs.
The Five Processes for Digestion
There are five processes that happen for food to be
digested and the nutrients to be absorbed. The first step is mechanical processing
and movement. This is when food is chewed into small pieces and moved forward.
The second process is secretion. This is the digested enzymes, acid, alkali,
bile and mucus being secreted to the GI tract and some hormones that help with
digestion being secreted into the blood. Digestion is next and this is when the
content that is in the lumen is broken down until is results in nutrient
molecules. The fourth process is absorption and happens when the nutrient
molecules enter the blood or lymph. And the last process is elimination and is
the undigested food is passed out of the body through the anus.
Types of Motility
There are two kinds of motility that occur in the GI
tract. Peristalsis is one of them and it pushes food forward. The way this
works is a lump of food stretches the GI tract which causes the muscle behind
it to contract. The contracting muscle pushes the food forward. That part of
the muscle now relaxes and the next part contracts. This happens in all parts
of the GI tract. The other type of motility is segmentation. Segmentation mixes
food together by short sections of muscle contracting and relaxing. This causes
the food in the lumen to be mixed together by the back and forth movement it
creates. This happens mostly in the small intestine.
The Mouth
The mouth is where food enters the GI tract. The mouth
starts the digestive process begins with the food being chewed and broken into
smaller pieces until it is able to be swallowed.
Teeth
Teeth are located in the mouth and are what is used to
break the food into pieces small enough to be swallowed. There are four types
of teeth. Incisors have sharp edges to help cut food. Canines are pointed teeth
that help to tear up the food. Premolars and molars have a flat surface and grind
and crush the food. Children have 20 teeth and adults usually have 32. Teeth
have two parts, the root, which is below the gum line and the crown that is
above the gum line. The crown is surrounded by enamel which is made of calcium
and phosphate and is not living. Under the enamel is dentin which is like bone
and is living. There is an inner pulp cavity where there are blood vessels and
nerves. There are a lot of bacteria in the mouth that thrives on pieces of food
that are in between the teeth. This releases acids that eat away at the enamel
and cause cavities. If the decay is not treated, it can cause inflammation in
the gum tissue and is called gingivitis. This can cause inflammation in the
periodontal membrane and lead to periodontitis. Good dental hygiene and seeing
a dentist regularly can prevent dental problems from becoming serious.
The Tongue
The tongue is a muscle that helps move food over the
teeth so that it can be chewed into smaller pieces. It also smashes food up by
placing it between it and the roof of the mouth. The tongue muscle is
surrounded by mucous membrane and we can control its movement. The tongue also
helps with speech and gives us a sense of taste.
Saliva
There are three pairs of salivary glands and they make saliva
which is a watery fluid. They are the parotid gland that is located by the back
of the jaw, the sublingual gland that is located under the lower jaw, and the
submandibular gland that is below the tongue. Some things saliva contains are
mucin, salivary amylase, bicarbonate, and lysozyme. Mucin is a protein and it
helps chewed up food be swallowed easier because of its mucus like substance.
Salivary amylase starts digesting carbohydrates. Bicarbonate keeps the pH of
the mouth where it needs to be, between 6.5 & 7.5 and might protect teeth
from bacteria. Lysozyme stops bacteria from growing.
The Pharynx and The Esophagus
Once food has been chewed up and mixed with the saliva
the tongue pushes the food into the pharynx where it is swallowed. When you
swallow, there is a series of events that take place. First the food enters
into the pharynx. When food enters the pharynx, it stimulates receptors and the
second event takes places. The second event is called the swallowing reflex.
The soft palate raises enough so that the passage into the nasal cavity is
closed off. The larynx also rises during this process. The epiglottis closes
off the airway so that food does not enter the airway. The tongue pushes the
food back even more so that it goes into the esophagus. Once you start to
swallow something you cannot stop the process. The esophagus is just past the
pharynx and is made of skeletal and smooth muscle and connects the pharymn to
the stomach. The esophagus makes mucus so that food can go down easily. Peristaltic
contractions and gravity move the food through the esophagus. The base of the
esophagus, the sphincter, opens so that food can enter into the stomach then
closes back off. The sphincter sometimes doesn’t work properly and stomach acid
enters the esophagus, a condition known as acid reflux. Acid reflux causes a
burning felling called heartburn. Hitatal hernia can also cause acid reflux.
