FSG120 Respiratory System Lecture Three 2024 PDF

FSG120 Respiratory system (Lecture three ) Dr. M Gamede [email protected] BMS building: Room No.7:13 References: vender’s human physiology (12th edition) Learning objectives ❖ Transport of oxygen ❖ Oxygen carrying capacity ❖ Haemoglobin saturation ❖ Oxygen-haemoglobin dissociation curve ❖...

FSG120 Respiratory system (Lecture three ) Dr. M Gamede [email protected] BMS building: Room No.7:13 References: vender’s human physiology (12th edition) Learning objectives ❖ Transport of oxygen ❖ Oxygen carrying capacity ❖ Haemoglobin saturation ❖ Oxygen-haemoglobin dissociation curve ❖ Carbon dioxide transport Transport of oxygen ❖ Each liter of arterial blood normally contains 200mL od O2 at atmospheric pressure ❖ The O2 is present in two forms: dissolved in plasma and erythrocytes cytosol ❖ Reversible bound in hemoglobin molecule in erythrocytes ❖ The amount of O2 dissolved in blood is directly proportional to the PO2 in blood (Henrys law) ❖ Of the 200mL O2 in 1L of blood , only 3mL is dissolved , the remaining 197 mL is haemoglobin bound at normal PO2 of 100mmHg Transport of oxygen ❖ Each hemoglobin molecule is made up of four subunits bound together ❖ Each subunit is made up of a molecular group known as heme and a polypeptide attached to heme ❖ The four polypeptides are collectively called globin ❖ Each heme in haemoglobin contains iron, Fe2+ to which oxygen binds, therefore each haemoglobin molecule binds to four O2 molecules Oxygen-haemoglobin dissociation curve Haemoglobin saturation ❖ The major determinant of the degree to which haemoglobin is saturated with oxygen is PO2 ❖ Haemoglobin is almost 100% saturated at normal systemic arterial PO2 of 100mmHg ❖ However, the Po2 of about 60mmHg results in more than 90% of Hb saturation, this permits a relative uptake of oxygen even if alveolar PO2 is moderately reduced ❖ Haemoglobin is 75% saturated at the normal systemic mixed venous PO2 of 40mmHg ❖ Only 25% of oxygen dissociates from haemoglobin and diffuse into tissues Oxygen carrying capacity ❖ 𝑂2 + 𝐻𝑏 = 𝐻𝑏𝑂2 ❖ Deoxyhaemoglobin(Hb) and oxyhaemoglobin(HbO2) ❖ The fraction of all haemoglobin in the form of oxyhaemoglobin is expressed as the %Hb saturation 𝑂2 𝑏𝑜𝑢𝑛𝑑 𝑡𝑜 𝐻𝑏 ❖ %Hb saturation = × 100 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝐻𝑏 𝑡𝑜 𝑏𝑖𝑛𝑑 𝑂2 ❖ Maximum capacity of Hb to bind O2 is also known as oxygen carrying capacity of blood Oxygen carrying capacity Haemoglobin saturation ❖ The affinity of haemoglobin to oxygen is decreased by increased PCO2,H+ concentration and temperature ❖ All these conditions exist in tissues and facilitate the dissociation of oxygen form haemoglobin ❖ 2,3 diphosphoglycerate is frequently produced by erythrocytes during glycolysis and increased inadequate oxygen supply also facilitates the unloading of oxygen from haemoglobin ❖ Carbon monoxide causes sickness due to its high haemoglobin affinity, about 210 times higher than that of oxygen Oxygen-haemoglobin dissociation curve (PO2) ❖ Sigmoidal curve: The binding of the oxygen molecule in one subunit facilitates the binding of oxygen to the next subunit ❖ The binding of one oxygen molecule leads to a conformation change in the haemoglobin structure, exposing more oxygen-binding sites ❖ The slope is steep between 10 and 60 mmHg of PO2 and flat or plateau between 70 and 90 mmHg Oxygen-haemoglobin dissociation curve ❖ At any given PO2, there are other factors that influence the degree of haemoglobin saturation, these include PCO2, H+ concentration, temperature and 2,3- diphosphoglycerate (DPG) ❖ An increase in any of these factors causes the dissociation curve to shift to the right, meaning at any given PO2, haemoglobin has less affinity for O2 ❖ While a decrease in any of these factors causes the dissociation curve to shift to the left, meaning at any given PO2, haemoglobin has more affinity for O2 Haemoglobin saturation Oxygen-haemoglobin dissociation curve ❖ The effects of increased PCO2,H+ concentration and temperature are continually exerted on the blood in tissue capillaries ❖ CO2 from cellular respiration ❖ H+ concentration from metabolically produced lactic acid ❖ Temperature from metabolically produced heat ❖ The more metabolically active a tissue is the greater the PCO2, H+ concentration and temperature will be Oxygen-haemoglobin dissociation curve ❖ At any given PO2, this causes the haemoglobin to release O2 as the blood pass through the tissue’s capillaries , giving more oxygen to the active tissue ❖ 2,3-DPG produced during glycolysis from erythrocytes allosterically bind with the haemoglobin reducing the O2 affinity ❖ Increased DPG production is associated with inadequate O2 supply conditions , facilitating the O2 release to the tissues from haemoglobin Oxygen-haemoglobin dissociation curve Oxygen-haemoglobin dissociation curve Carbon dioxide transport ❖ Carbon dioxide is transported in the blood in three forms: ❖ Dissolved in plasma (7%) ❖ Chemically bound to haemoglobin: 23% is carried in RBCs as carbaminohaemoglobin ❖ Bicarbonate ion in plasma: 70% is transported as bicarbonate (HCO –) Carbon dioxide transport Thank You