The Digestive System

1. UNIT VII
THE DIGESTIVE SYSTEM
SUBMITTED TO
MRS. JISHA S.
PRINCIPAL,
ST. CATHERINE’S HOSPITAL
& SCHOOL OF NURSING
SUBMITTED BY
MR. EARNEST LAMUEL
NURSING TUTOR,
ST. CATHERINE’S HOSPITAL
& SCHOOL OF NURSING

2. STRUCTURE AND
FUNCTIONS OF
ALIMENTARY TRACT AND
ITS ACCESSORY ORGANS

4. Introduction
The purpose of digestion is to change the foodstuffs by mechanical
and chemical action to simple forms, which can be easily absorbed
into blood and utilized by various tissues in the body. It is also
involved in maintaining the water and electrolyte balance of the
body. The gastrointestinal tract consists of an alimentary canal of 8
to 10 meters length, extending from the mouth to the anus, salivary
glands, liver and exocrine part of pancreas.

5. Introduction
The process of digestion involves breaking up of large particles of
food stuff like polysaccharides, fats and proteins into smaller particles
like monosaccharides, fatty acids and amino acids, which can be easily
absorbed. These absorbed products are metabolized for the
production of energy for various activities of the body two types of
organs
 Primary Digestive Organs
 Accessory Digestive Organs

6. Primary Digestive Organs
Primary digestive organs are
the organs where actual
digestion takes place. These
organs are
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine

8. Accessory Digestive Organs
Accessory digestive
organs are the organs
which help the primary
digestive organs in the
process of digestion.
These organs are
 Teeth
 Tongue
 Salivary glands
 Exocrine part of pancreas
 Liver
 Gall bladder

10. Process of Digestion
The process of digestion takes place in the elementary canal and is
assisted by some accessory organs like salivary glands, liver and
pancreas. Food is processed within the body in 4 steps
 Ingestion
 Digestion
 Absorption
 Excretion

11. PARTS OF
DIGESTIVE SYSTEM

12. ORAL
CAVITY

13. Oral Cavity
The oral cavity is the first part of the digestive tube. This contains
lips, cheeks, gums, teeth, palate, tongue and taste buds. Each of
these have their specific function contributing to the breaking
down, moistening and swallowing of the food particles.

15. Lips
Lips are fleshly folds lined externally by skin and internally by
mucous membrane. Each lip is composed of skin, superficial
fascia and orbicularis oris muscle, sub mucosa and mucous
membrane.

17. Cheeks
Cheeks are fleshly flaps, forming a large part of each side of the
face. The cheeks are composed of skin, buccinators muscle,
parotid duct, vessels and nerves, buccal pad of fat lies on the
buccinator.

19. Gums
Gums are the soft tissues which cover the alveolar processes of
the upper and lower jaws and surround the necks of the teeth.
The gums are made up of dense fibrous tissue, covered by
stratified squamous epithelium.

21. Teeth
Oral and paraoral tissues comprise of oral mucous membrane,
three pairs of major and innumerable minor salivary glands, jaw
bones bearing deciduous temporomandibular joint. Teeth
constitute approximately 20% of the surface area of mouth, the
upper teeth significantly more than the lower teeth.

23. Palate
Palate forms the arched roof of the oral cavity and the floor of
the nasal cavities. It separates the nasal cavities and nasopharynx
from the oral cavity.

25. Tongue
The tongue is a highly mobile muscular organ that can vary
greatly in shape. It is situated partly in the mouth and partly in
the oropharynx.

27. Taste Buds
They are small, barrel-shaped structures, arranged along the
sides of the grooves that surround the vallate or fungiform
papillae. A taste bud has a layered appearance like an onion
under the microscope. There is a pit, called inner taste pore, near
the surface of the bud.

29. Salivary Glands
The secretions of these glands help to keep the mouth moist, and
provide a protective and lubricant coat of mucus. Salivary glands are
divided in two divisions on the basis of presence or absence of duct –
Major salivary glands and Minor salivary glands and on the basis of
types of cells – Serous glands, Mucus glands and Mixed glands.

