Digestive System

Prof . Mhaske S. A.
(M. Pharm Pharmacology)
For- First Year (B. Pharmacy)

Digestive System
By. Prof. Mhaske S.A. 2

1.1 Anatomy of G.I. Tract
Gastrointestinal Tract Definition
“Gastrointestinal tract is the part of an organ system in humans and other
animals that take in food, digest it, absorb nutrients and expel it out in the form
of faeces.”
The regions of Digestive Tract consists of:
 The mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine- Duodenum, Jejunum & ileum. With the liver, gall bladder,
& Pancreas.
 Large intestine- Cecum, colon, rectum and anal canal with mucous glands.
 The anus.

1.2 Functions of Digestive system
1. Ingestion : Introduction of solid or liquid food into the stomach. Route of
ingestion (Oral cavity).
2. Mastication : it is the process by which food taken into the mouth is
chewed by the teeth.
3. Propulsion in the digestive tract: movement of food from one end of the
digestive tract to the other. (Total time 24-36 hrs.)
a) Deglutition/ swallowing: movement of food & liquids, called bolus, from
the oral cavity into the esophagus.
b) Peristalsis: It is the process of muscle contractions that move food through
the digestive tract
4. Mixing : Mixing of food with saliva.
5. Secretion: food moves through digestive tract, secretion are added to
lubricate, liquefy, and digest the food.
6. Digestion: it is the breakdown of large organic molecule into their smaller
fragments. Such as carbohydrates into monosaccharides, proteins into
aminoacids & triglycerides into fatty acid & glycerol.

Digestion are of two types:
a) Mechanical digestion- is the process of physically breaking down
food into smaller pieces.
b) Chemical digestion- Chemical digestion is the process of chemically
breaking down food into simpler molecules. The process is carried out by
enzymes in the stomach and small intestines.
7. Absorption: it is the movement of molecules out of the digestive tract into
the circulation or into lymphatic system.
8. Elimination: (Defecation) process by which the waste products of
digestion are removed from the body.

1.3 Histology of Digestive Tract
 The digestive tube consists of four layers:

The digestive tube consists of four layers: These 4 tunics are present in all areas
of the digestive tract from the esophagus to the anus.
1) Mucosa
2) External serosa
3) Submucosa
4) Muscularis Externa
Mucosa: The innermost layer which consists of three layers:
A]Inner mucosa epithelium,
B] loose connective tissue (Lamina Propria]
C] Outer smooth muscle layer (muscularis mucosa)
Submucosa- A loose connective tissue layer, with larger blood vessels,
nerves, and can contain mucous secreting glands.
Muscularis- it consists of an inner layer of circular smooth muscle &
outer layer of longitudinal smooth muscle.
Serosa or Adventitia: Connective tissue layer.

2.1 Parts of Gastrointestinal
Tract
• It is also known as Gastrointestinal (Gl) tract or alimentary
canal or digestive tract.
1] Mouth (Oral cavity)
2] Pharynx (Throat)
3] Esophagus
4] Stomach (gaster)
5] Small intestine- Duodenum, Jejunum, ileum.
6] Large Intestine- Caecum,
Ascending colon
Transverse colon’
Descending colon
Sigmoid colon
7] Rectum
9
By. Prof. Mhaske S.A.

Mouth
10

1. Mouth:
Human mouth consists of following parts:
A] Vestibule- it is a slit like space bounded externally by lips & cheeks.
B] Oral cavity (Buccal cavity)- The mouth is also called the buccal cavity or
the oral cavity. mouth is the upper end, or the beginning of the alimentary
canal, which leads to the pharynx and to the oesophagus.
C] Palate- the roof of the oral cavity is called palate. Anterior part of the
palate is known as hard palate. Posterior part of the palate is called soft
palate.
D] Tongue- Tongue is a muscular organ in your mouth that aids in chewing,
speaking and breathing
E] Lips & Cheeks- lips also called labia. The outer surfaces of the lips are
covered by skin. Important in process of mastication & speech.
Functions of Mouth:
1] To receive food (Ingestion)
2] To prepare food for digestion
3] To Begin the digestion of starch.

2. Pharynx (Throat):
The pharynx is in the middle of the neck. It starts at the bottom of the
skull and is about 4.5 inches long.
The Pharynx consists of following parts:
1] The nasopharynx
2] The Oropharynx
3] Laryngopharynx
The pharynx anatomy includes:
 Nasopharynx: The top part of the throat connects to the nasal cavities (nose)
and lets air pass through.
 Oropharynx: The middle part of the throat connects to the oral cavity
(mouth). It allows air, food and fluid to pass through.
 Laryngopharynx (or hypopharynx): The bottom part of the throat is near
the larynx (or voice box). It regulates the passage of air to the lungs and food
and fluid to the esophagus
Functions: Delivers food and liquid to the digestive system.

