🏥 Chapter 5 - Nutrition in Humans

• What is Nutrition


  the obtaining of food and energy for growth, repair and maintenance of the body
• The Pharynx


  connects the buccal cavity to the oesophagus and the larynx, as well s the trachea
• The Mouth


  • teeth break down large pieces of food --> smaller piece --> increases surface area-to-volume ratio --> to increase rate of digestion by amylase
  • salivary glands secrete salivary amylase in the mouth
  • tongue mixes food with saliva and moves food to the back of the mouth to aid in swallowing
  • alkaline environment of pH 7
• The Oesophagus


  • narrow, muscular tube
  • joins the mouth to the stomach
  • has the longitudinal muscles and circular muscles
• Peristalsis


  rhythmic, wave-like, muscle contractions in the wall of the alimentary canal
• To push food down the oesophagus


  • circular muscles contract, and the longitudinal muscles relax. This causes the wall of the gut constricts, and becomes narrower and longer, squeezing the food forward
• To allow food to enter the oesophagus


  • longitudinal muscles contract
  • circular muscles relax
  • gut becomes wider and shorter
  • widens lumen for food to enter
• The Stomach


  • distensible muscular bag
  • has numerous gastric glands that secrete gastric juice which contains pepsin
  • acidic environment of pH 2
• The Small Intestine


  • consists of duodenum and ileum
  • carries out most of the digestive process
  • secrete intestinal juice which contain intestinal lipase, intestinal maltase and intestinal protease
  • food is digested
  • H2O and nutrients are absorbed
• The Large Intestine

  • consists of colon, rectum and anus.
  • colon absorbs H2O and nutrients from undigested matter
  • undigested matter form faeces
  • faeces are stored in the rectum temporarily
  • faeces are then expelled through the anus (egestion)
• The Liver & Gall Bladder

  • liver produces bile which is alkaline at pH 8
  • bile emulsifies fats
  • bile is temporarily stored in the gall bladder, and bile flows in the duodenum via the bile duct.
• The Pancreas

  • produces pancreatic juice which contain pancreatic amylase, pancreatic lipase and pancreatic protease
  • pancreatic juice flows into the duodenum via the pancreatic duct which joins the bile duct
  • produces insulin and glucagon in the islets of Langerhans which control blood glucose level
• Digestion in the Mouth

  Digestion in the Mouth

  1. Food is ingested
  2. stimulates salivary glands to secrete saliva which contains salivary amylase
  3. optimum pH 7
  4. chewing breaks food up into smaller pieces, increasing surface area-to-volume ratio to increase rate of digestion by amylase
  5. tongue rolls food masses into small, slipper, round boli
  6. boli are swallowed into the oesophagus
• Digestion in Stomach

  1. Boli enters stomach
  2. Stimulate gastric glands to secrete gastric juice into the stomach
  3. protease in the stomach digest the proteins into polypeptides
  4. HCl in the gastric juice provides a acidic environment that is optimum for protease, kills off harmful microorganisms, and stops the action of salivary amylase by denaturing it
  5. mucus prevents stomach wall from being digested by the enzymes it produces
  6. food can remain in the stomach for 3-4h
  7. partially digested food liquifies, forming chyme, that passes into the duodenum
• Digestion in the Small Intestine

  1. Chyme enters duodenum
  2. stimulates pancreas to secrete pancreatic juice that travels through the pancreatic duct to the duodenum.
  3. stimulates gall bladder to release bile, which travels though the bile duct into the duodenum.
  4. epithelial cells in the small intestine produce intestinal juice
  5. All 3 juices are alkaline, which neutralizes acidic chyme, and provides and alkaline environment of pH 8 for pancreatic and intestinal enzymes
• Carbohydrate Digestion

  • begins in the mouth (starch --> maltose)
  • fully digested in the small intestine by pancreatic amylase and maltase (maltose --> glucose), (starch --> maltose)
• Protein Digestion


