Chapter 3 Notes.docx

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Simon Fraser University
Biomedical Physio & Kines
BPK 110
Diana Bedoya

CHAPTER 3 THE ORGANIZATION OF LIFE Atoms form molecules, form cells, form tissues, form organs, form organ systems, and form the entire organism.  Atoms – smallest units of an element that retain the properties of the elements.  Molecules – units of two or more atoms of the same or different elements bonding together.  Cells – the basic structural and functional units of living things.  Tissues – similar cells in structures and function.  4 main types of tissue: muscle, nerve, epithelial, and connective.  Organs – discrete structures composed of more than one tissue that perform a specialized function. DIGESTIVE SYSTEM  Responsible for digestion and absorption.  Digestion – process 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.  Break down foods into small pieces (digestion)  enter blood stream/lymphatic system (absorption).  Sugars, amino acids, fatty acids can be absorbed into the body, but polysaccharides, proteins and lipids cannot (in the form they are consumed). ORGANS OF THE DIGESTIVE SYSTEM Gastrointestinal tract – a hollow tube, about 30 feet long, runs from mouth to anus. Also called the gut, GI tract, alimentary canal or digestive tract.  Lumen – inside of the tube.  Inside of lumen is layered with mucosal cells called mucosa. DIGESTIVE SYSTEM SECRETIONS Mucus – a viscous fluid secreted by glands in the digestive tract and other parts of the body.  Lubricates, moistens and protects the digestive tract. Enzymes – crucial proteins which speeds up the rate of reaction in the digestive tract.  Condensation – brings two smaller molecules together to form a larger one, water is released.  Hydrolysis – uses water to break down larger molecules into smaller ones. THE MOUTH  Chemical digestion: saliva - Contains the enzymes:  Salivary amylase, which breaks down carbohydrates  Lingual lipase, which breaks down lipids - Saliva also contains lysozyme, an antibacterial substance - Water in saliva acts as a solvent  Mechanical digestion: use of tongue, teeth (32) to physically digest food. THE PHARYNX  The “throat”.  Conduit for food and inspired air  Epiglottis – a piece of elastic connective tissue that covers the opening to the links during swallowing.  Lies between the pharynx and the esophagus/trachea. - Directs food from the pharynx to the esophagus when closed. - Directs air from the pharynx to the trachea (windpipe) when open. THE ESOPHAGUS  Does not participate in digestion; conduit food  Food moved by peristalsis from the esophagus to the stomach.  Peristalsis – coordinated muscular contractions that move material through the GI tract.  Sphincter – a muscle that acts as a valve right at the entrance of the stomach from the esophagus. THE STOMACH  The stomach has three layers of smooth muscle: longitudinal, horizontal and diagonal. - Allows for optimal churning and mixing.  The pyloric sphincter at the bottom of the stomach controls how long food stays in the stomach.  Food is mixed with highly acidic stomach secretions to form chyme. (a semiliquid food mass)  Lining of stomach is covered with gastric pits that secrete gastric juice. CHAPTER 3 GASTRIC JUICE  Water: acts as a solvent.  Mucus: protects lining of stomach from digesting itself.  Pepsinogen: converts to pepsin, digests protein.  Hydrochloric acid: denatures proteins, activates pepsin. REGULATION OF STOMACH MOTILITY AND SECRETION  Chyme usually empties from the stomach to the small intestine within 2 to 6 hours.  Small, liquid meals empty more quickly than large, solid meals.  Carbohydrate-rich meals leave quickly, while fibre, protein rich meals and fatty meals stay longer.  The longer a meal stays in the stomach and the more it stretches the stomach, the more your hunger is controlled: mixed meals containing fibre promote a feeling of fullness. SMALL INTESTINE (SI)  Narrow 20 foot tube.  Majority of digestion and absorption occurs here,  3 segments: duodenum (25-30cm), jejunum (1.2m) and the ileum (1.5m),  Massive surface area. - Long length. - Various folds (villi, microvilli). - About the size of a tennis court. SECRETIONS FOUND IN THE SI  Pancreatic juice - Pancreatic amylase: converts starches into sugars - Bicarbonate: neutralize chyme - Pancreatic protease: protein-digesting enzymes - Lipases: break down lipids into fatty acids.  SI intestinal enzymes - Aid digestion of disaccharides (double sugars) and short amino acids.  Gallbladder - Secretes bile (made in liver, stored here) into the SI. - Bile helps emulsify fats. ABSORPTION MECHANISMS  After food has been digested into small subunits, it can now be absorbed into either the blood (small carbs, amino acids) or the lymphatic system (larger molecules, larger lipids).  Depending on the nutrient, it is absorbed in one of the following ways:  Simple diffusion – unassisted diffusion of a substance across the cell membrane.  Osmosis – unassisted diffusion of water across the cell membrane.  Facilitated diffusion – assisted diffusion of a substance across the cell membrane.  Active transport – transport of substance across a cell membrane with the aid of a carrier molecule and the expenditure of energy. LARGE INTESTINE  Approx. 5 feet long.  Peristalsis is slower here than in SI  Intestinal microflora = native bacteria which promote digestion  Unabsorbed matter is packaged into feces for excretion  Fibre and fluid rich diets promote more water in feces (easier to excrete). THE DIGESTIVE SYSTEM AND DISEASE PREVENTION  Most food contains bacteria (pathogens). - Actions of the Digestive Tract + immune system help us minimize infection and prevent its symptoms. - Ex. Mucosa of small intestine contains peyer’s patches, lymph nodules that are part of the immune system.  Mostly found in ileum.  When an absorbed foreign antigen enters the mucosa, the cells in peyer’s patches will recognize it as foreign. - Then, various immune cells help eliminate the pathogen  Ex. Phagocytes (“eaters”).  Ex. Lymphocytes o T lymphocytes kill infected cells directly and regulate/assist the immune response. o B lymphocytes secrete antibodies – surround foreign organisms and promote excretion.  Antibodies are specific for each antigen. CHAPTER 3 DIGESTIVE HEALTH: BACTERIA IN THE LARGE INTESETINE  300-500 species of bacteria in large intestine  Contribute to immune functions, growth and development of colon cells, intestinal motility/transit time, digestion, prevention of diarrhea (with antibiotic use).  Probiotic: living organisms (typically bacteria).  Prebiotic: a dietary fibre that promotes the growth of healthy intestinal bacteria. FOOD ALLERGIES  Occurs when immune system triggers an immune response to an allergen, a protein present in our diet or environment. - Ex. Nuts, eggs, milk, seafood protein. - Ex. Gluten found in wheat, barley or rye.  Symptoms of the response may include: tingling mouth, vomiting, intestinal pain, blood pressure drops, hives, breathing difficulties.  Best strategy is to avoid the food altogether. HEART BURN  Heart burn = gastroesophageal reflux. - Occurs when acidic stomach contents leak back, past the lower esophageal sphincter, into the esophagus.  If it occurs 2+ times per week, may become gastroesophageal reflux disease (GERD). - Can lead to bleeding, ulcers and cancers. MINIMIZING RISK FOR GERD, HEART BURN  Reduce volume of stomach during meals, reduce stomach acidity or promote gastric emptying.  Avoid fatty
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