Transport of Oxygen PDF

Transport of Oxygen Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Rules before lectures Review Questions Diffusion of respiratory gases are directly proportionate to …….. And indirectly proportionate to ………….. Diffusion coefficient = ……………….. Diffus...

Transport of Oxygen Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Rules before lectures Review Questions Diffusion of respiratory gases are directly proportionate to …….. And indirectly proportionate to ………….. Diffusion coefficient = ……………….. Diffusion of CO2 is ………………time O2 diffusion List the mechanisms of oxygen transport. Describe the oxygen-hemoglobin dissociation curve. Identify the significance of the oxygen-hemoglobin dissociation curve. List the factors that shift oxygen-hemoglobin dissociation curve. Describe the O2 dissociation curve for myoglobin. Oxygen transport Oxygen is carried in blood in 2 forms: 1- O2 in physical solution (2%) 2- O2 in chemical form (98%) Nature : free O2 dissolved in blood. Volume : 0.3 ml/100ml arterial blood (PO2 =100mmHg) 0.13 ml/100ml venous blood (PO2 =40mmHg) It determines O2 tension that determines Rate and direction of O2 diffusion. % of hemoglobin saturation. Nature: O2 combines with iron (Fe+2) of hemoglobin forming HbO2, HbO4, HbO6, and HbO8. It determines O2 capacity and O2 content Oxygen transport O2 Capacity: It is the volume of O2 in ml present in chemical combination with Hb in 100ml blood when Hb is fully saturated  Each gram Hb contains 1.36 ml O2  O2 Capacity= 1.36 mlO2 x Hb content = 1.36 mlO2 x 15gm% = 20ml/100mlblood O2 Content: It is the volume of O2 in ml present in chemical combination with Hb in 100ml blood. At PO2 100mmHg (arterial blood)→ O2 content = 19ml/100ml blood At PO2 40mmHg (venous blood) → O2 content = 14ml/100ml blood % O2 Saturation of Hb= 𝑶𝟐 𝒄𝒐𝒏𝒕𝒆𝒏𝒕 𝑶𝟐 𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚 At arterial blood = 19/20 = 95% or more At venous blood = 14/20 = 70% Oxygen- Hemoglobin Dissociation Curve It represents the relationship between partial pressure of O2 (blood PO2 )and % Hb saturation (SaO2) / /  PO2 100 →  PO2 60 → 90 % Hb saturation  PO2 40 → 75 % Hb saturation  PO2 20 → 30 % Hb saturation 97.5 % Hb saturation At high altitude: PO2 = 60mmHg → Plateau Steep 90% Hb Saturation Oxygen- Hemoglobin Dissociation Curve  Oxygen dissociation curve for hemoglobin is Sigmoid-shaped (S shape).  The saturation of Hb with oxygen varies with partial pressure of oxygen.  At the lung (Plateau): When partial pressure of oxygen is high, the oxygen is taken up by Hb Hb has an increasing affinity for oxygen, initial uptake of one oxygen molecule by Hb facilitates the further uptake of oxygen molecules.  At the tissues (Steep): When partial pressure of oxygen is low, oxygen is released to the tissue Low affinity of Hb to O2 Significance of Oxygen Hemoglobin Dissociation Curve S shape of the curve is important: At the lung ( Plateau or flat portion): Allow easy and almost complete saturation of Hb at the lung even when O2 tension is low (e.g. at high altitude or in lung diseases) At the tissues ( Steep portion): Allow easy and RAPID release of O2 from the hemoglobin to the tissues, because at low PO2, Hb has low affinity to O2. The S Shape nature of the curve is explained by the presence of 4 heme groups in the Hb, Each group can combine to one molecule of O2. there groups differs in their affinity to O2 as the O2 tension increases Oxygen- Hemoglobin Dissociation Curve p50 : is a reference point representing the PO2 at which 50% of hemoglobin is saturated. This normally occurs at about a blood PO2 of about 27 mm Hg. Shifting of of Oxygen Hemoglobin Dissociation Curve Causes of shift to right (Exercise) Increased blood PCO2 (Bohr effect) Increased concentration of 2,3 DPG Increased body temperature Increased blood H+ concentration (decreased blood pH, acidosis) there is decreased affinity of Hb to O 2 leading to increase O2 release to the tissues. Causes of shift to Left decreased blood PCO2 decreased concentration of 2,3 DPG decreased body temperature decreased blood H+ concentration (increased blood pH, alkalosis) Hemoglobin F (Fetal Hb) Carbon monoxide poisoning (CO-Hb) there is increased affinity of Hb to O2 leading to decrease O2 release to the tissues. Hemoglobin in relaxed form has high affinity to O2 → decrease release of O2 to tissues Hemoglobin in Taut form has low affinity to O2 → release O2 to tissues Hb (Relaxed form) Hb (Taut form) In Right shift of the curve → p50 is increased. In Left shift of the curve → p50 is decreased. Oxygen Dissociation Curve for Myoglobin Myoglobin: iron containing pigment present in skeletal muscle. It acts as O2 stores in the muscle One molecule of myoglobin combines with one What about Hb????? molecule of O2. Myoglobin dissociation curve is rectangular hyperbola At tissue level (without exercise) (PO2= 40mmHg): the myoglobin is fully saturated with O2 during rest. Muscle exercise (PO2 below 40mmHg): Myoglobin gives its O2 to the muscles. Review Questions You are a new intern on the medicine wards. Your team has recently admitted a patient who is having significant respiratory difficulty. Your senior resident asks you to calculate the patient’s blood oxygen concentration. Which tests do you need to order? A. B. C. D. E. Blood draw, arterial blood gas Blood draw, arterial blood gas, pulse oximetry, hemoglobin level Blood draw, blood oxygen concentration assay Blood draw, pulse oximetry Blood draw, venous blood gas, pulse oximetry Summary List the mechanisms of oxygen transport. Describe the oxygen-hemoglobin dissociation curve. Identify the significance of the oxygen-hemoglobin dissociation curve. List the factors that shift oxygen-hemoglobin dissociation curve. Describe the O2 dissociation curve for myoglobin. Learning Resources  Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2021. Chapter 40, 511-520 and Chapter 41, 521-530. https://www-clinicalkeycom.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000412  https://exchange.scholarrx.com/brick/oxygen-and-carbon-dioxide-transport  Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF MEDICINE Thank you