Lecture 23: The large intestine and liver

Question 1

What is the main role of the large intestine?

Answer 1

• Absorption of water (some sodium as well)
• Storage of feces until defecation

Question 2

What does the large intestine consist of?

Answer 2

• Consists of cecum, colon, and rectum

Question 3

What can the colon be divided into (terms)?

Answer 3

Colon divided into:
* Ascending
* Transverse
* Descending
* Sigmoid

Question 4

What are the locations of the respective parts of the large intestine?

Answer 4

• Ascending and descending colon are retroperitoneal
• Transverse and sigmoid colon are intraperitoneal

Question 5

What enables imaging of the large intestine?

Answer 5

• A Barium enema enables imaging to assess function

Question 6

What is the cecum?

Answer 6

• Blind-ended pouch
• Location of appendix
• Ileocecal valve regulates the passage of material into the
  large intestine

Question 7

What is the appendix and what is its function?

Answer 7

• known as the Vermiform appendix
• is a Reserve of large intestine bacteria
• Attached to cecum
• Can become inflamed = appendicitis

Question 8

Why does the large intestinal wall need to be modified?

Answer 8

Needs to be modified to:
* Store feces
* Expel feces during defecation
* Be lubricated
* Allow absorption of water

Question 9

What are some features of the large intestinal wall?

Answer 9

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

Question 10

Describe the muscularis of the large intestine:

Answer 10

• Inner circular layer
• Outer longitudinal layer forms three thick bands (Teniae coli)
• Allows for stronger contraction

Question 11

Describe the large intestine mucosa:

Answer 11

• Lack of villi
• Mucosa invaginates to form intestinal glands
• Simple columnar epithelium

Question 12

What cells can be found in the large intestinal mucosa?

Answer 12

• Absorptive cells for water and salt
• Goblet cells produce mucus for protection and lubrication

Question 13

Where is the rectum and what does it do?

Answer 13

• The rectum is the last part of the large intestine
• Stores feces

Question 14

What connects the rectum to the anus?

Answer 14

anal canal

Question 15

What marks the boundary where epithelium changes in the anal canal and anus and what types of epithelium are there?

Answer 15

Anal columns mark boundary where epithelium changes
* Before: simple columnar
* After (anus): stratified squamous

Question 16

What are the two anal sphincters composed of?

Answer 16

The internal anal sphincter
* composed of smooth muscle
* under involuntary control

The external anal sphincter
* composed of skeletal muscle
* under voluntary control

Question 17

Describe the defecation reflex:

Answer 17

• 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

Question 18

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

Answer 18

C

Question 19

What type of epithelium is found in the large intestine?

Answer 19

Simple columnar and goblet cells

Question 20

What is the function of the liver?

Answer 20

Function:
* metabolic processes
* detoxifies blood
* produces bile

Question 21

What is the location of the liver?

Answer 21

Location:
* Superior right quadrant of abdominopelvic cavity
* Wedge shaped organ
* Attached to stomach by lesser omentum

Question 22

What is the gall bladders function and where is it located?

Answer 22

• Hollow organ below liver
• Stores & concentrates bile
• Connects via cystic duct to bile duct
• Can become obstructed by gallstones

Question 23

What cell processes nutrient rich deoxygenated blood from the small intestine in the liver?

Answer 23

Processed by hepatocytes

Question 24

What is the blood supply of the liver?

Answer 24

• Receives ~25% of cardiac output
• 1/3 of blood supply to liver from hepatic artery
• 2/3 from hepatic portal vein

Question 25

Where does the hepatic portal vein, the hepatic artery
and the bile duct travel?

Answer 25

within the lesser omentum

Question 26

What are the two reflexes of the defecation?

Answer 26

1. Local/short triggers peristaltic contractions in the rectum to push faeces towards anus
2. 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

Question 27

What are the five structures of the liver?

Answer 27

• 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

Question 28

Describe the pathways of blood and bile within the liver:

Answer 28

• 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)

Question 29

What is the pathway for venous drainage of the liver?

Answer 29

• Central veins drain into hepatic vein which drains into
  inferior vena cava

Question 30

What is the difference between the hepatic portal vein and the hepatic vein?

Answer 30

Hepatic portal vein drains into the liver (from gut)

Hepatic vein drains FROM the liver towards the heart

Question 31

Where is bile stored and concentrated?

Answer 31

The gallbladder

Question 32

Where does the bile duct join to the pancreatic duct?

Answer 32

at the hepatopancreatic ampulla