anterior abdominal wall and GI tract

Question 1

how is the abdomen divided?

Answer 1

(1st - four quadrants, UL, UR, LL, LR)

then into nine regions:

Horizontal lines -
the transpyloric line (9th costal cartilage, going through pylorus of stomach, or L1)
Second horizontal line is intertubercular line, going through the pelvic tubercules
Goes through L5

Vertical lines -
Two midclavicular lines

from top to bottom, on the left and right side, you’ve got hypochondrium, lumbar and iliac
then the middle column goes epigastric, umbilical and hypogastric

Question 2

thew abdominal wall has two groups of muscles, flat and vertical.

Explain the flat group of muscles

Answer 2

Lie laterally (on the sides) on the abdomen, in order of front to back:

External oblique - most superficial, fibres run medially and downwards to midline (same direction as external intercostal muscles). rotation and twisting

Internal oblique - deep to external one, fibre perpendicular to external oblique (medially and upwards). causes flexion of the trunk

transversus abdominis - named as such because the fibres run horizontally
Deep to internal oblique
Can also see the posterior wall of rectus sheath. transversalis fascia runs beneath. supports back?

Question 3

what is the rectus sheath?

Answer 3

a multi-layered aponeurosis (an aponeurosis is flat thin sheaths of connective tissue where muscle can attach/insert, similar-ish to tendon but not the same).

It’s the big white-ish bit in the centre of the abdomen.

***Encloses the rectus abdominis muscles

Question 4

the rectus sheath - what is it composed of (anterior and posterior walls)?

Answer 4

The rectus sheath has an anterior and posterior wall

these walls are composed of a fusion of the aponeuroses (they have their own) of the three flat muscles mentioned

Anterior wall = aponeuroses of external oblique + half of internal oblique

Posterior wall = aponeuroses of other half of internal oblique, and all of transversus abdominis.
They fuse at the midline, linea alba

Question 5

there are two vertical muscles of the abdominal wall -
explain the one we need to know

Answer 5

Rectus abdominis - the long muscle spanning the entire Ant. Abd. wall, either side of the midline.

it extends from the xiphoid process to the pubic crest

Has fibrous bands intersected within, known as tendinous intersections (horizontal ab marks of six pack)
Rectus abdominis lies within the rectus sheath

flexion of the lumbar spine

Question 6

define the location of the abdomen

Answer 6

inferior to diaphragm and above the pelvic rim

Question 7

which nerves innervate the muscles of the anterior abdominal wall?

Answer 7

spinal nerves T8-T12

Question 8

blood supply of the anterior abdominal wall -

anteriorly?

laterally?

Answer 8

laterally the abdominal wall is supplied by segmental lumbar arteries arising directly from the abdominal aorta

anteriorly, the abdominal wall is supplied by the sup. and inf. epigastric arteries, arising form the int. and ext. iliac arteries respectively

Question 9

what are the functions of the anterior abdominal wall muscles?

Answer 9

● Protect the abdominal viscera from injury

● Form a firm but flexible wall keeping the abdominal viscera within the cavity

● Assist in quiet and forced expiration

● Increase intra abdominal pressure during coughing, vomiting, micturition and defecation

Question 10

peritoneum of the peritoneal cavity - what is it made up of and how is it structured?

Answer 10

Defined as a serous lining of the abdomen. Both layers are made up of simple squamous epithelial cells (mesothelium)

Has two layers -
Parietal lines inner aspect of the wall
Visceral peritoneum covers the structure and organs (so visceral is deeper)
Peritoneal cavity between the two layers - contains small amount of peritoneal fluid to allow smooth movement of organs sliding past each other

Question 11

how does the peritoneum develop to have two layers?

pain and peritoneum?

