Digestive System

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Digestive System

• Overview
• Motility and Mechanical Processing
• Secretion Digestion
• Absorption
• Elimination
• Hormones
• Vitamins Minerals

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Overview

• The whole goal of digestion is to produce
  monomers (i.e. glucose) that can be used in
  cellular respiration.
• Gastrointestinal (GI) tract is a hollow tube with
  accessory organs.
• Lumen inside of the tube. It is still
  considered outside of the body.

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Overview

• 5 basic tasks
• Mechanical processing and motility
• Secretion
• Digestion
• Absorption
• Elimination

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Overview

• 5 accessory glands
• Wall of the GI tract
• Salivary Glands
• Liver
• Gall Bladder
• Pancreas

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Overview

• 4 layers of the digestive tract
• Mucosa
• Submucosa
• Smooth muscle
• Serosa
• Sphincters control rate of flow and prevent
  backflow.

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Motility and Mechanical Processing

• Motility (mvmt)
• Peristalsis wavelike contractions that move
  food
• Segmentation slower mixing in the small
  intestine that allows for increased absorption

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Motility and Mechanical Processing

• The breakdown of food into smaller pieces by
  mashing and mixing.
• 2 main locations
• Mouth
• 32 teeth and tongue form a bolus
• Swallowing is both voluntary and involuntary
• Stomach
• Mixes food with chemicals ultimately making chyme.

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Secretion and Digestion

• Each organic macromolecule is broken down by
  different enzymes at different locations in the
  digestive system.
• Often many enzymes are involved in the breakdown
  of one molecule.
• These enzymes operate within a narrow pH range.

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Secretion and Digestion

• Carbohydrate Digestion
• Starts in the mouth when salivary amylase,
  produced by the salivary glands, breaks down
  polysaccharides into oligosaccharides and
  disaccharides.
• Then in the sm intestine pancreatic amylase,
  produced by the pancreas, breaks down
  polysaccharides into disaccharides and
  monosaccharides
• Finally disaccharidases from the intestinal
  lining finish the breakdown into monosaccharides.
  

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Secretion and Digestion

• Protein Digestion
• Starts in the stomach with pepsin HCl being
  produced by the stomach lining. This breaks the
  proteins into protein fragments.
• Trypsin and chymotrypsin are produced by the
  pancreas and continue the breakdown of proteins
  into fragments in the sm intestine.
• Also produced by the pancreas, carboxypeptidase
  also works in the sm intestine but it breaks
  proteins further into amino acids.
• Aminopeptidase, although produced by the
  intestinal lining plays the same role as
  carboxypeptidase.

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Secretion and Digestion

• Fat (Lipid) Digestion
• Digestion of fat does not begin until the sm
  intestine where the liver is pumping in bile.
  Bile can be stored in the gall bladder when not
  in use and it emulsifies fat so that it does not
  glob up.
• Lipase is a pancreatic enzyme that is released
  into the sm intestine that finishes the breakdown
  of fats into fatty acids and glycerol molecules.

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Secretion and Digestion

• Nucleic Acid Digestion
• Begins in the sm intestine where pancreatic
  nucleases and intestinal nucleases break the DNA
  RNA into nucleotides and ultimately into the
  bases and monosaccharides that make them up.

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Absorption

• Almost all absorption occurs in the sm intestine.
• Villi
• Microvilli
• Substances are absorbed by active transport,
  osmosis, and diffusion.

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Elimination

• Large intestine (aka colon) absorbs essential
  salts
• and remaining water
• Cecum (including the appendix)
• 4 parts
• Feces undigested/ unabsorbed food, water, and
  bacteria
• Rectum

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Hormones

• Many hormones dictate when and how food is
  digested.
• Ex) gastrin increases HCl production when aa.s
  are detected in the stomach.
• Ex) cholecystokinin (CCK) increases pancreas
  secretions and gall bladder contraction.

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Hormones

• Ex) secretin causes increased bicarbonate
  production
• Ex) glucose insulinotropic peptide (GIP) triggers
  release of insulin by the pancreas.
• View 41Bin Campbell simulation

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Vitamins Minerals

• Vitamins organic substances essential for
  growth and survival.
• Ex) vit-D bone growth enhances Ca absorption
• Ex) vit-C antioxidant collagen synthesis etc.
• Minerals inorganic substances also essential
  for growth and survival
• Ex) Ca bone formation neural and muscle action
• Ex) Fe hemoglobin ETC
• Ex) K Na muscle and neural function
• Shortages or excesses of vitamins and minerals
  can have adverse effects.