Identify main enzymes, substrates and products in breaking down carbohydrates
Mouth: salivary amylase (starch-> polysach/disacch)
Duodenum: -Pancreatic amylase (polysacch-> disacch.)
-Brush border enzymes (maltase, sucrase, lactase) disacch. -> monosach. (fruct, gluc, galac)
Identify main enzymes, substrates and products in breaking down protein
Stomach: HCl (denature)
- pepsin (protein-> polypept)
Pancreas: trypsin & chymotrypsin (polypept-> peptide)
-carboxypeptidase (splits AA from carboxyl end)
Bush border enzym: aminopeptidases (splits AA from amino end)
-dipeptidase (dipeptide-> AA)
Identify main enzymes, substrates and products in breaking down fat
Baby’s mouth: lingual lipase
Stomach: gastric lipase
SI: emulsification by bile
-pancreatic lipase (split T.G.-> FA + monoglyceride
Describe chemical & mechanical digestion in mouth
Mech: mastication (smaller peices), saliva lubricates food & form bolus
Chem: α-amylase (starch-> malt.+ isomaltose)
- Lingual lipase in babies (TG-> FA & glycerol)
Function of saliva
- lubricates food & from bolus
- dissolve food chem. = taste
- HCO3- buffers acidic foods
- Chem. digestion
- antimicrobial: lysozyme, IgA, defensin
- rinsing action =protect infection
- Ca & PO4- = teath enamel
Composition of saliva
- 5% water
0. 5% solutes: salts, mucin, lysozyme, amylase, lipase, IgA
State cells of stomach and their function
- Surface mucous cells (simple column.): viscous and alkaline mucous (»protection from acid & pepsin)
- Mucous neck: “
- parietal cells (oxyntic): HCl (»kill bact., denature protein & enzymes, convert pepsinogen into pepsin)
Cheif cells (zymogenic): pepsinogen
Describe the process of the cephalic phase
- Sight, taste, smell, thought of food create tactile sensation in mouth -> stimulate MO
- Impulses via vagus nerves (PSNS) to stomach -> enteric plexus activated
- Stimulate secretion of HCl &; pepsin from chief and parietal cells, and gastrin &; histamine
- Gastrin -> stomach (via circulation) => secrete more HCl & pepsin
Describe the process of the gastric phase
- distention of stomach -> activate parasym. relfex to MO (vagus)
- MO stimulate further stomach secretions
- local (enteric reflex) amplify stomach secretions
- Gastrin -> stomach (via circulation) & histamine => more secretion
Describe the process of the intestinal phase involving enterogastric reflex
Enterogastric reflex inhibits gastric secretions by:
- Chemoreceptors stimulated -> vagal sensory input in MO -> inhibit motor input to stomach = stop secreting HCl & pepsin
- local reflex inhibit gastrin
- Duodenum secrete secretin & cholecystokinin = decrease gastric secretions
What does G cells, Enterochromaffin-like cells and somatostatin-containing cells secrete?
- G: gastrin
- Enterochromaffin-like: histamine (>HCl secretion)
- Somatostatin-containing: somatostatin (>inhibit gastrin & insulin secretion)
What releases intrinsic factor (in stomach) and its function?
-parietal cells
> binds w/ Vit. B12 (for DNA synthesis) = help absorption across terminal ileum
Describe absorption of carbohydrates in SI
- Through apical: gluc. & galact. 2º active transport w/ Na+, and fructose by fac. diff.
- Basal: fac. diff.
Describe absorption of AA in SI
- Through apical: di+tripeptides active trans. w/ Na+ or H+
2. Basal: diff.
Describe absorption of lipids in SI
- Through apical: micelle diffuse in
- W/in cell: FFA + glycerol -> T.G. and fat droplets -> chylomicrons
- Exit via lacteals twd liver
Describe absorption of vitamins in SI (3 types)
- Fat-soluble (A,D,E,K): micelles absorbed by diff.
- Water soluble (B1,2,3,5,6, C + biotin): absorbed by diff.
- Vit B12: receptor mediated endocytosis
Describe absorption of electrolytes in SI
- Na & K: active trans. -> fac. diff.
- Cl-, I- & NO3-: diffuse & follow +ve Na+
- Ca2+: requires Vit. D & PTH
Where is secretin produced into & its effect?
Produced: duodenum
Effect: (stomach) Decrease gastric motility & secretions from stomach. (Pancreas and liver) Stimulate pancreatic and bile secretions and relax hepatopancreatic sphincter
Where is Cholecytokinin produced into & its effect?
Produced: duodenum
Effect: (stomach) Decrease gastric motility
WHat is in gastric secretions?
HCl, pepsin, intrinsic factor, mucus
WHat is brunner’s glands?
aka duodenal glands in submucosa sectrete mucus => neutralise acidic chyme & stimulated by vagus nerve and secretin
