Gastrointestinal anatomy Flashcards
Name all of the parts of the GI tract from proximal to distal
Mouth/oral cavity Oesophagus Stomach Duodenum Jejunum Ileum Caecum & appendix Ascending colon Hepatic flexure Transverse colon Splenic flexure Descending colon Sigmoid colon Rectum Anus
Which organs in the GI tract are foregut organs?
Oesophagus Stomach Mid-duodenum Liver Spleen Gallbladder 1/2 of pancreas
Which organs in the GI tract are midgut organs?
1/2 of duodenum
Small intestine
Proximal 2/3 of transverse colon
1/2 of pancreas
Which organs in the GI tract are hindgut organs?
Distal 1/3 of transverse colon
Sigmoid colon
Rectum
Proximal 1/2 of anal canal
What is the peritoneal cavity?
A thin, enclosed space containing a little peritoneal fluid secreted by the peritoneum
What is the peritoneum?
A sensitive, semi-permeable membrane
What name is given to the surgical procedure of opening the abdominal cavity?
Laparotomy
When undertaking paracentesis, why must the placement of the needle be lateral to the rectus sheath?
To avoid the inferior epigastric vessels which run in the anterior abdominal wall, deep to the rectus sheath
What is the deep inguinal ring?
The entrance to the inguinal canal
What is the inguinal canal?
A passage in the anterior abdominal wall which in men conveys the spermatic cord and in women the round ligament
What is the falciform ligament?
Attaches the liver to the anterior abdominal wall, lies between the right and left lobe of the liver
What two structures does the greater omentum connect?
The stomach to the transverse colon
What two structures does the lesser omentum connect?
The stomach to the liver
Which structure lies within the “free edge” of the lesser omentum?
The portal triad
How does the greater sac communicate with the lesser sac?
Through the omental foramen
What is the enteric nervous system?
An extensive network of nerves found only within the walls of the GI tract
Where do the sympathetic nerve fibres exit the spinal cord to reach the abdominal organs?
T5-L2
Where do the sympathetic nerve fibres supplying the abdominal organs synapse?
Prevertebral ganglia, located anterior to the aorta at the exit points of the major branches of the aorta
What nerves do the sympathetic nerves exit the sympathetic chain within?
Abdominopelvic splanchnic nerves
What are the names of the prevertebral ganglia within the abdomen?
Celiac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglion
How do postsynaptic sympathetic nerve fibres travel to the abdominal organs?
They travel on the surface of the arterial branches leaving the abdominal aorta
What are periarterial plexuses?
Nerve plexuses around the arteries consisting of sympathetic, parasympathetic and visceral afferents
What is unique about the nerve supply to the adrenal glands?
The sympathetic nerve fibres do not synapse at the prevertebral ganglia - instead, the presynaptic fibres are carried to the adrenal gland where they synapse directly onto the cells
At which level of the spinal cord do the sympathetic nerve fibres destined for the adrenal gland leave at?
T10-L1
Where do the presynaptic parasympathetic nerve fibres within the vagus nerve enter the abdominal cavity?
The surface of the oesophagus - “vagal trunks”
Up to which structure do parasympathetic nerve fibres supply in the GI tract?
Up to the distal end of the transverse colon
What parasympathetic nerve supply is there for the distal end of the transverse colon and down to the anal canal?
Pelvic splanchnic nerves S2, 3, 4
Where do pain fibres from foregut structures enter the spinal cord?
T6-T9
Where do pain fibres from midgut structures enter the spinal cord?
T8-T12
Where do pain fibres from hindgut organs enter the spinal cord?
T10-L2
What artery is the inferior epigastric artery a branch of?
External iliac
Where is the deep inguinal ring located?
Halfway between the ASIS and pubic tubercle
What three vessels make up the portal triad?
Hepatic artery
Hepatic portal vein
Common bile duct
What are the three initial branches of the celiac trunk?
Left gastric artery
Hepatic artery
Splenic artery
Which artery, originating from the celiac trunk, has a particularly tortuous course?
Splenic artery
Where is the spleen located?
It is an intraperitoneal organ located within the left hypochondrium
Which structure lies anterior to the spleen?
Stomach
Which structure lies medial to the spleen?
Left kidney
Which ribs protect the spleen?
Ribs 9-11
What is the blood supply to the stomach?
Mainly the right and left gastric arteries running along the lesser curvature
Right and left gastro-omental arteries running along the greater curvature
What percentage of the blood supply to the liver does the hepatic artery account for?
20-25%
What is the main blood supply to the liver?
Hepatic portal vein
How many segments does the liver have?
8
How many main hepatic veins are there that drain into the IVC?
3
What is the significance of the lack of valves in the IVC?
Any rise in central venous pressure, e.g. congestive cardiac failure, causes the liver to become engorged with blood resulting in hepatomegaly
What are the four lobes of the liver?
Right, left, caudate, quadrate
What structure lies posteriorly & inferiorly to the liver?
Gallbladder
Which structures lie posterior to the liver?
Right kidney, right adrenal gland, IVC and abdominal aorta
When a patient is bedridden, which part of the peritoneal cavity might fill with fluid or pus from an abcess?
Hepatorenal recess
What is the ligamentum teres or round ligament?
A remnant of the embryological umbilical vein
What is the blood supply to the gall bladder?
