Absorption in the Small
Intestines
IB Assessment Statement
• H.3.1 Draw and label a diagram showing a
transverse section of the ileum as seen
under a light microscope. Include mucosa
and layers of longitudinal and circular
muscle.
Small Intestines
• Most digested food is
absorbed in the small
intestines
– Mainly in the latter part of
the Intestines called the
ileum.
H.3.1: The ileum
• The ileum is the
main site for
absorption of
digested food,
however, cellulose,
lignin, bile
pigments, bacteria
and intestinal cells
are not absorbed
into the body.
IB Assessment Statement
• H.3.2 Explain the structural features of an
epithelial cell of a villus as seen in electron
micrographs, including microvilli,
mitochondria, pinocytotic vesicles and tight
junctions.
Small Intestines – the ileum
• The ileum is composed of small structures called
villus.
Small Intestines – Ileum -- Villus
• The out layer of cells of the villus is where
most absorption of digested food occurs.
Outer layer of Cell on Villus
• The outer layer of
cells on the villus is
called the villus
epithelium cells.
Villus Epithelium Cells
• Vllius epithelium
cells features
– Tight junctions
– Microvilli
– Mitochondria
– Pinocytic vessels
Epithelium Cell of Villi
IB LEARNING OBJECTIVE
H.3.3 Explain the mechanisms used by the
ileum to absorb and transport food, including
facilitated diffusion, active transport and
endocytosis.
Animation for Absorption:
http://nutrition.jbpub.com/resources/animatio
ns.cfm
Epithelium Cells of villi
• Microvilli protrusions of plasma (cell
membrane) - increase surface area of plasma
membrane exposed to digested food.
– Thus increase the rate of absorption of food by:
• Simple diffusion – no energy required, moves with
concentration gradient, permeable to plasma membrane
• Facilitated diffusion – no energy required, moves with
concentration gradient, can not pass through plasma
membrane thus requires protein channel
• Active Transport– requires energy, move against
concentration gradient, require protein pump
• Endocytosis -- pinocytosis
Uptake of carbohydrates by villi
• The Carbohydrates,
(glucose & galactose) are
actively transported into
the epithelial cells
• Frustose enters the
epithelial cells via
facilitated diffusion
• All carbohydrates enter
the blood stream via the
capillary in the villus.
Uptake of Proteins by the villi
• Products of protein
digestion (amino
acids) are actively
transported in to the
epithelial cells
• Amino acids then
diffusion into the
blood stream via the
capillary in the villi
Uptake of Lipids by the villi
• The products of digested
lipids ( fatty acid chains
and glycerol enter the villi
cells via simple
diffusion.
• Some are then transport
into the blood stream via
simple diffusion
• Others enter the lacteals
of the villi via
endocytosis
IB LEARNING OBJECTIVE
H.3.3 Explain the mechanisms used by the
ileum to absorb and transport food, including
facilitated diffusion, active transport and
endocytosis.
Animation for Absorption:
http://nutrition.jbpub.com/resources/animatio
ns.cfm
IB Assessment Statement
• H.3.4 List the materials that are not
absorbed and are egested
– Limit this to cellulose, lignin, bile pigments,
bacteria and intestinal cells
•