Gastrointestinal Physiology 1 Flashcards
What does GIT stand for?
Gastrointestinal tract
What is the GIT also known as?
Alimentary canal
What is the GIT?
A series of specialised organs, associated with digestion and absorption
Which organs does the GIT include?
Mouth Pharynx (back of the throat) Oesophagus Stomach Small intestine (duodenum, jejunum, ileum) Large intestine (colon) Rectum Anus
What salivary glands classed as?
An accessory structure attached to the GIT
What do the salivary glands produce/contain?
Mainly fluids containing the enzymes analyse (digests starch) and lipase (digests fats)
Also contain mucin (glycoprotein), which helps with lubrication and swallowing of food
What is a glycoprotein?
A protein with carbohydrates attached
How many sets of salivary glands are there?
3
What are the names and positions of these sets of salivary glands?
Sublingual
Submandibular (in the lower jaw)
Parotid (in the side of the cheek)
The _ gland is primarily responsible for producing _.
Parotid
Amylase
To which family does the mumps virus belong?
Paramyxovirus
How does the mumps virus work?
Affect the salivary glands, in particular the virus targets the parotid gland
The virus infects cells by binding to a surface cell receptor, sialic acid
What are some of the complications associated with the mumps virus?
Infertility - in post-adolescent males, the testes (also a glandular structure) can become infected
Temporary or permeant diabetes - the pancreas (also an accessory structure) can become infected
Meningitis - inflammation of the meninges
Deafness
How does swallowing occur?
Receptors sense the presence of material in the mouth and back of throat and relay this information back to the brain
This sensory information travels up into the medulla oblongata (brain stem) where it is processed
Nerve impulses then travel down out of the brain and into the muscles in the throat to allow swallowing
This is a process we take for granted but is actually incredibly complex
Which are the nerves involved in swallowing?
Trigeminal
Facial
Which other neves are also important in swallowing?
Glossopharyngeal (leads from brain stem down to the back of the throat) Hypoglossal Vagus (extends from the brain stem down into the intestine)
Damage to these nerves affects…
The swallowing process
Give an example of a condition where these nerves are affected.
Stroke
Around 40-65% of stroke survivors experience dysphagia
Where does food bolus/medication go after being swallowed?
Enters the oesophagus
Where is the oesophagus positioned?
Travels down the chest and through the diaphragm
What is the oesophageal hiatus?
The point at which the oesophagus passes from the chest into the abdomen through the diaphragm
What is a hiatus hernia?
When the upper part of your stomach pushes out through the oesophageal hiatus
What does a hiatus hernia often result in?
Acid reflux (the movement of stomach acid out of the stomach and up into the oesophagus)
What does a healthy oesophagus look like?
Very pink
What is the oesophagus lined with?
Squamous (meaning scale) epithelial cells
What is the lower oesophageal sphincter or cardiac sphincter?
A specialised muscle where the oesophagus joins the stomach
What is the function of the lower oesophageal sphincter or cardiac sphincter?
Essentially to seal the stomach and prevent movement of acid and digestive enzymes out into the oesophagus
What happens when acid and digestive enzymes move into the oesophagus?
Gastroesophageal reflux disease (acid reflux) occurs
What is the pathophysiology associated with Barrett’s oesophagus?
The cells which line the oesophagus are exposed to digestive juices (acid, digestive enzymes)
This causes erosion of the cell layer
The healthy cells that were present are then replaced by abnormal cells
This abnormal type of cell is precancerous (we do not usually find this type of cell within the healthy body)
Even if reflux is controlled and the oesophagus heals, these abnormal cells remain
What is the name of the type of abnormal cells present in Barrett’s oesophagus?
Specialised columnar (taller like columns)
What does the presence of these abnormal cells predispose you to?
Increased risk of developing adenocarcinoma than the general population
Once the food bolus/medicine has passed through the oesophagus, where does it go next?
The stomach
What are the names of the array of different cells present in the stomach?
Mucous cells
G cells
Chief cells
Parietal (oxyntic) cells
What is the role of mucous cells in the stomach?
Secrete mucus
What is the role of G-cells in the stomach?
Located in the antrum (lower part of the stomach) Enteroendocrine Secrete gastrin (which binds to a receptor and leads to acid production)
What is the role of chief cells in the stomach?
Located in the fundus/body (top/middle part of the stomach)
Secrete pepsinogen and lipase into the lumen of the stomach
Pepsinogen is an inactive form of pepsin (a zymogen)
What is the role of parietal cells in the stomach?
Located in the fundus/body (top/middle part of the stomach)
HCl secretion
Pumps out acid (H+) into the lumen of the stomach
How does the stomach know when we are about to eat and how does it act as a result?
The sight or smell of food sends signals to the brain
There are nerves running down from the brain into the stomach and these nerves promote the release of acetyl choline, gastrin from G cells and histamine
These 3 products bind to receptors, which in turn promotes the release of HCl
The H+, K+ ATPase pump pumps protons out into the stomach lumen
How is histamine released in the stomach?
When you take in food, the stomach stretches and as it does it releases histamine
How does a parietal cell work at a molecular level?
Present on the apical membrane are 2 pumps
One of these is the H+, K+ ATPase pump which pumps protons out into the stomach lumen by primary active transport
The other is a Cl- ion channel which allows the passage of Cl- ions into the stomach lumen
The H+ and Cl- ions then combine to give HCl
How do H2 receptor antagonists work?
Bind to the H2 histamine receptor, competitively with histamine, to reduce its effect
The knock on effect is that you reduce gastric acid production
Name 2 examples of H2 antagonists.
Cimetidine (Tagamet)
Ranitidine (Zantac)
How do proton pump inhibitors (PPI’s) work?
Block the pump that moves protons out of parietal cells and into the stomach lumen
Name an example of a PPI and explain how it works.
Omeprazole
Works by circulating around the body and targeting the proton pump, binds irreversibly to -SH groups of the H+, K+ ATPase pump and therefore reduces gastric acid (HCl) production
