Gas Exchange and Transport Chapter 18 Gas Exchange and Transport

About this Chapter Getting CO2 & O2 dissolved for transport How oxygen is transported, role of hemoglobin How carbon dioxide is transported Regulators that sense and coordinate respiration with circulation for gas transport

Overview of Respiratory Exchange Figure 18-1: Overview of oxygen and exchange and Transport CO2

Figure 18-2: Gases in solution Solubility of Gasses Pressure gradient: lower at high altitudes Temperature: constant in warm blooded humans Solubility (solute & solvent): O2 or CO2 in water Figure 18-2: Gases in solution

Gas Exchange in the Lungs and Tissues: Oxygen Diffusion through alveolar thin cells Down diffusion gradient Higher in alveoli Lower in blood Diffusion from blood Also down gradient To ECF To tissue cells (convert O2 to CO2)

Gas Exchange in the Lungs and Tissues: Oxygen Figure 18-3a: Gas exchange at the alveoli and cells

Gas Exchange in the Lungs and Tissues: Carbon Dioxide Diffusion out of cells (down diffusion gradient) Into blood Buffer role Conversions: Plasma Bicarbonate On Hb Into alveolus & expiration

Gas Exchange in the Lungs and Tissues: Carbon Dioxide Figure 18-3b: Gas exchange at the alveoli and cells

Movement of Gases in Body

Alveolar Exchange and Diseases Related to Exchange Wet surface Thin epithelia Little ECF Diseases: Emphysema Fibrotic Lung Pulmonary edema Asthma

Alveolar Exchange and Diseases Related to Exchange Figure 18-5: Oxygen diffuses across the alveolar and endothelial cells to enter the plasma

Diseases of the Lung Figure 18-4: Pulmonary pathologies that affect alveolarventilation and gas exchange

Gas Transport in the Blood: Oxygen 2% in plasma 98% in hemoglobin (Hb) Blood holds O2 reserve Figure 18-6: Summary of oxygen transport in the blood

Gas Transport in the Blood: Oxygen Figure 18-7 : The role of hemoglobin in oxygen transport

Hemoglobin Transport of Oxygen: Disassociation Curve 4 binding sites per Hb molecule 98% saturated in alveolar arteries Resting cell PO2 = 40 mmHg Working cell PO2 = 20 mmHg More unloaded with more need 75% in reserve at normal activity

Hemoglobin Transport of Oxygen: Disassociation Curve Figure 18-8: Oxygen-hemoglobin dissociation curve

Factors that Modify Hb Transport of Oxygen Bohr effect: pH  causes  O2 binding -releasing it  2,3 DPG decreases O2 binding to hemoglobin (response to high altitude)  PCO2 decreases O2 binding–releasing it (Temperature affects the curve but doesn't vary in humans)

Factors that Modify Hb Transport of Oxygen Figure 18-9: Physical factors alter oxygen binding to hemoglobin

Summary of Oxygen Transport How many of these choices are likely to be variable? Figure 18-12: Factors contributing to the total oxygen content of arterial blood

Gas Transport in the Blood: Carbon Dioxide Excess CO2 in blood (Hypercapnia) Leading to: acidosis, CNS depression & coma 7% in plasma, 23% bound to Hb 70% as HCO3- acts as a buffer [H+]

Gas Transport in the Blood: Carbon Dioxide Figure 18-13: Carbon dioxide transport in the blood

Review of Respiratory Exchange & Transport Figure 18-14: Summary of gas transport

Movement of Gases in Body

Regulation of Ventilation: Central pattern generator Integrates input from cortex, limbic & chemoreceptors Rhythmic contractions of ventilation

Regulation of Ventilation: Central pattern generator Figure 18-15: Reflex control of ventilation

Regulation of Ventilation: Pons Center Dorsal respiratory group – inspiration Ventral respiratory group – forced breathing

Regulation of Ventilation: Pons Center Figure 18-16: Rhythmic breathing

Regulation of Ventilation: Chemoreceptors Carotid & aortic bodies: O2, CO2 & H+ receptors Medullary CO2 receptor Low [O2], high [CO2] & low pH  ventilation Figure 18-17: Carotid body oxygen sensor releases neurotransmitter when decreases PO2

Regulation of Ventilation: Chemoreceptors Figure 18-18: Central chemoreceptor monitors in cerebrospinal fluid

Summary of Regulatory Ventilation Reflexes Figure 18-19: Chemoreceptor response to increased PCO2

Protective Reflexes Bronchoconstriction Irritant receptors Toxic particles Irritating particles (i.e. pollen) Hering-Breuer Reflex prevents over inflation via the activation of stretch receptors (present in smooth muscle of the airways) Unconscious reflexes take over voluntary breathing

Summary Oxygen is transported bound to Hb and this is affected by temperature, pH, CO2 , and DPG Carbon dioxide is transported in plasma, bound to Hb and acts as the buffer bicarbonate Respiration is regulated by CNS central pattern generator, pons center and peripheral carotid and aortic receptors Feedback reflexes coordinate circulation and ventilation to maintain blood O2, CO2, and H+ concentrations