Transport Across Alimentary Tract Flashcards
(45 cards)
What nervous systems are present in the gut?
The gut has an intrinsic and enteric nervous system
- large neuronal connections in the gut
Name the 2 intrinsic neural plexus of the gut
Submucosal Meissner Plexus
- regulates digestive glands
Myenteric Auerbach’s Plexus
- connected to gut motility
What are the intrinsic neural controls of the GI tract?
Nerve plexus’ near GI tract initiate short reflexes mediated by local ENS plexus
What are the extrinsic neural controls of the GI tract?
Long reflexes arising within/outside GI tract
Involve CNS and extrinsic Parasympathetic reflexes
What type of neurons are within the plexi?
The nerve plexi contain local sensory + motor neurones as well as inter-neurons for communication
What stimulates the motor neurons in the myenteric plexus?
Motor neurons stimulated by Ach (m receptors) and substance P release
What do inhibitory Motor neurons release?
Cause the release of VIP/NO
What is the Serosa?
tissue of the outer serous membrane of the gut
Is continuous with the mesentery containing blood vessels, lymph vessels and nerve fibres
Where are sensory neurons found in the gut?
Connected to mucosal chemoreceptors and stretch receptors
What is the function of sensory neurons in the GI tract?
Respond to gut wall tension caused by food and chyme
What type of cells is the small intestine composed of?
epithelial folds
villi + microvilli
- to provide a large SA of 200 m²
What is the fate of the small intestine contents?
all dietary nutrients, water and electrolytes that enter the upper small intestine are absorbed
What are crypt cells?
Cells located where the epithelia of villi extend down into the lamina propria to form crypts
Where us the lamina propria located?
Beneath the epithelium
Which cells are located within the crypts?
Many important cells reside in the crypts including host defence + signalling cells, and stem cells for replacement
What is transcellular transport (give an example)?
Transport of solutes by a cell through a cell
e.g. glucose transport from intestinal lumen →ECF by epithelial cells
What is paracellular transport?
Passage of solutes between cells; passive but selective, variable and regulated
e.g. Na+, Cl-, H₂O
How are carbohydrates absorbed?
Can only be absorbed as Monosaccharides
complex CHO need to be reduced to disaccharides by amylase
How are disaccharides converted to monosaccharides?
Specific brush border enzymes convert disaccharides → monosaccharides (e.g. glucose and galactose)
Give examples of disaccharides conversions to monosaccharides via their specific enzymes
Sucrose → Glucose + fructose
- via sucrase
Starch →glucose oligomers
- via salivary + pancreatic amylase
Glucose oligomers →glucose
- via glucoamylase
Lactose→glucose + galactose
- via lactase
How are glucose and galactose transported?
Rapidly absorbed by a secondary active transport mechanism
Explain how glucose and galactose are transported
- Na generates an electrochemical gradient
- Na+ flux out of cell
- K+ moves into cell
- Glucose moves out along with Na+ as it’s pumped out
due to SGLT1 transporter binding site - Galactose also joins due to a similar binding site
- GLUT2 transporters transport glucose → bloodstream
- Fructose →blood via passive diffusion through GLUT5
transporter
Which molecules does SGLT transport?
Glcose and fructose
Which enzyme facilitates protein production?
Pepsin action produces polypeptides
