NTR 213 Chapter 3 Notes
NTR 213 Chapter 3 Notes NTR 213
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This 6 page Class Notes was uploaded by bjwall on Monday September 12, 2016. The Class Notes belongs to NTR 213 at University of North Carolina - Greensboro taught by Dr. Seth Armah in Fall 2016. Since its upload, it has received 10 views. For similar materials see Introduction to Nutrition in Nutrition at University of North Carolina - Greensboro.
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Date Created: 09/12/16
Chapter 3 – Digestion: From Meals to Molecules 3.1 The Organization of Life Atoms – smallest unit of an element that retains the properties of the element Molecules – group of 2 or more atoms of the same or different elements bonded together Cells – basic structural and functional unit of living things o Cells that are similar in structure and function form tissues. 4 types – muscle, nerve, epithelial, connective Organs – discrete structure composed of more than one tissue that performs a specialized function o Organ doesn’t function alone but is part of an organ system Hormones – chemical messenger that is produced in one location in the body, is released into the blood and travels to other locations, where it elicits responses ATOMS > CELLS > TISSUES > ORGANS > ORGAN SYSTEMS > ORGANISM 3.2 The Digestive System Digestion – process by which food is broken down into components small enough to be absorbed into the body Absorption – process of taking substances from the gastrointestinal tract into the interior of the body Proteins broken down into amino acids, CHO to sugar, fats into fatty acids Feces – body waste, including unabsorbed food residue, bacteria, mucus, and dead cells, which is eliminated from the gastrointestinal tract by way of the anus Organs of the Digestive System Digestive system composed of gastrointestinal tract o Hollow tube (30 feet long) that runs from mouth to anus o Inside of tube called lumen o Only after substances have been absorbed into the cells that line the intestine can they be said to be inside the body. Lumen is lined with a layer of mucosal cells called mucosa. Live only 2-5 days because in constant contact with churning food and harsh digestive secretions. o Mucosa has high nutrient requirements and is one of the 1 st parts of the body to be affected by nutrient deficiencies. The time it takes food to travel the length of the GI tract from mouth to anus is called the transit time. o Healthy adult: 24-72 hours Digestive System Secretions Mucus – viscous fluid secreted by glands in the digestive tract and other parts of the body. It lubricates, moistens, and protects cells from harsh environments. Enzymes – protein molecule that accelerates the rate of a chemical reaction without itself being changed Digestive system and endocrine system – GI tract 3.3 Digestion and Absorption of Nutrients The Mouth Digestion involves chemical and mechanical processes Saliva – watery fluid that is produced and secreted into the mouth by the salivary glands. It contains lubricants, enzymes, and other substances o Saliva contains the enzyme salivary amylase which begins the chemical digestion of food by breaking starch molecules into shorter sugar chains. Chewing begins the mechanical aspect The Pharynx The pharynx is responsible for swallowing. Epiglottis – piece of elastic connective tissue that covers the opening to the lungs during swallowing The Esophagus Connects the pharynx with the stomach Peristalsis – coordinated muscular contractions that move material through the GI tract To leave the esophagus and enter the stomach, food must pass through a sphincter, a muscle that encircles the tube of the digestive tracts and acts as a valve. o Contacts, valve closes o Relaxes, open, allowing food to pass o Sphincter prevents food from moving from stomach back into esophagus, heartburn o Vomiting causes sphincter to relax and muscles to contract The Stomach Bolus mashed and mixed with highly acidic stomach secretions to form chyme. Very little absorption occurs in stomach Gastric Juice Gastric juice promotes chemical digestion in the stomach. Mixture of water, mucus, hydrochloric acid, and inactive form of the protein digesting enzyme pepsin. o Inactive so doesn’t damage gastric glands that produce it o Hydrochloric acid kills most bacteria o Mucus prevents protein that makes up stomach wall from being damaged by acid and pepsin Regulation of stomach activity How much churns and how much gastric juice released regulated by signals from nerves and hormones – brain, stomach, small intestine – where signals come from The Small Intestine Narrow tube (20 feet long) Segmentation slosh the material back and forth Main site for chemical digestion of food, completing the process that the mouth and stomach have started Primary site for absorption of water, vitamins, and minerals Secretions that aid in digestion Pancreas – pancreatic juice which contains bicarbonate and digestive enzymes o Neutralizes the acid in the chyme, making environment neutral or slightly basic rather than acidic as in the stomach Pancreatic amylase continues job of breaking down starches into sugars that was started in mouth Pancreatic proteases break protein into shorter and shorter chains of amino acids, and fat digesting enzymes called lipases break down fats into fatty acids. Bile – digestive fluid made in liver and