12.0 Nutrition and Digestion

• Nutrition


  All animals require matter and energy for: Metabolism, Homeostasis, Growth, Reproduction
• Organic molecules


  • Carbohydrates and fats
  • Provide energy
  • Building blocks for complex biological molecules
• Important classes of organic macromolecules


  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
• Carbohydrate

  Biological molecule consisting of: Simple single monomer sugars (monosaccharides), Two-monomer sugars (disaccharides), and other multi-unit sugars (polysaccharides)
• Monosaccharide


  Smallest kind of sugar molecule, a simple sugar, a single unit sugar, building blocks of more complex sugar
• Monosaccharides


  • Characterized by several hydroxyl groups (-OH) and a carbonyl group (>C=O)
  • In aqueous solutions, some monosaccharides form rings
  • Monosaccharides are the main fuel that cells use for cellular work
• Disaccharide


  Consists of two monosaccharides linked via a dehydration reaction
• Polysaccharides


  Polymers of monosaccharides, long chains of sugar units
• Polysaccharides


  • Starch: long chain of glucoses, found in plants
  • Glycogen: long chain of glucoses with branches, found in animals
  • Cellulose: long chain of glucoses with different linkage, found in cell walls of plants
• Cellulose


  • The most abundant organic compound on Earth
  • Forms cable-like fibrils in the tough walls that enclose plants
  • Major component of wood
  • Also known as dietary fiber
• Lipids


  Organic compound consisting mainly of carbon and hydrogen atoms linked by non polar, covalent bonds and therefore is mostly hydrophobic and insoluble in water
• Fats


  • A type of lipid molecule, dietary fat is composed mostly of triglycerides
  • Triglycerides are made from glycerol (an alcohol) + three fatty acids
• Fats


  • Functions: Energy storage, Cushioning, Insulation
• Unsaturated/Saturated fats

  • Unsaturated: fewer than the maximum number of hydrogens bonded to the carbon resulting in a double bond (which creates a "bend" in the fatty acid chain)
  • Saturated: all carbons of the fatty acid backbone are bonded to the maximum number of hydrogens (no "bend")
• Unsaturated/Saturated fats


  • Unsaturated triglycerides tend to be liquid at room temp ("oils"), most plant and some fish triglycerides are unsaturated
  • Saturated triglycerides tend to be solid at room temperature, most animal triglycerides are saturated
• The bend in unsaturated fats

  • Unsaturated fats (bent shape) cannot stack easily, less likely to form solids
  • Saturated fats can easily stack, tend to be solid at room temperature
• Monounsaturated fats


  Have a single double bond in their fatty acids
• Polyunsaturated fats


  Have two or more double bonds in their fatty acids
• Unsaturated fats

  • Double bonds are rigid, introduce a kink in the molecule
  • Unsaturated fats have a lower melting point than saturated fats
• Oils


  Most unsaturated fats are liquid at room temperature, so we call them oils
• Plant fats tend to be unsaturated (therefore "oils"), fats from animals like cattle tend to be saturated
• Diets rich in saturated fats contribute to atherosclerosis (lipid containing deposits build up in blood vessel walls, reducing blood flow and causing heart attacks/strokes)
• Essential nutrients


  Substances animals require in their diets that they cannot make for themselves, including essential amino acids, essential fatty acids, essential minerals, and vitamins
• Human nutritional requirements (adults)

  • 8 essential amino acids
  • 13 vitamins
  • Water-soluble vitamins
  • Fat-soluble vitamins
  • A large number of essential minerals
  • Macronutrients
  • Micronutrients
  • Trace elements
• Vitamins


  Organic molecules required in small quantities that an animal cannot synthesize for itself
• Vitamins


  • Water soluble vitamins - often precursors of coenzymes
  • Fat soluble vitamins - variety of special roles
• Minerals


  Ions, important for excitability of neurons, cardiac muscle contraction, structural material, and as parts of other molecules
• Animal digestion


  • Food particles and molecules are pushed through the digestive tube by muscular contractions of its wall
  • Storage of food at various locations in the tube allows animals to digest food while engaged in other activities
• 4 major levels of the gut


  • Mouth, pharynx, and esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Sphincters


  Rings of smooth muscle that form valves between major regions of the digestive tract
• Examples of sphincters


  • Lower esophageal sphincter: between esophagus and stomach
  • Pyloric sphincter: between stomach and small intestine
• 4 major layers of the vertebrate gut

  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa
• Mucosa layer


  • Lines inside of gut
  • Epithelial cells: absorb nutrients, seal off digestive contents from body fluids
  • Glandular cells: secrete enzymes, mucus, pH regulation
• Submucosa layer


  • Elastic connective tissue, neuron network, blood and lymph vessels
  • Neural network: local control of digestive activity
• Muscularis layer


  • Formed by circular layer (constricts gut diameter) and longitudinal layer (shortens and widens gut): push contents through gut (peristalsis)
  • Oblique layer (stomach only)
• Serosa layer


  • Outermost gut layer, made of connective tissue that is continuous with mesentery (tissue that suspends digestive organs in the abdomen)
  • Secretes a lubricating fluid to reduce friction between digestive organs and other organs
• Peristalsis


  Coordinated contractions of circular and smooth muscles produce peristaltic waves that move digestive contents from mouth to anus
• Proper nutrition is essential for optimal function. Nutrients are obtained from food via the digestive process, which is highly organized and tightly regulated.