An overview of the anatomy of the Digestive System.

1. ANATOMY
OF THE
DIGESTIVE SYSTEM
Victor EKPO
MSc Medical Physics, College of Medicine, University of Lagos. 2017

2. OUTLINE
 Introduction to the Digestive System
 Divisions
 Alimentary Canal
 Accessory Organs
 Organs
 Location
 Functions
THE ROLE OF COMPUTERS IN MEDICAL PHYSICS. VICTOR EKPO. CMUL - LAGOS

3. INTRODUCTION
The Digestive System is a group of
organs working together to
convert food into energy and
basic nutrients to feed/nourish the
body.
ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS

4. ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS
Fig: Anterior view of the Digestive System

5. Fig: Posterior view of the Digestive System

6. DIVISIONS
The alimentary canal is also called the digestive tract
OR gastrointestinal tract GIT (though GIT is
technically stomach + intestines only).
The alimentary canal is the long tube that runs from
the mouth through to the anus.
ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS
The Digestive System consists of 2 parts: the
Alimentary Canal, and their Accessory Organs.

7. ALIMENTARY CANAL
The main parts of the Alimentary Canal are:
* Mouth (Oral cavity)
* Pharynx (Throat) * Oesophagus (also esophagus)
* Stomach * Small intestine
* Large intestine * Rectum and anal canal (anus).

8. ACCESSORY ORGANS
The Accessory Organs include other organs (mainly glands) that aid
digestion. These include:
Tongue, salivary glands and tonsils (for mouth)
Tubular mucous glands (for pharynx, oesophagus, large intestine)
 Liver, Gallbladder, and Pancreas (for small intestine);
Epiglottis: which tips posteriorly at the pharynx to prevent food
from entering the larynx/respiratory tract.
Mesentery* (newly discovered organ that helps hold the intestines
to the posterior abdominal cavity).

9. ANATOMY OF THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS
Digestion starts in the mouth, where food is chewed and
mixed with saliva to form a bolus.
The bolus produced is then swallowed down the pharynx and
oesophagus via peristaltic contractions and into the stomach.
In the stomach, it is mixed with gastric juice to form a
semifluid substance called chyme, then moved to the
duodenum (small intestine).
Most of the digestion takes place in the stomach and
duodenum of the small intestine.
Water and some minerals are reabsorbed in the colon of the
large intestine. The chyme is turned to faeces. The faeces is
defecated from the anus via the rectum.
DIGESTION>>>

10. LOCATION OF ORGANS
Fig: Abdominopelvic Regions

11. MOUTH (ORAL CAVITY)
The mouth or oral cavity is
bounded by muscles and bones:
Anteriorly – by the lips
Posteriorly – it is continuous with
the oropharynx (part of pharynx)
Laterally – by the muscles of the
cheeks
Superiorly – by the bony hard
palate and muscular soft palate
Inferiorly – by the muscular tongue
and the soft tissues of the floor of
the mouth.

12. TONGUE
The tongue is a large, muscular organ
that occupies most of the oral cavity.
It is attached by its base to the hyoid
bone, and by thin fold of tissue called the
frenulum, to the floor of the mouth.
A groove called the terminal sulcus
divides the tongue into two parts.
• Anterior: covered by papillae (contains
some taste buds).
• Posterior: contains few small glands
and a large amount of lymphoid tissue,
the lingual tonsil. Fig: Dorsal surface of tongue & tonsils

13. TEETH (SKELETAL) The teeth are embedded in
the mandible and maxilla
bones.
Movement of the mandible
(lower jaw) allows chewing.
The mandible is the only
moveable bone in the jaw.
There are 20 temporary teeth.
Later, 32 permanent teeth
replace the 20.
There are incisors (8), canines
(4), premolars (8), and molars
(12).
Fig: Skeletal system of the mouth

14. ANATOMY OF TEETH The teeth is composed of a crown,
neck and root. The crown is covered
by thin but hard enamel.
The root is covered with bone-like
cementum, which secures the tooth
in its socket. Periodontal ligaments
hold the teeth in the alveoli.
Blood vessels and nerves enter the
tooth through the apical foramen.
The tongue and teeth are important
for proper mastication of food, and
also for speech.
Fig: Cross section of a lower tooth

15. PHARYNX
It connects to the oral cavity anteriorly, and is continuous
with the oesophagus. Food passes from the oral cavity into
the pharynx then to the oesophagus below it.
The pharynx consists of three parts:
 nasopharynx,
 oropharynx, and the
 laryngopharynx.
It prevents food from entering the nasal cavity (by the soft
palate) and the lower respiratory tract (by the epiglottis).

16. Figs: Actions of soft palate and Epiglottis in Pharynx during swallowing
EPIGLOTTIS

17. OESOPHAGUS
Also called gullet or esophagus, it
is an organ through which food
passes from the pharynx to the
stomach, aided by peristaltic
contractions, of its musculature.
It is about 25 cm long and 2 cm in
diameter, and lies in the median
plane (mediasternum) in the
thorax, anterior to the spinal
column, but posterior to the
trachea.

18. CONSTRICTIONS OF THE OESOPHAGUS
The oesophagus follows the curvature of the
vertebral column.
It also has 3 constrictions (narrowing), where
adjacent structures produce impressions:
1. Cervical Constriction (Upper Oesophageal
Sphincter) – where Pharynx meets
Oesophagus.
2. Thoracic (Broncho-Aortic) Constriction –
where it is first crossed by arch of aorta.
3. Diaphragmatic Constriction: where it
passes through the oesophageal hiatus of
the diaphragm at t10, before entering the
stomach.

