The document provides an overview of the digestive system. It discusses that the digestive system breaks down food into smaller particles for absorption by cells in the body. The two main functions are digestion and absorption. The digestive system is divided into the gastrointestinal tract and accessory organs. The gastrointestinal tract extends from the mouth to the anus. Accessory organs include things like the liver and pancreas which release substances into the GI tract.

1. The Digestive System
1

2. Introduction
• Every body cell needs a constant supply of nutrients to provide
energy and building blocks for the manufacture of body substances.
• Food as we take it in, however, is too large to enter the cells.
• It must first be broken down into particles small enough to pass
through the cell membrane. This process is known as digestion.
• After digestion, food must be carried to the cells in every part of the
body by the circulation.
• The transfer of food into the circulation is called absorption.
• Digestion and absorption are the two chief functions of the
digestive system.
5/10/2023 Lecture note of Human Anatomy ASU 2

3. Introduction
• For our purpose the digestive system may be divided into two
groups of organs:
1. The Gastrointestinal (GI) tract (Alimentary Canal) a
continuous passageway beginning at the mouth, where food
is taken in, and terminating at the anus, where the solid
waste products of digestion are expelled from the body
2. The accessory organ, which are necessary for the digestive
process but are not a direct part of the digestive tract.
• They release substances into the digestive tract through ducts.
5/10/2023 Lecture note of Human Anatomy ASU 3

4. Layers of GI tract
•GIT from esophagus to anus has the same basic
arrangement of tissues.
•The four coats or tunics of the tract from the inside
out are:-
1. Mucosa
•Inner lining of the tract
•It is composed of layer of epithelium
•It composes three layers.
4

5. a. Lining epithelium
•Direct contact with contents of the GI tract
Composed of
•Non-keratinized cells serves as protection and
secretion and
•Simple epithelium which serves as secretion and
absorption
b. Lamina propria
•Composed of loose connective tissue that contains
many blood and lymph vessels.
•c. Mascularis mucosa: containing smooth muscle
5

6. 2. Submucosa
•Consists of areolar connective tissue
•It binds the mucosa to the muscularis
•It is highly vascular and contains portions of the
submucosa plexus (plexus of Meissner), which is
part of the autonomic nerve supply to muscularis
mucosa.
6

7. 3. Muscularis
•In the mouth, pharynx, and portion of esophagus
consists of skeletal muscles that produce voluntary
swallowing.
•The rest consists of smooth muscles found as inner
ring of circular fibers and an outer sheet of
longitudinal fibers.
7

8. 4. Serosa
•Outer most layer around organs of the GI tract
below the diaphragm.
•The membrane composed of simple squamous
epithelium and areolar connective tissue.
•The serosa secretes slippery, watery fluid that
allows the tract to glide easily against other
organs.
8

9. 9

10. Structure of the GI tract
10

11. Peritoneum
•Largest serous membrane of the body.
•Parietal peritoneum – lines wall of abdominal
cavity.
•Visceral peritoneum - covers some organs and
constitutes their serosa.
•Peritoneal cavity
•Potential space b/n the parietal and visceral
portions of peritoneum.
11

12. Peritoneum
•Contains serous fluid
•Extra fluid in the peritoneal cavity➔ results in
ascites.
Based on the peritoneal covering
•Intraperitoneal organs→ stomach, liver, gall
bladder, spleen, jejunum, ileum, transverse colon,
sigmoid colon, uterus and ovaries (essentially
mobile organs “slung” in mesentery)
12

13. •Retroperitoneal organs
•Kidneys, adrenal glands, aorta, IVC, bladder,
vagina, rectum, descending and ascending
colon, duodenum and pancreas
13

14. H Ye. G 14

15. Omentum
• Double layered peritoneum that passes from stomach
and proximal duodenum to adjacent abdominal organs
• Two parts
1. Greater→ greater stomach curvature inferiorly and
back up to anterior surface of transverse colon.
• Parts
• Gastrophrenic lig→ stomach to inferior
diaphragm
• Gastrosplenic lig→ stomach to spleen
• Gastrocolic→ stomach to transverse colon
15

