- Overview of the Digestion
- First Part of the Digestive Tract
- The Stomach and Small Intestine
- Three Accessory Organs and Regulation of Secretions
- The Large Intestine and Defecation
- Nutrition and Weight Control
macromolecules and breaks them down to the unit molecules which can then cross the plasma membranes. There are four layers in a GI tract wall. The central space where the food is digested is known as the lumen. The firt layer after this is the mucosa (produces mucus to protect the wall from digestive enzymes). Submucosa is the second layer (loose connective tissue containing blood and lymphatic vessels, and nerves). Third layer is muscularis ( two layers of smooth muscle. Inner encircles the tract and outer lies same direction of tract. Contracti0n of these muscles moves digested food). Serosa is the last layer (secretes serous fluid and is part of the peritoneum)- Ingestion- this is when food enters the mouth
- Digestion- Either mechanical (food broken into pieces that digestive enzymes can work on) or chemical (digestive enzymes.)
- Movement- Food passes from one organ to another through the digestive tract.
- Absorbtion- Unit molecules resulting from digestion are now able to move across the GI tract into the cells that line the GI tract, where they enter the blood for transportation.
- Elimination- Indigestible wastes are defecated through the anus
First Part of the Digestive Tract
Your mouth, pharynx, and esophagus make up the first section of the GI tract. The food enters through the mouth, and this is the beginning of mechanical and chemical digestion. The mouth is made up of your hard palate, soft palate, tonsils (lymphatic tissue), and salivary glands(send saliva containing salivary amylase to the mouth). Teeth (20 baby teeth, replaced by 32 adult teeth) function as a mechanical aspect. Your tongue helps in mechanical digestion along with taste buds that send nerve impulses to the brain.
Pharynx is the next stop after food enters the mouth. This is where the food and air passages intersect (trachea is front of the esophagus). Swallowing is voluntary until food reaches the pharynx, here it becomes automatic. The soft palate blocks off nasal passages, and the epiglottis covers the glottis, blocking food from going into the trachea. The only place left to go is down the esophagus. Peristalsis moves the food down the esophagus and sphinters allow the food to enter the stomach, but prevent stomach acids from entering the esophagus.
The Stomach and Small Intestine
The stomach sits on the left side of the body under the diaphragm. Th
e esophagus conects to the top of the stomach and the duodenum of the small intestine connects on the bottom. In the stomach, food is stored, protein
digested and chyme is moved into the small intestine. There are also four layers of the stomach wall: Three layers of smooth muscle(circular, longitudal and obliquely) and a mucosa layer on the inside in which rugae produce gastric juice that contains pepsin, HCl and mucus.
The small intestine completes the digestion process. Here there 
are many enzymes capable of digesting all types of food including carbohydrates, proteins, and fats. This wide array of enzymes is secreted in the pancreas and enters the duodenum along with bile to emulsify fat. Nutrients are absorbed here. The small intestine's large surface area is designed perfectly for this absorption. Mucosa contains villi which have extensions called microvilli. Each villus has a small lymphatic capillary (lacteal). The vessels in here allow the unit molecules to be carried to all the other cells in your body through the bleed stream.
Three Accessory Organs and Regulation of Secretions
Digestive secretions are regulated by the nervous system and digestive hormones.
1. Pancreas- located behind the stomach. Pancreatic cells produce pancreatic juice containing digestive enzymes for all the types of food.(amylase digests starch, trypsin is for protein, and lipase is for fat). This organ is also very important because it is responsible for producing insulin. When the bodies blood glucose level rises, this triggers an excess amount of insuling to be produced which in turn, brings the glucose level back to normal range. Diabetes type 2 occurs when a body's cells become resistant to the insulin. Type one diabetes occurs when the pancreas does not secrete insulin like it should, and thus blood sugar must be checked frequently and insulin injected when needed.
2. Liver- is the largest metabolic gland. Located in the upper right quadrant of abdominal
cavity. Blood travels through the hepatic portal vein into the capillaries of the liver lobules where poisonous substances are removed. The liver also stores iron and vitamins. Glucose is stored as glycogen which is broken down when there is insulin, effectively keeping your blood glucose level constant. The liver also produces plasma proteins and regulates cholesterol and breads down hemoglobin, forming bile
Liver diseases can be life threatening. Two big diseases are hepatitis(inflammation) and cirrhosis(liver tissue replaced by scar tissue)
3. Gallbladder- located below the liver. Bile is stored here.
The Large Intestine and Defecation
The cecum, colon, and rectum all are part of the large intestine. The cecum is loc
ated behind the junction of the small intestine with the large intestine and has a projection known as the vermiform appendix. The colon is the ascending, transverse, descending and sigmoid. This leads into the rectum and opens at the anus.
The large intestine functions to absorb water and proteins produced by intestinal flora. The bacteria here break down the indigestible material to form feces. Diseases of the large intestine include: diarrhea, constipation, hemorrhoids, diverticulitis, irritable bowel syndrome, inflammatory bowel disease, polyps and cancer. Most of these can be prevented by exercising a good diet, and good bowel habits.
Nutrition and Weight Control
Obesity affects 33% of adults today. This is determined by your body mass index (BMI). A healthy BMI 19.1-26.4, overweight 26.5-31.1, obese 32.3-39.9 and morbidly obese 
40+.
Nutrients are an important part of diet. They are classified into
1. Carbohydrates- either simple or complex. Glucose is preferred by the body for energy. As fatty acids cannot be converted to glucose, it is important to include carbohydrates in your diet. Unrefined products are best
2. Proteins- these are broken down into amino acids when digested and used to synthesize cellular proteins. 8 out of 20 amino acids are essential for children's growth. Absence of just one essential amino acid, and the other 19 will not function properly. Since amino acids are not stored, a daily intake is needed.
3. Lipids- these are the fats, oils and cholesterol. Unsaturated fats do not encourage cardiovascular disease. Polyunsaturated fats are actually needed since they contain linoleic and linolenic acids which the body does not produce on its own.
Minerals are either major( structural components of cells) or trace (part of a larger molecule). Exampels are: calcium, vitamin D, and sodium. Vitamins are organic compounds that the body cannot produce enough of, but is needed for metabolic reasons. There are 13 vitamins and they are either fat soluble or water soluble. Vitamins C, E, and A are antioxidants and can be found in fruits and vegetables.
A healthy diet consists of eating a variety of foods and being physically active. More fruits, vegatables and whole grains should be consumed, and less sugars, saturated fat, salt and cholesterol.
Anorexia, bulima, binge eating and muscle dysmorphia are all eating disorders that effect people everyday.
Works Cited
Mader, Sylvia. Human Biology 10th ed
Frolich Powerpoint
Website links for pictures
1.http://www.mc.vanderbilt.edu/histology/labmanual2002/labsection3/EsophagusandStomach03_files/image004.jpg 2. http://cache.eb.com/eb/image?id=1354&rendTypeId=4
3. http://www.acm.uiuc.edu/sigbio/project/digestive/middle/stomach2.jpg
4.http://a-s.clayton.edu/biology/biol1152l/digestive_system_anatomy/stomach_rugae.jpg
5. http://www.rivm.nl/interspeciesinfo/Images/small-intestine_tcm75-26441.gif
6. http://www.foxriverwatch.com/color_liver2a.jpg
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