St. Wilfred's Institute Digestive System Presentation

St. Wilfred’s Institute of Pharmacy, Panvel.
DTE CODE: 3485
TOPIC : Digestive System
Presented by : Mr.Vijay Ikale(Ass.Professor Pharmacology)

Warm water / Warm lemon water
Banana
Eggs
Oats
Watermelons
Oranges
Mosambi

Ohh…I am feeling hungry…
क
ु छ खा लेते हैं

Feeling Energized
Feeling sleepy

Sleeping
Digestive system is inactive

Activation of digestive system
Warm water / Warm lemon water
Banana
Eggs
Oats
Watermelons
Oranges
Mosambi

Exercise
Ohh…I am feeling hungry…
क
ु छ लेकर खा लेते हैं

The body’s system for regulating food intake is coordinated by the hypothalamus. Within the
hypothalamus are nerve cells that when activated produce the sensation of hunger. They
do so by producing two proteins that cause hunger: neuropeptide Y (NPY) and agouti-
related peptide (AGRP).
Quite close to these nerve cells is another set of nerves that powerfully inhibit hunger.
They produce two different proteins that inhibit hunger: cocaine and amphetamine-regulated
transcript (CART) and melanocyte-stimulating hormone (α-MSH).
The activity is mainly controlled by hormones that circulate in the blood
Activation and deactivation come from tissues in various parts of the body that deal with
energy intake and storage, including the gut (which receives and digests the food), the fat
(which stores the energy) and the pancreas (which makes hormones that are involved in
energy storage, such as insulin).
Hormones in the blood
Let’s take a closer look at how each of these blood-circulating hormones work.
Ghrelin is made in the stomach. As the stomach empties, the release of Ghrelin increases. It
stimulates hunger by entering the brain and acting on the neurons in the hypothalamus to
increase the activity of the hunger-causing nerve cells and reducing the activity of hunger-
inhibiting cells. As soon as the stomach is filled, it decreases.
Insulin-like peptide 5 (ILP-5) was found to stimulate hunger. It is the second circulating
hormone to have this effect and is mainly produced in the colon.
Cholecystokinin (CCK) is produced in the upper small intestine in response to food and
gives a feeling of fullness.

Peptide YY, glucagon-like peptide 1 (GLP-1), oxyntomodulin and uroguanilin are
all made from the last part of the small intestine and make us feel full. They are
released in response to food in the gut.
Leptin is the most powerful appetite-suppressing hormone and is made in fat cells. The
more fat cells we have, the more leptin the body produces.
Amylin, insulin and pancreatic polypeptide are made in the pancreas. have shown
that when insulin enters the brain it inhibits hunger, telling the brain “there is enough
energy in the body, take a rest”.
Amylin is made in the same cells that make insulin (the beta cells). It has been shown
to inhibit food intake.
Pancreatic polypeptide inhibits hunger.
The hypothalamus also receives signals from pleasure pathways that use dopamine
and serotonin as messengers, which influence eating behaviour.
Once full, the stomach reduces the desire to eat both by lowering Ghrelin production
and by sending a message to the hypothalamus.
Levels of hormones that make us feel full – CCK, PYY, GLP-1, amylin and insulin – all
increase following a meal to reach a peak about 30 to 60 minutes later.
All the hormones then gradually return to their fasting levels three to four hours after a
meal.

What is digestion ?
Digestion is the breakdown of large
(complex) insoluble food molecules into
small (simple) water - soluble food
molecules with the help of digestive
processes such as chewing, churning and
enzymatic breakdown so that they can be
absorbed easily into blood stream.

Digestive System
 MOUTH
 ESOPHAGUS
 STOMACH
 SMALL INTESTINE
 LARGE INTESTINE
 ANUS

Basic terminologies
 Balanced Diet: Suitable amounts of all nutrients (carbohydrates, proteins, lipids, mineral
salts, vitamins, fiber and water) required for normal healthy living.
 Digestion: Large insoluble molecules of food are broken down into small molecules
 Egestion: Food that can’t be digested or absorbed is removed from the body.
 Ingestion: Food is taken into the alimentary canal (digestive system).
 Absorption: The small molecules are absorbed into the blood.
 Mechanical Digestion: Food is broken by the teeth and CHURNING movements of the
alimentary canal.
 Chemical Digestion: After the food has been chewed, the large molecules in it are broken
down into small soluble molecules with the help of enzymes.

