lecture 2 Flashcards
what is the peritoneum
lining of abdominal cavity; single continous membrane made of simple squamous epithelium (mesothelium)
what is in between the abdominal wall and peritoneum
abdominal cavity
what is the peritoneal cavity
potential space within layer of peritoneum (between parietal peritoneum surrounding the abdominal wall, and visceral peritoneum, surrounding the internal organs), containing small amount of peritoneal fluid to allow organs to slide
what are the peritoneal reflections which suspend components of GI tract called
mesentries
components of GI tract in order
mouth and pharynx, oesophagus, (below diaphragm) stomach, duodenum, jejenum and ileum, caccum and large intestine, (within pelvic cavity just above pelvic floor) sigmoid colon, rectum and anus
early development of gut tube
originates from endoderm and splanchnic (from visceral - not part of body wall) mesoderm at 4 weeks - separates from yolk sac; suspended from posterior abdominal wall by peritoneal fold (dorsal mesentery - may be absorbed in adult life)
mesentries
peritoneal folds attaches to viscera, attaching viscera to abdominal walls; act as conduit for vessels, nerves and lymphatics supplying viscera
visceral peritoneum
covers suspended organs
parietal peritoneum
lines abdominal wall
intraperitoneal structures
within peritoneal cavity; most of small intestine, suspended from abdominal wall by mesentries
retroperitoneal structures
behind or outside parietal peritoneum: kidneys and great vessels that lie between parietal peritoneum and abdominal wall
retroperitoneal organs on posterior abdominal wall: SADPUCKER
kidneys and ureters, suprarenal glands, aorta/inferior vena cava, nerves (lumbar plexus, sympathetic trunk), oesophagus and rectum
secondarily retroperitoneal organs on posterior abdominal wall that originally had a mesentry but which fused with body wall
duodenum (except first part), pancreas (tail is intraperitoneal), colon (ascending and descending only)
3 divisions of GI tract (different blood and nerve supplies)
foregut (distal 3rd of oesophagus to 2nd part of duodenum at entrance of bile duct - major duodenal papilla), midgut (2nd part of duodenum to 2/3rds along transverse colon), hindgut (distal third of transverse colon to rectum)
dorsal and ventral mesenteries
entire gut tube suspended from dorsal mesentery (posterior); foregut also has a ventral mesentery (anterior) - contains liver, which splits ventral mesentery into falciform ligament and lesser omentum
formation of omental bursa (lesser sac) of peritoneal cavity
only in foregut region - rest of gut in greater sac region; communication between each other through narrow foramen; as liver grows, moves to right while dorsal mesentery and spleen move left; original right side of peritoneal cavity is now posterior - lesser sac of peritoneal cavity (omental bursa)
where is omental bursa
epiploic foramen is entrance to lesser sac between liver and lesser curvature of stomach; part of ventral foregut mesentery
what is greater omentum
lower part of dorsal foregut mesentery extending down as a double fold anterior to intestine
why is rotation of foregut important
only then can formation of sacs occur
lesser omentum on right free edge
portal vein, hepatic artery and bile duct run between abdominal wall and liver
why is lesser omentum free edge present
ventral mesentery ends at start of midgut
greater and lesser sacs in sagittal view
lesser sac: mainly behind stomach and posterior aspect of liver; greater sac anterior
clinical importance of peritoneal compartments
if infection occurs in a compartment can have abscess formation - virulent material can flow into different parts of cavity
what is present either side of ascending and descending colon
paracolic gutter - abscess material can flow down these into other compartments
compartments above mesentery of transverse colon
supracolic compartment
compartments below mesentery of transverse colon
infracolic compartment
falciform ligament
attaches liver to underside of diaphragm; prevents abscess material flowing from left to right paracolic gutters
where do all infections from abscess come to
pelvic area - most dependent part
directions of peritoneal fluid movement in peritoneal cavity
moves upwards (e.g. through paracolic gutters) to underside of diaphragm to be reabsorbed
where does inflammatory exudate from abscess move
downwards towards pelvis
