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Digestive System

Digestive system definition:

The digestive system is related with the digestive processes i.e. intake of food material, its digestion, absorption, assimilation and excretion of the undigested waste material. Digestive system also related with alimentary canal and its associated organs and digestive glands.

The digestive system

The five main activities of the digestive system are as follows:-

  • Ingestion: This is the intake of food by mouth into the alimentary tract, i.e. eating and drinking.
  • Propulsion: This mixes and moves the food particles along the alimentary tract.
  • Digestion: The breakdown of food, e.g. mastication (chewing) and chemical digestion of food into small molecules by enzymes secreted by glands and organs of digestive system.
  • Absorption: The process of passing digested food through the walls of some organs of alimentary canal into the blood capillaries for circulation and use by body cells.
  • Elimination: The process if eliminating undigested and unabsorbed food substances from the alimentary canal as feces by the process of defecation.

Alimentary canal:

Alimentary canal: It is also known as the gastrointestinal (GI) tract, it is a long tube like structure through which food passes. It starts from mouth and terminates at the anus, the alimentary canal contains following parts:-

  • Mouth
  • Pharynx
  • Oesophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum and anal canal

Digestive glands:-

The digestive glands secrete various types of secretions that are poured into the alimentary tract, some secreted by glands e.g. gastric juice secreted by glands in the lining of the stomach, and some secreted by the glands situated outside the tract. These secretions pass through ducts to enter the tract:

These are:-

• The salivary glands

• The pancreas

• The liver and biliary tract.

The alimentary canal:-

  1. Mouth: The mouth is the anterior opening of alimentary canal, food is taken by mouth and the mouth opens into the buccal cavity/oral cavity that is made by muscles and bones.

Buccal cavity: The next part of alimentary canal is made by bones and muscles:

Anteriorly – by the lips

Posteriorly – it is continuous with the oropharynx

Laterally – by the muscles of the cheeks

Superiorly – by the hard palate and soft palate

Inferiorly – by the tongue and the soft tissues

  • The buccal cavity is lined by mucous membrane, consisting of squamous epithelium and contains small mucus-secreting glands.
  • The anterior part of the buccal cavity is called as hard palate. The hard palate is formed by the maxilla and the palatine bones.
  • The posterior part is called as soft palate, which is muscular, and blends with the walls of the pharynx at the sides.
  • In the last of the posteriors part, there is present a soft structure hanging down which is called as uvula. It is a curved fold of muscle covered with mucous membrane.
  • On the both side of uvula there are present the tonsils.
Diagram of tongue

Diagram of buccal cavity


  • The base of tongue is attached by hyoid bone and it is composed of voluntary muscle.
  • The tongue is a muscular sense organ.
  • It is attached by a fold of its mucous membrane covering, called the frenulum, to the floor of the mouth.
  • The superior surface consists of stratified squamous epithelium, with numerous little projections called papillae.
  • Most of the papillae contain sensory receptors (specialized nerve endings) for the sense of taste in the taste buds.
Diagram of tongue

Diagram of tongue

Blood supply: The main artery that supplies the blood to the tongue is the lingual branch og external carotid artery. Venous drainage is by the lingual vein, which joins the internal jugular vein.

Nerve supply:

The nerves involved are:

• The hypoglossal nerves (12th cranial nerves), it supplies the voluntary muscle.

• The lingual branch of the mandibular nerves, that arise from the 5th cranial nerves, these are the nerves of somatic (ordinary) sensation, i.e. pain, temperature and touch

• The facial and glossopharyngeal nerves (7th and 9th cranial nerves), the nerves of taste.

Functions of the tongue:

The functions of the tongue are as follows:

1. Chewing (mastication)

2. Swallowing (deglutition)

3. Speech

4. Taste


  • The teeth are the hardest part of human body
  • They are embedded in the sockets of the alveolar ridges of the mandible and the maxilla.
  • Every human having two sets of teeth:
  1. Temporary teeth or deciduous teeth (10 in each jaw-20)
  2. Permanent teeth (32)
  • Teeth help in cutting, biting, grinding and chewing the food.