Extended acid reflux can lead to ulcers in the esophagus so it is important to
seek medical care.
The Stomach
The stomach
expands when we eat and shrinks when it is empty. The stomach has three jobs
that are essential. One of its jobs is to store food until it can be digested.
Digesting food is the next job. This is done with acid and protein digesting
enzymes. The stomach muscle contracts and mixes the food with the acid and
enzymes which helps in breaking down food. The acid also kills bacteria. The
third job of the stomach is sending the food to the small intestine at the
correct rate.
Gastric Juice
The stomach wall has four layers which are mucosa,
submucosa, muscularis and serosa. The mucosal later has millions of small
openings. These openings are called gastric pits and they go to gastric glands.
The cells that are around the gastric glands make hydrochloric acid, mucus,
pepsinogen, intrinsic factor or gastrin. Pepsinogen turns into pepsin which is
a protein digesting enzyme when it comes into contact with stomach acid.
Hydrochloric acid, mucus and pepsinogen are called gastric juice. Most stomach fluid is made right after
eating. The pepsin and acid digest proteins and peptides into amino acids. Once
this is done they are able to be absorbed into the intestine. The gastric
fluids mixed with the food is produces a product called chyme when it goes into
the small intestine. There is a pyloric sphincter that separates the stomach
and small intestine and manages the speed at which chyme enters the small
intestine. The cells in the stomach and gastric glands are always making mucus
to protect them from being harmed by the acid. If for some reason the mucus
becomes weakened, a peptic ulcer may form. These are open sores that are found
in the esophagus and upper small intestine. Intrinsic factor is a protein and
its attaches to vitamin B12 and is absorbed by the small intestine.
Gastrin is a hormone that goes into the bloodstream.
Stomach Contractions
Your stomach is kept small when it is empty by the
stomach contracting. After you eat the stomach stretches and the contractions
stop. When the stomach stretches it is the signal for peristalsis to start.
This pushes the chyme forward and backward and each time there is a contraction
chyme enters the small intestine. These contractions occur every 15-25 seconds.
Peristalsis is more powerful right after you eat and slows down as food goes
out of the stomach.
Small Intestine
Once chime enters the small intestine the digestive
process continues. Proteins, carbohydrates and lipids are digested in the small
intestine. The intestine and pancreas add enzymes that digest food so this can
happen. The proteins, carbohydrates and lipids are turned into small amino
acids, monosaccharides, fatty acids and glycerol and are able go through
mucosal cells and enter the blood. The small intestine has three parts. The
duodenum is where most of the digestion happens. The other parts are the jejunum
and the ileum and this is where absorption mostly happens.
Other Digestive and Absorption Organs
Pancreas
The pancreas is behind the stomach and has a couple of
different jobs. One is it makes hormones that help keep blood glucose levels
constant. It also makes different digestive enzymes that help with digesting
proteins, carbohydrates and lipids. It also makes sodium bicarbonate which
works at a neutral pH level. There are two ducts that connect to the duodenum
so that these can reach the small intestine.
Liver
The liver is in the upper right abdomen. It performs many
different functions and some of them help with the digestive process. One of
the things the liver does that help with digestion is makes bile. Bile includes
electrolytes, cholesterol, bile salts, lecithin and pigments. The liver is
where nutrients are stored. Some other jobs of the liver are:
· Store
fat soluble vitamins
· Store
iron
· Store
glycogen
· Change
glycogen into glucose
· Make
plasma proteins
· Store
and make lipids
· Inactivate
chemicals
· Change
ammonia into something less toxic
· Destroy
old red blood cells
The liver has many essential jobs and it is important
that it functions properly.
Gallbladder
The bile that the liver makes is transported through a
duct to the gallbladder. Most of the water in bile is removed by the
gallbladder and then it stores until. After you eat it enters the small intestine
through the duct.
