GI week 1 Flashcards
Name the muscles of mastication (4) and the nerve supply?
Masseter – runs outside of your jaw
Temporalis – Inside part of the mandible
Lateral and medial pterygoid
Mandibular division of trigeminal nerve
What foramen does mandibular division of trigeminal nerve go through?
Foramen Ovale
What two stages make oral phase?
Preparatory and Transit
Describe the preparatory phase (4)
- Voluntary
- Produces the food bolus
- Posterior tongue elevated
- Soft palate depressed to close off pharynx
Describe the Transit phase (4)
- Movement of bolus towards pharynx by tongue
- Soft palate elevated inhibiting inspiration
-Initiation of swallowing reflex - Uvula tops food going into nasopharynx
What is the purpose of saliva? (4)
- Break down food
- Produce the bolus
- Protect oral taste
- Help us taste
What type of glands are salivary glands
Exocrine
What are the 3 primary salivary glands and how are they classed?
- Parotid (serous)
- Sublingual gland (seromucous)
- Submandibular gland (seromucous)
What do Parietal cells secrete?
HCL for digestion and intrinsic factor which is essential for b12 absorption
What do chief cells secrete
Pepsinogen, which is essential for protein digestion
Where are chief and parietal cells found?
In the corpus, composed of surface epithelial cells, mucus neck cells
Where does not contain Parietal cells
The antrum
What G cells do?
secrete gastrin, stimulating parietal cells to secrete acid.
What do D cells do?
Secrete somatostatin to inhibit gastrin secretion from G cells
What is the process of forming HCL? (8)
Takes place in parietal cells
The NKCC1 channel permits entry of 1 sodium, 1 potassium and 2 chloride ions into the cell using the concentration gradient of sodium as the energy source
Chloride is then released into the gastric lumen through passive diffusion through chloride channels
Water and CO2 enter the cell passively through the basolateral membrane.
Through the enzymatic action of carbonic anhydrase, these compounds are turned into hydrogen ions and bicarbonate.
Bicarbonate is pumped out of the basolateral cell membrane through AE2 channels, which in turn pump chloride ions into the cell.
Hydrogen is pumped out of the apical membrane through the hydrogen-potassium ATPase (closely related to the sodium-potassium ATPase).
With hydrogen pumped out of the cell, it can interact with the chloride to form hydrochloric acid
What is used to treat gastroesophageal reflux disease and peptic ulcers?
Proton pump inhibitors, e.g., omeprazole, work by blocking this pump thus preventing hydrogen ions from entering the gastric lumen.
What three ways stimulate acid secretion?
- Vagus nerve can directly stimulate parietal cells.
- Vagus nerve stimulates enterochromaffin-like cells. These ECL cells secrete histamine which acts on parietal cells.
- Gastrin, (secreted by G-cells of the antrum) act on CCK-2 receptors on both parietal and ECL cells causing release of histamine from ECL cells.
Name one pharmacological approach for the treatment of gastro-oesophogeal reflux disease?
Histamine receptor antagonists (H2), inhibit the action of ECL cells.
Name one bacteria causing excess gastric production & and the physiology behind this?
Helicobacter pylori infection. If H. pylori infects the antrum region (lowest part of the stomach) the consequent inflammation can lead to G cell stimulation, resulting in elevated gastrin secretion and subsequently elevated acid secretion. The inflammation can also degrade the gastric mucosa leading to loss of mucus producing cells leading to the stomach becoming susceptible to acid erosion.
Name a rare cause of elevated gastric secretion?
Extra-gastric gastrinoma (a gastrin producing tumour) – so called Zollinger-Ellison syndrome. These tumours are typically located in the pancreas or duodenum and secrete gastrin, which has the effect of increasing HCl production
Enzyme which breaks down starch molecules?
Ptyalin (an alpha-amylase) through hydrolysis to maltose (2 glucoses)
Where does carbohydrate digestion occur?
5% in mouth but most in duodenum
What cells in Pancreas secrete amylase?
Acinar cells
What is the composition of the pancreas?
85% exocrine tissue (amylase etc.)
15% endocrine tissue (glucagon + insulin)
Where does final stage of carbohydrate digestion occur?
Within the small intestine. Enterocytes have a brush border of the villi which contain four different carbohydrate enzymes.
What are the 4 carbohydrate enzymes and what sugars do they convert into?
- Enzyme is Lactase
Lactose - Glucose + Galactose - Enzyme is Sucrase
Sucrose - Fructose + Glucose - Enzyme is Maltase
Maltose - 2x Glucose - Enzyme is α-dextrinase
Dextrin - Maltose
Where are the simplest sugars stored
Enterocytes are also the site of sugar absorption, so carbohydrates are broken down and immediately absorbed. Glucose, (galactose and fructose, taken to liver and metabolises or principally stored as fat in the liver).
Where are the sites of protein digestion?
- 20% in stomach by pepsin
- Majority in Duodenum and Jejunum
