Gas Exchange

1. IB DP Biology: Core Material + Further Human Physiology Option H6 Gas Exchange

2. IB DP Biology: Core Material

3. CT Scan of Bronchial tree

4. Breathing is not respiration!! Ventilation – a mechanical process moving air into an out of the lungs in two stages: Inspiration and expiration. This is controlled by movement of the diaphragm and rib cage. http://scienceinspiration.blogspot.com/2012/04/human-respiratory-system.html Gas Exchange - the diffusion of O2 and CO2 to and from the blood at The alveoli and respiring tissues. http://www.beltina.org/health-dictionary/alveolus-definition-function-bronchioles.html Cell respiration – this is production of ATP at the cellular level using mitochondria

5. The ventilation system For gas exchange to be efficient high concentration gradients must be maintained in the alveoli Breathing in increases the concentration gradient of oxygen Between the alveoli and the blood - so It diffuses into the blood Breathing out removes CO2(and unused O2) increasing the concentration gradient of CO2 between blood and alveolus so CO2 will diffuse out. If the alveoli were not ventilated equilibrium would be reached and no gas could be exchanged.

6. http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP15104http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP15104

7. Alveoli are well adapted to gas exchange Alveoli increase the surface area for gas exchange. They are millions in number , each with their own network of capillaries, and a rich blood supply maintains a high concentration gradient to CO2 and O2 Membranes are very thin – both the capillaries and alveoli- so the diffusion path is short. Surfaces are wet so gasses are dissolved making diffusion easier.

8. The ventilation system Intercostal muscles control movement of the rig cage.

9. http://kent.skoool.co.uk/content/keystage3/biology/pc/learningSimulations/BRVSC/launch.htmlhttp://kent.skoool.co.uk/content/keystage3/biology/pc/learningSimulations/BRVSC/launch.html

10. The mechanics of ventilation Inspiration:External intercostals muscles contract. Diaphragm contracts (drops). Abdominal muscles relax . Chest volume increases, pressure in lungs decrease, air enters . Expiration:Internal intercostal muscle contract. Diaphragm relaxes(rises). Abdominal muscles contract. Chest volume decreases, volume in lung decreases, air is pushed out.

11. A doubled-walled closed sac called the pleural sac separates each lung from the thoracic wall and other surrounding structures. It is lubricated with intra-pleural fluid.

12. Asthma Can be caused by environmental and genetic factors. Asthma attacks can be triggered by many conditions and must be treated quickly. Inhalers contain hormones which cause the muscles of the bronchi to relax and reduce inflammation. This allows air to enter the lungs normally. Asthma suffers must be aware of their triggers to avoid a dangerous situation. Click to start video http://www.nhs.uk/Video/Pages/Asthmaanimation.aspx

13. IB DP Biology: Further Human Physiology – Option H6

14. Gasses move down partial pressure gradients • Gas exchange at both the pulmonary capillary, and tissue capillaries involves simple passive diffusion of O2 and CO2 down partial pressure gradients. • Atmospheric air is a mixture of gasses. Dry air contains about 79% N2 and 21% O2. Negligible amounts of CO2, H2O vapor, and other gasses. • Because 79% of the air consists of N2 molecules 79% of the 760 mm Hg (600 mm Hg) is exerted by N2 molecules.

15. Gasses move down partial pressure gradients • O2 represents 21% of the atmosphere. 21% of 760 mm Hg atmospheric pressure, or 160 mm Hg, is exerted by O2. • The individual pressure exerted independently by a particular gas within a mixture of gases is know as partial pressurePgas

16. http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter44/animations.html#http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter44/animations.html#

17. Because of humidification & small turnover of alveolar air, the average alveolar PO2 is 100 mm Hg.

18. Oxyhemoglobin dissociation curve Partial pressure of oxygen is the pressure exerted by oxygen in a mixture of gasses. At low PO2hemoglobin is not saturated with O2, at high PO2 saturation occurs. http://missinglink.ucsf.edu/lm/abg/abg1/saturation3.html • The first oxygen molecule if relatively hard to bind. The second and third are easier, & the fourth is again hard to bind. • At higher PO2 it is easy to attach oxygen to hemoglobin. At low PO2 they are released to tissues.

19. The most important factor determining the % Hb saturation is the PO2 of the blood, which in turn is related to the concentration of O2 dissolved in the blood. A plateau region exists between 60 – 100 mm Hg

20. Oxygen dissociation curve for adult hemoglobin • The initial uptake of one oxygen molecule by hemoglobin facilitates the further uptake of oxygen molecules (hemoglobin has an increasing affinity for O2). • The curve shows how the saturation of hemoglobin with O2 varies with partial pressure of oxygen. The curve is sigmoid-shaped.

21. Oxygen dissociation curve for adult hemoglobin • Low partial pressure of O2 corresponds to the situation in the tissue when partial pressure of oxygen is low, oxygen is released. • High partial pressure of oxygen corresponds to the situation in the lungs. When partial pressure of oxygen is high, oxygen is taken up by hemoglobin.

22. Fetal hemoglobin - The oxygen dissociation curve for fetal Hb is shifted to the left of adult Hb http://cnsnews.com/image/baby-0 • This means that fetal Hb is able to take up oxygen at lower partial pressures than adult Hb. It has a higher affinity for oxygen. • The fetus obtains oxygen through The placenta. The oxygen dissociates from the mother Hb and is attached to the fetal Hb.

