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Digestion and
Absorption
- Peristalsis
- contraction of circular
and longitudanal small
intestine muscles to
mix food and enzymes
- gut muscles
- smooth
- short cells
- continuous moderate
force with periods of
vigorous contraction
- smooth
- circular muscles prevent
food from going back
- longitudanal muscles push
the food along the gut
- unconsciously
performed
- away from mouth
- one wave down
esophagus
- contraction of circular
and longitudanal small
intestine muscles to
mix food and enzymes
- Pancreatic juice
- pancreas secrets
enzymes into lumen
of small intestine
- pancreas contains 2
types of gland tissue
- small groups of cells secret
glucagon and insulin; rest
secret digestive enzymes
- enteric nervous system
= mediation of
hormones synthesized
and stomach secretions
- ducts = small group of cells
clustered around tubes into
which enzymes are secreted
- sythesized on
ribosomes in rER
- processed by Golgi
apparatus and
secreted by exocytosis
- ducts merge into pancreatic
duct; 1L of pancreatic juice
secreted to lumen per day
- enzymes
- amylase for starch
- lipase for trigylcerides
and phospholipids
- protease for proteins
and peptides
- amylase for starch
- pancreas secrets
enzymes into lumen
of small intestine
- Digestion in the
small intestine
- enzymes digest macromolecules
in food to monomers
- hydrolysis reactions
- starch to maltose by amylase
- triglycerides to fatty acids and glycerol or
fatty acids and monoglycerides by lipase
- phospholipids to fatty acids, gycerol
and phosphate by phospholipase
- starch to maltose by amylase
- proteins and polypeptides to
shorter peptides by protease
- wall of small intestines
produce enzymes to
digest more
- DNA and RNA to
nucleotides by nucleases
- maltose to glucose
by maltase
- lactose to glucose and
galactose by lactase
- sucrose to glucose and
fructose by sucrase
- dipeptides to amino
acids by dipeptidases
- peptide to dipeptide
by exopeptidases
- DNA and RNA to
nucleotides by nucleases
- most immobilized enzymes in
plasma membrane of epithelium
cells; some in intestinal juice
- takes hours due to length
- some not synthesized
eg. cellulose
- enzymes digest macromolecules
in food to monomers
- Villi and the surface
area for digestion
- increases epithelium surface area
for increased rate of absorption
- absorption = taking substances
into cells and blood
- in small intestine (7m long; 25-30mm wide)
- folds on inner surface for increased surface area
- villi = small finger like projections of
mucosa lining inner wall of intestine
- villus 0.5-1.5 mm long (40/sq mm)
- increase surface area 10x
- increases epithelium surface area
for increased rate of absorption
- Absorption by villi
- absorbs monomer,
vitamins and mineral ions
- glucose, fructose, galactose,
other monosaccharides
- all 20 amino acids
- fatty acids, monoglycerides, glycerol
- bases from digestion of nucleotides
- calcium, potassium, sodium
- ascorbic acid (Vit C)
- glucose, fructose, galactose,
other monosaccharides
- epithelium cover: barrier for
harmful substances; permeable
to allow useful nutrients to enter
- harmful substances that
enter removed from
blood, detoxified by liver
- bacteria removed by phagocytic cells
- useless substances in urine
- absorbs monomer,
vitamins and mineral ions
- Methods of absorption
- nutrients small intestine lumen
--> capillaries/lacteals in villi
- absorbed through
plasma membrane
of epithelium cells
- detailed example of
triglycerides and
glucose in textbook
- plasma membrane surface
area increased by microvilli
- nutrients exit through plasma
membrane facing inward
towards capillaries/lacteals
- nutrients small intestine lumen
--> capillaries/lacteals in villi
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