The mouth or oral cavity is the first part of the digestive tract. It is adapted to receive food
by ingestion, break it into small particles by mastication, and mix it with saliva.
The lips, cheeks, and palate form the boundaries. The oral cavity contains the teeth
and tongue and receives the secretions from the salivary glands.
Mouth

Lubrication of food : Dry food entering the mouth is moistened and lubricated by saliva before
it can be made into a bolus ready for swallowing.
Enzymatic breakdown of food : Saliva contains the enzyme amylase that begins the breakdown
of complex sugars (Starch, Gums, Pectins and cellulose), reducing them to the disaccharide
maltose. The optimum pH for the action of salivary amylase is 6.8 (slightly acid).
Non-specific defense : Lysozyme, Immunoglobulins (secretory IgA and IgG) kills invading
microbes
Formation of a bolus. : When food is taken into the mouth it is masticated or chewed by the
teeth and moved round the mouth by the tongue and muscles of the cheeks. It is mixed with
saliva and formed into a soft mass or bolus ready for swallowing (deglutition).
Digestion in Oral Cavity

Oral Cavity
1. Tongue
2. Teeth
Homework

Esophagus
The esophagus is a muscular tube that serves as a passageway
between the pharynx and stomach , it empties into the stomach.
The mucosa layer of esophagus has glands that secrete mucus to
keep the lining moist and well lubricated to ease the passage of
food. Rhythmic contraction and relaxation of muscles
(Peristalsis) in esophagus allows movement of food through the
digestive tract.
Upper and lower esophageal sphincters control the movement of
food into and out of the esophagus.
Sphincters : A sphincter is a circular muscle that normally
maintains constriction of a natural body aperture

Stomach
The stomach is a muscular, J-shaped organ lies just below the diaphragm in the upper part of
the abdominal cavity.
The main divisions of the stomach are the following:
•Cardia
• Fundus
• Body of stomach
• Greater curvature
• Lesser curvature
• Cardiac sphincter
• Pyloric sphincter
• Pyloric canal
• Pyloric antrum
• Rugae of mucosa

Stomach
1. Cardia : The cardia (or cardiac region) is the point where the esophagus connects to
the stomach and through which food passes into the stomach
2. Fundus : The fundus is the enlarged portion to the left and above the cardiac region.
3. Body : The body, or corpus, is the central part of the stomach.
4. Pylorus : The funnel-shaped pylorus connects the stomach to the duodenum
a. Pyloric antrum : The wider end of the funnel, the pyloric antrum which connects to
the body of the stomach
b. Pyloric canal : The narrower end is called the pyloric canal which connects to the
duodenum.

Stomach
The wall of the digestive tract is composed of four principal layers: the mucosa, submucosa,
muscularis externa and serosa.

Stomach
The stomach mucosa’s epithelial lining consists only of surface mucus cells, which secrete a
protective coat of alkaline mucus. A vast number of gastric pits present on surface of the
epithelium mark the entry to each gastric gland, which secretes a complex digestive fluid
referred to as gastric juice.

Stomach
The submucosa is a dense, irregular layer of connective tissue with large blood vessels,
lymphatics, and nerves that supports the mucosa. The absorbed elements that pass through the
mucosa are picked up from the blood vessels of the submucosa.

Stomach
The muscularis externa is formed of outer longitudinal fibers, middle circular fibers and inner
oblique fibers. The muscularis externa is responsible for contractions and
peristaltic movement in the GI tract. These muscles cause food to move and CHURN together
with digestive enzymes down the GI tract
Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduce the
friction from muscle movements.

Stomach
The gastric glands are made up of different types of cells. The glands of the cardia and pylorus
are composed primarily of mucus-secreting cells. Cells that make up the pyloric antrum secrete
mucus and gastrin.
The much larger glands of the fundus and body of the stomach, the site of most chemical
digestion, produce most of the gastric secretions. These glands are made up of a variety of
secretory cells. These include parietal cells, chief cells, mucous neck cells, and
enteroendocrine cells.

