Unit 1. Energy Production and Transport OPTION H: Gas exchange Unit 1. Energy Production and Transport

Mechanism of Oxygen Transport in the Human Body

Oxygen dissociation curves.- Hemoglobin is an oxygen transport protein in the blood. The degree to which oxygen binds to hemoglobin (oxygen saturation) is determined by the partial pressure of Oxygen (PO2) Partial pressure is the total pressure of a mixture of gases within which a gas occurs, multiplied by the percentage of the total volume the gas occupies. It is measured in mm Hg or KPa (kilopascals).

The dissociation curves illustrate the behavior of hemoglobin during loading and unloading of oxygen. The shape of the curve can be explained by the changing affinity that each hemoglobin molecule has for oxygen as it becomes saturated with oxygen.

 At low PO2, such as what occurs in muscles, O2 will dissociate (unload) from hemoglobin. At high PO2, as occurs in the lungs, the hemoglobin will become saturated (loaded).

Oxygen Saturation Curve

Bohr Shift Increased metabolism = greater release of CO2 into the blood  lower pH of blood. Increased acidity shifts the oxygen dissociation curve to the right  greater release of oxygen from hemoglobin at the same partial pressure of oxygen. This is known as the Bohr shift.

Bohr Shift Ensures that respiring tissues have enough oxygen when their need for oxygen is greatest. Also in the lungs, if PO2 is lower, saturation of hemoglobin can occur at lower partial pressures of oxygen.

Myoglobin Myoglobin is a specialized oxygen transport protein in muscles. It has a much higher affinity for oxygen and will only release its oxygen when the PO2 is quite low, for example in muscles during heavy exercise. While hemoglobin has four chains with four heme groups, myoglobin has only one heme group. The release of each O2 from myoglobin triggers a conformational change, which cause the hemoglobin to more rapidly release subsequent O2 molecules.

Fetal Hemoglobin Fetal hemoglobin has a higher affinity for O2 at all partial pressures. This ensures that O2 is transferred to the fetus from the maternal blood across the placenta. The PO2 in fetal tissues is very low due to the high metabolic rate associated with fetal growth rates. Although fetal Hb has a higher affinity for oxygen in such a low partial pressure environment of the fetal tissue it unloads oxygen readily. At birth the foetal Hb is replaced with adult type Hb.

Exercise and Ventilation a) Exercise increases metabolism and leads to an increase in the production of CO2. Increased CO2 causes blood pH to decrease as it forms carbonic acid (H2CO3) b) c) Chemoreceptors in the aorta and the carotid artery are able to detect a change in blood pH. If a drop in pH is detected, the chemoreceptors send a message to the breathing center of the medulla oblongata. d) The cardiac center responds to the same stimuli and increases heart rate e) Nerve impulses are sent from the medulla to the diaphragm and the intercostals muscles causing them to increase the ventilation rate (e). This leads to an increased rate of gas exchange. The long-term effect of exercise is increased lung surface area.

Time to work on the DBQ

Gas exchange at high altitudes low PO2 in the air hemoglobin may not become fully saturated tissues may not be adequately supplied with oxygen.

Adaptations to high altitude increased red blood cell production increased amount of circulating hemoglobin. Increased ventilation rate and gas exhange Muscles produce more myoglobin to ensure delivery of oxygen to the tissues. http://www.asianscientist.com/wp-content/uploads/2013/07/Genomic-Analysis-Reveals-High-Altitude-Adaptations-In-A-Mongolian-Population.jpg

Adaptations to high altitude Populations living permanently at high altitude have greater mean lung surface area and larger vital capacities than people living at sea level. Their oxygen dissociation curve shifts to the right, encouraging release of oxygen into the tissues. http://www.pnas.org/content/99/26/17215/F3.large.jpg

Asthma Asthma is a chronic lung condition that is characterized by inflammation of the air passages in the lungs. Often the bronchioles constrict in an over-reactive fashion. The consequence is breathing problems, coughing and shortness of breath. It is often triggered by environmental factors such as allergies, exercise, cold, viral illness, or strong responses to environmental triggers such as pollen. Asthma sufferers are more likely to live in industrial areas. http://clearcorpsdetroit.org/wp-content/uploads/2012/11/child-asthma-print-version-.jpg

Asthma is often treated using drugs that act as bronchodilators or anit-inflammatories. These are usually administered by inhalation. http://life.familyeducation.com/images/ChildAsthma_H.jpg

Answer the end of the chapter 19 questions.  

Sources Allot, A., & Mindorff, D. (2010). IB Biology Course Companion. New York: Oxford University Press. Click 4 Biology. (n.d.). Option H: Gas exchange. Retrieved from http://click4biology.info/c4b/h/h6.htm Damon, A., McGonegal, R., Tosto, P., & Ward, W. (2007). Biology Higher Level. London: Pearson Baccalaureate.