How food moves through the GI Tract
- Esophagus: When a person swallows, food pushes into the esophagus. Once swallowing begins, it becomes involuntary and proceeds under the control of the esophagus and brain. The sphincter relaxes and lets food pass to the stomach.
- Stomach: The stomach stores food and liquid, mixes the food and liquid with the digestive juice it produces, and slowly empties its contents. called chyme, into the small intestine.
- Small intestine: The muscles of the small intestine mix food with digestive juices and push the mixture forward to help with further digestion. The walls of the small intestine absorb the digested nutrients into the blood stream.
- Large intestine: The waste products of the digestive system process include undigested parts of food and older cells from the GI tract lining. These wastes are then stored in the large intestine.
Hormone Regulators: The cells in the lining of the stomach and small intestine produce and release hormones that control the functions of the digestive system
Nerve Regulators: Extrinsic, or outside, nerves connect the digestive organs to the brain and spinal cord. Intrinsic, or inside, nerves within the GI tract release many different substances that speed up or delay the movement of food and production of digestive juices.
Six Major Functions: Ingestion, Secretion, Mixing and Movement, Digestion, Absorption, Excretion.
- Ingestion: The intake of food
- Secretion: The body secretes around 7 liters of fluids a day. These fluids include saliva, mucus, hydrochloric acid, enzymes, and bile.
- Mixing and Movement: Has three Major processes: Swallowing, Peristalsis, Segmentation. Swallowing- Smooth and skeletal muscles in the mouth, tongue, and pharynx push food into the esophagus. Peristalsis- a muscular wave that moves partially digested food through the GI tract. Segmentation- Occurs only in the small intestine, and helps increase the absorption of nutrients by mixing food.
- Digestion: Turning large portions of food into chemicals. Food is mechanically and chemically digested. Mechanical digestions begins when the food is chewed, chemical digestions begins with saliva.
- Absorption: Begins in the stomach. Simple molecules are absorbed into the bloodstream. Most absorption takes place in the walls of the small intestine.
- Excretion: Removes indigestible substances from the body so they don't accumulate in the gut. Excretion is controlled voluntarily by the conscious part of the brain.
Major Organs of the Digestive System
Mouth: Teeth- chew up food into smaller parts for digestion. Tongue- Small organ made up of many pairs of muscles. The outside of the tongue contains many papillae that grip food, and help push the food toward the back of the mouth to be swallowed. Salivary Glands- There are 3 sets of glands in the mouth. They produce saliva, which helps moisten the food for digestion and movement through the mouth, pharynx, and esophagus.
Pharynx: Another name for throat and passes chewed food to the esophagus. It contains a flap of tissue called the epiglottis because it serves dual functions. It acts as a switch to route food to the esophagus and air to the larynx.
Esophagus: Muscular tube that connects the pharynx to the stomach. It carries chewed food through it after it's swallowed. At the lower end of the esophagus there is a muscular ring that closes to trap food in the stomach.
Liver: A triangular accessory organ located in the right of the stomach below the diaphragm and above the small intestine. It is the largest organ of the body weighing about 3 pounds. Its main function is the production of bile and secretion into the small intestine.
Gallbladder: Behind the liver, it can be reused for the digestion of following meals. It also stores and recycles excess bile form the small intestine.
Pancreas: Secretes digestive enzymes into the small intestine to complete the chemical digestion of food.
Typically sugars, starches, and fibers found in many foods. They are classified as simple or complex depending on the chemical structure.
- One example is cellulose. It is a more complex carbohydrate that is abundant in food, giving celery its crunch and lettuce crispness.
- Cellulose provides bulk against which the muscular wall of the digestive system can push, facilitating food.
Organic compounds that include fats, oils, and fat like substances. They supply energy for cellular processes and build cell membranes. Their main function is to supply energy and supply flavor to food.
- Saturated fats- found mainly in food of animal origin. Excess saturated fat is a risk of cardiovascular disease.
- Unsaturated Fats- found in seeds, nuts, and oils.
- Monounsaturated fats- found in olive, peanut, and canola oils.
- Cholesterol- Abundant in liver and egg yolks. Found in lesser content in whole milk, butter, cheese, and meats. Not found in foods of plant origin.
Polymers of amino acids with a wide variety of funcitons
Foods rich in proteins include: Meats, Fish, Poultry, Cheese, Nuts, Eggs, and Cereals.
- Control metabolic rates, clotting factors, the keratin of the skin and hair, elastin and collagen of connective tissues, muscle components actin and myosin, and the antibodies to fight infections.
- Supply energy after digestion that breaks them down to amino acids.
- The liberated amino acids are transported to the liver and undergo deamination, losing their nitrogen containing portions that are excreted in urine.
- Most people should consume about 60-150 grams of proteins a day.
Organic compounds other than carbs, lipids, and proteins that are required in small amounts for normal metabolism.
Vitamins are classified on the basis of solubility.
Fat Solubles include vitamins A, D, E, and K; Water Solubles are vitamins B and C.
Vitamin B: several commands that are essential for normal cellular metabolisms. Help oxidize carbohydrates, lipids, and proteins. Cooking and food processing destroy most of them.
Vitamin C: One of the least stable vitamins, it is needed for collagen production and the metabolism of certain amino acids. It promotes iron absorption. Found in guava, red and green peppers, kiwi, and brussels sprouts.
Vitamin A: Promotes healthy eyes, teeth, skin, general cell growth, and development. Found in carrots and other orange foods including sweet potatoes and cantaloupe melons.
Vitamin D: A group of steroids resistant to heat stored in the liver, skin, spleen, and bones. Necessary for strong bones. Besides spending a few minutes in the sun, you can get this vitamin from eggs, fish, ad mushrooms.
Vitamin E: Stored in muscles and adipose tissues, contributes in blood circulation, and protection from free radicals. The best vitamin rich food are almonds.
Vitamin K: Occurs in several forms and is essential for preventing blood clots. Leafy greens are the best resource of this vitamin.
Folic Acid: Important vitamin for preventing birth defects during pregnancy. Found in dark leafy greens, citrus fruits, and beans.
Calcium: Structure of bones and teeth and is essential for nerve impulse conduction. The best sources are dairy products, tofu, and black molasses.
Iron: Primarily found in blood and is incorporated into a number of enzymes. Found in red meat, pork, and poultry.
Zinc: Enzymes involved in digestion. It also contributes to healing wounds and maintaining skin integrity. Seafoods like oysters are zinc rich, along with spinach, cashews, beans and dark chocolate.
Chromium: Widely distributed and essential for use of carbohydrates. If you have a balanced diet you should be getting enough chromium.
Enzymes: Complex proteins that assist in or enable chemical reactions to occur. Thousands of different enzymes are produced by your body.
Magnesium: Maintains muscle and nerve function, keeps heart rhythm steady, and keeps bones strong. Foods with high amounts of magnesium include almonds, cashews, and green vegetables.