Lecture 3 - Anterior abdominal wall & gastrointestinal tract

Question 1

What are the 3 parts of the abdomen?

Answer 1

• Muscles - (anterior and posterior abdominal wall)
• Peritoneum - and associated structures (mesenteries/ligaments/omenta)
• GI tract - abdominal oesophagus, stomach, small intestine, large intestine, rectum

Question 2

What are all the other parts of the abdomen?

Answer 2

• liver and gallbladder
• pancreas
• spleen
• kidneys and adrenal glands
• arteries (abdominal aorta & branches)
• veins (IVC - inferior vena cava & tributaries)
• ureters
• biliary tree (i.e. the bile ducts)

Question 3

Describe the axis of the abdominal cavity

Answer 3

Completely vertical

Question 4

Describe the axis of the pelvis cavity

Answer 4

Tilted to the left

Question 5

What are the different quadrants in the abdominal cavity

Answer 5

Right descending: right hypochondrium, right lumbar, right iliac

Middle descending: epigastic, umbilical, hypogastric

Left descending: left hypochondrium, left lumbar, left iliac

Question 6

What are anterolateral abdominal wall muscles?

Answer 6

• flat muscles
• protect the abdominal viscera (organs)
• increase intra-abdominal pressure (e.g. for defecation and childbirth)
• maintain posture and move the trunk

Question 7

What are the 2 groups of anterolateral muscles?

Answer 7

Anterior muscles - 2 muscles on either side of the midline

Lateral muscles - 3 muscles on either side of abdomen

Connected by rectus sheath

Question 8

What is the rectus sheath?

Answer 8

Formed by the aponeurosis (a broad, flat sheet of connective tissue) of the lateral 3 lateral muscles, enclosing the rectus abdominis

Question 9

What is the anterior wall?

Answer 9

aponeuroses of external oblique and anterior 1/2 internal oblique

Question 10

What is the posterior wall?

Answer 10

aponeuroses of posterior 1/2 internal obliques and transverus abdominis aponeurosis

Question 11

What is the midline?

Answer 11

Linea alba

Question 12

Describe features of the rectus abdominis muscle

Answer 12

• long vertical muscles on either side of the linea alba
• extends the length of the anterior abdominal wall
• intersected by tendinous intersections - easily visible in an individual with well-developed rectus abdominus
• lies within the rectus sheath

Question 13

Describe features of the external oblique muscle

Answer 13

• most superficial of the 3 lateral muscles
• fibres run MEDIALLY and INFERIORLY towards the midline
• aponeurosis of EOm: anterior wall of the rectus sheath

Question 14

Describe features of the internal oblique muscles

Answer 14

• deep to external oblique muscles
• fibres orientated perpendicular to EOm, running medially and superiorly
• aponeurosis if IOm: anterior 1/2 forms anterior wall, posterior 1/2 forms posterior wall

Question 15

Describe features that are transversus abdominis muscles

Answer 15

• deep to internal oblique muscle
• fibres orientated horizontally
• aponeurosis of Tam: posterior wall of the rectus sheath

Question 16

Describe peritoneum and peritoneal cavity

Answer 16

serous membrane lining the abdomen
- pariental peritoneum lines the inner aspect of the abdominal wall
- visceral peritoneal covers organs and structures within the peritoneum

Question 17

What is a serous membrane?

Answer 17

A serous membrane is a thin membrane that secretes serous fluid to lubricate and reduce friction between organs and body cavities.

Question 18

What is the peritoneal cavity?

Answer 18

thin cavity between the 2 layers, it contains a small of peritoneal fluid that allow the visceral to slide alongside each other.

Question 19

What is the mesentery?

Answer 19

• organ compromised of a double found of peritoneum
• encloses the small intestines and parts of the colon (transverse and sigmoid) and attaches them to the posterior abdominal wall
• embedded within - blood vessels, lymph and nerves

Question 20

What is the foregut, midgut & hindgut?