23. Myoglobin Myoglobin releases a lot of oxygen over a narrow range of low partial pressures In the tissues. http://www.kidsbiology.com/human_biology/muscles2.php Myoglobin is used to store oxygen in muscle tissues and release it when needed in respiration. It gives muscle tissue Its characteristic color. Myoglobin increase efficiency of respiration in the muscle tissues as it is more sensitive to a change on PO2(at low values). So it releases O2 to the muscles rapidly as they use it in respiration.

24. Myoglobin Myoglobin has a higher affinity for oxygen at low PO2 so when the blood reaches the muscle tissue oxygen dissociates from hemoglobin and binds with myoglobin Myoglobin is sensitive to changes in PO2 at low oxygen levels so when a demand for oxygen is created during respiration I can quickly dissociate for use in the cells A flow of oxygenated blood quickly replenishes depleted myoglobin in the muscle tissue and ensures aerobic respiration can continue. Myoglobin releases a lot of oxygen over a narrow range of low partial pressures In the tissues.

26. Carbonic anhydrase speeds up the production of hydrogen carbonate (HCO3-)

30. Carbon Dioxide & Blood Transport • CO2 is carried in three forms: • Dissolved in the plasma • Dissociated carbonic acid (H2CO3). • Carbaminohemoglobin (bound to hemoglobin). • Carbonic anhydrase found in red blood cells (erthrocytes) speeds up production of hydrogen carbonate. • Chloride shift occurs to balance movement of hydrogen carbonate ions movement out.

31. The Bohr shift: effect of pH of oxygen dissociation. • Respiration produces CO2 in the tissues. • Increased CO2 causes a decrease in pH • As pH decreases the affinity of Hb for O2 decreases. • This causes more O2 to dissociate from Hb, which can be used in the tissues. http://www.austincc.edu/~emeyerth/bohr.htm At the lungs there is a higher PO2 & a lower PCO2. So oxygen binds with Hb again. Click for animation

32. Bohr Shift • Bohr effect occurs when there is lower pH due to increased CO2 and lactic acid. • Hard working muscles generate CO2 and lactic acid as a result of cell respiration and lactic acid fermentation.

33. Bohr Shift • The overall effect is that the curve is shifted to the right, meaning that oxygen is more readily released to respiring tissues.

34. What about lactic acid? Increase, Decrease?

35. How & Why Breathing Rate Varies with Exercise • Oxygen becomes limited. • CO2 & lactic acid concentration builds up in the blood which lowers the pH. • Chemosensors detect lowered pH. • Sensors in carotid artery & aorta send impulses to breathing center at brain stem.

36. How & Why Breathing Rate Varies with Exercise • Impulse sent to diaphragm & intercostal muscles. • Breathing rate increases or decreases. • Muscles contract or relax under involuntary control • Breathing rate increases to remove more CO2 from blood.

37. Asthma – Another look

38. Asthma – A review Asthma attacks are an allergic response to dust, pollen, or house mites. During an asthma attach the smooth muscle walls of the bronchi contract , blocking air flow into the lungs. If the blockage is total the attack can be fatal. Inhalers act as bronchodilators - they open up the bronchi to allow air to flow more freely during an attack. Click to start animations & video

39. Effects of lung cancer • Lung cancer is abnormal cell growth of the lung tissue. • It can be caused by smoking or inhaling other carcinogens such as asbestos, or radioactive ores in industry. • Tumors in the lings can have the following affects: • Reduce surface for gas exchange. • Put pressure on blood vessels and prevent transport. • Damage pleural membranes, diaphragm, or intercostal muscles. • Treatment of lung cancer can involve a lobectomy – the removal of the affected tissue, sometimes the entire lung is removed. Click to run videos and animations.

40. The Effects of Altitude On Gas Exchange

41. Effects of altitude on gas exchange • Atmospheric pressure progressively declines as altitude increases. • At 18,000 ft atmospheric pressure is only 380 mm Hg. Half of its normal sea level value. • The PO2 of air at this altitude is 21% of 380 mm Hg or 80 mm Hg with alveolar PO2 being even lower at 45 mm Hg.

42. Effects of altitude on gas exchange • At any altitude above 10,000 ft the arterial PO2 falls into the steep portion of the O2 – Hb curve below the safety range of the plateau region. • As a result the %Hb saturation in the arterial blood declines steeply with any additional increase in altitude.

46. The effects of altitude on gas exchange • “Thinner air” at higher altitudes has a much reduced PO2 resulting in reduced uptake of oxygen by normal ventilation. Hb cannot reach 100% saturation . This is called hypoxia. The body compensates by increasing HR and breathing rates, but this may not be sufficient. • Symptoms of altitude sickness: • Headache, nausea, & vomiting • Dizziness or loss of consciousness • Muscles weakness, rapid pulse, & breathing rate. • Acclimatization to altitude helps the body produce more Red blood cells, myoglobin, & mitochondria, and helps the body develop more adequate circulation around the muscles. Ventilation rate also increases. • Populations living at high altitude have shown signs of natural selection at work in humans: bigger chests, more dense alveoli, more red blood cells and a higher affinity for oxygen. http://www.youtube.com/watch?v=hiUgX4WrjX0

47. Other Human Adaptations to High Altitude • Bigger chests and more alveoli = greater lung surface area. • Bigger chests and more alveoli = larger vital capacity than people living at sea level. • Greater myoglobin production encourages O2 to diffuse into muscles. • Hemoglobin dissociation curve shifts to the right to encourage O2 release into tissues.