Digestion and Nutrition Digestion The mechanical and chemical

Digestion and Nutrition

Digestion Ø The mechanical and chemical breakdown of foods and the absorption of the resulting nutrients by cells Ø Mechanical: large pieces into smaller pieces Ø Chemical: food into simpler chemicals

Alimentary Canal Muscular tube which extends 8 meters from mouth to anus Ø Structure of wall Ø l l Mucosa: protects the tissues beneath it and carries on secretion and absorption Submucosa: vessels nourish surrounding tissues and carry away absorbed materials Muscular layer: produces movement of the tube Serosa: secrete fluid which moistens and lubricates the tube’s outer surface

Ø Movements of the tube l l Mixing: Smooth muscles in small segments contract rhythmically Propelling: wavelike motion called peristalsis

Mouth Ø Receives food and begins digestion by mechanically reducing the size of solid particles and mixing them with saliva Ø Cheeks contain muscles for chewing Ø Lips judge temp. and texture of foods Ø Tongue is mostly skeletal muscle which mixes food particles and moves food underneath the teeth for chewing

Palate forms the roof of the oral cavity and closes opening between the nasal cavity and the pharynx Ø Teeth Ø l l l 20 deciduous (primary) teeth 32 permanent (secondary) teeth Incisors used to bite off large pieces of food Cuspids grasp and tear food Bicuspids grind food particles Molars grind food particles

Salivary Glands Amylase – enzyme splits starch and glycogen molecules into disaccharides Ø Mucus – binds food particles and lubricates during swallowing Ø

Swallowing Mechanism (p. 394) Food is chewed and mixed with saliva. Tongue rolls mixture into a mass, or bolus, and forces it into the pharynx. 2. Food stimulates sensory receptors around the pharyngeal opening triggering the swallowing reflex. 3. Peristalsis transports the food in the esophagus to the stomach. 1.

Esophagus Ø Straight, collapsible tube 25 cm long Ø Food passageway from the pharynx to the stomach Ø Contains mucous glands Ø Just above meeting stomach, cardiac sphincter prevents stomach contents from regurgitating into the esophagus

Acid Reflux Ø liquid content of the stomach regurgitates into the esophagus Ø chronic condition Ø reflux occurs as frequently in normal individuals as in patients with GERD Ø Contributing factors: l l the lower esophageal sphincter hiatal hernias esophageal contractions emptying of the stomach

Stomach Ø Receives food from the esophagus Ø Mixes food with gastric juices Ø Initiates protein digestion Ø Carries on limited absorption Ø Moves food into small intestine Ø Pepsin – most important enzyme

Ulcer Ø Open sore in the skin or mucous membrane resulting from localized tissue breakdown Ø Gastric ulcers occur in the stomach Ø Caused by a bacterium Ø Treated with antibiotics

Chyme Ø Semifluid paste of food particles and gastric juice Ø Rate at which stomach empties depends on the fluidity of the chyme and the type of food present Ø Fatty foods may remain in the stomach from three to six hours Ø As chyme enters the duodenum the pancreas, liver, and gall bladder add their secretions

Vomiting Triggered by irritation or distension in the stomach or intestines Ø Steps of vomiting Ø l l l l Sensory impulses travel to medulla oblongata Take a deep breath Raise soft palate (closes nasal cavity) Close glottis (closes off trachea) Relax cardiac sphincter Contract diaphragm Contract abdominal wall (increase pressure in stomach)

Pancreas Ø Extends horizontally across the posterior abdominal wall in the C-shaped curve of the duodenum Ø Pancreatic juice contains enzymes that digest carbohydrates, fats, nucleic acids, and proteins

Liver Ø Each lobe divided into lobules Ø Metabolizes carbohydrates, lipids, and protein Ø Stores glycogen, iron, and vitamins A, D, and B 12 Ø Filters blood Ø Detoxifies Ø Secretes bile

Hepatitis Inflammation of the liver Ø A: spreads by contact with food or objects contaminated with virus-containing feces Ø B: spreads by contact with virus-containing body fluids, such as blood, saliva, or semen Ø C: transmitted by blood (razors, needles, mother to fetus) Ø D: occurs in people already infected by B; associated with blood transfusions and intravenous drug use Ø E: transmitted by water contaminated with feces Ø G: sudden, severe hepatitis Ø

