Textbook Notes (369,067)
United States (206,185)
Nutrition (22)
NTR 306 (22)
Chapter 3

NTR 306 Chapter 3 Notes.docx

7 Pages

Course Code
NTR 306
Deanna Staskel

This preview shows pages 1 and half of page 2. Sign up to view the full 7 pages of the document.
Chapter Three: Digestion, Absorption and Transport 3.1 Digestion Digestion – the process by which food is broken down into absorbable units Absorption – the uptake of nutrients by the cells of the small intestine for transport into either the blood or the lymph Anatomy of the Digestive Tract Gastrointestinal (GI) tract – flexible muscular tube that extends from the mouth, through the esophagus, stomach, small intestine, large intestine, and rectum to the anus  Inner space within the GI tract is called the lumen Mouth:  Process of digestion begins here  Mastication [process of chewing]  Fluids help dissolve the food so the tongue can taste it o Only particles in solution can react with taste buds  4 basic taste sensations o Sweet o Sour o Bitter o Salty  Some scientists include the flavor associated with monosodium glutamate called savory  Aroma, appearance, texture and temp affect food flavor  A mouthful of food is swallowed  pharynx [short tube share by the digestive system and the respiratory system] o Epiglottis closes off the airway so choking doesn’t occur  Bolus – the substance a mouthful of food becomes after being chewed and swallowed Esophagus:  Has a sphincter muscle at each end o During a swallow,  The upper esophageal sphincter opens  Bolus slides down the esophagus  Then it passes through a hole in the diaphragm to the stomach  Lower esophageal sphincter at the entrance to the stomach closes behind the bolus Stomach:  Retains the bolus for a while in its upper portion  Little by little, stomach transfers the food to its lower portion o Add juices to it o Grinds it to a semiliquid mass called chyme o Releases chime through the pyloric sphincter  Which opens into the small intestine and then closes behind the chyme Small intestine:  Beginning of small intestine o Chyme bypasses the opening from the common bile duct  Which is dripping fluids into the small intestine from two organs outside the GI tract  Gallbladder [stores bile until needed]  Pancreas [secretes digestive enzymes and juices into duodenum] o Chyme travels on down the small intestine through its three segments Chapter Three: Digestion, Absorption and Transport  Duodenum [top portion of small intestine]  Jejunum [first 2/5ths beyond duodenum]  Ileum [last segment of small intestine] Large intestine (colon):  Ileocecal valve o Located at the beginning of the large intestine in the lower right side of the abdomen  Contents can slip into another opening – the appendix o A narrow blind sac o Contains bacteria and lymph cells o Not an intended route for the contents  After entering the large intestine by the ileocecal valve, it goes to the ascending  transcending  then descending colon to the rectum o During this journey, colon withdraws water, leaving semisolid waste [poop]  2 sphincters of the anus open to allow passage of the waste Muscular Action of Digestion Motility – the ability of the GI tract muscles to move Peristalsis:  Entire GI tract is ringed with circular muscles o Longitudinal muscles o When the rings tighten and the long muscles relax, the tube is constricted o When the rings relax and the long muscles tighten, the tube bulges  Stress, medicine and medical conditions interfere with normal GI tract contractions Stomach action:  Stomach has the thickest walls and strongest muscles of ALL the GI tract organs  Has third layer of diagonal muscles  The 3 sets of muscles help force the chyme downward o With the pyloric sphincter remaining tightly closed  Stomach wall releases gastric juices o When chyme is completely liquefied with gastric juices, the pyloric sphincter opens briefly  Allows small portions of chyme to pass through  Chyme no longer resembles food Segmentation:  A periodic squeezing or partitioning of the intestine at intervals along its length by its circular muscles  Mixes the chyme and promote close contact with the digestive juices and the absorbing cells of the intestinal walls Sphincter contractions:   represents the direction of the chyme  Upper esophageal sphincter  esophagus  lower esophageal sphincter [sometimes called cardiac sphincter because of its proximity to the heart]  stomach  pyloric sphincter  small intestine  ileocecal valve  large intestine  rectum  two sphincters of the anus  Lower esophageal sphincter prevents reflux of the stomach content The Secretions of Digestion Breakdown of food into nutrients requires secretions from five organs:  Salivary glands, stomach, pancreas, liver (via gallbladder) and small intestine Enzyme – a protein that facilitates a chemical reaction Chapter Three: Digestion, Absorption and Transport Catalyst – speeds up a chemical reaction Hydrolysis – one molecule is split into two molecules, with H added to one and OH to the other (from H2O) Digestive enzymes – proteins found in digestive juices that break down food substances into simpler compounds Saliva:  Salivary glands – exocrine glands that secrete saliva into the mouth  Saliva contains water, salts, mucus and enzymes that initiate the digestion of carbohydrates  Protects the teeth and linings of the mouth, esophagus and stomach from substances that might be harmful Gastric juice:  Gastric glands – exocrine glands in the stomach wall that secrete gastric juice into the stomach o Mixture of water, enzymes and hydrochloric acid [protein digestion]  Hydrochloric acid is so acidic  Can cause heartburn if it reflux into the esophagus  The strong acidity prevents bacterial growth and kill most bacteria that enter the body with food  Cell of the stomach wall protect themselves from this acid by secreting mucus [thick slippery, white substance that coats the cells]  pH scale o Bile has pH of between 8 and 9 o Pancreatic juice has pH of 8 o Saliva has pH of between 6 and 7 o Gastric juice has pH of 2 Pancreatic juice and intestinal enzymes:  Digestion of 3 energy nutrients (carbohydrates, fats and proteins) begin  Pancreatic juice – exocrine secretin of the pancreas o Also contains sodium bicarbonate [alkaline compound]  Neutralizes the acidic chyme Bile:  Bile – emulsifier [substance with both water-soluble and fat-soluble portions] that prepares fats and oils for digestion by mixing them into a watery solution o An exocrine secretion made by the liver o Stored in the gallbladder o Released into the small intestine when needed o NOT AN ENZYME Summary of Digestive Secretions and their Major Actions Organ or Gland Target Organ Secretion Action Salivary glands Mouth Saliva  Fluid eases swallowing  Salivary enzyme breaks down some carbohydrates Gastric glands Stomach Gastric juice  Fluid mixes with bolus  Hydrochloric acid uncoils proteins  Enzymes break down proteins  Mucus protects stomach cells Pancreas Small intestine Pancreatic juice  Bicarbonate neutralizes acidic gastric juices Chapter Three: Digestion, Absorption and Transport  Pancreatic enzymes break down carbohydrates, fats an proteins Liver Gallbladder Bile  Bile is stored until needed Gallbladder Small intestine Bile  Bile emulsifies fat so that enzymes can have access to break it down Intestinal glands Small intestine Intestinal juice  Intestinal enzymes break down carbohydrate, fat and protein fragments  Mucus protects the intestinal wall 3.2 Absorption Anatomy of the Absorptive System Absorption of nutrients in 3 ways: simple diffusion, facilitated diffusion and active transport Villi – fingerlike projections from the folds of the small intestine  In constant motion  Lined by a thin sheet of muscle Microvilli – tiny, hairlike projections on each cell of every villus that can trap nutrient particles and transport them into the cells Crypts – tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestine Goblet cells – cells of the GI tract (and lungs) that secrete mucus A closer look at the intestinal cells Specialized cells:  Absorb different nutrients o Nutrients ready for absorption early are near the top of the GI tract o Those that take longer to be digested are absorbed farther down  Learned by dietitians and medical professionals to treat digestive disorders o If one part of GI tract becomes dysfunctional, the diet can
More Less
Unlock Document

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.