Blood supply

Arterial blood supply by branches of the maxillary arteries

The venous drainage is by a number of veins which empty into the internal jugular veins.

Nerve supply

The nerve supply to the upper teeth is by branches of the maxillary nerves and to the lower teeth by branches of the mandibular nerves. These are both branches of the trigeminal nerves (5th cranial nerves).

Salivary glands:

Salivary glands secretes into ducts that lead to mouth.

The three main pairs are:

  1. The parotid glands
  2. The submandibular glands
  3. The sublingual glands.

There are also various smaller salivary glands scattered around the mouth.

Parotid glands

  • These are situated one on each side of the face just below the ear.
  • There is a parotid duct in each gland, opening into the mouth at the level of the second upper molar tooth.

Submandibular glands

  • These are present one on each side of the face under the angle of the jaw.
  • The two submandibular ducts open in the mouth floor, one on each side of the frenulum of the tongue.

Sublingual glands

  • These glands are situated under the mucous membrane of the mouth in front of the submandibular glands.
  • They have numerous small ducts that open into the mouth.

Blood supply

Arterial supply is by various branches from the external carotid arteries and venous drainage is into the external jugular veins.


  • It is the combined secretions of all salivary glands and the small mucous secreting glands of oral mucosa.
  • 1.5 liter of saliva is produced in one day.

Saliva consist of

  • Water
  • mineral salt
  • salivary amylase; a digestive enzyme
  • mucus
  • antimicrobial substances; immunoglobulins
  • enzyme lysozyme

Saliva secretion

Saliva is secreted by submandibular glands.

Functions of saliva

  • The breakdown of complex sugars and starches into maltose with the help of amylase.
  • The saliva lubricates the food into the mouth, make it soft for swallowing.
  • It helps in speech by making movement of tongue.
  • The saliva has the pH value 7.0, so it prevent tooth decay.
  1. Pharynx:
  • The pharynx is common structure for food and air.
  • The buccal cavity opens in the pharynx, the upper part of pharynx is called oropharynx.
  • The lower part is called laryngopharynx.
  • The oropharynx lead to oesophagus.
  • The laryngopharynx leads to larynx (part of respiratory system).
  • Just at the starting of oropharynx, there is present of the small muscular structure called epiglottis.
  • Epiglottis prevents food entry in larynx.
  • Length of pharynx is about 12cm.

Structure of Pharynx:

Pharynx contains five layers form inside to outside which are as following:

    1. Mucosa
    2. Sub mucosa
    3. Pharangobasilar fascia
    4. Muscular coat
    5. Bucco pharangeal fascia

Muscles of pharynx

    1. Longitudinal muscle
    2. Circular muscle
Anatomy of pharynx

Diagram of pharynx and esophagus

  1. Oesophagus:
  • It is also called food pipe.
  • The oesophagus is approx. 25 cm long and approx. 2 cm in diameter.
  • It lies in the median plane in the thorax in front of the vertebral column behind the trachea and the heart.
  • It is continue with the pharynx above and just below the diaphragm
  • Oesophagus joins the stomach.
  • The upper and lower ends of the oesophagus are closed by sphincters.
  • The role of the upper cricopharyngeal or upper oesphageal sphincter is to prevent the air passing into the oesophagus during inspiration and the aspiration of oesophageal contents.
  • The cardiac or lower oesophageal sphincter prevents the reflux of acid gastric contents into the oesophagus.

Blood supply

Arterial: by oesophageal arteries, and abdominal region is supplied by branches from the inferior phrenic arteries and the left gastric branch of the coeliac artery.

Venous drainage: by azygos and hemiazygos veins.

Functions of oesophagus:

  • The oesophagus passes food to stomach by peristaltic movement after swallowing.
  • The cardiac sphincter allow food into the stomach.
  • Diagram of stomach.
  1. Stomach
  • The stomach is a J-shaped bag like structure of alimentary canal.
  • It is situated in epigastric, umbilical and left hypochondriac regions of the abdominal cavity.