Large Intestine
Most nutrients and water have been absorbed by the time
it reaches the large intestine. The large intestine absorbs most of what is
left over. It holds the rest until it can be discarded. The diameter of the
larger intestine is bigger the small intestine but it is only half as long. The
cecum is a pouch that chyme enters into from the small intestine. There are
four sections of large intestine that make up the colon. The four sections of
colon are ascending colon, transverse colon, descending colon and sigmoid
colon. The sigmoid colon is where feces are stored.
Here is a short video showing the process.
(Parkison)
How Nutrients Are Absorbed
Proteins and Carbs
When the proteins reaches the small intestine, enzymes
from the pancreas, stomach and small intestine break down the protein until it
turns into an amino acid. The amino acids are moved into the mucosal cells
where they end up in the capillaries. The process of digesting carbohydrates
starts in the mouth by salivary amylase breaking down the polysaccharides and turning
them into disaccharides. The process is then moves to the small intestine where
pancreatic amylase and enzymes from the small intestine work to turn it into
monosaccharide. They then follow a transport path that is very much like the
path of amino acids.
Lipids
When lipids are digested they turn into fatty acids and
monoglycerides. They are nonpolar. Micelles are small beads that are made of
bile salts and lecithin. They move fatty acids and monoglycerides to the
outside of mucosal cells so they can be absorbed. When they have been absorbed
by the cells they come back together and make triglycerides. They are coated
with water and make beads called chylomicrons. Chylomicrons go into the
permeable lacteals and move around by lymph vessels.
Water Absorption
The small intestine can absorb a limitless amount of
water. When there is a high concentration of water in the lumen it is let out
of the small intestine and into the blood. Water passes into the large
intestine and the absorption process continues. The large intestine does have a
limit on how much water it can handle. If the small intestine sends the wrong
mixture of water to food, diarrhea or constipation can occur, depending on
whether there is too much water or not enough.
Vitamins and Minerals
Fat soluble vitamins are dissolved in micelles and are
spread out in the same process as lipids. Water soluble vitamins are spread out
through pores or through active transport. Minerals are spread out through
transport proteins or pores or active transport. The body digests new food we
eat and the gastric juice, pancreatic juice, digestive enzymes and bile we
produce digesting food.
Endocrine and Nervous System Regulate
Digestion
Regulating the digestion system means keeping the
digestion system functioning rapidly and smoothly and absorbing nutrients no
matter what else is happening.
Volume and Content of Food
The volume and content of food effect how digestion is
regulated. When the stomach stretches and protein is present in the stomach a
hormone called gastrin is released. This hormone then lets the body know more
gastric juice is needed. The duodenum stretches when the chyme arrives there.
This helps to mix the chyme. The acid in chyme causes the duodenum to release
the hormone secretin. That causes the pancreas to make water and bicarbonate
which neutralizes the acid. Pat and protein cause cholecystokinin to be
released. Cholecystokinin tells the pancreas to make digestive enzymes.
Cholecystokinin and the duodenum stretching also cause the gallbladder to
release bile.
Nutrients
Lipids, carbohydrates and proteins can be changed to
storage forms of if the body does not need them right away then used when
needed. If we continually consume more than our body can use and our body is
storing nutrients, this may lead to weight gain. When we consume less than our
body needs, our body uses what has been placed in storage and we lose weight.
Nutrition
Nutrients arrive in our bodies through the digestive
system. What nutrients does our body need to be health?
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| (USDA) |
MyPyramid
The MyPyramid was made may the USDA to help people ensure
that they are eating enough of each food group and getting exercise. Foods are
divided into the six food groups and examples of what food fits in the food
groups are given. You can go to the MyPyramid website and get a personalized
plan. There are some people who do not agree with all of the pyramids
recommendations, but it is a good place to start if you are not sure how to eat
healthy.
Carbohydrates
Carbohydrates are a main source of energy and about half
of your daily calories should come from carbs. There are both simple and
complex carbs. Simple carbs are sugars. They may be natural such as those found
in fruits or refined such as those found in granulated sugar and corn syrup.
