Respiratory Physiology and Pathophysiology

Respiratory Physiology and Pathophysiology

• This presentation covers respiratory physiology and pathophysiology.
• The respiratory system's primary functions include supplying oxygen and eliminating carbon dioxide.
• Other important functions include behavioral processes (talking, laughing, singing), defense mechanisms (humidification, particle expulsion), and secretions (mucus).
• The respiratory tract is divided into two zones: conducting and respiratory zones.
• The conducting zone includes structures like the mouth, nose, pharynx, larynx, trachea, and bronchi. It warms and humidifies inspired air, filters particles, and moves mucus via cilia.
• The respiratory zone includes respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, the primary sites for gas exchange.
• Alveoli are characterized by a large surface area, Type I simple squamous epithelial cells, Type II cells secreting surfactant, and alveolar macrophages.
• Respiration is a process involving ventilation by the lungs (inspiration and expiration), gas exchange across alveolar membranes, diffusion in the alveoli, and the transport of gases in the blood (hemoglobin's role).

Mechanics of Breathing

• Inspiration is an active process involving diaphragm and external intercostal muscle contraction, increasing thoracic volume and lowering pressure, enabling air intake.
• Expiration is mainly a passive process at rest, where the diaphragm relaxes, and elastic recoil of the lungs reduces lung volume, increasing pressure.
• During exercise, expiration can be active.

Surface Tension and Surfactant

• Surface tension arises from forces between water molecules at the air-water interface, contributing to inward recoil force in alveoli, especially in smaller alveoli.
• Pulmonary surfactant reduces surface tension, secreted by Type II alveolar cells, decreasing the work of breathing.

Clinical Application: Respiratory Distress Syndrome of the Newborn

• Developing fetal lungs synthesize surfactant later in pregnancy.
• Premature babies might not have enough surfactant, leading to respiratory distress syndrome.
• Infants may exhibit strenuous inspiratory efforts to overcome high surface tension and inflate their lungs.

Bronchial Asthma

• Bronchial asthma involves spasmodic smooth muscle contraction in smaller bronchi and bronchioles.
• Allergens trigger increased secretions from bronchial mucous glands leading to attacks.
• Mast cells release mediators (e.g., histamine) causing bronchospasm.
• Clinical manifestations include shortness of breath, wheezing respirations, airflow obstruction during expiration, and lung overinflation.
• Asthma treatment involves drugs (e.g., epinephrine, theophylline) relaxing bronchospasms and blocking mediator release.

Summary of Gas Exchange in Lungs and Tissues

• Gas exchange in the lungs and tissues involves the movement of oxygen and carbon dioxide between the alveoli, blood, and tissues.
• Key factors in this process are partial pressures of oxygen (PO2) and carbon dioxide (PCO2), with higher PO2 in the alveoli driving oxygen into the blood and higher PCO2 in the tissues driving CO2 into the blood.

O2 Transport in Blood

• Oxygen is transported in the blood in two forms: physically dissolved in the blood (a small fraction) and chemically bound to hemoglobin (the major portion).
• Hemoglobin contains four subunits, each binding oxygen reversibly, a process termed oxygenation, not oxidation.

CO2 Transport in Blood

• Carbon dioxide is transported in three ways: most as bicarbonate ions (HCO3−), dissolved CO2, and CO2 bound to hemoglobin.

Control of Respiration

• Respiratory centers in the brainstem control the basic rhythm of breathing.
• Breathing is modified by input from sensory receptors and other brain regions.
• Chemoreceptors (central and peripheral) detect changes in arterial PCO2, PO2, and pH, influencing respiration to maintain homeostasis.

Hypoxia

• Hypoxia is a decreased oxygen delivery to tissues. There are multiple types:
• Hypoxic - most common, often associated with high altitudes or lung disease.
• Anemic - reduced hemoglobin or red blood cell count.
• Stagnant - decreased blood flow to tissues (e.g., severe hemorrhage or heart failure).
• Histotoxic - the cells can't use oxygen despite normal delivery (e.g., cyanide poisoning).

Explore the intricacies of respiratory physiology and pathophysiology in this comprehensive quiz. Learn about the functions of the respiratory system, the division into conducting and respiratory zones, and the critical role of alveoli in gas exchange. Test your knowledge on essential concepts such as ventilation, defense mechanisms, and the overall importance of respiratory health.