DIGESTIVE SYSTEM
The digestive system comprises of the gastrointestinal tract with various glands attached to it.
The tract starts from the mouth and ends at anus. The tract is 8-10 meters in length and from
above downwards and is subdivided into 1. Mouth 2. Pharynx 3. Oesophagus 4. Stomach 5.
Small intestine 6. Large intestine 7. Rectum 8. Anal canal 9. Anus.
ORAL CAVITY: This is the first enlarged part of the tract. It opens externally through upper
and lower lips. The cavity has dome shaped roof called the palate. The hard palate is in front and
the soft palate is behind. This forms an arch, with uvula hanging behind in the centre. In the oral
cavity food is teared and grinded with the help of teeth and also mixed thoroughly with saliva.
The bulk food at this time is referred as bolus. The process of tearing, grinding and mixing the
food with saliva involves movement of jaws, cheeks, lips and tongue is known mastication.
Tongue is the posterior part of oral cavity. It is a musculo-membranous structure with taste buds
and papillae on its surface. The tongue is a mobile organ with a tip, body and a base. Its
movement is governed by a number of muscles, through their nerve supply.
Epithelium of the tongue is modified into papillae and taste buds. Papillae may be (i) Filiform
(ii) Fungiform (iii) Circumvallate.
Filiform papillae are narrow and conical, distributed all over the surface of the tongue. The taste
buds are absent in filiform papillae.
Fungiform papillae are narrow at the base and expanded on the surface. A few taste buds are
present in these papillae.
Circumvallate are few in number. They can be seen with the naked eye along ‘V’ at the base of
the tongue. Taste buds are more on the sides of these papillae.
Glands of the tongue may be: mucous, serous and or lymph glands.
Teeth: There are 16 ± 16 = 32 teeth in the mouth and are fixed in the sockets in the upper jaw
(maxilla) and lower jaw (mandible). Teeth are arranged in curved form. The front ones are for
biting and cutting, the rear ones are for crushing and grinding. The order of teeth from front to
the back is incisors, canine, pre-molars and molars.
A tooth has three parts (1) Crown at the top, (2) Neck in the middle (3) Root at the bottom.
Type and Positions of Teeth:
RIGHT: M P C I ICPM: LEFT
Upper Jaw: 3 2 1 2 2 1 23: Upper Jaw
Lower Jaw: 3 2 1 2 2123: Lower Jaw
M = Molar: P = Premolar; C = Canine; I = Incisor.
The tooth is composed of three substances. They are (1) Dentine (2) Enamel and (3) Cementum.
Dentine forms the major part of the teeth and has a bone-like structure. Enamel is the outermost
covering that covers the crown of the tooth. It is harder than the bone. Cementum is in the neck
and it is as hard as a bone.
SALIVARY GLANDS: There are three pairs of major salivary glands: (1) Parotid (2)
Submaxillary or submandibular (3) Sublingual. Their ducts open inside in the oral cavity of the
mouth.
1. Parotid Glands: These are situated on each side of the face below external auditory meatus. It
is a serous type of gland which secretes ptyalin. The parotid duct opens into the cheek of the
mouth on either side.
2. Submaxiliary or Submandibular Glands: They are situated on each side of the face under
the jaw. These are seromucous. i.e. mixed glands. Their ducts open on the tongue.
3. Sublingual Glands: These are situated below the tongue and have small ducts that open into
the floor of the mouth.
Saliva: It is the mixed secretion of all the glands in the oral cavity. It contains inorganic salts,
sodium chloride, potassium chloride and enzymes like ptyalin(salivary amylase), phosphatase,
lipase and mucin. The pH of salvia is usually neutral or slightly acidic (6.0 to 7.0).
Functions of saliva
1. It keeps the mouth moist and facilitates speech.
2. It helps in mastication of food and forms the bolus.
3. It dilutes hot and pungent substances and prevents injury to mouth. It also acts as a solvent.
Soluble substances are dissolved and taste buds appreciate the taste only when substances are in
liquid state.