Refined sugars do not have many nutrients. Complex carbs have many sugar units
strung together. Complex carbs are better for us because they also give us
fiber, vitamins and minerals we need. Starch and glycogen are complex carbs.
They are stored until the body needs them then turned into glucose.
Lipids
Lipids are an important part of every cell. Lipids such
as phospholipids and cholesterol make the cell membrane and cholesterol is the
backbone of steroid hormones and makes bile. Energy is stored in fat. Fat also
provides padding for some organs and stores some vitamins. The liver can make
most lipids but not all. Some of the things the liver cannot make are essential
fatty acids. These must come from food. Most people get more lipids a day than
are recommended. If we are taking in to many then our diet is too high in
saturated fat, cholesterol and trans fat and may make our risk of
cardiovascular disease higher.
Proteins
Proteins are also necessary for every cell. Proteins make
enzymes that help with metabolism. They may be receptor or transport molecules,
they help build muscle and some are hormones. Proteins are made of 20 amino
acids. There are 8 that the body cannot make, they must come from food. These
are called essential amino acids. A complete protein refers to a protein that
has all 20 amino acids. It is important for a diet to be a balance of all
20amino acids otherwise it may result in protein deficiencies which can effect
growth and physical and mental performance.
Vitamins
Vitamins are a group of 13 chemical that are needed for
the body to function as it should. We can make vitamin D if we are exposed to
sunlight and bacteria that are found in the colon can make vitamins K, B6 and
biotin. The rest need to come from food we eat. Vitamins can be either fat or
water soluble.
Minerals
Minerals are necessary for the body to perform processes
correctly. They are ions in plasma and cell cytoplasm, they are chemicals in
the bone; they help with the nerve and muscle activity. There are 21 essential
minerals. 9 are called trace mineral because of the small amount that is
recommended.
Fiber
Our bodies cannot digest fiber but it is an important
part of our diet. It helps feces pass through the colon easier. People who do
not get enough fiber may experience constipation, hemorrhoids, and diverticulosis
and is associated with colon cancer. Most people do not have a diet high enough
in fiber.
Weight Control
Energy that we consume is called calories.
BMR
To keep our weight stable we need to burn the calories we
ingest each day. If we consume more calories than we use, we gain weight. If we
burn more calories than we consume, we lose weight. The BMR, basal metabolic
rate, is used to calculate the number of calories we need to keep our weight
stable.
Physical Activity
Exercise changes the number of calories we burn every
day. Exercise also improves cardiovascular health, strengthens bones, tones
muscles and helps a person to just feel better.
Digestive System Disorders
Most digestive system disorders are not deadly. The most
common one is food poisoning, which is when a person eats something that has
bacteria in it and results in diarrhea and vomiting.
GI Tract Disorders
Some common GI tract disorders include lactose
intolerance. This happens when the enzyme lactase is lost. When someone with
lactose intolerance eats dairy products, they experience diarrhea, gas,
bloating and cramps. Peptic ulcers, which are sores found in the stomach, are
also a GI tract disorder. Another disorder is Celiac disease which is gluten
intolerance. When gluten is eaten the villi in the small intestine is damaged
by the immune system. Diverticulosis is a weak wall in the large intestine.
Colon polyps are a growth in the colon that is not cancerous. Polyps can turn
into cancer so they are removed when found.
Accessory Organ Disorders
Hepatitis is a disease of the liver. There are 5 viruses
that cause hepatitis. There are vaccinations available for some types of
hepatitis. Without treatment hepatitis will lead to liver failure. Gallstones
in the gallbladder can block the flow of bile. If the gallstones grow large
enough to block the bile, treatment is needed.
Malnutrition
Malnutrition is a condition caused by a diet that is not
balanced or is insufficient. It is caused by both over nutrition and under
nutrition. Under nutrition is the more common cause of malnutrition.
Eating Disorders
Eating disorders are most common in industrialized Western
countries and mostly found in women. One type of eating disorder is anorexia
nervosa. This is when someone diets excessively or stops eating entirely.
