M19: Small Intestine Flashcards
3 regions of small intestine
- DUODENUM (25cm)
- retroperitoneal
- c-shaped - JEJUNUM (1m)
- ILEUM (2m)
- connects to large intestine at ileocecal sphincter
small intestine - circular folds
aka PLICAE CIRCULARIS
- created by ridges in submucosa
- submucosa makes fingerlike projections
- increase surface area in SI
- spiral pattern - allows all chyme to come in contact with SI walls for nutrient absorption
in the SI, microvilli are extensions of ____ while vili are extensions of _____
microvilli: epithelia
villi: lamina propria
structures in SI villi
- large vascular network
- LACTEALS: lymphatic system extension. Take things too large to enter into capillaries
specialized epithelial cells on villi
top to bottom on villi
- ABSORPTIVE CELLS (absorb nutrients via microvilli)
in pit (intestinal gland)
- GOBLET CELLS (interspersed between absorptive cells)
- PANETH CELLS (secrete lysozymes that break down foreign materials, capable of phagocytosis)
- ENTEROENDOCRINE CELLS (secrete hormones secretin and cholecystokinin)
name of pits between SI villi
intestinal gland
hormones secreted by enteroendocrine cells in SI
secretin and cholecystokinin
functions of paneth cells in SI
- secretes lysozyme
- capable of phagocytosis
- mantains SI microbiome
order of structures, smallest to largest, that help increase surface area in small intestine
microvilli
villi
circular folds
paneth cells
- secrete lysozymes that break down foreign materials
- capable of phagocytosis
absorptive cells
- epithelial cells on villi
- absorb nutrients via microvilli
enteroendocrine cells
secrete hormones secretin and cholecystokinin
qualities of intestinal juice
- body produces 1-2L per day
- pH 7.6
- made of water, mucous, bicarbonate ions
brush border enzyme
- Digestive enzymes embedded into intestinal wall (SI designed to move chyme via circular folds to come in contact with them)
- Different enzymes to digest carbohydrates, proteins and nucleotides
brush border enzymes that digest carbohydrates
α-dextrinase
maltase
sucrase
brush border enzymes that digest proteins
aminopeptidase
dipeptidase
brush border enzymes that digest nucleotides
nucleosidases
phosphatases
2 main types of movement in the small intestine
- SEGMENTATION: local mixing of chyme with intestinal juices
- circular muscles contracting (creates pouches of chyme to mix)
- stops when enough fluid and nutrients are absorbed (~90%), triggers migrating motility complex - MIGRATING MOTILITY COMPLEX
- circular muscles squeeze leftover chyme to ileum
- may cause “tummy rumbling” sounds
basics of chemical digestion in mouth
CARBS: salivary amylase breaks down starch, stays active until it hits stomach acids
LIPIDS: lingual lipase released, not active
PROTEINS: n/a
basics of chemical digestion in stomach
CARBS: n/a
LIPIDS: lingual lipase, gastric lipase not very active
PROTEINS:
HCL -> denatures proteins
Pepsin -> proteins to peptides
chemical digestion of carbohydrates in small intestine
PANCREATIC AMYLASE: digests any polysaccharides not digested by salivary amylase
BRUSH BORDER ENZYMES: α-dextrinase, lactase and maltase -> monosaccharides
what does α-dextrinase break down?
Specifically, a carbohydrate called dexterin
chemical digestion of proteins in small intestine
PANCREATIC JUICE
- digestive enzymes: typsin, chymitrypsin, carboxypeptidase, elastase -> split peptide bonds between different amino acids
BRUSH BORDER ENZYMES (final breakdown into amino acids)
- aminopeptidase, dipeptidase -> split off amino acid at amino end of molecule
chemical digestion of lipids in small intestine
BILE
- emulsification
PANCREATIC LIPASE
- cleaves fatty acids from glycerol -> splits into fatty acids and monoglycerides
NO ENZYMES IN BRUSH BORDER
Can lipids be digested by brush border enzymes?
no
Where are most fats digested?
small intestine
chemical digestion of nucleic acids in small intestine
Pancreatic juice - 2 nucleases
- RIBONUCELASE - RNA
- DEOXYRIBONUCLEASE - DNA
Nucelotides further digested by brush border enzymes (NUCELOSIDASE and PHOSPHATASE)
Absorbable molecules for cho, pr- and lipids
CHO
- monosaccharides (glucose, fructose, galactose)
PRO
- single amino acids, dipeptides, tripeptides
LIPIDS
- free fatty acids, glycerol, monoglycerides
% of digestion that occurs in stomach vs small intestine
90% SI
10% stomach
types of muscle in muscularis, superficial to deep
longitudinal
circular
what layer of GI contain the vili?
mucosa
what layer of GI creates the circular folds?
submucosa
