The Intestines Flashcards
What are the characteristics of chyme when in the intestines?
Isotonic
Neutral
Digestion nearly complete
What is the role of the intestines?
Absorb nutrients
Absorb water/electrolytes
How does the characteristics of the gut allow for maximal absorption?
Surface area = villi/microvilli
Slow movement = maximal time against surface area
What are plicae circulares?
Permanent crescentic folds of mucous membrane in the SI especially in the lower part of the duodenum and the jejunum
Increase the surface area available for absorption
What cell types are present in the intestines
Ep = enterocytes
Crypts (glands) = stem cells at base maturing as they migrate to surface, enteroendocrine glands, paneth cells
Briefly outline carb digestion
Only monosaccharides can be absorbed
Glucose can only enter with Na
Final enzyme digestion takes place in brush border
Name the common dietary carbs
Starch
Lactose
Sucrose
Describe the digestion of starch
Amylase = break alpha 1-4 bonds
End up with = glucose, maltose, alpha dextrins
How do monosaccharides get absorbed?
Na/K ATPase on basolateral mem = maintains low intracellular Na
Na binds SGLT-1 = allows gluose binding = Na/glucose moves into cell
GLUT2 = transports glucose out of enterocyte down gradient into capillary
What is the principle of oral rehydration
Uptake of Na generates osmotic gradient = water follows
Glucose uptake stim Na uptake = stim max water uptake
In what structure can proteins be absorbed?
AA
Dipeptides
Tripeptides
How are proteins digested?
Chief cells = pepsinogen = pepsin via HCL = acts on proteins = oligopeptides/AA
What is trypsinogen?
Zymogen
Converted to trypsin by enteropeptidase
Trypsin = activates other proteases
Name the major proteases
Endopeptidases = trypsin, chymotrypsin, elastase
Exopeptidases = carboxypeptidase
How are AA transported into cells?
Na/AA co-transporters
How are di/tripeptides absorbed?
H co-transporter
Peptide transporter 1 (pepT1)
Inside cell these are converted to AA
How does Na move on the apical membrane in the SI vs the large?
SI = Na co-transported
Large = Na channels
Outline the uptake of Ca
When low = active transcellular, requires vit D
When normal/high = passive paracellular
Outline the uptake of iron
When low = binds transferrin (transported to stores)
When high = contained in ferritin complexes (trapped in enterocytes)
How are water soluble vits absorbed?
Cotransport with Na
Vit B12 absorbed in terminal ileum bound to intrinsic factor
What cells secrete intrinsic factor?
Gastric parietal cells
What is coeliac disease?
Intolerance of gliadin fraction of gluten
Results in immune response =absence of intestinal villi, lengthening crypts, lymphocytes infiltrate ep = impaired digestion/malabsorption
What investigations can be used to identify coeliac disease?
Upper Gi endoscopy + biopsies
Bloods = serology, electrolyte imbalances, anaemia
What significant artery can be injured if a duodenal ulcer perforates?
gastro-duodenal artery
