Lecture 23: The large intestine and liver Flashcards
What is the main role of the large intestine?
- Absorption of water (some sodium as well)
- Storage of feces until defecation
What does the large intestine consist of?
- Consists of cecum, colon, and rectum
What can the colon be divided into (terms)?
Colon divided into:
* Ascending
* Transverse
* Descending
* Sigmoid
What are the locations of the respective parts of the large intestine?
- Ascending and descending colon are retroperitoneal
- Transverse and sigmoid colon are intraperitoneal
What enables imaging of the large intestine?
- A Barium enema enables imaging to assess function
What is the cecum?
- Blind-ended pouch
- Location of appendix
- Ileocecal valve regulates the passage of material into the
large intestine
What is the appendix and what is its function?
- known as the Vermiform appendix
- is a Reserve of large intestine bacteria
- Attached to cecum
- Can become inflamed = appendicitis
Why does the large intestinal wall need to be modified?
Needs to be modified to:
* Store feces
* Expel feces during defecation
* Be lubricated
* Allow absorption of water
What are some features of the large intestinal wall?
Teniae Coli:
* Bands of longitudinal muscle
Haustra:
* Series of pouches
Omental appendices:
* Sacs of fat
Semilunar folds (between haustra)
- increase SA and help stores things longer
Describe the muscularis of the large intestine:
- Inner circular layer
- Outer longitudinal layer forms three thick bands (Teniae coli)
- Allows for stronger contraction
Describe the large intestine mucosa:
- Lack of villi
- Mucosa invaginates to form intestinal glands
- Simple columnar epithelium
What cells can be found in the large intestinal mucosa?
- Absorptive cells for water and salt
- Goblet cells produce mucus for protection and lubrication
Where is the rectum and what does it do?
- The rectum is the last part of the large intestine
- Stores feces
What connects the rectum to the anus?
anal canal
What marks the boundary where epithelium changes in the anal canal and anus and what types of epithelium are there?
Anal columns mark boundary where epithelium changes
* Before: simple columnar
* After (anus): stratified squamous
What are the two anal sphincters composed of?
The internal anal sphincter
* composed of smooth muscle
* under involuntary control
The external anal sphincter
* composed of skeletal muscle
* under voluntary control
Describe the defecation reflex:
- Movement of feces into rectum stimulates stretch
receptors - Internal anal sphincter relaxes
- Conscious decision to defecate -> external anal sphincter relaxes
- Muscular contractions expel feces from body
Which of the following statements is CORRECT?
A. Teniae coli are bands of circular muscle
B. There are three haustra in the large intestine
C. The large intestine lacks villi
D. The appendix is attached to the rectum
C
What type of epithelium is found in the large intestine?
Simple columnar and goblet cells
What is the function of the liver?
Function:
* metabolic processes
* detoxifies blood
* produces bile
What is the location of the liver?
Location:
* Superior right quadrant of abdominopelvic cavity
* Wedge shaped organ
* Attached to stomach by lesser omentum
What is the gall bladders function and where is it located?
- Hollow organ below liver
- Stores & concentrates bile
- Connects via cystic duct to bile duct
- Can become obstructed by gallstones
What cell processes nutrient rich deoxygenated blood from the small intestine in the liver?
Processed by hepatocytes
What is the blood supply of the liver?
- Receives ~25% of cardiac output
- 1/3 of blood supply to liver from hepatic artery
- 2/3 from hepatic portal vein
Where does the hepatic portal vein, the hepatic artery
and the bile duct travel?
within the lesser omentum
What are the two reflexes of the defecation?
- Local/short triggers peristaltic contractions in the rectum to push faeces towards anus
- Longer reflex which is a spinal cord reflex coordinated by sacral parasympathetic motor neurons. This reflex stimulates mass movements and pushes more faeces into the rectum from the descending and sigmoid colon - this further relaxes the internal anal sphincter
What are the five structures of the liver?
- Lobules are functional units
- Rows of hepatocytes produce bile
- Liver sinusoids between rows of cells (larger, things can get through eg. drugs)
- Bile canaliculi between cells (small)
Portal Triad:
- Branch of hepatic artery
- Branch of hepatic portal vein
- A bile duct
Describe the pathways of blood and bile within the liver:
- Blood flows towards central vein - Is Processed by hepatocytes, which also produce bile
- Bile is secreted into canaliculi, travels to bile duct (opposite direction to blood)
What is the pathway for venous drainage of the liver?
- Central veins drain into hepatic vein which drains into
inferior vena cava
What is the difference between the hepatic portal vein and the hepatic vein?
Hepatic portal vein drains into the liver (from gut)
Hepatic vein drains FROM the liver towards the heart
Where is bile stored and concentrated?
The gallbladder
Where does the bile duct join to the pancreatic duct?
at the hepatopancreatic ampulla
What makes up the portal triad in the liver?
- Branch of hepatic artery
- Branch of hepatic portal vein
- A bile duct