3. Oesophagus:
The esophagus is the hollow, muscular tube that passes food and liquid from
your throat to your stomach.
Function:
Oesophagus is to carry food and liquid from your mouth to your stomach.

4. Stomach:
stomach is a J-shaped organ that digests food. It produces enzymes (substances
that create chemical reactions) and acids (digestive juices).
Stomach has Five Parts:
1. The cardia : is the top part of your stomach.the name is because it is
present near the heart. It contains the cardiac sphincter, which prevents
food from traveling back up your esophagus.
2. Fundus: it is commonly filled with air or gas.
3. Body: main part of stomach.
4. antrum lies below the body. It holds food until your stomach is ready to
send it to your small intestine.
5. Pylorus:is the bottom part of your stomach. It includes the pyloric
sphincter. This ring of tissue controls when and how your stomach
contents move to your small intestine.

Functions of Stomach
1] Received food form esophagus.
2] Mixed food with gastric juices.
3] Carries on limited absorption.
4]Moved food into small intestine.
5] Store meal for 2 hours.
6] pH of 2.0 with HCL added.
7] Protein digestion.
8] It promotes mechanical Digestion.
9] It also secretes gastrin (Hormone).

5. Small Intestine:
It is the longest part of the alimentary canal. The entire intestine is about 6 m
long (range 4.6- 9 m )
Parts of small intestine:
1] Duodenum: The duodenum is the first part of the small intestine. It is
about 25 cm long (means 12 inchs long). Two glands are associated
that is liver & pancreas. Most of digestion & absorption takes place.
2] Jejunum: The remaining small intestine lays in many coils inside the
lower abdominal cavity. Its middle section, called the jejunum. Is about
2.5 m long.
3] ileum: The ileum is the last and longest section of the small intestine
Is about 3.5 m long.
Functions of small intestine:
1.Absorption of nutrients into the blood & lymph.
2. Completion of digestion of protein, carbohydrates, fats & nucleic acids.
3. Secretion of digestive enzymes.

6. Large Intestine:
The large intestine is the last part of the gastrointestinal (GI) tract, the long,
tube-like pathway that food travels through your digestive system.
parts of the large intestine
1] Cecum
2] Colon
3] Rectum
4] Anus
1.Caecum: it is a pouch like structure, that is about 6 cm. cecum is the
beginning of the colon. small intestine feeds into the cecum through a small
channel in the side of it (the ileocecal valve), so the end of the cecum is
actually closed like a pouch.
2. Colon: the caecum leads into the colon, that is divided into 4 regions:
 Ascending colon
 Transverse colon
 Descending colon
 Sigmoid colon

Large Intestine:
3] Rectum:
The sigmoid colon opens into the rectum. The rectum comprises the last 20
cm. of the digestive tract, & terminates in the 2 cm long anal canal .
The opening of anal canal is called “anus”.
Functions of Large Intestine:
1)Absorption of water & electrolytes
2) Elimination of solid wastes.
3) Antibody production
4) Acid reduction

Large Intestine

3.1 Digestive Glands:
1] Salivary Glands: salivary glands discharge their secretion into the oral
cavity. In man the salivary glands has three pairs.
1) Parotid glands- largest salivary glands, which are situated near the ears.
2) Sublingual glands- smallest salivary glands located near the tongue.
3) Submandibular glands- also called “Maxillary glands.” it is the medium
sized salivary glands which are located at the angles of the lower jaw.

2] Gastric Glands: The gastric glands are glands in the lining of
the stomach that play an essential role in the process of Digestion.
Types:
1] chief cells or peptic cells (zymogenic cells): These cells secrete gastric
enzymes as proenzyme, pepsinogen, pro-renin. Also produce small amount of
gastric amylase & gastric lipase.
2] Oxyntic cells (Parietal cells): they are called Oxyntic cell because they
stain strongly with eosin.
3] Mucous cells (Goblet cells): These are present throughout the epithelium
& secrete mucus.

