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The Digestive System Vocabulary Headings Important Info
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Overview of GI tract Functions
Mouth: bite, chew, swallow Pharynx and Esophagus: transport Stomach: mechanical disruption; absorption of water & alcohol Small Intestine: chemical & mechanical digestion & absorption Large Intestine: absorb electrolytes & vitamins (B and K) Rectum & Anus: defecation
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Layers of the GI Tract 1. Mucosal Layer
secretes enzymes & absorbs nutrients 2. Submucosal Layer containing BV, glands & lymphatic tissue 3. Muscularis Layer Skeletal:control over swallowing and defecation Smooth: mixes, crushes & propels food along by peristalsis 4. Serosa Layer Covers all organs and walls of cavities not open to outside of body Secretes slippery fluid
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Peritoneum Peritoneum Peritoneal Cavity visceral layer covers organs
parietal layer lines the walls of body cavity Peritoneal Cavity potential space containing a bit of serous fluid
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Salivary Glands Parotid below your ear and over the masseter
Submandibular is under lower edge of mandible Sublingual is deep to the tongue in floor of mouth All have ducts that empty into the oral cavity
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Composition and Functions of Saliva
Wet food for easier swallowing Dissolves food for tasting Protects mouth from infection with its rinsing action: 1 to 1 ½ qt/day Bicarbonate ions buffer acidic foods Bulimia---vomiting hurts the enamel on your teeth Salivary Amylase (enzyme): Starts chemical digestion of starch Lysozyme (enzyme): helps destroy bacteria
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Mumps Myxovirus that attacks the parotid gland Symptoms
inflammation and enlargement of the parotid fever, malaise & sour throat (especially swallowing sour foods) swelling on one or both sides Sterility rarely possible in males with testicular involvement (only one side involved) Vaccine available since 1967
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Structure and Function of the Tongue
Muscle of tongue is attached to hyoid, mandible, hard palate and styloid process Papillae are the bumps: taste buds are protected by being on the sides of papillae
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Tooth Structure & Composition
Crown Neck Roots Pulp cavity Enamel hardest substance in body calcium phosphate or carbonate Dentin calcified connective tissue Cementum bone-like periodontal ligament penetrates it
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Dentition Permanent teeth differing structures indicate function
Primary/baby teeth 20 teeth that start 6months 1 new pair of teeth per month Permanent teeth 32 teeth erupt b/t 6 & 12 years of age differing structures indicate function incisors for biting Canines/cuspids for tearing premolars & molars for crushing/grinding food
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Primary and Secondary Dentition
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Digestion in the Mouth Mechanical Digestion (Mastication/Chewing)
breaks into pieces mixes with saliva forming: Bolus Chemical Digestion Amylase begins starch digestion at: pH of 6.5 or 7.0 found in mouth when bolus & enzyme hit pH 2.5 gastric juices hydrolysis ceases Lingual Lipase secreted by glands in tongue begins breakdown of triglycerides into fatty acids and glycerol
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Pharynx Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and larynx (anteriorly) Skeletal muscle lined by mucous membrane Deglutition/swallowing is facilitated by saliva and mucus starts when bolus is pushed into the oropharynx sensory nerves send signals to deglutition center in brainstem soft palate is lifted to close nasopharynx larynx is lifted as epiglottis is bent to cover glottis
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Esophagus Collapsed muscular tube In front of vertebrae
Posterior to trachea Posterior to the heart Pierces the diaphragm at hiatus hiatal hernia or diaphragmatic hernia
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Physiology of the Esophagus - Swallowing
Voluntary Phase: tongue pushes food to back of oral cavity Involuntary Phase: pharyngeal stage breathing stops & airways are closed soft palate & uvula are lifted to close off nasopharynx vocal cords close epiglottis is bent over airway as larynx is lifted
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Swallowing Upper sphincter relaxes when larynx is lifted
Peristalsis pushes food down circular fibers behind bolus longitudinal fibers in front of bolus shorten the distance of travel Travel time: 4-8 seconds for solids 1 sec for liquids Lower sphincter relaxes as food approaches