Symptoms are:
· Refusing
to stay at a healthy body weight.
· Fear
of gaining weight even though they are underweight.
· Distorted
idea of their body weight and shape.
· Menstruation
cycle stops for at least 3 months in a row.
Bulimia
is another eating disorder. Bulimia has a binge and purge cycle where someone
eats then vomits to get rids of the calories they ate. Signs of bulimia are:
· Repeated
times of binge eating.
· Taking
laxatives, diuretics, enemas and self-induced vomiting in an attempt to prevent
weight game.
· Bingeing
and purging twice a week for three months.
· Preoccupied
with body shape.
Bulimics
tend to maintain a normal body weight. What causes eating disorders is not
known but there seems to be psychological and cultural issues associated with
them.
(chichin85)
The
Nervous System
The nervous system has four main traits:
· It
gets information for more than one sense at the same time.
· It
integrates the information it receives.
· It
works very quickly.
· It
initiates certain responses.
Usually
the nervous system works without us being conscious of it but sometimes the
information is brought to our awareness.
The
Nervous System Has Two Parts
The
two parts of the nervous system are the central nervous system or CNS and
peripheral nervous system or PNS. The CNS is made up of the brain and spinal
cord. The PNS takes information to the CNS and takes information from the CNS
to other body parts. The PNS is divided into the somatic division and autonomic
division. The autonomic has the two subdivisions sympathetic and parasympathetic.
Neurons
Neuron
cells conduct electrical impulses so that different body parts can communicate.
There are three types of neurons: Sensory neurons are in the PNS and respond to
pressure and light. They send the information to the CNS. Interneurons send
impulses within the CNS. And motor neurons carry information away from CNS. If
a neuron is not making impulses it is at resting potential. The
sodium-potassium pump maintains the resting potential. When an impulse is
incoming there is a series of steps that cause a change in the resting
potential. These are graded potentials because they are not all the same size.
If the graded potential is strong enough it causes the membrane to reach
threshold and the result is action potential. Action potential has three
events: depolarization, repolarization and reestablishing resting potential.
There is a period called absolute refractory period is which another action
potential cannot be produced. After this period is the relative refractory
period and it is harder than normal for another action potential to be
produced.
Neuroglial
Cells
About
20% of humans cells are neurons, the rest are neuroglial cells and they give
support and protection to neurons and help there be the right concentration of
chemicals in the fluid around them. Most of the neuron axons in the PNS are
protected by neuroglial cells. These are called Schwann cells. They make a
material called myelin with is a fatty insulation. Schwann cells are wrapped
around parts of the axon. This protective layer is called a myelin sheath. The
spaces in between where the axon is not covered are called the nodes of
Ranvier. The parts of the axon that are wrapped in a myelin sheath are called
myelinated neurons. The myelin sheath provides three jobs. It saves the neurons
energy, speeds up the transmission of impulses and helps damaged parts of the
axon regenerate. In the CNS the myelin sheaths are made by a cell called
oligodendrocyte. Neurons in the CNS do not repair themselves after they have
been injured. If the axon is damaged, the myelin sheath degenerates.
Transferring
Information
When
action potential reaches its threshold the information changes to a form that
can be sent to where it needs to go. This is called a neurotransmitter. The
neuron sending information creates a synapse. The presynaptic membrane is from
the membrane sending the information. The postsynaptic membrane is from the
membrane receiving the information. The gap between these two is the synaptic
cleft. Neurotransmitters are excitatory, inhibitory or both.
Sensory
Mechanisms
Your sensory mechanisms give your brain information about
the world that is around you and about your body.
Receptors Receive and Convert Stimuli
Stimuli are something that causes a change in or out of
the body. It is usually some kind of energy but may be a chemical. A receptor
receives the stimuli and turns the energy it receives into another form of
energy. This creates an impulse in a sensory neuron. When the impulse is
acquired by the central nervous system we usually experience some sort of
sensation. When we experience the sensation we then become aware of the
stimuli. Then we may experience perception which is when we understand the
meaning of the sensation.
