Gas Exchange And Transport

A state of too little oxygen - occurs if the diffusion of gases between the alveoli and blood is impaired or oxygen is inadequate.

State of excess CO2 in the blood.

1. Hypoxic - low arterial PO2

2. Anemic - Decreased total O2 bound to Hemoglobin

3. Ichemic - Reduced blood flow

4. Histotoxic - Failure of cells to use oxygen due to poisoning

Body avoids hypoxia through arterial blodo composition sensors:

1. Oxygen sensors

2. CO2 sensors

3. pH sensors

High levels depress the CNA and induce acidosis via the production of HCO3-:

CO2 + H2O <> H2CO2 <> H+ + HCO3-

prevent denaturation of proteins.

1. Amount of O2 reaching the alveoli

2. Gas diffusion between alveoli and blood

3. Adequate perfusion of alveoli

1. Composition of the inspired air

2. Alveolal ventilation

1. Lung compliance

2. Airway resistance

3. Rate and depth of breathing

1. Surface area

2. Diffusion distance

1. Barrier thickness

2. Amount of fluid

Distance of diffusion.

Diffusion is inversely proportional to Surface Area times by barrier permeability, divided by distance squared

D ¬ SA * BP/Di^2

0.1 - 1.5 micrometers (um)

1. Emphysema

2. Fibrotic lung disease

3. Pulmonary Edema

4. Asthma

Causes alveolar destruction which decreases the surface area available for gas exchange.

Causes a thickened alveolar membrane and a loss of lung compliance. This increases the distance for diffsion and lowers alveolar ventilation by causing less oxygen to reach the lungs.

Causes a build up of fluid in the interstitial space which greatly increases the diffusion distance AND pCO2 increases as it dissolves in the interstitial fluid - unlike O2

Because it has a very low water solubility and so is not carried in the plasma.

Arterial O2 transport - Venous O2 transport = QO2

O2 transport = cardiac output (CO) * Oxygen concentration

The Fick equation determines the rate at which a person uses oxygen in their body. It is a combination of the mass flow and mass balance equations: QO2 = Cardiac Output * (arterial [O2] - venous [O2])

200ml / O2 / L of blood.

2,3 Bisphosphoglycerate - produced by erythrocytes - lowers oxygen binding affinity

1. CO2 diffuses out of cells into the blood - some dissolves in the blood.

2. About a quarter of the blood binds to hemoglobin to form carbaminohemoglobin

3. Most of the CO2 is converted to bicarbonate (HCO3-) and H+ - Hemoglobin buffers the H+ (HbH)

4. HCO3- enters the plasma in exchange for Cl-

5. CO2 dissolved in plasma diffuses into lungs

6. CO2 unbinds from Hemoglobin by law of mass action

7. Carbonic acid reenters the cell in exchange for Cl-.

8 Carbonic acid combines with protons from HbH forming H2CO3.

9. H2CO3 breaks apart to form H2O and CO2 which then diffuse into the lungs.

The medulla oblongata

1. Medullary chemoreceptors in the brain

2. Carotid and aortic chemoreceptors via afferent sensory neurons.

Higher brain centres and the limbic system affect the medulla oblongata & pons.

Somatic motor neuron excitation of inspiration and expiration muscles.

A positive feedback loop which ceases when fully respired.

1. Detect low pO2 which closes K+ channels

2. Depolarises cell

3. Voltage gated Ca2+ channel opens

4. Neurotransmitter release

High CO2 and H+ concentrations - (pH)