THE DIGESTIVE SYSTEM
THE DIGESTIVE SYSTEM
The digestive system is mostly in the ABDOMINAL CAVITY.
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The two main digestive organs in the abdominal cavity are the stomach and intestines.
MOUTH
(Actually, digestion begins on the kitchen stove)
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A. ORAL CAVITY
a. PALATE (ROOF of mouth)
i. HARD PALATE: bone
ii. SOFT PALATE: soft tissue (can feel with tongue on roof)
B. UVULA: an extension of the soft palate; helps close off the nasopharynx during swallowing to prevent food from going down the wrong place.
C. TONSILS are in the back of the mouth, on either side of the tongue. They help protect from infections.
D. TONGUE is all muscle, good ROM. Some people can curl tongue, others can’t.
FUN FACTS ABOUT THE TONGUE
Just like fingerprints, every person has a unique tongue print. A giraffe’s tongue is 22 inches long!
E. SALIVARY GLANDS produce saliva; two functions:
1) To moisten food so you can swallow, especially crackers.
2) To inhibit growth of bacteria (which like dark, warm, moist areas). What does this are the antibodies and enzymes in the saliva.
The average human produces enough spit in a lifetime to fill two swimming pools!
F. TEETH: How many teeth does the average adult have? 32
FUN FACTS ABOUT TEETH
What animal bite causes the most human deaths? Snakes take their toll, but Mosquitoes cause millions of deaths a year. The Komodo dragon has saliva so toxic with bacteria, it just bites its prey and waits for it to die of infection a few days later.
When bacteria eat away at the enamel, what’s it called? CAVITY
Bacteria between the gums and the teeth is called GINGIVITIS. This is the major cause of tooth loss. The tooth loosens and falls out. That’s why you need to floss.
GI TRACT
This is a tube through the body, the function is to digest and absorb.
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It is made of muscles which allow for PERISTALSIS: a rhythmic contraction to push something along. (Take a yardstick = lumen, open and close one hand after the other, go hand-over-hand down the tube). This pushes food down by smooth muscle contraction. Some areas have thicker smooth muscle called a SPHINCTER, which acts like a valve to control the flow of food from one region to another.
ESOPHAGUS
The esophagus goes through the thoracic cavity.
It needs to go through a hole in the diaphragm. Rats have a sphincter here, but humans and dogs do not. That’s why we can vomit. A rat can’t vomit. That’s why rat poison kills rats, but it won’t kill people or dogs; they can vomit the poison back up.
STOMACH
Functions:
1. Store Food, so it can be slowly released into a small intestine. Your whole
Thanksgiving dinner can take your stomach diameter from 2” to 8” diameter.
2. Churn food. Secretions from the stomach turns everything gooey, called CHYME.
3. Kill bacteria. The stomach is very acidic (pH 1) like battery acid. Chyme will even
eat through clothing.
4. Some digestion: of proteins.
5. Some absorption: of water, alcohol (alcohol is absorbed in the mouth, too!)
Food takes four hours to completely leave the stomach.
It is folded over into RUGAE, to allow for expansion of the stomach.
STOMACH ACID
There are gastric pits in the stomach lining. “Gastric” refers to the stomach.
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Cells in the gastric pits make acid and digestive enzymes.
There are also lots of goblet cells which make mucus to prevent the stomach from digesting itself. Bacterial infection can erode this area = GASTRIC ULCER.
HEARTBURN is when acid goes from the stomach up into the esophagus (ACID REFLUX). People can take a mild antacid like Tums for relief.
FUN FACTS ABOUT THE STOMACH
The Tasmanian Devil can swallow 40 percent of its body weight in a half-hour. That's like eating 216 hamburgers for lunch!
If you ate like a vulture, you could ear 108 hamburgers in one meal. They eat 20% of their body weight. Their stomach acid is so strong they can dissolve botulism and cholera.
SMALL INTESTINE (Small bowels)
These are the longest part of the GI tract (9 feet long, 1” diameter)
The small intestine is the most important region of the GI tract because almost all of the digestion and absorption of food takes place here.
Structure
The small intestine needs a lot of surface area: 200 square meters, which is the floor space of a typical house. How do you get such a lot of surface area? There are lots of folds called MICROVILLI, which make a brush border (looks like a brush). Just like the stomach has gastric pits, the small intestine has INTESTINAL CRYPTS where there are cells that produce enzymes for digestion.
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The DUODENUM is the first part of the small intestine. This is where digestion begins. There are two ducts at the beginning of the duodenum from the pancreas and gallbladder.
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PANCREAS is a gland that makes hormones, digestive enzymes, and INSULIN, which is a protein that grabs a sugar molecule in the bloodstream and carries it into each cell. If the pancreas is malfunctioning and does not make insulin = DIABETES. The pancreas also produces BICARBONATE to reduce the pH of the stomach contents so you don’t get an ulcer.
GALL BLADDER secretes bile, which breaks down fats. When you go to McDonalds and order the Big Mac, fries, and shake, you get 200 grams of fat (one week supply), which globs together in the intestine, and that much more bile is needed to break it down.
