11 Bio Chapter Summary

Digestion

Chapter Summary

  • Food provides energy for different activities in the body. Food also provides organic materials for growth and repair.
  • The process of converting complex food into absorbable forms is called digestion. Various mechanical and biochemical methods are involved in digestion of food.
  • The human digestive system consists of the alimentary canal and the associated glands.
  • The alimentary canal can be divided into five main parts, viz. mouth, oesophagus, stomach, small intestine and large intestine.
  • Each tooth is embedded in a socket of jaw bone. This type of attachment is called thecodont.
  • The arrangement of different types of teeth in the jaws of an animal is called dentition.



  • The type of dentition in which an animal gets two sets of teeth during its lifetime is called diphyodont. This type of dentition is present in most of the mammals.
  • When different types of teeth are present, this arrangement is called heterodont dentition.
  • An adult human has four different types of teeth, viz. incisors (I), canine (C), premolars (PM) and molars (M). There are 32 permanent teeth in an adult human being.
  • There are three major parts in the stomach, viz. the cardiac, fundic and pyloric regions.
  • Small intestine is divided into three regions, viz. duodenum, jejunum and ileum.
  • The large intestine consists of caecum, colon and rectum.
  • There are three pairs of salivary glands, viz. parotids, sub-maxillary/submandibular and sbublinguals.
  • Liver is situated in the abdominal cavity, just below the diaphragm.
  • Pancreas is a compound gland, i.e. both exocrine and endocrine. It is an elongated organ. This is situated between the limbs of the U-shaped duodenum.
  • Salivary amylase initiates the chemical process of digestion. About 30% of starch is hydrolysed by salivary amylase (optimum pH 6.8); into a disaccharide, i.e. maltose.
  • Successive waves of muscular contractions in the alimentary canal are called peristalsis.
  • The proenzyme pepsinogen gets converted into the active enzyme pepsin; on exposure to hydrochloric acid. Pepsin converts proteins into proteoses and peptones (peptides).
  • The pancreatic juice contains inactive enzymes; trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases.
  • The intestinal juice contains various enzymes; like disachharidases (e.g. maltase), dipeptidases, lipases, nucleosidases, etc.
  • Proteins, proteoses and peptones are acted upon by the proteolytic enzymes of pancreatic juices.
  • Carbohydrates are hydrolysed by pancreatic amylase into disaccharides.
  • Fats are broken down by lipases with the help of bile into di- and monoglycerides.
  • The simple substances; formed after digestion; are absorbed in the jejunum and ileum regions of the small intestine. The undigested and unabsorbed substances go to the large intestine. No significant digestive activity occurs in the large intestine.