3. Liver
 It is the largest internal organ of the body.
26

Anatomy of Liver

 The liver is located in the upper right-hand portion of the abdominal cavity,
beneath the diaphragm, and on top of the stomach, right kidney, and
intestines.
 It is a cone shape. dark reddish-brown organ that weighs about 3 pounds.
There are 2 distinct sources that supply blood to the liver:
 Oxygenated blood flows in from the hepatic artery
 Nutrient-rich blood flows in from the hepatic portal vein
o The liver consists of 2 “major lobes called left & Right lobe”. andd two
minor lobes called “Caudate & quadrate.”
o Both are made up of 8 segments that consist of 1,000 lobules.
o Bile is secreted by the liver cells. (Hepatocytes).
Definition of Bile
Bile is a fluid that is made and released by the liver and stored in the gallbladder.
Bile helps with digestion. It breaks down fats into fatty acids, which can be taken
into the body by the digestive tract. Bile contains: Mostly cholesterol.

Functions of the liver
The liver regulates most chemical levels in the blood and excretes a
product called bile.
1) Production of bile: liver produces and secretes about 600-1000
mL of bile each day.
2) Production of certain proteins for blood plasma
3) Regulating blood clotting
4) Processing of hemoglobin for use of its iron content (the liver stores
iron)
5) Regulation of blood levels of amino acids, which form the building
blocks of proteins
6) Detoxification: the liver forms major line of defense against many of the
harmful substances.
7) Synthesis: the liver can also produce its own unique new compounds.

4. Gall Bladder

Gall Bladder
 It is sac like structure on the inferior surface of the liver.
 It is about 8 cm long and 4 cm wide.
 There are 3 layers from the gallbladder wall:
1] Inner mucosa- folded into rouge that allow the gallbladder to expand.
2] Muscularis- layer of smooth muscle that allow gallbladder to contract.
3] Serosa- outer covering , the cystic duct connect the gallbladder to common
bile duct.
Three main parts of gallbladder:
1) Fundus- large end that stores bile juices.
2) Body– The largest part of the gallbladder.
3) Neck- The gallbladder tapers to become continuous with the cystic
duct,
“Bile is continually secreted by the liver & flows to the gall bladder. About 40-
70 ml of bile can be stored in gall bladder.”

Functions of Bile
Bile is a watery greenish fluid mixture containing bile pigments, bile salts,
cholesterol & Phospholipids.
1] Neutralization of HCL:
2] Emulsification- sodium glycocholate & sodium taurocholate break the large
fat droplets into the smaller ones, this process is called emulsification.
3] Absorption of Fat & fat soluble vitamins: (vit A, D, E, & K ) in the small
intestine.
4] Excretion: Bile pigment are excretory product.
5] Prevention of decomposition: bile is alkaline hence it prevents the
decomposition of food by preventing the growth of bacteria on it.
6] Stimulation of peristalsis: bile increase peristalsis of the intestine.
7] Activation of lipase: Bile contains no enzyme but activates the enzyme
lipase.

5. Pancreas

5. Pancreas Gland
 The pancreas is a complex organ & composed of both endocrine &
exocrine tissues.
Anatomy includes:
 The pancreas consists of head, body, & Tail.
 Head: The wider part of the pancreas that sits in the curve of
your duodenum.
 Neck: The short part of the pancreas extending from the head.
 Body: The middle part of the pancreas between the head and
neck, which extends upward.
 Tail: The thinnest part of the pancreas, located near your spleen.
 It is soft, greyishpink colour which weight about 60 gm.
 2.5 cm diameter wide & 12-15 cm long.
 Located posterior to the stomach in the abdominal cavity.

 The pancreas performs two main functions:
 Exocrine function: Produces substances (enzymes) that help with
digestion.
 Endocrine function: Sends out hormones that control the amount of sugar
in your bloodstream.
 Exocrine system: The exocrine system consists of glands that
make substances that travel through a duct (tube). Besides the
pancreas, the exocrine system includes:
o Lacrimal glands (tear glands).
o Mammary glands.
o Mucous membranes.
o Prostate.
o Salivary glands.
o Sebaceous (oil) glands.
o Sweat glands.

 Endocrine function: The endocrine part of the pancreas consists of group
of islet of Langerhans. The human pancreas has about n million islets.
 Each islet of Langerhans consists of the following types cells.
 A] Alpha cells( α cells): constitute 15 % of langrhans. They produce
glucagon hormone.
 B] Beta cells (β cells): present middle of islet & About 65% of the islet of
Langerhans. They produce insulin hormone which converts glucose into
glycogen.
 C] Delta cells : constitute 5 % of the islet Langerhans. They secrete
somatostatin (ss) hormone.
 D] Pancreatic polypeptide cells: constitute about 15 % of Islet of
Langerhans. These cells secrete pancreatic polypeptide which
inhibit the release of pancreatic juice.
 Functions of Pancreas:
1] secretion of pancreatic juice which contains digestive juice.
2] Production of hormones.

