Anatomy%20-%20Digestive%20System%20part%20II.pdf.pdf

Anatomy of digestive system parts 2

1. Digestive Tract
Part II

2. PHARYNX
•superior expanded part of the alimentary
system
•posterior to the nasal and oral cavities,
•inferiorly past the larynx.
The pharynx extends from the cranial base to
the inferior border of the cricoid cartilage
anteriorly and the inferior border of the C6
vertebra posteriorly.

3. PHARYNX

4. PHARYNX
•The pharynx is widest (approximately 5 cm)
opposite the hyoid and narrowest
(approximately 1.5 cm) at its inferior end,
where it is continuous with the esophagus.
•The flat posterior wall of the pharynx lies
against the prevertebral layer of deep cervical
fascia.

5. PHARYNX

6. Interior of Pharynx
It is divided into three parts:
•Nasopharynx: posterior to the nose and superior to the soft
palate.
•Oropharynx: posterior to the mouth.
•Laryngopharynx: posterior to the larynx.
The nasopharynx has a respiratory function; it is the posterior
extension of the nasal cavities.
The nose opens into the nasopharynx through two choanae (paired
openings between the nasal cavity and the nasopharynx).
The roof and posterior wall of the nasopharynx form a continuous
surface that lies inferior to the body of the sphenoid bone and the
basilar part of the occipital bone.

7. PHARYNX

11. Esophagus
•is a muscular tube
•approximately 25 cm long
•an average diameter of 2 cm
•Conveys food from the pharynx to the
stomach

12. Esophagus

13. Esophagus
has three constrictions:
•Cervical constriction
(upper esophageal
sphincter): at its
beginning at the
pharyngoesophageal
junction,
approximately 15 cm
from the incisor
teeth; caused by the
cricopharyngeus
muscle

14. Esophagus
•Thoracic (broncho-aortic)
constriction: a compound
constriction where it is first
crossed by the arch of the
aorta, 22.5 cm from the
incisor teeth, and then
where it is crossed by the
left main bronchus, 27.5
cm from the incisor teeth;
the former is seen in
anteroposterior views, the
latter in lateral views.

15. Esophagus
•Diaphragmatic
constriction:
where it passes
through the
esophageal hiatus
of the diaphragm,
approximately 40
cm from the
incisor teeth.

16. The esophagus:
•follows the curve of the vertebral column as it descends through
the neck and mediastinum.
•has internal circular and external longitudinal layers of muscle.
•its superior third, the external layer consists of voluntary striated
muscle; the inferior third is composed of smooth muscle, and the
middle third is made up of both types of muscle.
•passes through the esophageal hiatus in the muscular right crus of
the diaphragm, just to the left of the median plane at the level of
the T10 vertebra.
•terminates by entering the stomach at the cardial orifice of the
stomach the left of the midline at the level of the 7th left costal
cartilage and T11 vertebra.

17. The esophagus
•is attached to the margins of the esophageal
hiatus in the diaphragm by the
phrenico-esophageal ligament, an extension
of inferior diaphragmatic fascia.
•This ligament permits independent movement
of the diaphragm and esophagus during
respiration and swallowing.

18. Stomach
The stomach is the expanded part of the digestive
tract between the esophagus and small intestine.
The gastric juice gradually converts a mass of food
into a semiliquid mixture, chyme, which passes fairly
quickly into the duodenum.
An empty stomach is only of slightly larger caliber
than the large intestine; however, it is capable of
considerable expansion and can hold 2–3 L of food.

19. Stomach

20. The stomach has four parts:
•Cardia: the part surrounding the cardial orifice (opening), the
superior opening or inlet of the stomach. In the supine position,
the cardial orifice usually lies posterior to the 6th left costal
cartilage, 2–4 cm from the median plane at the level of the T11
vertebra.
•Fundus: the dilated superior part, limited inferiorly by the
horizontal plane of the cardial orifice. The cardial notch is
between the esophagus and the fundus. The fundus may be
dilated by gas, fluid, food, or any combination of these. In the
supine position, the fundus usually lies posterior to the left 6th rib.
•Body: the major part of the stomach between the fundus and
pyloric antrum.
•Pyloric part: the funnel-shaped outflow region of the stomach; its
wider part, the pyloric antrum, leads into the pyloric canal, its
narrower part .

