The pulmonary system Chp. 16 Ventilation Chp. 17 Respiration

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Overview About 250 ml of O2 are consumed by cells per minute while 200 ml CO2 is produced /min.

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Partial pressures of gases Dalton’s law: the pressure of a gas is directly proportional to the number of moles of the gas in a defined volume The total pressure of a mixed gas is = pressure of the individual gases contained in the mixture P total = P 1 +P 2..+P n P air = P N2 + P O2 + P CO2 + P H2O P N2 = 0.79 x 760 mmHg = 600 mmHg P O2 = 0.21 x 760 mmHg = 160 mmHg P CO2 = x 760 mmHg = 0.23 mmHg

Solubility of gases Henry’s law: At constant temperature, the solubility of a gas is proportional to its partial pressure Applications: -- the bends or decompression sickness = formation of gas bubbles in the blood and tissues when a diver surfaces too quickly. -- NOT to be confused with nitrogen narcosis: a state of confusion due to excess nitrogen accumulating in the blood

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Gas exchanges in the alveoli Driven by diffusion

Factors affecting alveolar P O2 and P CO2 1- PO2 and PCO2 of inspired air 2- alveolar ventilation (rate of air exchange) 3- Rate of CO2 production and O2 use by tissue (gas pressure of venous blood)

Table 17.2

Factors affecting gas exchanges in alveoli 1- Gas partial pressure  ? 2- Surface area for gas exchange  ?? 3- Diffusion distance  ?? 4- Rate and depth of breath  ?? ?

Factors affecting gas exchanges in alveoli 1- Gas partial pressure  mountain sickness 2- Surface area for gas exchange  emphysema 3- Diffusion distance  pulmonary edema 4- Rate and depth of breath  high anatomical dead space, low RR

Gas pressures in arteries and veins

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Oxygen transport in the blood O 2 from the alveoli diffuse into the blood Then O 2 enters the RBC and binds to hemoglobin 2% of O 2 is dissolved in plasma while 98% is bound to Hb  oxyHb The binding is reversible Hb + O 2  HbO 2

Oxygen transport and uses Hb is 100% saturated with O2 when the RBCs pass through the lungs  all Hb molecules are fully loaded with O2 200 ml O2 carried per liter  x 5 liters  1000 ml O2 carried/min Tissues only use 250 ml O2 per minute  only 25% of O2 molecules are used Thus venous blood should have a saturation rate of 75% Anemia: decrease in oxygen-carrying capacity of the blood

Oxygen in the blood

Hemoglobin + O2  HbO2 oxyhemoglobin  pinkish red color of the skin (normal) Hemoglobin with no oxygen Hb  dark bluish-red color  skin appears blue  cyanosis Hemoglobin + CO (same O2 binding site)  cherry red color of the skin Hemoglobin + CO2 (different binding site)  carbaminohemoglobin

Clinical applications Jimmy had a serious bleeding following a car accident. - His Hematocrit is He also was diagnosed with pneumonia. - He become severely short of breath upon climbing the hospital stairs. - You check his O2 sat and find it to be 100%. You are satisfied that he has no problem breathing. Mindy has severe bronchitis. As you walk into her room, you found her coughing and having a bluish tinge to her skin. - You check her O2 sat. and find it to be 80%. - Her hematocrit is 42%. Which of the two has the least oxygen available for his/her metabolism? Which of the two will have the most problem with gas exchanges?

Clinical applications Jimmy: Hct= 23, O2 sat.= 100%. Mindy: Hct= 42, O2 sat. 80%. Which of the two persons has the least oxygen available (in the blood) for his/her metabolism? Which of the two will have the most problem with gas exchanges?

In tissues O 2 moves from HbO 2 to free O 2 in the plasma, then into the tissues This is passive transport  diffusion

Factors affecting Oxygen binding to hemoglobin Temperature PCO 2 pH 2,3-BPG (2,3- biphosphoglycerate) 2,3-BPG formed during low O 2 level diminishes Hb affinity for O 2

Carbon dioxide transport CO 2 diffuses into the blood = 5% CO 2 enters the RBC: --- binds to Hb  carbaminoHb = HbCO 2 10% --- it is converted into bicarbonate ions (HCO 3 - ) by carbonic anhydrase, an enzyme present in the RBCs 90%

The reverse occurs at the blood-alveoli interface HCO 3 - is reconverted to CO 2 by the reverse reaction CO 2 moves out of HbCO 2 The dissolved CO 2 moves into the alveoli through diffusion Note: the movement of HCO 3 - is compensated by movement of Cl - (Chloride shift)

CO 2 + H 2 O  =  H 2 CO 3  =  HCO H + Note: the production of H+ means that respiration will have an effect on the acid-base balance of the blood

Effect of oxygen on CO 2 transport A high pO 2 decreases the affinity of Hb for CO 2  Haldane effect

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Regulation of ventilation - CNS Under both voluntary and involuntary control The main respiratory center is in the medulla oblongata (kind of pacemaker)  initiates basic respiratory rhythm This center stimulates contraction of the diaphragm and external costal muscles  inspiration The apneustic and pneumotaxic centers of the Pons modify the breathing rate and depth by acting on the medullary center

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Respiratory regulation: chemoreceptors The respiratory rate needs to adapt to body needs Chemoreceptors sense pO 2, pCO 2 and pH. Pulmonary stretch receptors Other receptors monitoring lung conditions Some drugs modify the respiratory rate: ex: morphine (↓RR)

Aortic and carotid bodies monitor arterial pO 2, pCO 2 and pH (peripheral monitors). They are activated by pO 2 lower than 60 mmHg Central chemoreceptors monitor pCO 2 and pH Change in blood pH is the main factor controlling the breathing rate. If pO 2 is too low, then the aortic and carotid bodies will also kick in

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Local control Changes in perfusion and ventilation can occur ↓pO 2 and ↑ pCO 2  bronchodilation and vasoconstriction of the arterioles  improved perfusion

Outline Overview of pulmonary circulation Diffusion of gases Gas exchanges Gas transport in blood Regulation of ventilation - CNS - chemoreceptors Local regulation Acid-base Homeostasis

Acid-base balance CO 2 + H 2 O  =  H 2 CO 3  =  HCO H + Blood pH = Hb can bind (and buffer) H + Respiratory acidosis: excess H +  due to CO 2 retention (hypoventilation) Respiratory alkalosis  loss of H +  due to loss of CO 2 (hyperventilation)