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Chapter 8. Digestive System and Nutrition. Outline. Overview of Digestion The First Part of the Digestive Tract The Stomach and Small Intestine Three Accessory Organs and Regulation of Secretions The Large Intestine and Defecation

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chapter 8

Chapter 8

Digestive System and Nutrition

  • Overview of Digestion
  • The First Part of the Digestive Tract
  • The Stomach and Small Intestine
  • Three Accessory Organs and Regulation of Secretions
  • The Large Intestine and Defecation
  • Nutrition and Weight Control (Should reviewCh.2, Molecules of Life, pp. 22-30)
overview of digestion
Overview of Digestion
  • Also called the alimentary tract, gastrointestinal tract (G.I. tract), “gut”.
  • From the mouth to the anus.
  • There are two types of digestive processes:
    • 1. Mechanical. . . .
    • 2. Chemical. . . .
  • Digestion of food is an extracellular process due to enzymes secreted into the gut by glands that reside in the lining or lie nearby.
overview of digestion1
Overview of Digestion
  • Functions of this system include:
    • Ingest food.
    • Digest it into small molecules that can cross the cell membrane.
    • Movement of contents along tract.
    • Absorb nutrient molecules.
    • Eliminate nondigestible wastes.
the wall of the digestive tract
The Wall of the Digestive Tract
  • Layers from inside, out: (MSMS)
    • Mucosa - Mucus membrane layer.
    • Submucosa - Submucosal layer.
    • Muscularis – Longitudinal and circular smooth muscle layer.
    • Serosa - Serous membrane layer.
  • Disorders:
    • Diverticulosis, diverticulitis, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), appendicitis, peritonitis.
the digestive tract mouth food receiver
The Digestive TractMouth : “Food Receiver”
  • Functions: ingest, break down (mechanical), begin digestion (chemical), taste, form into bolus for swallowing.
  • Roof of the mouth composed of two parts.
      • Anterior (front) hard palate.
      • Posterior (back) soft palate.
  • Tonsils help protect against infection.
  • Three pairs of salivary glands (exocrine glands) send juices through ducts to the mouth.
    • Saliva contains digestive enzymes (bicarbonate and salivary amylase).
the digestive tract mouth food receiver1
The Digestive TractMouth : “Food Receiver”
  • Teeth used to chew food into pieces small enough to swallow.
    • Each tooth has two main divisions.
      • Crown.
      • Root.
  • Tongue mixes chewed food with saliva and forms a bolus in preparation for swallowing.
the pharynx a crossroad
The Pharynx : “A Crossroad”
  • The pharynx (throat) receives air from the nasal cavities and food from the mouth.
    • Swallowing is a reflex action that occurs in the pharynx.
      • Soft palate moves to close off nasopharynx, and the trachea moves under the epiglottis to cover the glottis.
the esophagus a food conductor
The Esophagus : “A Food Conductor”
  • Function?
  • The esophagus is a muscular tube that passes from the pharynx through the thoracic cavity and diaphragm into the abdominal cavity.
    • Rhythmic peristalsis pushes food along the digestive tract.
    • Sphincters encircle tubes and act as valves.
    • Heartburn vs. Acid reflux disease ( gastroesophageal reflux disease, GERD)
health focus


Heartburn (GERD)

the stomach food storer and grinder
The Stomach : “Food Storer and Grinder”
  • Functions: stores food, mixes food (mechanical), kills bacteria, and aids in digestion (chemical).
    • Columnar epithelial lining contains gastric pits leading into gastric glands.
      • Produce gastric juice containing HCl (pH ~2) and enzyme pepsin.
    • Walls of stomach have folds which help churn and mix food and gastric juices.
      • Chyme leaves the stomach and enters the small intestine.
the stomach food storer and grinder1
The Stomach : “Food Storer and Grinder”
  • Ulcers?
  • Form when HCl penetrates mucus barrier and disintegrates tissue.
  • Called a peptic ulcer.
  • However, recently discovered that may be caused by bacteria (Helicobacter pylori ) that inhibit mucus production!
  • What is the significance of this discovery?
  • William Beaumont and Alexis St. Martin !?
historical focus