Types and Functions of gastric gland
Types of gastric gland :
1. Oxyntic(fundus)
2. Cardiac
3. Pyloric
 Surface mucous cell : Forms protective coat on stomach surface to prevent damage
from stomach acid
 Parietal cells : Produces stomach acid ( HCl )
 Chief cell : Releases pepsinogen
 Enterochromaffin cell : Releases histamine
 D cells : Inhibit gastric secretion

Vagus nerve
Acetylcholine
Vagal activation of stomach

Vagus nerve
G cells Enterochromaffin cells
Stomach

M3(Gq)
H2(Gs)
CCK Receptor(Gq)

Physiology of Acid Production
 Acetylcholine, Histamine and Gastrin acts on M3, H2 and CCK receptor
 Activates GPCR pathway
 Stimulates fusion of water molecule with carbon dioxide in presence of carbonic
anhydrase to form carbonic acid
 Carbonic acid breaks into H+ and HCO3
–
a. H + exchange with K+ with the help of H+ - K+ ATPase pump
( Hydrogen ions enters stomach lumen)
b. HCO3
– exchange with Cl – ions
( Bicarbonate ions moves out and chloride ions enters parietal cell)
c. Chloride ions enters stomach with the help of chloride channel
 In stomach lumen Hydrogen ions fused to Chloride ions and forms HCL

Pepsin
Pepsin role in protein digestion
Pepsinogen is a powerful and abundant protein digestive enzyme secreted by
the gastric chief cells as a proenzyme (Inactive) and then converted by gastric acid in
the gastric lumen to the active enzyme pepsin.
Gastric gland of human stomach produces four types of pepsinogen: pepsinogen
I, pepsinogen II , cathepsin E, and cathepsin D. Pepsinogen is secreted from peptic (or
chief) cells.
Some pepsinogen is also secreted from mucosal cells in the pyloric antrum and the
duodenum. Gastric acid stimulates a local cholinergic reflex that triggers pepsinogen
secretion from peptic cells
Pepsinogen

Pepsin
Pepsin role in protein digestion
Pepsin helps in digestion of proteins.
Low pH (1.5 to 2) activates pepsin.
In the presence of gastric acid this proenzyme is converted into active
pepsin.
Pepsin is an endopeptidase that breaks down dietary proteins reaching the
stomach into amino acids. It functions by digesting peptide bonds, the
predominant chemical bonds found in proteins
PROTEIN

Functions of the stomach
 Temporary storage allowing time for the digestive enzymes to act .
 Chemical digestion — pepsins convert proteins to polypeptides
 Mechanical breakdown — the three smooth muscle layers enable the stomach to act as a
churn, gastric juice is added and the contents are liquefied to chyme (The thick fluid mass of
partially digested food)
 Limited absorption of water, alcohol and some lipid soluble drugs
 Non-specific defense against microbes — provided by hydrochloric acid in gastric juice.
Vomiting may be a response to ingestion of gastric irritants, e.g. Microbes or chemicals
 Production of intrinsic factor needed for absorption of vitamin B12 in the terminal
ileum
 Regulation of the passage of gastric contents into the duodenum. When the chyme is
sufficiently acidified and liquefied, the pyloric antrum forces small jets of gastric contents
through the pyloric sphincter into the duodenum.

Small Intestine
The small intestine extends from the pyloric sphincter to the ileocecal valve, where it
empties into the large intestine. The small intestine finishes the process of digestion,
absorbs the nutrients, and passes the residue on to the large intestine.
The liver, gallbladder, and pancreas are accessory organs of the digestive system that
are closely associated with the small intestine. Exocrine cells in the mucosa of the small
intestine secrete mucus, peptidase, sucrase, maltase, lactase, lipase, and
enterokinase(activation of trypsinogen). Endocrine cells
secrete cholecystokinin and secretin(Inhibit motility and acid release)
Anatomy of the Small Intestine :
The small intestine is a tube measuring about 2.5 cm in diameter. The complete small
intestine is approximately 525 cm (Nearly 20 feet) long and coiled in loops, which fill
most of the abdominal cavity.
1. Duodenum : The duodenum is about 25 cm long and curves around the head of the
pancreas. Secretions from the gall bladder and pancreas are released into the duodenum.
The opening into the duodenum is guarded by the hepatopancreatic sphincter
2. Jejunum : The jejunum is the middle section of the small intestine and is about 2
meters long.
3. Ileum : The ileum, or terminal section, is about 3 meters long and ends at the
ileocecal valve, which controls the flow of material from the ileum to the Caecum, the
first part of the large intestine, and prevents regurgitation.