Structure of the stomach

  • The oesophagus leads the stomach at the cardiac sphincter and with the duodenum at the pyloric sphincter
  • The stomach curves upwards to complete the J shape just before the pyloric sphincter.
  • Where the oesophagus joins the stomach the anterior region of the stomach makes an upward acute angle, curving downwards and forms the greater curvature and then slightly upwards towards the pyloric sphincter.

The stomach is divided into three regions:

    1. The fundus
    2. The body
    3. The pylorus.

At the distal end of the pylorus is the pyloric sphincter, guarding the opening between the stomach and the duodenum. When the stomach is not active the pyloric sphincter is relaxed and open, and when the stomach has food the sphincter is closed.


Diagram of stomach

Walls of the stomach

There are two types of walls present in the stomach are as follows:

Muscle layer: This consists of three layers of smooth muscle fibers:

• An outer layer of longitudinal fibers

• A middle layer of circular fibers

• An inner layer of oblique fibers

Mucosa: it consist some special cells that secrete gastric juice.

Blood supply: Arterial supply to the stomach is by the left gastric artery, a branch of the coeliac artery, the right gastric artery and the gastroepiploic arteries.

Venous drainage is by the portal vein.

Function of stomach:

  • The size of stomach varies; it depends on the volume of food it contains, which may be 1.5 liters or more in an adult.
  • When a meal has been eaten the food accumulates in the stomach in layers, the last part of the meal remaining in the fundus for some time.
  • Now the food mixes with the gastric juice gradually and it may take some time before the food is sufficiently acidified to stop the action of salivary amylase.
  • The gastric muscle generates a churning action that breaks down the bolus and mixes it with gastric juice, and peristaltic waves that propel the stomach contents towards the pylorus.
  • When the stomach is active the pyloric sphincter gets close.
  • Strong peristaltic contraction of the pylorus forces chyme, gastric contents after they are sufficiently liquefied, through the pyloric sphincter into the duodenum in small spurts.

About 2 liters of gastric juice is produced by the stomach daily, it consist of:

  1. Water
  2. Mineral salts
  3. Mucous
  4. Hydrochloric acid
  5. Inactive enzyme: pepsinogen

Functions of gastric juice

• Water helps to liquefy the swallowed food.

• Hydrochloric acid: it acidifies the food and stop the action of salivary amylase

– kills ingested microorganisms

– provides the acid environment, important for the action of pepsins.

• By hydrochloric acid pepsinogens are activated into pepsins and by the pepsins which is already present in the stomach. These enzymes start the digestion of proteins by breaking them into smaller molecules. Pepsins are most effectively at a low pH i.e. in between 1.5 and 3.5. 12.7

• Intrinsic factor (a protein) is necessary for the absorption of vitamin B12 from the ileum. (Deficiency leads to pernicious anemia)

• Mucus lubricates the stomach contents to prevent mechanical injury to the stomach. It also acts as barrier between the stomach wall and the corrosive gastric juice to prevent chemical injury.

Functions of the stomach

• Temporary storage for the food to digestive enzymes, pepsins, to act

• Chemical digestion – pepsins break proteins into polypeptides

• mechanical breakdown – the three smooth muscle layers enable the stomach to act as a churn, gastric juice is added and the food contents are liquefied to chyme.

• Limited for absorbing water, alcohol and some lipid-soluble drugs

• Non-specific defense against microbes – provided by hydrochloric acid in gastric juice.

• Secretion of the hormone gastrin.


  • The stomach opens posteriorly in the duodenum. The duodenum is a tube like structure.
  • The bile duct and pancreatic duct open in the duodenum which brings the bile juice and pancreatic juice and mix with the food.
  • The duodenum sends food materials into small intestine.

5) Small intestine

Small intestine
  • It is the largest part of alimentary canal.
  • The length of small intestine is about 6.5meters.
  • This is a coiled, narrow tube like structure

It has following parts:

Duodenum: this is the proximal fixed part of the small intestine and it is about 25cm in length.

Jejunum: it is about 8feet in length.

