2. What Is Elementary System???
• It is the digestive system
• The system that is concerned with the digestion of foods
inside the body
• Each and every part of digestive system is concerned with the
digestion of foods that includes processing and break down of
food, enzymatic hydrolysis, maintaining optimum condition for
proper activity of enzymes
• Digestive canal also acts as the site of absorption of nutrition
into the bloodstream
3. Digestive Tract
• The human digestive tract is a long, coiled, muscular tube that
stretches from the mouth to the anus.
• From mouth to the anus, the human food tube or the
digestive tract is about nine meters long.
4. Digestive Tract
Oral cavity
• Main parts that are involved include teeth and tongue
Pharynx and Esophagus
Stomach
Small intestine
• Consists of the duodenum, the jejunum, and the ileum
Large Intestine
• Terminates in the rectum
6. Oral Cavity: Mouth
• The mouth opens to the outside at the lips and empties into
the throat at the rear
• Its boundaries are defined by the lips, cheeks, hard and soft
palates, and glottis
• Lower part of oral cavity is mostly filled by the tongue, a large
muscle firmly anchored to the floor of the mouth
• The oral cavity is entirely lined by mucous membranes
containing numerous small glands
• Main glands include the three pairs of salivary glands
7. Oral Cavity: Tongue
• The mammalian tongue consists of a mass of interwoven,
striated (striped) muscles together with glands and fat and
covered with mucous membrane, which varies in different
regions
• An important function of the tongue is taste sensation, which
is derived from taste receptor cells located in clusters within
taste buds
• Taste buds are innervated by nerves that respond to chemicals
from food in solution, thereby providing the sensation of taste
• There are five fundamental taste sensations: salty, sweet, sour
(acid), bitter, and umami, which represents the taste of amino
acids
8. Oral Cavity: Salivary Glands
• There are three major pairs of salivary glands: the parotid, the
submandibular, and the sublingual glands
• The parotid glands, the largest of the pairs, are located at the
side of the face, below and in front of each ear
• The submandibular glands, which are rounded in shape, lie
near the inner side of the lower jawbone
• The sublingual glands lie directly under the mucous
membrane covering the floor of the mouth beneath the
tongue
10. Pharynx
• The pharynx, or throat, is the passageway leading from the
mouth and nose to the esophagus and larynx
• The pharynx permits the passage of swallowed solids and
liquids into the esophagus
• The pharynx has roughly the form of a flattened funnel
• It is attached to the surrounding structures but is loose
enough to permit gliding of the pharyngeal wall against them
in the movements of swallowing
• There are three main divisions of the pharynx: the oral
pharynx, the nasal pharynx, and the laryngeal pharynx. The
latter two are airways, whereas the oral pharynx is shared by
both the respiratory and digestive tracts
11. Esophagus
• The esophagus is about 25 centimeters (10 inches) in length;
the width varies from 1.5 to 2 cm (about 1 inch).
• Anatomically, it lies behind the trachea and heart and in front
of the spinal column
• The esophagus contains four longitudinal layers of tissue- the
mucosa, submucosa, muscularis, and tunica adventitia
• The upper third of the esophagus is composed of striated
(voluntary) muscle. The middle third is a mixture of striated
and smooth (involuntary) muscle, and the lower third consists
only of smooth muscle
• The two sphincter muscles of the esophagus act like
drawstrings in closing channels
12. Stomach
• The stomach is located in the left upper part of the abdomen
immediately below the diaphragm
• The stomach is capable of dilating to accommodate more than one
liter of food or liquids without increasing pressure on the stomach
• The stomach is more or less concave on its right side, convex on its
left. The concave border is called the lesser curvature; the convex
border, the greater curvature
• When the stomach is empty, its mucosal lining is thrown into
numerous longitudinal folds, known as rugae
• The uppermost part of the stomach, located above the entrance of
the esophagus, is the fundus
• The largest part of the stomach is known simply as the body
• The antrum, the lowermost part of the stomach, is somewhat funnel
shaped, with its narrow end connecting with the pyloric canal, which
empties into the duodenum
13. Stomach Muscle
• The muscles of the stomach wall are arranged in three layers,
or coats
• The external coat, called the longitudinal muscle layer, is
continuous with the longitudinal muscle coat of the
esophagus
• The middle, or circular muscular layer, the strongest of the
three muscular layers, completely covers the stomach. At the
pyloric end of the stomach, the circular muscle layer becomes
greatly thickened to form the pyloric sphincter
• The innermost layer of smooth muscle is called the oblique
muscular layer
15. Gastric Mucosa
• The inner surface of the stomach is lined by a mucous
membrane known as the gastric mucosa
• The mucosa is always covered by a layer of thick mucus that is
secreted by tall columnar epithelial cells
• Gastric mucus is a glycoprotein that serves two purposes: the
lubrication of food masses in order to facilitate movement
within the stomach and the formation of a protective layer
over the lining epithelium of the stomach cavity
• The gastric mucosa contains six different types of cells
• In addition to the tall columnar surface epithelial cells, there
are five common cell types found in the various gastric glands
16. Cells In Gastric Mucosa
• Mucoid cells secrete gastric mucus and are common to all types of
gastric glands
• Zymogenic, or chief cells are located predominantly in gastric
glands in the body and fundic portions of the stomach. These cells
secrete pepsinogen, from which the proteolytic (protein-digesting)
enzyme pepsin is formed.
