Unit 6 BIO 277 Objectives

Describe (or draw) the pathway that oxygen follows starting from the alveoli and ending up in a working cell. Include partial pressures of oxygen in the atmosphere, alveoli, arterial blood, cells and venous blood.

@ rest: PPO2 < or = to 40 mmHg PPCO2 < or = to 46 mmHg

Pressure v Time Graph

Air flow in versus Air Flow out

Explain how ventilation rate is controlled.

Control Total Pulmonary Ventilation (L/min) aka alveolar minute volume = Tidal volume (L/breath) aka residual volume (subtract residual volume first)x Ventilation rate (breath/min) Vital capacity= max tidal volume= breathing in as much as you can and out as much as you can (still have a residual volume) Ventilation rate is controlled by central pattern generator and what influences the central pattern generator is: -most important factor for normal cicrum: chemoreceptors for increased H+ (dec pH) and increased partial pressure of CO2 cause increased respir. rate *too much CO2 = too acidic so must increase respir. rate -emotions and voluntary control -peripheral chemoreceptors in aortic arch and carotid artery respond to H+ and CO2. ALSO respond to O2, but only under extreme conditions of hypoxia!

Explain why alveolar airflow and blood flow to alveoli are matched.

Matched because want to maximize O2 diffusion into blood and regulate plasma pH which is influenced by CO2 in the blood. @ rest: not using all pulmonary capacity or all Cardiac output (and could over-ventilate lungs and lose too much CO2) -so have to regulate degree to which you ventilate so don't lose too much CO2 from blood so divert away alevoli that are poorly ventilated so that you don't over ventilate and lose more CO2 than needed

Define pneumothorax.

Occurs if the membrane is punctured, equalizing the intrapleural, alveolar and atmospheric pressures. Lung basically collapses bc alveoli collapse and stick together Example: Heimlich Maneuver This principle is the basis of the Heimlich maneuver, where thrusting a fist up under the ribs simulates a relaxed diaphragm and increases alveolar pressure with the hope of expelling whatever a person might be choking on. This would represent a situation where PALV = PATM = PIP (pressure of interpleural space)

Determinants are most important where?

PP of CO2 would go up and PP of O2 would go down in a poorly ventilated alveolus In response to this: pulmonary arteriole will constrict so blood gets diverted from O2 poor to O2 rich (via simple diffusion) O2 is the most important determinant of state of ctrn of pulmonary arterioles CO2 i the most important determinant of state of ctrn of bronchioles

Explain the difference between paracrine control of airway circular smooth muscle and vascular circular smooth muscle in both the systemic and pulmonary arterioles.

Paracrine signals on airway circular smooth muscle: -pulmonary arteries: increased CO2 dilates bronchioles, constricts pulmonary arteries, dilates systemic arteries; increased O2 constricts bronchioles, dilates pulmonary arteries, constricts systemic arteries; the diam of pulmonary arterioles is controlled by O2 levels in alveoli so if decreased O2 then= vasoconstriction bc only send blood where the good stuff is! -systemic arteries: CO2 affects bronchiolar diameter (incr CO2 relaxes bronchiolar smooth muscle --> bronchiodilation); Epi binds beta-adren in bronchioles relaxing smooth muscle causing bronchiodilation; Histamine released by mast cells leads to bronchioconstriction and difficulty breathing; leukotrienes and parasympathetic neurons also cause this Paracrine signals on vascular circular smooth muscle: -systemic: -pulmonary:

Draw the relationship between atmospheric pressure, alveolar pressure and intrapleural pressure on a graph of pressure as a function of time for inspiration and expiration.

Pressure differences between alveolar space and interpleural space help keep lungs expanded: -interpleural space pressure is ALWAYS < Alveolar pressure (PALV) -interpleural pressure is ALWAYS < atmospheric pressure (PATM) P v T: atm pressure stays same, alv pressure like a cos curve, interpleural pressure is lowest and mimicks alv pressure curve (see image above) --------------- Pleural space is fluid filled and under lower pressure than the alveolar space Way more CO2 in the blood than in the alveolar space, more O2 in the alveolar space than in the blood Diaphragm relaxes and air flows out of lungs; Diaphragm (skeletal muscle) contracts and flattens and air flows into lungs! Air moves from high to low pressure.

Explain how skeletal muscles are used to change the alveolar pressure.

Skeletal muscles contracting and relaxing compress and enlarge the thoracic space, thus increasing or decreasing pressure in the alveolar space.

List factors that affect the partial pressure of oxygen in the blood.

The affinity, or ability of hemoglobin to bind oxygen tightly varies depending on temperature, pH, [CO2], [2,3-DPG] in the blood

Describe where gas exchange occurs in the airway.

between alveolar space and the blood (at alveolar membranes into the blood and blood into cells) via simple diffusion

Describe which parts of the airway have airway circular smooth muscle.

bronchioles

List the factors that affect the state of airway circular smooth muscle and explain what factors determine their activity level.

