Anatomy of the Respiratory System

Pleural Fluid

• Lubricates the lungs and chest wall, allowing them to move smoothly during breathing.
• Maintains surface tension, helping to keep the lungs expanded.

Lobes of the Lungs

• The left lung has two lobes: the upper lobe and the lower lobe.
• The right lung has three lobes: the upper lobe, middle lobe, and lower lobe.

Alveolar Cells

• Type I alveolar cells: Primarily responsible for gas exchange, thin and flat.
• Type II alveolar cells: Secrete surfactant, a substance that reduces surface tension in the alveoli and prevents collapse.

Anatomical Feature of the Left Lung

• The heart is located on the left side of the chest, causing a small indentation in the left lung, known as the cardiac notch, contributing to its smaller size.

Alveolar Macrophages

• Immune cells that reside in the alveoli.
• Phagocytose foreign particles, debris, and pathogens, helping to protect the lungs from infection.

Inhalation

• Diaphragm: The primary muscle for inhalation, contracts and flattens, increasing volume in the chest cavity.
• External intercostal muscles: Assist in raising the rib cage, further expanding the thoracic cavity.

Exhalation

• During normal quiet breathing, exhalation is primarily passive.
• The diaphragm and intercostal muscles relax, reducing the volume of the chest cavity, effectively pushing air out of the lungs.

Arterial Occlusion - O2 & CO2 Levels

• Oxygen levels will decrease in tissue cells due to reduced blood flow.
• Carbon dioxide levels will increase as cells continue to produce it and its removal is hindered.

Conducting Zone

• The passageways that conduct air to the respiratory zone.
• This includes the trachea, bronchi, and bronchioles, which warm, humidify, and filter incoming air.

Cough Reflex Trigger

• The carina, the point where the trachea divides into the right and left primary bronchi, is highly sensitive to irritants and initiates the cough reflex.

Beta 2 (β2) Adreno-receptors in Bronchioles

• β2 receptors are located in the smooth muscle walls of the bronchioles.
• They mediate bronchodilation, relaxing the smooth muscle and widening the airway, allowing easier airflow.

Beta 2 Receptor Blockade

• Blocking these receptors has the opposite effect, causing bronchoconstriction and narrowing the airways, making breathing more difficult.

Trachea Structure

• It is a cartilaginous tube with a smooth muscle layer.
• The C-shaped cartilaginous rings provide structural support, preventing the airway from collapsing.

Pleura

• Visceral pleura: The layer directly covering the lung surface.
• Parietal pleura: The layer lining the chest cavity.

Pleural Cavity

• The space between the visceral and parietal pleura.
• It contains a thin layer of pleural fluid that lubricates the lungs and chest wall during breathing.

Bronchial Tree Surgical Removal

• The lobar bronchus is the largest segment of the bronchial tree that can be surgically removed.

Oxygen Function in Tissues

• Oxygen is essential for cellular respiration, a process that produces energy (ATP) for cellular activities.

Partial Pressure of Oxygen in Alveolar Air

• During external respiration, the partial pressure of oxygen (PO2) in the alveolar air is typically around 100 mmHg.

Carbon Dioxide During Internal Respiration

• Carbon dioxide (CO2), a waste product of cellular respiration, diffuses from the tissues into the blood.

Oxygen Usage by Cells at Rest

• Cells at rest typically use about 25% of the available oxygen.

Partial Pressure of CO2 in Deoxygenated Blood

• The typical partial pressure of carbon dioxide (PCO2) in deoxygenated blood within pulmonary capillaries is around 45 mmHg.

Hemoglobin Role in Oxygen Transport

• Hemoglobin, a protein found in red blood cells, binds to oxygen in the lungs and delivers it to the tissues.

Carbon Dioxide Diffusion During External Respiration

• Carbon dioxide diffuses from the blood into the alveoli.

Oxygen Partial Pressure During External Respiration

• The partial pressure of oxygen (PO2) in blood increases during external respiration as it picks up oxygen from the alveoli.

Oxygen Diffusion

• Oxygen flow is driven by its partial pressure gradient; it flows from areas of higher partial pressure to areas of lower partial pressure.

Oxygen in Pulmonary Capillaries

• Oxygen moves from the alveoli into the pulmonary capillaries due to a higher partial pressure in the alveoli.

Oxygen-Hemoglobin Dissociation Curve

• This curve shows the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen.
• It is sigmoidal in shape, indicating that hemoglobin's affinity for oxygen changes with PO2.

Peripheral Chemoreceptors Role

• Located in large arteries, they are sensitive to changes in blood oxygen and carbon dioxide levels.
• They send signals to the respiratory center in the brainstem to adjust breathing rate and depth.

Oxygen Release from Hemoglobin

• Factors that promote the release of oxygen from hemoglobin include decreased PO2, increased PCO2, and increased acidity (lower pH).

Central Chemoreceptors and Elevated CO2

• If carbon dioxide levels are continuously elevated, central chemoreceptors in the brainstem become more sensitive to changes in PCO2, leading to increased ventilation to remove excess carbon dioxide.

CO2 Trap

• This refers to the tendency of carbon dioxide to accumulate in the blood, especially during hypoventilation.

75% Hemoglobin Saturation

• A 75% saturation level of hemoglobin in deoxygenated blood indicates that tissues are actively using oxygen, and the blood is carrying a significant amount of deoxygenated hemoglobin.

Factors Influencing Hemoglobin Affinity for Oxygen

• pH: Lower pH levels (more acidic) reduce hemoglobin's affinity for oxygen.
• Temperature: Increased temperature decreases hemoglobin's affinity for oxygen.
• 2,3-BPG: An organic compound that binds to hemoglobin, reducing its affinity for oxygen, promoting oxygen release to tissues.