19. OESOPHAGUS (contd.)
Immediately the oesophagus has
passed through the esophageal
hiatus (opening) of the diaphragm, it
curves upwards before opening into
the stomach.
This sharp angle, as well as the
sphincters at each end (e.g. cardiac
sphincter), prevents the regurgitation
(backflow) of gastric contents into the
oesophagus.
The oesophagus has thick walls consisting of the four layers/tunics common
to the digestive tract: mucosa (innermost), submucosa, muscularis, and
serosa/adventitia (outermost).

20. STOMACH
Fig: Anterior view of stomach and its adjacent structures

21. LOCATION OF THE STOMACH
It is the enlarged hollow part of
the digestive tract specialized in
the accumulation of ingested
food, and also acts as food
blender.
It is located between the
oesophagus and the small
intestine.
It is located in the epigastric,
umbilical & left hypochondriac
regions of the abdominal cavity. Gastroenterology deals with the study of
diseases of the stomach and intestines
and their associated organs

22. PARTS OF THE STOMACH
The stomach has four (4) parts:
 Cardiac
 Fundus
 Body
 Pylorus
The Pyloric Sphincter guards the opening between the stomach and the
duodenum. When the stomach is inactive, the pyloric sphincter is relaxed and
open, and when the stomach contains food, the sphincter is closed.
The stomach is continuous with the
oesophagus at the Cardiac Sphincter,
and with the Duodenum at the Pyloric
Sphincter.

23. SMALL INTESTINE
The small intestine is the part of the
GIT between the stomach and large
intestine.
The small intestine is continuous
with the stomach at the Pyloric
Sphincter and leads into the large
intestine at the ileocaecal valve.
It is about 2.75 – 10.49 m long. For
an average person, it is 3-5m.
It lies in the abdominal cavity
surrounded by the large intestine.

24. PARTS OF SMALL INTESTINE
There are 3 parts of the Small Intestine:
Duodenum: First, shortest, widest and
most fixed part (0.25m long).
Jejunum: This is the middle section of
the small intestine (about 2.5m long) –
about 2/5th
Ileum: Joins the large intestine at the
Ileocecal Junction
(3- 3.5m long) – about 3/5th
The mesentery, a double layer of peritoneum, supports and attaches the
jejunum and ileum (small intestine) to the posterior abdominal wall.

25. PERITONEUM & MESENTERY
The peritoneum (yellow portion) is the largest
serous membrane of the body. It is a closed sac,
containing a small amount of serous fluid, within
the abdominal cavity.
It provides attachment to organs of the GIT, and
acts as a physical barrier to localize spread of
infection.
It invaginates the stomach, small intestine, liver,
pancreas, kidney, spleen, and other pelvic
organs.
The mesentery associated with the small
Intestine is sometimes called the Mesentery
other parts, e.g. of the colon: transverse mesocolon.
Proper. There are mesenteries of

26. LIVER & GALL BLADDER
The liver is an accessory digestive gland,
and largest internal organ.
It is involved in the:
• Synthesis of glucose from amino acid
• Breaking down of carbohydrates
• Synthesis of cholesterol
• Production of fat, through lipogenesis.
• Production of bile.
The bile produced is stored in the gall bladder, and secreted to the small
intestine during food digestion. The gallbladder is a saclike structure on the
inferior surface of the liver that is about 8 cm long and 4 cm wide.

27. PANCREAS
The pancreas is a pale grey
gland weighing about 60g. It is
about 12–15 cm long and is
situated in the
epigastric and left
hypochondriac regions of the
abdominal cavity.
It consists of a broad head, a
body and a narrow tail.
It secrets pancreatic juice
(exocrine pancreas), and insulin
and glucagon (endocrine
pancreas).

28. LARGE INTESTINE
The Large Intestine meets the Small
Intestine at the ileocaecal valve,
then continues to the anal canal.
It is about 1.5m long and 6.5cm
wide (Small Intestine: 2.5cm).
It consists of the
 Cecum (proximal end),
 Appendix,
 Colon (ascending, descending,
sigmoid, transverse),
 Rectum,
 Anal canal (distal end)
Fig: Parts of the Large Intestine

29. FUNCTIONS OF THE DIGESTIVE
SYSTEM Ingestion,
 Mastication,
 Propulsion,
 Mixing,
 Secretion,
 Digestion,
 Absorption, and
 Elimination.

30. ORGAN FUNCTIONS
Mouth
Ingestion, Taste, Mastication, Digestion,
Swallowing, Communication, Protection.
Pharynx Swallowing, Breathing, Protection
Oesophagus Propulsion, Protection.
Stomach
Storage, Digestion, Absorption, Mixing and
Propulsion, Protection.
Small Intestine
Neutralization, Digestion, Absorption, Mixing and
Propulsion, Excretion, Protection.
Large Intestine
Absorption, Storage, Mixing and Propulsion,
Protection, Excretion.

31. REFERENCES
Waugh A, Grant A. Ross and Wilson Anatomy and Physiology. 12th Ed.,
New York NY: Elsevier; 2004.
Seeley RR, Stephens TD, Tate P: Anatomy and Physiology. 6th Ed.,
New York, NY: McGraw-Hill Companies; 2004.
Moore KL, Dalley AF, Agur AM. Clinical Oriented Anatomy 6th Ed.,
Baltimore BA: Lippincott Williams & Wilkins; 2010.
Coffey JC. The Mesentery: Structure, Function and Role in Disease.
The Lancet Gastroenterology & Hepatology; 2016.
Sherwood L. Fundamentals of Physiology: A Human Perspective. 3rd Ed.,
Florence KY: Cengage Learning. 2006.

32. THANK YOU
THE DIGESTIVE SYSTEM. VICTOR EKPO. CMUL - LAGOS