Gastrointestinal Anatomy Flashcards
What separates abdominal cavity from thorax?
Diaphragm
GI Tract organs found in abdominal cavity
Stomach, small intestine, large intestine
Hepatobiliary system organs found in the abdominal cavity
liver and gallbladder
Urinary system organs found in the abdominal cavity
kidneys and ureters
Endocrine system organs found in abdominal cavity
pancreas and adrenal glands
What are the abdominal walls composed of?
Anterior, lateral and posterior walls compose skin, subcutaneous tissue and muscles and associated aponeuroses (flat tendons)
3 abdominal wall functions
protect abdominal viscera
Increase intra-abdominal pressure (for defecation and childbirth)
Maintain posture and move trunk
Internal abdominal wall lined with…
Parietal peritoneum (serous membrane like the internal thoracic wall is lined with parietal pleura)
How are the 4 quadrants named and divided?
RUQ, RLQ, LUQ, LLQ
Vertically down midline of lower sternum, umbilicus and pubic symphysis
Horizontally at the level of the umbilicus
How are the 9 regions divided horizontally?
-Subcostal line (through
inferior most parts of L
and R costal margins
through 10th costal
cartilage)
-Intertubercular line (drawn through the tubercles of the R and L iliac crests and the body of L5)
How are the 9 regions divided vertically?
R and L midclavicular lines which extend vertically from the midclavicular point to the mid-inguinal point
What is the mid-inguinal point?
Halfway between anterior superior iliac spine and the pubic tubercle
Name the 9 regions of the abdominal cavity
(First left to right then top to bottom)
Left hypochondriac region
Epigastric region
Right hypochondriac region
Left lumbar region
Umbilical region
Right lumbar region
Left iliac fossa (region)
Hypogastric region
Right iliac fossa (region)
Where is the transumbilical plane?
Transverse plane at L3 but can vary dependent on amount of subcutaneous fat in an individual
The 4 muscle pairs that comprise the anterolateral abdominal wall
External obliques (diagonally orientated fibres)
Internal oblique (diagonally orientated fibres)
Transversus abdominis (horizontally orientated fibres)
Rectus abdominis (rectus = stright, vertical)
Rectus abdominis position and attachments (this is the 6 pack, the other 3 abdomen muscles are lateral to it)
R and L rectus abdominis muscles lie either side of midline attaching to sternum and costal margin superiorly and pubis* inferiorly
It’s surrounded by an aponeurotic rectus sheath
External oblique (EO) fibre orientation
Medially and inferiorly towards the midline
Internal Oblique (IO) fibre orientation (lies deep to EO)
Medially and superiorly towards midline (perpendicular to EO)
Transverse abdominis fibre orientation (lies deep to IO)
Horizontal orientation
Aponeurosis is…
Flat tendons found associated with the abdominal muscles (aponeuroses of the rectus abdominis form the rectus sheath)
Linea alba
Tough midline seam formed by fusion of aponeuroses on both sides of the rectus abdominis
Rectus abdominis lies within rectus sheath. Rectus sheath anterior and posterior walls are formed by…
Aponeuroses of EO, IO and transversus abdominis
-Approaching the
midline, aponeurosis of
the IO splits into
anterior and posterior
layers
-EO aponeurosis and
anterior layer of IO
aponeurosis form
anterior wall of rectus
sheath
-Posterior layer of IO
aponeurosis and
transversus abdominis
aponeurosis form
posterior wall of rectus
sheath
Transversalis fascia lies ____ to transversus abdominis. Deep to the fascia lies _____
Deep
The Parietal Peritoneum
Most inferior part of EO aponeurosis is attached to _____ laterally and _____ medially forming the _____
Anterior superior iliac spine
Pubic tubercle
Inguinal ligament
3 arteries that supply anterolateral abdominal wall (these vessels are accompanied by deep veins and an extensive network of superficial veins is found in anterolateral abdominal wall)
Musculophrenic artery (branch of internal thoracic)
Superior epigastric artery (continuation of internal thoracic and descends through rectus sheath)
Inferior epigastric artery (branch of external iliac artery. Ascends in rectus sheath and anastomoses with superior epigastric)
Muscles/skin of anterolateral abdominal wall innervated by…
-Thoraco-abdominal nerves (T7-T11) (somatic nerves containing sensory and motor fibres)
-Subcostal nerve (T12 so called as it runs along inferior border of 12th rib)
-Iliohypogastric and ilioguinal nerves - both L1
Parietal Peritoneum (lines abdominal wall) innervation
Innervated by somatic nerves that supply overlying muscles and skin of abdominal wall (so pain is usually sharp, severe and well localised)
Visceral Peritoneum (covers abdominal viscera) innervation
Innervated by visceral sensory nerves which convey painful sensations back to CNS along path of sympathetic nerves that innervate the organ it covers (pain usually dull, diffuse, can’t be pinpointed)
Why is pain from visceral peritoneum referred but pain from parietal is not?