21. Stomach

22. Pylorus
The pylorus is the distal, sphincteric region of the pyloric part.
It is a marked thickening of the circular layer of smooth
muscle that controls discharge of the stomach contents
through the pyloric orifice into the duodenum.
Intermittent emptying of the stomach occurs when
intragastric pressure overcomes the resistance of the pylorus.
The pylorus is normally tonically contracted so that the pyloric
orifi ce is reduced, except when emitting chyme. At irregular
intervals, gastric peristalsis pushes the chyme through the
pyloric canal and orifice into the small intestine for further
mixing, digestion, and absorption.

23. Pylorus

24. Stomach
The stomach has two curvatures:
•Lesser curvature: forms the shorter concave right
border of the stomach. The angular incisure (notch),
the most inferior part of the curvature, indicates the
junction of the body and pyloric part of the stomach.
•Greater curvature: forms the longer convex left
border of the stomach. It passes inferiorly to the left
from the 5th intercostal space, then curves to the
right, passing deep to the 9th or 10th left cartilage as it
continues medially to reach the pyloric antrum.

25. Stomach

26. RELATIONS OF STOMACH
•The stomach is covered by visceral peritoneum, except where
blood vessels run along its curvatures and in a small area posterior
to the cardial orifice.
•The two layers of the lesser omentum extend around the stomach
and leave its greater curvature as the greater omentum.
•Anteriorly, the stomach is related to the diaphragm, left lobe of
liver, and anterior abdominal wall.
•Posteriorly, the stomach is related to the omental bursa and
pancreas; the posterior surface of the stomach forms most of the
anterior wall of the omental bursa.
•The transverse colon is related inferiorly and laterally to the
stomach as it courses along the greater curvature of the stomach
to the left colic flexure.

27. Lesser Omentum

28. Greater Omentum

29. Omentum Bursa

30. VESSELS AND NERVES OF STOMACH

31. VESSELS AND NERVES OF STOMACH

32. VESSELS AND NERVES OF STOMACH
The veins of the stomach are parallel to the arteries in
position and course.
The right and left gastric veins drain into the hepatic
portal vein; the short gastric veins and left
gastro-omental veins drain into the splenic vein, which
joins the superior mesenteric vein (SMV) to form the
hepatic portal vein.
The right gastro-omental vein empties in the SMV. A
prepyloric vein ascends over the pylorus to the right
gastric vein. Because this vein is obvious in living
persons, surgeons use it for identifying the pylorus.

33. VESSELS AND NERVES OF STOMACH

34. VESSELS AND NERVES OF STOMACH
The parasympathetic nerve supply of the stomach is from the anterior and posterior
vagal trunks and their branches, which enter the abdomen through the esophageal
hiatus.
The anterior vagal trunk, derived mainly from the left vagus nerve (CN X), usually enters
the abdomen as a single branch that lies on the anterior surface of the esophagus.
It runs toward the lesser curvature of the stomach, where it gives off hepatic and
duodenal branches, which leave the stomach in the hepatoduodenal ligament.
The sympathetic nerve supply of the stomach, from the T6 through T9 segments of the
spinal cord, passes to the celiac plexus through the greater splanchnic nerve and is
distributed through the plexuses around the gastric and gastroomental arteries.

35. Small Intestine

36. Small Intestine
extends from the pylorus to the ileocecal
junction where the ileum joins the cecum (the
first part of the large intestine)
The small intestine, consists of the:
•duodenum
•jejunum
•ileum

37. DUODENUM
The duodenum, the first and shortest (25 cm) part
of the small intestine, is also the widest part.
The duodenum pursues a C-shaped course around
the head of the pancreas.
It begins at the pylorus on the right side and ends at
the duodenojejunal flexure (junction) on the left
side. This junction occurs approximately at the level
of the L2 vertebra, 2–3 cm to the left of the midline.
Most of the duodenum is fixed by peritoneum to
structures on the posterior abdominal wall and is
considered partially retroperitoneal.

38. DUODENUM

39. DUODENUM

40. Divisions
The duodenum is divisible into four parts:
•Superior (first) part: short (approximately 5 cm) and
lies anterolateral to the body of the L1 vertebra.
•Descending (second) part: longer (7–10 cm) and
descends along the right sides of the L1–L3 vertebrae.
•Inferior (third) part: 6–8 cm long and crosses the L3
vertebra.
•Ascending (fourth) part: short (5 cm) and begins at the
left of the L3 vertebra and rises superiorly as far as the
superior border of the L2 vertebra.