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Gastroesophageal Reflex Disease
If lower sphincter fails to open distension of esophagus feels like chest pain or heart attack If lower sphincter fails to close stomach acids enter esophagus & cause heartburn (GERD) for a weak sphincter---don't eat a large meal & lay down in front of TV smoking & alcohol make sphincter relax worsening situation Control symptoms by avoiding coffee, chocolate, tomatoes, fatty foods, onions & mint take Tagamet HB or Pepcid AC 60 minutes before eating neutralize existing stomach acids with Tums
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Anatomy of Stomach Parts of stomach
Cardia Fundus Body Pylorus: starts to narrow as approaches Pyloric Sphincter Empties as small squirts of chyme leave the stomach through the pyloric valve
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Pylorospasm and Pyloric Stenosis
Abnormalities of the pyloric sphincter in infants Pylorospasm muscle fibers of sphincter fail to relax trapping food in the stomach vomiting occurs to relieve pressure Pyloric Stenosis narrowing of sphincter indicated by projectile vomiting must be corrected surgically
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Histology of the Stomach
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Mucosa & Gastric Glands
Hydrochloric acid converts pepsinogen from chief cell to pepsin Intrinsic factor absorption of vitamin B12 for RBC production Gastrin hormone (g cell) “get it out of here” release more gastric juice increase gastric motility relax pyloric sphincter constrict esophageal sphincter preventing entry
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Muscularis Three layers of smooth muscle: Outer Longitudinal Circular
Inner Oblique Permits greater churning & mixing of food with gastric juice
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Physiology of Digestion— Mechanical vs. Chemical
Protein digestion begins HCl denatures protein molecules HCl transforms Pepsinogen into Pepsin breaks peptide bonds b/t certain a.a. Fat digestion continues gastric lipase splits the triglycerides in milk fat most effective at pH 5 to 6 (infant stomach) HCl kills microbes in food Mucous cells protect stomach walls from being digested w/ mm thick layer of mucous Gentle mixing waves every 15 to 25 seconds mixes bolus with 2 quarts/day of gastric juice to turn it into chyme (a thin liquid) More vigorous waves travel from body of stomach to pyloric region Intense waves near pylorus opens & squirts out 1-2 teaspoons full w/each wave
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Cephalic Phase = “Stomach Getting Ready”
Cerebral Cortex: sight, smell, taste & thought stimulate PNS Vagus Nerve: increases stomach muscle and glandular activity
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Gastric Phase = “Stomach Working”
Nervous control keeps stomach active stretch receptors & chemoreceptors provide info vigorous peristalsis and glandular secretions continue chyme is released into duodenum Endocrine influences over stomach activity distention & presence of caffeine or protein cause G cells secretion of gastrin into bloodstream gastrin hormone increases stomach glandular secretion gastrin hormone increases stomach churning and sphincter relaxation
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Intestinal Phase = “Stomach Emptying”
Stretch receptors in duodenum slow stomach activity & increase intestinal activity Distension, fatty acids or sugar signals medulla SNS slow stomach activity Hormonal influences secretin hormone decreases stomach secretions Cholecystokinin (CCK) decreases stomach emptying Gastric Inhibitory Peptide (GIP) decreases stomach secretions, motility & emptying
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Absorption of Nutrients by the Stomach
Water especially if it is cold Electrolytes Some drugs (especially aspirin) & alcohol Fat content in the stomach slows the passage of alcohol to the intestine where absorption is more rapid Gastric mucosal cells contain alcohol dehydrogenase that converts some alcohol to acetaldehyde more of this enzyme found in males than females Females have less total body fluid that same size male so end up w/higher blood alcohol levels with same intake of alcohol
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Digestive Hormones Gastrin Gastric inhibitory peptide--GIP Secretin
stomach, gastric & ileocecal sphincters Gastric inhibitory peptide--GIP stomach & pancreas Secretin pancreas, liver & stomach Cholecystokinin--CCK pancreas, gallbladder, sphincter of Oddi, & stomach