Small Intestine
Pyloric sphincter
ileocecal valve

Large Intestine
The large intestine. This is about 1.5 meters long.
Colon is divided into the Caecum, rectum and anal canal.
Caecum : This is the first part of the colon. . It is usually about 13 cm long. It contains
more lymphoid tissue
Colon : Ascending colon, Transverse colon, Descending colon, Sigmoid colon
Rectum : This is a slightly dilated section of the colon about 13 cm long. It starts from
the sigmoid colon and terminates in the anal canal.

Large Intestine
Anal canal : This is a short passage about 4 cm long in the adult and leads from the
rectum to the exterior. Two sphincter muscles control the anus; the internal sphincter,
consisting of smooth muscle fibers, is under the control of the autonomic nervous
system and the external sphincter, formed by skeletal muscle, is under voluntary
control
Defecation : Defecation is the term given for the act of expelling feces from the
digestive tract via the anus

Functions of Large Intestine
1. Absorption of water takes place in the large intestine
2. Mineral salts, vitamins and some drugs are also absorbed into the blood capillaries
from the large intestine.
3. Microbial activity : The large intestine is heavily colonized by certain types of
bacteria, which synthesize vitamin K and folic acid. They include Escherichia coli,
Enterobacter aerogenes, Streptococcus faecalis and Clostridium perfringens .
4. They may become pathogenic if transferred to another part of the body, e.g.
Escherichia coli may cause cystitis if it gains access to the urinary bladder.
5. Hydrogen, carbon dioxide and methane are produced by bacterial fermentation of
unabsorbed nutrients, especially carbohydrate.
6. Gases pass out of the bowel as flatus.

Functions of Large Intestine
The large intestine does not exhibit peristaltic movement as it is seen in other parts of
the digestive tract. Only at fairly long intervals (about twice an hour) does a wave of
strong peristalsis sweep along the transverse colon forcing its contents into the
descending and sigmoid colons. This is known as mass movement and it is often
precipitated by the entry of food into the stomach

Liver
 The liver is the largest gland in the body, weighing between 1 and 2.3 kg. It is
situated in the upper part of the abdominal cavity.
The liver is connected to two large blood vessels: the hepatic artery and the portal
vein. The hepatic portal vein supplies 75% of the blood to the liver, while the hepatic
arteries supply the remaining 25%.
 Traditionally, the liver is divided into four lobes: left, right, caudate, and quadrate.
The lobes are further divided into lobules. Each lobule is made up of millions of hepatic
cells that are the basic metabolic cells of the liver.

Liver
Hepatocytes are unique in that they are one of the few types of cells in the human body
that are capable of regeneration.
Hepatocytes are involved in:
1. Protein synthesis
2. Protein storage
3. The transformation of carbohydrates
4. The synthesis of cholesterol, bile salts, and phospholipids.
5. Detoxification, modification, and excretion of exogenous and endogenous
substances.

Liver
Approximately half of the liver’s oxygen demand is met by the hepatic portal vein, and
half is met by the hepatic arteries.
The hepatic portal system connects the capillaries of the gastrointestinal tract with the
capillaries in the liver. Nutrient-rich blood leaves the gastrointestinal tract and is first
brought to the liver for processing before being sent to the heart.
Bile :
 Bile is a brownish-yellow or greenish-yellow secretion produced by the liver, stored
in the gallbladder, and discharged into the duodenum, where it aids the process of
digestion and the absorption of lipids in the small intestine.
 Bile is a composition of the following materials: water (85%), bile salts (10%),
mucus and pigments (3%), fats (1%), inorganic salts (0.7%), and cholesterol (0.3%).
 Bile can either drain directly into the duodenum or be temporarily stored in the
gallbladder. Bile, which is alkaline, also has the function of neutralizing any excess
stomach acid in the small intestine.