Ileum: this is about 12 feet in length

Structure of small intestine

  • The small intestine is designed for the digestion and absorption of food.
  • The internal covering mucosa contain the maximum circular folds, these folds increase the surface area for absorption.
  • There are present very small finger like structures which are called as villi.
  • There are also present maximum intestinal glands in the mucosa.
  • The villi help in the absorption of the digested food material.
  • There are present many lymphatic follicles called as the payer’s patches.
  • The numbers of intestinal wall crushes the food material and mix it with the intestinal juice.

Anatomy of small intestine:

The upper part of the small intestine is called jejunum lower part it called ileum.

Jejunum forms the 2/5th of the small intestine. Ileum 3/5th of small intestine

The ileum is the mobile part of small intestine.

The difference between jejunum and ileum:



Circular foldsLarge and closely present Small and not closely set
MesenteryThinner, near the upper part, contain wide arteries Thicker, arteries are narrow
VilliMore in number, large, thicker & leaf like structureLesser, thinner & shorter

Blood supply:

Arterial supply: by superior mesenteric artery.

Venous drainage: by portal vein.

Nerve supply: by parasympathetic branches of Vagus nerve.

  1. Large intestine:
  • The large intestine starts from the ileoceical junction to the anal canal.
  • It is about 1.5 meters in length.
  • It contains the following parts
  1. Caecum = 6cm
  2. Appendix = 9cm
  3. Ascending colon = 15cm
  4. Transverse colon = 50cm
  5. Descending colon = 25cm
  6. Sigmoid colon = 40cm
  7. Rectum = 12cm
  8. Anal canal = 3.8cm
  • Structurally the large intestine is designed for the storage of fecal matter temporarily and adsorption of water.
  • The villi are absent here.
  • The mucus membrane contains the mucus secreting goblet cells.
  • The large intestine is much wider, but the length is smaller than the small intestine.
  • The maximum part is fixed except the appendix, transverse colon and sigmoid colon.

Caecum: it is about 6cm in length and 7.5cm in width. Ileum opens into the caecum, which is guarded by the ileocaecal valve which prevents the reflux from caecum to ilium.

Ascending colon: It starts from caecum and turns at the hepatic flexure.

Transverse colon: This is present in the abdomen.

Descending colon: Starts from the splenic flexure to the lower part of the left pelvic brim bone.

Sigmoid colon: It starts from the left pelvic brim bone & ends in front of sacrum-3 bone.

Diagram of large intestine

  1. Rectum and anus

Rectum: This is the lower dilated part of the large intestine. It is situated in the pelvic cavity.

Anal canal: This is the last part of alimentary canal. It starts from the anorectal junction to the anus. It contains the internal & external sphincters.

Anus: This is the posterior opening of alimentary canal by which the undigested material is given out of the body.

Digestive glands

  1. Liver

Diagram of liver

The liver is located in right hypochondrium region.

Structure of liver:

  • The liver is the largest gland in human body & the weight is about 1.5-2 kg.
  • The color of the liver is dark reddish brown.
  • It is situated in right hypochondria region of the abdomen.
  • The liver contains four lobes when looked from posterior side the right, left, quadrate and caudate lobes.
  • The liver cells are nucleated, polyhedral in structure.
  • The protoplasm of the cells contains large number of enzymes.
  • The masses of cells make the hepatic lobule. There diameter is about 1mm. These lobules are separated by the connective tissue.
  • In each lobule the hepatic capillaries are present.
  • The bile juice is manufactured in small spaces in hepatic cells.
  • The bile juice is collected and put in the hepatic duct
  • The large bile ducts are lined by columnar epithelium tissue.
  • The bile secretion is about 500ml daily.
  • The bile juice contains the bike pigments, organic salts. The bile salt helps in the digestion and absorption of the fat.
  • The liver contains the gall bladder which helps in the storage of bile juice.