4. It removes food particles and thus prevents the growth of microbes. It also serves as an
antiseptic to the mouth.
5. Ptyalin present in saliva splits starch into maltose.
6. Maltase changes maltose into glucose to some extent. So, if one chews food well he enjoys a
sweet taste of glucose.
7. Saliva helps in maintenance of water balance. If saliva stops, tongue becomes dry and man
becomes thirsty.
8. Saliva acts as buffer by maintaining the level of bicarbonate and phosphate in the blood and
thus changes the pH of blood, so as to keep up the consistency of blood pH.
PHARYNX: It is a tubal space situated between the mouth and the oesophagus. It is subdivided
into three parts: 1. Nasopharynx, 2. Oropharynx 3. Laryngopharynx.
OESOPHAGUS: It is a long hollow tube 25 cm in length and opens into the stomach at the
cardiac orifice. Food passes from the pharynx through the oesophagus to be finally pushed into
the stomach. The tube distends during the passage of food which is pushed downwards by
contraction of the muscles. Its passage is through the neck and chest and finally opens into the
stomach.
STOMACH: The stomach is continuous with the oesophagus at the cardiac sphincter and with
the duodenum at the pyloric sphincter. It has two curvatures. The lesser curvature is short, lies on
the posterior surface of the stomach and is the downwards continuation of the posterior wall of
the oesophagus. Just before the pyloric sphincter it curves upwards to complete the J shape.
Where the oesophagus joins the stomach the anterior region angles acutely upwards, curves
downwards forming the greater curvature then slightly upwards towards the pyloric sphincter.
The stomach is divided into three regions: the fundus, the body and the antrum. At the distal end
of the pyloric antrum is the pyloric sphincter, guarding the opening between the stomach and the
duodenum. When the stomach is inactive the pyloric sphincter is relaxed and open and when the
stomach contains food the sphincter is closed.
Gastric Glands: There are numerous microscopic glands which lie in the mucous membrane of
stomach and have 3 types of gland cells i.e. peptic or zymogen cell which secrete enzyme xyntic
cells which secrete HCl and mucous cell which secrete mucous. Its pH is 2 and acidic in nature.
About 2 to 3 liter gastric juice is secreted daily. It contains water, mucin, salt and two inactive
enzymes (propepsin and prorennin) and gastric lipase enzyme.
Secretion of gastric juice
There is always a small quantity of gastric juice present in the stomach, even when it contains no
food. This is known as fasting juice. Secretion reaches its maximum level about 1 hour after a
meal then declines to the fasting level after about 4 hours.
There are three phases of secretion of gastric juice:
1. Cephalic phase: The flow of juice occurs before food reaches the stomach and is due to reflex
stimulation of the vagus nerve initiated by the sight, smell or taste of food. When the vagus
nerves have been cut (vagotomy) this phase of gastric secretion stops.
2. Gastric phase: On stimulated by the presence of food, the enteroendocrine cells in the pyloric
antrum and duodenum secrete gastrin, a hormone which passes directly into the circulating
blood. Gastrin stimulates the gastric glands to produce more gastric juice. In this way the
secretion of digestive juice is continued after the completion of the meal and the end of the
cephalic phase. Gastrin secretion is suppressed when the pH in the pyloric antrum falls to about
1.5.
3. Intestinal phase. When the partially digested contents of the stomach reach the small intestine,
a hormone complex enterogastrone is produced by endocrine cells in the intestinal mucosa,
which slows down the secretion of gastric juice and reduces gastric motility. Two hormones
forming this complex are secretin and cholecystokinin (CCK). By slowing the emptying rate of
the stomach, the contents of the duodenum become more thoroughly mixed with bile and
pancreatic juice. This phase of gastric secretion is most marked when the meal has had a high fat
content. The rate at which the stomach empties depends to a large extent on the type of food
eaten. A carbohydrate meal leaves the stomach in 2 to 3 hours, a protein meal remains longer and
a fatty meal remains in the stomach longest.
