Digestive System Outline
V. Digestive System
A. Digestion - The physical and chemical breakdown of food.
B. Organs (structure & function)
1. Oral cavity = Mouth
a. Teeth - Allow for the physical breakdown of food
through chewing.
1. 32 adult teeth, 20 baby teeth.
2. Enamel - This is the hardest substance in
the body and provides hardness and durability
to the teeth. Erosions in the enamel are
cavities.
b. Salivary glands - These glands, located in the
head/neck region, make saliva for the mouth. Saliva, which
is mostly water, allows lubrication of the food, some
chemical breakdown (via enzymes) of the food and it is
antibacterial.
2. Pharynx - This is your throat. This is the location of swallowing of
food and drink. If you have pharyngitis, you have a sore throat. One of
the reasons why people, especially young children, get so many ear
infections when they have sore throats, is because the Auditory or
Eustachian tube connects the pharynx with the middle ear, to act as a
pressure-relief tube for the ears. However, it can also be a pathway for
infection to migrate from throat to ear.
3. Esophagus - This muscular tube takes food from your pharynx to
your stomach. It functions by peristalsis, or ripple-like contraction
waves.
4. Stomach
a. "gastr-" means stomach.
b. The stomach is located just below your ribcage on the
left side of your abdomen. It serves as a storage vat for
food. It mixes and liquefies food. Hydrochloric acid is
secreted into the stomach to help break down the food especially proteins. Hydrochloric acid is a very strong acid
and could eat through the wall of the stomach if it were
not protected by a thick layer of mucus. Hydrochloric acid
is also a strong antibacterial substance.
5. Small Intestine - The small intestine is small in its diameter, not its
length. It is normally about 18 feet long and, if stretched out, it would
be over 20 feet long. It receives food from the stomach and takes
unabsorbed food material to the large intestine.
a. Villi & Microvilli - These finger-like extensions line the
small intestine to increase the surface area available for
absorption of broken down food or nutrients.
b. Numerous blood vessels are present to receive the
nutrients.
c. Absorption - Almost all absorption of broken down food
and drink occurs in the small intestine. That is why you
have over 20 feet of small intestine plus the villi! The
noted exception of absorption is alcohol, which is
absorbed from the stomach, rather than the intestine. This
is why it takes very little time from drinking alcohol to it
being present in your bloodstream.
d. Peristalsis - Peristalsis is the wavelike contraction that
moves the digested food along the intestine.
6. Pancreas - Although food does not pass through the pancreas, it
serves a very important role in digestion. It is located just below the
stomach and has a duct (small tube) that carries its "juices" into the
beginning part of the small intestine. The pancreatic juice contains
enzymes to chemically breakdown all types of foods plus a base to
neutralize the acidic contents coming out of the stomach.
7. Liver - Although food does not pass through the liver either, it also
plays a role in digestion. The liver is a huge organ located just below
your ribcage on the right side of the abdomen.
a. "hepat-" means liver.
b. The liver makes bile which is secreted into the
beginning of the small intestine. Bile helps to chop
ingested fats into tiny pieces, so that the pancreatic
enzymes can chemically digest them.
c. The liver is also the major site of detoxification in the
body. With large blood supply, toxic substances pass
through the liver and are broken down by hepatic enzymes.
Thus, if the toxic substance is very harmful, often the liver
suffers damage (as in chronic alcohol abuse).
d. Storage of nutrients (such as glycogen which is stored
glucose), minerals and vitamins occurs in the liver.
e. Center of all metabolic pathways
f. Blood proteins are made in the liver. This includes
clotting factors necessary for blood clotting.
8. Gall bladder - A small pouch adjacent to the liver, serves only as a
site of bile storage. If you had your gall bladder removed, what foods
would you have to monitor very closely in your diet? Hint: What does
bile do?
9. Large Intestine - The large intestine is large because of its
diameter, not its length, in fact, it is only about 5 feet long in
comparison to about 21 feet for the small intestine. By the time food
enters the large intestine, it is primarily watery waste.
a. Appendix - At the beginning of the large intestine is a
small finger-like pouch called the appendix. It is an
evolutionary leftover and serves no useful function. The
small opening into the appendix serves as both the
entryway and the exit.
b. Colon - The bulk of the large intestine is the colon. The
course of the colon ascends in your abdomen, transverses
right to left, descends,and finally has an s-shaped curve
(sigmoid colon).
c. Rectum - Once the colon enters into the pelvic cavity, it
becomes the terminal portion of the large intestine, called
the rectum.
d. Anus - The terminal opening of the rectum is the anus.
It is two circular (=sphincter) muscles. One is smooth
muscle, so you have no voluntary control over it. But,
luckily, the other one is skeletal muscle so that you do
have voluntary control over defecation.
e. Function of large intestine
1. Form & Store feces (feces are waste)
2. Mucus secretion - For lubrication of
contents
3. Some water absorption
4. Vitamin K & some Vitamin B Synthesis This is actually done by some bacteria that
normally live inside of the colon!!
