Respiratory System Gas Exchange

Why do we need a respiratory system? respiration for respiration Why do we need a respiratory system? Need O2 in For aerobic respiration Make ATP Need CO2 out Waste product from Krebs cycle food ATP O2 CO2

Some vocabulary Ventilation Gas exchange Cell respiration The exchange of air between the lungs and the atmosphere; it is achieved by the physical act of breathing Gas exchange The exchange of O2 & CO2 in the alveoli and the blood stream; it occurs passively via diffusion Cell respiration The release of ATP from organic molecules; it is greatly enhanced by the presence of oxygen (aerobic respiration)

Gas exchange O2 & CO2 exchange between environment & cells Need moist membrane Need high surface area

Optimizing gas exchange Why high surface area? Maximizing rate of gas exchange CO2 & O2 move across cell membrane by diffusion Rate of diffusion proportional to surface area Why moist membranes? Moisture maintains cell membrane structure Gases diffuse only dissolved in water High surface area? High surface area! Where have we heard that before?

Gas exchange in many forms … one-celled amphibians echinoderms cilia insects fish mammals size • water vs. land • endotherm vs. ectotherm

Why is this exchange with the environment RISKY? Exchange tissue: spongy texture, honeycombed with moist epithelium Lungs Why is this exchange with the environment RISKY?

Alveoli Gas exchange across thin epithelium of millions of alveoli Total surface area in humans ~100 m2

Alveoli T: thin wall R: rich capillary network I: increases SA/Vol ratio M: moist Adaptation Advantage Spherical shape Provides large surface area for diffusion of gases Single, cell thickness Increases rate of diffusion (decreases distance) Moist inner lining Allows for efficient diffusion Capillary bed nearby

Negative pressure breathing Breathing due to changing pressures in lungs Air flows from higher pressure to lower pressure Pulling air instead of pushing it

Partial pressure Partial pressure is the pressure exerted by a single type of gas when it is found within a mixture of gases The partial pressure of a given gas will depend on: The concentration of the gas in the mixture i.e. O2 levels may differ in certain environments The total pressure of the mixture Air pressure decreases at higher altitudes

Mechanics of breathing Air enters nostrils Filtered by hairs, warmed & humid 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

Mechanics of breathing

Autonomic breathing control don’t want to have to think to breathe! 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 O2 & CO2 in blood

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

Transporting CO2 in blood Dissolved in blood plasma as carbonate ion Tissue cells Plasma CO2 dissolves in plasma CO2 combines with Hb CO2 + H2O H2CO3 H+ + HCO3– HCO3– CO2 Carbonic anhydrase Cl– carbonic acid CO2 + H2O  H2CO3 hyrdogen carbonate H2CO3  H+ + HCO3– carbonic anhydrase ~75% ~25% Called carbaminohemaglobin -reversed @ the lungs

Transporting CO2 in blood Dissolved in blood plasma as carbonate ion HCO3- diffuses out through a carrier protein HCO3- diffuses out Cl- diffuses in “chloride shift” H+ attaches to Hb- Helps maintain pH Known as buffering hydrogen carbonate H2CO3  H+ + HCO3– Tissue cells Plasma CO2 dissolves in plasma CO2 combines with Hb CO2 + H2O H2CO3 H+ + HCO3– HCO3– CO2 Carbonic anhydrase Cl–

Releasing CO2 from blood at lungs Lower CO2 pressure at lungs allows CO2 to diffuse out of blood into lungs Plasma Lungs: Alveoli CO2 dissolved in plasma HCO3–Cl– CO2 H2CO3 Hemoglobin + CO2 CO2 + H2O HCO3 – + H+

Breathing & homeostasis ATP Homeostasis Keeping the internal environment of the body balanced Need to balance O2 in and CO2 out Need to balance energy (ATP) production Exercise Breathe faster Need more ATP Bring in more O2 & remove more CO2 Disease Poor lung or heart function = breathe faster Need to work harder to bring in O2 & remove CO2 CO2 O2

Diffusion of gases Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue capillaries in lungs capillaries in muscle O2 O2 O2 O2 CO2 CO2 CO2 CO2 blood lungs blood body

Hemoglobin Why use a carrier molecule? Reversibly binds O2 O2 not soluble enough in H2O for animal needs Blood alone could not provide enough O2 to animal cells Hemocyanin in insects = copper (bluish/greenish) Hemoglobin in vertebrates = iron (reddish) Reversibly binds O2 Loading O2 at lungs/gills & unloading at cells heme group cooperativity

Cooperativity in hemoglobin Binding O2 Binding of O2 to 1st subunit causes shape change in other subunits Conformational change Increases attraction for additional O2 Releasing O2 When 1st subunit releases O2, causes shape change to other subunits Lowers attraction for additional O2

Cooperativity in hemoglobin As each oxygen molecule binds, it alters the conformation of hemoglobin, making it easier for others to be loaded (cooperative binding) Conversely, as each oxygen molecule is released, the change in hemoglobin makes it easier for other molecules to be unloaded

O2 dissociation curve for hemoglobin Bohr shift Drop in pH lowers affinity of Hb for O2 Active tissue (producing CO2) lowers pH & induces Hb to release more O2 Effect of pH (CO2 concentration) PO2 (mm Hg) 10 20 30 40 50 60 70 80 90 100 120 140 More O2 delivered to tissues pH 7.60 pH 7.20 pH 7.40 % oxyhemoglobin saturation

O2 dissociation curve for hemoglobin Bohr shift Increase in temperature lowers affinity of Hb for O2 Active muscle produces heat Effect of Temperature PO2 (mm Hg) 10 20 30 40 50 60 70 80 90 100 120 140 More O2 delivered to tissues 20°C 43°C 37°C % oxyhemoglobin saturation

Adaptations for pregnancy Mother & fetus exchange O2 & CO2 across placental tissue Why would mother’s Hb give up its O2 to baby’s Hb?

Fetal hemoglobin (HbF) HbF has greater attraction to O2 than Hb Low % O2 by time blood reaches placenta Fetal Hb must be able to bind O2 with greater attraction than maternal Hb What is the adaptive advantage? 2 alpha & 2 gamma units

What is the adaptive advantage? Myoglobin Myoglobin has only 1 heme group Cannot undergo cooperative binding Has a greater affinity for O2 and can become saturated at lower concentrations Found in muscle cells Stores O2 until levels are low Delays anaerobic respiration during exercise What is the adaptive advantage?

Gas exchange at high altitudes High altitude = lower air pressure = lower partial pressure of O2 Makes oxygen uptake difficult Results in fatigue, breathlessness, rapid pulse, nausea, and headaches Over time, the body acclimates Increase production of red blood cells Increase hemoglobin concentration in rbc Increase ventilation rate Muscles produce more myoglobin & have increased vascularization Increase diffusion of O2 into muscles Long-term exposure = greater lung surface area, more dense alveoli, & larger chest size

Take a deep breath. Any questions?