Lecture 1: Brief intro to GI Tract Flashcards
How do you divide the GI tract up into different sections?
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.
What other organs input into the GI tract?
-salivary glands
-liver
-pancreas
(via tubes)
What types of cells line the GI tract?
Range of specialised cells that differ along the length of the gut to match what that section of the gut does.
What are the different sections of the gut in order?
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.
What is the substance that leaves the stomach called?
Chyme
How many sections does the duodenum consist of?
4 (25cm long in total)
What is the longest section of gut?
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
Where does the width of the GI tract change most (except the stomach)?
Terminal ileum to cecum. The cecum is the start of the large intestine
Why can’t you see the part of the stomach on a human?
The right side of the liver obscures it (this has to be lifted up in a cadaver to show the stomach)
Where abouts are the different areas of the gut anatomically located?
- small intestine is central (middle) and occupies a small space
- colon occupies a peripheral position
What are the functions of the mouth?
- physical breakdown of food
- initial digestive enzymes released (saliva acts as lubricant and also contains enzymes e.g. amylase/lysozymes)
- infection control (innate barrier)
What are the functions of the oesophagus?
-rapid peristalsis through thorax to stomach
What is the thorax?
Region b/w root of neck and abdomen.
What are the functions of the stomach?
-storage facility
To produce chyme:
- physical breakdown (stomach is muscular)
-chemical breakdown (proteases and acidic environment)
-
Why is the acidic nature of the stomach beneficial?
- 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
What other substance does the stomach release?
Intrinsic factor. Beneficial in absorbing vit B12
What sphincter releases the stomach contents (chyme) into the duodenum?
Powerful pyloric sphincter
What secretions come from the vasculature/pancreas/liver into the start of the duodenum?
- 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
What does the liver produce to enter the duodenum?
Bile, which helps greatly with the breakdown of fats.
pancreatic secretions are very enzyme rich
Why is the duodenum an important anatomical landmark in the gut?
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
What are the functions of the jejunum/ileum?
-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
What is the function of the large intenstine?
-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)
What part of the gut does the appendix come off?
Cecum
How do you get diarrhoea?
If too much water enters the large intestine
Where is bacteria are present in the gut?
- 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
How do you prevent bacteria reaching the epithelium in the large intestine?
Lots of muscus secretion to provide a barrier
How do the bacteria in the gut survive?
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
What gives us the urge to go to the toilet?
The stretching of the rectum (as it isusually empty)
What is the function of the rectum/anus?
Defaecation