Blood supply

Arterial supply: hepatic artery & portal vein

Venous drainage: inferior vena cava

Functions of liver:

  • The most important function of liver is to secrete bile juice. The bile juice contain many digestive enzymes which are very important for the digestion of fat.
  • The liver changes the glucose into glycogen.
  • The liver helps in the production of plasma protein like prothrombin and fibrinogens which helps in the blood clotting.
  • The liver produces the chemical heparin which is an anticlotting factor.
  • The liver helps in the metabolism of fats and carbohydrates.
  • The liver destroys the old RBCs and protects the hemoglobin.
  • The liver manufactures the RBCs during fetal life
  • The liver removes the harmful toxic materials like urea by the kidney.
  • The liver manufactures vitamin A from citric substances.
  • The liver removes the extra bilirubin from the blood.
  1. Gall bladder:

Diagram of gall bladder

  • The gall bladder is a muscular pear shaped structure. This is a bag like structure present in the liver
  • The size of gall bladder is about 8-10cm.
  • The volume of gall bladder is 60ml.

It has three parts

  • Fundus
  • Body
  • Neck

The neck is connected with cystic duct. It contains three layers. The outer covering is perineal, middle is the muscular covering and internal is mucus layer. The neck is connected with the cystic duct, which is 4 cm in length. It joins with the right and left hepatic duct and make the common bile duct. It takes bile juice to the duodenum.

Function of gall bladder:

  • The gall bladder functions as the storage of the bile juice.
  • It concentrate the bile juice

Composition of bile juice: The bile is an alkaline secreted by the liver cells. It is secrete about 500ml per day. The bile juice contains about 86% water and bile salts + bike pigments + cholesterol + mucin.

Bile juice helps in fat digestion.

  1. Pancreas

Diagram of pancreas

  • The pancreas is the double gland this is both endocrine and exocrine.
  • The exocrine portion secretes the pancreatic enzymes and the endocrine portion secretes the pancreatic hormones.
  • The pancreas present transversely in the abdomen on the left side just below the pyloric part of the stomach above the transverse colon.
  • The pancreas is a leaf like structure present near the L1 & L2 vertebra.
  • The size of the pancreas is about 15-20cm; the weight is about 100gm.

The pancreas has four parts:-

  • Head
  • Neck
  • Body
  • Tail

The head of pancreas present in duodenum.

The exocrine portion contains the acini cells which secrete pancreatic enzymes.

The exocrine portion contains the pancreatic islets cells which secrete pancreatic hormones like insulin and glucagon.

Blood supply:

Arterial supply: by splenic artery

Venous drainage: by portal vein


  1. The pancreas produces about 1200-1500ml of the pancreatic juice per day.
  2. The pancreatic juice is alkaline.
  3. It contains more HCo3 content.
  4. It contains the following enzymes.

1. Alfa amylase: It digests the starch.

2. Pancreatic: It digests the protein.

3. Phospholipase: It functions on the phosphor lipids.

Within a few minutes of taking the food the pancreatic juice secretion increases under the effect of Vagus nerve. When the gastric content passes in the duodenum the two hormones secretion and pancrcoxgymic are produced in mucosa which further stimulates the secretion of the pancreatic juice.

The endocrine portion the pancreatic islets cells are present in the small group in the epithetical cells.

The pancreatic islet cell secretes the different hormones one of the most important hormone is insulin. This is the anti-diabetic hormone.

The insulin is a protein which can be affected by the protein digestive ferments.

Therefore the insulin is not given by the mouth but it is given by the substances (under the skin).

The insulin contents and absorbs the glucose and fats.

Hyperglycemia: This is the high bland slyer, loss of weight, fatigue, polyuria, mouth dryness and tongue thirst and also increased berating.

Important pancreatic hormones:

  1. Glucagon: This hormone is produced is produced by the Alfa-cells. It increases the blood sugar lead in the body.
  2. Insulin: This hormone is produced by the beta-cells. It decreases the sugar level in the blood. It also decreases the level of the amino acids, fatty acid and promotes their metabolism.
  3. Somato station: this hormone is produced by the delta-cells. The important function of their hormones is the control the functions of the other endocrine cells of the pancreatic islets.
  4. Pancreatic poly peptide: Produced by F (PP) cells and it effects the digestion and distribution of the food molecules.

Physiology of digestive system (Digestion):

The physiology of digestion starts from the mouth.

The food is taken from the mouth into the buccal Carty. The buccal cavity contains the tongue and teeth.