Role of parasympathetic nervous system in control of acid secretion: Parasympathetic
neurons stimulate HCl secretion from the parietal cells through the release of acetylcholine.
Functions of Stomach
1. Mechanical Functions: (a) It acts as a reservoir of food. (b) Movement of the stomach helps in
mixing of food with the digestive juices. (c) It liquefies and propels the food further into the
duodenum (mechanical digestion).
2. Secretion: It secretes gastric juice which converts food into chyme and helps in digestion.
3. Antiseptic: Hydrochloric acid of gastric juice destroys microbes and prevents infection, thus
acting as an antiseptic.
4. Digestion: Gastric juice partially digests proteins and fats.
5. Absorption: Water, alcohol, glucose and certain drug are absorbed from the wall of the
stomach. Vitamin B12 is also absorbed form stomach with the help of extrinsic factor.
6. Excretion: It helps in the excretion of some toxins and drugs.
7. Reflex Functions: (a) Gastro-salivary reflex causes stimulation of the salivary juice. (b)
Gastro-iliac reflex which starts after the entry of food causes the starting of peristalsis in the
lower part of the ileum. (c) Gastric-colic reflex produces mass peristalsis after the eaten food. (d)
When food is in the stomach, pancreatic and biliary secretions are also stimulated.
LIVER: The liver is the largest gland in the body, weighing between 1 and 2.3 kg. It is situated
in the upper part of the abdominal cavity occupying the greater part of the right hypochondriac
region, part of the epigastric region and extending into the left hypochondriac region. Its upper
and anterior surfaces are smooth and curved to fit the under surface of the diaphragm, its
posterior surface is irregular in outline. The liver has four lobes. The two most obvious are the
large right lobe and the smaller, wedge-shaped, left lobe. The other two, the caudate and
quadrate lobes, are areas on the posterior surface.
Functions of the liver
Carbohydrate metabolism: Conversion of glucose to glycogen in the presence of insulin, and
converting liver glycogen back to glucose in the presence of glucagon.
Fat metabolism: Desaturation of fat, i.e. converts stored fat to a form in which it can be used by
the tissues to provide energy.
Protein metabolism: Deamination of amino acids
• Removes the nitrogenous portion from the amino acids not required for the formation of new
protein; urea is formed from this nitrogenous portion which is excreted in urine.
• Breaks down genetic material of worn-out cells of the body to form uric acid which is excreted
in the urine.
Transamination — removes the nitrogenous portion of amino acids and attaches it to other
carbohydrate molecules forming new non-essential amino acids.
Breakdown of erythrocytes and defense against microbes: This is carried out by phagocytic
Kupffer cells (hepatic macrophages) in the sinusoids.
Detoxification of drugs and noxious substances: These include ethanol (alcohol) and toxins
produced by microbes.
Production of heat: The liver uses a considerable amount of energy, has a high metabolic rate.
Secretion of bile: The hepatocytes synthesize the constituents of bile from the mixed arterial and
venous blood in the sinusoids. These include bile salts, bile pigments and cholesterol.
Functions of Bile:
1)
2)
3)
4)
5)
6)
7)
It is alkaline and helps in digesting and absorbing fat.
It emulsifies the fat into fat droplets.
It disinfects the food by checking the bacterial growth.
It creates an alkaline medium for digestion in intestine.
It helps in the absorption of fat soluble of vitamin i.e. Vitamin A, D, E and K.
It increases the solubility of fatty products.
It is stored in the gall bladder when there is no food in the duodenum for digestion.
Pancreas:
It is an elongated yellowish gland lying below the stomach and is often called heterocrine gland.
It is made of exocrine and endocrine tissues. Its exocrine tissue secretes enzymes while
endocrine secrete hormone. It secretes about 1 liter pancreatic juice daily which has 8.8 pH. It
contains sodium bicarbonate, three proenzymes i.e. trypsin, chymotrypsinogen and
procarboxypolypeptidases and several enzymes like pancreatic enzyme, pancreatic lipase and
nucleases.
SMALL INTESTINE: It is a coiled up tubular structure which consists of three parts:
Duodenum, Jejunum and Ileum.
