HUMAN DIGESTIVE SYSTEM
1) The human digestive system consists of the alimentary or the digestive tract and associated glands.
2) It occupies a part of the thoracic cavity, abdominal cavity and part of the pelvis.
3) It is about 9m long in adults and has two openings, a superior opening called the mouth or oral cavity and an inferior opening called the anus.
4) Organs of the system are- oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
Organ /part Location
Structural features
Function
Oral cavity - Is the initial part of the alimentary 1) It is superiorly bounded by the bony hard palate and soft
tract and is the superior opening
palate, anteriorly by the lips, laterally by the gums and
of the tract.
teeth. Posteriorly it communicates with the pharynx.
2) The mucous membrane covering the oral cavity forms a
thick conical projection in the centre, at the junction of
the mouth and pharynx. This projection is called UVULA.
3) A pair of lymphoid tissue called tonsils is located
sideways and posterior to the uvula. Inflammation of the
tonsils is called tonsillitis.
Tongue
Is located at the base of the oral
1) The tongue is a highly mobile, muscular organ packed
1) Being a muscular organ, the tongue
cavity and is attached to the base
with voluntary muscles and covered by mucous
helps to convert the food in the mouth
by means of its root.
membrane.
into a soft rounded mass called BOLUS.
2) It is divided in a broad root, body, and apex.
2) The taste buds are gustatory in
3) The surface of tongue has numerous small projections
function.
called papillae which lodge the taste buds.
3) The tongue also helps in swallowing,
chewing and articulated speech.
Pharynx
Posteriorly the oral cavity opens
Is a 5” long muscular tube communicating anteriorly with
Is therefore a common passage for both
into a 5” long muscular tube
both nasal and oral cavities and posteriorly with both
air and bolus.
called pharynx
oesophagus and trachea.
Oesophagus Initial part lies in the neck region, 1) Is a 10” long muscular tube.
greater part lies in the thoracic
2) The oesophagus pierces the diaphragm, ethers the
cavity. It lies between trachea (in
abdominal cavity and ends at the cardiac orifice of the
front) and vertebral column
stomach.
(behind).
Stomach
It lies in the abdominal cavity, just 1) It is the most dilated part of the alimentary tract. It is Jbelow the diaphragm, to the left.
shaped highly muscular bag shaped structure.
2) It begins at the cardiac orifice where the oesophagus
ends and ends at the pyloric orifice, which opens into the
first part of the small intestine, the duodenum.
3) Both the openings are guarded by sphincters.
4) Sphincters are a ring of involuntary muscles located at
the opening of one organ into another. The sphincters
ensure unidirectional movement of substances from one
organ into another, thus preventing backflow.
5) The sphincters of the stomach close the orifices when
the food is being churned and digested in the stomach.
Thus preventing the food from spilling into oesophagus
or duodenum during the churning action of stomach.
6) The inner epithelial layer of the stomach is made up pf
columnar epithelial cells, that secrete plenty of mucus.
The inner lining of stomach thus has a thick layer of
mucus . this mucus layer protects the epithelial and
muscular layers of stomach from the action of gastric
juices.
7) The epithelial layer of the stomach is modified to form
gastric glands. Gastric glands secrete gastric juice into
the lumen of the stomach. Gastric juice contains
Hydrochloric acid, Pepsinogen , the inactive form of the
protein digesting enzyme, pepsin
It acts as a passage for bolus to enter the
stomach as it connects the pharynx to the
stomach.
1) The muscular action of the walls of the
stomach helps in the mechanical
digestion of food. This action converts
the bolus into a thick viscous mass
called chyme.
2) Stomach is the site where the initial
digestion of protein begins. The
enzyme pepsin present in the gastric
juice acts on proteins converting them
into proteoses and peptones.
Small
intestine
Is located in the abdominal cavity
and is bordered by the ascending,
transverse and descending colon
of the ;arge intestine.
Is a highly coiled muscular tube. It is distinguished into 3
regions- Duodenum, Jejunum and Ileum.
The inner lining of small intestine is drawn into finger like
projections called VILLI. The villi increase the surface area
for the absorption of nutrients. [Rest of the points refer text
book].
Refer text for structure and function
Large
intestine
Salivary
glands
Located in the abdominal cavity
bordering the small intestine
1) Parotid glands- situated just
Are accessory digestive glands. There are three pairs of
below and in front of each ear salivary glands –parotid glands, sub maxillary/sub, embedded in the cheek
mandibular glands, sublingual glands.
muscles. Its duct opens at the
second molar tooth. [ the virus
causing mumps infects these
glands]
2) Sub- maxillary glands-they are
present in the floor of the oral
cavity, lying close to the inner
side of the lower jaw.
3) Sublingual glands-situated
under the tongue in the oral
cavity. Its ducts open directly
into the floor of the oral cavity.
Site of complete digestion of food and
absorption of nutrients.
To secrete saliva.
FUNCTIONS OF SALIVA
1) Saliva contains water, mucus and
enzymes-ptyalin/salivary amylase and
Lysozyme. As saliva contains water, it
helps to keep the mouth moist thus
facilitating speech.
2) Saliva moistens the food and with the
help of tongue and teeth, helps
convert food into a soft rounded mass
called bolus.
3) Salivary amylase/ptyalin acts on starch
and converts it into the disaccharide ,
maltose.
4) Lysozyme is a bactericidal enzyme,
hence cleans the mouth and destroys
bacteria.
Pancreas
Liver
It lies transversally across the
posterior abdominal cavity
just behind stomach.
Is the digestive gland that is
located in the abdominal cavity,
just below the diaphragm, to the
right.
Is the second largest digestive gland. It is a grayish pink
organ.
Is the largest gland.
It secretes the digestive juice called
pancreatic juice. Pancreatic juice contains
the following enzymes- pancreatic
amylase, trypsinogen , the inactive form
of protein digesting enzyme trypsin, and
lipase or steapsin – the fat digesting
enzyme .
Refer text book