Nutrition

Food and Nutrition

I.  Overview of Digestion

    First Part of the Digestive Tract

    The Stomach and Small Intestine

    The Three Accessory Organs & Regulation of Secretions

    The Large Intestine

II.  Nutrition

Overview of Digestion

The organs of the within the gastrointestinal tract make up the digestive system. Foods are broken down to unit molecules, sugars, amino acids, fatty acids, and glycerol, so it can be transported by the blood to the cells. Digestion requires ingestion, movement, absorption, and elimination. Ingestion takes place in the mouth by chewing the food. Digestion is mechanical when food is divided into pieces in preparation for digestive enzymes and occurs in the stomach and mouth. Chemical digestion starts at the mouth and ends at the small intestines. Movement of the GI tract passes food from organ to organ. When the unit molecules cross the walls of the tract absorption occurs. Elimination is the removal of unwanted wastes.

The Gi tract resembles a garden hose that has four layers. The first layer the mucosa protects the wall from the enzymes and produces mucus. The submucosa the second layer protect against disease and responds by inflammation. It is made of connective tissue, blood vessels, lymphatic vessels and nerves. The third layer contracts to move food along the tract. It contains two layers of smooth muscle. The fourth outermost layer the serosa secretes serous fluid.

First Part of the Digestive Tract

The mouth, pharynx, and esophagus make up the first part of the digestive tract. From the mouth food is taken in which begins the process of mechanical and chemical digestion. Salivary glands produce an enzyme, salivary amalase that starts the process of digesting starch. As chewing starts mechanical digestion occurs. The food passes the pharynx as is is swallowed. It is at this point that the food can go the wrong way like to the nasal passages. The action of peristalsis pushes the food along the esophagus where chemical digestion takes place. At the stomach a sphincter lets food pass as it is relaxed but when the contents back up along the esophagus, acid reflux known as heartburn occurs. 

The  Stomach and Small Intestine

Digestion is completed at the stomach and small intestine. The stomach is sack shaped sitting beneath the diaphragm. It does not absorb nutrients but mechanically breaks down food with gastric juice. The juice contains pepsin that digests protein, hydrochloric acid (HCI) and mucus. HCI breaks down connective tissue in meat. The small intestine is long and narrow in diameter. Enzymes within the intestine digest primary carbohydrates, proteins, and fats. The duct at the duodenum receives secreted enzymes from the pancreas and bile from the liver and gallbladder to emulsify fat and hydrolyzed to glycerol and fatty acids by lipase in pancreatic juice. The digestion of carbohydrates and glucose starts with amylase and is completed by intestinal enzymes. And proteins and amino acids are  broken down by trypsin and an intestinal enzyme. The intestine have a slightly pH balance. 

Absorption of sugars, amino acids, fatty acids, and glycerol occur in the walls of the small intestine. Fingerlike projection call villi line the walls of the intestine and extensions called microvilli  provide more surface area for absorption. It is here in the villus where nutrients are absorbed, the lacteals of the villus, a small lymphatic capillary. Sugars and amino acids enter the blood capillaries of the a villus and glycerol and fatty acids the epithelial cells. From this they reach the cells by the blood.

The Three Accessory Organs & Regulation of Secretions

These three organs include the pancreas, liver, and gallbladder. A grayish pink fish shaped organ stretched behind the stomach. It produces pancreatic juice, and is also an endocrine gland that secretes insulin. Insulin is a protein usually secreted after a meal stimulating cells to take up glucose for storage or metabolism. If the blood glucose level is too high insulin is produced to to regulate glucose. Type 2 diabeties is the result of this extended condition. Type 1 diabetics produce no insulin. The liver and pancreas regulate constant blood glucose level. 

