Chapter 8: Digestive System and Nutrition
8.1- Overview of Digestion
8.2- First Part of the Digestive Tract
8.3- The Stomach and the Small Intestine
8.4- Three Accessory Organs and Regulation of Secretions
8.5- The Large Intestine and Defecation
8.6- Nutrition and Weight Control
8.1- Overview of Digestion
The GI tract is the tube that holds the digestive system organs. Ingestion is whenever the mouth takes in food. Digestion can be either mechanical or chemical. Chemical digestion begins in the mouth and is completed once the food reaches the small intestine. Mechanical digestion happens in the mouth and stomach and occurs when food is cut into pieces. Movement of the GI tract gets food from one organ to the next. Absorption helps nutrients enter the blood to get to the cells. Defecation is what eliminates molecules that can’t be digested.
GI tract consists of four layers, 1- mucosa which produces mucus protecting the wall from digestive enzymes. A disorder associated with the first layer is known as diverticulosis is when parts f this layer push through other layers causing pouches that can collect food. 2- submucosa contains blood vessels, lymphatic vessels and nerves. Inflammatory bowel disease is associated with the second layer. 3- muscularis has two layers of smooth muscle, contraction of these muscles gets digested food from the esophagus to the anus. A disorder associated with the third layer is irritable bowel syndrome. 4- serosa- secretes a serous fluid. Appendicitis is a disorder associated with the fourth and final layer of the GI tract.
8.2- First Part of the Digestive Tract
First parts of the digestive tract consist of the mouth, pharynx and esophagus.
The mouth is what receives the food and starts the process of mechanical and chemical digestion. The roof of the mouth is what separates the nasal and oral cavities. Roof consists of two parts hard palate which is in the front and a soft palate which is in the back. Three salivary glands send saliva with the ducts to the mouth. Saliva consists of mucus and water. When we chew our food into smaller pieces making it easier to swallow we are mechanically digesting. As adults we have thirty-two teeth. Teeth have two main divisions- crown and root. Crown has a layer of enamel and an inner pulp. When bacteria in the mouth metabolizes sugar and gives off acids then cavities and/or tooth decay can occur. Brushing and flossing daily and limiting amount of sweets can help prevent this. Gum disease is linked to cardiovascular disease.
Food passage and air passage cross in the pharynx, where the mouth and nasal passages lead to. Esophagus takes food to the stomach. Swallowing is voluntary until a food or drink is pushed back into the pharynx. The soft palate closes the nasal passage and the trachea moves under the epiglottis to cover the glottis during swallowing to make the food go through the esophagus. Glottis- opening to larynx or voice box. We don’t breath when we swallow. If food goes down wrong its in the nasal cavity or trachea which coughing gets up and back down the right way. Peristalsis is a contraction that gets food along the esophagus and in all organs of the digestive tract, moves food bolus from mouth to the stomach. Sphincters are muscles that act as valves encircling tubes. Sphincter relaxing (valves open) lets food pass into the stomach and when constricted (valves closed) keeps acid of the stomach backing up into the esophagus. Sphincters relax a few seconds when something is swallowed allowing it to get from the esophagus into the stomach. Heartburn is caused by acid efflux- stomachs contents get into the esophagus. Diaphragm- muscle separating thoracic and abdominal cavities- and abdominal muscles contract when throwing up.
8.3- The Stomach and the Small Intestine
The stomach and small intestine are what complete the digestion process. The stomach is on the left side and is thick walled, consisting of the four usual layers. Food is stored in the stomach and normally empties in two to six hours. Food leaves in a thick, soapy liquid that is called chyme.
Small intestine is about eighteen feet long and the large intestine is only about four and a half feet. The small intestine consists of enzymes that digest all sorts of foods. The enzymes are secreted by the pancreas and enter through a duct at the duodenum, which is the first twenty-five centimeters of the small intestine. Bile is brought from the liver and gallbladder to the duodenum, bile is what emulsifies fat. The small intestine absorbs nutrients.
