S6.2 The Intestines Flashcards
What factors allow substances to be absorbed in the bowel?
Large surface area: villi, microvilli
Plicae circulares: slow down movement of contents.
Briefly describe the cells in the intestines
Simple columnar epithelium.
Enterocytes (main), goblet cells, intestinal crypt with stem cells at base, enteroendocrine cells (secretin) and Paneth cells (innate immunity).
Describe the digestion of lactose and sucrose
Lactose into glucose and galactose (lactase)
Sucrose into glucose and fructose (sucrase)
Describe the digestion of starch
Amylase breaks alpha-1,4 bond in amylose producing dextrins.
Isomaltase breaks alpha-1,6 bonds in amylopectin producing glucose and maltose
On the luminal membrane of the enterocyte, what is the role of SGLT1?
Na+ glucose cotransport
On the luminal membrane of the enterocyte, what is the role of GLUT5?
Fructose absorption
On the apical membrane of the enterocyte, what is the role of GLUT2?
Glucose and fructose enter the blood
How does the stomach cause protein digestion?
Pepsinogen released by chief cells gets converted to pepsin by HCL.
Pepsin breaks proteins into amino acids for absorption via Na+/aa cotransport
How does the pancreas cause protein digestion?
Pancreas releases proteases as zymogens which later get activated eg trypsinogen to trypsin
Describe the uptake of water and electrolytes in the intestines
NaKATPase on BLM creates gradient for Na+ movement into the cell
In small intestine this is via Na+ cotransporters, in large it is via Na+ channels
Na+ entering increases the osmotic gradient leading to water uptake - isosmotic fluid uptake
How is calcium absorbed in the small intestine?
Enters via facilitated diffusion, requires calbindin
Can also occur via paracellular reabsorption
How is iron absorbed in the small intestine?
In the form of haem, H+ cotransport
Low iron binds to transferrin and stored
High iron is contained in ferritin complexes
How is Vit B12 absorbed?
In the terminal ileum bound to intrinsic factor (secreted by parietal cells).
What is the effect of B12 deficiency?
Can lead to megaloblastic anaemia
Caused by lack of intrinsic factor (causing pernicious anaemia), poor diet and Crohns
What is lactose intolerance?
Deficiency of lactase prevents lactose breakdown, which remains in the gut, so water is not absorbed causing diarrhoea.
What are the symptoms of IBS?
Abdominal pain, bloating, flatulence
What is coeliacs disease?
Intolerance of the gliadin fraction of gluten, found in wheat, rye and barley.
Results in damaged mucosa of intestines causing absence of villi and reduced absorption
What are the symptoms of coeliacs disease?
Diarrhoea, weight loss, anaemia (reduced iron absorption)
What are the investigations and treatments for coeliacs disease?
Endoscopy, blood (IgA)
Gluten free diet
How does the SMA supply the colon?
Via the ileocolic, right colic and middle colic
All of these anastomoses to form the marginal artery
Hows does the IMA supply the colon?
Left colic artery supplies the descending colon
As the IMA passes into the pelvis, it becomes the superior rectal artery
What is the venous drainage of he gut?
All of the gut drains into the portal vein
