packet 21 Flashcards
20 feet long----1 inch in diameter Large surface area for majority of absorption 3 parts duodenum---10 inches jejunum---8 feet ileum---12 feet ends at ileocecal valve
small intestine
Histology of the Small Intestine
–Structures that increase surface area
plica circularis
villi
microvilli
permanent ½ inch tall folds that contain part of submucosal layer
not found in lower ileum
can not stretch out like rugae in stomach
plica circularis
1 Millimeter tall
Core is lamina propria of mucosal layer
Contains vascular capillaries and lacteals(lymphatic capillaries)
villi
cell surface feature known as brush border
microvilli
Absorption and digestion
Digestive enzymes found at cell surface on microvilli
Digestion occurs at cell surfaces
Significant cell division within intestinal glands produces new cells that move up
Once out of the way—rupturing and releasing their digestive enzymes & proteins
microvilli
Submucosal layer has duodenal glands
secrete alkaline mucus
Mucosal layer contains intestinal glands = Crypts of Lieberkuhn (deep to surface
secretes intestinal juice
1-2 qt./day—— at pH 7.6
brush border enzymes
paneth cells secrete lysozyme kills bacteria
Mouth—salivary amylase
Esophagus & stomach—nothing happens
Duodenum—-pancreatic amylase
Brush border enzymes (maltase, sucrase & lactase) act on disaccharides produces monosaccharides--fructose, glucose & galactose lactose intolerance (no enzyme; bacteria ferment sugar) -- gas & diarrhea
digestion of carbohydrates
Mucosal cells of small intestine fail to produce lactase
essential for digestion of lactose sugar in milk
undigested lactose retains fluid in the feces
bacterial fermentation produces gases
Symptoms
diarrhea, gas, bloating & abdominal cramps
Dietary supplements are helpful
We’re all a bit milk intolerant: infant vs. adult stomach pH
lactose intolerance
HCl denatures or unfolds proteins
pepsin turns proteins into peptides
digestion of proteins–stomach
digestive enzymes—split peptide bonds between different amino acids
brush border enzymes—–aminopeptidase or dipeptidase——split off amino acid at amino end of molecule or split dipeptide
digestion of proteins–pancreas
Mouth----lingual lipase Small intestine emulsification by bile pancreatic lipase---splits into fatty acids & monoglyceride no enzymes in brush border
digestion of lipids
Pancreatic juice contains 2 nucleases
ribonuclease which digests RNA
deoxyribonuclease which digests DNA
Nucleotides produced are further digested by brush border enzymes (nucleosidease and phosphatase)
pentose, phosphate & nitrogenous bases
Absorbed by active transport
digestion of nucleic acids
Absorption into epithelial cell
glucose & galactose—-sodium symporter(active transport)
fructose—–facilitated diffusion
Movement out of epithelial cell into bloodstream
by facilitated diffusion
absorption of monosaccharides
Small fatty acids enter cells & then blood by simple diffusion
Larger lipids exist only within micelles (bile salts coating)
Lipids enter cells by simple diffusion leaving bile salts behind in gut
Bile salts reabsorbed into blood & reformed into bile in the liver
Fat-soluble vitamins are enter cells since were within micelles
absorption of lipids
Inside epithelial cells fats are rebuilt and coated with protein to form chylomicrons
Chylomicrons leave intestinal cells by exocytosis into a lacteal
travel in lymphatic system to reach veins near the heart
removed from the blood by the liver and fat tissue
absorption of lipids (2)
Sources of electrolytes
GI secretions & ingested foods and liquids
Enter epithelial cells by diffusion & secondary active transport
sodium & potassium move = Na+/K+ pumps (active transport)
chloride, iodide and nitrate = passively follow
iron, magnesium & phosphate ions = active transport
Intestinal Ca+ absorption requires vitamin D & parathyroid hormone
absorption of electrolytes
Fat-soluble vitamins
travel in micelles & are absorbed by simple diffusion
Water-soluble vitamins
absorbed by diffusion
B12 combines with intrinsic factor before it is transported into the cells
receptor mediated endocytosis
absorption of vitamins`
9 liters of fluid dumped into GI tract each day
Small intestine reabsorbs 8 liters
Large intestine reabsorbs 90% of that last liter
Absorption is by osmosis through cell walls into vascular capillaries inside villi
absorption of water
on test
bile salt
michelle
on test
coated protein
chlomicron