Bronchodilation: increased bad stuff = bronchodilation to get rid of it faster -decreased resistance to air flow by increasing diameter of airways -epi in the lungs causes dilation @ beta-adrenergic receptors -CO2 increased Bronchoconstriction: increases resistance to air flow and amnt of fresh air that reaches alveoli -decreased airway diameter decreases air flow (usually from mucus) -L and viscosity are constant unless in a steam room (then water droplets in steam will incr viscos of air so increasing resistance to flow)

Describe the function of the ciliary escalator.

The ciliary escalator runs the whole length of the airway pharynx to alveoli. Goblet cells secrete mucous which traps inhaled dust and pathogens. Ciliated epithelial cells sweep mucous and inhaled particles up into the pharynx where it is swallowed. Note that smoking paralyzes the ciliary escalator, making it harder to keep the lungs clear of germs and mucous. That's why smokers cough a lot, and are susceptible to respiratory ailments.

Describe the relationship between partial pressure of carbon dioxide in the blood and pH using the law of mass action.

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- CA = carbonic anhydrase (@ first arrow) Carbon dioxide combines with water and forms carbonic acid (catalyzed by carbonic anhydrase); the carbonic acid then spontaneously dissociates into hydrogen ions and bicarbonate ions. Note that this is a reversible reaction. Following the Law of Mass action then, if we increase substrates on the left, we increase production of products on the right. If we reduce the concentration of substrates on the left, then we drive the reaction to the left, and the concentration of products decreases. So more CO2 in the blood = increase [H+] or decreased pH and makes the plasma more acidic (respiratory acidosis)

Describe the 3 ways that carbon dioxide is transported in the blood.

CO2 is transported in 3 different ways: 7% simply dissolved in the plasma 23% bound to hemoglobin (Hb●CO2) 70% as bicarbonate (HCO3-) in the plasma

Explain how prolonged exposure to high altitude causes pulmonary edema, respiratory alkalosis and an elevated hematocrit.

If we increase the amount of CO2 in the blood we increase the [H+] and make the plasma more acidic. This is called respiratory acidosis. If we lose too much CO2, eg. by hyperventilating, then then we lose H+ and the plasma becomes too alkaline. This is called respiratory alkalosis. @ high altitude: have increased pulmonary arterial blood pressure bc low O2 levels constrict the pulmonary arterioles which causes blood to collect in the arteries --> increased hematocrit bc additional hemoglobin increases the total O2-carrying capacity. This also increases the blood viscosity so increases the resistance to flow, so blood flow will decrease. Pulmonary edema: -fluid in interstitial space increases diffusion distance. Arterial PCO2 is higher due to higher CO2 solubility in water. -slower O2 diffusion means less O2 reaching the blood which worsens the normal hypoxia of altitude

Be able to draw the oxygen-hemoglobin saturation curve and describe factors that affect the affinity of hemoglobin for oxygen.

The affinity, or ability of hemoglobin to bind oxygen tightly varies depending on temperature, pH, [CO2], [2,3-DPG] in the blood. http://people.eku.edu/ritchisong/301notes6.htm Hemoglobin is a protein, so just like any other kind of protein, can change its shape in response to changes in temperature, pH and allosteric modulation. .......................................................................................................... Conditions for blood around a working muscle= Hemoglobin with lower affinity (right-shifted curve; shape change) for O2 is caused by decreased pH (more acidic), increased temp of blood, more CO2 in blood, more 2-3 DPG (which binds to Hb so O2 can be released) --> breaking down oxyhemoglobin --> Hb and O2. Maternal Hb also causes a right-shifted curve or decreased affinity for O2. Increased Affinity of Hb for O2 (binds O2 more tightly)= left-shift for less active tissues (so in pulmonary capillaries)= caused by high pH, low temp, less CO2 and less 2-3 DPG. Different type of Hb (aka Fetal-Hb, fetus steals away O2 from mom's blood and brkdown fetal Hb when born so causes jaundice in babies). Increased affinity equation= Hb and O2 -> oxyhemoglobin -for the curve, right-shift causes equation to move in reverse direction (so to the left) and the left-shift causes reaction to move in the forward direction (so to the right)

CO2 is more soluble in water than is O2

The amount of carbon dioxide that dissolves in water is much higher that the amount of oxygen that dissolves in water even if they are the same partial pressure in the air above, because carbon dioxide is much more soluble than oxygen.

Dalton's Law

The total pressure of a mixture of gases is the sum of the individual pressures (Ptotal=P1+P2+P3...) In our atmosphere on earth: PATM = PN2 + PO2 + PH2O + PCO2 100% = 76 + 21 + 3 + 0.0003 760 mmHg = 556 + 155 + 24 + 0.24

Distinguish between Type I and Type II alveolar cells

Type I- very large and very thin; main site of gas exchange Type II-far less abundant; secrete surfactant (important for reducing surface tension of alveoli, they make it easier for lungs to expand and thus to breathe)