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ANATOMY AND PHYSIOLOGY
OF THE DIGESTIVE SYSTEM
Medical Surgical Nursing -1

anatomyandphysiologyofdigestivesystem-180313110438.pptx

WHAT IS THE DIGESTIVE SYSTEM?
• The gastrointestinal tract (digestive tract, digestional
tract, GI tract, GIT, gut, or alimentary canal) is
an organ system within humans which takes in
food, digests it and absorb energy and nutrients, and
expels the remaining waste as feces.
The major organs of the digestive system:
• Mouth.
• Pharynx.
• Esophagus.
• Stomach.
• Small Intestine.
• Large Intestine.
• Rectum.

Accessory digestive organs:
liver
gallbladder
pancreas.
Salivary gland
Functions of GI tract
• Ingestion: taking of food into the alimentary tract. i.e.
eating & drinking.
• Propulsion: mixes & moves the contents along the
alimentary tract.
• Digestion: consist of:
Mechanical breakdown of food e.g. mastication (chewing)
Chemical digestion of food into small molecules by
enzymes.

• Absorption:this is the process by which
digested food substances pass through
the walls of the alimentary canal into
the blood for circulation.
• Elimination: Undigested and
unabsorbed foods are excreted from the
alimentary canal as faeces by the
process of defecation.

MOUTH
• The mouth is the first portion of
the alimentary canal that receives food and
produces saliva.

• The palate forms the roof of the mouth & is
divided into the anterior hard palate & posterior
soft palate.
• The uvula is a curved fold of muscle covered with
mucous membrane,hanging down from the
middle.
• TONGUE
• The tongue is a muscular organ in the mouth, that
manipulates food for mastication, and is used in
the act of swallowing.
• It is of importance in the digestive system and is
the primary organ of taste in the gustatory system.

• FUNCTIONS
• Mastication (chewing)
• Deglutition (swallowing)
• Speech
• Taste
TEETH
• The human teeth function to mechanically break
down items of food by cutting and crushing them in
preparation for swallowing and digesting. Humans have
four types of teeth: incisors, canines, premolars, and
molars, each with a specific function.

• PRIMARY TEETH
• Among deciduous (primary) teeth, ten are
found in the maxilla (upper jaw) and ten in the
mandible (lower jaw), for a total of 20.
The dental formula for primary teeth
is 2.1.0.2/2.1.0.2.
• Start to come in (erupt) at about 6 months of
age
• All primary teeth are normally later replaced
with their permanent counterparts.

• PERMANENT TEETH
• Among permanent teeth, 16 are found in the maxilla
and 16 in the mandible, for a total of 32. The dental
formula is 2.1.2.3/2.1.2.3.
• Age 21, all 32 of the permanent teeth have usually
erupted.
• The permanent teeth are the:
• Two incisor (for cutting)-central incisor, lateral incisor
• One canine (for tearing)
• Two premolar(for crushing)-first premolar, second
premolar,
• Three molar (for grinding)-first molar, second molar,
and third molar.

SALIVARY GLANDS
• The salivary glands in are exocrine glands that
produce saliva through a system of ducts.
Humans have 3 paired major salivary glands:
Parotid: largest
submandibular and
Sublingual

• FUNCTION OF SALIVA
• Saliva contributes to the digestion of food and
to the maintenance of oral hygiene.
• Lubricant
• Saliva, coats the oral mucosa, mechanically
protecting it from trauma during eating,
swallowing and speaking.
• Saliva maintains the pH of the mouth.

THE PHARYNX
• The pharynx is the part of the throat that is
behind the mouth and nasal cavity and above
the esophagus and the larynx
• The pharynx is the portion of the digestive
tract that receives the food from your mouth.
• Branching off the pharynx is the esophagus,
which carries food to the stomach,

THE ESOPHAGUS
• The esophagus,commonly known as the food pipe or gullet, The
esophagus is a muscular tube connecting the throat (pharynx) with the
stomach.
• Length :25 cm
• Diameter:2 cm
- The esophagus has three layers:
1. Mucosa (innermost layer, lined with epithelial cells)
2. Submucosa (middle layer, contains glands and blood vessels)
3. Muscularis externa (outermost layer, contains smooth muscle)
- esophagus has two sphincters (ring-like muscles):
1. Upper esophageal sphincter (UES, separates the pharynx and
esophagus)
2. Lower esophageal sphincter (LES, separates the esophagus and
stomach)

- The esophagus secretes mucus to lubricate
food and protect its lining.
- The UES and LES relax and contract to control
food passage and prevent reflux (backflow of
stomach contents).
- The esophagus is lined with stratified
squamous epithelium, which provides
protection from abrasion and corrosion.
- The esophagus has no digestive enzymes or
absorptive functions; its primary role is food
transport.

