Lecture 3 - Anterior abdominal wall & gastrointestinal tract Flashcards
What are the 3 parts of the abdomen?
- Muscles - (anterior and posterior abdominal wall)
- Peritoneum - and associated structures (mesenteries/ligaments/omenta)
- GI tract - abdominal oesophagus, stomach, small intestine, large intestine, rectum
What are all the other parts of the abdomen?
- 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)
Describe the axis of the abdominal cavity
Completely vertical
Describe the axis of the pelvis cavity
Tilted to the left
What are the different quadrants in the abdominal cavity
Right descending: right hypochondrium, right lumbar, right iliac
Middle descending: epigastic, umbilical, hypogastric
Left descending: left hypochondrium, left lumbar, left iliac
What are anterolateral abdominal wall muscles?
- flat muscles
- protect the abdominal viscera (organs)
- increase intra-abdominal pressure (e.g. for defecation and childbirth)
- maintain posture and move the trunk
What are the 2 groups of anterolateral muscles?
Anterior muscles - 2 muscles on either side of the midline
Lateral muscles - 3 muscles on either side of abdomen
Connected by rectus sheath
What is the rectus sheath?
Formed by the aponeurosis (a broad, flat sheet of connective tissue) of the lateral 3 lateral muscles, enclosing the rectus abdominis
What is the anterior wall?
aponeuroses of external oblique and anterior 1/2 internal oblique
What is the posterior wall?
aponeuroses of posterior 1/2 internal obliques and transverus abdominis aponeurosis
What is the midline?
Linea alba
Describe features of the rectus abdominis muscle
- 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
Describe features of the external oblique muscle
- most superficial of the 3 lateral muscles
- fibres run MEDIALLY and INFERIORLY towards the midline
- aponeurosis of EOm: anterior wall of the rectus sheath
Describe features of the internal oblique muscles
- 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
Describe features that are transversus abdominis muscles
- deep to internal oblique muscle
- fibres orientated horizontally
- aponeurosis of Tam: posterior wall of the rectus sheath
Describe peritoneum and peritoneal cavity
serous membrane lining the abdomen
- pariental peritoneum lines the inner aspect of the abdominal wall
- visceral peritoneal covers organs and structures within the peritoneum
What is a serous membrane?
A serous membrane is a thin membrane that secretes serous fluid to lubricate and reduce friction between organs and body cavities.
What is the peritoneal cavity?
thin cavity between the 2 layers, it contains a small of peritoneal fluid that allow the visceral to slide alongside each other.
What is the mesentery?
- 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
What is the foregut, midgut & hindgut?
- different embryological origins of different parts of the GI tract
- important for understanding blood supply, nerve supply etc.
Where is the foregut found?
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
Where is the midgut found?
From major duodenal papilla to ends 2/3 of the way along the transverse colon
Blood supply - superior mesenteric artery
Where is the hindgut found?
From last 1/3 of transverse colon to the upper anal canal
Blood supply - inferior mesenteric artery
How is the stomach broken up?
- 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
Describe the blood supply of the stomach
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
Describe features of the small intestine - duodenum
- Above the level of umbilicus
- continuous with the pylorus of the stomach
- widest lumen
What are the 4 parts of the duodenum?
- 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
What are features of Jejunum?
- intraperitoneal
- mostly in left upper quadrant
- more plicae circulares (mucosa fold)
- less prominent arterial arcades
- longer vasa recta (straight arteries)
- few solitary lymph nodes
What are features of ileum?
- intraperitoneal
- mostly in right upper quadrant
- few plicae circulares
- more arterial arcades
- shorter vasa recta
- Peyer’s patches
What is the large intestines?
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)
Describe abdominal blood supply
- coeliac trunk –> foregut
- superior mesenteric artery (SMA) –> midgut
- inferior mesenteric artery (IMA) –> hindgut
What are the branches of the superior mesenteric artery?
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
What are the branches of the inferior mesenteric artery?
Under duodenum
Branches:
- left colic artery –> last 1/3 descending colon
- sigmoid (sigmoidal) arteries –> rectum
Summarise the anterior abdominal wall & gastrointestinal tract
- 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.
