Anatomy and Physiology of Digestive System

ANATOMY AND
PHYSIOLOGY OF
DIGESTIVE SYSTEM
Digestive System
■ gastrointestinal tract, digestive tract, GI
tract, GIT, gut, or alimentary canal.
■ is an organ system within humans and other
animals which takes in food, digests it and
absorb energy and nutrients, and expels the
remaining waste as feces.
Major Organ of
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:
- 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 some organs of the alimentary canal into the blood for circulation.
■ Elimination: food substances that have been eaten but cannot be digested & absorbed
are excreted from the alimentary canal as feces by the process of defecation.
MOUTH
■ The mouth is the first portion of the alimentary

canal that receives food and produces saliva.
■ The oral mucosa is the mucous membrane
epithelium lining the inside of the mouth.
■ 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.
■ The tongue is a muscular organ in the mouth, that
manipulates food for mastication, and is used in the
act of swallowing. It is the primary organ of taste in
the gustatory system.
■ The human teeth function to mechanically break
down items of food by cutting and crushing them in
preparation for swallowing and digesting
MOUTH
FUNCTIONS:
■ Mastication(chewing)
■ Deglutition(swallowing)
■ Speech
■ Taste
SALIVARY GLANDS
■ The salivary glands are exocrine glands that
produce saliva through a system of ducts.
■ Humans have 3 paired major salivary glands:
- Parotid
- Submandibular
- Sublingual
as well hundreds of minor salivary glands
Saliva
COMPOSITION OF SALIVA
About 1.5 litres of saliva is produced daily & it consists of:
– Water
– Mineral salts
– An enzyme
– Mucus
– Lysozyme
– Immunoglobulins
FUNCTION OF SALIVA
– Lubricant
– Digestion
– Role in taste
– Maintains the pH
THE PHARYNX
■ The pharynx is funnel in shape and can be divided

into the nasal, the oral, and the laryngeal parts
■ The pharynx is the part of the throat that is behind
the mouth and nasal cavity and above the
esophagus and the larynx, or the tubes going down
to the stomach and the lungs.
■ 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.
■ The esophagus runs behind the windpipe
(trachea) and heart, and in front of the spine.
■ • Length :25 cm • Diameter:2 cm
THE ESOPHAGUS
■ It has two muscular rings or sphincters in its

wall, one at the top and one at the bottom.
■ A sphincter is a circular muscle that normally
maintains constriction of a natural body passage or
orifice and which relaxes as required by normal
physiological functioning.
■ The lower sphincter helps to prevent reflux of
acidic stomach content.
THE ESOPHAGUS
FUNCTIONS
■ Formation of a bolus
– formation of a food bolus makes the process of swallowing easier and safer
■ Swallowing
– Food is ingested through the mouth and when swallowed passes first into the
pharynx and then into the esophagus.
■ Reducing gastric reflux
– Constriction of the upper and lower esophageal sphincters help to prevent reflux
(backflow) of gastric contents and acid into the esophagus, protecting the
esophageal mucosa.
Blood supply
• Esophageal arteries
• Inferior phrenic arteries
Venous drainage
• Left gastric vein
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.
■ A pouch-like organ primarily designed for food
storage (for 2-4 hours) , some mechanical and
chemical digestion also occur .
STOMACH
STOMACH
Blood supply
• right gastroepiploic artery
• left gastroepiploic artery
• gastric artery
Venous drainage
• gastric vein
THE PANCREAS
■ The pancreas is a glandular organ in the digestive

system and endocrine system of vertebrates.
■ It is located in the abdominal cavity behind the
stomach.
■ It is an endocrine gland producing several
important hormones, including insulin, glucagon,
somatostatin, and pancreatic polypeptide, all of
which circulate in the blood.
■ Length: 15 cm or 6 inch
THE PANCREAS
THE PANCREAS
BLOOD SUPPLY
• superior mesenteric artery
• splenic artery
VENOUS DRAINAGE
• superior mesenteric veins
• Splenic veins
LIVER
■ The liver is a reddish-brown wedge-shaped organ with four lobes of unequal size and
shape.
■ weighs 1.44–1.66 kg
■ width -15 cm.
■ It is both the heaviest internal organ and the largest gland in the human body.
■ The liver detoxifies various metabolites, synthesizes proteins, and produces
biochemicals necessary for digestion.
LIVER
• The liver is grossly divided into two parts
when viewed from above – a right and a
left lobe.
• The falciform ligament, divides the liver

into a left and right lobe.
LIVER
BLOOD SUPPLY
Hepatic artery
VENOUS DRAINAGE
Hepatic veins
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.
THE GALLBLADDER
STRUCTURE
– sits in a shallow depression below the right lobe of the liver
– Length-7 to 10 cm or 2.8 to 3.9 inches
– Diameter -4 cm or 1.6 inch
FUNCTIONS
– The main purpose of the gallbladder is to store bile, also
called gall, needed for the digestion of fats in food.
– bile flows through small vessels into the larger hepatic ducts
and ultimately though the cystic duct into the gallbladder,
where it is stored.
BLOOD SUPPLY
the cystic artery
VENOUS DRAINAGE
the cystic veins
THE GALLBLADDER
SMALL INTESTINE
■ The greater part of digestion and food
absorption occurs in the small intestine,
which extends from the pylorus of the
stomach to the ileocecal junction.
■ STRUCTURE:
- Length: 3m – 5m
- Diameter: 2.5 – 3 cm or 1 inch
■ PARTS: The small intestine is divided
into three structural parts:
(I)The duodenum
(II)The jejunum
(III)The ileum
SMALL INTESTINE
■ The duodenum is a short structure ranging from 20 cm to 25 cm in length, and shaped
like a "C".
■ The jejunum is the midsection of the small intestine, connecting the duodenum to the
ileum. It is about 2.5 m long.
■ The ileum is the final section of the small intestine. It is about 3 m long, and contains
villi similar to the jejunum.
■ BLOOD SUPPLY
- the coeliac trunk
- the superior mesenteric artery
■ VENOUS DRAINAGE
- the superior mesenteric veins
THE LARGE INTESTINE
■ The large intestine, also known as the large bowel or colon, is the last part of the gastrointestinal
tract and of the digestive system in vertebrates.
■ Water is absorbed here and the remaining waste material is stored as feces before being removed
by defecation.
■ STRUCTURE
- Male colon is 166 cm
- Female colon 155 cm
■ The colon consists of five sections:
1. the cecum
2. ascending colon,
3. the transverse colon,
4. the descending colon,
5. the sigmoid colon and the rectum.
THE LARGE INTESTINE
■ BLOOD SUPPLY
- the superior mesenteric artery (SMA)
- inferior mesenteric artery
■ VENOUS DRAINAGE
- the inferior mesenteric vein
- the superior mesenteric vein
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.

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ANATOMY AND

■ The mouth is the first portion of the alimentary

■ The pharynx is funnel in shape and can be divided

■ The esophagus, commonly known as the food

■ It has two muscular rings or sphincters in its

■ The stomach is a muscular organ located on the left

■ The pancreas is a glandular organ in the digestive

• The falciform ligament, divides the liver

■ The mouth is the beginning of the digestive tract.

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