CH5 Nutrition in Humans

• Nutrients


  Substances obtained from food that are required for growth, repair, and maintenance of the body
• Digestion, absorption and assimilation

  Processes by which nutrients are released from food and used by the body
• Alimentary canal


  • Designed to carry out digestion, absorption and assimilation efficiently
• Peristalsis


  Rhythmic wave-like contractions of the circular and longitudinal muscles of the alimentary canal to mix and propel contents
• Circular and longitudinal muscles in alimentary canal

  • Work antagonistically to control the lumen of the alimentary canal
• Physical digestion


  Mechanical breakdown of large pieces of food into smaller pieces to increase surface area to volume ratio
• Chemical digestion


  Enzymatic breakdown of large and complex nutrient molecules to smaller, simpler molecules that can be absorbed
• Hydrochloric acid in gastric juice


  Destroys microorganisms, activates pepsinogen, provides acidic environment for pepsin
• Digestive processes


  • Physical digestion
  • Chemical digestion

  
• Parts of the digestive system


  • mouth
  • oesophagus
  • liver
  • small intestine
  • duodenum
  • jejunum
  • ileum
  • large intestine
  • rectum
  • anus
  • salivary gland
  • gall bladder
  • pancreas
  • stomach
• Ingestion


  Intake of food into the alimentary canal through the mouth
• Peristalsis


  Occurs throughout alimentary canal from opening of oesophagus to anus
• Effects of circular and longitudinal muscle contractions


  • Becomes narrower to push food forward
  • Becomes wider to allow food to enter
• Digestive processes in different parts of the alimentary canal

  • Buccal cavity: Chewing/mastication to cut, grind, crush large pieces of food into smaller pieces
  • Stomach: Churning to crush and liquefy smaller pieces of food into chyme
  • Small intestine (duodenum): Emulsification of lipids by bile, enzymatic digestion of carbohydrates, proteins, lipids

  
• Digestive enzymes


  • Salivary amylase
  • Pepsin
  • Sucrase
  • Maltase
  • Erepsin
  • Lactase
  • Intestinal lipase
  • Trypsin
  • Pancreatic amylase
  • Pancreatic lipase
• Absorption


  Intake of digested nutrient molecules into body cells by diffusion and active transport
• Nutrients absorbed


  • Fatty acids and glycerol
  • Glucose, fructose, galactose, amino acids
• Absorption pathways


  1. Fatty acids and glycerol: Intestinal lumen -> Intestinal epithelial cells -> Lacteal -> Subclavian vein -> Blood stream

  2. Glucose, fructose, galactose, amino acids: Intestinal lumen -> Intestinal epithelial cells -> Blood capillaries -> Hepatic portal vein -> Liver
• Most water and mineral salts are absorbed in the small intestine, remaining water and mineral salts will be absorbed in the large intestine
• Hepatic portal vein transports nutrient-rich blood from the small intestine to the liver
• Adaptations of small intestine for absorption

  • Highly folded inner wall
  • Finger-like projections called villi
  • Microvilli on epithelial cells
  • One-cell thick epithelium
  • Villi richly supplied with blood capillaries
  • Epithelial cells have numerous mitochondria

  
• Egestion


  Expulsion of undigested material and water as faeces through the anus
• Assimilation


  Process of using absorbed nutrient molecules to produce new protoplasm or release energy
• Roles of the liver


  • Detoxification
  • Amino acid metabolism
  • Regulation of blood glucose levels
  • Fat digestion
  • Breakdown of hormones
• Detoxification


  Enzymatic conversion of harmful substances into less harmful substances
• Deamination


  Process of converting excess amino acids into urea for excretion
• Regulation of blood glucose levels


  Liver cells increase glucose uptake and convert excess glucose to glycogen when blood glucose is high, and convert glycogen to glucose and synthesise glucose when blood glucose is low
• Bile


  Produced by the liver, stored in the gall bladder, released into the duodenum to emulsify fats
• Breakdown of hormones


  Liver breaks down hormones after they have exerted their effects to prevent excessive stimulation
• Short-term effects of alcohol


  • Slurred speech
  • Blurred vision
  • Unsteady gait
  • Increased reaction time
  • Reduced self-control
• Long-term effects of alcohol

  • Gastric ulcers leading to stomach cancer
  • Fatty liver leading to liver cirrhosis
  • Brain damage
• Social implications of alcohol consumption


  • Work absenteeism
  • Work accidents
  • Increased expenditure on alcohol
  • Increased domestic violence
  • Sexual adventuresomeness