Functions of Liver
1. Carbohydrate metabolism. Conversion of glucose to glycogen in the presence of
insulin, and converting liver glycogen back to glucose in the presence of glucagon .
2. Fat metabolism : Desaturation of fat, i.e. converts stored fat to a form in which it
can be used by the tissues to provide energy.
3. Protein metabolism : Deamination of amino acid
4. Breakdown of erythrocytes and defence against microbes : This is carried out by
phagocytic Kupffer cells (hepatic macrophages) in the sinusoids.
5. Detoxification of drugs and noxious substances : These include ethanol (alcohol)
and toxins produced by microbes.
6. Metabolism of ethanol : This follows consumption of alcoholic drinks.
7. Inactivation of hormones: These include insulin, glucagon, cortisol, aldosterone,
thyroid and sex hormones.
8. Synthesis of vitamin A from carotene. Carotene is the provitamin found in some
plants, e.g. carrots and green leaves of vegetables.

Pancrease
The pancreatic islets each contain four varieties of cells:
1. The alpha cell (20 %) produces the glucagon hormone. Low blood glucose levels
stimulate the release of glucagon. It increases level of glucose in blood by stimulating
the process of glycogenolysis.
2. The beta cell (75 %) produces the hormone insulin which decreases excessive blood
glucose level by increasing uptake and metabolism of glucose.
3. The delta cell (4 %) secretes the peptide hormone somatostatin. It is an inhibiting
hormone, pancreatic somatostatin inhibits the release of both glucagon and insulin.
4. The pancreatic polypeptide cell (PP cell) accounts for about 1 % of islet cells and secretes
the pancreatic polypeptide hormone. It is thought to play a role in appetite, as well as in the
regulation of pancreatic exocrine and endocrine secretions.
Pancreatic polypeptide released following a meal may reduce further food consumption.

Pancrease
Regulation of Blood Glucose Levels by Insulin and Glucagon :
Glucose is utilized in cellular respiration as a fuel for cells of the body. The body
derives glucose from the breakdown of the carbohydrate-containing foods and drinks
we consume.
Glucose not immediately taken up by cells for fuel can be stored by the liver and
muscles as glycogen, or converted to triglycerides and stored in the adipose tissue.
Hormones regulate both the storage and the utilization of glucose as required.
Receptors located in the pancreas sense blood glucose levels, and subsequently the
pancreatic cells secrete glucagon or insulin to maintain appropriate blood glucose.

Pancrease
Glucagon
Receptors in the pancreas can sense the decline in blood glucose levels such as,
During periods of fasting
During prolonged labor or exercise .
In response, the alpha cells of the pancreas secrete the hormone glucagon, which has
several effects:
1. Glucagon stimulates the liver to convert its stores of glycogen back into glucose.
This response is known as glycogenolysis. The glucose is then released into the
circulation for use by cells throughout the body.
2. Glucagon stimulates the liver to take up amino acids from the blood and convert
them into glucose. This response is known as gluconeogenesis.
3. Glucagon stimulates lipolysis : The breakdown of stored triglycerides into free fatty
acids and glycerol. Some of the free glycerol released into the bloodstream travels to
the liver, which converts the glycerol into glucose. This is also a form of
gluconeogenesis.

Pancrease
Insulin :
The presence of food in the intestine triggers the release of gastrointestinal tract hormones such
as glucose-dependent insulinotropic peptide. This is in turn the initial trigger for insulin
production and secretion by the beta cells of the pancreas. Once nutrient absorption occurs, the
resulting increase in blood glucose levels further stimulates insulin secretion.
The primary function of insulin is to facilitate the uptake of glucose into body cells. Red blood
cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have
insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although
all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal
muscle cells and adipose cells are the primary targets of insulin.