How Receptors are Classified
Receptors are categorized based on what type of stimulus
energy they convert. Mechanoreceptors react to mechanical energy. Some types of
mechanical energy are sound waves, something touching you, gravity or acceleration.
Thermoreceptors react to temperature such as hot or cold. Pain receptors react
to damaged tissue, pressure and temperature. Chemoreceptors react to chemicals
that are near them. Photoreceptors react to light. Joint receptors just give as
a sense of where are limbs should be, they do not give a sensation. Some
receptors are silent and work to keep homeostasis in the body.
CNS Interprets Nerve Impulses
Nerve impulses are sent from the receptor to a certain
area of the brain and that area of the brain interprets what the impulse means.
The stronger the stimuli are the more receptors are activated meaning there are
more impulses being sent to the brain.
Receptors Adapt to Continuing Stimuli
Receptor adaptation is when the impulse is not sent any
longer even though the stimulus is still happening. The book gives the example
of wearing clothes. When they are first put on we feel them but the sensation
goes away even though the clothes are still there. Receptors for touch in the
skin and smell receptors adapt pretty quickly. Pain, joint and muscle receptors
do not adapt well if at all.
Somatic Sensations and Special Senses
Sensations that we experience are either somatic or
special. There are five special senses; taste, smell, hearing, balance, and
vision. The receptors that send impulses are only found in certain areas of the
body. Somatic sensations are impulses from receptors that are located in more
than one place in the body.
Somatic Sensations
Somatic sensations enable us to coordinate muscle
movements, stay away from danger, and keep our body temperature constant.
Somatic sensations receptors are found in skin, joints, skeletal muscles,
tendons and internal organs. Sensory neurons are attached to these receptors
and send the signals to the brain. The more sensitive the body part is the more
sensory neurons there are in that part of the body.
Mechanoreceptors
Mechanoreceptors are receptors that sense touch,
pressure, and vibrations. The amount of pressure and the degree that the
receptors adapt depends on where they are located in the body. Mechanoreceptors
also let us know what position our limbs are in due to mechanoreceptors in the
joints, skeletal muscles and tendons. Muscle spindles are mechanoreceptors that
are made for monitoring muscle length. These mechanoreceptors respond to the
muscles being stretched.
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| (KarlinBark) |
Thermoreceptors
Thermoreceptors are found close to the skins surface and
they give information about external temperatures. They are fast adapting
receptors. There are also thermoreceptors located in parts of the body that
keep track of internal temperature. These thermoreceptors do not adapt quickly.
Pain Receptors
Pain receptors let us know that there has been some sort
of injury from pressure, heat, light or chemicals. Knowing that something
causes pain is necessary for survival.
Vision
There are photoreceptors in the eyes that focus and
collect light.
Eye Structure
The sclera is the white part of the eye and covers the
entire outer surface but the cornea, which in in the very front. Light goes through
the cornea and then strikes the iris or goes through the pupil. The iris is the
colored disk shape in the eye. It is a muscle and it decides how much light can
enter the eye. The pupil is the black circle in the middle of the iris and it
can change sizes. When light has gone through the pupil it then hits the lens.
The lens is a see through, pliable configuration that is attached by connective
tissue fibers to smooth muscle called ciliary muscle. Light then reaches the
back and side layers of the eye which is the retina. The retina is made of
photoreceptors, neurons and some blood vessels. The choroid is at the back of
the eye between the retina and sclera. It is made of pigmented cells and blood
vessels and the pigmented cells absorb light if the photoreceptors do not. The
optic nerve is found at the back of the eye. The optic nerve takes information
to the thalamus which then forwards the information to the visual cortex to be
interpreted. The muscles around the eye are skeletal muscles which mean we can
control the eye movements. The macula is in the middle part of the retina and
is where there are the most photoreceptors. The fovea centralis is in the very
middle of the macula and is a little pit. The optic disk is where the axons of
the optic nerve and blood vessels leave the eye. There are no photoreceptors
here which results in a blind spot in every eye.
