Respiratory System Quiz

Physiology of the Respiratory System

• The respiratory system's function is to supply the body's cells with oxygen (O2) and remove carbon dioxide (CO2) produced by cellular activities.
• The respiratory system consists of respiratory passages, including the nose, pharynx, larynx, trachea, bronchi, bronchioles, and an area for gas exchange containing alveoli.

Types of Respiration

• External Respiration: The inhalation of O2 and removal of CO2. This process occurs in the lungs.
• Internal Respiration: The utilization of O2 and the production of CO2 by cells, also known as cellular respiration. This happens throughout the body's tissues.

External Respiration Detail

• Divided into four main parts:
  • Pulmonary Ventilation: The inflow and outflow of air between the atmosphere and lung alveoli, and distribution of air in the lungs. It happens through breathing movements and controlled by respiratory centers in the brain stem.
  • Pulmonary Perfusion: The distribution of blood through the lungs. The normal blood volume is 5 liters per minute, equal to the cardiac output of the right ventricle.
  • Diffusion of Gases: The exchange of oxygen (O2) and carbon dioxide (CO2) between the air in the alveoli and blood in the pulmonary capillaries. This is a passive process driven by pressure gradients.
  • Gas Transport: The transport of O2 from the lungs to tissues and CO2 from tissues to the lungs in the blood.

Respiratory Airways

• The airways are branching tubes that become narrower, shorter, and more numerous as they enter the lungs.
• Functionally divided into conducting and respiratory zones.
• Conducting Zone: Contains the passageways that conduct air to the gas exchange sites, including the trachea, bronchi, and bronchioles. This area helps with air conduction, conditioning, humidification, immunity, filtration, and phonation (sound production).
• Respiratory Zone: This area, encompassing respiratory bronchioles, alveolar ducts, alveoli sacs, and alveoli, is the actual site of gas exchange.

Mechanism of Breathing

• Inspiration: An active process involving the diaphragm moving downward and the external intercostal muscles elevating the ribs, expanding the chest cavity, and drawing air into the lungs.
• Expiration: A passive process where the diaphragm relaxes, the ribs return to their resting position, and the elastic recoil of the lungs forces air out.
• Tidal Volume (TV): The volume of air inhaled or exhaled in a normal breathing cycle.

Intra-pleural Pressure

• The pressure within the pleural space (between the lungs and chest wall).
• It is negative, meaning it is less than atmospheric pressure, and this causes the lungs to expand along with the chest wall.
• Negative pressure is maintained due to the lack of air in the pleural cavity, elastic recoil of the lungs, surface tension of fluid lining the alveoli, and elastic properties of the chest wall.
• Important for lung expansion, negative intrathoracic pressure (enabling venous return), and overall mechanics of breathing.

Minute Respiratory Volume

• The volume of air breathed in per minute, calculated by multiplying tidal volume and respiratory rate.
• Normal values are in the 6 liter/minute range.
• Note: Respiratory rates vary by age.

Surfactant

• Definition: A surface tension-lowering agent produced by Type II alveolar epithelial cells that decreases the surface tension in the fluid lining the alveoli.
• It keeps the alveoli dry and prevents them from collapsing during expiration. This reduces the work of breathing.
• Factors that affect its formation:
  • Stimulatory: Thyroid hormones and glucocorticoids
  • Inhibitory: Smoking, insulin, long-term pure O2 inhalation, and prolonged pulmonary circulation stoppage.
• Deficiency can lead to:
  • Adults: Increased work of breathing
  • Preterm infants: Respiratory distress syndrome

Gas Exchange and Transport

• External Gas Transfer at Lungs: Exchange of (02 and CO2) between the air in alveoli and blood in pulmonary capillaries (an example of diffusion).
  • Factors affecting gas exchange rate: thickness of respiratory membrane (inversely proportional), surface area of respiratory membrane (directly proportional), pressure gradient (directly proportional), solubility of gases in respiratory membrane (directly proportional), and molecular weight (inversely proportional).
• Gas Transport
  • Oxygen Transport: About 3% dissolved in plasma, the remaining 97% bound to hemoglobin in red blood cells, which carries a total of 4 oxygen molecules per Hb molecule.
  • Carbon Dioxide Transport: Mostly (95%) as bicarbonate in the blood. A smaller portion (5%) is bound to hemoglobin and/or dissolved in plasma.

Hypoxia and Cyanosis

• Hypoxia: Oxygen deficiency at the tissue level.
  • Types of Hypoxia: Hypoxic, anemic, stagnant, and histotoxic. Specific causes of each subtype are discussed throughout the notes.
• Cyanosis: Bluish discoloration of the skin and mucous membranes. Occurs when the amount of reduced hemoglobin (deoxygenated blood) in the blood is above 5 grams/100mL of blood.