Gallbladder Ø Pear-shaped sac located in a depression on the liver’s interior surface Ø Stores bile between meals, reabsorbs water to concentrate bile, and contracts to release bile into the small intestine Ø Cholesterol in bile may precipitate and form crystals called gallstones

Small Intestine Tubular organ that extends from the pyloric sphincter to the beginning of the large intestine Ø Receives secretions from the pancreas and liver Ø Completes digestion of the nutrients in chyme, absorbs the products of digestion, and transports the residues to the large intestine Ø Duodenum, jejunum, ileum Ø Mesentery suspends portions and supports the blood vessels, nerves, and lymphatic vessels that supply the intestinal wall Ø Inner wall of intestine lined with tiny projections of mucous membrane called intestinal villi which aid in the absorption of digestive products Ø

Lactose Intolerance Ø Individual does not produce sufficient lactase to adequately digest lactose Ø Increased osmotic pressure of the intestinal contents Ø Intestinal bacteria metabolize undigested sugar, producing organic acids and gases Ø Overall result is bloating, intestinal cramps, and diarrhea

Large Intestine Diameter greater than small intestine Ø Ascends on rt. side, crosses obliquely left, descends into pelvis Ø Cecum (vermiform appendix below), ascending colon, transverse colon, descending colon, rectum, anus Ø Anus guarded by two sphincter muscles (one involuntary, one voluntary) Ø No digestive function Ø Secretes mucus to protect intestinal wall Ø Home to 100 trillion bacteria Ø

Hemorrhoids Enlarged or inflamed branches of the rectal vein cause itching, sharp pain, and sometimes bright red bleeding Ø Caused by obesity, pregnancy, constipation, diarrhea, and liver disease Ø Eating more fiber-rich foods and drinking lots of water can usually prevent or cure hemorrhoids Ø Warm soaks in the tub, cold packs, external creams, surgery Ø

Nutrition Ø calorie: amt. of heat required to raise the temp. of a gram of water by 1°C Ø Carbohydrates supply energy for cellular processes Ø Lipids supply energy for cellular processes and for building structures such as cell membranes Ø Proteins are polymers of amino acids with a wide variety of functions

Vitamins Ø Ø Ø Ø Organic compounds that are required in small amounts for normal metabolism See chart p. 417 A: synthesis of visual pigments; found in liver, fish, whole milk, butter, eggs, leafy green veggies, yellow and orange vegetables C: necessary for collagen production, synthesis of hormones; found in citrus fruits, tomatoes, potatoes D: promotes absorption of calcium and phosphorus; produced in skin exposed to UV light, in milk, egg yolk, fish liver oils E: antioxidant; found in oils from cereal seeds, salad oils, margarine, shortenings, fruits, nuts, and veggies K: synthesis of prothrombin, which functions in blood clotting; found in leafy green veggies, egg yolk, pork liver, soy oil, tomatoes, cauliflower

Minerals (p. 419) Calcium – milk; milk products; leafy green veggies Ø Phosphorus – meats; cheese; nuts; whole-grain cereals Ø Potasssium – avocadoes; dried apricots; meats; nuts; potatoes; bananas Ø Sulfur – meats; milk; eggs; legumes Ø Sodium – table salt; cured ham; sauerkraut, cheese Ø Chlorine – same as for sodium Ø Magnesium – milk; dairy products; legumes Ø

Adequate Diets P. 421 Ø BMI (body mass index) found by dividing weight in kg (kg=2. 2 lbs) by your height in meters squared (one ft=0. 3 meters) Ø <18. 5 underweight; 18. 5 -24. 0 normal; 25 -29. 9 overweight; >30 obese Ø Obesity increases risk of developing cardiovascular disease, type 2 diabetes mellitus, certain cancers, osteoarthritis, and other health problems Ø

Ø http: //www. nutrition. gov/ Ø http: //www. webmd. com/diet/calc-bmi-plus Ø http: //www. kidshealth. org/teen/food_fitnes s/dieting/weight_height. html