Digestive System

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Chapter 7

• Digestive System
• Attempt the pattern puzzles of digestion with a
  neighbor

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Points to Ponder

• What are the digestive system structures and
  their functions?
• Where does carbohydrate, protein and fat
  digestion and absorption occur?
• What are proteins, lipids, carbohydrates,
  minerals and vitamins needed for?
• What are the 3 accessory organs of digestion?
• What is obesity and why is it a problem?
• What is LDL and HDL?
• What are the components of a healthy diet?

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What are the 4 major layers that make up the wall
of the GI tract?
8.1 Overview of digestion

• Mucosa innermost epithelium that produces mucus
  that protect the lining and also produce
  digestive enzymes
• Submucosa 2nd layer of loose connective tissue
  that contains blood vessels, lymphatic vessels
  and nerves
• Muscularis 3rd layer made of 2 layers of smooth
  muscle that move food along the GI tract
• Serosa outer epithelium that is part of the
  peritoneum

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Visualizing the layers of the GI tract
8.1 Overview of digestion
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The mouth
8.2 First part of the digestive tract

• 3 pairs of salivary glands secrete salivary
  amylase that begins carbohydrate digestion
• Tonsils at the back of the mouth and other
  lymphatic tissues are important in fighting
  disease
• Contains teeth that begin the mechanical
  breakdown of food
• The tongue is covered in taste buds and also
  assists in the mechanical breakdown and movement
  of food
• The tongue forms a bolus (mass of chewed food)
  and moves it toward the pharynx

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The pharynx and esophagus
8.2 First part of the digestive tract

• Pharynx is a cavity between the mouth and
  esophagus that serves as a passageway for food
  (and air)
• Esophagus is a long, muscular tube that carries
  food to the stomach

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How do we swallow food?
8.2 First part of the digestive tract
8
Health focus Heartburn
8.2 First part of the digestive tract

• Occurs when acids from the stomach pass into the
  esophagus (acid reflux)
• Burning sensation in the esophagus
• Chronic heartburn is called gastroesophageal
  reflux disease (GERD)
• Tips for decreasing heartburn
• Avoid high fat meals
• Dont overeat
• Eat several small meals
• Exercise

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The stomach
8.3 The stomach and small intestine

• Mechanical digestion continues
• Gastric juice contains pepsin, an enzyme that
  breaks down proteins, and HCl and mucus
• HCl gives the stomach a pH of 2 which activates
  pepsin and helps kill bacteria found in food
• A bacterium, Helicobacter pylori, lives in the
  mucus and can cause gastric ulcers
• The stomach empties chyme into the small
  intestine after 2-6 hrs.

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The small intestine
8.3 The stomach and small intestine

• Averages 6m (18 ft) in length
• Mechanical digestion continues
• Enzymes secreted by the pancreas into the small
  intestine digest carbohydrates, proteins and fats
• Bile is secreted by the gallbladder into the
  small intestine to emulsify fats
• Digested food is absorbed through large surface
  area created by numerous villi (finger-like
  projections) and microvilli

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How are nutrients digested and transported out of
the small intestine?
8.3 The stomach and small intestine
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The three accessory organs
8.4 Three accessory organs and regulation of
secretions

• Pancreas
• Liver
• Gallbladder

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The pancreas
8.4 Three accessory organs and regulation of
secretions

• Functions of the pancreas
• 1. Secretes enzymes into the small intestine
• Trypsin
• Lipase
• Pancreatic amylase
• 2. Secretes bicarbonate into the small intestine

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The liver and gallbladder
8.4 Three accessory organs and regulation of
secretions

• Filters blood from the GI tract thus acting to
  remove poisons and detoxify the blood
• Makes bile that is then stored in the gallbladder
  to be secreted into the small intestine to
  emulsify fats

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The large intestineReview your pattern puzzles
8.5 The large intestine and defecation

• Functions to
• Absorb water to prevent dehydration
• Absorbs vitamins (B complex and K) produced by
  intestinal bacteria
• Forms and rids the body of feces

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Disorders of the colon and rectum
8.5 The large intestine and defecation

• Diverticulosis occurrence of pouches of mucosa
  from weak spots in the muscularis layer that can
  become infected
• Irritable bowel syndrome (IBS) muscularis layer
  contracts with power but without its normal
  coordination that is characterized by chronic
  diarrhea and abdominal pain
• Inflammatory bowel disease/colitis (IBD) a
  group of inflammatory disorders such as
  ulcerative colitis or Crohns disease
• Polyps and cancer small growths found in the
  epithelial lining that can be benign or cancerous
  

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Carbohydrates
8.6 Nutrition and weight control

• Digested into glucose
• Pancreas secretes insulin
• Insulin binds to receptors on cells
• Glucose can now enter cells to make ATP
• What if your insulin receptors become less
  sensitive?
• Cells scream at pancreas to release more insulin
  
• High insulin leads to higher blood pressure, high
  cholesterol and fat deposition
• Increased risk of type 2 diabetes, heart disease
  and liver problems

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What changes can you make today?
8.6 Nutrition and weight control

• Exercise-helps insulin attach to receptors
• Get lean-Fat cells sabotage muscle cells
• Eat original, whole grain vs. refined, processed
• Insulin receptors work best if you keep your
  blood sugar steady
• Eat fiber
• Slows down sugar absorption process
• Friend to your digestive tract
• Aim for 25-35 grams per day

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Proteins
8.6 Nutrition and weight control

• Made of amino acids
• 9 essential amino acids can not be made by the
  body
• 11 nonessential amino acids can be made by the
  body if the building blocks are there
• Come from plant and animal sources
• Animal sources and soy provide all 9 essential
  amino acids
• Empties stomach slowly and leaves you feeling
  full longer
• What if you eat more protein that what you need?
• Deposited as body fat

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What changes can you make today?
8.6 Nutrition and weight control

• Eat 0.8grams of protein per kg of body weight.
• Choose wisely
• Fish, shellfish, skinless (white meat) poultry
• Lean beef (gt85) with visible fat removed
• Beans, lentils, tofu, peanut butter, seeds
• Grill, bake, broil, roast, poach, stir fry

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Lipids
8.6 Nutrition and weight control

• Fats help to maintain healthy skin, hairand
  transports vitamins (ADEK)
• Saturated vs. Unsaturated
• Trans-fatty acids
• reduce the ability of cells to clear cholesterol
  from the bloodstream
• High density lipoproteins (HDL) cholesterol
• carries cholesterol to the liver where it is
  converted to bile salts
• Low density lipoproteins (LDL) cholesterol
• Deposits within walls of arteries and increases
  risk of heart attacks and stroke

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What changes can you make today?
8.6 Nutrition and weight control

• Choose unsaturated fats
• Found in most plants, nuts, seeds and fish
• Choose polys and monos
• Include omega fatty acids
• Dont smokeit will increase your LDLs and lower
  your HDLs

• Limit saturated fats
• Found in animals and processed snack food
• Avoid trans fats
• Ingredient list will say hydrogenated
• Limit cholesterol to 300 mg per day