Glossary: Digestion & Absorption | Biology for Grade 11 PDF Download

Digestion

• Digestion: The process in alimentary canal by which the complex food is converted mechanically and biochemically into simple substances suitable for absorption and assimilation in the body of animals/organisms.
• Food: A substance which is taken and digested in the body to provide material for growth, repair & energy for reproduction and resistance from disease or regulation of body processes.

Digestive System

• Thecodont: The teeth embedded in the sockets of the jaw bone, e.g., in
• mammals.
• Diphyodont: The teeth formed twice in life time e.g., in mammals.
• Heterodont: Different types of teeth. An adult human has 32 permanent
• teeth which are of four different types.
• Tongue: The tongue is a freely movable muscular organ attached to the floor of the oral cavity by the frenulum.
• Papillae: The upper surface of the tongue has small projections called papillae, some of which bear taste buds.
• Epiglottis: A cartilaginous flap called epiglottis prevents the entry of food into the glottis – opening of the wind pipe – during swallowing.
• Oesophagus: The oesophagus is a thin, long tube which extends posteriorly passing through the neck, thorax and diaphragm and leads to a ‘J’ shaped bag like structure called stomach.
• Serosa: Serosa is the outermost layer of wall of alimentary canal and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues.
• Muscularis: Muscularis (layer of wall of alimentary canal) is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer.
• Submucosal layer: The submucosal layer (layer of wall of alimentary canal) is formed of loose connective tissues containing nerves, blood and lymph vessels. 
• Mucosa: The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine.
• Microvilli: The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance. These modifications increase the surface area enormously. 

Digestion of Food

• Bolus: The masticated food mixed with saliva.
• Deglutition: The masticated food mixed with saliva.
• Peristalsis: The involuntary movement of the gut by which the food bolus is pushed forward.
• Chyme: The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme.
• Goblet Cells: The intestinal mucosal epithelium has goblet cells which secrete mucus.

Absorption of Digested Products

• Absorption: Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph. It is carried out by passive, active or facilitated transport mechanisms.
• Facilitated transport: Some substances like glucose and amino acids are absorbed with the help of carrier proteins. This mechanism is called the facilitated transport.
• Micelles & chylomicrons: Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into small droplets called micelles which move into the intestinal mucosa. They are re-formed into very small protein coated fat globules called the chylomicrons.
• Assimilation: The absorbed substances finally reach the tissues which utilise them for their activities. This process is called assimilation.