Nutrition in Humans

• Nutrition

  The process by which organisms obtain food and energy for growth, repair and maintenance of the body
• Processes of nutrition in humans

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


  Taking in food into the body
• Digestion


  Breaking down large, insoluble food molecules into smaller, soluble molecules for absorption into the body cells
• Absorption


  Nutrients moving into the bloodstream from the small intestine
• Assimilation


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

  Removal of undigested food
• The main function of the digestive system is to break down large and complex food substances into smaller and simple food substances
• Types of digestion

  • Physical
  • Chemical
• Physical digestion

  Mechanical breakdown of large pieces of food into smaller pieces, identities of food substances remain unchanged
• Chemical digestion

  Breaking down large and complex food substances into smaller, soluble simple substances, identities of food substances change
• Human digestive system

  • Long tube called the gut or alimentary canal with associated organs such as liver, gallbladder and pancreas
  • Contraction and relaxation of muscles
  • Mucus along the gut acts as a lubricant
  • Digestion takes place outside living cells within the gut
• Mouth and buccal cavity


  1. Food received into the human body

  2. Ingestion - act or process of taking food and other substances into the animal

  3. Salivary glands produce saliva with salivary amylase and mucus

  4. Tongue aids mixing food and moves it to the back of the mouth during swallowing

  5. Physical digestion by action of teeth

  6. Chemical digestion by salivary amylase

  7. Saliva provides neutral pH for amylase

  8. Tongue rolls food into boli

  9. Food travels to oesophagus via pharynx
• Physical digestion in mouth

  Food chewed to cut and grind into smaller pieces, increasing surface area-to-volume ratio
• Chemical digestion in mouth

  Starch digested into maltose by salivary amylase
• Pharynx

  Connects buccal cavity to oesophagus and larynx
• Oesophagus

  1. Narrow, muscular tube leading to stomach

  2. Muscles contract and relax to push food along
• Stomach


  1. Acts as food storage

  2. Protein digestion to form chyme

  3. Strong muscular walls and peristalsis churn food

  4. Gastric glands secrete gastric juice with HCl, mucus, pepsin

  5. HCl provides acidic environment, kills microbes, stops salivary amylase

  6. Mucus protects stomach wall

  7. Cardiac and pyloric sphincters prevent uncontrolled exit of food

  8. Food remains 3-4 hours, then chyme passes to duodenum
• Physical digestion in stomach

  Churning action breaks food into smaller pieces, increases surface area
• Chemical digestion in stomach

  Protease digests proteins into polypeptides
• Small intestine


  1. Duodenum where most digestion occurs, ileum mainly for absorption

  2. Pancreatic juice, intestinal juice, and bile secreted

  3. Pancreatic juice contains amylase, lipase, protease

  4. Intestinal juice contains maltase, protease, lipase

  5. Bile emulsifies fats

  6. Enzymes complete digestion of food into simpler forms for absorption
• Physical digestion in small intestine

  Emulsification of fats by bile salts
• Chemical digestion in small intestine

  Enzymes in pancreatic and intestinal juices digest starch, fats, proteins into simpler forms
• Large intestine


  1. Absorbs water and mineral salts from undigested food

  2. Undigested food and unabsorbed materials form faeces

  3. Faeces stored in rectum before egestion
• Faeces is not a metabolic waste product, so its removal is not called excretion
• Pancreas

  • Produces pancreatic juice with amylase, lipase, protease
  • Also secretes hormones insulin and glucagon
• Liver and gallbladder

  • Liver produces and secretes bile containing bile salts
  • Gallbladder stores and releases bile into duodenum
• Absorption of food substances

  Process where digested food materials are taken up from the small intestine into the bloodstream
• Excretion is the process of removing waste products that occur within the body cells, so its removal from the body is not called excretion
• Organs and glands associated with the gut

  • The pancreas
  • The liver and the gallbladder
• The pancreas

  It is connected to the duodenum by the pancreatic duct
• What the pancreas produces

  • Pancreatic juice which contains digestive enzymes: pancreatic amylase, pancreatic lipase, pancreatic protease
  • Hormones insulin and glucagon, which are essential in controlling blood sugar level in the body
• Blood vessels attached to the liver

  • Hepatic artery - Carries oxygenated blood to the liver
  • Hepatic vein - Carries deoxygenated blood away from the liver
  • Hepatic portal vein - Carries blood containing absorbed nutrients from the small intestine to the liver
• Bile

  Liver cells produce and secrete an alkaline greenish-yellow liquid called bile containing bile salts
• Bile does not contain enzymes
• Gallbladder

  Stores bile temporarily. When it contracts, it releases bile into the duodenum via the bile duct
• Absorption


  The process whereby digested food materials are taken into the body cells
• Digested foods absorbed by the villi of the ileum and the small intestine

  • Simple sugars (glucose, fructose and galactose)
  • Amino acids
  • Glycerol
  • Fatty acids
• Both digestion and absorption processes take place in the ileum
• The complete process of digestion in the ileum produces simple food substances such as simple sugars (glucose, fructose and galactose), amino acids glycerol and fatty acids