Nutrition and the Digestive System

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CHAPTER 29

• Nutrition and the Digestive System

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Digestive System

• Your cells obtain the energy they need from
  cellular respiration.
• Molecules used in this process, ingested as
  food, must first be broken down into usable
  molecules by the digestive system.
• Each of the three types of large food molecules -
  starch, fat, protein - presents a different
  digestive challenge.

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Digestive System

• There are two types of digestion
• mechanical - breaks large pieces into smaller
  pieces of the same type
• chemical - changes food from one type of molecule
  to another

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Digestion 4 Stage Processmouth to anus
alimentary canal
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The Digestive System

• Includes mouth, pharynx, esophagus, stomach,
  sm/lg intestines.
• Accessory structures include salivary glands,
  liver, pancreas, gall bladder.

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Gastrointestinal Tract

• Mouth
• Mechanical digestion by teeth and tongue
• Chemical digestion by saliva (amylase) which
  breaks down starches

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Gastrointestinal Tract

• Esophagus
• Food enters the esophagus through control of the
  epiglottis
• Muscle contractions in the esophagus move food
  down to the stomach - peristalsis
• No additional digestion

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Gastrointestinal Tract

• Stomach
• Muscular organ
• Muscle contractions carry out mechanical
  digestion
• Gastric pits release
• mucus (to protect lining)
• hydrochloric acid (to unfold proteins chemical
  digestion)
• digestive enzymes (pepsin) to break down proteins
• An ulcer results when the mucous coating breaks
  down and the acid burns the stomach lining

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Gastrointestinal Tract

• Stomach
• Both openings to the stomach are controlled by
  sphincter muscles
• Prevent back flow and regulate flow into small
  intestine
• Material leaving stomach (partially digested
  food,
• and secretions) is called chyme

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Gastrointestinal Tract

• Small Intestine - top
• Complete chemical digestion and breakdown of food
  by first section
• Helped by secretions of the pancreas and liver in
  top portion of small intestine.
• Secretes 4 digestive enzymes to complete the
  digestion of disaccharides, polypeptide chains
  and fats. (Fig. 38-12)

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Gastrointestinal Tract

• Liver
• Secretes bile which emulsifies fats helps their
  breakdown
• Gallbladder stores and concentrates bile

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Gastrointestinal Tract

• Pancreas
• Secretes three digestive enzymes (chemical
  digestion) into small intestine to breakdown
  fats, proteins and polysaccharides
• Neutralizes the acidic chyme

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Gastrointestinal Tract

• Small Intestine -bottom
• Absorption of raw materials from digestion into
  the blood
• Huge surface area of small intestine (aids
  absorption) provided by villi
• takes place in lower part of small intestine

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Gastrointestinal Tract

• Large intestine (colon)
• Absorption of water, minerals and vitamins
• Undigested material, feces, leaves body via the
  rectum through the anus.
• About 9L of material passes through digestive
  system daily (about 98 is kept!).

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Diet and Nutrients

• You obtain energy and raw materials from the
  foods you eat.
• This energy is stored in the chemical bonds of
  the food you must break these chemical bonds to
  release the energy and convert it to ATP.
• The raw materials you obtain from food are used
  by your body to make other molecules needed by
  your body - ex. calcium is used to make bone.

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Nutrients (food groups)

• Carbohydrates - major energy source
• average 4 C per gram
• cannot be stored by body ? quick energy
• Proteins - used as building materials
• enzymes, hormones, muscles
• also average 4 C per gram
• only used for energy as a last resort
• amino acids (20) - needed to make protein
• 12 can be made by body nonessential
• 8 cannot be made essential
• complete protein contains all 8 (animal protein)

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Nutrients (food groups)

• Fats - stores energy (mainly)
• used also for cell membrane structure,
  insulation, cushioning
• average 9 C per gram
• Vitamins - for normal growth and activity
• organic substances
• needed in very small amounts
• SEE Fig. 29.11
• Water soluble B,C
• Fat soluble A, D, E, K
• Overdose is as bad as deficiency especially fat
  soluble vitamins!!!

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Nutrients (food groups)

• Minerals - for normal metabolism
• inorganic substances like Ca, Fe, Na
• some needed in extremely small amounts trace
  elements ex. I, Zn, Mg
• Minerals see figure 29.12

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Actual Figures for U.S.