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Digestive Enzymes When chyme enters the duodenum, proteins & carbohydrates are only partly digested, & fat digestion needs to be carried out Enzymes aid in digestive breakdown & absorption of chyme _____________________________________________________________ Bile Salts (Liver & Gallbladder) Pancreatic & Salivary Amylase (Pancreas & Mouth) Fat Fat Droplets Starch + H2O Maltose Trypsin & Pepsin (Pancreas) Protein + H2O Peptides Lipase (Pancreas) Fat Droplets + H2O Glycerol + Fatty Acids Peptidases (Intestinal Juice) Peptides + H2O Amino Acids Maltase (Intestinal Juice) Maltose + H2O Glucose Bile is a thick digestive fluid secreted by the liver and stored in gallbladder. Facilitates digestion by emulsifying fats into fatty acids, which can be absorbed by the digestive tract
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Vomiting (Emesis): Reverse Peristalsis
A deep breath is taken, the glottis is closed, and the larynx is raised to open the upper esophageal sphincter. Soft Palate is elevated to close of external nares Diaphragm contracts down to create a negative pressure in the thorax, which facilitates opening of the esophagus and esophageal sphincter Simultaneously with the downward movement of the diaphragm, the abdominal muscles contract elevating inner gastric pressure. With the pylorus closed and the esophagus open the exit route is clear
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Anatomy of the Pancreas
5" long by 1" thick Head close to curve in C-shaped duodenum Main duct joins common bile duct from liver Sphincter of Oddi on major duodenal papilla Bile and pancreatic secretions enter the digestive system through this point Opens 4" below pyloric sphincter
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Composition and Functions of Pancreatic Juice
1.5 Quarts/day pH 7.1 to 8.2 Contains water, enzymes & sodium bicarbonate Digestive enzymes pancreatic amylase, pancreatic lipase, proteases Ribonuclease to digest nucleic acids deoxyribonuclease
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Pancreatitis Pancreatitis:
inflammation of the pancreas occurring with the mumps Acute Pancreatitis: associated with heavy alcohol intake or biliary tract obstruction result is patient secretes trypsin in pancreas & starts to digest themselves
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Regulation of Pancreatic Secretions
Secretin acidity in intestine causes increased sodium bicarbonate release GIP fatty acids & sugar causes increased insulin release CCK fats and proteins cause increased digestive enzyme release
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Anatomy of the Liver and Gallbladder
weighs 3 lbs. below diaphragm right lobe larger gallbladder on right lobe size causes right kidney to be lower than left Gallbladder fundus, body & neck The gallbladder stores about 50 ml of bile
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Liver Functions—Carbohydrate Metabolism
Turn proteins glucose Turn triglycerides glucose Turn excess glucose glycogen & store in the liver Turn glycogen back glucose as needed
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Liver Functions: Lipid Metabolism
Synthesize cholesterol Synthesize lipoproteins HDL (high-density lipoprotein) helps move cholesterol back to liver for removal from bloodstream (GOOD) LDL (low-density lipoprotein) helps cholesterol stick to artery walls (BAD) Breaks down some fatty acids
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Liver Functions: Protein Metabolism
Deamination = removes NH2 (amine group) from amino acids so can use what is left as energy source Converts resulting toxic ammonia (NH3) into urea for excretion by the kidney Synthesizes plasma proteins utilized in clotting mechanism and immune system Convert one amino acid into another
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Other Liver Functions Detoxifies blood by removing or altering drugs & hormones (thyroid & estrogen) Removes the waste product: Bilirubin Releases bile salts help digestion by emulsification Stores fat soluble vitamins: A, B12, D, E, K Stores iron and copper Phagocytizes worn out blood cells & bacteria Activates Vitamin D: the skin can also do this with 1 hr of sunlight a week
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Bile Production 1 quart of bile/day is secreted by the liver
yellow-green in color & pH 7.6 to 8.6 Components water & cholesterol Bile Salts = Na & K salts of bile acids Bile Pigments (bilirubin) from hemoglobin molecule Globin = a reuseable protein Heme = broken down into iron and bilirubin
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Pathway of Bile Secretion
Bile capillaries Hepatic ducts connect to form common hepatic duct Cystic duct from gallbladder & common hepatic duct join to form common bile duct Common bile duct & pancreatic duct empty into duodenum
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Regulation of Bile Secretion
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Blood Supply to the Liver
Hepatic Portal Vein nutrient rich blood from stomach, spleen & intestines Hepatic artery branch off the aorta