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| (Berg) |
(margrabihospitals1)
Light and Focusing
The iris has two sets of smooth muscle that adjust how
much light enters the eye. When we are in bright light, the muscles that are
circularly spaced around the pupil contract. These muscles contracting cause
the pupil to contract also. If this didn’t happen, the brightness of the light
would be too intense and we would be blinded for a short time. If the light is
dark, the smooth muscle that is radially spaced around the pupil begins to
contract. These muscles contracting cause the pupil to dilate. These muscles
are controlled by nerves. Sometimes a light is shone in a person’s eyes to see
if the pupils dilate. If they do not, it may indicate a serious nervous system
problem. When light enters the eye it is focused by the cornea and lens. The cornea
bends almost all of the light. The curve of the cornea does not adjust so
changing focus from near to far objects is done by the lens. The ciliary muscle
is in charge of this. The ciliary muscle contracts causeing the inner part of
the muscle to shrink which lessens the tension on the fibers that are fastened
to the lens. This causes the lens to bulge and we are able to focus on
something that is near. If the ciliary muscle relaxes, the muscle causes there
to be more tension on the lens and stretches it, causing it to flatten. This
brings things that are far away into focus.
Eye Shape
The way the eye is shape may influence the eyes ability
to focus. Myopia is a condition when the eyeball is longer than normal. People
with this condition cannot see things that are far away. Corrective concave
lenses can fix this. Hyperopia is when the eyeball is shorter than normal.
People with this condition have trouble seeing things that are close by. This
is corrected with convex lenses. Astigmatism is an irregular shaped cornea or
lens and causes blurred vision. Specially ground lenses are needed to correct
this.
Sensory Disorders
Disorders of the Ears
Deafness is when someone has loss of hearing. It can be
caused by damaged hair cells which cause nerve damage and sounds are not able
to be changed into impulses. Damaged tympanic membranes or the bones in the
middle ears are conduction dearness. In this type of deafness sound waves are
not taken to the middle ear at all. Depending on what type of hearing loss
there is, a hearing aid may provide some correction. Cochlear implants are tiny
microprocessor that changes sound waves into electrical signals and can help
people who have hearing loss due to nerve deafness. Otitis media is
inflammation of the middle ear. This is caused by fluid becoming trapped in the
middle ear and is usually cleared up with antibiotics. Meniere’s syndrome is an
inner ear problem that affects hearing and balance. This is a chronic condition
and the cause is not known.
Disorders of the Eyes
Retinal detachment is when the retina separates from
choroid. This can usually be correct by surgery. Cataracts are when the lens
turns opaque. Treatment involves removing the lens by surgery and then putting
in an artificial lens. Glaucoma is when pressure inside the eye goes up.
Glaucoma is usually not noticed until some vision has been lost. If not
treated, glaucoma will lead to blindness. Treatment is medication or surgery.
Age related macular degeneration is caused by the retina becoming detached and
degeneration of photoreceptor cells. This causes a loss of vision in the center
of the visual. There is no cure for this. Color blindness is when the full
range of colors cannot be distinguished.
Human
Impact on the Environment
Humans have done things that have changed the
environment. We have built houses, changed land by plowing, planting and
irrigating, destroyed mountains looking for fossil fuels and spread chemicals
such as herbicides and insecticides over the land. By doing this we have
changed the ecosystems we live in.
Pollution and Air Quality
Chemicals or particles that are in the air that has a
negative impact on living things are referred to as pollution. Pollution is
causing four major areas of concern. Global warming, the ozone layer being destroyed,
acid precipitation and smog are the four areas. There are multiple causes of
pollution that impact each of these areas.
Global Warming
The upper layer of the earth’s atmosphere acts like a
green house in that it does not allow heat to escape. Since it acts similar to
a greenhouse the gases that are produced from this are called greenhouse gases.