C. Pathology
1. Indigestion - Anything abnormal in digestion.
a. Heartburn - Heartburn is the most common form of
indigestion in the U.S. The most common reason one has
indigestion is due to overeating. The term is a misnomer
because it has nothing to do with your heart. The acid
from the stomach spills upward into the esophagus and
actually burns or stings the lining of the esophagus.
b. Colic - Babies often get digestive pain too and this
manifests as a fussy baby or a baby that won't stop crying.
Although changes in diet (mom's too if she is breast
feeding) can result in painful gas, the most common cause
of baby colic is due to difficult digestion of lactose, which
is milk sugar. Changing these babies over to a nondairy
formula usually stops the colic.
2. Vomit - When stomach irritation occurs, reverse peristalsis sends
the stomach contents back up. Complications from prolonged vomiting
include dehydration from fluid loss, loss of acids resulting in a change
in the pH of your body, and tissue (esophagus, mouth, teeth) damage
due to contact with the stomach acids.
3. Diarrhea - When intestinal irritation occurs, it can result in
increased peristalsis or increased water content of the feces.
Complications of prolonged diarrhea include dehydration due to fluid
loss.
4. Food Poisoning is the most common cause of gastroenteritis
(inflammation of stomach and intestine).
a. Staphylococcus food poisoning (Staph. for short) - This
bacteria is a normal inhabitant of the skin, nose, mouth
and especially sores on the skin. If this bacteria comes in
content with a moist, high protein food at room
temperature or hotter for about 4 hours, it multiplies and
releases a toxin or poison. Subsequent heating of the
contaminated food will kill the bacteria, but not its toxin.
Ingestion of the contaminated food can lead to vomiting
and diarrhea occurring acutely after eating it. Although
you may feel awful, no fever accompanies the food
poisoning and it is typically gone within 24 hours.
b. Salmonella food poisoning - This food poisoning is a bit
more serious and is caused by Salmonella bacteria. This
bacteria is normally found in the intestines of poultry and
hogs. It could contaminate the meat at the slaughter plant.
If contaminated food is left at room temperature for at
least four hours, the bacteria rapidly reproduces. If, at this
point, the food is thoroughly cooked, it will kill all of the
bacteria. If not, food poisoning follows a chronic course.
Typically signs of vomiting, diarrhea and fever begin 12-24
hours later. Signs subside about three days later.
Infrequently, the food poisoning is so severe, that
hospitalization is needed and life-threatening
complications can occur.
d. Campylobacter food poisoning - This is likely the most
common cause of food poisoning, but was only discovered
in 1977. It is responsible for 1-7 million cases of food
poisoning per year and is responsible for 100-1000 deaths
per year due to complications. If is found mainly in raw
chicken. It is killed by properly cooking the chicken.
Consumption results in fever and diarrhea for about one
week, but in some can last longer. In about 10% of the
cases, it becomes chronic and serious complications can
occur.
5. Ulcer - An ulcer is an erosion of a surface, typically found in the
stomach. Causes include bacteria in the stomach and excessive acid
production irritation the stomach lining. Ulcers can be serious if
chronic, in that they can cause internal bleeding and, if very severe,
can actually perforate (make a hole in) the stomach.
6. Appendicitis - If an infection takes hold in the appendix, it can
cause the doorway into & out of the appendix to swell closed. This
causes the appendix to enlarge due to infection and swelling. The
enlarged appendix causes severe pain in the right lower abdomen. As it
enlarges even more, the appendix points towards the left lower
abdomen. Shifting of pain from right to left abdomen is often a serious
symptom. The reason for the seriousness, is that the next stage can be
rupturing of the appendix, spilling all of the infected contents all over
the abdominal cavity. This is definitely a life-threatening situation.
Treatment is surgical removal of the appendix. (Will you ever miss it
since has no purposeful function?) Supportive treatment is aggressive
and includes antibiotics.
7. Cirrhosis - Cirrhosis is a permanent scarring of the liver. Normal
liver tissue becomes connective tissue similar to scar tissue. Although
some repair can occur in hepatocytes that are not yet scarred, once the
scar tissue replaces the liver cell, it is a permanent, irreversible
change. Thought question: Can you live without your liver? Review all
of the various functions of the liver.
The most common cause of cirrhosis is chronic alcohol abuse. It is a
process that takes many many years to develop. Signs and symptoms
include: 1) Prolonged bleeding, since clotting factors are made in the
liver, 2) Fluid retention and accumulation in various tissues and spaces
in the body, 3) Inability to detoxify substances (e.g. even protein
metabolism byproducts can be highly toxic in someone with cirrhosis),
4) Jaundice which is a yellowing of skin, eyes and mucous membranes
such as the gums. Jaundice is caused by the build up of pigments that
are supposed to be secreted in the bile, but accumulate in the failing
liver.
8. Eating Disorders - It is interesting, that U.S. is one of the best fed
nations in the world, yet leads the world in eating disorders.
a. Anorexia nervosa - This psychologically-based disease
is caused by not eating enough or exercising incessantly
after eating due to a psychological need to be very thin. It
is most commonly seen in young girls/teens.
b. Bulimia - This psychologically-based disease is caused
by eating and often overeating (bingeing) followed by a
regret that eating will make you fat and you purge the food
- either by vomiting or by the use of laxatives.