Transport across alimentary tract Flashcards
What are the intrinsic neuronal plexuses of the gut?
submucoal plexus (meissner plexus) Myenteric plexus (Auerbach plexus)
What are the extrinsic control of GI tract?
- long reflexes arising within or outside GI tract
- involve CNS centres and extrinsic autonomic nerves
- parasympathetic reflexes
Describe the structure of small intestine?
epithelial folds, villi and microvilli (large SA)
thin and highly vascularised
can replace itself -> has stem cells particularly within crypt cells that can allow rejuvenation + replacement of dead cells
What are 2 type of transport across enterocyte?
transcellular (across cell) e.g. gluocse transport
paracellular(between gap junctions, between 2 cells) e.g. Na+, Cl- and H2O
What is enterocyte?
cell of intestinal lining
Describe how carbohydrate is digested and absorbed?
can only be absorbed in form of monosaccharides
complex carbohydrate reduced disaccharide by amylases
specific brush border convert disaccharides to monosaccharides
In what process is glucose and galactose rapidly absorbed?
Secondary active transport process
What is basolateral side?
Blood side of gut
What is SGLUT1?
Is cotransporter
Good at transporting galactose so if galactose gets there first before glucose it will inhibit it
What does GLUT2 transport?
Transports glucose, fructose and galactose
What does SGLUT1 co transport?
Na+ along with glucose and galactose
What is apical side?
Top side of the gut
What is basolateral side?
Bottom side
Blood side of gut
Polypeptides are produced by action of..
Pepsin
What do dipeptidases in the brush border do?
They complete digestion to amino acids
Are dipeptides and tripeptides able to cross/ pass through gap junctions?
No because they are complex structures so we generally digest tripeptides and dipeptides into amino acids which are then transported
How are amino acids transported?
Transported on a sodium coupled carrier system similar to that of glucose
Digestion and absorption of lipids are facilitated by 2 important processes. What are they?
Emulsification
Micelle formation
What is emulsification of fats?
Bile salts emulsify fats-> break large fat globules into smaller globules
What is benefit of emulsification?
Surface area where lipase can act is increased
What is function of colipase?
It helps lipase action
It binds to this emulsion droplet and will allow lipase to attach to other end of lipid core. It then flips and is able to bury into lipid core and allows digestion to occur more efficiently
What are 3 phase of fat digestion?
Oil phase
Viscous isotropic phase
Micellar phase
How are lipids transported?
Digestive components of lipids don’t end up directly into blood -> go via lymphatic system
How are bile salts recycled by the body?
Some will be excreted in faeces but only small percentage will be recirculated via process called enterohepatic recirculation
What are some disorders of fat digestion/absorption?
Gallstones, pancreatitis, Crohn’s disease and liver disease can lead to fat malabsorption ( steatorrhoea or fat diarrhoea=excess fat in faeces)
