Lecture 23- The large intestine and comments of the liver Flashcards
What does the large in large intestine refer to?
Diameter
How long is the large intestine and how does this compare to the small intestine?
- 1.5 meters
- A lot shorter
What are the three sections of the large intestine?
- Cecum (blind ended pouch)
- Colon
- Rectum (straight)
What can the colon be further divided into?
- Ascending
- Transverse
- Descending
- Sigmoid (S shaped)
In the colon what is the bend after the ascending colon called? What is the bend after the transverse colon?
- Right colic/ hepatic flexure
- Left colic/ splenic flexure
Where is the large intestine located in terms of the peritoneal cavity?
-The rectum, ascending and descending colon are
retroperitoneal
-The cecum, transverse and sigmoidal colon are intraperitoneal
What is the Ileocecal Valve?
- Between the ileum (small intestine) and cecum
- Important function is to regulate the passage of material into the cecum (ensures that backflow doesn’t occur)
What is the name of the blind ended tubular structure joint to the cecum? What does this name mean?
- The vermiform appendix
- Vermiform= worm like, Appendix= sticks out
What is the function of the appendix?
-Acts as a reserve of large intestine bacteria population
which means that in the event where gut bacteria has been wiped out the large intestine is key to regrowth
-Contains lymph tissue so has important immune functions
Is the location of the appendix fixed?
No, varies between people
Due to its structure what is the appendix prone to and what are the consequences of this?
- Prone to getting blocked
- This can cause it to swell and get inflamed (appendicitis) eventually bursting
- Once burst this spreads the bacteria contained into the peritoneal cavity where they easily spread due to optimal growth conditions
What is a barium enema? What does it allow?
- Metallic substance (barium) passes through the gut backwards
- This allows x-ray image to be taken of large intestine to assess functioning
- If the Ileocecal Valve is working properly we shouldn’t be able to see the small intestine as material is prevented from flowing back
What are three gross differences in structure between the large and small intestine?
The large intestine has…
- Teniae Coli
- Haustra
- Omental appendices
What are Teniae coli?
- 3 bands of longitudinal smooth muscle (modification of the Muscularis layer)
- Literal translation is ‘ribbons of the colon’
- Result in stronger contraction to help propelle the feces
What are Haustra?
- Series of pouches in the wall of colon
- Semilunar folds are between
What are Omental appendices?
- Sacs of fat
- Used for fat storage?
Are there villi in the large intestine? Why/ why not?
- No villi
- The large intestine is not specialized for absorption so no need to increase surface area in this way
What does the mucosa of the large intestine do?
- Invaginates to form intestinal glands which increases the surface area for secretion
- Goblet cells in the mucosa produce mucus for protection and lubrication (makes it easy for feces to pass through)
- Mucosa also absorptions water and salts
What does the mucosa consist of? Which parts invaginate to form glands?
- Consists of epithelium, lamina propria, Muscularis mucosae
- The Muscularis mucosae does not invaginate and instead is a solid baseline
What is the change in epithelium that occurs at the rectum?
- Anal columns mark boundary where epithelium changes.
- Before this point: simple columnar
- After: epithelium of the anal canal is stratified squamous which eventually becomes continuous with the skin
Why is the epithelium of the rectum stratified squamous?
For protection against abrasion (from feces)
What are the two sphincters found within the rectum? How do they differ from each other?
-The internal anal sphincter is smooth muscle (under
involuntary control)
-The external anal sphincter is skeletal muscle (under voluntary control)
What is the defecation reflex?
- Movement of faeces into rectum stimulates stretch receptors
- Internal anal sphincter relaxes (involuntary)
- Conscious decision to defecate – external anal sphincter relaxes (this last step prevents defecation in unwanted places)
Where is the liver located? What is the function we are focusing on?
- Superior right quadrant of abdominopelvic cavity
- Produces bile which is stored in the gall bladder
How is the liver supplied with blood?
- 1/3 of blood supply from hepatic artery
- 2/3 is venous blood from hepatic portal vein
Where is the hepatic artery?
Branch off the abdominal aorta
What is the blood coming through the hepatic portal vein like?
- Nutrient rich, deoxygenated blood from small intestine
- Processed by hepatocytes in the liver which detoxifies it + takes some nutrients for the liver itself
How much of the cardiac output does the liver receive?
25%
In relation to the liver what is found within the lesser omentum?
- Hepatic portal vein
- The hepatic artery
- Bile duct
What are the functional units of the liver called and how are these structured?
- Called lobules
- Consist of rows of Hepatocytes: produce bile
- These surround a central vein
- Liver sinusoids (leaky capillaries) between rows, bile canaliculi between cells.
What makes up the portal triad?
- Branch of hepatic artery
- Branch of hepatic portal vein
- A bile duct
What is the direction of blood flow through the liver? How does this relate to the direction of bile flow?
- Blood flows towards central vein is processed by hepatocytes, which produce bile
- Bile is secreted into canaliculi and travels to bile duct (opposite direction of flow)
What is the drainage that occurs in the liver?
Central veins drain deoxygenated + detoxified blood into hepatic vein which drains into inferior vena cava (goes to right atrium of heart)
Where does bile go once it is produced in the liver?
-Bile travels to gall bladder, where it is stored and
concentrated
-Bile duct ultimately joins pancreatic duct at hepatopancreatic ampulla