The cystic artery, a branch of the right hepatic artery (in approx. 75% of people)
What structure lies posterior to the gall bladder?
Duodenum
Where do the pain afferents from the gall bladder enter the spinal cord?
T6-T9
The common bile duct is formed from the union of which two structures?
Cystic duct and common hepatic duct
Where does the bile duct drain into?
The second part of the duodenum
What is endoscopic retrograde cholangiopancreatography (ERCP)?
Investigation used to study the biliary tree and pancreas and treat certain associated pathologies
Using an endoscope, radio-opaque dye is injected into the major duodenal papilla and radiographic images taken of the dye-filled biliary tree
Where does the bile duct descend to reach the second part of the duodenum?
Posterior to the first part of the duodenum and into a groove in the posterior aspect of the pancreas
Where do the pancreatic duct and the common bile duct both drain into?
Ampulla of Vater
Which structure controls the drainage of products from the biliary tree into the duodenum?
Sphincer of Oddi/major duodenal papilla
What does the uncinate process of the pancreas lie posterior to?
The superior mesenteric vessels
Where is the pancreas?
Retroperitoneal organ
Lies transversely across the posterior abdomen at the level of T12 and L1
What lies posterior to the pancreas?
Kidneys and adrenal glands, IVC, bile duct, abdominal aorta, superior mesenteric vessels (except uncinate process)
What lies anteriorly to the pancreas?
Stomach
What is the blood supply to the pancreas?
Pancreatic artery - a branch of the splenic artery
Gastroduodenal artery - becomes the superior & inferior pancreaticoduodenal artery
Which part of the duodenum is partially intraperitoneal, and where lies the rest of it?
1st part is partially intraperitoneal
2nd, 3rd and 4th parts are retroperitoneal
What structure do the vessels supplying the jejunum and ileum lie within?
The mesentery
What is the name given to the specialised lymphatic vessels of the small intestine which absorb chylomicrons?
Lacteals
What are the main groups of lymph nodes draining the abdominal organs?
Celiac (draining foregut organs) Superior mesenteric (draining midgut organs) Inferior mesenteric (draining hindgut organs) Lumbar (draining kidneys, posterior abdominal wall, pelvis and lower limbs)
What is the main function of the rectum, anal canal and anus?
To excrete formed stool/faeces
What are the three requirements for faecal continence?
A “holding area” i.e. the rectum
Normal visceral afferent fibres to sense fullness of rectum
Functioning muscle sphincters
Which anatomical cavity does the rectum lie within?
The pelvis
Which anatomical cavity do the anus & anal canal lie within?
Perineum
What is the levator ani?
Pelvic floor muscles
What is the rectosigmoid junction?
The point at which the sigmoid colon becomes the rectum at the level of S3
At which point does the rectum become the anal canal?
Just anterior to the tip of the coccyx, just prior to passing through the levator ani muscle
What is the rectal ampulla and where does it lie?
Dilated distal part of the rectum, used for holding faeces
Lies immediately superior to the levator ani muscle
What is the nerve supply to the levator ani muscle?
The “nerve to levator ani”, a branch of the sacral plexus
Which part of the levator ani muscle is particularly important in maintaining faecal continence and why?
Puborectalis muscle
Contraction of this muscle decreases the anorectal angle - it acts like a sphincter
Which type of muscle does the internal anal sphincter consist of?
Smooth muscle
Which type of muscle does the external anal sphincter consist of?
Skeletal muscle
Where does the internal anal sphincter surround in relation to the anal canal?
Superior 2/3 of anal canal
Where does the external anal sphincter surround in relation to the anal canal?
Inferior 2/3
Which nerve stimulates contraction of the external anal sphincter?
Pudendal nerve
Contraction of the internal anal sphincter is stimulated by which nerve supply?
Sympathetic
What do the somatic motor nerve fibres in the pudendal nerve and levator ani muscle do and where in the spinal cord do they exit?
Pudendal (S2, S3, S4)
Nerve to levator ani (S3, S4)
Stimulate the external anal sphincter and puborectalis to contract
What do the visceral afferent nerve fibres from the rectum run alongside and where do they enter the spinal cord?
Parasympathetic nerve fibres
Enter spinal cord at S2, S3, S4
What do the visceral afferent nerve fibres from the rectum do?
They sense ischaemia, stretch and fullness of rectal ampulla
What is the pectinate line?
Marks the junction between the endoderm and ectoderm from embryological development
Marks the difference between the two types of tissue in the anal canal - columnar epithelium superiorly, stratified squamous epithelium inferiorly
Which structures do the internal iliac lymph nodes drain?
Inferior pelvic structures
Which structures do the external iliac lymph nodes drain?
Superior pelvic structures
Lower limb
Where do the common iliac nodes drain from and to?
Drain from the external and internal iliac nodes
Drain to the lumbar nodes
Which artery supplies the proximal 1/2 of the anal canal?
Superior rectal artery - a branch of the IMA
Which artery supplies the distal 1/2 of the anal canal?
The middle and inferior rectal arteries - branches of the internal iliac artery
What is a haemorrhoid?
The prolapse of the internal and external rectal venous plexus
This is not related to portal hypertension
What are the ischioanal fossae?
Structures consisting of fat and loose connective tissue which lie on either side of the anal canal
