8.1 Overview of Digestion
Five basic steps of digestion:
1. Ingestion – taking in food
2. Digestion – mechanical or chemical breakdown food prior to reaching the small intestine
3. Movement – the transfer of food along the GI tract
4. Absorption – nutrients crossing the wall of the GI tract for delivery to the body
5. Elimination – discarding unused matter
There are 4 layers of the digestive tract:
1. Mucosa – inner layer either produces protective mucus or receives digestive enzymes. Diverticulosis are pockets formed in the mucosa that push through the other layers. These can become infected or inflamed.
2. Submocosa – connective tissue that contains blood vessels and nerves. Lymphatic nodules called Peyer’s patches providing immune surveillance and response.
3. Muscularis – smooth muscle in circular and longitudinal directions that provides movement of particles in the digestive tract.
4. Serosa – peritoneal lining which secretes serous fluid.
5. Appendix – small dead-end appendage at proximal large intestine. Just recently the following was published regarding this small, misunderstood part. “The appendix "acts as a good safe house for bacteria," said Duke surgery professor Bill Parker, a study co-author. Its location _ just below the normal one-way flow of food and germs in the large intestine in a sort of gut cul-de-sac -- helps support the theory, he said.” http://www.medicinenet.com/appendicitis/article.htm
http://www.cnn.com/2007/HEALTH/10/05/appendix.purpose.ap/index.html
8.2 First Part of the Digestive Tract
The Mouth
http://www.medicalook.com/systems_images/Mouth.jpg
Mine’s a size 7 ½; I know because my foot’s been there quite a number of times.
The pharynx is located immediately behind the tongue. Nasal and oral passages meet in that cavity. The soft palate will close off the nasal passage to guide food down the esophagus and the epiglottis will cover the airway (trachea) so food does not travel to your lungs.
If all goes well, the rhythmic movement of the esophagus (peristalsis) will push the food to the stomach. There is a sphincter separating the stomach and the esophagus which will open to allow food into the stomach and narrow to prevent acid reflux up the esophagus. If acid does find its way up the esophagus, heartburn occurs.
8.3 The Stomach and Small Intestine
The stomach is located on the left side just beneath the diaphragm. It has an additional layer of muscle that is oblique to the other two. This allows it to stretch and break down food as it mixes with gastric juices. Deep folds (rugae) in the mucosa of the stomach will flatten as the stomach fills. Gastric glands produce pepsin (digests protein), hydrochloric acid (HCl)(breaks down connective tissue in meats), and mucus. This reduces food to a thick, foamy liquid called “chyme” which is released in small amounts into the small intestine.
The duodenum is the next portion of the GI tract. It is the first 25cm following the pyloric sphincter. Enzymes from the pancreas, liver, and gall bladder are introduced here. Bile will breakdown (emulsify) fats to disperse in water. Lipase from the pancreas will hydrolyze the fat to glycerol and fatty acids. Amylase, also from the pancreas, will begin the digestion of carbohydrates and trypsin contributes to reducing proteins to amino acids. The remaining section of the small intestine will absorb the molecules that resulted from the breakdown of foods. These are basically amino acids, fatty acids, sugars, and glycerol.
The small intestine is lined with small fingerlike columns called villi. This greatly increases the surface area of the intestine permitting easier absorption of nutrients.
Cross section of a Villi
http://www.agen.ufl.edu/~chyn/age2062/lect/lect_20/27_27.GIF
Notice the lymph vessel (lacteal) located in the center of the villi, surrounded by capillaries. Sugars and amino acids enter the capillaries. Glycerol and fatty acids enter the lacteal.
Lactose intolerance is caused by lack of an enzyme called lactase which helps break down the sugar in dairy products called lactose. When unabsorbed, residual amounts left in the GI tract causes fluid retention, gas and bloating.