The food is tasted by the tongue. The buccal cavity receives the saliva from the salivary gland which makes the food soft.

The saliva is secreted by the parotic submandibular and sub lingual.

The food is chewed or masticated the teeth. The starch dextrin and the glycogen are converted into the limit dextrin’s maltose and isomaltose.

Now, the food passes in the esophagus which doesn’t contain any enzyme. It passes the food material into the stomach by the cardiac sphincter.

The wall of the stomach undergoes the macular contraction 15-20 times per minute. By this action the food is properly mixed with the gastric juice. Gastric juice contains the mucin + HCL + pepsin + renin.

  1. Mucin: Protects the wall of stomach.
  2. HCL: Kills the harmful bacteria.
  3. Pepsin: Changes the proteins into peptones
  4. Renin: Changes casein (milk) into Para casein (Curd)

Secretion of gastric juice in the stomach is controlled by the nervous system.

The food material remains in the stomach for the average meal is about 3-5 hours.

It is different for the different food material

  1. Carbohydrate – 1-2 hours
  2. Proteins – 3 hours
  3. Fats – 3-6 hours

Food starts coming into duodenum. The food material receives the bile juice from the gall bladder and pancreatic juice from the pancreas. No action of these enzymes takes place in duodenum.

They pass with the food material to small intestine, the small villi (0.5-1.5mm long) it also contains maximum intestinal glands.

Action of bile juice in the lower part of the small intestine

Action of pancreatic juice starts in the upper part of small intestine.

Now food enters in upper part small int.

  1. Amylase: Starch + Dextrins + Glycogen – limit dextrins + maltose + IsoMaltese
  2. Trypsin: Protein – Peptides
  3. Lipase: Fats – fatty acids
  4. Bile juice (Lower part): Lipase – Eats – fatty acids (Triglycerides- monoglycerides)

Food passes is lower part of the small intestine: It is mixed with the intestinal juice it is also called as (succus-entericus).

The intestine juice is secreted about 3 little in 24 liter in 24 hours with PH value 7.8-8. It contains the following enzymes- Amino peptidase, maltose, sucrose, lactase and lipase.

  1. Peptides (amino peptidase) – Smaller peptides + amino acids
  2. Maltose – Glucose
  3. Sucrose – Glucose
  4. Lactose – Glucose
  5. Glycerol + fatly acids (lipase) – mono glycerol + fatly acids

The maximum food is absorbed by the villi which are mixed with the blood and goes in the blood circulation the unabsorbed part of the food material passes in the large intestine which simply reabsorbs the water and some salts.

The unabsorbed material passes into the rectum which stores it temporary and finally passes out of the body by the anus.

Physiology of digestion of carbohydrates protein and fats:

  1. Carbohydrates: 50 to 60% part of the diet is carbohydrate. It contain the poly carbohydrates like starch glycogen.

Disaccharides: Sucrose, lactose and maltase

Monosaccharaides: Glucose and fructose

The carbohydrates are not digested by the stomach. The digestion starts in the mouth (buccal cavity) by the action of salivary glands and then in small intestine by the action of pancreatic amylose this results in the small chains of polymers- oligosaccharides and disaccharides.

The enzymes in the small intestine alfa dextrinase maltose, sucrose, lactose complete the process of digestion of carbohydrates and changes to glucose and fructose.

The glucose is very quickly absorbed from the small intestine. Absorption of glucose depends on Na+ the high sodium ion concentration in the lumen helps in maxM absorption of glucose.

The maximum rate of glucose absorption in small intestine is 120gm/hm.

  1. Protein: The digestion of protein starts in stomach by the action of enzyme pepsin.

The pepsin is secreted by the cells of mucosa. Pepsin breaks peptide bonds.

The best action of pepsin is all PH= 1.6 – 3.2 and the action finishes as the food passes in the small intestine.

The further digestion of proteins takes place in duodenum by the photolytic enzyme.

Proteolytic enzyme (Tripsin + chemotripsin etc.)

In the smalls intestine the compute digestion of the polypeptides takes place at three sites.