The primary sugar in milk is lactose. Lactose intolerance occurs in people who don’t have the brush border enzymes called lactase. Any dairy products that are lactose free or that the lactose has already been broken down in can be consumed without the side effects that have not. Side effects include cramps, gas, bloating and diarrhea. Too much sugar can lead to obesity. Diabetes type two and cardiovascular disease are linked to obesity.8.4- Three Accessory Organs and Regulation of Secretions
Three accessory organs that help the digestive process are the pancreas, the liver and the gallbladder. The pancreas is behind the stomach and is fish shaped. Pancreas secretes insulin into the blood. If the blood glucose level rises too fast the pancreas will make more than enough insulin to bring it all under control. If our cells become insulin resistant then diabetes type two can occur. The liver is the largest gland in the body and is located in the upper right section of the abdominal cavity. The liver stores iron and vitamins, regulates blood glucose level and cholesterol in blood. The liver produces bile, which is stored in the gallbladder. The gallbladder sits just below the liver in our body. If liquid that’s stored in gallbladder gets hard then its called gallstones.
Some disorders of the liver are jaundice which leaves a yellow tint to people and occurs when bile pigments get into the blood. Hepatitis is inflammation of the liver, hepatitis A can come from sewer infected water and hepatitis B is sexually transmitted or bought on by using dirty needles or blood transfusions. Both A and B have vaccines. Hepatitis C can lead to chronic hepatitis, liver cancer and death. Hep C is brought on by having contact with infected blood. Cirrhosis of the liver is another liver disorder and is common in alcoholics, alcohol causes the liver to break down.
8.5- The Large Intestine and Defecation
The cecum, colon, rectum and anal canal make up the large intestine. The ascending colon goes up the right side of the body, transverse colon goes across the abdomen and the descending colon goes down the left side if the body. The rectum is the last twenty centimeters of the large intestine, it opens at the anus where feces leave the body. The large intestine absorbs vitamins produced by the intestinal flora, it produces feces and defcates which gets rid of all the feces.
Some disorders of the colon and rectum include diarrhea, constipation, hemorrhoids, irritable bowel syndrome, inflammatory bowel disease and polyps and cancer.
8.6- Nutrition and Weight Control
Obesity, being grossly overweight, has double in the U.S. in the last twenty years and is rising throughout the world. The body mass index is a tool used to measure obesity by using a persons weight and height. BMI helps to see how much of a persons weight is due to fat. Obesity can lead to cardiovascular disease, diabetes type 2, stroke, respiratory disfunction and death among others.
Nutrients are components of food that perform a physiological function that provide us with energy, promote growth and regulate cellular metabolism. Carbohydrates can be simple or complex, glucose is simple and preferred for an energy source to the body. A high intake of carbohydrates can lead to obesity. There are twenty different amino acids, eight of which must be present in our diets. They are not stored in the body and are needed daily. Some fats have to be supplied in the diet these are called essential fatty acids. Lipids can be harmful if too much is consumed leading to cardiovascular disease like plaque buildup.
Major minerals and trace minerals make up the mineral category. Trace minerals are parts of larger molecules. Women generally don’t get enough iron, calcium, magnesium and zinc. Calcium helps with the bones and teeth without it osteoporosis can occur, magnesium can help prevent the bone loss cycle. Sodium has a part in the water balance, too much can lead to hypertension.
Vitamins are organic compounds used for metabolic purposes. Vitamin C, E, and A are antioxidants, they help protect the body. Fruits and vegetables may help keep cancer and cardiovascular disease away. Vitamin D is converted from a skin cell containing a precursor cholesterol molecule after UV exposure. If children don’t get enough vitamin D they can get bow legs.
Nutritious meals include variety, eating less junk (added sugars, salt, alcohol, high in saturated and trans fats) and eating more fruits, vegetables and whole grains.
The food guide pyramid is shown below..
Eating disorders are common in people who are dissatisfied with their bodies. Anorexia nervosa is where people starve themselves or binge eat then purge. Bulimia nervosa is where a person will binge eat then purge to avoid weight gain. Muscle dysmorphia is where a person thinks their body is underdeveloped and affects more men than women.
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