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Anatomy of the Small Intestine
20 feet long: 1 inch in diameter Large surface area for majority of absorption 3 parts Duodenum: 10 inches Jejunum: 8 feet Ileum: 12 feet ends at Ileocecal Valve
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Small Intestine Plica Circularis Villi Microvilli
permanent ½ inch tall folds that contain part of submucosal layer not found in lower ileum cannot stretch out like stomach Villi 1 Millimeter tall Contains vascular capillaries and lacteals (lymphatic capillaries) Microvilli Absorption and digestion Digestive enzymes found at cell surface on microvilli Digestion occurs at cell surfaces Small Intestine
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Small Intestine: Regions and Structures
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Mechanical Digestion in Small Intestine
Weak peristalsis in comparison to the stomach: chyme remains for 3 to 5 hours Segmentation: local mixing of chyme with intestinal juices sloshing back & forth
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Digestion of Carbohydrates
Digestion of Nucleic Acids Mouth: salivary amylase Esophagus & stomach: nothing happens Duodenum: pancreatic amylase Brush Border Enzymes (maltase, sucrase & lactose) act on disaccharides produces monosaccharides--fructose, glucose & galactose lactose intolerance (no enzyme; bacteria ferment sugar)--gas & diarrhea Pancreatic juice contains 2 nucleases ribonuclease which digests RNA deoxyribonuclease which digests DNA Nucleotides produced are further digested by brush border enzymes Absorbed by active transport
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Digestion of Lipids Digestion of Proteins Stomach Pancreas
HCl denatures or unfolds proteins pepsin turns proteins into peptides Pancreas digestive enzymes: split peptide bonds b/t different amino acids brush border enzymes: split off amino acid at amino end of molecule or split dipeptide Mouth: lingual lipase Small intestine emulsification by bile Pancreatic Lipase: splits into fatty acids & monoglyceride No enzymes in brush border
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Absorption in Small Intestine
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Absorption of Monosaccharides
Absorption into epithelial cell glucose & galactose: sodium symporter(active transport) Fructose: facilitated diffusion Movement out of epithelial cell into bloodstream by facilitated diffusion Absorption of Amino Acids & Dipeptides Absorption into epithelial cell active transport w/Na+ or H+ ions Movement out of epithelial cell into blood diffusion
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Absorption of Lipids Small fatty acids enter cells & then blood by simple diffusion Larger lipids exist only within micelles (bile salts coating) Lipids enter cells by simple diffusion leaving bile salts behind in gut Bile salts reabsorbed into blood & reformed into bile in the liver
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Absorption of Electrolytes
Sources of electrolytes GI secretions & ingested foods and liquids Enter epithelial cells by diffusion & secondary active transport sodium & potassium move = Na+/K+ pumps (active transport) chloride, iodide and nitrate = passively follow iron, magnesium & phosphate ions = active transport Intestinal Ca+ absorption requires vitamin D & parathyroid hormone
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Absorption of Vitamins
Fat-Soluble Vitamins A, D, E, K travel in micelles & are absorbed by simple diffusion Water-Soluble Vitamins Vitamin B complex, Ca absorbed by diffusion B12 combines with intrinsic factor before it is transported into the cells receptor mediated endocytosis
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Absorption of Water 9 liters of fluid dumped into GI tract each day
Small intestine reabsorbs 8 liters Large intestine reabsorbs 90% of that last liter Absorption is by osmosis through cell walls into vascular capillaries inside villi
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Anatomy of Large Intestine
5 feet long by 2½ inches in diameter Ascending & descending colon are retroperitoneal Cecum & appendix Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx Anal canal = last 1 inch of GI tract internal sphincter----smooth muscle & involuntary external sphincter----skeletal muscle & voluntary control
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Appendicitis Inflammation of the appendix due to blockage of the lumen by chyme, foreign body, carcinoma, stenosis, or kinking Symptoms high fever, elevated WBC count, neutrophil count above 75% referred pain, anorexia, nausea and vomiting pain localizes in right lower quadrant Infection may progress to gangrene and perforation within 24 to 36 hours
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Mechanical Digestion in Large Intestine
