The Digestive System

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The Digestive System
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THE DIGESTIVE SYSTEM

• THE MOUTH
• THE STOMACH
• THE PHARYNX AND ESOPHAGUS
• THE INTESTINES
• ACCESSORY ORGANS

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FUNCTION

• To ingest food, break it down into usable
  molecules, absorb those molecules, and eliminate
  the indigestible material.

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THE MOUTH

• Sensitive to taste and texture
• Makes eating enjoyable
• Teeth chew food into small bits
• Salivary glands add the enzyme salivary amylase
• begins to break down starch (amylose)
• Tongue mixes the food and saliva into a mass
  called a bolus

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PHARYNX AND ESOPHAGUS

• Pharynx accepts the food bolus and transfers it
  to the esophagus
• Shared with respiratory system
• Respiratory system is closed off by the glottis
  and the soft palate
• Esophagus moves the bolus to the stomach
• Peristalsis is a rhythmic contraction of the
  muscles of the esophagus

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THE STOMACH

• Thick-walled organ that stores food and mixes it
  with gastric juice
• A mix of
• Pepsin that breaks down protein
• HCl that breaks down connective tissues
• Mucus that protects the stomach from HCl
• pH of the stomach is 2 (highly acidic) which
  kills many invading organisms
• Muscles churn this mixture into chyme
• Chyme enters the small intestine through a
  sphincter that opens and closes

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THE INTESTINES

• Small Intestines 6 M length, small diameter
• Duodenum - beginning of small intestine
• A duct from the liver and pancreas enters the
  duodenum and and passes bile and pancreatic juice
  to be mixed with the chyme
• Bile - emulsifies fats (become small droplets)
• Pancreatic juice - neutralizes chyme through the
  addition of sodium bicarbonate and adds enzymes

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• Wall of the intestine contain villi
• Fingerlike projections that add to the surface
  area for absorption of nutrient molecules
• Villi have columnar epithelial cells with
  microvilli
• Microvilli give the CELL membrane additional
  surface area for absorption
• Each villus contains blood vessels for transport
  of sugars and amino acids and a lymphatic
  capillary for transport of fats
• Villi are sites for glandular secretions
• Gastrin and Gastrin Inhibitory Peptide control
  the production of gastric juice
• Secretin and cholecystokinin increases output of
  pancreatic juice

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• Large Intestine 1.5 M in length, larger diameter
• absorbs water, salt and some vitamins
• Mostly indigestible materials like fiber, water,
  and bile juices are stored in the rectum until
  defecation through the anus expels the waste.

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ACCESSORY ORGANS

• Pancreas
• Located in abdominal cavity
• Both endocrine and exocrine gland
• In the digestive system it is an exocrine gland
• Produces pancreatic juice
• Sodium bicarbonate (NaHCO3)
• Pancreatic amylase - starch digestion
• Trypsin - digests protein
• Lipase - digests fats

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• Liver
• Large organ in the upper right section of
  abdominal cavity
• Produces bile that emulsifies fats
• Removes and destroys toxic materials in the blood
• Removes and stores iron, and fat soluble vitamins
• Produces plasma proteins from absorbed amino
  acids
• Regulates cholesterol levels in the blood
• Removes excess glucose in the blood and stores it
  as glycogen, adds glucose to the blood when needed

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• Gall Bladder
• Attached to the surface of the liver
• Stores bile until it is needed

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Nutrition
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NUTRIENTS

• Macronutrients supply the energy and building
  blocks needed to synthesize cellular components
• Carbohydrate, Protein and Fats
• Micronutrients are necessary for cellular
  metabolism
• Vitamins and Minerals

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CARBOHYDRATES60 of total calories

• Carbohydrates are digested to simple sugars
• Glucose or sugars that are converted to glucose
• Brain cells require glucose so carbohydrates must
  be included in your diet
• Stored in the liver as glycogen
• Complex carbohydrates are the best
• Starches
• Simple carbohydrates (sugars)
• provide energy and convert to fat easily

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SOURCES OF COMPLEX CARBOHYDRATES

• BREADS
• CEREALS
• RICE
• PASTA
• Also supply the diet with fiber that is required
  for proper functioning of the digestive system

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PROTEINS 10 of total calories

• Digests to amino acids that are carried to the
  cells in the bloodstream
• Used to build structural, hemoglobin, plasma
  proteins, enzymes, and hormones
• Human body requires 20 different amino acids
• Eight essential amino acids cannot be synthesized
  in the body and MUST come from your diet
• Meat, milk and eggs provide complete protein that
  contain all 20 amino acids
• Vegetables and grains provide incomplete protein
  because one of the essential amino acids is
  missing

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ESSENTIAL AMINO ACIDS

• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

• Arginine and Histidine are required during
  childhood because the body cannot supply enough
  during rapid growth

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SOURCES OF PROTEIN

• Meats
• Dairy complete proteins
• Eggs
• Vegetables - incomplete proteins
• (must eat from two or three groups to get
  complete protein)
• Legumes (beans , peas, etc.) relatively high in
  protein
• Grains are good sources
• Nuts and seeds
• Vegetables

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FATS 30 of calories

• Includes lipids and cholesterol
• Cholesterol is carried in the blood by
  lipoproteins
• HDL (high density lipoprotein) carries
  cholesterol to the liver where it is broken down
  to bile salts - GOOD LIPOPROTEIN
• LDL ( low density lipoprotein) carries
  cholesterol from the liver to the cells - BAD
  LIPOPROTEIN
• lower than 30 is better because fat causes
  weight gain, increased risk for cancer and
  cardiovascular disease

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SOURCES OF FATS

• anything that tastes good
• Meats, dairy, eggs
• Butter, margarine, and oils
• Fake Fat - Olestra
• Is a fat that the body does not metabolize
• Tends to remove fat soluble vitamins from the body

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VITAMINS

• Organic molecules that are required in small
  amounts and serve important functions in the body
• - parts of enzymes
• - energy carrier
• - some neutralize free-radicals
• you must eat a variety of food to obtain
  necessary vitamins

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TYPES OF VITAMINS

• Two types according to solubility
• 1. water soluble vitamins - cannot be stored in
  the body
• - B vitamins, niacin, C, panthothenic acid,
  biotin, folic acid
• - only niacin can be made in the body
• 2. fat soluble vitamins are absorbed with fats
  in the small intestine
• - A, D, E, and K
• - stored in adipocytes
• - large amounts of these are toxic
• - only vitamin D can be made in the body

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MINERALS

• Inorganic molecules required in small amounts
• 1. calcium, phosphorous, potassium, sulfur,
  sodium, chloride, magnesium
• 2. trace minerals - very small amounts
• - iron for hemoglobin
• - iodine for thyroid hormones