16. Lesser omentum- extends from porta hepatis of
liver to lesser curvature of stomach and first part
of duodenum
•hepatogastric part - from liver to lesser
curvature of stomach
•hepatoduodenal part - free margin of lesser
omentum from liver to first part of duodenum
& contains:
•portal vein, bile duct & proper hepatic artery
16

19. The Digestive Tract
• The digestive tract is a muscular tube extending through the body.
• It is composed of several parts: the mouth, pharynx, esophagus, stomach,
small intestine, and large intestine.
• The digestive tract is sometimes called the alimentary tract, derived from a
Latin word that means "food".
• It is more commonly referred to as the gastrointestinal (Gl) tract because of
the major importance of the stomach and intestine in the process of digestion.
5/10/2023 Lecture note of Human Anatomy ASU 19

20. 5/10/2023 Lecture note of Human Anatomy ASU 20
Digestive system

21. Mouth /Oral/ Buccal cavity
Formed by Cheeks, hard & soft palates, & tongue
Cheeks
• Forms lateral walls of oral cavity
• Muscular structures externally covered with skin
• Anterior portion terminates in the superior and inferior lips
Hard palate
• Anterior portion of the roof of the mouth
• Formed by the maxillary and palatine bones
• Covered by mucous membrane, and forms a bony portion b/n the
oral and nasal cavities.
Soft palate
• Forms posterior portion of the roof of mouth
• An arch-shaped muscular portion b/n the oropharynx and
nasopharynx and lined by mucus membrane 21

22. 22

23. Tongue
•Forms floor of the oral cavity
•Accessory structure of the Digestive System composed of
skeletal muscle covered with mucus membrane.
•Divided into symmetrical lateral halves by a median
septum that extends through out its length and is attached
inferiorly to the hyoid bone.
23

24. The tongue consists of
Extrinsic muscles
•Originate outside the tongue & insert into it.
•In includes hyoglossus, genioglossus, styloglossus and
palatoglossus
•Moves tongue from side to side and in and out.
•The movement food for chewing, shape the food, and
force the food to the back of the mouth for swallowing.
Intrinsic muscles
•Originate and insert within the tongue.
•Alters shape & size of tongue for speech & swallowing.
•It includes longitudinal superior and inferior,
transverses lingual, and verticalis lingual.
24

25. 25

26. Teeth/dentes
•Located in sockets of alveolar processes of mandible and
maxillae
•Alveolar processes are covered by the gingival/gums;
extend slightly into each socket forming the gingival
sulcus.
•Sockets are lined by the periodontal ligament, which
consists of dense, fibrous connective tissue. It anchors the
teeth in position.
26

27. Typical tooth consists of
1. Crown - portion above the level of the gums.
2. Root - 1 to 3 projections embedded in socket.
3. Neck - constricted junction lien of the crown and the
root
Dentin – (consist of calcified connective tissue) is a
composition of teeth that gives its basic shape and
rigidity.
Pulp cavity - is formed by the dentin that lies in the
crown and filled with pulp, a connective tissue
containing blood vessels, nerves, and lymphatic.
Root canals - narrow extension of the pulp cavity run
through the root of teeth.
27

28. Apical foramen - an opening at its base of each root,
where blood vessels bearing nourishment, lymphatic's
affording protection, and nerves providing sensation.
Enamel
• Covers dentin of the crown
• Consists of calcium phosphate and calcium
carbonate
• Hardest substance of the body
• Protects the tooth from wear of chewing
Cementum
• Covers dentin of the root
• Attach the root to the periodontal ligament
28

29. 29

30. Dentitions
•Every one has two dentations or sets of teeth. The
first of these are the deciduous teeth, milk teeth
or baby teeth.
•Erupt at about age of 6 month. They are 20
Types of teeth
Incisors
•These are 4 in one jaws
•Closer to midline
•Chisel shaped
•Adapted for cutting
30

31. Cuspids (canines)
•These 2 in one jaw
•Next to incisors
•Has pointed surface
•Used to tear and shared food
Premolar
•4 in one jaws
•Found next to the incisors
Molars
•6 in one jaw
•Has four cusps
•Used to crush and grind food
31

32. Human Deciduous Teeth
32

33. 33
Permanent Teeth

34. 34

35. 35
Salivary glands
•Saliva is a fluid that is continuously secreted into the
mouth for moistening, lubrication, dissolving and
chemical breaking down of food.
•There are three pairs of major salivary glands and minor
buccal glands.
1. The parotid glands: located inferior and anterior to
the ears b/n the skin and the masseter muscle.
2. The sub-mandibular glands: - found beneath the base
of the tongue in the posterior part of the floor of the
mouth.
3. Sablingual glands:- are located superior to the
submandibular glands.