31. Saliva
Total amount of saliva secreted is 1500 ml/day. Contribution of each
major salutary gland is –
 Parotid glands – 25%
 Submaxillary glands – 70%
 Sublingual glands – 5%

33. PHARYNX

34. Pharynx
The pharynx is a wide muscular tube, situated behind the nose,
mouth and larynx. It is about 13 cm long. It's upper par is the
widest and lowest part is the narrowest part of gastrointestinal
tract. Inferiorly it continues with the esophagus through
oropharyngo junction.

36. Parts of Pharynx
The cavity of pharynx is divided into –
 The nasal part – Nasopharynx
 The oral part – Oropharynx
 The laryngeal part - Laryngopharynx

37. Nasopharynx
This part is situated behind the nose. It resembles the nose
structurally and functionally. It is respiratory in function, it is lined
by ciliated columnar epithelium. Anteriorly, it communicates with
the nasal cavities, through the posterior nasal apertures.
Inferiorly, it becomes continuous with the oropharynx.

38. Oropharynx
It is the middle part of the pharynx situated behind the oral
cavity. Superiorly it communicates with oral cavity through the
oropharyngeal isthmus. Inferiorly, it opens into the
laryngopharynx.

39. Laryngopharynx
Laryngopharynx is situated behind the larynx. It extends from the
upper border of epiglottis to the lower border of cricoid cartilage.
The literal wall of laryngopharynx shows a depression called the
piriform sinus, one on each side of the inlet of larynx.

40. ESOPHAGUS

41. Esophagus
The esophagus is a narrow part of the alimentary canal extending
from the lower end of pharynx to the cardiac orifice of stomach.
External Appearance - It is a tubular structure which remains
collapsed anteroposteriorly. It shows anteroposterior curvatures
which are similar to those of the vertebral column, to which it is
closely applied.
Dimensions – Its length is 25 cm and diameter is 1.5 cm
Parts - *Cervical *Thoracic * Abdominal

43. STOMACH

44. Stomach
Stomach is the most dilated part of the alimentary tract. It extends
from the cardiac end to the pyloric end. At its upper end, it is
continuous with esophagus and at the lower end, it is continuous with
the duodenum.
Position – In the supine position, the stomach occupies parts of the
epigastric, umbilical and left hypochondriac regions.
Shape – It is J shaped. The upper part is broader than the lower part.
It has two ends – upper cardiac and lower pyloric regions, two
borders or curvatures – right border or lesser curvature and left
border or greater curvature. The greater curvature is four to five times
longer than the lesser curvature.

46. Functions
 It acts as a reservoir of food.
 By its peristaltic activity, it makes the food particles smaller and
softer and mixes the food thoroughly with gastric juice.
 The gastric enzymes, produced by gastric glands have an
important role in digestion.
 The hydrochloric acid secreted by gastric glands destroys
many organisms present in food and drink.
 Stomach secretes the intrinsic factor necessary for the
absorption of Vitamin B12

47. Parts
Four descriptive purposes, stomach can be divided into five parts:
 Cardiac part
 Fundus
 Corpus
 Pylorus

48. SMALL & LARGE
INTESTINES

50. Small Intestine
The small intestine or small bowel is an organ in the gastrointestinal tract
where most of the end absorption of nutrients and minerals from food
takes place. It lies between the stomach and large intestine, and receives
bile and pancreatic juice through the pancreatic duct to aid in digestion.
Extent – The small intestine extends from the pylorus to the ileocecal
junction. It is about 6 meters long. Its structure is adapted for digestion
and absorption.

51. Parts
It is divided into
(a) an upper fixed part called the duodenum, approximately 25 cm long
(10 inches)
(b) a lower (distal) mobile part. The proximal two fifth of this long
convoluted tube is continuous with the duodenum and is known as the
Jejunum. The distal three-fifth is called Ileum. The coils of jejunum and
ileum the mesentery from the posterior abdominal wall.

52. Functions
 Segmental contractions in the small intestine help in mixing the chime
coming from stomach with pancreatic juice, bile and intestinal juice for
proper digestion.
 End stages of digestion occur in the small intestines.
 Final products of digestion, vitamins, minerals, water, etc. are absorbed
in the small intestine.
 Activation of trypsinogen occurs by enterokinase secreted by small
intestinal mucosa.

