AP Biology Lungs exchange surface, but also creates risk: entry point for environment into body spongy texture, honeycombed with moist epithelium

AP Biology Alveoli  Gas exchange across thin epithelium of millions of alveoli  total surface area in humans ~100 m 2

AP Biology 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  mucus traps dust, pollen, particulates  beating cilia move mucus upward to pharynx, where it is swallowed

AP Biology 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 Autonomic breathing control  Medulla sets rhythm & pons moderates it  coordinate respiratory, cardiovascular systems & metabolic demands  Nerve sensors in walls of aorta & carotid arteries in neck detect O 2 & CO 2 in blood Don’t have to think to breathe!

AP Biology Medulla monitors blood  Monitors CO 2 level of blood  measures pH of blood & cerebrospinal fluid bathing brain  CO 2 + H 2 O  H 2 CO 3 (carbonic acid)  if pH decreases then increase depth & rate of breathing & excess CO 2 is eliminated in exhaled air

AP Biology Diffusion of gases  Concentration & pressure drives movement of gases into & out of blood at both lungs & body tissue bloodlungs CO 2 O2O2 O2O2 bloodbody CO 2 O2O2 O2O2 capillaries in lungscapillaries in muscle

AP Biology Pressure gradients Lungs

AP Biology Hemoglobin  Why use a carrier molecule?  O 2 not soluble enough in H 2 O for animal needs  hemocyanin in insects = copper (bluish)  hemoglobin in vertebrates = iron (reddish)  Reversibly binds O 2  loading O 2 at lungs or gills & unloading in other parts of body

AP Biology Hemoglobin  Binding O 2  loading & unloading from Hb protein depends on cooperation among protein’s subunits  binding of O 2 to 1 subunit induces remaining subunits to change shape slightly increasing affinity for O 2  Releasing O 2  when 1 subunit releases O 2, other 3 quickly follow as shape change lowers affinity for O 2 Heme group

AP Biology 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 Carbon Dioxide Transport  Most CO2 is converted to bicarbonate.  This conversion releases H+ ions into the blood.

AP Biology  Dissolved in blood plasma  Bound to Hb protein  Bicarbonate ion (HCO 3 - ) & carbonic acid (H 2 CO 3 ) in RBC  enzyme: carbonic anhydrase reduces CO 2 Transporting CO 2 in blood

AP Biology Adaptations for pregnancy  Mother & fetus exchange O 2 across placental tissue  why would mothers Hb give up its O 2 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. 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.