Visceral afferents enter spinal cord at T5-T9 same point as nerves from others parts of abdomen so pain often felt in those sections instead
What is found between the parietal and visceral peritoneum?
The peritoneal cavity containing a thin film of peritoneal fluid allowing viscera to slide freely alongside each other
Abdominal viscera are intraperitoneal if they’re…
Almost completely covered by peritoneum (stomach)
Abdominal viscera are retroperitoneal if they’re…
Posterior to peritoneum so only covered on their anterior surface (pancreas and abdominal aorta)
Secondarily retroperitoneal organs
Originally intraperitoneal in early development but came to be “stuck down” onto the posterior abdominal wall
What are mesenteries?
Folds of peritoneum that contain fat and suspend small intestine and parts of large intestine from posterior abdominal wall. Arteries supplying intestine (from abdominal aorta) and veins that drain gut (tributaries of portal venous system) are embedded in tributaries
Greater omentum
Mesentery, usually fatty, hanging form greater curvature of stomach and lies superficial to small intestine
Lesser omentum
Mesentery, usually fatty, that connects stomach and duodenum to the liver
The portal triad (hepatic artery, hepatic portal vein and bile duct) are embedded within its free edge
Falciform ligament
Connects anterior surface of liver to abdominal wall
What connects the superior surface of the liver to the diaphragm?
The coronary and triangular ligaments
How does the shape of peritoneal folds arise?
They’re raised from the internal aspect of the lower abdominal wall and created by the structures they overlie (like a carpet running over cable)
What is the median umbilical fold?(peritoneal fold)
Lies on midline and is the remnant of the urachus (embryological structure connecting bladder to umbilicus)
What folds are lateral to median umbilical fold?
The medial umbilical folds which are remnants of paired umbilical arteries (return venous blood to placenta in foetal life)
What are folds are lateral to the medial umbilical folds? What is contained within them?
Lateral umbilical folds (inferior epigastric arteries lie deep to these peritoneal folds which supply anterior abdominal wall)
Peritoneal cavity is divided into 2 regions of unequal size called…
Lesser Sac - Space that lies posterior to stomach and anterior to pancreas
Greater Sac - Remaining part of cavity
How do the greater and lesser sacs of peritoneal cavity communicate?
Through a passageway posterior to the free edge of the greater omentum called the epiploic foramen
GI system develops from the…
Embryonic gut tube which lies in the midline and is suspended from the posterior abdominal wall by the dorsal mesentery
What connects stomach to anterior abdominal wall?
Ventral mesentery
The liver develops within the _____ _____
As it develops, the anterior part of the ___ ___ becomes the ____ ___ and the posterior part becomes the ___ ___
Ventral Mesentery
Ventral Mesentery
Falciform Ligament
Lesser Omentum
Oesophagus passes through oseophageal hiatus in diaphragm at the level of…
Role of Muscles around the hiatus?
How long is abdominal segment of oesophagus?