STOMACH
• The stomach is a muscular organ located on the left side
of the upper abdomen. The stomach receives food from
the esophagus.
• As food reaches the end of the esophagus, it enters the
stomach through a muscular valve called the lower
esophageal sphincter.
• primarily designed for food storage (for 2-4 hours) &
some mechanical and chemical digestion also occur .
• Contains two sphincters at both ends to regulate food
movement :
 cardiac sphincter near the esophagus ,
 pyloric sphincter near the small intestine .

FUNCTIONS
- The stomach's primary function is to break down food into
smaller particles and mix it with digestive enzymes and acids.
- The stomach lining secretes:
1. Mucus (protects the stomach from acid and enzymes)
2. Pepsinogen (converted to pepsin, which breaks down
proteins)
3. Gastric amylase (breaks down carbohydrates)
4. Hydrochloric acid (HCl, creates an acidic environment)
- The stomach muscles contract and relax in a rhythmic
manner to mix food with digestive juices (peristalsis).
- The stomach takes about 1-2 hours to empty its contents
into the small intestine.

• The stomach's acidic environment has a pH of
around 2, which helps kill bacteria and activate
digestive enzymes.
• The stomach's mucous lining is replaced every
3-4 days to prevent damage from acid and
enzymes.
• The stomach's contractions can be influenced
by hormones like gastrin and secretin, which
regulate digestion.

Gastric Secretory Cells
• Chief cells: secrete pepsinogen (an inactive
enzyme).
• Parietal cells: secrete hydrochloric and (HCl) and
"intrinsic factor" (which helps absorption of
vitamin B12 in the intestines).
• Mucous cells: secrete mucus and alkaline
substances to help neutralize HCl in the gastric
juice .
• G cells: secrete a hormone called gastrin , which
stimulates the parietal cells and overall gastric
function.

THE PANCREAS
• The pancreas is a glandular organ located in the
abdominal cavity, behind the stomach and below the
diaphragm.
• Although it is primarily an exocrine gland(80%),
secreting a variety of digestive enzymes, the
pancreas also has endocrine cells(20%).
• Its pancreatic islets—clusters of cells formerly
known as the islets of Langerhans—secrete the
hormones glucagon, insulin, somatostatin, and
pancreatic polypeptide (PP).

FUNCTION
-Exocrine function:
• Produces digestive enzymes (e.g., amylase, lipase, trypsin) to
break down carbohydrates, fats, and proteins
• Enzymes are released into the small intestine through the
pancreatic duct
Endocrine function:
Produces hormones to regulate blood sugar levels:
1. Insulin (lowers blood sugar)
2. Glucagon (raises blood sugar)
• Also produces other hormones like somatostatin and
pancreatic polypeptide

LIVER
The liver is a vital organ located in the upper right side of
the abdominal cavity, below the diaphragm.
The liver, an organ only found in vertebrates, detoxifies
various metabolites, synthesizes proteins, and produces
biochemicals necessary for digestion
STRUCTURE
The liver is a reddish-brown wedge-shaped organ with
four lobes of unequal size and shape.
weighs 1.44–1.66 kg
It is both the heaviest internal organ and the largest gland
in the human body.

Function of Liver
1. Detoxification: removes toxins, drugs, and waste products from the blood
2. Metabolism: regulates carbohydrate, protein, and fat metabolism
3. Production:
- Bile (digestive enzyme)
- Proteins (albumin, clotting factors)
- Cholesterol
- Hormones (insulin-like growth factor)
4. Storage:
- Glycogen (carbohydrate storage)
- Vitamins (A, D, E, K, B12)
- Minerals (iron, copper)
5. Filtration: removes old red blood cells and bacteria from the blood
6. Immune function: produces immune factors and filters pathogens

- The liver has a unique ability to regenerate
itself if damaged.
- The liver's blood supply is about 25% of the
total cardiac output.
- The liver produces about 1 liter of bile daily.
- Conversion of poisonous ammonia to urea
(urea is an end product of protein metabolism
and is excreted in the urine)

THE GALLBLADDER
The gallbladder is a small hollow organ where
bile is stored and concentrated before it is
released into the small intestine.
In humans, the pear-shaped gallbladder lies
beneath the liver.

• FUNCTIONS
1. Bile storage: stores bile produced by the liver,
holding about 50-60 ml of bile.
2. Bile concentration: concentrates bile by absorbing
excess water and electrolytes, making it more potent.
3. Bile release: releases bile into the small intestine
through the common bile duct to aid in fat digestion.
4. Fat emulsification: Bile salts in the released bile
emulsify fats, breaking them down into smaller
particles for easier digestion.
5. Vitamin absorption: Bile salts help absorb fat-
soluble vitamins (A, D, E, and K) in the small intestine.