It is about 5-7 meters long.
1.Duodenum: It is the first part of the small intestine and is a C- shaped tube. The descending
part of the duodenum contains openings of bile duct and pancreatic duct. Former carries bile and
later carries the pancreatic juice. They open jointly as a common-bile duct. Bile is secreted from
the liver. It is stored and concentrated in the gall bladder. Pancreatic juice is secreted by the
exocrine part of the pancreas. The main function of duodenum is partial digestion of food.
2. Jejunum: It is the continuation of duodenum and it forms two-fifth of the small intestine. It is
a coiled up structure and performs peristaltic movements because of its muscular coats. It is
bound behind by a fold of peritoneum called mesentery which carries the blood vessels, the
autonomic nerves and the lymphatic’s to jejunum. The main function of jejunum is digestion of
food. It however, also performs the function of absorption.
3. Ileum: It is the distal three-fifth part of the long and coiled up small intestine, it follows
jejunum and ends at caecum which is the beginning of large intestine. Ileum has similar structure
as jejunum but is has in addition many more villi.
There are number of Peyer’s patches in ileum. They are minute lymphoid structures which serve
to defend against the microbial invasion.
LARGE INTESTINE: Ileum of the small intestine merges in the large intestine. There is an
ileocaecal valve at the junction which guards the entry of food in the large intestine (colon)
Colon measures about 1.5 metres in length. It is subdivided into:
1 caecum with its appendix, 2. Ascending colon, 3.Transverse colon, 4. Descending colon and 5.
Sigmoid or pelvic colon.
Caecum is the first part of the colon, situated in the right iliac fossa. ileocaecal junction is
guarded by ileocaecal valve which opens one way and does not allow the food to travel back to
the small intestine.
Appendix is a worm-like blind projection from the caecum, projecting generally downwards. It
is less than 1 cm. in thickness and 5-8 cm. in length. The wall is full of lymph nodules and
lymphatic. Sometimes, the appendix gets inflamed and then it becomes a medical emergency. It
is a vestigeal organ and does not have any function in the body.
Ascending Colon: It is situated vertically on the right side of the abdomen. It continues from the
caecum and merges with the transverse colon under the inferior surface of the liver.
Transverse Colon: It lies transversely below the stomach. It is suspended by its own mesentery
from the posterior abdominal wall. It reaches to the left, below the spleen to merge (under the
splenic corner) with the descending colon.
Descending Colon: It is situated vertically on the left side of the abdomen. It continues from the
transverse colon and merges with the sigmoid colon.
Sigmoid Colon: It is also called pelvic colon because it lies in the pelvis.
Functions of Large Intestine:
1. Absorption of water and formation of solid stool.
2. Absorption of saline, glucose, amino acids and some drugs.
3. Secretion: Mucus is secreted by the goblet cells of the large intestine. This prevents
mechanical irritation and acts as a lubricant, making the reaction alkaline and decreasing the
acidity of bacterial fermentation.
4. Excretion: Heavy metals are excreted from the blood directly into the colon and are passed
out in the faeces.
5. Synthesis of vitamins by Bacteria: Colon has an established microflora. These bacteria
synthesize folic acid, cyanocobalamin (Vit B12) and some other vit. B factors. They also
synthesize Vit. K.
6. Microbial Digestion: Human body obtains its cytochrome pigment from the dead bacterial
products. Microbes present in colon digest away other pathogenic microbes and thus prevents the
infections.Some of the undigested products of food are digested by microbes present here.
Undigested carbohydrates, proteins and fats are attacked in the colon to produce some useful and
some toxic products. The later gives rise to the typical faecal odour. If these toxic substances are
absorbed, they will result in ill-health.
Rectum: It is a straight tube lying centrally in the pelvis, starting from the sigmoid colon and
ending in the anal canal which opens externally.
In the male, the rectum lies behind the urinary bladder, prostate and the seminal vesicles. In the
female, it lies behind the uterus and vagina. Rectum lies as a straight tube on the inner surface of
the sacrum and the coccyx. The mucus coat of the rectum has transverse and longitudinal folds.
