the digestive system lecture 4

The Digestive SystemLecture 5

Peritoneal Folds of Posterior

Abdominal Wall

a. Mesentery of small intestine:

▪ It is a broad, fan-shaped peritoneal fold

connecting coils of jejunum and ileum to

posterior abdominal wall.

▪ The border attached to posterior wall of

abdomen is called the root of the

mesentery, which is about 15 cm long, and

extends obliquely downwards and to the

right from duodenjejunal flexure to the

upper part of right sacroiliac joint. 1

Root of

mesentery of

small intestine

2

Mesentery of small

intestine

3

▪ The intestinal border of mesentery is about 6

m long and is thrown into numerous pleats.

▪ At this border the two layers of the

peritoneum separate to enclose the gut,

forming its visceral layer.

b. Transverse mesocolon:

▪ It is a broad peritoneal fold that connects the

transverse colon to posterior abdominal wall.

▪ Its two layers pass from anterior aspect of

head and body of pancreas to posterior

surface of transverse colon, where they

separate to enclose that part of the colon. 4

▪ Between the two layers of the transverse

mesocolon are the blood vessels, nerves

and lymphatics of the transverse colon.

5

Root of

transverse

mesocolon

6

Transverse mesocolon

7

Transverse

mesocolon

8

c. Sigmoid mesocolon:

▪ This fold connects the sigmoid colon to

pelvic wall.

▪ The line of attachment to pelvic wall has

the form of an inverted V, the apex of which

lies near the division of the left common

iliac artery.

▪ The left limb descends medial to the left

psoas major muscle.

▪ The right limb descends into the pelvis and

ends in the medial plane. 9

▪ The sigmoid and superior rectal vessels

pass between the two layers of the sigmoid

colon.

10

Sigmoid mesocolon

11

Sigmoid Mesocolon

12

d. Mesoappendix: ▪ It is a triangular peritoneal fold around the

vermiform appendix.

▪ It is attached to the back of lower end of

the mesentery, close to ileocaecal junction.

▪ Usually, it extends to tip of the appendix.

▪ The blood vessels, nerves and lymph

vessels of the vermiform appendix,

together with a lymph nodes lie between its

two layers.

13

Mesoappendix

Inferior ileocecal recess

Superior ileocecal recess

ileocecal fold

14

Lesser Omentum▪ Constitute the two layers of peritoneum

that descends from the fissure for

ligamentum venosum and porta hepatis to

the lesser curvature of stomach, and

proximal 2 cm of duodenum.

▪ Between the liver and the 1st 2 cm of

duodenum, the omentum presents a free

right border, which forms the anterior

boundary of the epiploic foramen.

15

▪ This free border contains between its two

peritoneal layers the portal vein, hepatic

artery and bile duct.

16

Lesser

omentum

17

Epiploic

foramen

18

Lesser

omentum

Common bile duct

Proper hepatic artery

Portal vein

Epiploic

foramen

19

Greater Omentum▪ It is the largest peritoneal fold, and

consists of a double sheet of peritoneum,

folded on itself to form four layers.

▪ The anterior two layers descend from

greater curvature of stomach and first 2 cm

of duodenum, pass downwards in front of

loops of small intestine for a variable

distance, and then they turns round and

ascend up to the transverse colon where

they loosely blend with the peritoneum on

the anterior surfaces of the transverse

colon and mesocolon. 20

▪ The greater is a storage house for fat.

▪ In addition, the greater omentum contains

numerous fixed macrophages, which can

be mobilized as free macrophages.

▪ These cells may accumulate in places into

dense, oval or round patches, visible to the

necked eye as 'milky spots‘ on the

omentum.

21

22

Greater omentum

(posterior fold)

Transverse

mesocolonGreater

omentum

(anterior

fold)

23Greater omentum)

Lesser Sac▪ Anterior wall: Forms by the posterior layer of

the anterior fold of greater omentum; posterior

surface of stomach; and lesser omentum.

▪ Posterior wall: Forms by the anterior layer of

the posterior fold of the greater omentum; and

posterior abdominal wall.

24A

24B

Greater omentum

(posterior fold)

Transverse

mesocolonGreater

omentum

(anterior

fold)

Lesser

sac

Peritoneal Compartments▪ The peritoneal cavity can be divided into three

compartments, supracolic, infracolic, and

pelvic.

▪ The dividing line between the supracolic and

infracolic compartments is the attachment of

the transverse mesocolon to the posterior

abdominal wall.

▪ The attachments of the liver to the diaphragm

and supraumblical part of the anterior wall of

the abdomen define the subdivision of the

supracolic compartment.

25

▪ To the right and left of the falciform

ligament are the right and left subphrenic

spaces.

▪ Behind the right lobe of the liver and in

front of the right kidney is the right

subhepatic space.

▪ Below the transverse mesocolon, the

infracolic compartment is subdivided into

right and left infracolic spaces, by the

attachment of the root of the mesentery of

small intestine.

26

Paracolic GutterThese gutters lie on lateral and medial sides

of ascending and descending colons,

respectively.

Intraperitoneal OrgansAn organ is said to be intraperitoneal when it

is almost totally covered with visceral

peritoneum. The stomach, 1st 2 cm of

duodenum, jejunum, ileum, transverse colon,

sigmoid colon, and spleen are good examples

of intraperitoneal organs.