The intake of too many calories (usually fat and carbohydrates) will cause a person to gain weight eventually leading to obesity. Obesity is one of the strongest factors associated with heart disease and diabetes. Our dietary choices have a huge impact on our health and lifespan.
8.4 Three Accessory Organs and Regulation of Secretions
The pancreas is located behind the stomach and contributes enzymes to the digestion process. The three enzymes are:
Pancreatic amylase – digests starch
Trypsin – digests protein
Lipase – digests fat
Insulin is the best known product of the pancreas. Insulin is a blood sugar regulating hormone. When the glucose in our blood becomes elevated, the pancreas responds by releasing insulin. As we age, we can become resistant to insulin which can develop into Diabetes Mellitis II.
The liver is the largest metabolic gland in the body. It is located just beneath the diaphragm on the right side of the abdominal
cavity.
www.med.umich.edu/1libr/aha/aha_livergal_art.htm
The liver removes toxins from our blood and neutralizes them. It also stores the fat soluble vitamins, A, D, E, K and vitamin B12 and iron. The liver stores glycogen for use later and will break down glycerol and amino acids into the same. The byproduct of amino acids is urea which will be excreted by the kidneys.
The liver has yet another function, the production of plasma proteins and maintaining cholesterol levels in the blood. It produces bile salts which are stored in the gallbladder. Bile salts reduce fats into smaller droplets in the intestines allowing for further digestion by amylase Bile is green from the breaking down of hemoglobin. If a gallbladder is sluggish at removing the bile, the bile can harden causing gallstones – a painful condition requiring surgical removal or breaking down of such with medications or extracorporeal shockwave lithotripsy (submersion in water with pulsating waves aimed at the gallbladder to break up the stones). The latter has not been very successful.
Disorders of the liver can lead to death. Hepatitis (inflammation) of the liver can cause jaundice – a condition whereby the bile pigments leak into the blood. This causes the yellowing of the sclera and skin. There are 3 common types of viral hepatitis:
Hepatitis A – transmitted in the stool of an infected person. Contaminated food or water is the most common form of transmission. A vaccine is available.
Hepatitis B – transmitted through blood or sexual contact. Dirty needles are a common form of transmission. Also mother to child during childbirth. A vaccine is available.
Hepatitis C – transmitted through blood – dirty needles or bood transfusion prior to 1992. Also mother to child during childbirth. There is no vaccine. Tattoos or body piercing have been vehicles of transmission due to poor health practices. It is rare to become infected with Hepatitis C through sexual contact. Can be chronic, precursor to liver cancer and death.
Less common:
Hepatitis D – a defective virus that relies on Hepatitis B to exist.
Hepatitis E – extremely rare in the USA, transmits same as Hepatitis A.
Cirrhosis the process whereby healthy liver tissue is replaced with scar tissue. This can be an auto-immune disorder, and inherited disorder or by blocked bile ducts. Most commonly this is due to chronic alcoholism. The malnourished individual taxes the liver with removing the toxins from alchohol. Obesity is now recognized as another contribution towards cirrhosis because of a diet high in fatty foods.
When we smell something yummy, our parasympathetic nervous system stimulates secretions in our stomach. I’ve noticed a salivary response as well. Baking cookies does this for me . . .
Dashboard Oven
MSNBC carried this story on August 3, 2006 datelined in Bedford New Hampshire about a women who uses the dashboard in her SUV as an oven to bake cookies. Blistering heat was just what Sandi Fontaine needed to bake cookies for her co-workers — on the dash of her Toyota RAV4. With temperatures soaring Wednesday, Fontaine placed two trays of cookie dough on the dashboard, shut the doors and retreated inside to her air-conditioned office.Fontaine first tested her dashboard oven three years ago. She said anyone can do it; the only requirement is for the outside temperature to be at least 95 degrees, so it will rise to about 200 degrees in the car. "When you open the door to that car," she said, "it's like, oh, my God. It's a wonderful smell." 
www.kk.org/streetuse/archives/vehicles/
A meal high in protein will stimulate gastrin. The duodenum will produce
secretin – stimulates production of bicarbonate from the liver and pancreas – and CCK (cholecystokinin) – stimulates pancreatic enzymes and bile production.
