Physiology of GI Flashcards
How are carbohydrates absorbed?
Glucose and galactose move across apical membrane through SGLT1 (sodium coupled glucose transporter 1) transporter, then through basolateral membrane via a Glut-2 transporter.
Fructose can move across the apical membrane due to Glut-5 but needs Glut-2 to move across the basolateral membrane.
Glucose and galactose rely in the sodium concentration gradient to be absorbed as their levels are closely controlled by the body. Where as fructose uses its own concentration gradient.
If a movement is coupled to sodium transport, what can it be described as?
Secondary active transport
How are proteins absorbed?
Either as amino acids or short chains.
AAs use SAAT1 to move across apical membrane and use tranporters specific to that particular aa to cross the basolateral membrane.
Short chains cross the apical membrane via PepT1, this is driven by H+ gradient, the gradient is formed by NH3 pumping H+ out of the cells in to the brush border in the lumen.
Journey of fats before absorbtion.
Emulsified then converted into micelles (micelle=bile salt+ monoglyceride+ fatty acids+phospholipids)
How are fats absorbed?
Micelle breakdown at the brush border due to the acidic climate, the fatty acids chains and glycerol can then free cross the membrane as the are lipophillic. Inside the cell they go straight to the smooth ER to be packed in to vesicles, then processed at golgi body and finally transported to the basolateral membrane.
At bl membrane they are exocytosed upon which they form chylomicrons which then pass into lacteals (too big to pass through capillary basement membrane)
How is b12 absorbed?
Binds to intrinsic factor to stomach and the complex is absorbed in distal ileum.
How is iron absorbed?
Apical membrane- DMT1
either then incorporated into ferritin (until cell dies)
or transported across basolateral membrane be ireg1 and incorporated into transferrin in blood.
What is the overall structure of the walls of the GI tract?
Mucosa ( epithelium, lamina propria, muscular mucosae)
Submucosa
Muscularis propria ( circular layer of muscle and longitudinal layer of muscle) an serosa/adventitia
Describe the structure of the oesophagus?
The oesophagus is a muscular tube that transports food from the mouth to the stomach. The first 1/3 have skeletal muscle and the distal 2/3 contains smooth muscle.
It follows the normal 4 layers of wall found in the GI tract. It contains stratifed squamous (non keritinised) epithelium and adventitia. (as it is not peritonised)
Explain the difference between serosa and adventitia.
Serosa is found when the organ is peritonised (has viseral peritoneum covering it) and adventitia is present when the GI tract organ is not peritonised.
What controlls the swallowing reflex?
The swallowing centre in the medulla coordinates this reflex.
The softplate reflexes upwards and backwards to close off the nasopharynx, then the UOS relaxes and epiglottis moves to cover larynx. Bolus then enters oesophagus and UOS contracts to prevent reflux.
Describe the structure of the stomach.
The stomach wall consist of the mucosa ( epithelium)- , submucosa (these two layers are folded in to rugae which allow the stomach to expand greatly in size to accomodate the amount of food we have at a meal), muscularis layer- contains three sub layers: oblique, circular and longitudinal, the extra layer helps to churn up the contents of the stomach more)
How does each salivary gland appear histologically?
Parotid- mainly serous acini- these stain more /dark compared to mucous acini
Submandibular- mixed
Sublingual- mainly mucous acini - so appears with mostly weakly stained cells
What are the functions of the stomach?
Storage of ingested material Initiate digestion Controls delivery of contents to small intestine Kill pathogens/sterilise contents Produce intrinsic factor
Name the different regions of the stomach
Cardiac region Fundus Body Pyloric region Pyloric sphincter