Salivary gland
Human salivary glands (SG) are fundamental for the maintenance of the oral cavity homeostasis.
They synthesize and secrete saliva, a multi‐functional fluid, which provides mucosal lubrication,
salivary electrolytes, antibacterial compounds and various enzymes to protect the oral mucosa
and teeth surface.
Major salivary glands consist of three pairs of glands known as parotid, submandibular, and
sublingual glands; together they are responsible for 90% of the total saliva. Minor salivary
glands secrete <10% of the total secretion, this secretion serves as the main lubricant saliva due
to its protective and mucous components

Salivary gland
The ductal network of salivary gland is made up of different types of ducts
(intercalated, striated and excretory ducts).
Intercalated ducts are the first structures to receive the initial secretion, which is then
conveyed to the striated ducts, where several electrolytic changes occur between the
salivary fluid and the extracellular matrix via plasma membrane.
As the saliva turns more hypotonic, wide extralobular excretory ducts collect all fluid
from the glandular lobules, and secrete it to the oral cavity.

Salivary gland
Major salivary glands
1. Parotid glands
Human parotid glands are the major salivary glands (average weight: 25–30 g) located
on each side of the head, behind the external auditory canal of the mandible and the
skull base. Parotid glands are exclusively formed by serous acini, which secrete
aqueous saliva, rich in amylase, sulfomucins and sialomucins . The salivary secretion
parotid glands is stimulated by sympathetic nerves and the auriculotemporal plexus
Secretions are of 2 types : -
1. Serous – Watery fluid rich in Proteins
2. Mucus - Watery fluid contains mucin
Acini : Means a rounded secretory cells

Salivary gland
Submandibular glands :
Representing the second largest pair of human salivary glands, submandibular glands range in
weight from 7 to 15 g and are located in the submandibular triangle behind the free insertion of
the mylohyoid muscle.
Regarding the salivary secretion, submandibular glands are composed of mixed acini with
mucous and serous components. In general, the serous acini are predominant, although the
proportion may vary among lobes . Submandibular glands contribute substantially to the amount
of secreted saliva within the oral cavity, secreting a viscous saliva composed mainly of
glycoproteins sulfated cystatins and neuronal and epidermal growth factors, promoting
lubrication and protection of the oral mucosa. The neural component which stimulates the
submandibular gland occurs via facial and lingual branches of the mandibular nerve and
the sympathetic trunk, arising from the submandibular ganglion . The intercalated ducts of
the submandibular parenchyma are shorter compared to the parotid gland, whereas striated ducts
are more branched and extensive.

Salivary gland
Sublingual glands
Human sublingual glands are the last pair of major glands to form.
With an average weight of ∼3 g, the sublingual glands represent the smallest group of
the major salivary glands.
They are deeply located between the connective tissue of the floor of the mouth and the
mylohyoid muscle .The sublingual glands present predominantly mucous acinar cells
and serous acini are rarely found.

Salivary gland
Minor salivary glands
Minor salivary glands are located throughout oral submucosa, except in the gum and hard palate. They are
predominantly formed by mucous acini that are surrounded by loose connective tissue.
Importantly, the salivary secretion from minor glands usually occurs homogeneously through several small
ducts spread over the oral mucosal surface, instead of being collected by a single large duct, which
contributes to an efficient lubrication of the oral cavity
Paradoxically, minor salivary glands are considered the most important for the mucosal protective and
lubricant functions due to their saliva composition .Representing 6–10% of the daily secretion of saliva,
minor salivary glands play a crucial role in the protective mechanisms of oral mucosa and enamel surface,
where saliva forms the dental biofilm. They produce about 70% of the salivary mucins and significant
quantities of immunoglobulins (mainly IgA), salivary acid phosphatase and lysozymes, preventing
colonization of microorganisms on the teeth surface and the occurrence of infections

Process of Digestion
Digestion in oral cavity :
Digestion begins in the mouth. When you chew your food it is mixed with saliva, which not only supplies
moisture but also the carbohydrate-digesting enzyme, amylase. When you eat raw food, its enzymes work
with the salivary amylase to begin digestion.
Enzymatic breakdown of food : Saliva contains the enzyme amylase that begins the breakdown of complex
sugars, reducing them to the disaccharide maltose. The optimum pH for the action of salivary amylase is 6.8
(slightly acid).
Non-specific defense : Lysozyme, Immunoglobulins kills invading microbes
When you swallow, your tongue pushes the food into your throat. A small flap of tissue, called the epiglottis,
folds over your windpipe to prevent choking and the food passes into your esophagus. Once you begin
swallowing, the process becomes automatic. Your brain signals the muscles of the esophagus and peristalsis
begins. When food reaches the end of your esophagus, a ringlike muscle—called the lower
esophageal sphincter —relaxes and lets food pass into your stomach.