6. Pest control: Bile has antimicrobial properties,
helping to control the growth of bacteria and
other microorganisms in the small intestine.
7. Hormone regulation: The gallbladder releases
hormones like cholecystokinin (CCK), which
helps regulate digestion and satiety.
8. Waste removal: The gallbladder helps remove
waste products, like bilirubin, from the liver.

THE SMALL INTESTINE
• The small intestine or small bowel is found between the
stomach and the large intestine, and is where most of the end
absorption of food takes place.
• STRUCTURE
• length- 3m-5m.
• diameter -2.5–3 cm or 1 inch
It is divided into three parts:
1. Duodenum : receives bile and pancreatic juice from the liver
and pancreas.
2. Jejunum : primary site of nutrient absorption.
3. Ileum : absorbs remaining nutrients, especially vitamin B12
and bile salts.

FUNCTIONS
Digestion
• The partially digested food is absorbed by the
duodenum of the SI along with the digestive
juices from the liver, pancreas and its own walls.
• Many of the digestive enzymes that act in the
small intestine are secreted by the pancreas and
liver and enter the small intestine via the
pancreatic duct.

Nutrient absorption:
• The SI absorbs about 90% of nutrients from
food, including:
• - Carbohydrates (broken down into simple
sugars).
• - Proteins (broken down into amino acids).
• - Fats (emulsified by bile salts, absorbed as
fatty acids and glycerol).
• - Vitamins and minerals.

• Immune function: The SI contains immune
cells (Peyer's patches) to protect against
pathogens.
• The SI has a large surface area (about 2,700
square feet/250 square meters) due to finger-
like projections called villi.
• The SI is the primary site of drug absorption.
• The SI's mucosa regenerates every 3-5 days to
maintain its absorptive function.

THE LARGE INTESTINE
• The large intestine, also known as the large
bowel or colon, is the last part of the
gastrointestinal tract.
• Water is absorbed here and the remaining
waste material is stored as feces before being
removed by defecation.

Parts of Large Intestine
- It is divided into four parts:
1. Ascending colon
2. Transverse colon
3. Descending colon
4. Sigmoid colon

FUNCTIONS
The LI absorbs about 90% of the remaining water and
electrolytes & absorbable nutrients from the food
before sending the indigestible matter to the rectum.
• The colon absorbs vitamins that are created by the
colonic bacteria, such as vitamin K.
• Gut flora: LI houses over 700 species of bacteria
that perform a variety of functions.
• Vitamin production: The LI's gut microbiome
produces vitamins K and B12.
• Storage and elimination: The LI stores waste
material until it is eliminated through the anus.

ANUS
• The anus is the external opening of
the rectum.
• Its function is to control the expulsion of feces.
• Two sphincters control the exit of feces from
the body during an act of defecation.

PHYSIOLOGY OF DIGESTION
• The mouth is the beginning of the digestive tract.
• Chewing breaks the food into pieces that are
more easily digested, while saliva mixes with
food to begin the process of breaking it down
into a form your body can absorb and use.
• From pharynx food travels to the esophagus or
swallowing tube.
• By means of a series of contractions, called
peristalsis, the esophagus delivers food to the
stomach.
• The lower esophageal sphincter keep food from
passing backwards into the esophagus.

• The stomach secretes acid and powerful
enzymes that continue the process of breaking
down the food.
• When it leaves the stomach, food is the
consistency of a liquid or paste.
• From there the food moves to the small
intestine.
• The small intestine continues the process of
breaking down food by using enzymes released
by the pancreas and bile from the liver.
• Bile is a compound that aids in the digestion of
fat and eliminates waste products from the
blood.

• Peristalsis is also at work in this organ, moving
food through and mixing it up with digestive
secretions.
• The duodenum is largely responsible for
continuing the process of breaking down food,
with the jejunum and ileum being mainly
responsible for the absorption of nutrients
into the bloodstream.
• pancreas secretes enzymes into the small
intestine.
• These enzymes break down protein, fat, and
carbohydrates from the food we eat.

• Stool, or waste left over from the digestive
process, is passed through the colon by means
of peristalsis, first in a liquid state and
ultimately in solid form as the water is
removed from the stool.
• A stool is stored in the sigmoid colon until a
"mass movement" empties it into the rectum
once or twice a day.

Q1
Which juice secreted by the organs of digestive
trats plays an important role in fat digestions?
1. HCL,Mucus
2. Pancreatic juice, Saliva
3. Bile juice & Pancreatic juice
4. Saliva & HCL

Q2
BILE JUICE is formed in the
1. Liver
2. Gall bladder
3. Salivary gland
4. duodenum

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