The lower portion of the rectum is dilated and is called rectal ampulla.
ANUS: The rectum ends in the anus which is a small canal guarded by two sphincters. The
internal sphinctre is involuntary and the external sphincter is voluntary. It gives stretch sensation
and dilates during defecation and then it again contracts.
Intestinal Glands:
There are numerous microscopic glands present in the wall of intestine and are of two types i.e.
Crypts of lieberkuhn and Brunner’s gland.
Crypts of lieberkuhn are simple, tubular and occur throughout the small intestine between the
microvilli and secrete enzymes & mucus. The Brunner’s glands are tubular and occur only in the
duodenum below crypts of lieberkuhn. They only secrete alkaline watery fluid, mucus and little
enzyme.
PHYSIOLOGY OF DIGESTION
It includes the following steps:
Ingestion:
Food is taken into the buccal cavity through mouth with the help of hands.
Digestion:
It is a process in which the non- diffusible form of food products is converted into their diffusible
form with the help of digestive enzymes secreted by digestive glands that are associated with the
alimentary canal.
Basic Mechanism of Digestion:
The subunits of macromolecules of food are held together by anhydro bonds i.e. bonds formed
by the removal of water. Digestion of the macromolecules involves hydrolysis in which anhydro
bonds are broken by the addition of water with the help of hydrolytic enzymes.
(C6H10O5)n + H2O
n (C6H12O6)
Digestion of Carbohydrates:
Carbohydrates are the major contents of the animal diet. In the food of man the carbohydrates are
sucrose, disaccharides, lactose and starch which are digested in the alimentary canal as follows:
30% of starch is digested in the buccal cavity with the help of ptyalin and maltase present in the
saliva in the presence of Cl- as show below:
Starch
Ptyalin
Maltose
Maltase
Glucose
Semi digested food reach into stomach. Here no carbohydrate digesting enzymes are present. In
small intestine, carbohydrates are mixed with the enzymes secreted by the pancreas and intestinal
gland.
Pancreatic Enzymes: Amylase converts the starch into double sugar i.e. maltose, isomaltose
and limitdextrine which are further converted into glucose with the help of maltase, isomaltase
and limitdextrinase respectively.
Intestinal juices contain amylase, maltase, isomaltase, limit dextrinase which convert the starch
into glucose as follows :
Starch
Amylase
Maltose
Maltase
Starch
Amylase
Isomaltose
Isomaltase
Starch
Amylase
Limitdextrin
Glucose
Limitdextrinase
Glucose
Glucose
Digestion of Protein:
No protein is digested in the buccal cavity as the saliva does not contain any protein digesting
enzyme.
It is digested with the help of enzymes present in gastric juice of stomach, pancreatic juice and
intestinal juice present in intestine.
Gastric juice contains two proenzymes: propepsin and prorennin. Propepsin is converted into
pepsin by HCl which convert the protein into peptides in an acidic medium as shown below:
Propepsin
Protein
HCl
Pepsin
Pepsin
Peptide.
Prorennin is converted into rennin by HCl which convert the soluble milk protein (casein) into
insoluble compound called paracasein which is further converted into peptides by pepsin.
Prorennin
HCl
Rennin
Casein
Rennin
Paracasein
Pepsin
Peptides
From the stomach food reaches into the intestine where it is mixed with the pancreatic juice and
intestinal juice, and intestinal juice show its action which digests the protein in an alkaline
medium created by the bile juice. Pancreatic juice contains 2 proenzymes- trypsinogen,
chymotrypsinogen and enzyme carboxypolypeptidases.
Trypsinogen is converted into trypsin by a non digestive enzyme called enterokinase which
digests the protein into peptide.