general plan of GI tract: inner to outer layers
mucosa (epithelium, mucous membranes, muscularis mucosa which produces movement to move mucosal surface) - submucosa (MALT, glands, endocrine cells, Meissner’s plexus) - muscularis (inner circular and outer longitudinal - peristaltic movement, Auerbach’s plexus) - serosa (connective tissue) - mesentery peritoneum (autonomic nerves and arteries)
abdominal oesophagus
pierces diaphragm at T10 on right crus (muscular part), contributing to lower oesophageal sphincter (prevents food going upwards or reflux)
where does abdominal oesophagus join stomach
gastro-oesophageal junction
4 sections of stomach
fundus, body, pyloric antrum, pyloric canal
where does stomach join duodenum
gastro-duodenal junction
what prevents food entering duodenum
ring of smooth muscle at distal end of pyloric canal called pyloric sphincter (can palpate)
3 sections of small intestine
duodenum, jejenum, ileum
what is first part of duodenum
duodenal cap
what occurs most at duodenal cap
duodenal ulcers
what does second part of duodenum contain
entrance for common bile duct (major duodenal papilla)
what is most of duodenum
retroperitoneal
4 sections of duodenum
superior, descending, inferior, ascending
jejunum
proximal 2/5ths; larger in diameter; upper left quadrant of abdomen; less prominent arterial arcads; longer vasa recta
ileum
distal 3/5ths; smaller in diameter; lower right quadrant of abdomen; prominent arterial arcads; shorter vasa recta
5 sections of large intestine in order
caecum, ascending colon, transverse colon, descending colon, sigmoid colon
features distinguishing large intestine from small intestine
fatty tags (appendices epiploicae), 3 ribbons of of longitudinal muscle (taeniae coli) which go to caecum, where appendix takes origin, segmented or pocketed walls
3 unpaired arteries arising from anterior of aorta to supply gut
coeliac trunk (foregut, liver, pancreas, spleen), superior meseneric artery (SMA; midgut), inferior mesenteric artery (IMA, hindgut)
3 coeliac trunk branches
common hepatic artery, left gastric artery, splenic branches
branches of common hepatic artery
cystic artery (gall bladder), gastroduodenal arteries
retroperitoneal strutures in lesser sac behind stomach and liver
loop of duodenum, head and body of pancreas, coeliac trunk, inferior vena cava, abdominal aorta, kindeys, adrenal glands
branches of superior mesenteric artery
middle colic artery, right colic artery, ileocolic artery, ileal arteries, jejunal arteries
branches of inferior mesenteric artery
left colic artery, superior rectal artery, sigmoid arteries
where is there a change from superior to inferior mesenteric artery (with anastomoses between)
junction of mid- and hindgut near left splenic flexure of colon
venous drainage
portal vein, splenic vein, superior mesenteric vein, inferior mesenteric vein
what does portal vein arise from
splenic vein and superior mesenteric vein posterior to 1st part of duodenum and pyloris of stomach
where does portal vein run
in free edge of lesser omentum to liver, draining blood from all abdominal viscera and liver
what are portal-systemic anastomoses
where veins draining to portal vein and inferior vena cava communicated (only if higher pressure) e.g. if left gastric vein blocked so can’t drain to portal, goes up oesophageal vein into systemic azygos veins
what can liver or portal obstruction cause to these veins
dilate widely, possibly leading to severe venous haemorrhage from oesophagus or rectum
what does lymphatic drainage of bowel follow
arterial supply, not venous drainage
where does all lymph drain
into cisterna chyli
what is cisterna chyli
elongated sac in front of L1 and L2
what commences from cisterna chyli
thoracic duct
lymph nodes
coeliac, superior and inferior mesenteric
innervation of gut
mainly autonomic, own nervous system (can do peristalsis on own), controlled by sympathetic sensory fibres (mediate pain and close sphincters) and parasympathetic sensory fibres (regulate reflex gut function and gland secretion)
sympathetic sensory nerves
thoracic splanchnic (T5-T12; greater T5-T9, lesser T10-T11, least T12), lumbar splanchnic (L1, L2)
parasympathetic sensory nerves
vagus, pelvic splanchnic (S2-S4)
parasympathetic efferents
increase peristalsis, relax sphincters, increase secretion
sympathetic efferents
decrease peristalsis, constrict sphincters, decrease blood flow and secretions