T10
Act as a sphincter preventing reflux of stomach contents into oesophagus
Less than 2cm
Blood supply of distal oesophagus?
Branches of L gastric artery
Venous drainage of distal oesophagus? (site of portosystemic anastomoses)
-Systemic system of veins (via oesophageal veins draining into azygos veins)
-Portal venous system (left gastric veins)
Stomach breaks down food into…
Chyme
What is contained within the fundus of the stomach?
Usually filled with gas as it’s superior to level of entry of oesophagus
Where is the pyloric sphincter?
What is it’s role?
Pyloric Canal
Formed of circular smooth muscle and regulates passage of chyme into duodenum
Stomach surface covered in…
Visceral peritoneum
What forms anterior and posterior walls of lesser sac?
Anterior - Posterior surface of stomach
Posterior - Pancreas, left kidney, spleen
What connects the lesser curvature to the liver?
Lesser omentum
Free edge of lesser omentum contains… (3)
Hepatic artery
Hepatic portal vein
Bile duct
What is found posterior to lesser omentum free edge?
Epiploic foramen (entrance of lesser sac)
3 large unpaired vessels that leave the anterior aspect of the abdominal aorta?
Coeliac trunk (leaves at T12)
Inferior and superior mesenteric arteries
What conveys parasympathetic fibres to the stomach?
What does stimulation of these fibres result in?
Vagus nerve
Parasympathetic stimulation promotes peristalsis and gastric secretion
What conveys sympathetic fibres to the stomach?
What is the pathway?
What does this inhibit?
Greater splanchnic nerve (which is formed of preganglionic sympathetic fibres that leave spinal cord at T5-9 and pass through sympathetic trunk without synapsing)
Fibres synapse in prevertebral ganglia around coeliac trunk
Post ganglionic fibres then travel to stomach inhibiting peristalsis and secretion
3 components of small intestine?
Duodenum
Jejunum
Ileum
What part of stomach does duodenum attach to?
Pylorus
What is the major duodenal papilla?
Where is it?
Opening of bile duct and main pancreatic duct into duodenum
Approx half way along internal wall of duodenum
Is duodenum retro or intraperitoneal?
Most of the length is retroperitoneal
1st half duodenum develops from ____ ____ and is supplied by arterial branches of ___ ___
2nd half develops from ___ ___ and supplied by arterial branches of ___ ___ ___
The Embryological Foregut
The Coeliac Trunk
The Embryological Midgut
The Superior Mesenteric Artery
What follows duodenum in small intestine?
Where is this found in the abdomen?
Where is the thing that proceeds it found?
Jejunum
Left Upper Quadrant
Ileum - Right Lower Quadrant
Both jejunum and ileum derive from where?
Embryological midgut
Are jejunum and ileum retro or intraperitoneal?
Intraperitoneal
Suspended from posterior abdominal wall by the mesentery of the small intestine
Small intestine is long and its mucosa is folded for its role in nutrient absorption. What are the folds called?
Plicae Circulares - These mucosal folds bear billi and microvilli on the luminal surface of each epithelial cell (greater SA)
Differences between jejunum and ileum?
Plicae more pronounced in the jejunum
Ileum characterised by Peyer’s patches (large submucosal lymph nodules)
What is Meckel’s diverticulum?
Outpouching/bulge in ileum approx 1m from its termination
Embryological remnant of connection that was present between the midgut loop to the yolk sac
Only present in some and may mimic appendicitis if inflamed
In which of the 9 regions is the ileocaecal junction?
Right ileac fossa
Name all sections of the Large Intestine
Caecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal
(some segments retroperitoneal, some intraperitoneal)
Muscle arrangement in the large intestine
Outer longitudinal layer organised into 3 bands (the taeniae coli)
Inner circular layer forms bulges called haustra (or haustrations)
What structures mark the points at which blood vessels penetrate the large intestinal wall?
Fatty tags called epiploic appendages
Does the caecum have a mesentery?