53. Large Intestine
The large intestine extends from the ileocecal junction to the
anus. It is about 1.5 m long. The large intestine has caecum is the
caecum, the ascending colon, transverse colon, descending colon
and sigmoid colon. In the angle between caecum and terminal
ileum, there is a narrow diverticulum called the vermiform
appendix.

54. Parts
Caecum – The caecum is the first part of the large intestine. It is a
broad, blind pouch about 5-7 cm in length. It is situated in the
right iliac fossa. It is continuous with the ascending colon
The Vermiform Appendix – This narrow, worm-like, blind tube
joins the caecum about 2.5 cm inferior to the ileocecal junction.

55. Parts
Ascending Colon – It ascends on the right side of the abdominal
cavity from the caecum to the right lobe of liver where it turns to
the left as the right colic flexure or hepatic flexure.
Transverse Colon – This part of the large intestine actually hangs
down as a loop. It is about 45 cm long. It is the largest and most
mobile part of the large intestine.

56. Parts
Descending Colon – It descends from the left colic flexure into the
sigmoid colon. It is about 25-30 cm long. The diameter of the
descending colon is lesser than that of the ascending colon.
Sigmoid Colon – The sigmoid colon forms as S shaped loop, usually
40 cm long. Sigmoid colon is the part of large intestine situated
between the descending colon and rectum.

57. Rectum
The rectum is the fixed terminal part of the large intestine. It
begins anterior to the level of the third sacral vertebra, it follows
the curve of the sacrum and coccyx and ends 3-4 cm
anteroinferior to the tip of the coccyx, where it becomes
continuous with the anal canal.

58. Anal Canal
It is the terminal part of large intestine. It is about 3.8 – 4 cm
long. It extends from the anorectal junction to the anus. The
anus is the surface opening of the anal canal, situated about
4 cm in front of the tip of the coccyx, in the cleft between the
two buttocks. The surrounding skin is pigmented, thrown into
folds and rich in apocrine glands.

59. ACCESSORY
ORGANS OF
DIGESTION

60. LIVER

62. Liver
It is the largest gland in the body. It is reddish brown in color,
highly vascular and weighs about 1.5 kg in adults.
It occupies the right hypochondrium and extends into the
epigastrium and left hypochondrium. It is wedge shaped. It
has an apex, base or right lateral surface, and anterior,
superior and inferior surfaces.

63. Functions of Liver
 The liver acts as an exocrine gland for the secretion of bile.
However, the architecture of the liver has greater resemblance to
that of an endocrine gland, the cells being in intimate relationship
to blood in sinusoids.
 The liver plays a prominent role in metabolism of carbohydrates,
proteins and fats. Metabolic functions include synthesis of plasma
proteins – fibrinogen and prothrombin, and the regulation of
blood glucose and lipids.
 The liver acts as a storehouse for various substances including
glucose, lipids, vitamins and iron. When necessary, the liver can
convert lipids and amino acids into glucose.

64. GALLBLADDER

66. Gallbladder
It is a pear shaped reservoir of bile, situated in a fossa on the
inferior surface of the right lobe of the liver. It is about 7-10
cm length, 3 cm broad at its widest part and about 30 ml in
capacity. It has three parts, fundus, body and neck.

67. Functions of Gallbladder
 Storage of bile
 Concentration of bile
 Alteration of pH of bile
 Secretion of mucus
 Maintenance of pressure in biliary system

68. PANCREAS

70. Pancreas
It is a gland that is partly exocrine and partly endocrine. It lies
transversely across the posterior abdominal wall at the level
of L1 and L2 vertebrae. It is situated behind the stomach and
retroperitoneally. In an adult, it is about 15-20mcm long,
weighing 90 g, and 3 cm broad.

71. Pancreatic Juices
It is the name given to the secretions of exocrine pancreas.
Normally about 1500 mL of pancreatic juice is produced
everyday.
 Trypsinogen
 Chymotrypsinogen
 Proelastase
 Procarboxypeptidases

72. THANK YOU