2. The digestive system is the collective name
used to describe the alimentary canal, its
accessory organs and a variety of digestive
processes that take place at different levels in
the canal.
Function : Break down food into simpler
molecules
High-energy adenosine triphosphate
3. Activities in the digestive
system
Ingestion
Propulsion
Digestion
Absorption
Elimination
4. Organs of the digestive system
Alimentary canal Accessory organs
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum and anal
canal
Three pairs of
salivary glands
The pancreas
The liver and biliary
tract
6. Basic structure of alimentary
canal
The walls of the
alimentary tract are
formed by four
layers of tissue:
Adventitia or serosa
– outer covering
Muscle layer (tunica
muscularis)
Submucosa (tunica
submucosa)
Mucosa – lining
(tunica mucosa)
7.
8. Tongue
Voluntary muscle
Extrinsic muscles –
for movement
Intrinsic muscle – for
changing size and
shape.
Papillae – containing
sensory receptors.
9. Teeth
They are embedded in
the alveoli or sockets of
the alveolar ridges of
the mandible and the
maxilla.
Used for mastication of
food.
8 incisors, 4 canines
(cuspids), 8 premolars
(bicuspids) and 12
molars (tricuspids) = 32
teeth
A. Deciduous teeth, B. Permanent
teeth
10. Salivary glands
There are three pairs of
salivary glands:
Parotid glands
Submandibular
glands
Sublingual glands
11. Composition of saliva:
Water
Mineral salts
Salivary amylase
Mucus
Lysozyme
Immunoglobulins
Blood-clothing factors
12. Pharynx
Divided into three parts, the nasopharynx,
oropharynx and the laryngopharynx.
Walls of pharynx has three layers:
1. Lining membrane (mucosa)
2. Middle layer consists of connective tissue and
contains blood and lymph vessels and nerves.
3. Outer muscle layer of involuntary muscles.
13. Oesophagus
25 cm long, 2 cm diameter and lies in median
plane in the thorax.
Present anterior to vertebral column and posterior
to the trachea and heart.
Oesophagus curves upwards before opening to
stomach.
14. Swallowing (deglutition)
Initiated voluntarily but completed by a reflex
(involuntary) action.
The mouth is closed, muscles of tongue and
cheeks push the food into the pharynx.
Muscles of pharynx are stimulated which
contracts and propels the bolus down into
oesophagus. This is coordinated by the medulla
and lower pons in brain stem.
15. The soft palate rises up and closes off the
nasopharynx; tongue and pharyngeal folds block
the way back into the mouth.
17. Stomach
It is a J-shaped
dilated portion of the
alimentary tract
epigastric, umbilical
and left
hypochondriac
regions of the
abdominal cavity.
18. Structure of the stomach
Two curvatures:
lesser and greater
curvature.
It divided into three
regions:
1. The fundus
2. The body
3. The pylorus
(Antrum)
20. Secretions of the stomach
Gastric acid (HCl) from parietal cells
Pepsin from chief cells
Mucus and bicarbonate from mucus neck cells
21. Small intestine
Comprised of three
continuous parts:
Duodenum 25cm
Secretions from gall
bladder and pancreas
– through duodenal
papilla
Jejunum 2m
Ileum 3m
22. Structure of small intestine
Mucosa – greater
surface area
Permanent circular
folds – villi and
microvilli
Goblet cells secrete
mucus
Cells replaced from
time to time
(replaced every 3-5
days)
23. A highly magnified diagram
of a villus in the small
intestine
Scanning electron
micrograph showing
many villi
24. Intestinal juice
1500 ml secreted daily
Consists of: water, mucus and mineral
salts
pH 7.8 and 8.0
25. Large intestine, rectum and
anus
Large intestine: 1.5 m long, 6.5 cm
diameter, begins at caecum and terminates
at the rectum.
Caecum
The colon – The ascending colon
The transverse colon
The descending colon
The sigmoid colon
Rectum (13 cm long)
Anal canal (3.8 cm long)
26.
27.
28.