42. Superior part of the duodenum
•ascends from the pylorus
•Is overlapped by the liver and gallbladder
•Peritoneum covers its anterior aspect rather
than posterior.
•The proximal part has the hepatoduodenal
ligament (part of the lesser omentum)
attached superiorly and the greater omentum
attached inferiorly

43. Superior part of the duodenum

44. Descending part of the duodenum
•runs inferiorly, curving around the head of the
pancreas
•bile and main pancreatic ducts enter its
posteromedial wall. These ducts usually unite to
form the hepatopancreatic ampulla, which opens
on an eminence, called the major duodenal
papilla, located posteromedially in the descending
duodenum.
•The descending part of the duodenum is entirely
retroperitoneal.

45. Descending part of the duodenum

46. Inferior (horizontal) part of the duodenum
•Runs transversely to the left, passing over the IVC,
aorta, and L3 vertebra.
•It is crossed by the superior mesenteric artery and
vein and the root of the mesentery of the
jejunum and ileum.
•Superior to it is the head of the pancreas and its
uncinate process.
•Posteriorly it is separated from the vertebral
column by the right psoas major, IVC, aorta, and
the right testicular or ovarian vessels.

47. Ascending part of the duodenum
•runs superiorly and along the left side of the aorta to reach the inferior
border of the body of the pancreas.
•joins the jejunum at the duodenojejunal flexure, supported by the
attachment of a suspensory muscle of the duodenum (ligament of Treitz).
•This muscle is composed of a slip of skeletal muscle from the diaphragm
and a fibromuscular band of smooth muscle from the third and fourth
parts of the duodenum.
•Contraction of this muscle widens the angle of the duodenojejunal flexure,
facilitating movement of the intestinal contents.
•The suspensory muscle passes posterior to the pancreas and splenic vein
and anterior to the left renal vein.

48. Ascending part of the duodenum

49. Vasculature of Duodenum
The arteries of the duodenum arise from the celiac trunk
and the superior mesenteric artery.
The celiac trunk, via the gastroduodenal artery and its
branch, the superior pancreaticoduodenal artery,
supplies the duodenum proximal to the entry of the bile
duct into the descending part of the duodenum.
The superior mesenteric artery, through its branch, the
inferior pancreaticoduodenal artery, supplies the
duodenum distal to the entry of the bile duct.

50. Vasculature of Duodenum

51. Vasculature of Duodenum
The veins of the duodenum follow the arteries
and drain into the hepatic portal vein, some
directly and others indirectly, through the
superior mesenteric and splenic veins.

52. Vasculature of Duodenum

53. Innervation of Duodenum
The nerves of the duodenum derive from the
vagus and greater and lesser (abdominopelvic)
splanchnic nerves by way of the celiac and
superior mesenteric plexuses.

55. JEJUNUM AND ILEUM
•the jejunum, begins at the duodenojejunal
flexure
•the ileum, ends at the ileocecal junction, the
union of the terminal ileum and the cecum
•jejunum and ileum are 6–7 m long
•the jejunum constituting approximately two
fifths and the ileum approximately three
fifths of the intraperitoneal section of the
small intestine.

56. JEJUNUM AND ILEUM

57. DUODENUM, JEJUNUM AND ILEUM

58. JEJUNUM AND ILEUM
•Most of the jejunum lies in the left upper quadrant
(LUQ) of the infracolic compartment,
•the ileum lies in the right lower quadrant (RLQ).
•terminal ileum usually lies in the pelvis from which it
ascends, ending in the medial aspect of the cecum.
•Although no clear line of demarcation between the
jejunum and ileum exists, they have distinctive
characteristics that are surgically important

59. Mesentery
•is a fan-shaped fold of peritoneum that attaches the
jejunum and ileum to the posterior abdominal wall.
•origin or root of the mesentery (approximately 15 cm
long) is directed obliquely, inferiorly, and to the right.
•extends from the duodenojejunal junction on the left
side of vertebra L2 to the ileocolic junction and the
right sacro-iliac joint.
•average length of the mesentery from its root to the
intestinal border is 20 cm
•Between the two layers of the mesentery are the
superior mesenteric vessels, lymph nodes, a variable
amount of fat, and autonomic nerves.

