Nutrition in humans

• The liver, gall bladder and pancreas aid in the digestion of food in the gut.
• The gall bladder stores bile temporarily.
• The liver produces and stores bile
• The pancreas secretes pancreatic juice, which

  helps digest food.
• Bile pigments are waste products Removed from faeces
• Bile is an alkaline, greenish-yellow liquid
• Bile salts is made up of bile salts and pigments which aids in fat digestion by emulsification of fats
• labelling

  
• Pancreas produces and secretes pancreatic juice which contain pancreatic amylase, pancreatic liapase and trypsin
• Pancreas secretes and produces glucagon and insulin
• Bile emulsifies large fat globules into small fat droplets to increase the surface area to volume ratio for faster digestion of fats, by lipase, to form fatty acids and glycerol.
• mouth: starch -> maltose (salivary amylase)

  small intestine: starch ->maltose(pancreatic amylase) —> gucose (maltase)

  lactose ->glucose + galactose (lactase)

  Sucrose -> glucose + fructose (sucrase)
• The end products of carbohydrate digestion are simple sugars (glucose, fructose and galactose).
• In the stomach:

  (pepsin activated by HCL from gastric juice from pepsinogen) proteins -> polypeptides

  In the small intestine:

  proteins -> polypeptides (trypsinogen -> trypsin) ->amino acids (peptidases)
• The end products of protein digestion are amino acids.
• large fat globules ->small fat globules (bile) -> fatty acids and glycerol (intestinal lipase & pancreatic lipase)
• The end products of fat digestion are fatty acids and glycerol
• Ileum is the main region of absorption
• The rate of absorption depends on:

  • surface area
  • thickness of separating membrane
  • concentration gradient
• Pancreas secretes and produces glucagon and insulin
• How is the small intestine adapted for absorption?

  •The thin walls (one cell thick epithelium) of the villi make it easy for nutrients to pass through to the bloodstream.

  •The length of the small intestine (~ 6 m) increases the time for absorption.

  •Many capillaries are present to help carry away absorbed nutrients quickly to maintain a steep concentration gradient
• Numerous folds in its inner wall -> villi in the inner walls -> microvilli on the epithelium (increase SA to volume ratio)
• villus (singular) , villi (plural)
• • Villi are minute finger-like projections on the folds of the small intestines
  • The villus has a one cell thick epithelium to decrease distance for faster absorption of digested food
• Lacteal/lymphatic capillary absorb and transport fats to the body
• Blood capillaries network absorb and transport amino acids and glucose to the body
• • Glucose and amino acids diffuse into the blood capillaries.
  • Glycerol and fatty acids diffuse into the epithelium, and combine to form minute fat globules which enter the lymphatic capillary.
• • Glucose and amino acids are absorbed by active transport.
• Undigested and unabsorbed matter enters the large intestine and are stored temporarily in the rectum and discharged as faeces through the anus.
• The discharging of faeces from the body is known as egestion.
• The hepatic portal vein transports glucose and amino acids to the liver.

  
• In the liver:

  • Most of the glucose (excess) are converted to glycogen and stored.
  • Glucose is transported by the hepatic vein to the different parts of the body.
• Glucose is the energy source for all cells in the body.
• Insulin regulates the amount of glucose that enters the blood stream.
• Insulin stimulates the liver to convert excess glucose to glycogen.
• In the liver:

  • Excess amino acids are converted to urea by deamination.
  • Amino acids are transported by the hepatic vein to the different parts of the body to be utilised.
• The hepatic vein distributes amino acids to be used by the cells.
• Amino acids that enter the cells are converted into new cytoplasm that is used for growth and repair of worn-out parts of the body.
• Amino acids are also used to form enzymes and hormones.
• • When there is enough glucose, fats are not broken down and are used to build protoplasm like cell membranes.
  • When glucose is in short supply, fats are broken down to provide the energy needed for vital activities in the body.
  • Excess fat is stored in adipose tissues beneath the skin and around the heart and kidneys.
  • Adipose tissues protect organs by acting as shock absorbers.