29. Functions of large intestine
Absorption
Microbial activity : Synthesis of vitamin
K & folic acid, bacteria – Escherichia
coli, Enterobacter aerogenes,
Streptococcus faecalis and Clostridium
perfringens.
Mass movement – gastrocolic reflex
Defaecation
30. Digestive enzymes and their
functions
Oral cavity (pH 6.8) secretes Amylase: Digests
carbohydrates - Converts polysaccharides to
disaccharide maltose.
Stomach (pH 1.5 -3.5) secretes Pepsin:
Digests of proteins - Converts polypeptides
to tripeptides, dipeptides and amino acid.
31. Small intestine (pH 8) secretes
Trypsin and Chymotrypsin for digestion of
proteins - Converts polypeptides to
tripeptides, dipeptides and amino acid.
Pacreatic amylase for digestion of
carbohydrates - Converts polysaccharides to
disaccharide.
Lipase for digestion of fats - Converts fats
into fatty acids and glycerol.
Sucrase, maltase, lactase for complete
digestion of carbohydrates: converts
disaccharides such as sucrose, maltose and
lactose to monosaccharides.
32. Location Enzyme Function
Oral cavity
(pH 6.8)
Salivary Amylase
Digestion of carbohydrates:
Converts polysaccharides to
disaccharide maltose
Stomach
(pH 1.5 -3.5)
Pepsin
Digestion of proteins: Converts
polypeptides to tripeptides,
dipeptides and amino acid
Small intestine
(pH 8)
Activated
by
enterokinas
e
Trypsin Digestion of proteins: Converts
polypeptides to tripeptides,
dipeptides and amino acid
Chymotrypsi
n
Pacreatic amylase
Digestion of carbohydrates:
Converts polysaccharides to
disaccharide
Lipase
Digestion of fats:
Converts fats into fatty acids and
glycerol
Complete digestion of
Digestive enzymes and their
functions
33. Bile
Secreted by the liver
stored in gall bladder
Consists of: water,
mineral salts, mucus,
bile salts, bile
pigments (bilirubin),
cholesterol.
Enters the duodenum
through the
hepatopancreatic
sphincter – when
sphincter is closed
goes to the gall
bladder through cystic
34.
35. Gall Bladder
The gall bladder is a pear-shaped sac attached to
the posterior surface of the liver by connective
tissue.
It has a fundus or expanded end, a body or main
part and a neck, which is continuous with the
cystic duct.
Function:
reservoir for bile
concentration of the bile by up to 10- or 15-fold,
by absorption of water through the walls of the
gall bladder
release of stored bile.
36. Pancreas
Pale grey gland weighing about 60 gm, it is 12
to 15 cm long.
Situated in the epigastric and left
hypochondriac region.
Consists of a broad head, a body and a
narrow tail.
It is both an exocrine as well as an endocrine
gland.
37.
38. Liver
Largest gland in the body, weighing
between 1 to 2.3 kg.
Occupies right hypochondriac region
and part of epigastric region.
Liver has four lobes: Right and left lobe,
and other two the caudate and quadrate
lobe.
40. Functions of the Liver
The functions of the liver are so numerous
and important that we cannot survive
without it. The liver has six major
functions:
The liver manufactures the
anticoagulant heparin and most of the
other plasma proteins, such as
prothrombin and thrombin, that are
involved in the blood clotting
mechanism.
41. Liver cells contain various enzymes that either
break down poisons or transform them into
less harmful substances. If the body cannot
break down and excrete certain poisons, it
stores those poisons. When we digest
proteins into amino acids, the amino acids go
to the mitochondria to be converted into ATP.
This process produces ammonia as a waste
product, which is toxic to cells. The liver cells
convert ammonia to urea (harmless) that is
then excreted by the kidneys or the sweat
glands.
42. Excess glucose and other
monosaccharides can be stored as
glycogen (animal starch) or converted
to fat. When needed, the liver can then
transform glycogen and fat into glucose.
The liver stores glycogen, copper and
iron, as well as vitamins A, D, E, and K.
The liver produces bile salts that break
down fats. These bile salts are sent to
the duodenum of the small intestine for
