Chapter 18Chapter 18

Dee Unglaub Silverthorn, Ph.D.

H ^UMAN P ^HYSIOLOGY H ^UMAN P ^HYSIOLOGY

PowerPoint

Lecture Slide Presentation by

Dr. Howard D. Booth, Professor of Biology, Eastern Michigan University

AN INTEGRATED APPROACH

T H I R D E D I T I O N

Chapter 18 Chapter 18

Gas Exchange and Transport

About this Chapter About this Chapter

• Getting CO 2 & O 2 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 Overview of Respiratory Exchange

Figure 18-1: Overview of oxygen and exchange and Transport CO

• Pressure gradient: lower at high altitudes

• Temperature: constant in warm blooded humans

• Solubility (solute & solvent): O 2 or CO 2 in water

Solubility of Gasses

Solubility of Gasses

Gas Exchange in the Lungs and Tissues: Oxygen 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 (O 2 utilized--CO 2

produced)

Gas Exchange in the Lungs and Tissues: Oxygen 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

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

Gas Exchange in the Lungs and Tissues:

Carbon Dioxide

Movement of Gases in Body

Movement of Gases in Body

Alveolar Exchange and Diseases Related to Exchange

Alveolar Exchange and Diseases Related to Exchange

• Wet surface

• Thin epithelia

• Little ECF

• Diseases:

• Emphysema

• Fibrotic Lung

• Pulmonary edema

• Asthma

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Alveolar Exchange and Diseases Related to Exchange

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 Diseases of the Lung

Figure 18-4: Pulmonary pathologies that affect alveolarventilation and gas exchange

Gas Transport in the Blood: Oxygen Gas Transport in the Blood: Oxygen

• 2% in plasma

• 98% in

hemoglobin (Hb)

• Blood holds O 2

reserve

Gas Transport in the Blood: Oxygen Gas Transport in the Blood: Oxygen

Figure 18-7 : The role of hemoglobin in oxygen transport

Hemoglobin Transport of Oxygen:

Disassociation Curve

Hemoglobin Transport of Oxygen:

Disassociation Curve

• 4 binding sites per Hb molecule

• 98% saturated in alveolar arteries

• Resting cell P O2 = 40 mmHg

• Working cell P _O2 = 20 mmHg

• More unloaded with more need

• 75% in reserve at normal activity

Hemoglobin Transport of Oxygen:

Disassociation Curve

Hemoglobin Transport of Oxygen:

Disassociation Curve

• Bohr effect: pH  causes  O ₂ binding -releasing it

•  2,3 DPG decreases O ₂ binding to

hemoglobin (response to high altitude)

•  P _CO2 decreases O ₂ binding–releasing it

• (Temperature affects the curve but doesn't vary in humans)

Factors that Modify Hb Transport of Oxygen

Factors that Modify Hb Transport of Oxygen

Factors that Modify Hb Transport of Oxygen

Factors that Modify Hb Transport of Oxygen

• How many of these choices are likely to be variable?

Summary of Oxygen Transport Summary of Oxygen Transport

Figure 18-12: Factors contributing to the total oxygen content of arterial blood

• Excess CO ₂ in blood (Hypercapnia)

• Leading to: acidosis, CNS depression &

coma

• 7% in plasma, 23% bound to Hb

• 70% as HCO 3- acts as a buffer [H ⁺ ]

Gas Transport in the Blood: Carbon Dioxide

Gas Transport in the Blood: Carbon Dioxide

Gas Transport in the Blood: Carbon Dioxide Gas Transport in the Blood: Carbon Dioxide

Figure 18-13: Carbon dioxide transport in the blood

Review of Respiratory Exchange & Transport

Review of Respiratory Exchange & Transport

Regulation of Ventilation: Central pattern generator Regulation of Ventilation: Central pattern generator

• Integrates input from cortex, limbic &

chemoreceptors

• Rhythmic contractions of ventilation

Regulation of Ventilation: Central pattern generator

Regulation of Ventilation: Central pattern generator

Regulation of Ventilation: Pons Center Regulation of Ventilation: Pons Center

Figure 18-16: Rhythmic breathing

• Carotid & aortic

bodies: O ₂ , CO ₂ & H ⁺ receptors

• Medullary CO 2 receptor

• Low [O 2 ], high [CO 2 ]

& low pH  ventilation

Regulation of Ventilation: Chemoreceptors Regulation of Ventilation: Chemoreceptors

Figure 18-17: Carotid body oxygen sensor releases neurotransmitter when decreases PO2

Regulation of Ventilation: Chemoreceptors Regulation of Ventilation: Chemoreceptors

Figure 18-18: Central chemoreceptor monitors in cerebrospinal fluid

Summary of Regulatory Ventilation Reflexes Summary of Regulatory Ventilation Reflexes

Figure 18-19: Chemoreceptor response to increased PCO2

Protective Reflexes 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

What’s the difference between hypoxia, hypoxemia and ischemia?

What’s the difference between hypoxia, hypoxemia and ischemia? _• Hypoxia is lack of oxygen to a tissue from any

cause. 

• Hypoxemia can be defined as a condition where arterial oxygen tension or partial pressure of

oxygen (PaO2) is below normal (normal value is between 80 and 100 mmHg). On the other

hand, hypoxia is defined as the reduction of oxygen supply at the tissue level, which is not measured

directly by a laboratory value.

• Ischemia is the decrease of blood supply to a

tissue. It can be local, caused locally by a thrombus or embolus, or global due to a low perfusion

pressure. Can you think of a situation in which there might be hypoxia without ischemia? There

could be a reduced oxygen carrying capacity of the

blood due to carbon monoxide or anemia or even a

Summary Summary

• Oxygen is transported bound to Hb and this is affected by temperature, pH, CO ₂ , 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 O 2 , CO 2 ,