• Gastrin cells, also called G cells, are located throughout the
antrum. These endocrine cells secrete the acid stimulating
hormone gastrin
• Parietal, or oxyntic cells, found in the glands of the body and
fundic portions of the stomach, secrete hydrogen ions that
combine with chloride ions to form hydrochloric acid
• Endocrine cells called enterochromaffin-like cells (ECL cells)
secrete several substances, including the hormone serotonin
17. Small Intestine
• The small intestine is the principal organ of the digestive tract
• The small intestine, which is 670 to 760 cm (22 to 25 feet) in
length and 3 to 4 cm (1.2 to 1.6 inches) in diameter, is the
longest part of the digestive tract
• It begins at the pylorus, the juncture with the stomach, and
ends at the ileocecal valve, the juncture with the colon
• The main functional segments of the small intestine are the
duodenum, the jejunum, and the ileum
• The arrangement of the muscular coats of the small intestine
is uniform throughout the length of the organ.
• The inner, circular layer is thicker than the outer, longitudinal
layer
• The outermost layer of the small intestine is lined by the
peritoneum
18. Small Intestine: Duodenum
• The duodenum is 23 to 28 cm (9 to 11 inches) long and forms
a C-shaped curve that encircles the head of the pancreas
• Its first segment, known as the duodenal bulb, is the widest
part of the small intestine
• The second part of the duodenum runs vertically downward. It
is into this part through the duodenal papilla (papilla of
Vater) that the pancreatic juice and bile flow
• The third part of the duodenum runs horizontally while the
fourth part ascends then bends sharply downward and
forward to join the second part of the small intestine, the
jejunum
19. Small Intestine:
Jejunum and Ileum
• The jejunum forms the upper two-fifths of the rest of the
small intestine
• It, like the ileum, has numerous convolutions and is attached
to the posterior abdominal wall by the mesentery, an
extensive fold of serous-secreting membrane
• The ileum is the remaining three-fifths of the small intestine
• At its termination the ileum opens into the large intestine
20. Intestinal Mucosa
• Its total absorptive surface area is approximately 4,500 square
metres (5,400 square yards)
• This enormous absorptive surface is provided by the unique
structure of the mucosa, which is arranged in concentric folds.
These folds are known as plicae circulares which are
approximately 5 to 6 cm (2 inches) long and about 3 mm (0.1
inch) thick
• Plicae circulares are present throughout the small intestine
except in the first portion, the duodenal bulb
• Another feature of the mucosa that greatly multiplies its
surface area is that of tiny projections called villi
• The villi usually vary from 0.5 to 1 mm (0.02 to 0.04 inch) in
height
21. Intestinal Mucosa: Villi
• The villi are covered by a single layer of tall columnar cells
called goblet cells
• At the base of the mucosal villi are depressions called
intestinal glands, or Lieberkühn glands
• There are three other cell types in the Lieberkühn glands:
goblet cells, endocrine cells, and undifferentiated cells
• A remarkable feature of the mucosa villi is the rough,
specialized surface of the epithelial cells known as the brush
border
23. Large Intestine
• The large intestine, or colon, serves as a reservoir for the
liquids emptied into it from the small intestine
• The large intestine can be divided into the cecum, ascending
colon, transverse colon, descending colon, and sigmoid colon
• The cecum, the first part of the large intestine, is a sac with a
closed end
• Guarding the opening of the ileum into the cecum is the
ileocecal valve
• The ascending colon extends up from the cecum at the level
of the ileocecal valve to the bend in the colon called the
hepatic flexure
• The transverse colon is variable in position, depending largely
on the distention of the stomach
24. Large Intestine
• The descending colon passes down and in front of the left
kidney and the left side of the posterior abdominal wall to the
iliac crest
• The sigmoid colon is commonly divided into iliac and pelvic
parts
• The inner surface of the colon has many crypts that are lined
with mucous glands and numerous goblet cells
• The pelvic part of sigmoid colon finally forms into the rectum
