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Content :-. Alimentary canal Digestive glands. Digestion Absorption Assimilation. Alimentary canal. Alimentary canal of man measures 8-10 meters in length. It starts with mouth and ends at the anus. - Mouth. Mouth is a transverse slit bounded two
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Content:- • Alimentary canal • Digestive glands. • Digestion • Absorption • Assimilation
Alimentary canal • Alimentary canal of man measures 8-10 meters in length. • It starts with mouth and ends at the anus.
- Mouth • Mouth is a transverse slit bounded two soft ,movable lips , the upper lip and the lower lip . • The lips are covered with skin . • Lips prevent the falling down of bitten food particles. Note–That during swallowing of food ,glottis remains closed .
Buccal cavity • Buccal cavity is bounded by lips in front .It contains cheeks ,upper and lower jaws, gums ,teeth and tongue .in man there are 16 teeth in each jaws. there are four different types of teeth .they are
(i) Teeth • In man two sets of teeth appear during life .in humans, the first set or milk teeth consists of 20 teeth . These are called deciduous or temporary teeth .these are completely replaced by the permanent teeth by about 12 years of age . Teeth help in cutting, tearing and grinding the food .
Structure of a Tooth • The sensitive nerves and blood vessels at the centre of each tooth are protected by several layers of tissue, the outermost (the enamel) being the hardest substance in the body. • Under the enamel, surrounding the pulp from crown to root, lies a layer of bonelike dentin.
Contd:-Structure of a Tooth A hard tissue called cementum separates the root from the periodontal ligament, which in turn holds the root in place and cushions the tooth against the gum and jaw during the grinding, jarring activity of chewing. Separates the root from the periodontal ligament, which in turn holds the root in place and cushions the tooth against the gum and jaw during the grinding, jarring activity of chewing.
(ii) Tongue • It is a muscular ,sensory organ, which is attached to the lower jaw. • It bears taste buds .it helps in the tasting the food it mixes food with saliva and helps in swallowing. • It also helps in speech and makes it soft and slippery for chewing.
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Pharynx • The buccal cavity opens into the pharynx . • It is the common passage for food and air . • It leads into the oesophagus . • When food is swallowed , the glottis remains closed (by eppiglottis ). • If a small particle of food enters the tracheal opening . • It is throw out by coughing.
oesophagus • Oesophagus is a muscular tube about ten inches(25cm)long . • Food passes down the oesophagus by peristaltic movements of its muscular wall. • The rhythmic contraction and relaxation of muscles of alimentary canal to push the food downwards is known as peristalsis fig 1.15.
4- Stomach • The stomach is alarge muscular J shaped sac located below the diaphragm. It secrets gastric juice. The wall of stomach contains numerous branched and tabular gastric glands. These glands secrete gastric juice,which contains enzymes (Pepsin,Rennin )HCl and mucus. The sight , smell or thought of appetizing food can also initiate secretion of gastric juice.
5-Small intestine • Small intestine is about 6 meters in length and 2.5 cm I in diameter. It remains coiled in the abdominal cavity . The small intestine consists of three parts : • Duodenum. It is the first part (proximal) of intestine and is about25 cm(10 inches) long. It is U- shaped In appearance. The opening of common bile duct and pancreatic duct opens in it. • Jejunum. It is about 2.5metres long and narrower than duodenum. • Ileum . It is about 3.5metres long. It is distal in position.
Contd:-Small intestine • Small intestine serves both for digestion and absorption of digested food it has numerous tiny finger like –projections called villi. • The villi increases the inner surface area of absorption of digested food . • At the bases of villi are present intestinal glands . • These secrete digestive enzymes for the digestion of carbohydrates ,proteins and fats.
Large intestine • Large intestine is wider than small intestine . It is about 1.5-1.8 meters long . It is divided into caecum ,colon &rectum. • Caecum is a small blind pouch situated at the junction of small and large intestines its blind end is produced into vermiform appendix.in man it is a vestigial organ. • Colon is an inverted U-shaped tube about a meter long. • Rectum is the last part of alimentary canal. It opens to the exterior by anus. Rectum absorbs excess of water from the undigested food ,secretes mucous and helps in egestion of undigested food matteer.