A Window to the Stomach: Alexis St. Martin and Dr. William Beaumont

the small intestine food processor
The Small Intestine : “Food Processor”
  • Functions:
    • Receives secretions from liver, pancreas.
    • Mechanical, chemical digestion of food.
    • Absorption of nutrients.
    • Transports undigested material to large intestine.
  • Thus, is the primary site for chemical breakdown of food and nutrient absorption.
  • ~ 1 inch wide, ~ 18 feet long (6 meters).
the small intestine food processor1
The Small Intestine : “Food Processor”
  • The duodenum (first ~10”) is where the chemical breakdown of food gets under way.
    • Receives bile from liver (gall bladder) to “emulsify” fat.
    • Receives digestive enzymes and sodiumbicarbonate from the pancreas for chemical breakdown of food and to neutralize the chyme.
    • Duodenal ulcers?
  • Along the small intestine are the villi (s. villus) – the structural unit of the small intestine.
the small intestine food processor2
The Small Intestine : “Food Processor”
  • Are covered by microvilli to increase the surface area for absorption of nutrients.
  • Surface area ~ that of NFL football field!!!
  • Blood vessels absorb sugars (from CHO) and amino acids (from proteins).
  • Lacteal – small lymph vessels which absorb “fats” and transport / return them and fluids to the blood stream.
  • Lactose intolerance?
  • Link between obesity, type 2 diabetes, and cardiovascular disease?
three accessory organs
Three Accessory Organs
  • Pancreas
    • Exocrine part produces digestive enzymes
    • Endocrine part secretes insulin and glucagon that regulate blood glucose levels.
  • Liver maintains homeostasis by. . . .
    • Produces bile (from breakdown of RBC’s).
    • Detoxifies blood.
    • Stores iron, fat-soluble vitamins: A, D, E, K
    • Maintains blood glucose levels (< 0.1%)
    • Produces urea.
    • Makes blood proteins (clotting, etc.)
    • Helps regulate blood cholesterol level (bile salts)
three accessory organs1
Three Accessory Organs
  • Liver disorders:
    • Jaundice.
      • Hemolytic - RBC broken down.
      • Obstructive - bile duct blocked due to gallstones.
      • Hepatitis – viral infection causing inflammation.
    • Cirrhosis.
      • Common among alcoholics.
      • Liver becomes fatty and tissue is replaced by inactive fibrous scar tissue . . . . liver cancer!
  • Gallbaldder stores excess bile. . . . Gallstones?
regulation of digestive secretions
Regulation of Digestive Secretions
  • Secretion of digestive juices is promoted by the nervous system and by hormones.
    • Hormones are produced by one set of cells and affect a different set of cells.
      • Gastrin.
      • Gastric inhibitory peptide (GIP).
      • Secretin.
      • Cholecystokinin (CCK).
the large intestine h 2 o salt processor
The Large Intestine : “H2O, salt Processor”
  • Functions:
    • Absorbs water and salts.
    • Prepares and stores nondigestible material until “defecation”.
    • Absorbs vitamins produced from bacterium E. coli.
  • Is ~ 2 ½ in. wide, ~ 5 feet long.
  • Parts:
    • Cecum is blind end of large intestine below entrance from small intestine.
      • Contains the vermiform (“worm-like”) appendix – plays role in immunity.
the large intestine h 2 o salt processor1
The Large Intestine : “H2O, salt Processor”
    • Appendicitis?  peritonitis?
  • Colon.
    • Ascending, transverse, descending, sigmoid.
    • May develop polyps – small growths arising from the epithelial lining.
    • May be benign or malignant.
    • May increase likelihood of colon cancer.
    • Can be removed surgically.
    • Risk reduced by eating a low-fat, high-fiber diet.
the large intestine h 2 o salt processor2
The Large Intestine : “H2O, salt Processor”
    • Rectum.
      • Muscular, last 8 inches.
    • Anus: “defecation” of “feces”.
  • Diarrhea is caused by infection of the lower intestinal tract and nervous stimulation, and results in increased peristalsis – too much water. . . .
    • Dehydration.
  • Constipation can be caused by a lack of H2O and fiber, and leads to dry, hard feces. . . .
    • Hemorrhoids (“piles”).
    • Laxatives!?
disorders of the colon and rectum continued
Disorders of the Colon and Rectum - continued
  • Hemorrhoids (“piles”) ?
  • Diverticulosis ?
  • Irritable Bowel Syndrome (IBS)
  • or spastic colon ?
  • Inflammatory Bowel Disease (IBD) or colitis ?
  • Polyps and cancer ?
health focus1