27

Retroperitoneal OrgansRetroperitoneal organs lie behind the

peritoneum and are only partially covered

with visceral peritoneum. The pancreas,

ascending and descending colons, kidneys,

and ureters are examples of retroperitoneal

organs.

28

Nerve Supply of the Peritoneum

1. The parietal peritoneum:

▪ Is sensitive to pain, temperature, touch,

and pressure.

▪ The parietal peritoneum lining the central

part of diaphragm is supplied by the

phrenic nerve (C4) --- hence referred pain

from this area to tip of shoulder.

▪ The peritoneum lining the peripheral part

of diaphragm is supplied by the lower six

intercostals nerves. 29

▪ The remainder of the parietal peritoneum is

supplied by the lower six intercostals and

L1 nerves.

▪ In the pelvis the obturator nerve is the

chief source of supply.

2. The visceral peritoneum:

• Is sensitive only to stretch and tearing and is

not sensitive to touch, pressure, or

temperature.

. It is innervated by afferent nerves which

travel with the autonomic supply to the

viscera. 30

▪ Overdistension of a viscus leads to the

sensation of pain.

31

Stomach▪ Is the most dilated part of the

gastrointestinal tract, interposed between

end of esophagus and beginning of

duodenum.

▪ It lies in epigastric, umblical, and left

hypochondriac regions of abdomen.

▪ Its main functions is storage of food mixed

the food with gastric secretion to form a

semifluid chyme, and the controlled the rate

of delivery of chyme to the small intestine.

32

▪ It is roughly J-shaped and has two

openings, two borders, and two surfaces

33

Cardiac orifice▪ Is the opening by which esophagus

communicates with stomach.

▪ Lies on the left of median plane, behind the

7th left costal cartilage 2.5 cm from its

junction with the sternum (at the level of

T11 vertebra).

Pyloric orifice▪ Is the opening by which stomach

communicates with duodenum.

34

▪ Lies about 1.2 cm to the right of median

plane near the level of lower border of L1

vertebra (transpyloric plane), when the

body is in the supine position.

Right border (lesser curvature)▪ Continuous with right border of

esophagus.

▪ The angular incisure is a notch on this

border, nearer pylorus than esophagus.

Left border (greater curvature) Joins the left border of esophagus at an

acute angle, the cardiac notch. 35

Cardiac orifice

Pyloric

orifice

36

Anterior surfaceIs related to anterior abdominal wall, left

costal margin, left pleura and lung,

diaphragm, and left lobe of liver.

Posterior surface Is related to stomach bed (lesser sac,

diaphragm, spleen, left suprarenal gland,

upper part of left kidney, splenic artery, body

of pancreas, transverse mesocolon, and

transverse colon).

37

38

Stomach (Anterior Relations)

Greater omentum

(posterior layers)

39

Stomach (Posterior Relations)

The stomach is divided into three parts:

fundus, body and pylorus.

Fundus▪ Is dome-shaped and projects upwards and

to the left of cardiac orifice.

▪ It is usually filled with swallowed air.

BodyIs the largest part of stomach, extends from

cardiac orifice to level of angular incisure.

40

Pyloric part▪ Extends from body to pyloric orifice.

▪ It is subdivided into three regions: pyloric

antrum, pyloric canal, and pylorus.

a. The pyloric antrum:

Is the dilated proximal portion of pylorus.

b. The pyloric canal:

Is the narrow, cylindrical portion, 2 – 3 cm

long, which continues distally with pylorus.

41

c. The pylorus:

▪ Is the thickened portion of the stomach

that unites it to duodenum.

▪ The thickening is due to an increase in the

amount of circular muscle to form the

pyloric sphincter, which is concerned with

controlling the rate of discharge of stomach

contents into duodenum.

42

Pylorus

43

▪ When the stomach is empty, the mucosa

lies in large folds, called rugae.

▪ The stomach is completely enclosed by

visceral peritoneum, which leaves the

lesser curvature as the lesser omentum and

the greater curvature as the greater

omentum.

44

Arterial Supply:The arterial supply of stomach arises from

celiac trunk.

a. Right and left gastric arteries:

▪ Are branches of hepatic and celiac arteries,

respectively.

▪ They form an anastomosing arch along lesser

curvature.

b. Right and left gastroepiploic arteries:▪ are branches of gastroduodenal and splenic

arteries, respectively.

▪ They form a similar arch along the greater

curvature. 45

C. Short gastric arteries: • Branches of the splenic artery.

• They supply the fundus.

Venous Drainage▪ Veins from stomach drain into portal

circulation.

▪ The right and left gastric veins drain directly

into portal vein.

▪ The right gastroepiploic vein joins the

superior mesenteric vein.

46

▪ The left gastroepiploic and short gastric veins

join the splenic vein.

Lymph Drainage:▪ Lymph vessels from stomach follow the

arteries and drain into right and left gastric

nodes, the right and left gastoepiploic nodes,

and the short gastric nodes.

▪ Lymph from these node drains into the celiac

nodes.

47

Nerve Supply:The stomach is supply by sympathetic and

parasympathetic fibers (vagi) via the celiac

plexus.

48