Principles - Lower GI System Flashcards
What is the lower GI tract?
Caecum Appendix Colon Rectum Anal canal Anus
What is the end of the upper GI tract?
The ileocaecal junction
What is the small intestine made up of?
The duodenum - leaves the stomach and curves round the head of the pancreas
The jejunum
The ileum - terminal part of the small intestine, connects with first part of the large intestine
From proximal to distal, name the sections of the large intestine.
The colon (caecum, appendix, ascending colon, transverse colon, descending colon and sigmoid)
The rectum
The anal canal
The anus
What are the different layers of the walls of the intestine?
Mucosa (innermost)
Inner circularly arranged smooth muscle
Outer longitudinally arranged smooth muscle
Visceral peritoneum
What are mesenteries?
An organ’s double layer of visceral peritoneum
What does the outer longitudinal layer of smooth muscle do in the intestine?
Shortens the tube during peristalsis
What does the inner circular layer of smooth muscle do in the intestine?
Constricts the diameter of the tube during peristalsis
What does the abdominal cavity contain?
Peritoneal cavity and retroperitoneum
What is the retroperitoneum?
The space within the abdominal cavity posterior to the peritoneum
How do the abdominal organs fit into the abdominal cavity?
By pushing into the peritoneal cavity - they never enter the cavity, they just push into it
What is the peritoneum?
The serous membrane that forms the lining of the abdominal cavity
What is visceral peritoneum?
The peritoneum that touches the organs
What is parietal peritoneum?
the peritoneum that lines the abdominal and pelvic cavities
What is an intraperitoneal organ? Give an example.
An organ almost completely covered with visceral peritoneum - minimally mobile as it has been anchored by the peritoneum
e.g. liver
What is a retroperitoneal organ? Give an example.
Located in the retroperitoneum - visceral peritoneum only on its anterior surface
e.g. pancreas and kidneys
What is an organ with mesentery?
An organ covered in visceral peritoneum and suspended from the posterior abdominal wall by a mesentery - organ is highly mobile
e.g. parts of the intestines
What are the organs of the foregut?
Oesophagus to mid-duodenum Liver Gallbladder Spleen Half the pancreas
What are the organs of the midgut?
Mid-duodenum to proximal 2/3rds of the transverse colon
half of the pancreas
What are the organs of the hind gut?
Distal 1/3rd of the transverse colon to proximal 1/2 of the anal canal
What are the 3 midline branches of the abdominal aorta?
- coeliac trunk - foregut organs
- superior mesenteric artery - midgut organs
- inferior mesenteric artery - hindgut organs
Where do branches of the superior mesenteric artery go?
Into the mesentery of the small intestine
Where do branches of the inferior mesenteric artery go?
Into the mesentery of the sigmoid colon
What does the inferior vena cava drain?
The cleaned blood from the hepatic veins into the right atrium
What does the hepatic portal vein do?
Drains the blood from the foregut, midgut and handgun structures to the liver for first pass metabolism
What does the splenic vein do?
Drains the blood from the foregut structures into the hepatic portal vein
What does the inferior mesenteric vein do?
Drains blood from the hindgut structures to the splenic vein
What does the superior mesenteric vein do?
Drains the blood from the midgut structures to the hepatic portal vein.
What is the portal venous system?
This is via the hepatic portal vein
It drains blood from the absorptive parts of the GI tract and the associated organs of the GI tract to the liver for first pass metabolism
What are the two venous systems present in the GI tract? Where do they meet?
Portal venous system
Systemic venous system
Meet in the liver - hepatic portal vein carries venous blood from the portal venous system to the liver
The liver then passes the blood int the IVC via the hepatic veins to return to the heart
What is the systemic venous system?
IVC and SVC
Drains deoxygenated blood from the rest of the body to the right atrium of the heart, including blood draining from the liver via the hepatic veins
What is the blood supply of the liver?
Hepatic artery and hepatic portal vein
Where do foregut structures drain their lymph?
via nodes located along the splenic artery towards the coeliac nodes
Where do midgut structures drain their lymph?
Via nodes located along the superior mesenteric artery towards the superior mesenteric nodes
Where do hindgut structures drain their lymph?
Via nodes located along the inferior mesenteric artery towards the inferior mesenteric nodes
Where is the pyloric sphincter? Is it smooth or skeletal muscle?
in-between stomach and duodenum
smooth muscle
What are anatomical sphincters?
Discrete areas where muscle completely encircles the lumen of the tract - can be smooth muscle or skeletal muscle
Where is the cricopharyngeal sphincter?
at the junction between laryngopharynx and oesophagus
Where is the external anal sphincter?
At the junction between anus and external environment