Digestive Glands 1- salivary glands. Three pairs of salivary glands open into the buccal cavity .These secrete saliva, which performs following functions: • It moistens and lubricates food and helps in swallowing. • It contains an enzyme ,salivary amylase, which carries out partial digestion of starch into maltose The salivary glands, especially the parotid, in front of each ear of human beings are affected by the disease called mumps.
liver Liver is the largest gland in the human body. It secretes bile juice, which is stored in the gall bladder before it is poured into duodenum through a common bile duct .Bile is alkaline due to the presence of bile salts and bile pigments. Bile helps in : • Emulsification of fat (emulsification means breaking of fat into small globules ). • Activates the pancreatic and intestinal enzymes by making the food alkaline. • Stores glucose in the form of glycogen. • Forms urea. • Destroys dead and worn out red blood corpuscles. The bile secreted by the liver cells is normally stored in the gall bladder until needed in the duodenum.
Pancreas • Pancreas is the second largest gland of the body . It secretes pancreatic juice , which carries out digestion of carbohydrate, proteins and fats. it also secretes insulin and glucagon hormone. pancreatic juice contains trypsin for digesting protein, pancreatic amylase for breaking down starch. Bicarbonate ions make the medium alkaline which is required for the action of pancreatic enzymes. It is secreted by duodenum wall. Both bile and pancreatic juice enter duodenum through common bile duct .
Digestion The process of breakdown of complex food particles in simpler forms is known as digestion. It is necessary to digest so that food can be absorbed in the blood stream and can be utilized by the cells.
Process of digestion 1- digestion of food in buccal cavity. 2- digestion in stomach . 3- digestion in small intestine.
digestion of food in buccal cavity In buccal cavity food is chewed and masticated to increase the surface area of food for digestion .salivary amylase (ptyalin) acts upon starch and breakdown into maltose .(raw bread tastes sweeter because starch has changed into maltose) No digestion occurs in pharynx and oesophagus.
digestion in stomach • In stomach gastric juice is released . • The gastric juice is acidic due to the presence of hydrochloric acid . • Gastric juice contains pepsin and rennin. • Pepsin works only in acidic medium . • Pepsin enzymes break down the proteins of the food into smaller molecules , which passes into intestine. • Rennin digests milk protein.
digestion in small intestine In duodenum food is mixed with :- • Bile from the liver • Pancreatic juice from the pancreas and • Intestinal juice (succus entericus).
Contd:- digestion in small intestine The bile has no enzymes but makes food alkaline and emulsifies fats for easier digestion. A-Pancreatic juice (in duodenum)digests carbohydrate ,proteins and fats. • Pancreatic amylase acts on starch and converts it into maltose. • Trypsin converts peptons to amino acids . • Pancreatic lipase converts fats to fatty acids.
Contd:- digestion in small intestine B- succus entericus (intestinal juice, in ileum) also digests carbohydrate, proteins ,fats :- • Maltose acts upon maltose to form two glucose molecules; lactase acts upon lactose to form glucose and galactose molecules ,sucrase acts upon sucrose to form glucose and fructose molecules . • Intestinal lipase also converts fat to fatty acids. • Erepsin acts upon peptides to form amino acids. No digestion takes place in large intestine.
Absorption of food The final products of digestion are glucose (from carbohydrates), amino acids (from proteins), and fatty acids and glycerol( from fats) .The glucose and amino acids enter the blood stream, while glycerol and fatty acids enter the lymph. The absorbed food is sent to different parts of the body. The main site for absorption of food is small intestine because it is long and it has minute finger-like projections called villi, which increases the surface area of absorption. Excess of water is absorbed in large intestine and the contents become semi-solid faeces.
Assimilation The absorbed food is either used by the body to produce energy or it can be stored in the body.Glucose is utilized in respiration to release enregy. If in excess glucose is stored in the formof glycogen in lever and muscles, amino acids are converted in the form of proteins for synthesis of new cells whereas fatty acids and glycerol convert into fat and are stored in the adipose tissue.
Egestion • The undigested waste is passed out through anus.
