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objectives
- overview of small intestine functional anatomy
- digestion of carbohydrates, protein, fat
- absorption of sugar
- absorption of aminoacids and small proteins
- absorption of fat
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overview of the small intestine
- site of the most absorption and digestion
- sections: duodenum, jejunum, ileum
- motility includes: segmentationmigrating and motility complex
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lecture notes
- carbs proteins a lipids are absorbed mainly in the duodenum
- calcium folat and iron are only absorbed in tthe duodenum
- bile and acids are mainly absorbed in the ileum
- cobalamin is only absorbed in the ileum
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secretion
- juice secreted by the small intestine does not contain any digestive enzymes
- synthesized enzymes ac within the brush border membrane of epithelial cells
- enzymes: enterokinase, disacharridases, amino peptidases
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lecture notes
- termed succus entericus
- these peptidases are found on the brush border membrane and will lskdfjlkdfj
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Digestion
- pancreactice enzymes continue carbohydrate and protein digestion
- brush border enzymes complete digestion of carbohydrates and protein
- fat is digested entirely withinthe small intestine lumen by pancreatic lipase
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Absorption
- absorbs almost everything presented to it
- most occurs in duodenum and jejunum
- surface area is increased by: circular folds with finger like projections on them called villi,. that have brusbhh borader on them know as micro villi that arrise from the luminal surface of epithelial cells
- lining replaced every 3-5 days
- products of fat digestion undergo transformationsthat enable them to be passively absorbed (eventually enter the lymph)
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lecture notes
lining replaced 3-5 days
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Brush border CHO hydrolases
- sucrase- breaks downsucrose into 1 glucose and 1 fructose
- isomoltase- breaks down maltose into 2 glucose
- lactase breaks down lactose into 1 glucose and 1 galactose
- these are all monosacharrides
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lecture notes
glucose and galactose
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Na Glucose coTransport
- lumina NA enters through SGLT1 and exists through baso lateral Na, K, ATPase
- Na solute cotransporters uses the energy of the electro chemical gradient for Na to driveco transported solute above its equilibrium value
- 2 Na ions are coupled to 1 glucose; intracellular levels of glucose increase 100 fold
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lecture notes:
- cotransport also termed symport
- Na concentration is high outside the cell and low inside the cell thus driving sodium together with glucose into the cell
- galactose can also be a substrate other than glucose
- (cotransported with the SBLT1)
- glucose enters via the Glut2 and the fructose exits via Glut5
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Carbohydrate Digestion and Absorption
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lecture notes
look closely into the picture
- glut 2 knock out animal still live
- glucose can also leave via exo cytosis thus allowing the glut 2 knock outs to live
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Endopeptidase/ Exo Peptidase
- endo: digests internal peptide bonds
- exo: digests terminal bonds to releaseamino acids
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lecture notes
- endo peptidase makes 2 maller peptides
- exo peptidase
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lecture notes
- SGLCT
- humming bird eates every 12 minutes
- python only eats 2 times a year
- they use same glucose co transporter that humans use (lasts the test of evolution)
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Protein Digestion and Absorption
look closely at the picture
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Volume regulation by co transport
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Bile salts
- 1: bile salts from liver coat fat droplets
- 2: pancreatic lipase and colipase break down fats into mono glycerides and fatty acids stored in micelles
- 3a: monoglycerides and fatty acids move out of micelles and enter cells by diffusion
- 3b: cholesteral is transportedinto cells by membrane transporter
- 4: absorbed fats combine with cholesteral and proteinsin the intestinal cells to form chylomicrons
- 5: chylomicrons are released into the lymphatic system
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