Movements of GIT
1] Movements of the Stomach:
a) Stomach Filling : food enters the stomach , the rugae flatten, & stomach
volume increase.
 The pressure within the stomach doesn’t increase until the volume nears
maximum capacity because smooth muscle can stretch without increase
tension.
b) Mixing of stomach Contents: ingested food is mixed with the secretion of
stomach glands to form chyme.
 It that mixing peristaltic like contraction occur about every 20 sec. &
proceed from the body toward the pyloric sphincter to mix the ingested
material with the secretion of stomach.
 More solid material near the center of the stomach is pushed toward the
cardiac region for further digestion.
C) Stomach Emptying:
 liquid exit the stomach within 11/2- 21/2 hours after ingestion.
 After a typical meal, the stomach is empty within 3-4 hours.

2] Movement in the small intestine:
 Peristaltic contraction may proceed the entire length of the intestine. These
contraction both mix & propel substances through the small intestine as the
contraction proceed.
 The movement are slightly faster at the proximal end of the small intestine .
And slightly slower at the distal end.
3] Movement in the Large Intestine:
o Peristaltic waves are largely responsible for moving chyme along the
ascending colon.
o Large part of transverse & descending colon undergo strong peristaltic
contractions, is called mass movement.
chyme : semifluid mass of partly digested food expelled by
the stomach into the duodenum

Digestion & Absorption of Nutrients:
 Digestion: it is the breakdown of large organic molecule into their smaller
fragments.
Digestion are of two types:
a) Mechanical digestion- is the process of physically breaking down
food into smaller pieces.
b) Chemical digestion- Chemical digestion is the process of chemically
breaking down food into simpler molecules. The process is carried out
by enzymes in the stomach and small intestines.
 In chemical digestion, carbohydrates re broken down into
monosaccharide's, protein are broken down into amino acids & fat are
broken down into fatty acid.& glycerol.”.
 Most absorption are occurs in the duodenum & Jejunum but some
absorption occurs in the ileum also.
 Once the digestive product have been absorbed, they are transported to
other part of the body.

 What is Absorption: Absorption is the process by which the products
of digestion are absorbed by the blood to be supplied to the rest of the
body.
Digestion and Absorption of Carbohydrates:

Carbohydrates:
 Carbohydrates are one of the essential nutrients in the human diet.
There are two types of carbohydrates that can be digested by
the human digestive system– sugar and starch.
 Sugar is broken down in the gastrointestinal tract by the small
intestine and three enzymes present in the mouth, namely, Lactase,
Sucrase, and Maltase.
 starch is broken down with the help of the Amylase enzymes which
are present in the mouth and the stomach. After digestion,
carbohydrates are absorbed in the small intestine.
 chemical digestion of carbohydrates begins in the mouth.

Digestion and Absorption of Proteins:
Digestion and Absorption of Proteins:
 digestion of proteins takes place in
the stomach with the help of
protease and pepsin enzymes, which
breaks down the proteins into amino
acids.
 The process is facilitated by the
hydrochloric acid present in the
stomach.
 Amino acids are tiny elements which
get absorbed into the blood system
through the wall of the small
intestine.

Digestion and Absorption of Lipids
 These organic compounds are nonpolar molecules, which are soluble only
in nonpolar solvents and insoluble in water because water is a polar
molecule.
 The insoluble property of lipids makes the digestion and absorption of fats
a complicated process.
 It is broken down with the help of bile juice, which contains bile salts.
These broken molecules are then acted upon by pancreatic lipase, the major
fat-absorbing enzymes in the body.
 Pancreatic lipase breaks down fats into tiny molecules of free fatty acids
and monoglycerides, which are small enough for the small intestine to push
through into the bloodstream.

Water:
 About 9 L of water enters into digestive tract each day ,
 Out of which about 92 % is absorbed in the small intestine & another 6-7%
id absorbed in the large intestine.

