Download Chapter 42.

Lungs
spongy texture, honeycombed
with moist epithelium
exchange surface, but
also creates risk:
entry point for
environment
into body
AP Biology
2005-2006
Alveoli
 Gas exchange across thin epithelium of
millions of alveoli

AP Biology
total surface area in humans ~100 m2
2005-2006
Mechanics of breathing
 Air enters nostrils


filtered by hairs, warmed & humidified
sampled for odors
 Pharynx  glottis  larynx (vocal cords) 

trachea (windpipe)  bronchi  bronchioles
 air sacs (alveoli)
Epithelial lining covered by cilia & thin film
of mucus


AP Biology
mucus traps dust, pollen, particulates
beating cilia move mucus upward to pharynx,
where it is swallowed
2005-2006
Negative pressure breathing
 Breathing due to changing pressures in lungs

air flows from higher pressure to lower pressure

pulling air instead of pushing it
AP Biology
2005-2006
Autonomic breathing control
 Medulla sets rhythm & pons moderates it

coordinate
respiratory,
cardiovascular
systems &
metabolic
demands
Don’t
have to
think to
breathe!
 Nerve sensors in
walls of aorta &
carotid arteries in
neck detect
O2 & CO2 in blood
AP Biology
2005-2006
Medulla monitors blood
 Monitors CO2 level of blood

measures pH of blood & cerebrospinal
fluid bathing brain
 CO2 + H2O  H2CO3 (carbonic acid)
 if pH decreases then
increase depth & rate
of breathing & excess
CO2 is eliminated in
exhaled air
AP Biology
2005-2006
Diffusion of gases
 Concentration & pressure drives
movement of gases into & out of blood
at both lungs & body tissue
capillaries in lungs
AP Biology
capillaries in muscle
O2
O2
O2
O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body
2005-2006
Pressure gradients
Lungs
AP Biology
2005-2006
Hemoglobin
 Why use a carrier molecule?

O2 not soluble enough in H2O for animal needs
 hemocyanin in insects = copper (bluish)
 hemoglobin in vertebrates = iron (reddish)
 Reversibly binds O2

AP Biology
loading O2 at lungs or gills &
unloading in other parts of body
2005-2006
Hemoglobin
 Binding O2


loading & unloading from Hb protein depends on
cooperation among protein’s subunits
binding of O2 to 1 subunit induces remaining subunits
to change shape slightly increasing affinity for O2
 Releasing O2

AP Biology
when 1 subunit releases
O2, other 3 quickly follow
as shape change lowers
affinity for O2
Heme group
2005-2006
Oxygen Transport
 How is oxygen transported throughout
the body?
 Erythrocytes, RBC’s, attach oxygen to
hemoglobin proteins
 As hemoglobin and oxygen combine
the blood turns bright red
AP Biology
2005-2006
Carbon Dioxide Transport
 Most CO2 is converted to bicarbonate.
 This conversion releases H+ ions into
the blood.
AP Biology
2005-2006
Transporting CO2 in blood
 Dissolved in blood plasma
 Bound to Hb protein
 Bicarbonate ion (HCO3-) & carbonic acid (H2CO3)
in RBC
AP Biology

enzyme: carbonic anhydrase reduces CO22005-2006
Adaptations for pregnancy
 Mother & fetus exchange O2 across placental tissue

why would mothers Hb give up its O2 to baby’s Hb?
Both anemia and relative iron deficiency are common during
pregnancy. Low hemoglobin concentrations are a normal physiologic
response to the expansion in plasma volume that occurs during
pregnancy. The normal pattern is for hemoglobin concentrations to fall
by about 20 g/L, reaching a nadir in the second trimester, and to return
to near pre-pregnancy levels by term.<1> Pregnant women are
generally considered to be anemic when hematologic indices fall two or
more standard deviations below "normal" levels, although definitions for
normal vary. In pregnancy, women require a greater amount of iron due
to an expanded red blood cell volume, the needs of the fetus and
placenta, and blood loss at delivery.
AP Biology
2005-2006