Smooth muscle: mechanical digestion Peristaltic Waves 3 to 12 contractions/minute Haustral Churning: relaxed pouches filled from below by muscular contractions (elevator) Gastroileal Reflex when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room Gastrocolic Reflex when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum
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Chemical Digestion in Large Intestine
No enzymes are secreted only mucous Bacterial Fermentation undigested carbohydrates into carbon dioxide & methane gas undigested proteins into simpler substances (indoles)----odor turn bilirubin into simpler substances that produce color Bacteria produce vitamin K and B in colon
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Absorption & Feces Formation in Large Intestine
Some electrolytes: Na+ and Cl- After 3 to 10 hours, 90% of H2O has been removed from chyme Feces are semisolid by time reaches transverse colon Feces = dead epithelial cells, undigested food such as cellulose, bacteria (live & dead)
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Defecation Gastrocolic reflex moves feces into rectum
Stretch receptors signal sacral spinal cord Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter External sphincter is voluntarily controlled
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Defecation Problems Diarrhea Constipation
chyme passes too quickly through intestine H20 not reabsorbed Constipation decreased intestinal motility too much water is reabsorbed Remedy = fiber, exercise and water
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Dietary Fiber Insoluble Fiber Soluble Fiber
Woody parts of plants (wheat bran, veggie skins) speeds up transit time & reduces colon cancer Soluble Fiber gel-like consistency beans, oats, citrus white parts, apples lowers blood cholesterol by preventing reabsorption of bile salts so liver has to use cholesterol to make more
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Aging and the Digestive System
Changes that occur: decreased secretory mechanisms & motility loss of strength & tone of muscular tissue changes in neurosensory feedback diminished response to pain & internal stimuli Symptoms: sores, loss of taste, peridontal disease, difficulty swallowing, hernia, gastritis, ulcers, malabsorption, jaundice, cirrhosis, pancreatitis, hemorrhoids and constipation Colon or rectum is common
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Nutrition & Health Nutrient:
Substance used by the body for growth, maintenance, and repair Nutrient:
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Categories of Nutrients
Carbohydrates Most are derived from plants Exceptions: lactose from milk and small amounts of glycogens from meats Lipids Saturated fats from animal products Unsaturated fats from nuts, seeds, and vegetable oils Cholesterol from egg yolk, meats, and milk products Proteins Complete proteins – contain all essential amino acids Most are from animal products Legumes and beans also have proteins, but are incomplete Vitamins Most vitamins are used as cofactors and act with enzymes Found in all major food groups Minerals Play many roles in the body Most mineral-rich foods are vegetables, legumes, milk, & some meats
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The sum of all chemical reactions necessary to maintain life
Metabolism The sum of all chemical reactions necessary to maintain life Catabolism Substance is broken down to simpler products Energy is released Anabolism Larger molecules are built from smaller ones Energy Required
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Basal Metabolic Rate (B.M.R.)
The amount of energy expended while at rest, (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). Release of energy in this state is sufficient only for vital organ function Wt (kg) = wt (lbs) / 2.2lbs/kg Age BMR Equation (how many cal you need) Males (60.9 x wt) - 54 (22.7 x wt) + 495 (17.5 x wt) + 651 (15.3 x wt) + 679 (11.6 x wt) + 879 >60 (13.5 x wt) + 487 Females (61.0 x wt) - 51 (22.5 x wt) + 499 (12.2 x wt) + 746 (14.7 x wt) + 496 (8.7 x wt) >60 (10.5 x wt) + 596
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Body Mass Index (B.M.I.) 1. Convert your weight in pounds to kilograms by dividing by 2.2 161lbs / 2.2kg = 73.18kg 2. Convert your height in feet to inches (1 foot = 12 inches). 5’5’’ = 65’’ 3. Convert your height to meters: multiply your height in inches by Then divide by 100 65’’ x 2.54 = 165.1m 165.1m/100 = 1.651 4. Multiply your height (in meters) by itself. 1.651 x = 5. Divide your weight in kilograms (step 1) by your height squared (step 4) 73.18kg/ m2 = B.M.I. of 26.85 (Mrs. Warren is Overweight—Yikes!—see ya at LA Fitness)
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BMI Categories Underweight: Less than 18.5 Normal Weight: 18.5 - 24.9
Overweight: Obese: 30 or higher
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