8.5 The Large Intestine and Defecation
http://www.mtsinai.on.ca/familialgicancer/Diseases/FAP/where.htm
The large intestine is where feces is formed. This is material composed of indigestible materials and bacteria. The large intestine absorbs water – not nutrients. The bacteria in the large intestines produce the B vitamins and most of vitamin K. Peristalsis (involuntary contractions that move GI contents) culminates in defecation or elimination of fecal matter.
Some disorders of the large intestine:
Diarrhea – loose watery stools caused by infection or nervous stimulation.
Constipation – hard, dry stools preventing regular defecation.
Hemorrhoids – painful, enlarged and inflamed blood vessels at the anus. This can be due to straining, pregnancy, or may be hereditary.
Diverticulosis – pockets that form in the mucosa that have pushed through the next layer of bowel. These can become inflamed and painful.
Irritable Bowel Syndrome – strong irregular contractions that may cause cramping, gas, and urgency.
Inflammatory Bowel Disease – inflammation that can develop into ulcers. Symptoms are very similar to irritable bowel syndrome.
Polyps and Cancer – growths that will develop from the lining of the epithelium. Diet is believed to have a profound influence on it’s development and progression.
8.6 Nutrition and Weight Control
Obesity is becoming a global problem. Its incidence has doubled in the USA in the last 20 years. It seems that wherever personal income increases, obesity soon follows. In Brazil and Colombia the figure is now 40% of the population. Obesity is defined by one’s body mass index (BMI). 
http://www.gov.ky/pls/portal/url/page/cighome/pressroom/archive/200608/goodnutrition/bodymassindex
The BMI determines the percentage of body fat in your weight. This is most accurate for the average person. A weight lifter with a lot of muscle mass will have a misleading BMI.
Nutrients are substances from the environment that plants and animals need to function.
http://www.bim.ie/uploads/text_content/images/naf_comparison_nutrients.gif
Carbohydrates – simple and complex are the 2 types of carbohydrates. “Simple carbohydrates included sugars such as fruit sugar (fructose), corn or grape sugar (dextrose or glucose), and table sugar (sucrose). Complex carbohydrates included everything made of three or more linked sugars. Complex carbohydrates were thought to be the healthiest to eat, while sugars weren't so great. It turns out that the picture is more complicated than that. “ http//www.hsph.harvard.edu/nutritionsource/carbohydrates.html The body handles all carbs the same and will break them down into single sugar molecules. It’s the fiber in the sources of complex carbohydrates that cannot be broken down. This undigested fiber will absorb excess fats to be excreted later thereby lowering cholesterol.
The glycemic index is the most accurate way of determining the impact of specific carbohydrates on the blood glucose levels and insulin response. It measures how quickly these foods raise glucose levels in our blood. It is believed that chronic elevated glucose levels can lead to diabetes, insulin resistance, heart and liver disease.
Proteins – the building block of cells. Proteins are broken down into amino acids which are utilized by our cells to form cellular proteins. There are 20 different amino acids – eight which are essential. Two servings of meat a day will complete our body’s requirements for proteins. A vegetarian will ingest proteins by eating beans and peas. These individually are incomplete protein sources and must be combined to provide the essential 8 needed for protein synthesis. Too much protein will tax the liver and kidneys as they work to maintain homeostasis.
Lipids are the fats in our diet. Saturated fats are solid at room temperature – these are usually animal sources with the exception of palm and coconut oils. These will raise low-density lipoprotein (“bad” cholesterol) levels. Polyunsaturated are favorable and don’t promote cardiovascular disease. These supply linolenic and linoleic acids. Monosaturated fats are considered protective against CV disease. Some fish sources and olive and canola oils are examples of these. These will lower LDL levels.