  • begins in the stomach (protein to polypeptide)
  • fully digested in the small intestine by intestinal protease(polypeptide - amino acid), (undigested protein-polypeptides)
• Fat Digestion

  • bile produced by liver and stored temporarily in the gall bladder is released into the duodenum via the bile duct.
  • bile salts emulsify fats
  • Emulsification is the break up of large fat droplets to tiny fat droplets
  • increases surface area-to-volume ratio to increase rate of digestion by lipase
  • digested by pancreatic and intestinal lipase to fatty acids and glycerol
• Small Intestine Adaptations for Absorption


  1. inner surface of the ileum is folded extensively and these folds have villi, to increases surface area for absorption
  2. Epithelium (wall of villi) is one cell thick to reduce diffusion distance
  3. cells of the epithelium have many microvilli to further increase surface area
  4. Each villus has many blood capillaries to maintain a steep diffusion gradient
  5. Each villus contains a lacteal that transports absorbed fat away to maintain a steep diffusion gradient
  6. Epithelial cells have many mitochondria to provide energy for active transport of nutrients
• Small Intestine absorption

  • glucose and amino acids are absorbed by blood capillaries in the villi & active transport ( when someone is fasting or vigorously exercising)
  • glycerol and fatty acids diffuse into the epithelium and form tiny fat droplets that enter the lacteal
• Assimilation


  • process whereby absorbed nutrients are converted to new protoplasm or used to provide energy
• Glucose Utilisation

  • hepatic portal vein transports glucose from the small intestine to the liver
  • most are stored in the liver as glycogen
  • rest are broken down during tissue respiration to release energy
  • excess glucose returns to the liver as glycogen, and will be converted to glucose when needed
• Amino Acid Utilisation

  • hepatic portal vein transports amino acids from the small intestine to the liver
  • converted to new cytoplasm for growth and repair of worn-out cells in the body
  • form enzymes, hormones and antibodies
  • excess amino acids are deanimated
• Fat Utilisation

  • lympathic capillaries --> lympathic vessels
  • fats are discharged into the bloodstream
  • when glucose is sufficient fat is used for building of new protoplasm
  • when glucose is NOT sufficient fats are broken down to release energy
  • excess fats are stored in adipose tissues
• Liver Functions

  1. Production of Bile
  2. Deanimation of Amino Acids
  3. Regulation of Blood Glucose concentration
  4. Breakdown of Hormones
  5. Detoxification
• Liver - Bile Production

  • emulsifies fats
  • produced by liver
• Liver- Deamination of excess amino acids

  • amino groups are removed from excess amino acids and converted to urea
  • removed in urine
  • remains of deaminated amino acids are converted to glucose and stored as glycogen
• Liver-Regulation of Blood Glucose Concentration

  • islets of Langerhans secrete insulin and glucagon
  • when blood glucose concentration is high, insulin is secreted to decrease blood glucose concentration level to normal, and converts glucose to glycogen
  • when blood glucose concentration is low, glucagon is secreted to increase blood glucose concentration level to normal, and converts glycogen to glucose
• Liver - Hormone Breakdown

  • hormones are broken down in the liver after they serve their purpose
• Liver- Detoxification

  • process whereby harmful substances --> harmless substances
  • alcohol is broken down to compounds that can be used for respiration and to provide energy for cell activities
• Effects of Alcohol on the liver

  • alcohol stimulates excessive acid secretion in the stomach.
  • lead to cirrhosis of the liver whereby liver cells are destroyed and replaced with fibrous tissue, making liver less able to function
  • cirrhosis may lead to haemorrhage, which can lead to liver failure and death
  • reduced self-control and may do regretful things
  • slurred speech, blurred vision, clumsy and poor muscle coordination, underestimating speed --> accident
  • wet brain, dementia caused by brain damage
  • shrinkage of brain volume
• yt video on chapter

  https://www.youtube.com/watch?v=vMI46qGQMDw&t=56s