Blood pH Regulation and Disorders

Blood pH

• The normal pH of arterial blood is 7.40, with a range of 7.35 to 7.45.
• pH below 7.35 is termed acidosis.
• pH above 7.45 is termed alkalosis.

Carbon Dioxide and Blood pH

• Carbon dioxide, a volatile acid, can be eliminated in exhaled breath and contributes to the blood pH.
• Nonvolatile acids, like lactic acid and ketone bodies, are buffered by bicarbonate.

Respiratory Acidosis

• Hyperventilation causes respiratory alkalosis.
• Hypoventilation causes respiratory acidosis.

Metabolic Acidosis

• Metabolic acidosis stimulates hyperventilation.
• This causes respiratory alkalosis as a partial compensation.

Blood pH Maintenance

• Blood pH is maintained by a proper ratio of carbon dioxide to bicarbonate.

Lung and Kidney Function

• Lungs maintain the correct carbon dioxide concentration.
• Kidneys maintain the free-bicarbonate concentration.

Intrapleural and Intrapulmonary Pressure 

• Intrapulmonary pressure is the pressure inside the lungs.
• Intrapleural pressure is the pressure within the pleural cavity.
• The pleural cavity is the space between the visceral and parietal pleura that surrounds the lungs.
• The pressure difference between these spaces is essential for breathing.

Ventilation

• Inspiration: Air moves into the lungs when atmospheric pressure is greater than the intrapulmonary pressure.
• Expiration: Air moves out of the lungs when intrapulmonary pressure is greater than atmospheric pressure.
• Boyle’s Law: The pressure of a gas is inversely proportional to its volume, thus, changes in the volume of the lungs cause changes in pressure.

Pulmonary Surfactant

• Pulmonary surfactant lowers the surface tension of alveoli.
• This facilitates lung expansion and prevents collapse of alveoli.

Respiratory Distress Syndrome (RDS)

• RDS occurs in premature infants due to lack of surfactant.
• The lungs collapse due to a lack of surface tension.
• RDS can lead to difficulty breathing, cyanosis, and respiratory failure.

Acute Respiratory Distress Syndrome (ARDS)

• ARDS occurs in people with lung injury, often caused by sepsis.
• Inflammation leads to increased capillary permeability, resulting in fluid buildup in the lungs.
• This reduces lung compliance (ability to expand) and surfactant production, further decreasing compliance.

Diseases Associated with Breathing

• Bronchial asthma: This condition causes inflammation and bronchospasm, leading to difficulty breathing, wheezing, and chest tightness.
• Pneumothorax: This occurs when air enters the pleural cavity, causing the lung to collapse.
• Chronic Obstructive Pulmonary Disease (COPD): This encompasses emphysema and chronic bronchitis, characterized by airflow obstruction and damage to the lungs.
• Sleep apnea: This disorder involves repeated interruption of breathing during sleep, leading to fatigue, headaches, and other disturbances.

Dalton’s Law 

• The total pressure of a gas mixture is equal to the sum of the partial pressures of each gas in the mixture. 

Henry’s Law

• The amount of gas that dissolves in a fluid is directly proportional to the partial pressure of that gas in contact with the fluid.

Gas Exchange

• Gas exchange occurs across the respiratory membrane, which consists of the alveolar epithelium and capillary endothelium.
• The transfer of oxygen and carbon dioxide occurs by simple diffusion, following the partial pressure gradients.

Oxygen Transport 

• Oxygen is transported in the blood primarily bound to hemoglobin.
• Hemoglobin saturation (% of binding sites occupied by oxygen) is determined by the partial pressure of oxygen.
• The oxygen-hemoglobin dissociation curve illustrates this relationship.

Bohr Effect

• A decrease in pH or increase in temperature reduces the affinity of hemoglobin for oxygen. This promotes oxygen unloading.
• 2,3-diphosphoglyceric acid (2,3-DPG) also reduces hemoglobin's affinity for oxygen.

Carbon Dioxide Transport

• In the blood, carbon dioxide is transported in three forms: dissolved in plasma, bound to hemoglobin, and as bicarbonate.
• Carbonic anhydrase, an enzyme present in red blood cells, facilitates the conversion of carbon dioxide to bicarbonate.

Regulation of Breathing

• The rhythmicity center in the medulla oblongata controls the basic rhythm of breathing.
• The apneustic and pneumotaxic centers in the pons fine-tune breathing.
• Sensory feedback, chemoreceptors, and baroreceptors, provide input to regulate breathing.
• Voluntary control of breathing can be exerted by the cerebral cortex.

Diseases associated with the Respiratory System

• Emphysema: A condition characterized by destruction of alveolar walls, leading to reduced surface area for gas exchange and difficulty exhaling.
• Chronic Bronchitis: Inflammation and irritation of the bronchi, leading to mucus buildup, coughing, and shortness of breath.
• Cystic Fibrosis: A genetic disorder that causes thick mucus buildup in the lungs, leading to recurrent lung infections and other complications.
• Pneumonia: An infection of the lungs that can cause inflammation and fluid buildup, leading to coughing, fever, and difficulty breathing.
• Tuberculosis: A bacterial infection that primarily affects the lungs, leading to chronic cough, fever, and weight loss.
• Lung Cancer: A malignant tumor that forms in the lungs, often leading to coughing, chest pain, and shortness of breath. The most common cause is smoking.
• Asthma: A condition characterized by inflammation and narrowing of the airways, leading to wheezing, coughing, and shortness of breath.
• Pulmonary Embolism: A blood clot that travels to the lungs and blocks a pulmonary artery, leading to chest pain, shortness of breath, and potentially death.