Chapter 1 Digestive System
Digestive System
The digestive system is a system of body which breakdown food into forms that can be
absorbed and used by body cells. It also absorbs water, vitamins, and minerals, and eliminates
wastes from the body. It breakdowns the larger molecules present in food into molecules that are
small enough to enter body cells by a process known as digestion. The organs which are
involved in the breakdown of food are collectively called the digestive system. The digestive
system is a tubular system which extends from the mouth to the anus.
The digestive system
ASBASJSM College of Pharmacy, Bela, Ropar 1
,Chapter 1 Digestive System
The digestive system can be divided into two parts:
1. The gastrointestinal (GI) tract, or alimentary canal (alimentary = nourishment), is a
continuous tube that extends from the mouth to the anus. Organs of the gastrointestinal tract
include the mouth, most of the pharynx, esophagus, stomach, small intestine, and large
intestine.
2. The accessory digestive organs are the organs which assist in digestion of food. These
include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Teeth aid in the
physical breakdown of food, and the tongue assists in chewing and swallowing. The other
accessory digestive organs never come into direct contact with food but they produce
secretions which aid in the chemical breakdown of food.
Functions of digestive system:
1. Ingestion: This process involves taking foods and liquids into the mouth (eating).
2. Secretion: Cells within the walls of the GI tract and accessory digestive organs secrete about 7
liters of water, acid, buffers, and enzymes into the tract which help in digestion of food.
3. Mixing and propulsion: Alternating contractions and relaxations of smooth muscle in the
walls of the GI tract mix food and secretions and propel them toward the anus. This capability of
the GI tract to mix and move material along its length is called motility.
4. Digestion: Digestion is of two types- Mechanical and Chemical digestion. In mechanical
digestion the teeth cut and grind food into smaller pieces. Then smooth muscles of the stomach
and small intestine break it into further small pieces and mix it thoroughly with digestive
enzymes. In chemical digestion the large carbohydrate, lipid, protein, and nucleic acid molecules
in food are split into smaller molecules by hydrolysis and digestive enzymes. Vitamins, ions,
cholesterol and water can be absorbed without chemical digestion.
5. Absorption: The entrance of ingested and secreted fluids, ions, and the products of digestion
into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed
substances pass into blood or lymph and circulate to cells throughout the body.
6. Defecation: Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI
tract, and digested materials that were not absorbed in their journey through the digestive tract
leave the body through the anus in a process called defecation. The eliminated material is termed
feces.
ASBASJSM College of Pharmacy, Bela, Ropar 2
,Chapter 1 Digestive System
Layers of GI Tract:
The wall of the GI tract has four layers tissues. These four layers (from deep to superficial) are
the mucosa, submucosa, muscularis, and serosa.
Layers of GIT
1. Mucosa: It is the inner lining of the GI tract. It is subdivided into 3 layers called Epithelium,
Lamina propria and muscularis mucosae.
The epithelium may be simple or stratified which plays role in protection, secretion and
absorption. Epithelial cells also secrete mucus and fluid into the lumen of the tract.
The lamina propria (lamina = thin) is areolar connective tissue containing many blood
and lymphatic vessels, which transfers the absorbed nutrients to the other tissues of the
body. The lamina propria also contains the mucosa-associated lymphatic tissue (MALT)
which contains immune system cells that protect against disease.
Muscularis musosae is a thin layer of smooth muscle fibers which increases the surface
area of the stomach and small intestine by many folds to enhance digestion and
absorption.
2. Submucosa: The submucosa consists of areolar connective tissue that binds the mucosa to
the muscularis. It contains many blood and lymphatic vessels that receive absorbed food
ASBASJSM College of Pharmacy, Bela, Ropar 3
, Chapter 1 Digestive System
molecules. It also contains an extensive network of neurons known as the submucosal plexus
or plexus of Meissner (a part of ENS).
3. Muscularis: Muscularis contains both skeletal muscles and smooth muscles. Skeletal
muscles help in voluntary swallowing and defecation. Involuntary contractions of the smooth
muscle help break down food, mix it with digestive secretions, and propel it along the tract.
The bundle of neurons present in this layeri is called myenteric plexus.
4. Serosa: It is a protective and connective tissue which forms the outer layer of the GI tract
which are suspended in the abdominopelvic cavity.
Peritonium:
It is the largest serous membrane. The peritoneum is divided into the parietal peritoneum, which
lines the wall of the abdominopelvic cavity, and the visceral peritoneum, which covers some of
the organs in the cavity and is their serosa.
Parts of digestive system:
1. Mouth:
Mouth is also called Oral cavity or Buccal cavity. It is formed by cheeks, hard palate, soft
palate and tongue.
Cheeks form lateral walls of mouth and are covered by skin from outside and mucous
membrane from inside.
Hard palate forms anterior portion of roof of mouth. Hard palate is made up of palatine and
maxillae bones covered with mucous membrane. Hard palate forms bony partition between
oral and nasal cavity.
Soft palate forms posterior portion of roof of mouth. It forms partition between oropharynx
and nasopharynx. Soft palate is also covered with mucous membrane.
Uvula is small muscular process hanging from soft palate. It prevents entrance of swallowed
food and liquid into nasal cavity.
