FSG120 Respiratory System Lecture Three 2024 PDF
Document Details
Uploaded by YouthfulSunflower
University of Pretoria
2024
Dr. M Gamede
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Summary
This document is a lecture on the respiratory system, focusing on the transport of oxygen and carbon dioxide. It details the processes involved and the role of haemoglobin. Learning objectives are outlined, and the document includes diagrams and figures related to the topic.
Full Transcript
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