Trypsinogen
Enterokinase
Trypsin
Protein
Trypsin
Peptide
Chymotrypsinogen is converted into chymotrypsin by trypsin which converts the protein into
peptides.
chymotrypsinogen Trypsin
Protein
Chymotrypsin
Chymotrypsin
Peptide
Carboxypolypeptidases hydrolyse the last peptide bond of the polypeptide chain to release its last
amino acid thereby changing the polypeptide into dipeptide or peptide.
Intestinal juice contains aminopeptidases and dipeptidases which completes the digestion of
protein by converting the dipeptides into amino acids.
Digestion of Fats:
1) No fat is digested in the buccal cavity as saliva does not contain any fat digesting
enzyme.
2) Fat is digested by lipase enzyme which is soluble in water while the fats and oils are
insoluble in water. Therefore, they must be emulsified i.e. broken into small droplets
which is done by bile juice.
3) Gastric juice contain mild lipase enzyme which hydrolyze little fat into fatty acid and
glycerol.
4) In the intestine, the fats are first emulsified by the bile juice which are then emulsified
progressively by the pancreatic and intestinal lipase into diglyceride then into
monoglyceride and finally into fatty acid & glycerol in an alkaline medium.
Fats
Mild lipase
Fatty acid + Glycerol
Pancreatic lipase
Fats Bile juice Emulsification of fats
Diglyceride
Intestinal lipase
Pancreatic lipase
Intestinal lipase
Fatty acid +Gycerol
Monoglyceride
alkaline medium
Digestion of Nucleic Acids:
1) No nucleic acid is digested in the buccal cavity and stomach as the saliva and gastric
juice do not contain any nucleic acid splitting enzyme. They are digested with the help of
nucleic acid splitting enzyme secreted by the pancreas and intestinal glands.
2) Pancreatic juice and intestinal juice contain nucleases (deoxyribonucleases DNAase &
ribonucleases RNAase), nucleotidases (deoxyribonucleotidases & ribonucleotidases),
nucleosidases (deoxyribonucleosidases & ribonucleosidases). These enzymes digest the
nucleic acid (DNA & RNA) & convert them into pentose sugar (dioxyribose & ribose) &
nitrogen base.
Absorption:
It is a process in which the digested food from the alimentary canal passes into the cells of living
organism. It mainly occurs in small intestine. For this purpose its internal surface area is
increased up to 75000 cm2 due to the formation of about 4 millions microvilli.
Absorption of food occurs by the following process:
1) Active absorption
2) Passive absorption
3) Facilitated absorption
Passive Absorption: It is a process in which the molecules of the substance move from their
higher concentration to the lower. i.e. down the concentration gradient without utilizing any
energy. No carrier protein is used and it is a slow process.
It is of following types:
i)
Diffusion: It is a process in which the molecules of a substance move from their
higher concentration to their lower concentration till the concentration becomes the
same in the space available. Minerals and vitamins of food are absorbed by this
process.
ii)
Osmosis: It is a process in which the molecules of solvent or water move from their
higher concentration to their lower concentration through the semi-permeable
membrane which does not allow the diffusion of solute molecule. Water is absorbed
by this process.
iii)
Pinocytosis: It is a process in which the large food droplets are absorbed through the
cell membrane by the process of invagination and often called drinking of cell. Large
food droplets are absorbed by this process.
Active Absorption: It is a process in which the molecules of a substance move even from their
low concentration to higher concentration.
Energy is utilized in this process which is obtained by the hydrolysis of ATP molecules in the
presence of ATPase enzyme.
A carrier protein is used during this process for the transport of material across the cell
membrane. Food substances which have high nutrition value eg. Glucose, amino acid, Na+,
galactose, pentose sugar, some fatty acid and nitrogenous bases are absorbed by this process.
Facilitated Absorption:
It is a process in which the molecules of fructose or substance move from their higher
concentration to their lower concentration with the help of carrier protein without utilizing any
energy. Fructose is absorbed by facilitated absorption.
Assimilation of Food:
It is a process in which the absorbed and digested food is converted into protoplasm or is
converted into some other form for storage.
Egestion: (Role of Large Intestine)
The removal of unabsorbed food and other wastes in the form of faeces through the anus is
called egestion.