No, it is covered by peritoneum but has no mesentery
What is the appendix?
What connects the appendix to the caecum
Small diverticulum in from caecum containing lymphoid tissue
A small mesentery (the mesoappendix)
What is McBurney’s point?
Surface marking of the base of the appendix
What is the hepatic flexure?
Bend in the colon between ascending and transverse (also called right colic flexure)
Where is the ascending colon found?
Runs on right side of posterior abdominal wall (retroperitoneal) in the right paracolic gutter
What is the splenic flexure?
Bend between the transverse and descending colon (also called left colic flexure)
Transverse colon positioning
Intraperitoneal and is suspended from posterior abdominal wall by the transverse mesocolon
Splenic flexure tethered to the diaphragm by…
The phrenicocolic ligament
Where marks the transition point between the embryological midgut and embryological hidgut?
The proximal 2 thirds of the transverse colon develop from the embryological midgut
The distal third of the transverse colon develop from the embryological hindgut
Where does the descending colon run?
Left side of posterior abdominal wall in the left paracolic gutter
Retroperitoneal (like ascending colon it is secondarily peritoneal)
As sigmoid colon approaches midline, it makes a 90 degree inferior turn into the pelvis. This bend is called…
The rectosigmoid junction
The sigmoid colon has a mesentery called ___ ___ making it intraperitoneal
Sigmoid mesocolon
Is rectum retro or intraperitoneal?
Retroperitoneal
Artery of the foregut and where it leaves the aorta
Coeliac trunk leaves aorta at T12 (supplies oesophagus, stomach, 1st of half of duodenum, liver, gallbladder, bile ducts, pancreas and spleen)
What artery supplies the midgut and where does it leave the aorta?
Superior mesenteric artery (SMA) leaves aorta at L1 (supplies 2nd half of duodenum, small intestine, large intestine (up to 2/3 through transverse colon), branches also supply parts of pancreas)
What artery supplies the hindgut and where does it leave the aorta?
Inferior Mesenteric Artery (IMA) leaves aorta at L3 supplying hindgut structures (distal 1/3 of transverse, descending and sigmoid colon, rectum and upper anal canal)
Major branches of SMA?
Jejunal branches (supplies jejunum)
Ileal branches (ileum)
Ileocolic artery (caecum, appendix, ascending)
Right colic artery (supplies ascending colon)
Middle colic artery (supplies transverse)
Arcades
Anastomoses of jejunal and ileal branches of the SMA which are embedded in the mesentery of the small intestine
Major branches of IMA?
Left colic artery (supplies transverse, descending)
Sigmoid branches (supplies sigmoid colon)
Superior rectal artery (supplies upper rectum)
Branches of middle colic artery anastomose with…
At the…
Forming the…
Branches of left colic artery
Splenic flexure
Marginal artery
Branches of left colic anastomose with…
Branches of sigmoid
What supplies the lower rectum?
Blood vessels that originate from the internal-ileac arteries in the pelvis
Before entering the IVC, venous blood goes through the ….. system into the liver
The portal venous system
What drains the hindgut?
Inferior Mesenteric Vein (IMV)
Ascends in the left side of the abdomen and drains into the splenic vein at the spleen
What drains the midgut?
Superior Mesenteric Vein (SMV)
Ascends and unites with the splenic vein to form the hepatic portal vein
What happens to blood after nutrients are removed in the liver?
Enter small hepatic veins which unite within the liver to form 2 or 3 large hepatic veins which enter IVC as it passes posterior liver
Divide between foregut and midgut
Halfway along duodenum
Divide between midgut and hindgut
2/3 along the transverse colon
Foregut ANS innervation
S: Greater Splanchnic (T5-T9)
P: Vagus
Midgut ANS innervation
S: Lesser Splanchnic (T10-T11)
P: Vagus
Hindgut ANS innervation
S: Least Splanchnic (T12 +/- L1) and lumbar splanchnic nerves
P: Pelvic Splanchnics
Where is visceral pain felt from foregut?