Acid Production In the stomach
HCl is produced by the parietal cells of the stomach.
Hormonal Mechanism: It involves chemical signals that regulate stomach
secretions include the hormones gastrin, secretion, gastric-inhibitory
polypeptide & cholecystokinin , & histamine.
Regulation of stomach secretion is divided into 3 phases:
1] Cephalic
2] Gastric
3] Intestinal
1] Cephalic: Phase
 In this phase gastric regulation , the sensation of the taste & smell of food,
stimulation of receptor during the process of chewing & swllowing.
 Action potential are sent from the medulla along parasympathtic neurons within the
vagus (X) nerve to the stomach.
 In parietal cells, gastrin stimulates additional HCL & pepsinogen secretion.
 In addition gastrin stimulate endocrine cells to release histamine.
 Histamine stimulate parietal cells to secrete HCL.

2] Gastric Phase: 50-60% of total gastric acid secretion occurs during this
phase.
The greatest volume of gastric secretion is produce in this phase o f gastric
regulation.
The gastric phase is a period in which swallowed food and semi-
digested protein ( peptides and amino acids ) activate gastric activity.
 Gastric secretion is stimulated chiefly by three chemicals:
 Acetylcholine (ACh). This is secreted by the parasympathetic
nerve fibers of both the short and long reflex pathways.
 Histamine. This is a paracrine secretion from the enteroendocrine
cells in the gastric glands.
 Gastrin. This is a hormone produced by enteroendocrine G cells in
the pyloric glands.

3] Intestinal Phase:
 5-10% of gastric secretion occurs during this phase.
 The intestinal phase is a stage in which the duodenum responds to
arriving chyme and moderates gastric activity through hormones and
nervous reflexes.
 The duodenum initially enhances gastric secretion.

Pepsin Role In Protein Digestion
 Pepsin is a stomach enzyme that serves to digest proteins found in ingested
food.
 Gastric chief cells secrete pepsin as an inactive zymogen called pepsinogen.
1] Protein Digestion in the stomach:
 Pepsinogen is the inactive form of pepsin. It secreted by chief cells that line
the gastric glands.
 This enzyme is activated by hydrogen ions, H+ .
 These ions are form the hydrochloric acid secreted by parietal cells that also
line the gastric glands.
 Protein are long chains of amino acids.
 The enzyme pepsin hydrolyzes proteins into small fragment of various
sizes called peptides.

Protein Digestion in the small Intestine:
 The two major pancreatic enzymes that digest proteins in the small intestine
are chymotrypsin and trypsin
 Trypsin activates other protein-digesting enzymes called ”proteases” .
 These enzymes break proteins down to tripeptides, dipeptides, and
individual amino acids.
 The cells that line the small intestine release additional enzymes that also
contribute to the enzymatic digestion of polypeptides
 Tripeptides, dipeptides, and single amino acids enter the enterocytes of the
small intestine using active transport systems, which require ATP.
 Once inside, the tripeptides and dipeptides are all broken down to
single amino acids, which are absorbed into the bloodstream.

Disorder of GIT
1] Irritable bowel syndrome (IBS)
Irritable bowel syndrome (also called spastic colon, irritable colon, IBS, or
nervous stomach) is a functional condition where your intestinal muscles
contract more or less often than “normal.”
Symptoms of IBS include:
Abdominal pain and cramps, Excess gas, Constipation and/or diarrhea.
Change in bowel habits such as harder, looser, or more urgent stools than normal.
2] Constipation: Constipation is the term used to describe difficulty or
infrequency in passing stools (feces).
There are many different causes of constipation, such as dehydration, a lack of
fiber in the diet, pregnancy, inactivity.
Laxatives can help relieve constipation
3] Diarrhea: Symptoms of diarrhea include frequent, loose, watery stools
(feces) which are usually accompanied by an urgent need to go to the toilet.
Abdominal pain or cramping may also occur, and sometimes nausea or vomiting

Disorder of GIT
4] Peptic Ulcer Disease (PUD):
Peptic ulcer are is an umbrella term used to describe both gastric and
duodenal ulcers.
Symptoms: burning abdominal pain
Three types of peptic ulcer:
A ] Gastric Ulcer- it develop inside the stomach.
B] Esophageal Ulcer: It develop inside the esophagus.
C] Duodenal Ulcer: It develop in the upper section of the small intestine,
called the duodenum.
5] Enteritis: Enteritis is any inflammation of the intestines which result in
diarrhea, dehydration, fatigue, & weight loss.
6] Inflamm atory Bowel Disease: is a term for two conditions (Crohn's
disease and ulcerative colitis) that are characterized by chronic
inflammation of the gastrointestinal (GI) tract.
Symptoms: Diarrhea, abdominal pain and cramping may make it difficult
for you to eat

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