Answer 11

Duct tube pushes through the peritoneum, and the bit it takes with it, that invaginates, is then the visceral peritoneum

Pain from the visceral peritoneum is referred to areas of skin (dermatomes) which are supplied by the same sensory ganglia and spinal cord segments

Question 12

define intraperitoneal and retroperitoneal organs

Answer 12

Intraperitoneal organs -
enveloped by visceral peritoneum, which covers the organ both anteriorly and posteriorly. Examples include the stomach, liver and spleen

Retroperitoneal organs -
Retroperitoneal organs are not associated with visceral peritoneum; they are only covered in parietal peritoneum, and that peritoneum only covers their anterior surface

Question 13

what are the retroperitoneal organs?

Answer 13

SAD PUCKER

S = Suprarenal (adrenal) Glands
A = Aorta/IVC
D =Duodenum (except the proximal 2cm, the duodenal cap)
P = Pancreas (except the tail)
U = Ureters
C = Colon (ascending and descending parts)
K = Kidneys
E = (O)esophagus
R = Rectum

Question 14

which are the intraperitoneal organs?

Answer 14

stomach, spleen, liver, first and fourth parts of the duodenum, jejunum, ileum, transverse, and sigmoid colon, tail of pancreas

Question 15

what is mesentery?

organs that are m______ have it

what does it contain?

Answer 15

Suspends from posterior abdominal wall, it’s a double layer of visceral peritoneum, connecting an intraperitoneal organ (SI and part of LI) to the posterior abdominal wall

Required for mobile organs
Contains fat, makes it identifiable as seen in image
Contains BVs, lymphatics and nerves for an organ

Question 16

grater and lesser omentum?

gastrocolic ligament?

mesentery?

suspensory ligament?

transverse mesocolon?

Answer 16

greater and lesser omentum = double peritoneal folds (not mesentery i think) on lesser and greater curves (not fundus?) of stomach)

greater omentum connects to stomach and loosely to transverse colon, with thew gastrocolic ligament in the middle

mesentery seems to just be for jejunum and ileum

suspensory ligament = peritoneal folds at the duodenojejunal flexure

transverse mesocolon = mesentery of the transverse colon (and there’s the sigmoid mesocolon)

Question 17

define the three regions of the gastrointestinal tract

Answer 17

foregut = oesophagus, stomach and first half of duodenum (can include organs like liver, pancreas and gallbladder too)

Midgut = second half of duodenum, the jejunum and the ileum, cecum and ascending colon, the first 2/3s of transverse colon

Hindgut = distal ⅓ of transverse colon, descending colon, sigmoid colon and rectum, ending at the upper anal canal

Question 18

which branches of the abdominal aorta supply what?

Answer 18

Celiac trunk supplies foregut

Superior mesenteric artery supplies midgut

Inferior mesenteric artery supplies hindgut

Question 19

the first section of the small intestine is the duodenum.

what is it’s structure (four sections), location and associations?

Answer 19

C shaped, continues on from pylorus of stomach, has the widest lumen.

Has four parts :
*Superior (the only intraperitoneal part)
*Descending- where the major duodenal papilla is (opening of the bile duct and main pancreatic duct) , *Inferior (3rd part crosses IVC, aorta and vertebral column
*Ascending

Location - above level of the umbilicus
Most of its length is retroperitoneal (just not the proximal 2cm, duodenal cap)

Associations -
Inferior vena cava and abdominal aorta lie posterior to the duodenum

Question 20

jejunum - location and blood supply?

ileum?

Answer 20

second part of small intestine beginning at duodenojejunal flexure, located in upper left quadrant
entirely intraperitoneal
supplied by jejunal arteries form the SMA

ileum is in lower right quadrant
ileal and ileocolic arteries form SMA

Question 21

what are the four main differences between the jejunum and ileum?

Answer 21

Hard to tell apart externally

1. Jejunum has more plicae circulares (mucosa folds with microvilli for nutrients absorption) compared to ileum, as more absorption of nutrients occurs in J

2.Jejunum has longer vasa recta (straight arteries)

3. Arteries form loops called arterial arcades. Jejunum has LESS of these than ileum

Internal ileum has lymph nodules known as Peyer’s patches found more at terminal end

***All have mesentery and are intraperitoneal

Question 22

what are the regions of the large intestine and where does it start?

what is found at it’s terminal end?