Epigastric region
Where is visceral pain felt from midgut?
Umbilical region
Where is visceral pain felt from hindgut?
Suprapubic region
Things the ectoderm becomes
CNS and PNS
Skin, hair, nails
Pituitary gland, sweat glands, tooth enamel
Things the mesoderm becomes
Muscle, cartilage, bone
Urogenital system, spleen, adrenal cortex
Connective tissue of gut wall, pancreas, liver
Visceral peritoneum
Things the endoderm becomes
Epithelium of GI and resp tract
Hepatocytes
Pancreas cells
3 sections to mesoderm
Paraxial Mesoderm
Intermediate Mesoderm
Lateral Plate Mesoderm
Foregut and it’s derivatives
Oesophagus, stomach, 1/2 duodenum
Liver and pancreas (derivatives)
Dorsal and Ventral mesenteries
Dorsal mesentery
Spans from distal oesophagus to hindgut containing the abdominal aorta and suspends the gut from the posterior abdominal wall
Ventral mesentery
Spans from upper stomach to the duodenum
Liver grows into it creating: the lesser omentum (connects liver to stomach and duodenum) and the falciform ligament (connects liver to anterior abdominal wall)
Make up of upper 2/3 of oesophagus
Striated muscle innervated by Vagus
Make up of lower 1/3 of oesophagus
Smooth muscle innervated by splanchnic nerves
3 unpaired branches of abdominal aorta
Coeliac trunk at T12 (supplies foregut)
SMA at L1 (supplies midgut)
IMA at L3 (supplies hindgut)
2 types of veins in the abdomen
Systemic veins - carry venous blood to IVC
Portal system - nutrient rich venous blood gut->liver, blood enters hepatic veins and returns to IVC
Where does the AA bifurcate?
What does it bifurcate into?
L4/5
Into R and L common iliac arteries
3 branches of coeliac trunk
Left gastric artery - supplies stomach
Splenic artery - supplies spleen (primarily), stomach and pancreas
Common hepatic artery - supplies liver, gallbladder, stomach, duodenum
Branches of SMA and what they supply
Jejunal and ileal branches (supply jejunum and ileum)
Ileocolic artery (supplies ileum, caecum, appendix, ascending colon)
Right colic artery (supplies ascending colon)
Middle colic artery (supplies transverse colon)
Branches of IMA and what they supply
Left colic artery (supplies descending colon)
Sigmoid branches (supplies sigmoid colon)
Superior rectal artery (supplies upper rectum)
Portal system explained
IMV unites with splenic vein
Splenic vein unites with SMV forming the hepatic portal vein
Hepatic portal vein enters liver (blood processed, nutrients removed)
Venous blood enters hepatic veins which drain into IVC
What separates the R and L liver lobes anteriorly?
Falciform ligament
2 smaller accessory liver lobes
Caudate
Quadrate
Areas of liver not covered by peritoneum (bare areas)
Region in direct contact with diaphragm
Porta hepatis
Region where gallbladder lies in contact with liver
What is the porta hepatis?
Region where the portal triad (bile duct, hepatic artery proper, hepatic portal vein) enters/exits liver
Where does the gallbladder sit on the liver?
On the gallbladder fossa on the postero-inferior surface
Pain from gallbladder can be referred to…(3)
RUQ - gallbladder making contact with parietal peritoneum = sharp pain
Epigastrium
Right shoulder - contact w diaphragm which is innervated by phrenic which tracks back to skin over shoulder
2 parts of pancreas
Head, neck, body, tail (from the dorsal bud)
Uncinate process (from the ventral bud)
Where does the pancreatic duct meet the bile duct?
The hepatopancreatic ampulla (opening into duodenum at major duodenal papilla)
Accessory pancreatic duct opens at the minor duodenal papilla
Stomach nerve supply
Para: Vagus (promotes peristalsis and gastric secretion)
Symp: Greater Splanchnic Nerve (T5-9)