Answer 20

• different embryological origins of different parts of the GI tract
• important for understanding blood supply, nerve supply etc.

Question 21

Where is the foregut found?

Answer 21

from oesophagus to duodenum (first part of the small intestine) at the level of the major duodenal papilla (halfway along the duodenum)

Blood supply - coeliac trunk

Question 22

Where is the midgut found?

Answer 22

From major duodenal papilla to ends 2/3 of the way along the transverse colon

Blood supply - superior mesenteric artery

Question 23

Where is the hindgut found?

Answer 23

From last 1/3 of transverse colon to the upper anal canal

Blood supply - inferior mesenteric artery

Question 24

How is the stomach broken up?

Answer 24

• epigastric, umbilical and left hypochondrium regions

Divided into 4 parts:
- cardia
- fundus
- body
- pyloric region (antrum, canal & sphincter)

other features:
- lesser & greater curvature
- rugae - folds lining the stomach

Question 25

Describe the blood supply of the stomach

Answer 25

Branches of the coeliac trunk - left and right gastric arteries - left and right gastroepiploic arteries - short gastric arteries Nerves - innervated by the vagus nerve sympathetic fibres via the coeliac plexus

Question 26

Describe features of the small intestine - duodenum

Answer 26

- Above the level of umbilicus - continuous with the pylorus of the stomach - widest lumen

Question 27

What are the 4 parts of the duodenum?

Answer 27

- superior - descending - major duodenal papilla (opening of the bile duct and main pancreatic duct) - inferior - ascending Most of its length is retroperitoneal (behind the peritoneal

Question 28

What are features of Jejunum?

Answer 28

- intraperitoneal - mostly in left upper quadrant - more plicae circulares (mucosa fold) - less prominent arterial arcades - longer vasa recta (straight arteries) - few solitary lymph nodes

Question 29

What are features of ileum?

Answer 29

- intraperitoneal - mostly in right upper quadrant - few plicae circulares - more arterial arcades - shorter vasa recta - Peyer's patches

Question 30

What is the large intestines?

Answer 30

comprised of caecum, appendix, colon, rectum and anal canal Colon: ascending, transverse, descending and sigmoid Features: - epiploic appendices (Epiploic appendices are small pouches of the peritoneum filled with fat and situated along the colon) - tanae coli (line running through haustrations) - haustrations (bumps that the large intestine is made up of)

Question 31

Describe abdominal blood supply

Answer 31

- coeliac trunk --> foregut - superior mesenteric artery (SMA) --> midgut - inferior mesenteric artery (IMA) --> hindgut

Question 32

What are the branches of the superior mesenteric artery?

Answer 32

Over duodenum Branches: - inferior pancreaticoduodenal artery --> pancreas and last past of duodenum - jejunal and ileal arteries --> jejunum and ileum - middle colic artery --> ascending colon and 2/3 of transverse colon - right colic --> ascending colon - Ileocolic artery --> ileocaecal junction

Question 33

What are the branches of the inferior mesenteric artery?

Answer 33

Under duodenum Branches: - left colic artery --> last 1/3 descending colon - sigmoid (sigmoidal) arteries --> rectum

Question 34

Summarise the anterior abdominal wall & gastrointestinal tract

Answer 34

- the abdominal cavity is separated from the thorax by the diaphragm and it contains organs of the GI tract and many other structures. - the abdomen can be divided into 4 quadrants and 9 regions. - the anterolateral abdominal wall consists of 3 lateral (External oblique muscle - EOm, Internal oblique muscles - IOm, Transversus abdominis muscle - TAm) and 2 vertical (Rectus abdominis - RAm - one either side of the midline separated by the linea alba). - the GI tract is comprised of the stomach, small intestines and large intestines. - the small intestines have 3 parts (the duodenum, jejunum and ileum) with distinct features. - the colon has 4 parts - ascending, transverse, descending and sigmoid. - the SMA (superior mesenteric artery) and its branches supply the midgut structures. - the IMA (inferior mesenteric artery) and its branches supply the hindgut structures.