36. 36
Salivary Glands

37. Esophagus
•3rd organ involved in deglutition (swallowing)
•Muscular, collapsible tube that lies behind the
trachea
•Begins in the neck as a continuation of the
pharynx at the level if C6 and terminate at
esophagogastric junction (T10), where it enters
the cardial orifice of the stomach
•25 cm long with a diameter of 2 cm with three
parts (cervical, thoracic and abdominal)
•Diaphragm act like sphincter
37

38. Arteries- left gastric artery, a branch of the celiac trunk,
and the left inferior phrenic artery
Venous drainage -portal venous system through the left
gastric vein
38

39. Stomach
•It is J-shaped enlargement of GI tract directly
under the diaphragm in epigastric, umbilical and
left hypochondriac regions
•Superior portion of the stomach is a continuation of
esophagus
•Inferior portion empties into the duodenum.
39

40. •The stomach is divided into four areas: cardia,
fundus, body and pylorus.
•Cardia - surrounds the lower esophageal
sphincter.
•Fundus - the rounded portion above and to the
left of the cardia.
•Body - is largest central portion of the stomach.
•Pylorus - it is the narrow, inferior region of the
stomach.
40

41. Anatomy of the Stomach
41

42. Neurovasculature of the stomach
42
A) Arteries
1. Left gastric artery- from the ciliac trunk and
gives esophageal artery & gastric branches
2. Right gastric artery-from the hepatic artery
◦ Both on lesser curvature.
3. Right gastro-omental artery: from
gastroduodenal artery
4. Left gastro-omental artery: from splenic artery
◦ The above two are on the greater curvature
5. Short gastric artery - from the splenic artery to
fundus of stomach.

43. Neurovasculature…
43
B) Veins
• Left and right gastric veins drain directly into
the portal vein
• Short gastric & the Lt gastro-omental veins
drain into the splenic vein
• The Rt gastro-omental vein empties into the
SMV
C)Nerves
• Parasympathetic- the anterior and posterior
vagal trunks
• The sympathetic - T6-T9 passes to the celiac
plexus

44. Small Intestine
•Extends from pyloric
sphincter → ileocecal valve
•Regions
•Duodenum
•Jejenum
•Ileum
44

45. Small intestine cont…
•Major portion of digestion and absorption
•Begins at the pyloric sphincter of the stomach,
coils through the central and lower part of the
abdominal cavity, and opens into he large
intestine.
•Averagely 2.5cm in diameter and about 6.33m in
length.
45

46. 46

47. 47

48. Duodenum- the widest and most fixed part.
▪begins at the pylorus on the right side and ends
at the duodenojejunal junction on the left side.
▪ Four parts of the duodenum: superior (1st )
part, descending (2nd ) part, horizontal (3rd )
part and ascending (4th ) part.

49. Duodenum cont…
Descending (2nd) part: The bile duct and main
pancreatic ducts via the hepatopancreatic ampulla
enter its posterior medial wall
A) Arteries:
• Proximal ½- by celiac trunk
• Distal ½ - Superior mesenteric artery
B. Veins: follow the arteries and drain into the portal
vein directly/indirectly
C. Nerves: vagus & sympathetic nerves from
greater and lesser splanchnic

52. Jejunum and Ileum
•The jejunum begins at the duodenojejunal junction and
the ileum ends at the ileocecal junction, the union of
the terminal ileum and cecum.
Jejunum
•The jejunum is about 2.5m long & represents proximal
two-fifths.
•It is mostly in the left upper quadrant of the abdomen
•Is larger in diameter and has a thicker wall than the
ileum.
•less prominent arterial arcades & longer vasa recta
(straight arteries), compared to those of ileum, are a
unique characteristic of jejunum

