Digestive System and Nutrition

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Chapter 8

• Digestive System and Nutrition

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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
• Nutrition and Weight Control
  (Should review
  Ch.2, Molecules of Life, pp. 22-30)

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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.

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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.

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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.

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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).

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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.

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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.

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Swallowing
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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)

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HEALTH FOCUS

• Heartburn (GERD)

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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.

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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 !?

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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).

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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 sodium bicarbonate
  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.

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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?

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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 RBCs).
• Detoxifies blood.
• Stores iron, fat-soluble vitamins A, D, E, K
• Maintains blood glucose levels (lt 0.1)
• Produces urea.
• Makes blood proteins (clotting, etc.)
• Helps regulate blood cholesterol level (bile
  salts)

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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?

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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).

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Hormonal Control of Digestive Secretions
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Hepatic Portal Circuit
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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.

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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.

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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!?

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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 ?

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Health Focus

• Swallowing a Camera

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Digestive Enzymes / Nutrition

• Dehydration synthesis building, ().
• also called condensation reaction.
• Hydrolysis tearing down, (-).
• Prefixes mono- one, single / di- two /
  poly- many (gt 3).
• Words for Food Components
• peptide protein (from peptide bond).
• saccharide sugar (from latin for sugar).
• glyceride lipids (fats, oils, etc.).

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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.

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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).

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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.

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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. . . .

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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.

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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.

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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).

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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?
• 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?

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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
  LDLs.
• Exercise can increase HDLs.

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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.
  . . .

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For the fat-soluble vitamins, remember the word
ADEK
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Rickets (bowing of bones) Vitamin D deficiency.
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Dermatitis (Pellagra) of areas exposed to light
due to niacin (Vitamin B3) deficiency.
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• Bleeding of gums (Scurvy) Vitamin C
  deficiency.
• Limeys?

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Minerals

• The body also requires minerals.
• Macrominerals (Major) are present in the body at
  a minimal level of 5 grams each.
• gt 100 mg / day.
• Calcium, Potassium, Sodium, Magnesium,
  Phosphorus, Sulfur, Chloride.
• Microminerals (Trace) are present in the body at
  levels under 5 grams each.
• lt 20 mg / day.
• Iodine, Copper, Mangenese, Zinc, Iron, Selenium.

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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.

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HEALTH FOCUS

• Searching for the Magic Weight-Loss Bullet

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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 (gt 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.

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Eating Disorders

• Obesity.
• 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.

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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.

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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.

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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
• Nutrition and Weight Control
  (Should review
  Ch.2, Molecules of Life, pp. 22-30)

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