1A.Digestion and absorption

• The dental formula of adult human beings is 2123
• This formula denotes the arrangement of teeth in each half of both the jaws
• Teeth arrangement:

  • Incisors (I) = 2
  • Canines (C) = 1
  • Premolars (PM) = 2
  • Molars (M) = 3
• Bile juice does not contain digestive enzymes, but it contains bile salt
• Bile salts emulsify fats into very small micelles (Emulsified fats)
• Bile also activates lipase, which converts emulsified fats into fatty acids and glycerols
• Chymotrypsin of pancreas plays a role in the digestion of proteins, proteoses, peptones into 'Tripeptides' and 'Dipeptides'
• Other two enzymes from the pancreas are 'Trypsin' and 'Carboxypeptidase'
• If HCl were not secreted in the stomach:

  • Acidic pH (1.8) could not be maintained
  • Pepsin would not be activated
  • Protein digestion and milk digestion would not begin
  • Micro-organisms taken along with food would not be killed
• Thecodont dentition:

  • Teeth embedded in the sockets of jaw bones
  • Ex: Human beings
• Diphyodont dentition:

  • Formation of two sets of teeth during a lifetime
  • First set of temporary/milk teeth is replaced by the second set of permanent teeth
  • Ex: Most mammals including human beings
• Examples of autocatalysis:

  • Pepsin (Pepsinogen)
  • Trypsin (Trypsinogen)
• Chyme:

  • It is the acidic semi-digested fluid food formed in the stomach
  • Formed by the churning movements of the stomach muscles
• Auto catalysis:

  • The catalysis reaction in which the catalyst itself is one of the products of the reaction is called autocatalysis
  • When the same enzyme uses a catalyst for the activation of its proenzyme, the phenomenon is called autocatalysis
• Types of salivary glands in man:

  • Parotid glands: Located below the pinnae (ear lobe)
  • Submaxillary or submandibular glands: Located in the corner of the lower jaw
  • Sublingual glands: Located below the tongue
• Types of papillae present on the tongue of man:

  • Fungiform papillae: Located at the margin and tip of the tongue
  • Filiform papillae: Located on the upper surface of the tongue
  • Circumvallate papillae: Located at the base of the tongue
• Hardest substance in the human body:

  • Enamel (forms the crown of the tooth)
  • Secreted by ameloblasts of ectodermal origin
• Vestigial structure in human beings:

  • Vermiform Appendix
  • Well developed and useful in the digestion process in herbivores
  • Mostly formed with lymphoid tissue
• Deglutition:

  • Food bolus is swallowed into Pharynx and Oesophagus with the help of saliva & mucus
• Mastication:

  • Food is chewed and crushed by the teeth with the help of tongue & saliva
  • Food is mixed with salivary enzymes
• Diarrhoea:

  • Occurs when undigested liquid food that enters the large intestine is sent out by abnormal frequency of bowel movement
  • Results in loss of water (dehydration)
• Constipation:

  • Occurs when faeces are retained within the rectum due to low water content and irregular bowel movement
  • Faeces formed is hard
• Hormones secreted by duodenal mucosa:

  • Gastric inhibitory peptide (GIP)
  • Secretin
  • Cholecystokinin (CCK)
• Absorption:

  • Movement of digested food from the digestive system into the blood system
  • Occurs in the small intestine
• Assimilation:

  • Uptake of nutrients into cells and tissues after absorption
  • Occurs in every cell of the body