Swallowing a Camera

digestive enzymes nutrition
Digestive Enzymes / Nutrition
  • Dehydration synthesis – “building”, (+).
  • also called condensation reaction.
  • Hydrolysis – “tearing down”, (-).
  • Prefixes: mono- = one, single / di- = two / poly- = many (> 3).
  • Words for Food Components:
  • peptide = protein (from peptide bond).
  • saccharide = sugar (from latin for sugar).
  • glyceride = lipids (fats, oils, etc.).
digestive enzymes
Digestive Enzymes
  • Digestive enzymes are hydrolytic enzymes that break down substances into nutrient molecules.
    • Glucose and amino acids are absorbed into blood capillaries of the villi.
    • Fatty acids and glycerol reform within epithelial cells and enter lacteals as lipoprotein droplets.
digestive enzymes1
Digestive Enzymes
  • Are proteins.
  • Are specific.
  • Have a preferred pH.
  • Have a preferred temperature.
  • Are found (produced and released) in specific places:
    • Mouth.
    • Stomach.
    • Duodenum (pancreatic juice, epithelial cells of villus).
classes of nutrients
Classes of Nutrients
  • Nutrition?
  • Involves interaction between “food” and the organism.
  • Food is an organic, energy containing substance.
  • Nutrient is a substance found in food that is used by the body to maintain health.
  • Balanced diet is obtained by eating a variety of food from four food groups.
  • Represented by the Food Guide Pyramid, old followed by the new.
food components
Food Components
  • The body requires three major classes of micronutrients to supply energy and optimum cellular metabolism.
    • Carbohydrates.
    • Protein.
    • Fat.
  • In addition, the body requires.
    • Vitamins.
    • Minerals.
  • Human diet has changed substantially with the development of civilization. . . .
food components carbohydrates
Food Components - Carbohydrates
  • Carbohydrates (CHO) are digested to simple sugars, which are, or can be, converted to glucose.
    • Quickest, most readily absorbed source of energy for the body.
    • Complex CHO (breads, cereals) should make up the bulk of the diet, not simple sugars (candy, “sweets”, soft drinks).
    • Simple sugars are labeled “empty calories” because. . ? Glycemic index (GI)
    • Blood glucose is kept at ~0.1% by breakdown of glycogen or conversion of amino acids.
food components proteins
Food Components - Proteins
  • Found in meat, fish, poultry, dairy products, legumes, nuts, cereals.
  • Incorporated into structural proteins in muscles, skin, hair, nails.
  • Foods richest in protein are apt to be richest in fat!
  • Adequate protein formation requires twenty different amino acids, including 8 (adult), 9 (children) essential amino acids.
    • Body is unable to produce essential amino acids.
    • Complete protein contains all essential amino acids.
    • Amino acids are not stored in the body, and thus a daily supply is needed.
food components lipids
Food Components - Lipids
  • Found in butter, oils, high-protein foods.
  • Fats, oils, and cholesterol are all lipids.
  • Why essential to diet?
  • Body cannot make essential fatty acids, i.e. linoleic acid, which must be obtained from diet.
  • Fats have highest energy content / gram, . . .
    • Intake of fat increases weight gain, and increases the risk of cardiovascular disease and cancer (colon, breast, prostate, pancreas).
food components lipids1
Food Components - Lipids
  • Better to get from plant sources rather than from animal sources.
    • Plaque deposits contain saturated fats and cholesterol.
    • Saturated fatty acid (transformed -fatty acids), monounsaturated fatty acid, polyunsaturated fatty acid?
    • Which is best and why?
    • Avoid trans fats, reduce partially hydrogenated ingredients.
    • For optimal cardiovascular health, less than 30% of calories should come from fat and less than 10% from saturated fat.
    • Olestra, “fake fat”, side effects?
food components lipids2
Food Components - Lipids
  • Cholesterol
    • High blood cholesterol levels associated with cardiovascular disease.
    • Low density lipoproteins (LDL) carry cholesterol from the liver to cells.
    • High density lipoproteins (HDL) carry cholesterol from the cells to the liver.
    • LDL is bad, contributes to arterial plaques.
    • HDL is good, protects against clogged arteries.
    • A low saturated fat, low cholesterol diet with soluble fiber reduces blood cholesterol and LDL’s.
    • Exercise can increase HDL’s.
  • The body also requires minerals.
    • Macrominerals (Major) are present in the body at a minimal level of 5 grams each.
      • > 100 mg / day.
      • Calcium, Potassium, Sodium, Magnesium, Phosphorus, Sulfur, Chloride.
    • Microminerals (Trace) are present in the body at levels under 5 grams each.
      • < 20 mg / day.
      • Iodine, Copper, Mangenese, Zinc, Iron, Selenium.
iron calcium and sodium
Iron, Calcium and Sodium
  • Iron – adult females need more per day due to hemoglobin loss during menstruation.
  • Calcium counteracts osteoporosis and generally strengthens bones along with estrogen replacement and exercise.
  • Sodium helps maintain osmotic balance, but too much sodium can intensify hypertension.
health focus2