stored in gallbladder that is released into the small intestine, where it aids in fat digestion and absorption o Help divide large lipid droplets into small globules Absorption To be absorbed, pass thru GI tract into mucosal cells lining tract and into either blood or lymph o Some rely on diffusion, which is net movement of substances from high to low concentration o Simple Diffusion – unassisted diffusion of a substance across a cell membrane o Osmosis – unassisted diffusion of water across a cell membrane o Facilitated Diffusion – assisted diffusion of a substance across a cell membrane Carrier molecule needed o Active Transport – transport of substances across cell membrane with the aid of a carrier molecule and the expenditure of energy Low to high concentration The Large Intestine (5 feet long), divided into colon and rectum (8 inches) Intestinal microflora are permanent, beneficial residents of this part of the GI tract. o Break down unabsorbed portions of food, such a fiber, and synthesize nutrients 3.4 Digestion in Health and Disease Food allergies h ave their origins in the GI tract The Digestive System and Disease Prevention Most food contains bacteria, mostly never makes us sick, b/c mucosa of GI tract contains tissue that is part of the immune system. Prevents disease- causing bacteria and toxins from damaging Antigen – foreign substance that, when introduced into the body, stimulates an immune response st o When an antigen is present, phagocytes are 1 type of white blood cell to come into body’s defense o If phagocytes don’t eliminate, white blood cells called lymphocytes join the battle Antibodies – protein, released by a type of lymphocyte, that interacts with and deactivates specific antigens o Bind to antigens and destroy them o Each antibody is able to fight off only one type of antigen Food allergies Allergic reaction occurs when immune system produces antibodies to a substance, called an allergen, that is present in our diet or environment. Allergen – substance that causes an allergic reaction Food allergies occur when the body identifies proteins present in food as foreign substances and therefore initiates an immune response Celiac disease Celiac disease is a condition in which the protein gluten, found in wheat, rye, barley, triggers an immune system response that damages or destroys the villi of the small intestine. Digestive System Problems and Discomforts Heartburn and GERD Heartburn – burning sensation in chest or throat caused when acidic stomach contents leak back into the esophagus (gastroesophageal reflux) Gastroesophageal Reflux Disease (GERD) – chronic condition in which acidic stomach contents leak into esophagus, causing pain and damaging the esophagus Peptic Ulcers Peptic Ulcers – open sore in the lining of the stomach, esophagus, or upper small intestine o Occurs when mucus barrier is penetrated and acid and pepsin damage the gastrointestinal lining Gallstones Clumps of solid material that accumulate in either the gallbladder or bile duct are referred to as gallstones. Diarrhea and constipation Diarrhea refers to frequent, watery stools. Occurs when material moves thru colon too quickly for sufficient water to be absorbed or when water is drawn into lumen from cells lining the intestinal tract. Constipation refers to hard, dry stools that are difficult to pass. Diet containing insufficient fluid or fiber, lack of exercise, a weakening of the muscles of the large intestine, and medications 3.5 Delivering Nutrients and Eliminating Wastes After food has been digested and absorbed nutrients, they must travel to cells. Delivery handled by cardiovascular system, which consists of heart and blood vessels. Capillaries – small, thin-walled blood vessel thru which blood and the body’s cells exchange gases and nutrients o Amino acids, single sugars, water-soluble products go here Lacteals – lymph vessel in the villi of the small intestine that picks up particles containing the products of fat digestion o Not water soluble, such as cholesterol and large fatty acids The Cardiovascular System Circulates blood thru body The heart and blood vessels Blood vessels that carry blood toward heart are veins Those that carry away are arteries Smallest arteries are called arterioles, branch to form capillaries Smallest veins are called venules, which converge to form larger and larger veins for returning blood to the heart Delivering nutrients to the liver Once molecules are in capillaries, they are carried to the liver via hepatic portal vein The Lymphatic System Network of tubules and lymph organs that contain infection-fighting cells 3.6 An Overview of Metabolism Together, the chemical reactions that break down molecules to provide energy and those that synthesize larger molecules are referred to as metabolism. Many of the reactions of metabolism occur in a series known as metabolic pathways. Mitochondria are cellular organs that are responsible for breaking down molecules to release energy Releasing Energy Adenosine Triphosphate (ATP) – high-energy molecule that the body uses to power activities that require energy In the mitochondria, glucose, fatty acids, and amino acids derived from CHO, fats, and proteins, are broken down into the presence of O to produce CO2 and water and release energy. This process, called cellular respiration, is like cell breathing.
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