60. Vasculature
The superior mesenteric artery (SMA) supplies the
jejunum and ileum via jejunal and ileal arteries.
The SMA usually arises from the abdominal aorta at the
level of the L1 vertebra, approximately 1 cm inferior to
the celiac trunk, and runs between the layers of the
mesentery, sending 15–18 branches to the jejunum and
ileum.
The arteries unite to form loops or arches, called arterial
arcades, which give rise to straight arteries, called vasa
recta

63. Large Intestine

64. Large intestine
•Consists the cecum; appendix; ascending,
transverse, descending, and sigmoid colon;
rectum; and anal canal.

65. CECUM AND APPENDIX
•The cecum is the first part of the large intestine; it
is continuous with the ascending colon.
•The cecum is a blind intestinal pouch,
approximately 7.5 cm in both length and breadth.
It lies in the iliac fossa of the right lower quadrant
of the abdomen, inferior to the junction of the
terminal ileum and cecum.
•the cecum has no mesentery.
•The terminal ileum enters the cecum obliquely
and partly invaginates into it.

66. CECUM AND APPENDIX

67. CECUM AND APPENDIX
•The appendix (vermiform appendix; L. vermis,
wormlike) is a blind intestinal diverticulum (6–10
cm in length) that contains masses of lymphoid
tissue.
•It arises from the posteromedial aspect of the
cecum inferior to the ileocecal junction.
•The appendix has a short triangular mesentery,
the meso-appendix, which derives from the
posterior side of the mesentery of the terminal
ileum.

68. Vasculature
•The arterial supply of the cecum is from the
ileocolic artery, the terminal branch of the
SMA.
•The appendicular artery, a branch of the
ileocolic artery, supplies the appendix.
•Venous drainage from the meso-appendix,
which derives from the posterior side of the
mesentery of the terminal ileum.

70. COLON
•has four parts—ascending, transverse,
descending, and sigmoid.

71. Ascending colon
•is the second part of the large intestine.
•passes superiorly on the right side of the
abdominal cavity from the cecum to the right
lobe of the liver, where it turns to the left at
the right colic flexure (hepatic flexure).
•This flexure lies deep to the 9th and 10th ribs
and is overlapped by the inferior part of the
liver.
•is narrower than the cecum.

72. Vasculature
The arterial supply to the ascending colon and right colic
flexure is from branches of the SMA, the ileocolic and right
colic arteries.
These arteries anastomose with each other and with the right
branch of the middle colic artery, the first of a series of
anastomotic arcades that is continued by the left colic and
sigmoid arteries to form a continuous arterial channel, the
marginal artery (juxtacolic artery).
•Venous drainage from the ascending colon flows through
tributaries of the SMV, the ileocolic and right colic veins

75. Transverse colon
•is the third, longest, and most mobile part of
the large intestine.
•crosses the abdomen from the right colic
flexure to the left colic flexure, where it turns
inferiorly to become the descending colon.

76. Vasculature
The arterial supply of the transverse colon is mainly
from the middle colic artery, a branch of the SMA.
However, the transverse colon may also receive
arterial blood from the right and left colic arteries
via anastomoses, part of the series of anastomotic
arcades that collectively form the marginal artery
(juxtacolic artery).
Venous drainage of the transverse colon is through
the SMV.

78. Descending colon
•occupies a secondarily retroperitoneal
position between the left colic flexure and the
left iliac fossa, where it is continuous with the
sigmoid colon.
•As it descends, the colon passes anterior to
the lateral border of the left kidney.

79. Sigmoid colon
•characterized by its S-shaped loop of variable
length, links the descending colon and the
rectum.
•extends from the iliac fossa to the third sacral
(S3) vertebra, where it joins the rectum.

80. Vasculature
The arterial supply of the descending and sigmoid colon
is from the left colic and sigmoid arteries, branches of
the inferior mesenteric artery .
The superior branch of the superior sigmoid artery
anastomoses with the descending branch of the left colic
artery, thereby forming a part of the marginal artery.
Venous drain age from the descending colon and sigmoid
colon is provided by the inferior mesenteric vein, flowing
usually into the splenic vein and then the hepatic portal
vein on its way to the liver.

82. Thank you for attention!