  1. Amino acids: The absorption of amino acids is very quick in the upper part of small intestine jejunum and slow in ileum.
  2. The amino acids are absorbed by the simple diffusion.
  3. The absorption depends on the presence of Na+
  4. The hydrogen ion helps in the absorption of di and tri peptides.
  5. Fats: Food material contains simple fats which mainly contain the triglycerides, phospholipids, glycolipids, cholesterol.

The digestion of fats starts in the stomach by the action of the lingual lipase and gastric lipase.

In the duodenum by the action of pancreatic lipase the digestion of fats takes place.

The presence of the bile salts is very important because it helps in the fat digestion which is secreted by bile juice.

Bile slats + lipids help to convert the H2O soluble molecules. Therefore very well absorb.

The HCL produced in the stomach is so strong that it can even dissolve the zinc but the wall of the stomach is protected due to very quick regeneration of cells so that the HCL cannot get time to dissolve the cells of the wall of the stomach.

Water soluble vitamins: CB, B6, B12, B, B2 biotin and niacin.

Essential amino acids: Beans, Pea, Com

  1. Tryptophan
  2. Methionine
  3. Valine
  4. Threonine
  5. Phenylanine
  6. Leusine
  7. Isoleucine
  8. Lysine
  9. Infants
  10. Histidine

Clinical and applied aspects:

  1. Dental caries: It is disintegration of one of the calcified structures covering the pulp cavity. The main cause is unhygienic condition. It leads to pain and inflammation.
  2. Peptic ulcer: It is the break in the mucus lining of the stomach. It is due to the excess of secretion of gastrin juice (also contain HCL) which gives burning sensation.
  3. Dysphagia: Difficulty in swallowing in the elderly age it is oesophagal cancer.
  4. Vomiting: The forcefully coming out the gastric content vomiting centers is present in medulla oblongata in brain.
  5. Diarrhea: The passing out of stools in liquid form with maximum frequency is called diarrhea.


1. Due to bacterial or viral infection in the large intestine.

2. Intake of toxic materials or poisonous substance.

3. Drugs like ampicillin

  1. Appendicitis: The lumen of the appendix is very small and there is little scope of welling. The cause is generally microbial infection due to passing the hard stools and due to the kin-king of the hard material. The inflammation takes place and there is swallowing of that part in the mild cases the inflammation subsides. In more severe cases the bacterial infection takes place and put the pressure on the arteries or veins as a result of which it ruptures.
  2. Cholera: The disease caused by the vibrio chlorate and it is spread by the contaminated water, food, hands. The host is the men. The maximum water, bicarbonates, chlorides produced by intestinal glands leading to the diarrhea, blood, mucus and dehydration occurs that is called as cholera and may cause death.
  3. Dysentery: The host is the man. It is spread by fecal contamination in the food, drinks and the hands. The inflammation. Ulceration and swelling of intestinal mucosa. In acute cases of infection severe diarrhea, blood loss, mucus and dehydration occur.
  4. Acute pancreatitis: In this condition the protein splitting enzymes digests the parenchyma cells is the i.e. auto digestion. The cells of pancreas and damaged causing the cancer.
  5. Hernia: This is the condition of coming out of the part of the abdominal organ from the weak point of muscular part in the abdomen.
  6. Acute hepatitis: The viral infections of the most common cause of this problem are of type A, B and C. The virus enters the cells and causes the degenerated by the cell.

Type A: Spread by hands, food and feces.

Type B: Spread by blood or blood product

Type NANB: This is also spread by infected blood.

Chronic hepatitis: Any form of the hepatitis which persists more than 6 months may be due to viruses or drugs.

Gastritis: The inflammation of the gastric wall due to imbalance between the gastric juice and protective effect of mucus on the epithelial gastric surface.

Pyloric stenosis: This is the condition in which spasmodic (pain in stomach) constriction of the pyloric sphincters. The main symptom is the vomiting or weight loss. This is more common in the males.

Peptic reflux esophagitis: This is due to the acid juice in the esophagitis causing the irritation. The reflux of gastric contents is due to the:

  1. Increased intra-abdominal pressure in pregnancy
  2. High acidity
  3. Low secretion of the hormone.