chap 5 (bio)

• Nutrition


  The process by which organisms obtain food and energy for growth, and maintenance of the body
• Nutrition consists of


  • Feeding or ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Egestion
• Feeding or ingestion


  Food is taken into the body
• Digestion


  Large food molecules are broken into smaller molecules that can be absorbed into the body
• Absorption


  Nutrients move from the small intestine into the bloodstream
• Assimilation


  Nutrients are used by cells to provide energy or to make new cytoplasm for growth
• Egestion


  Undigested matter is removed from the body
• Human digestive system


  • Mouth and buccal cavity
  • Pharynx
  • Oesophagus
  • Stomach
• Teeth


  Break large pieces of food into smaller pieces
• Chewing


  Increases the surface area of food so enzymes can act on it more efficiently
• Salivary glands


  Secrete saliva into the mouth, mixing food with saliva and moving food to the back of the mouth during swallowing
• Pharynx


  Connects the buccal cavity to the oesophagus, larynx and trachea
• Epiglottis


  Closes over the glottis to prevent food from reaching the larynx and trachea when swallowing (prevents choking)
• Oesophagus


  A narrow, muscular tube that passes through the thorax and diaphragm, connecting the mouth and stomach
• Peristalsis


  The rhythmic, wave-like contractions in the wall of the alimentary canal that enable food to be mixed with digestive juices and help to push or propel the food along the gut
• Circular muscles


  -When they contract, they constrict the lumen of the gut

  -Inner wall of the gut
• Longitudinal muscles


  -When they contract, they shorten and widen the lumen of the gut

  -Outer side of the gut wall
• When the circular muscles contract, the longitudinal muscles relax, making the gut narrower and longer, squeezing/pushing the food forward
• When the longitudinal muscles contract, the circular muscles relax, making the gut wider and shorter
• Stomach


  Lies beneath the diaphragm, to the left side of the abdomen, and is partly covered by the liver. Has numerous pits and gastric glands found in the stomach lining that secrete gastric juice that plays an important part in digestion
• Small intestine


  • U-shaped duodenum
  • Much-coiled ileum
  • Carries out most of the digestive process
  • Contains glands in the wall lining that secrete digestive enzymes
  • Absorbs water and nutrients from food
• Large intestine


  • Shorter and broader than small intestine
  • Consists of colon, rectum and anus
  • Absorbs remaining water and mineral salts from undigested food
  • Temporarily stores faeces in the rectum
• Liver


  • Largest gland in the body, below the diaphragm
  • Portal vein, hepatic vein and hepatic artery are attached to the lower surface
  • Liver cells produce and secrete bile which contains bile salts that aid in emulsion of fats
• Gall bladder


  • Attached to the liver
  • Bile (produced by the liver) is stored temporarily
  • When gall bladder contracts, bile flows via the bile duct into the duodenum
• Pancreas


  • Connected to the duodenum by the pancreatic duct
  • Produces pancreatic juices which contains digestive enzymes such as amylase, lipase, protease
  • Secretes hormones insulin and glucagon that helps regulate the blood sugar concentration in the body
• Digestion


  1. Physical digestion

  2. Chemical digestion
• Physical digestion


  Mechanical break-up of food into small pieces (e.g. chewing, churning, emulsification)
• Chemical digestion


  Breaking down of large food molecules into small, soluble molecules (e.g. proteins, starch, fats)
• Physical digestion increases surface area to volume ratio of ingested food so that digestive enzymes can act on the food particles more effectively
• Carbohydrate digestion


  1. Carbohydrates are digested by carbohydrases, such as amylase and maltase

  2. Starch is broken down into maltose by amylase in mouth and small intestine

  3. Maltose is broken down into glucose by maltase in small intestine
• Protein digestion


  1. Proteins are digested by proteases in the stomach

  2. Stomach protease digests proteins for polypeptides

  3. Undigested proteins enter the small intestine and are digested by intestinal protease to polypeptides which are further digested to amino acids by intestinal protease
• Digestion of fats


  1. Bile is released into the duodenum

  2. Bile salts emulsify fats by lowering the surface tension

  3. Fats break into tiny fat droplets, increasing the surface area to volume ratio for enzyme action

  4. Emulsified fats are digested by lipases into fatty acids and glycerol in the small intestine
• Substrate


  • Starch
  • Protein
  • Amylose
  • Fats
• Enzyme


  • Amylase
  • Protease
  • Maltase
  • Lipase
• Product


  • Maltose
  • Glucose
  • Amino acids
  • Fatty acids and glycerol
• Absorption


  1. Digested food substances are absorbed into the blood cells

  2. Simple sugars, fatty acids, and amino acids are absorbed

  3. Water and mineral salts are absorbed
• Factors affecting rate of absorption in small intestine

  • Surface area to volume ratio
  • Thickness of separating membrane
  • Concentration gradient
• Adaptations for absorption in small intestine

  • Inner surface has numerous finger-like projections called villi to increase surface area
  • Epithelium of villi is one cell thick to provide a short diffusion distance
  • Cells of epithelium have many microvilli to further increase surface area
  • Each villus has many blood capillaries to transport absorbed nutrients
  • Each villus contains a lacteal to transport absorbed fats
  • Epithelial cells contain many mitochondria to provide energy for active transport
• How absorption takes place

  1. Glucose and amino acids are absorbed by diffusion into blood capillaries

  2. Glucose and amino acids are also absorbed by active transport when concentration is lower in lumen than blood

  3. Glycerol and fatty acids diffuse into epithelium to combine and enter lacteals
• Assimilation


  Conversion of digested food substances into new protoplasm or to provide energy