When Zero Is More Than Nothing

vitamins and antioxidants
Vitamins and Antioxidants
  • Vitamins are organic compounds used by the body for metabolic purposes, but cannot be produced in adequate quantities.
    • Many are coenzymes.
    • Antioxidants are vitamins (A, E, C) that defend the body against free radicals. . . .
      • Molecules that carry an extra electron.
  • If lacking in the diet, various symptoms develop. . . .
health focus3


Searching for the Magic Weight-Loss Bullet

weight loss the healthy way
Weight Loss the Healthy Way
  • Basal metabolic rate (BMR) is best measured 14 hours after the last meal with subject lying down at rest.
  • Is affected by sex, size, shape, weight, age, activity, etc.
  • To lose weight. . . .
  • Decrease calorics (> 2100 Cal/day), increase exercise.
  • Pills? Liquid Diets? Low-carbohydrate Diets? Single-category Diets?
  • Eat variety of foods, more fruits/vegetables, less in saturated fats, be physically active each day.
  • The key is “balance”.
eating disorders
Eating Disorders
  • Obesity.
    • 1/3 adults are obese !
    • Most often defined as body weight 20% or more above ideal weight.
    • Moderate obesity: 41-100% above.
    • Severe obesity: 100% or more above.
  • Also measured by Body Mass Index (BMI) = wt. of person in Kg / square of height in meters.

Most likely caused by a combination of hormonal, metabolic, and social factors.

        • Increases risk of heart disease, type 2 diabetes, cancer.
        • Treatment depends on degree of obesity.
eating disorders1
Eating Disorders
  • Bulimia and anorexia are serious disorders which require competent medical attention.
  • Bulimia Nervosa.
    • Habit of eating to excess and then purging by artificial means.
      • Alters blood composition leading to heart rhythm problems and kidney damage.
  • Anorexia Nervosa.
    • Morbid fear of gaining weight (perceptional).
      • Self-induced starvation.
      • Low blood pressure, irregular heartbeat, constipation, and constant chilliness.
eating disorders2
Eating Disorders
  • Binge-eating disorder ?
  • Condition characterized by episodes of overeating that are not followed by purging.
  • Stress, anxiety, anger, and depression can trigger food binges.
  • Muscle dysmorphia –
  • Individual thinks, perceives, that their body is underdeveloped when it is not.
  • Unlike anorexia nervosa and bulimia, it affects more men than women.
  • Overview of Digestion
  • The First Part of the Digestive Tract
  • The Stomach and Small Intestine
  • Three Accessory Organs and Regulation of Secretions
  • The Large Intestine and Defecation
  • Nutrition and Weight Control (Should reviewCh.2, Molecules of Life, pp. 22-30)