Undigested and unabsorbed food entering in the large intestine contains 75% water, salts and
protein bodies. Water and salts are absorbed in the colon to convert the waste into faeces. Protein
containing substances are broken into amino acids by E.coli and are then absorbed.
E.coli bacteria also synthesize vitamin B and K.
Faeces are stored temporarily in the rectum from where it is passed out through anus and the
process is also called defecation.
Table : SUMMARY OF DIGESTION
Organ
Secretion
Acts upon
Effect or Products
Enzyme Action
of
Mouth
Amylase in saliva
Carbohydrates
(polysaccharides)
Disaccharides
Stomach
Hydrochloric acid
Pepsinogen
Pepsin
Pepsin
Proteins
Peptones/peptides
Gastric lipase
Emulsified fats
Fatty acids and glycerol
Gastrin
Stomach glands
Secretion of gastric juice
Mucus
Mucosa
Lubrication and protection
form HCI
Liver
Bile
Fat globule
Emulsification of fat
Pancreas
Sodium bicarbonate Intestinal fluid
Provides alkaline pH
Amylase
Carbohydrates
Disaccharides
Pancreatic lipase
Emulsified fats
Fatty acids and glycerol
Trypsin and
chymotrypsin
Carboxypolypeptidase Terminal amino acid at the
Proteins
end of peptides and amino
acids
Enterogastrone
Gastric glands
Secretin
Pancreatic gland
Inhibits gastric acid
secretion and motility
Stimulation of pancreatic
juice secretion rich in sodium
bicarbonate
Pancreozymin
Pancreatic glands
Secretion of enzymes
Small intestine
Cholecystokinin
Gall bladder
Expulsion of bile
Enterokinase
Trypsinogen
Trypsin
Maltase
Maltose
Glucose
Sucrase
Sucrose
Glucose and fructose
Lactase
Lactose
Glucose and galactose
DISORDERS OF THE DIGESTIVE SYSTEM
Nausea: It is the upsetting feeling of vomiting prior to vomit.
Vomiting: It is a sudden expulsion of the contents of the stomach.
Anorexia: It is the loss of appetite.
Constipation: It is a state in which defecation is delayed and hard stool is formed. It may be due
to ignoring or preventing defecation reflex or due to decreased colonic motility.
Diarrhoea: It is a condition in which there is frequent defecation usually of high fluid fecal
matter i.e watery stools. It is due to greater intestinal motility with less time for absorption and
thus the delivery of a large volume of fluid to the large intestine overloading its capacity to
absorb salts and water.
Gastritis: It is an acute or chronic inflammation of gastric mucosa due to any infection or
irritation.
Cholecystitis: t is an acute or chronic inflammation of gall bladder.
Heart burn: It is the burning sensation of the upper part of the oesophagus.
Gastroenteritis: It is manifested by symptoms like nausea, vomiting, anorexia and diarrhoea.
Dysphagia: It is the difficulty in swallowing due to impaired digestion of food or matter from
pharynx to stomach.
Peptic Ulcer: It is characterized by the ulceration of the mucous membrane occurring in the
areas where acid and pepsin is secreted in the stomach and/or duodenum. When in the stomach it
is called as gastric ulcer and when in the duodenum it is named as duodenal ulcer.
Appendicitis: It is the inflammation of the vermiform appendix which is the vestigial structure
at the ileo-caecal junction.
Peritonitis: it is acute inflammation of visceral and parietal peritoneum of the abdomen.
Flatulance: It is the accumulation of gas in the stomach and/ or intestine.
Haemorrhoids(Piles): It is the inflammation of the varicose veins in the mucous membrane of
the rectum or skin around the anus.
Fatty Liver: It is the accumulation of triglycerides in the liver.
Hepatitis: It is an inflammatory process in the liver characterized by hepatocellular necrosis
affecting all lobules of the liver.
Liver Cirrhosis: It is the hardening of the liver and characterized by the blocking of the liver
sinusoids thus affecting liver functions. It often produces ascities i.e free fluid in the abdomen.