ASBASJSM College of Pharmacy, Bela, Ropar 4
Digestive System
The digestive system is a system of body which breakdown food into forms that can be
absorbed and used by body cells. It also absorbs water, vitamins, and minerals, and eliminates
wastes from the body. It breakdowns the larger molecules present in food into molecules that are
small enough to enter body cells by a process known as digestion. The organs which are
involved in the breakdown of food are collectively called the digestive system. The digestive
system is a tubular system which extends from the mouth to the anus.
The digestive system
ASBASJSM College of Pharmacy, Bela, Ropar 1
,Chapter 1 Digestive System
The digestive system can be divided into two parts:
1. The gastrointestinal (GI) tract, or alimentary canal (alimentary = nourishment), is a
continuous tube that extends from the mouth to the anus. Organs of the gastrointestinal tract
include the mouth, most of the pharynx, esophagus, stomach, small intestine, and large
intestine.
2. The accessory digestive organs are the organs which assist in digestion of food. These
include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Teeth aid in the
physical breakdown of food, and the tongue assists in chewing and swallowing. The other
accessory digestive organs never come into direct contact with food but they produce
secretions which aid in the chemical breakdown of food.
Functions of digestive system:
1. Ingestion: This process involves taking foods and liquids into the mouth (eating).
2. Secretion: Cells within the walls of the GI tract and accessory digestive organs secrete about 7
liters of water, acid, buffers, and enzymes into the tract which help in digestion of food.
3. Mixing and propulsion: Alternating contractions and relaxations of smooth muscle in the
walls of the GI tract mix food and secretions and propel them toward the anus. This capability of
the GI tract to mix and move material along its length is called motility.
4. Digestion: Digestion is of two types- Mechanical and Chemical digestion. In mechanical
digestion the teeth cut and grind food into smaller pieces. Then smooth muscles of the stomach
and small intestine break it into further small pieces and mix it thoroughly with digestive
enzymes. In chemical digestion the large carbohydrate, lipid, protein, and nucleic acid molecules
in food are split into smaller molecules by hydrolysis and digestive enzymes. Vitamins, ions,
cholesterol and water can be absorbed without chemical digestion.
5. Absorption: The entrance of ingested and secreted fluids, ions, and the products of digestion
into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed
substances pass into blood or lymph and circulate to cells throughout the body.
6. Defecation: Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI
tract, and digested materials that were not absorbed in their journey through the digestive tract
leave the body through the anus in a process called defecation. The eliminated material is termed
feces.
ASBASJSM College of Pharmacy, Bela, Ropar 2
,Chapter 1 Digestive System
Layers of GI Tract:
The wall of the GI tract has four layers tissues. These four layers (from deep to superficial) are
the mucosa, submucosa, muscularis, and serosa.
Layers of GIT
1. Mucosa: It is the inner lining of the GI tract. It is subdivided into 3 layers called Epithelium,
Lamina propria and muscularis mucosae.
The epithelium may be simple or stratified which plays role in protection, secretion and
absorption. Epithelial cells also secrete mucus and fluid into the lumen of the tract.
The lamina propria (lamina = thin) is areolar connective tissue containing many blood
and lymphatic vessels, which transfers the absorbed nutrients to the other tissues of the
body. The lamina propria also contains the mucosa-associated lymphatic tissue (MALT)
which contains immune system cells that protect against disease.
Muscularis musosae is a thin layer of smooth muscle fibers which increases the surface
area of the stomach and small intestine by many folds to enhance digestion and
absorption.
2. Submucosa: The submucosa consists of areolar connective tissue that binds the mucosa to
the muscularis. It contains many blood and lymphatic vessels that receive absorbed food
ASBASJSM College of Pharmacy, Bela, Ropar 3
, Chapter 1 Digestive System
molecules. It also contains an extensive network of neurons known as the submucosal plexus
or plexus of Meissner (a part of ENS).
3. Muscularis: Muscularis contains both skeletal muscles and smooth muscles. Skeletal
muscles help in voluntary swallowing and defecation. Involuntary contractions of the smooth
muscle help break down food, mix it with digestive secretions, and propel it along the tract.
The bundle of neurons present in this layeri is called myenteric plexus.
4. Serosa: It is a protective and connective tissue which forms the outer layer of the GI tract
which are suspended in the abdominopelvic cavity.
Peritonium:
It is the largest serous membrane. The peritoneum is divided into the parietal peritoneum, which
lines the wall of the abdominopelvic cavity, and the visceral peritoneum, which covers some of
the organs in the cavity and is their serosa.
Parts of digestive system:
1. Mouth:
Mouth is also called Oral cavity or Buccal cavity. It is formed by cheeks, hard palate, soft
palate and tongue.
Cheeks form lateral walls of mouth and are covered by skin from outside and mucous
membrane from inside.
Hard palate forms anterior portion of roof of mouth. Hard palate is made up of palatine and
maxillae bones covered with mucous membrane. Hard palate forms bony partition between
oral and nasal cavity.
Soft palate forms posterior portion of roof of mouth. It forms partition between oropharynx
and nasopharynx. Soft palate is also covered with mucous membrane.
Uvula is small muscular process hanging from soft palate. It prevents entrance of swallowed
food and liquid into nasal cavity.
ASBASJSM College of Pharmacy, Bela, Ropar 4
