Lecture 23: Large Intestine and Comments on the Liver

Question 1

What three parts does the large intestine consist of?

Answer 1

the cecum
the colon
the rectum

Question 2

What are the four parts of the colon called?

Answer 2

the ascending colon
the transverse colon
the descending colon
the sigmoidal colon

Question 3

What is the cecum and where is it located?

Answer 3

A blind ended pouch that makes up first part of the large intestine that the small intestine flows into. It sits in the right iliac fossa.

Question 4

Which parts of the colon are retroperitoneal and which parts are intraperitoneal?

Answer 4

the ascending and descending colon are both retroperitoneal

the cecum, transverse and sigmoidal colon are all intraperitoneal

Question 5

What are the names of the bends in the colon and where are they located?

Answer 5

the ascending colon bends into the transverse colon at the hepatic flexure and the transverse colon bends into the descending colon at the splenic flexure

Question 6

If the the ascending and descending colon are both retroperitoneal, how are they anchored in the body?

Answer 6

they are both fixed to the posterior wall but are covered anteriorly with visceral peritoneum

Question 7

What is the name of the valve that regulates the passage of material forwards and prevents back flow of material from the large intestine into the small intestine?

Answer 7

the ileocecal valve

Question 8

What does the appendix contain and how does this relate to potential function?

Answer 8

it contains lymphoid tissue so can have an immune role
it also contains gut bacteria which could be used to reestablish the healthy bacteria in the gut following an illness such as diarrhoea

Question 9

What is the danger of the appendix swelling and causing appendicitis?

Answer 9

It could burst which means that faeces can be released into the peritoneal cavity. Because of the optimal conditions for growth (warmth) the bacteria can flourish in the cavity and cause peritonitis.

Question 10

What are three features of the large intestine?

Answer 10

1. teniae coli
2. haustra
3. omental appendices

Question 11

What are the omental appendices?

Answer 11

Sacs of fat

Question 12

What are haustra?

Answer 12

They are pouches in the large intestine.

Question 13

What separated haustra?

Answer 13

semilunar folds

Question 14

What is the purpose of haustra?

Answer 14

faeces move from haustra to haustra causing distention of the wall which causes contraction to keep the faeces moving through the large intestine

Question 15

What is one modification to the muscularis (externa) present in the large intestine.

Answer 15

the teniae coli

Question 16

What are the teniae coli and what it its purpose?

Answer 16

it is a band of longitudinal smooth muscle to cause stronger contractions

Question 17

Describe the muscularis (externa) in the large intestine

Answer 17

The inner layer is continuous around the tube but the longitudinal smooth muscle layer is modified to form bands (teniae coli) to generate greater force

Question 18

How is the mucosa modified in the large intestine?

Answer 18

There is no villi
The mucosa form glands invaginating into the lamina propia
the muscularis mucosa is flat (it doesn’t invaginate)

Question 19

What is the function of the mucosa in the colon?

Answer 19

for water and salt absorption

Question 20

What is the primary epithelium in the colon?

Answer 20

Simple columnar epithelium

Question 21

As well as the simple columnar epithelium, there are lots of _______ ______ present. Why is this?

Answer 21

goblet cells
because if the large intestine is removing water from the faeces, the faeces will be very dry and so it needs lubrication
it is also for protection

Question 22

Superior to the anal columns, there is what type of epithelium?

Answer 22

simple columnar epithelium

Question 23

Inferior to the anal columns, there is what type of epithelium?

Answer 23

stratified squamous epithelium

Question 24

Why do we have stratified squamous epithelium in the rectum?

Answer 24

for protection from abrasion

Question 25

What are the two sphincters in the rectum?

Answer 25

the internal anal sphincter and the external anal sphincter

Question 26

The internal anal sphincter is under ________ control from _________ muscle

Answer 26

involuntary

smooth

Question 27

The external anal sphincter is under _________ control from _________ muscle

Answer 27

voluntary

skeletal

Question 28

Describe the defecation reflex

Answer 28

As the faeces moves along the sigmoid colon into the rectum, it causes distention of the rectal wall to activate stretch receptors to initiate a reflex. This causes the contraction of the rectum to propel the faeces further down to trigger relaxation of the internal sphincter but we control when the external sphincter relaxes

Question 29

What is the location of the liver?

Answer 29

superior right quadrant of abdominopelvic cavity

Question 30

What is one function of the liver

Answer 30

produce bile

Question 31

Describe the liver’s blood supply

Answer 31

1/3 comes from the hepatic artery

the rest comes from the hepatic portal vein

Question 32

What is the blood what comes to the liver via the hepatic portal vein?

Answer 32

deoxygenated, nutrient rich blood from the small intestines

Question 33

The blood that arrives at the liver is processed in which cells?

Answer 33

Hepatocytes

Question 34

The hepatic portal vein, the hepatic artery, and the bile duct travel within the ________ _________

Answer 34

lesser omentum

Question 35

What are the functional units of the liver called

Answer 35

lobules

Question 36

What do lobules contain?

Answer 36

rows of hepatocytes surrounding a central vein

Question 37

What do the rows of hepatocytes produce?

Answer 37

bile

Question 38

What is in between each hepatocyte?

Answer 38

bile canaliculi

Question 39

What is in between each row of hepatocytes?

Answer 39

sinusoids

Question 40

The portal triad is made up of what three vessels?

Answer 40

a branch of the hepatic artery
a branch of the hepatic portal vein
a bile duct

Question 41

Describe the flow of blood and bile passed hepatocytes in the liver

Answer 41

Blood from both the hepatic artery and hepatic portal vein flows in the sinusoids towards the central vein

Question 42

Bile is produced as a byproduct when the hepatocytes process blood to detoxify it. Where does the bile go?

Answer 42

into the canaliculi and out via through the bile duct

Question 43

Does the blood and the bile flow in the same or opposite directions?

Answer 43

opposite

Question 44

Where does the detoxified blood flow from the central vein?

Answer 44

Blood from the central veins meet at the hepatic vein (not the hepatic portal vein) which drains into the inferior vena cava

Question 45

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

Answer 45

The hepatic vein flows from the liver to the inferior vena cava and the hepatic portal vein flows from the small intestine to the liver

Question 46

Describe the flow of bile from the liver

Answer 46

it travels in the bile duct to the gallbladder to be stored
when we contract the gallbladder, we get the bile to flow into the bile duct to ultimately join the pancreatic duct at the hepatopancreatic ampulla and then into the duodenum via the duodenal papilla