Passive Transport
in the Body
Includes material from chapters 30 and 32
In the Digestive System…
 Most nutrient
absorption occurs
within the small
intestine
 Specifically, most
nutrients are
absorbed within the
jejunum

Chemical digestion
wraps up in the
duodenum
In the Digestive System…
 The small intestine is lined with villi (which
have microvilli) – this increases the surface
area to maximize nutrient absorption
In the Digestive System…
 Water-soluble
substances, including
vitamin C, are
absorbed along with
water
 By osmosis, these
substances move from
the intestines to the
bloodstream
 Small lipids also
diffuse into blood
In the Digestive System…
 Some substances,
including the sugar
fructose, need
transport proteins to
get across the cell
membrane
 These substances
still travel down the
concentration
gradient – so the
process is facilitated
diffusion
In the Digestive System…
 Some disorders of the digestive system can
interfere with nutrient absorption.
Hemochromatosis
is a condition,
typically hereditary,
that leads to
increased iron
absorption
In the Digestive System…
 Whipple’s disease is
a rare condition
caused by a
bacterial infection
that prevents the
small intestine from
properly absorbing
nutrients – it causes
irregular fold
patterns in the small
intestine and
thickened walls
In the Circulatory System…
 Once nutrients have
been absorbed by
the intestines, the
next step is to get
these nutrients to
the cells
 Cells need nutrients
for cellular
respiration, growth,
repair, and other
activities
In the Circulatory System…
 Nutrients are dissolved
in the plasma (liquid
portion) of the blood
 Plasma is mostly
water, but also
contains blood proteins
 In addition to
transporting nutrients,
plasma also carries
hormones and
electrolytes
The other components of
blood are cellular: red
blood cells, white blood
cells, and platelets
In the Circulatory System…
 Most nutrients are sent
to the liver first for
processing and
storage of excess
nutrients


The hepatic artery
takes blood to the
liver
The hepatic vein
returns blood from the
liver to the heart
In the Circulatory System…
 The heart is
responsible for
pumping blood
throughout the
body

The pumping
chambers of
the heart are
the ventricles
In the Circulatory System…
 Blood leaving the
heart to go to the
body – not the
lungs! – is
pumped out the
left ventricle and
into the aorta
In the Circulatory System…
 The blood
vessels carry
the blood –
and the
nutrients it
holds –
throughout
the body
In the Circulatory System…

1.
2.
There are three
major types of blood
vessels:
Arteries carry blood
away from the heart;
the largest artery is
the aorta; small
arteries are called
arterioles
Veins carry blood
toward the heart; the
largest artery is the
vena cava; small
veins are called
venules
3. Capillaries link arteries to
veins; these blood vessels
are so narrow that blood
cells have to pass through
them single file
In the Circulatory System…
 At the capillaries, nutrients diffuse from
bloodstream to body cells – and wastes
diffuse from the body cells into the
bloodstream
In the Circulatory System…
 Many wastes will
eventually be
carried through the
renal artery to the
kidney, which will
purify the blood

Some of these
wastes diffuse into
the kidney; others
are pulled from
the bloodstream
by active transport
In Gas Exchange…
 In addition to
nutrients and wastes
from food, the blood
also transports
oxygen and carbon
dioxide
 Red blood cells
carry oxygen on
hemoglobin
In Gas Exchange…
 Oxygen enters the
body through the
respiratory system
 Air travels from the
nose  pharynx 
trachea  bronchi
 bronchioles 
alveoli
In Gas Exchange…
 Each alveolus is an
air sac surrounded
by a network of
capillaries
 The pulmonary
arteriole brings
blood from the heart
while the pulmonary
venule carries blood
back to the heart
In Gas Exchange…
 Oxygen diffuses
from the alveolus
into the capillary; it
will then travel back
to the heart to be
pumped out to the
body
 Carbon dioxide and
water diffuse from
the capillary into the
alveolus; it will then
be exhaled
In Gas Exchange…
 Certain conditions
can impair gas
exchange
 In pneumonia, an
infection causes an
inflammation of the
lungs; the lungs
often become filled
with fluid
In Gas Exchange…
 In asthma,
the
airways of
the lungs
swell and
narrow
In Gas Exchange…
 In emphysema, the alveoli
(air sacs) are damaged -their walls break down
and the sacs become
larger.
 These larger air sacs
move less oxygen into
the blood.
 This causes difficulty
breathing or shortness
of breath that gets
worse over time.
In Gas Exchange…
 In anemia, a
person has fewer
red blood cells

Remember, red
blood cells are
responsible for
transporting
oxygen to the
body cells
 There are multiple
types and causes
of anemia