Lecture 2 - Anatomy of the abdomen Flashcards
What is the peritoneum?
Continuous membrane lining the abdominal cavity consisting of mesothelial layer supported by a layer of connective tissue
What is the abdominal wall?
Muscle and connective tissue deep into which lies the abdominal cavity
What is the peritoneum made of?
Single continuous membrane of simple SQUAMOUS epithelium (mesothelium)
What is the peritoneal cavity?
Potential space within the layer of peritoneum
What is present in the abdomino-pelvic cavity?
Abdomen: Small intestine, asc/desc colon, cecum and appendix Pelvic: Sigmoid colon, rectum Thoracic cage: liver, gall bladder, transverse colon, stomach, spleen
Where does the gut tube originate from?
Endoderm and splanchnic mesoderm - 4 weeks IUL
From where is the gut tube suspended?
From the posterior abdominal wall by the dorsal mesentery
What are mesenteries?
Peritoneal folds attaching viscera to abdominal wall
What are the functions of mesenteries?
Conduit for VESSELS, NERVES and LYMPHATICS supplying viscera.
What is the difference between visceral and parietal peritoneum?
Visceral peritoneum surrounding the viscera Parietal peritoneum lines the abdominal cavity.
What is the difference between intra and retroperitoneal?
INTRAperitoneal – structures, like most of small intestine, suspended from the abdominal wall by mesenteries. RETROperitoneal – structures, like kidneys and great vessels that lie between parietal peritoneum and abdominal wall.
What are some retroperitoneal organs on posterior abdominal wall?
Kidneys & ureters Suprarenal glands Aorta/Inferior vena cava Nerves: lumbar plexus, sympathetic trunk Oesophagus Rectum
What are some secondarily retroperitoneal organs and what does this mean?
They had a mesentery but it fused with the abdominal wall: Duodenum (except the first part) Pancreas (tail is INTRAperitoneal) Colon (ascending and descending only)
What are the 3 divisions of the GIT?
FOREGUT – Distal 3rd of oesophagus to the 2nd part of the duodenum at the entrance of the bile duct (Major duodenal papilla). MIDGUT – 2nd part of the duodenum to two-thirds along transverse colon. HINDGUT – Distal third of transverse colon to the rectum.
Why is it important to divide the GIT into 3 parts?
Each part of GIT has its own arterial supply, coeliac trunk, superior mesenteric artery
What does the dorsal mesentery do?
Suspend the entire gut
What is special about the foregut?
It is suspended by both dorsal and ventral mesentery
What is in the ventral mesentery?
Foregut, liver - split into falciform ligament and lesser omentum
How is the omental bursa (lesser sac) of the peritoneal cavity formed?
As the liver grows, it moves to the right, while the dorsal mesentery and spleen move to the left, so original right side of upper peritoneal cavity is now posterior
What does the omental bursa look like?
How are the greater and lesser omentum formed?
Lower part of dorsal foregut mesentery extends down as a double fold called greater omentum (apron) anterior to intestine Lesser omentum is part of ventral foregut mesentery
What is the epiploic foramen?
Entrance to lesser sac
What do the greater and lesser omentum look like?
Where do the portal vein, hepatic artery and bile duct run through?
Between the posterior abdominal wall and liver within lesser omentum near its free edge
Why is there a free edge present in the lesser omentum?
Due to ventral mesentery ending at start of midgut
What do the greater and lesser sacs look in sagittal view?
What are the names of the peritoneal compartments?
Supracolic compartment, mesentery of transverse colon, infracolic compartment (R/L), R/L paracolic gutter, mesentery of small intestine
Fill in the peritoneal compartments in this picture:
How does the peritoneal fluid flow in peritoneal cavity?
How does the inflammatory exudate flow in the peritoneal cavity?
What is the layout of the GI tract from outermost to innermost tissue layer?
Mesentery Serosa (alveolar connective tissue and epithelium) Muscularis (longitudinal/circular muscle) Submucosa Mucosa (epithelium, lamina propia, muscularis mucosae)
Where does the oesophagus cross into the abdomen?
T10 - pierces through the diaphragm, contributing to lower oesophageal sphincter
What are the 4 main parts of the stomach?
Cardia surrounding the opening Fundus Body Pyloric region consisting of pyloric atrium and pyloric canal (with pyloric sphincter preventing food from entering duodenum)
What are the 4 parts of the duodenum?
Superior – duodenal cap, common place for peptic ulcers. Passes anteriorly to bile duct, gastroduodenal artery, portal vein and IVC. Descending – contains minor/major duodenal papillae where accessory pancreatic duct and bile duct enter respectively. Inferior – crosses IVC and has SMA anterior to it. Ascending – terminates at duodenojejunal flexure
What are the differences between jejunum and ileum?
Jejunum: proximal 2/5ths, larger in diameter, ULQ of abdomen, less prominent arterial arcades, longer vasa recta Ileum: distal 3/5ths, smaller diameter, LRQ of abdomen, prominent arterial arcades, shorter vasa recta
What are the distinguishing features of the large intestine from the small intestine?
Large: appendices epiploicae, taeniae coli, segmented/pocketed walls
What are the 3 unpaired arteries arising from anterior of aorta and what do they supply?
Coeliac trunk - foregut, liver, pancreas, spleen Superior mesenteric artery - midgut Inferior mesenteric artery - hindgut
What does the coeliac trunk do?
Supplies entire foregut and derivatives - spleen shares a blood supply
Where is the coeliac trunk located?
What does the posterior relations of liver and stomach look like?
All part of retroperitoneum:
What are the branches of the superior mesenteric artery?
Middle/Right colic artery, ileocolic artery, jejunal arteries and ileal arteries
What are the branches of the inferior mesenteric artery?
Left colic artery, superior rectal artery and sigmoid arteries
To what is the junction of mid and hindgut close to?
Left flexure of colon - change from SMA to IMA supply at this level with anastamoses between them
How does venous drainage work in the peritoneal cavity?
Portal vein arises from SMV and splenic veins posterior to 1st part of duodenum/pylorus of stomach - portal vein then runs in the free edge of lesser omentum to the liver, draining blood from all abdominal viscera and liver
What are the major venous drainage veins in peritoneal cavity?
Portal vein, superior mesenteric vein, inferior mesenteric vein and splenic vein
What are portosystemic anastamoses?
Where veins draining into portal vein and IVC communicate
What happens if liver or portal obstruction occurs in the portosystemic anastamoses?
Veins dilate widely, possibly leading to severe venous haemorrhage from oesophagus/rectum
Which blood supply does the lymphatic drainage of the bowel follow?
Arterial supply
Where does all lymph drain into?
Cisterna chyli
What is the cisterna chyli?
An elongated lymphatic sac loncated in front of L1 and L2 bodies
Where does the thoracic duct begin?
From the cisterna chyli
Fill in the blanks of the lymphatic system in the abdomen
How is the abdominal viscera innervated?
Autonomic nervous system - sensory fibres are the most important
Which are the parasympathetic sensory nerves in the gut and what do they do?
Vagus nerve and pelvic splanchnic nerves (S2-4) They regulate reflex gut action
Which are the sympathetic sensory nerves in the gut and what do they do?
Thoracic splanchnic (T5-T12) and lumbar splanchnic (L1/2) Mediate pain
Fill in the blanks of the innervation of the gut
Which nerves mediate pain in viscera of gut?
Sensory fibres running with sympathetic (T1-L2)
Which nerves are involved in reflex regulation of gut function?
Sensory fibres with the parasympathetic (vagus/sacral)
