Lecture 1: Brief intro to GI Tract

Question 1

How do you divide the GI tract up into different sections?

Answer 1

Via sphincters, which usually contain a muscular component so it can contract and divide one section from another or control the flow of substance from one section to another.

Question 2

What other organs input into the GI tract?

Answer 2

-salivary glands
-liver
-pancreas
(via tubes)

Question 3

What types of cells line the GI tract?

Answer 3

Range of specialised cells that differ along the length of the gut to match what that section of the gut does.

Question 4

What are the different sections of the gut in order?

Answer 4

Mouth, oesophagus, stomach (dilated section of the gut), duodenum (start of the small intestine), jejunum, ileum, terminal ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus.

Question 5

What is the substance that leaves the stomach called?

Answer 5

Chyme

Question 6

How many sections does the duodenum consist of?

Answer 6

4 (25cm long in total)

Question 7

What is the longest section of gut?

Answer 7

Jejunum, which connects seamlessly to the ileum. The width of the gut decreases as you go down the tube. There are also more internal folds at the start of the jejunum than there are in the terminal ileum

Question 8

Where does the width of the GI tract change most (except the stomach)?

Answer 8

Terminal ileum to cecum. The cecum is the start of the large intestine

Question 9

Why can’t you see the part of the stomach on a human?

Answer 9

The right side of the liver obscures it (this has to be lifted up in a cadaver to show the stomach)

Question 10

Where abouts are the different areas of the gut anatomically located?

Answer 10

• small intestine is central (middle) and occupies a small space
• colon occupies a peripheral position

Question 11

What are the functions of the mouth?

Answer 11

• physical breakdown of food
• initial digestive enzymes released (saliva acts as lubricant and also contains enzymes e.g. amylase/lysozymes)
• infection control (innate barrier)

Question 12

What are the functions of the oesophagus?

Answer 12

-rapid peristalsis through thorax to stomach

Question 13

What is the thorax?

Answer 13

Region b/w root of neck and abdomen.

Question 14

What are the functions of the stomach?

Answer 14

-storage facility
To produce chyme:
- physical breakdown (stomach is muscular)
-chemical breakdown (proteases and acidic environment)
-

Question 15

Why is the acidic nature of the stomach beneficial?

Answer 15

• It helps to unravel proteins to increase its surface area and make it more available for proteases.
• Innate barrier towards live toxins entering our body through the gut

Question 16

What other substance does the stomach release?

Answer 16

Intrinsic factor. Beneficial in absorbing vit B12

Question 17

What sphincter releases the stomach contents (chyme) into the duodenum?

Answer 17

Powerful pyloric sphincter

Question 18

What secretions come from the vasculature/pancreas/liver into the start of the duodenum?

Answer 18

• bicarbonate rich secretions (HCO3). As the chyme from the stomach is very acidic, so needs to be neutralised.
• chyme is also a hypertonic mixture as macromolecules are broken down into smaller ones, so water enters the duodenum from surrounding vasculature

Question 19

What does the liver produce to enter the duodenum?

Answer 19

Bile, which helps greatly with the breakdown of fats.

pancreatic secretions are very enzyme rich

Question 20

Why is the duodenum an important anatomical landmark in the gut?

Answer 20

2nd part of the duodenum where the major pancreatic duct and common bile duct enter together into duodenum, is a junction of the foregut and the midgut

Question 21

What are the functions of the jejunum/ileum?

Answer 21

-final digestion
-nutrient absorption
(the above mostly happen in the jejunum, as it has many folds to increase its SA)
-water and electrolyte absorption
(mainly in ileum)

In the terminal ileum

• bile salts are reabsorbed (involved in bile recirculation so we don’t have to produce bile acids all the time)
• vit B12 absorption

Question 22

What is the function of the large intenstine?

Answer 22

-final water absorption (difficult as most water is absorbed in small intestine, against a high conc gradient as there is lots of water outside the gut compared to inside the gut so requires lots of energy and adaptations)

Question 23

What part of the gut does the appendix come off?

Answer 23

Cecum

Question 24

How do you get diarrhoea?

Answer 24

If too much water enters the large intestine

Question 25

Where is bacteria are present in the gut?

Answer 25

• small intestine is relatively sterile
• large intestine has large colonies of bacteria which is vital for normal function and whole body health (microbiome)
• some bile salt absorption
• not much nutrient absorption due to lack of folds and therefore a low SA
• temporary storage for gut contents, until it is triggered, when you get a mass movement- rapid peristalsis from transverse/distal colon into rectum

Question 26

How do you prevent bacteria reaching the epithelium in the large intestine?

Answer 26

Lots of muscus secretion to provide a barrier

Question 27

How do the bacteria in the gut survive?

Answer 27

Require short chain fatty acids as their energy (dietary fibre converted to short chain fatty acids)

-nutrients and support is secreted to aid the bacteria

Question 28

What gives us the urge to go to the toilet?

Answer 28

The stretching of the rectum (as it isusually empty)

Question 29

What is the function of the rectum/anus?

Answer 29

Defaecation