Digestion in Stomach : After food enters your stomach, the stomach muscles mix the food and liquid
with digestive juices. In the stomach, food undergoes chemical and mechanical digestion.
Mechanical digestion : Here, peristaltic contractions (mechanical digestion) churn the bolus, which mixes
with strong digestive juices that the stomach lining cells secrete (chemical digestion). The stomach walls
contain three layers of smooth muscle arranged in longitudinal, circular, and oblique (diagonal) rows. These
muscles allow the stomach to squeeze and churn the food during mechanical digestion.
Chemical digestion : Powerful hydrochloric acid in the stomach helps break down the bolus into a liquid
called chyme. A thick mucus layer that lines the stomach walls prevents the stomach from digesting itself.
When mucus is limited, an ulcer (erosion of tissue) may form.
Food is digested in the stomach for several hours. During this time, a stomach enzyme called pepsin breaks
down most of the protein in the food. Next, the chyme is slowly transported from the pylorus (end portion of
the stomach) through a sphincter and into the small intestine where further digestion and nutrient absorption
occurs.

Digestion in small intestine :
The small intestine is about 20 feet (6 meters) long and has three parts: the duodenum, jejunum,
and ileum. The duodenum is where most chemical digestion takes place. Here, bile from the
gallbladder and enzymes from the pancreas and intestinal walls combine with the chyme to begin
the final part of digestion
Bile liquid is created in the liver and stored in the gallbladder. Bile emulsifies (breaks into small
particles) lipids (fats), which aids in the mechanical digestion of fats. The pancreas and gland
cells of the small intestine secrete digestive enzymes that chemically break down complex food
molecules into simpler ones. These enzymes include trypsin (for protein digestion), amylase (for
carbohydrate digestion), and lipase (for lipid digestion).

When food passes through the duodenum, digestion is complete. From the duodenum, chyme passes to the
jejunum and ileum. Here, tiny villi (finger-like projections) cover the walls of the small intestine. The cells
that line the villi are covered with small projections called microvilli (brush border). These projections
increase the surface area of the small intestine, allowing the chyme to contact more of the small intestine
wall. The increased contact causes more efficient food absorption.
During food absorption, food molecules enter the bloodstream through the intestinal walls. Capillaries
(microscopic blood vessels) within the villi absorb products of protein and carbohydrate digestion. Lymph
vessels (lacteals) within the villi absorb products of fat digestion and eventually lead to the bloodstream.

From the small intestine, digested products travel to the liver, one of the body's most versatile
organs. Hepatocytes (liver cells) detoxify (filter) blood of harmful substances such as alcohol and
ammonia. And, hepatocytes store fat-soluble vitamins and excess substances such as glucose
(sugar) for release when the body requires extra energy.
Once food has passed through the small intestine, it is mostly undigestible material and water. It
enters the colon (large intestine), named for its wide diameter. The large intestine has six parts:
the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The
large pouch-shaped cecum marks the beginning of the colon.
The other parts of the colon absorb water and minerals from the undigested food and compact the
remaining material into feces. Defecation is the digestive process final stage: feces (undigested
waste products) are carried to the rectum through peristalsis and eliminated through the anus

Digestive Disorders
 Acidity
 Gastritis
 Ulcers
 IBD
 Colon cancer
 Diarrhoea
 Constipation
 Piles
Homework

Application in pharmaceutical science
Absorption of Drugs through GIT
Dissolution of drugs in oral cavity
Dissolution of drugs in gastric cavity
Dissolution of drugs in intestine
Drugs used to treat acidity
Drugs used to treat dental caries
Drugs used in treatment of Oral Ulcers
Drugs used in treatment of Gastric Ulcers
Drugs used in treatment of Duodenal Ulcers
Drugs used to treat diarrhoea
Drugs used in treatment of constipation
Drugs used in gastric larvage
Effect of Gastric pH on drug stability

THE END
Endocrine system loading……….

St. Wilfred's Institute Digestive System Presentation

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St. Wilfred's Institute Digestive System Presentation