The liver sits below the diaphragm consisting of approximately 100,000 lobules performing various functions. It filters blood via the hepatic portal vein from the capillary bed of the GI Tract and into the capillaries of the lobules. Besides glucose it also stores iron and vitamins A, D, E, K, and B12. Plasma proteins are made in the liver and cholesterol is also regulated here. The liver makes bile that is stored in the gall bladder, a pear shaped organ below the liver. Gallstones are created here. It's other functions are destroying old rbc's , excreting bilirubin, and producing urea after breaking down amino acids.

The nervous system and digestive juices control digestive juices. The smell of food stimulates gastric secretions. Gastrin is made after eating a protein rich meal. Other hormones made in the duodenal are secretin and CCK (cholecystokinin). Secretin is secreted by acid and fat and protein stimulate the release of CCK.

The Large Intestine

Shorter but wider than the small intestine it includes the cecum, colon, rectum, and anal canal. At the end of the cecum lies vermiform appendix for fighting infections. Appendicitis is when it becomes infected. The colon  follows the right side, where the traverse colon then crosses and follows the left side as the sigmoid colon enters the rectum which opens to the anus where defecation occurs.

The Function of the large intestine is to absorb water and vitamins made by intestinal flora and to break down indigestible material, and to produce B complex and vitamin K. Feces are formed of water and solids. The solids comprise of bacteria, fiber, and indigestible materials. Defecation is assisted by peristalsis. Feces collect in the rectum, nerve impulses contract the rectal muscles and the anal sphincters relax allowing feces to exit through the anus.     

Nutrition 

Classes of Nutrients

Nutrients assist in providing energy, cellular metabolism and growth and development. Carbohydrates are simple or complex. Used as the body's energy source, carbohydrates are needed to convert to glucose. The brain requires glucose. Cakes, cookies and white bread are refined so they lack nutrients. The healthier choice are complex carbs such as beans, whole-grains, nuts and fruits which supply nutrients and fiber. A diet high in refined carbs can cause health issues. Refined carbs have a high glycemic index (GI) that creates a response to glucose by overproducing insulin. This may lead to insulin resistance or diabeties type 2. The amino acid in proteins are essential to the body's functions. Deficiency in one leads to complications. Amino acids are found in legumes, vegetable, nuts, but are most plentiful in meats. Limiting proteins is harmful for the body. Too much protein leads to cause dehydration or kidney stones. Lipids include fats, oils, and cholesterol. Saturated fats can cause plaque and caardiovascular disease they are mainly butters and meats. Unsaturated fats or essential fatty acids come from plant sources like corn and safflower. Olive oil contain more monosaturated fatty acids. Omega -3 in olive oil is said to protect against heart disease. Salmon trout, and sardines are another good source. Trans-fatty acids are hydrogenated and may reduce the function of cell membrane receptors that clear cholesterol from the blood. they are found in vegetable shortening and commercially packaged products.

Minerals

Minerals are comprised of major and trace minerals. They are important to cll constitution, body fluids and tissues. Stress can reduce magnesium and a high fiber diet can deplete zinc. Calcium is essential to bones, teeth, nerve conduction, and muscle contraction. When it is deficient osteoporosis can set in. Sodium is very important in regulating the body's water balance. Hypertension is the result of excessive salt intake. Thus the balance of mineral intake is important.

Vitamins

The body utilizes vitamins for metabolic functions. There are 13 vitamins which are either water soluble or fat soluble. Antioxidants counter free radicals. Vitamin C, E, and A. are antioxidants and are found in fruits and vegetables. The food pyramid suggests a portion of fruit and vegetables daily. Vitamin D found in milk protects against rickets.

Nutritious Meals        

Many health problems are the result of diet. A person can determine the calories needed for daily activity and cut back calories that is not needed. By using the food pyramid as a guide you can distribute those calories in planning a more nutritious meal.

Eating Disorders

Eating disorder involve personal, cultural, emotional, and biological factors. Often a person is not happy with their self image.the conditions of anorexia, bulimia and obesity can cause health problems such as malnutrition, disability and even death.