Answer 22

Goes caecum -ascenidng colon - transverse colon - Descending colon -Sigmoid colon

Start = ileocecal valve, in the right iliac region (fossa)

Towards the terminal end of is the appendix which also has mesentery and is therefore quite mobile

Question 23

go along the large intestine, explaining it’s parts.

Answer 23

cecum - up, the ascending colon
Bends at the hepatic flexure - becomes transverse colon (now has/enters mesentery so suspends from posterior abd. Wall)

Bends again at splenic flexure to become descending colon (leaving the mesentery) -

S shape at end of that is the sigmoid colon which enters the pelvis

Continuous into the rectum, continues into the anal canal

Question 24

which parts of the large intestine are intra vs retroperitoneal?

Answer 24

Ascending and descending are retroperitoneal, the transverse and sigmoid are intra as they also have mesentery

Question 25

what are three distinct features of the large intestine?

Answer 25

Taenia coli = three fibrous bands of muscle running along the whole thing that cause the bulges (haustrations)

Appendices epiploicae = fatty tags, shows where blood vessels penetrate walls of the large intestine. Trans, and sig, have mesentery so are intraperitoneal

Question 26

explain the structure and features of the stomach

Answer 26

Cardia = stomach connects to oesophagus

Fundus of stomach (upper bit superior to cardia)

Then body of the stomach

Then the pyloric part, spilt into antrum and pyloric canal, which has the sphincter to control movement of chyme

Rugae = folds in stomach

Great omentum = folds of peritoneum suspends from the greater curvature

Question 27

define the greater and lesser curvature of the stomach

Answer 27

Lesser curvature = between cardia and pyloric sphincter

Greater curvature = the other curve, the long outer curve

Question 28

where is the stomach located?

Answer 28

size and position vary but always in LU quadrant, epigastric, umbilical and left hypochondrium regions

Question 29

at what level does the abdominal aorta penetrate the diaphragm?

Answer 29

T12

Question 30

the superior mesenteric artery:

where is it located?

Answer 30

arises from the abdominal aorta at L1

SMA lies behind pyloric section of the stomach, and in front of the renal vein and the uncinate process of the pancreas (the other big vessel seen is the SMV)

Question 31

what are the four branches of the SMA and what do they supply?

Answer 31

as it is SMA, supplies midgut…

1. Middle colic artery
   Goes up to supply 1st/proximal ⅔ of transcending colon
2. Right colic artery
   Supplies ascending colon
3. Ileocolic artery
   Supplies ileocecal junction (down and right)
4. Jejunal and ileal arteries
   Easy to identify with all the arterial arcades, vasa recta etc…The jejunal blood supply is characterised by a smaller number of arterial arcades, but longer vasa recta. In contrast, the ileal blood supply is marked by more arterial arcades with shorter vasa recta

Question 32

where is the IMA located?

Answer 32

arises from the abdominal aorta at L3, supplies the hindgut

Question 33

inferior mesenteric artery -

what are it’s three branches and what do they supply?

Answer 33

1. Left colic artery -
   supplies descending colon, and anastomoses with the middle colic to supply the distal ⅓ of transverse colon
2. Sigmoidal artery -
   supplies sigmoid colon
3. Superior rectal arteries -
   supplies rectum, branches on the left

Question 34

just to get a clear picture, explain the blood supply of the large intestine

Answer 34

● Right colic artery from the superior mesenteric artery supplying the ascending colon

● Middle colic artery from the superior mesenteric artery and the left colic artery from the inferior mesenteric artery supply the transverse colon

● Left colic artery from the inferior mesenteric artery supply the descending colon

● Sigmoidal arteries from the inferior mesenteric artery supply the sigmoid colon

Question 35

which section of stomach is seen to be filled with gas on X-rays?

Answer 35

the fundus