L6 - Pancreas, Liver and Intestinal Absorption Flashcards
describe how alcohol effects the 3 phases of control of gastric acid release
- a lack of switch-off would over-acidify the stomach -> risk of gastric reflux
- alcohol triggers gastric acid release (via increase of gastrin) -> aperitif before a meal to trigger gastric acid production
- too much alcohol, especially on an empty stomach, can cause gastric reflux (it also relaxes the muscles in the esophagus)
- alcohol dehydrates people (hangover, dehydration has an impact on oral health)
describe the secretions of the pancreas and how they compare to the plasma
Pancreas:
- 1.5L per day of secretions (less than plasma)
- osmolarity 300 mOsm (same as plasma)
- pH 7.8 (0.4 more basic than plasma, small number but actually a large difference)
- less chloride secretions but way more bicarbonate secretions
- sodium and potassium similar
- pancreatic secretions are alkaline (pH 7.8!) with a high bicarbonate concentration (more than 3x plasma)
describe the structure of the pancreas (endocrine and exocrine)
endocrine: (islets)
- alpha cells = glucagon
- beta cells = insulin
exocrine:
- bicarbonate
- enzymes for digestion
describe the stimulation of pancreatic secretion
- in the absence of food: low basal secretion
- during the cephalic phase and gastric phase: limited secretion
- during the intestinal phase - arrival of food in the intestine: largest volume of secretion, based on CCK (cholecytekinin) and secretin secretion
- stimulus for CCK: fat, products of protein digestion in the duodenal lumen
- stimulus for secretin: acidic chyme/bolus in the duodenal lumen
describe the volume and composition of pancreatic secretions
1-1.5L of an alkaline fluid and 5-15g of protein secreted per day
acinar cells:
- leak epithelium
- stimulation of protein secretion by CCK
- 20 different proteins secreted - mainly digestive enzymes
- primary isotonic fluid secretion (25% of total pancreatic solution) - same mechanism as in salivary acinar cells (but just way less volume)
duct cells:
- leaky epithelium! (different to duct cell salivary glands!)
- stimulation of section of a larger volume of bicarbonate rich solution
describe the differences between salivary vs pancreatic duct cell secretion (draw diagram)
- tight epithelium in salivary gland duct cells vs leaky epithelium in pancreatic gland duct cells
- chloride secreted to drive bicarbonate secretion (have receptors for secretin which boosts the activity of the CFTR in the pancreas)
- NO change in sodium content (pancreas)
- major site of fluid secretion in pancreas (75%)
- CFTR (cystic fibrosis transmembrane conductance regulator) is the key chloride channel for bicarbonate secretion in both organs!
what are the consequences of a mutation in the CFTR (cystic fibrosis transmembrane conductance regulator)?
Cystic fibrosis (CF):
cause:
- hereditary, mutations in CFRT
- 540 cases in NZ, 1 in 25 carrier
- lack of water secretion (lungs, pancreas)
- lack of bicarbonate secretion (salivary gland, pancreas)
symptoms:
- difficulty breathing
- thick mucus
- frequent respiratory infections
- pancreatitis
- malnutrition (vitamin A, D, E, K)
- poor growth
- 90% of all CF male are infertile
treatment:
- medication (anit-inflammitory)
- daily bronchial drainage and chest physiotherapy
- good nutrition (vitamins, enzymes)
dental health complications!!:
- higher risk of enamel defects (90% have at least one defect)
- tooth discolouration (antibiotics)
- less caries (antibiotics)
- more plaque
what are the functions of the liver?
processing of absorbed nutrients and control of metabolism:
- glucose buffering (glycogen), fatty acid oxidation, gluconeogenesis, synthesis of plasma proteins (eg. albumin)
secretion and excretion:
- provision of bile acids and alkaline fluid to: acid digestion and absorption of fats, neutralise gastric acid
- degradation of conjugation of waste products of metabolism
- detoxification of poisonous substances
- excretion of waste metabolites and detoxified substances in bile
liver is the gatekeeper, can determine what goes in to circulation or not
- liver does NOT secrete erythropoietin, the kidneys do
describe small intestinal Na+ and chloride absorption (draw out diagram)
- nutrient dependent: Na+-coupled solute absorption (SGLT1, amino acids)
- nutrient independent: Na+/H+ exchanger (NHE3) and Cl-/HCO3- exchanger
describe the digestion and absorption of sugars in the small intestine
200 - 300g per day:
- western diet - 40-50% of energy intake
- developing world - 90% of energy intake
dietary sugars:
- polysaccharides (45-60%) - glycogen and starch
- polysaccharides (30-40%) - sucrose, lactose and maltose
- monosaccharides (10%) - glucose, fructose
only monosaccharides are absorbed main monosaccharides are:
- glucose and galactose by Na+ dependent mechanism (SGLT1)
- fructose absorbed by Na+ independent mechanism (GLUT5)
digestion of sugars to release
monosaccharides is a 2-step process
luminal digestion:
- mouth - alpha-amylase
- small intestine - pancreatic amylase (for short oligosaccharides and some disaccharides)
contact or brush border digestion:
- enzymes attached to the apical membrane of epithelial cells
- release monosaccharides - glucose, galactose, fructose
the enzymes that break disaccharides into monosaccharides and the transporters are on the same membrane (brush border)
- eg. lactase breaks dow lactose
describe the digestion and absorption of proteins
proteins
- not a source of energy
- required for amino acids (essential ones: arginine, histidine, phenylalanine, tryptophan, and valine)
sources of protein:
- 50% diet
- 25% sloughed cells
- 25% digestive enzymes
digestion two-step process:
- luminal (into proteins, oligopeptides)
- contact: brush border membrane, into amino acids, di- and tri peptides (mains transporters: Na+/AA, PEPT1)
describe the digestion and absorption of fat, and absorption of vitamins and minerals
fat:
- broken down mechanically (stomach)
- vile acids (liver) and pancreatic lipase
- absorbed via the lymphatic system
fat soluble vitamins A,D and E:
- absorbed in the same fashion as fats
water soluble vitamins specific transport processes:
- Na+ dependent eg. vit C
- vitamin B12: intrinsic factor is released in the stomach, in duodenum B12 binds to intrinsic factor, IF/B12 complete attaches to specific receptors in the terminal ileum, complex absorbed by endocytosis and degraded to release B12 into portal blood
minerals (calcium and magnesium):
- via the paracellular pathway in leaky epithelium
