Digestion
and a bit of Absorption
Digestive System
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Gastrointestinal tract (GI)
Upper-jejunum and above
Lower-ileum and colon
Small-ileum and above
Large-colon
Mechanical Digestion
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Begins in mouth
Chewing crushes and softens
Saliva helps dissolve food
Only particles in solution
can react with taste buds
Mechanical Digestion
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Food called bolus
Bolus crosses epiglottis
Bypasses entrance to lungs
Moves to esophagus after
swallowing
Mechanical Digestion
• Bolus slides down esophagus
to stomach
• Cardiac sphincter closes
behind bolus
• Stomach retains bolus
& adds gastric juices
Mechanical Digestion
• Grinds bolus into semi-liquid mass
called chyme
• Bit by bit chyme pushed through
pyloric sphincter into duodenum
• Frequent ulcer sites-cardiac and
pyloric sphincters
Mechanical Digestion
• In small intestine:
– chyme passes by opening to common
bile duct
– bile is secreted to help with fat
digestion
– chyme continues through duodenum
jejunum
ileum
– ~20 feet
Mechanical Digestion
• Chyme passes through ileocecal
valve at start of colon
• LRS to RS across front, down LS to
back side ~5 feet to rectum
• Colon reabsorbs H20
• Anus opens to pass waste out
Mechanical Digestion
• Involuntary muscles at work
• Gastric motility and peristalsis
• Peristalsis– contraction of long muscles
– propels food forward
– always contracting and relaxing even if
food not present
Mechanical Digestion
• Segmentation
– only in small intestines
– squeezes diameter of tube
to help nutrients to be absorbed
Chemical Digestion
• Salvia in mouth starts process
• Breaks bonds in chains of starch
• Gets food in lump or bolus
Chemical Digestion
• Gastric juice in stomach
– kills most bacteria
– very strong acid
• Bolus stored in upper curvature
(antrum) as it enters stomach
– stretches to store big meals
– capacity is 1-2 liters
Chemical Digestion
• Bolus moves downward
– pepsin breaks down large protein
particles
– some fat digested by gastric lipase
– starch digested by gastric amylase
– intrinsic factor produced to pick
up B12 in ileum
Chemical Digestion
• Bolus reaches pyloric valve as
chyme-squirted into duodenal bulb
• Rate of emptying depends on
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volume of meal
osmotic pressure
physical and chemical makeup
liquids pass quickly, solids slower
Chemical Digestion
• Antacids and simethicone-used
mostly for pain relief and to help
with stomach gas
• New ulcer cause - H. Pylori
– ulcer diets not used much any more
– medications more common
Chemical Digestion
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Small intestine-action place
Bile emulsifies then enzymes work
Enzymes work on CHO, PRO, FAT
NabiCarb neutralizes acidic chyme
Contents of small intestine neutral
or alkaline
Chemical Digestion
• Protein
– broken into peptides
– then into A2
• CHO
– broken into disaccharides
– then into monosaccharides
Chemical Digestion
• Fats
– broken into glycerol and fatty acids
• Intestine contains bacteria that
produce small amounts of vitamins
– Vitamin K and biotin
• H20, vitamins, minerals absorbed
complete
Chemical Digestion
• Fibers continue through digestive
tract in semi-solid mass
– retain water
– carry bile acids/sterols/fat out of body
• Most digestion takes place before
bolus reaches colon
Chemical Digestion
• Colon
– intestinal bacteria degrade some fibers
– reabsorbs water and salts
– ileocecal valve controls passage of
chyme into colon
• holds bolus in small intestine until
adequate digestion completed
Absorptive System
• Small intestinal villi in constant
motion
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lined by thin sheet of muscle
wave and wiggle
small nutrients trapped by micovilli
drawn into cells beneath brush border
Transport of Nutrients
• 2 transport systems
– blood stream
• vascular system blood carried to digestive
system by artery
• leaves by vein to liver
– lymphatic system
• fluids travel to tissue spaces
• blood lipids travel bundled with protein on
lipoproteins
Lipoproteins
• Chylomicrons ~86% TG
– formed in intestinal wall
– carry fat load from recent meals
• VLDL ~ 55% TG, 19% CHOL
– very low density lipoproteins
Lipoproteins
• IDL or B VLDL ~23% TG, 38% CHOL
• LDL ~6% TG, 50% CHOL
– carry CHOL to cells
– elevated serum levels associated with
increased risk of CVD
Lipoproteins
• HDL ~5% TG, 22% CHOL, 40%
Protein
– formed in cell metabolism
– carry from cells to liver for breakdown
and elimination from body
– has protective effect
Lipoproteins
• Elevated serum levels of LDL and TG
associated with CVD
• Normal or elevated serum levels of
HDL has protective effect
Food Safety
• CDC reports 97% of foodborne
illnesses could be prevented with
basic hygiene and improved food
handling
• Occurrences:
– 33% restaurants
– 37 % unknown
Food Safety
• Bacteria to blame in 90% of cases
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Salmonella
S. aureus
C. botulinum
C. perfringens
E. Coli
• Safe handling instructions now
required on packages
Bacteria
• Clostridium perfringens
– Cafeteria germ
– Foods not kept hot enough
– 140° F until served
• Salmonella
– Raw or undercooked eggs & poultry
– Cook well done
• E. Coli
– Undercooked beef
– Cook thoroughly
Food Safety
• Countertop
thawing
• Leftovers left on
table
• Unclean cutting
boards
• Room temperature
marinating
• Store to
refrigerator delay
• Same platter for
raw & cooked
meats
Food Safety
• Shared knife for
raw meat and
vegetables
• Hide and eat
Easter eggs
• Doggie bag delay
• Same stirring and
tasting spoon