Trans fats are commercially altered fats to mimic the consistency of lards and butter. These have been found to cause atherosclerotic changes and should be avoided.
Macrominerals and microminerals (trace) are utilized by our bodies for a variety of functions. MIcrominerals are needed in lesser quantities than macro – less than 5 grams are present in our bodies. These trace minerals are attached to a larger molecules. Zinc, Iron, Copper, Iodine, Selenium, and Manganese are just a part of the family of trace minerals.
Macrominerals are present in our bodies in quantities greater than 5 grams.
Calcium strengthens bones and teeth, promotes nerve conduction and muscle contraction.
Phosphorus helps promote bone and soft tissue growth and is part of the makeup of ATP, nucleic acids and phospholipids. 85% of the body’s phosphorus is found in the bone. Phosphorus as also a buffer.
Potassium is a mineral needed for nerve conduction and muscle contraction. It is a positively charged ion, more abundant inside the cells.
Sodium and chloride are the principle ions extracellularly contributing to water balance. Elevated sodium levels can cause edema and HTN.
Magnesium is vital in over 300 metabolic processes, the conversion of ATP, protein synthesis, bone structure, ion transfer across cell membranes, etc.
Mineral content of assorted types of chocolate
http://www.allchocolate.com/images/Content%20Charts/4.2.3-MineralChart.gif
Vitamins are compounds needed by our bodies that we cannot produce on our own. Many vitamins are enzyme helpers (coenzymes). They are reusable resources and are needed only in small amounts. Vitamins C, E, and A are antioxidants that help to defend against free radicals. Those are extra unstable molecules that donate electrons to DNA resulting in cellular damage.
Vitamin A - Retinoids(retinol, retinoidsand carotenoids)
Fat soluable
900- 3000 µg a day Deficiencies cause
Night-blindness andKeratomalacia
Vitamin B1 - Thiamine
Water soluable
1.2 - ? mg a day
Deficiencies cause Beriberi
Vitamin B2-Riboflavin
Water Soluable
1.3 - ? mg a day
Deficiencies cause Ariboflavinosis
Vitamin B3-Niacin, niacinamide
Water Soluable
16.0 - 35.0 mg a day
Deficiencies cause Pellagra
Vitamin B6-Pyridoxine, pyridoxamine, pyridoxal
Water Soluable
1.3-1.7 mg not to exceed 100 mg a day
Deficiencies cause Anemia,
Vitamin B7-Biotin
Water Soluable
30.0 µg a day
Deficiencies cause Dermatitis, enteritis
Vitamin B9-Folic acid, folinic acid
Water Soluable
400 - 1000 µg a day
Deficiency during pregnancy is associated with birth defects, such as neural tube defects
Water soluable
2.4 µg a day
Deficiencies cause Megaloblastic anaemia[18]
Vitamin C-Ascorbic acid
Water soluable
90.0 - 2,000 mg a day
Deficiencies cause Scurvy
Vitamin D-Ergocalciferol, cholecalciferol
Fat soluable
5.0 -10 µg not to exceed 50 µg a day
Fat soluable
15.0 - 1,000 mg a day
Deficiency is very rare; mild hemolytic anemia in newborn infants.
Fat
120 µg
Deficiencies cause Bleeding diathesis
http://en.wikipedia.org/wiki/Vitamin
Eating disorders are more common among women than men. Anorexia nervosa is an irrational fear of becoming fat. Many women have self-imposed starvation culminating in their deaths as a result of this disorder. Bulimia nervosa is binging followed by purging. Purging is achieved by vomiting or laxatives. Again, the motivation is to avoid gaining weight. A bing-eating disorder is binging not followed by purging. Food binges can be triggered by emotional stresses or disorders. Muscle dysmorphia is a male-dominated disorder that causes the man to perceive himself as being underdeveloped. His life becomes consumed with weight lifting, supplements and dieting to achieve the perfect musculature.
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