53. Ileum
•It is about 4m long & makes up distal three-fifths
of small intestine
•It is mostly in right lower quadrant.
•Compared to jejunum, ileum has thinner walls,
shorter vasa recta, more arterial arcades & more
mesenteric fat
•ileum opens into large intestine

54. Vessels of jejunum & ilium
• The arterial supply- the superior mesenteric
artery through 15 -20 Jejunal and ilial branches
▪ unite to form arterial arcades which give rise
to straight vasa recta
• The veins run parallel to the arteries and typically
drain into the superior mesenteric vein
• From the mesenteric vein, the nutrient rich
venous blood from the small intestine drains into
the hepatic portal vein which carries it to the
liver

55. Distinguishing Characteristics of Jejunum and Ileum in Living Persons
Characteristic Jejunum Ileum
Color Deeper red Paler pink
Caliber 2-4 cm 2-3 cm
Wall Thick and heavy Thin and light
Vascularity Greater Less
Vasa recta Long Short
Arcades A few large loops Many short loops
Fat in mesentery Less More
Circular folds (L. plicae
circulares)
Large, tall, and closely
packed
Low and sparse; absent
in distal part
Lymphoid nodules
(Peyer patches)
Few Many
55

56. 56

57. Large Intestine
•Consists of the cecum, colon (ascending,
transverse, descending, and sigmoid), rectum, and
anal canal.
•The large intestine can be distinguished from the
small intestine by:
▪Teniae coli: three thickened bands of
longitudinal muscle fibers.
▪Haustra: sacculations or pouches of the colon
between the teniae.
▪Omental appendices: small, fatty appendices
(projections) of colon.
▪Caliber: the internal diameter is much larger.

58. 58

59. The vermiform appendix
•a variable position, but it is usually retrocecal (posterior
to cecum).
Arterial supply to cecum and appendix
•ilocolic a branch of superior mesenteric artery
•Appendicular a branch of iliocolic
Venous drainage of caecum and appendix- iliocolic vein
that drain into superior mesenteric vein
Lymphatic drainage- lymph nodes in mesoappendix and
iliocolic→superior mesenteric lymph nodes
•Innervation- from celiac and superior mesenteric
ganglia

60. The colon
• The colon is described as having four parts
ascending, transverse, descending, and sigmoid
that succeed one another in an arch.
1. The ascending colon
• passes superiorly from cecum to the right lobe
of the liver and it turns to the left as the right
colic flexure (hepatic flexure).
• lies retroperitoneally along the right side of
the posterior abdominal wall.
• Arterial supply -iliocolic and right colic
arteries from superior mesenteric artery
• Venous drainage -iliocolic and right colic
veins that drains to superior mesenteric vein

61. 2. The transverse colon- the largest and most
mobile part of the large intestine
◦ crosses the abdomen from the right colic
flexure to the left colic flexure, where it bends
inferiorly to become the descending colon.
 Arterial supply- middle colic & right colic
from superior mesenteric artery for the right 2/3,
left colic from inferior mesenteric artery for the
left 1/3
 Venous drainage- superior mesenteric vein

62. 3. The descending colon - passes retroperitoneally
from the left colic flexure into the left iliac fossa,
where it is continuous with the sigmoid colon.
◦ arterial supply- left colic & sigmoid arteries
from the IMA
◦ venous drainage- by IMV
4. The sigmoid colon- S-shaped; extends from the
iliac fossa to the third sacral segment, where it
joins the rectum
◦ termination of the teniae coli indicates the recto
sigmoid junction.
◦ Arterial supply -three sigmoid artery from IMA
◦ Venous drainage- IMV

65. •Rectum and Anal Canal
•The rectum, the fixed terminal part of the large
intestine, is continuous with the sigmoid colon at
the level of the S3 vertebra.
•The junction is at the lower end of the mesentery
of the sigmoid colon.
•The rectum is continuous inferiorly with the anal
canal