Water vapor is the most represented greenhouse gas. The other greenhouse gases
are manmade. They include carbon dioxide, methane, nitrous oxide,
chlorofluorocarbons and halons. These gases result in what is called the
greenhouse effect. This is a natural occurrence but humans have done things to increase
greenhouse gases. The increase in greenhouse gases has led to an increase in
the greenhouse effect which has led to global temperatures being raised which
is referred to as global warming. Burning fossil fuels and deforestation are
the 2 main things humans are doing that contribute to greenhouse gases.
Ozone
 |
| (Ozone Layer Depletion) |
The ozone is in two different places in the atmosphere.
The first place it is found is near the earth surface and it as made from the
oxygen reacting to automobile exhaust and industrial pollution. This ozone is a
little toxic and causes respiratory issues and some plant damage. The second
ozone is higher in the atmosphere and is beneficial. It helps shield
ultraviolet ray, which can cause skin cancer and maybe cataracts. It was
discovered in the 1980s that chlorofluorocarbons had damaged this ozone layer.
Skin cancer rates were predicted to increase because of this. To try to prevent
this, the production of CFCs was phased out. The hole in the ozone stopped
growing and is now stable. It is thought that in 100-150 years the ozone can
recover from the damage humans made.
Acid Precipitation
Acid precipitation is caused by sulfur dioxide. Sulfur
dioxide is made by burning high sulfur coal and oil. These are burned to make energy.
Acid precipitation is also cause by nitrogen oxide. Nitrogen oxide is caused by
automobile exhaust. These 2 chemicals mix with the water vapor that is in the
air. This makes sulfuric acid and nitric acid and dissolves in rain. When these
raindrops fall it is as acid precipitation. This can corrode metal and stone
and can damage forests and aquatic ecosystems. Power plants that burn these
coals have been made to install sulfur removal systems to lessen the emission
of sulfur dioxide. The amount of acid precipitation in the US has declined
since these have been put in place. There have been more recent regulatory
actions put in place that is expected to eliminate almost all of sulfur
emissions by 2014.
Smog
Nitrogen oxides and hydrocarbons mix with sunlight and
water vapor can cause the reaction of smog. Smog is a hazy brown layer that
hangs over an area. Smog has some chemicals that irritate the eyes and lungs
and can result in asthma and emphysema. Smog has been decreased by
antipollution laws and states using clean burning fuels.
Pollution and Water Supplies
Humans are affecting the water supplies by using more
water than needed, which decreases the freshwater supply. Humans also are
removing native vegetation and putting in buildings and roads. This results in
rainwater not being able to be soaked in and causes runoff. Thirdly, humans
sometimes pollute water by their choices.
Water is Scarce
Only 1% of the earth’s water is available for use. 97% is
salt water and 2% is frozen. Water is also not evenly distributed. Some
populations have more fresh water available to them than others. Populations
that have a lot of water available often use more than is necessary. In some
parts of the world they have reached their capacity of humans due to not enough
water. In some parts of the US water rights are a huge issue.
Water Runoff
Urbanization has led to storm water runoff. In some areas
this can cause big issues. In the eastern US storm runoff mixes with sewage and
causes sewage to overflow. This causes pathogens that cause gastroenteritis,
eye and ear infections, skin rashes, respiratory infections, and hepatitis.
Pipes being used to divert water can lead to flooding during rains and dry beds
during dry periods. This leads to aquatic life being loss.
Pollution of Fresh Water
Pollution such as untreated sewage, chemicals, runoff of
pesticides and fertilizer, rubber and oil from streets may end up in the soil
or water. Some pollutants that enter water cause bacteria to grow and when the
bacteria grows so fast in can threaten the animals that live in the water.
Groundwater pollution
If pollutants are soaked into groundwater they may cause
health issues in humans. It takes a very long time for pollution to leave
water.
Oil Pollution
Oil spills in oceans cause major environmental issues.
The extent of harm done from an oil spill may take decades to be known. Oil
spills cause damage to marine and shoreline ecosystems. Cleanup is very costly
and moves some of the pollution to the land or air so it still has an effect on
us.
Pollution Damages Land
Humans change landscape to suit their own purpose. Humans
have dammed up rivers, destroyed mountains, and cut down forests. Humans have
changed the land by building roads and cities.
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