THE DIGESTIVE SYSTEM

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THE DIGESTIVE SYSTEM
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• formed by the alimentary canal or
  gastrointestinal (GI) tract accessory organs
  (teeth, tongue, salivary glands, pancreas, liver)

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FUNCTIONS OF THE DIGESTIVE SYSTEM?

• 1. ingestion taking food in
• 2. propulsion via peristalsis (wave-like
  muscular contractions)
• 3. mechanical digestion physically breaking
  food into smaller pieces

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FUNCTIONS OF THE DIGESTIVE SYSTEM?

• 4. chemical digestion breaking food down into
  its building blocks using enzymes
• proteins gtamino acids
• lipids gt fatty acids glycerol
• carbohydrates gt monosaccharides
• nucleic acids gt nucleotides
• 5. absorption of nutrients

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FUNCTIONS OF THE DIGESTIVE SYSTEM?

• 6. defecation to eliminate wastes in the form
  of feces
• PATHWAY OF FOOD
• mouth? pharynx? esophagus? stomach? small
  intestine? large intestine? rectum? anus

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MOUTH? oral cavity

• mechanical digestion biting chewing food
  (mastication)
• chemical digestion breaking starches
  (polysaccharides) into disaccharides using the
  enzyme amylase

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MOUTH? oral cavity

• different teeth do different jobs
• incisors cut / bite
• canines or cuspids tear shred
• molars crush / grind

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MOUTH? oral cavity

• the tongue is made of skeletal muscle it moves
  food around the mouth and it aids in swallowing
  its covered with taste buds
• food is moved through
• the esophagus via peristalsis
• the epiglottis covers the
• opening to the respiratory tract

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MOUTH? oral cavity

• the uvula is a fingerlike projection of the soft
  palate
• the tonsils are part of the bodys defense system

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ESOPHAGUS? gullet

• runs from the pharynx through the diaphragm to
  the stomach
• about 10 inches long, conducts peristalsis to
  move food along

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STOMACH?

• C-shaped, on the left side, about 10 inches long,
  holds 1 gallon or so
• the cardiac sphincter opens, allowing food into
  the stomach
• mechanical digestion continues here, as the
  stomach churns

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STOMACH?

• chemical digestion also continues here, as the
  food is mixed with gastric juices
• pepsin breaks down proteins into peptides
• hydrochloric acid (HCl) lowers the pH to 2 where
  pepsin works best

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STOMACH?

• the stomach lining is protected by a mucus layer
• food remains here 2-4 hours reaches the
  consistency of tomato soup (now called chyme)
• the pyloric sphincter opens, allowing chyme into
  the small intestine

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SMALL INTESTINE?
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SMALL INTESTINE?

• a long (6 m) but narrow (2.5 cm) tube where
  digestion is completed
• 1st section duodenum, 2nd jejunum, 3rd ileum

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SMALL INTESTINE?

• mechanical digestion continues via smooth muscle
  contractions
• chemical digestion also continues with the help
  of enzymes from the pancreas, liver gall bladder

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• pancreas
• a soft, flattened gland
• secretes digestive enzymes and hormones
• neutralizes the acidic chyme as it leaves the
  stomach

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SMALL INTESTINE?

• uses pancreatic amylase to turn starch into
  disaccharides
• uses trypsin to turn proteins into peptides
• uses pancreatic lipase to turn fats into fatty
  acids glycerol
• uses nucleases to turn nucleic acids into
  nucleotides

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SMALL INTESTINE?

• liver
• produces bile to emulsify fats (mechanical
  digestion)
• bile travels from the liver to the hepatic duct
  to the gall bladder to the bile duct into the
  duodenum
• high cholesterol can cause gall stones which
  consist of crystallized bile salts. They can
  block the bile duct

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• gall bladder
• stores bile produced by the liver
• may be surgically removed, but that decreases a
  persons ability to digest fats efficiently

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SMALL INTESTINE?

• the small intestine makes several enzymes to
  chemically digest food
• maltase turns maltose into a monosaccharide
• sucrase turns sucrose into a monosaccharide

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SMALL INTESTINE?

• lactase turns lactose into a monosaccharide
• peptidase turns peptides into amino acids
• nuclease turns nucleotides into sugar and
  nitrogen bases

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SMALL INTESTINE?

• liquid food stays in the small intestine 3-5
  hours is moved along via peristalsis toward the
  large intestine
• passes through the ileocecal valve into the large
  intestine

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SMALL INTESTINE?

• food molecules are absorbed into the cells of
  villi (fingerlike projections) and enter into the
  bloodstream
• villi covered with microvilli greatly increase
  the surface area of the small intestine to aid
  absorption of food

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LARGE INTESTINE? colon

• a short (1.5 m) but wide (6.5 cm) tube that
  receives indigestible material from the small
  intestine
• the primary site of water and salt absorption
• too much water in feces diarrhea, not enough
  constipation

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LARGE INTESTINE? colon

• anaerobic bacteria synthesize vitamins B and K
• major divisions cecum, appendix, colon, rectum,
  anal canal
• the appendix hangs from the 1st section on the
  right side and may become inflamed
  appendicitis

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LARGE INTESTINE? colon

• the colons main regions are the ascending colon,
  the transverse colon, the descending colon, and
  the sigmoid colon

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LARGE INTESTINE? colon

• after 18-24 hours, the indigestible material
  reaches the rectum
• now called feces, it is eliminated through the
  anus via the anal sphincter

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LARGE INTESTINE? colon
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