The main purpose of the small intestine is to absorb nutrients from the food into the bloodstream to be taken to all the cells of the body. After the food passes through the small intestine, it goes to the large intestine.
LARGE INTESTINE (Colon, or large bowel)
This is 5 feet long and 4” diameter
The large intestine is important for several reasons:
1. Absorbs a LOT of water from the food
2. Absorbs electrolytes (Na, K, etc) out of the food
3. Stores feces for defecation
4. Contains bacteria (E. coli), about 3 pounds of it! These bacteria have functions:
a. Make vitamins (B12, K)
b. Allow material to move through large intestine easier
c. Keep out harmful bacteria
d. They eat things you can’t digest
i. Fiber
ii. Some sugars that we don’t have enzymes for
When these bacteria are happy and dividing, they produce gas. If you are lactose intolerant, you are missing the enzyme to break down lactose so the bacteria gets more sugar and you get more gas! Beans also have these sugars, so they give you gas. Mexico has different strains of E. coli in their water; the two strains battle it out and you get diarrhea. Diarrhea is when the large intestine does not absorb water ( dehydration. Cholera is a disease which attacks the large intestine, preventing water absorption, and can be fatal in 24-48 hours. The difference between diarrhea and constipation is the amount of water absorbed.
Right where the small intestine enters into the large intestine is a little sack filled with E. coli as well, called the APPENDIX.
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It might become inflamed, which closes off the opening. It can rupture = APPENDICITIS, which needs antibiotics and surgery or can be fatal. Most common age for this is late teens to early 20’s because a child has a larger opening which shrinks with age. When you’re done growing, it’s done shrinking, so if you haven’t had a problem by then, you might be ok.
Up from the cecum is the ASCENDING COLON, TRANSVERSE COLON, and DESCENDING COLON. Then there is an “S” shaped section called the SIGMOID COLON, which leads to the RECTUM, and out the ANUS.
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PROBLEMS
COLON CANCER is the #1 most deadly cancer (kills more people) because it metastasizes and there are no symptoms. It can be diagnosed by seeing blood in the stool; this is an easy test, but no very accurate.
COLONOSCOPY is a more accurate test for colon cancer. A tube with a light and a camera is inserted into the colon, and they look for growths on the walls of the intestine = POLYPS, which are pre-cancerous growths.
DIARRHEA is too much water in the stool (not enough water absorbed from intestine), usually caused from food poisoning or other infection, stress, or laxative abuse. Chronic diarrhea causes dehydration and irregularities in heart beat.
CONSTIPATION is when there is not enough water in the stool (too much water absorbed by the intestine). Prevention includes drinking more water and fiber. Avoid laxatives because of their side effects. Chronic constipation can lead to hemorrhoids.
HEMORRHOIDS are varicose veins. There are large veins along the rectum, which have become enlarged, painful, and inflamed. They are common in pregnant women, senior citizens, those who have anal intercourse, and in fighter pilots from the g-forces they pull. People use Preparation “H” for the symptoms, but it makes you wonder what happened to Preparations A-G? Hemorrhoids can be surgically removed if needed.
HOW LONG DOES IT TAKE TO DIGEST A MEAL?
Because plant cells are made of cellulose and we cannot digest that, you can swallow a few kernels of corn (whole, without chewing), and you’ll be able to easily see them in your stools and find out how long it takes to go all the way through your digestive tract. Should be about one day.
OTHER DIGESTIVE ORGANS: Liver and Gall Bladder
LIVER (Hepatic, hepatocytes)
This is the largest internal organ of the body, located on the right side, below the diaphragm, and extends below the rib margin. The function of the liver is more complex than any other organ except the brain.
1. Stores iron
2. Makes blood plasma proteins (clotting factors)
3. Stores glucose
4. Breaks down fats and regulates cholesterol
5. Breaks down amino acids, producing urea
6. Detoxifies chemicals in blood (That’s why CSI autopsies look at the liver for poisons)
PROBLEMS WITH THE LIVER
Infection of the liver = HEPATITIS (can be deadly)
CIRRHOSIS is when the liver cells die and are replaced by connective tissue. This is often from alcoholism, which kills the hepatocytes.
With any liver disorder bile cannot be broken down. Bile is yellow-green, so it builds up and can been seen as a yellowish color in the skin = JAUNDICE. Jaundice is not a disease; it is a symptom of liver disorder. It first shows up in the whites of the eyes.
Newborns get jaundice from a lot of red blood cells being broken down, and the liver gets overloaded, but it’s harmless. The treatment is UV light or sunlight, goes away in a few days.
GALL BLADDER
This is located inferior to the liver, and its function is to store and concentrate bile.
Bile contains hemoglobin, cholesterol and other things needed to break down fats. If there are no fats to digest, the bile stays in the gall bladder until it’s needed.
PROBLEMS WITH THE GALL BLADDER
GALL STONES are bile salts that crystallize because the bile is backed up.
(Show real gall stone, small and large). The stones block the duct where it enters the small intestine. Treatment is to remove the gall bladder. Now that person can only eat small amounts of fats at a time.
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