Transcript Human Biology: Digestive System - TangHua2012-2013

Human Biology: Digestive System
Lesson 3: Absorption and Digestion in the Intestines
Today’s Objectives
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Analyse the functional inter-relationships of the
structures of the digestive system, including:
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Describe the functions of anaerobic bacteria in the colon
Describe how the small intestine is specialized for chemical
and physical digestion and absorption
Describe the structure of the villus, including microvilli, and
explain the functions of the capillaries and lacteals within it
Digestion in the Duodenum
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The small Intestine is about 7
meters long
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The first 25 cm is the duodenum
Digestive actions in the Duodenum:
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Stomach chyme is neutralized (sodium
bicarbonate)
Bile breaks down fat into fat droplets
Pancreatic juice: amylase breaks down
starch; trypsin breaks down protein;
lipase breaks down fat droplets after
bile has emulsified the fat
Digestion in the Small Intestine
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Remainder of small intestine is also has digestive actions:
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Despite this, the primary function of the small intestine is
absorption of molecules:
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Final digestion of protein and carbohydrates by intestinal juices
(peptidases and maltase) from millions digestive glands
Amino acids
Glucose
Fatty acids
Glycerol
Other disaccharides are digested in the small intestine by their
own enzymes (lactase aids in lactose digestion, which is a sugar
in milk)
Absorption in the Small Intestine
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Small Intestine is specialized for absorption:
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Extremely long with convoluted (folded) walls
Walls have villi (finger-like projections along the walls)
Villi themselves have tiny microvilli on columnar epithelial cells
Within each villus are blood vessels and a small lymph vessel
called a lacteal which absorbs fluids and returns it to the veins
later on
Absorption occurs across the walls of each villus by active
transport (uses energy):
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Sugars and amino acids enter the blood vessels and travel to
the liver
Glycerol and fatty acids enter the lacteals which will go back
into the bloodstream later at the subclavian veins
Villi and Microvilli
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The folded walls, villi
and microvilli all
greatly increase the
surface area of the
interior of the small
intestine
Greater surface area
means more surface
for absorption to
occur
Absorption in the Large Intestine
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The Large Intestine’s main function is the absorption of
water
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Some vitamins may also be absorbed in the large intestine
The large intestine also contains a large population of E.
Coli bacteria which consume any substances that were
not digested earlier
When the bacteria break down these substances, they
give off odorous molecules that cause the characteristic
odor of feces or “passing gas”
Bacteria in the Large Intestine
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Some vitamins, amino acids, and
other growth substances required
by the body (growth factors) are
produced by these bacteria
The growth factors are absorbed
by the lining of the gut (intestine)
E. Coli helps us metabolize what
our bodies were unable to
metabolize, thereby providing us
with a vital service