Respiratory Physiology Quiz

Introduction to the Respiratory System

• The respiratory system absorbs oxygen and excretes carbon dioxide.
• Its primary function is gas exchange, supplying cells with oxygen and disposing of carbon dioxide from cellular respiration.
• To achieve this, the respiratory and cardiovascular systems work together.
• Respiration is a collective term for four processes, carried out by both systems.

Four Processes of Respiration

• Pulmonary Ventilation (Breathing): The process of moving air into and out of the lungs (inspiration and expiration).
• Pulmonary Gas Exchange: Oxygen diffuses from the lungs into the blood, while carbon dioxide diffuses from the blood into the lungs.
• Transport of Respiratory Gases: The cardiovascular system transports respiratory gases in the blood. Oxygen is transported from the lungs to the tissue cells, and carbon dioxide is transported from the tissue cells to the lungs.
• Tissue Gas Exchange: Oxygen diffuses from the blood to the tissue cells, while carbon dioxide diffuses from the tissue cells to the blood. The cells then use oxygen to produce carbon dioxide.

Major Respiratory Organs and Structures

• Nose: Supported by bone and cartilage; internal nasal cavity, nasal septum, olfactory epithelium.
• Paranasal Sinuses: Mucosa-lined, air-filled cavities in cranial bones, surrounding nasal cavity, function to lighten the skull and warm, moisten, and filter incoming air.
• Pharynx: Passageway connecting the nasal cavity, larynx, and oral cavity, to the esophagus; has three subdivisions (nasopharynx, oropharynx, and laryngopharynx). Houses tonsils (lymphoid tissue masses) for protection against pathogens.
• Larynx: Connects the pharynx to the trachea and prevents food from entering the lower respiratory tract; houses vocal folds (true vocal cords). Includes epiglottis, cartilage, and vocal folds.
• Trachea: Flexible tube connecting the larynx to the bronchial tree; contains C-shaped cartilages.
• Bronchial Tree: A branching system of tubes within the lungs: right and left main bronchi, which subdivide into lobar and segmental bronchi and bronchioles. Bronchioles have smooth muscle, affecting expiration.
• Alveoli: Microscopic air sacs where gas exchange occurs. Walls are thin simple squamous epithelium, and are associated with pulmonary capillaries (an extensive network of tiny blood vessels). Alveolar cells produce surfactant to reduce surface tension, preventing alveolar collapse
• Lungs: Paired composite organs that flank the mediastinum in the thorax. Composed of alveoli and respiratory passageways. Stroma is elastic connective tissue, allowing recoil during expiration.
• Pleurae: Serous membranes; parietal pleura lines the thoracic cavity, and visceral pleura covers the external lung surfaces. Produce lubricating fluid within compartmentalized lungs

Conducting vs. Respiratory Zones

• Conducting Zone: Conduits that transport air. They contain structures that cleanse, warm, and humidify incoming air (nose, nasal cavity, pharynx, larynx, trachea, bronchial tree).
• Respiratory Zone: Sites of gas exchange (alveolar ducts, respiratory bronchioles, and alveoli)

Pressure Relationships in the Thoracic Cavity

• Atmospheric pressure (P_atm): Pressure exerted by air surrounding the body (at sea level, 760 mm Hg).
• Intrapulmonary pressure (P_pul): Pressure within the alveoli, fluctuating during breathing. Equalizes with P_atm at the end of each breath (inspiration and expiration).
  • Inspiration: P_pul < P_atm to suck air into lungs.
  • Expiration: P_pul > P_atm to push air out of lungs.
• Intrapleural Pressure (P_ip): Pressure within the pleural cavity, always negative relative to atmospheric and intrapulmonary pressures. This negative pressure keeps the lungs expanded against the chest wall.

Pulmonary Ventilation

• Inspiration: Active process, requires muscle contraction to enlarge thoracic cavity and lower lung pressure below atmospheric pressure to pull air into the lungs. Primarily involves diaphragm and external intercostal muscles.
• Expiration: A passive process, involves relaxation of inspiratory muscles, elastic recoil of the lungs, and surface tension. Also involves active process of expelling a larger volume of air in deep/forced expiration (e.g., forced exhalation, exercise). These involve more muscles, including abdominal muscles and internal intercostals.

Pulmonary Gas Exchange

• Factors include: partial pressure gradients (O2 and CO2), membrane thickness and surface area.
• Partial pressure gradients promote diffusion of O2 into blood, and CO2 into lungs.
• Thickness is very thin (0.5-1 µm).
• Large surface area due to millions of alveoli.

Tissue Gas Exchange

• Partial pressure gradients dictate diffusion from blood into tissues (O2) and from tissues into blood (CO2).
• Partial pressures reversed compared to pulmonary gas exchange, pushing oxygen from the blood into tissues and pulling CO2 from tissues to blood.

Oxygen Transport

• Oxygen is carried in two ways: dissolved in plasma and loosely bound to hemoglobin.
• Hemoglobin carries 98.5% of oxygen in blood.
• Factors affecting Hb saturation include temperature, pH, partial pressure of carbon dioxide (PCO2), and 2,3-bisphosphoglycerate (BPG) concentration

Carbon Dioxide Transport

• CO2 is transported in three forms: dissolved in plasma, chemically bound to hemoglobin (carbaminohemoglobin), and as bicarbonate ions (HCO3-).

Ventilation-Perfusion Coupling

• Ventilation = amount of air reaching alveoli
• Perfusion= amount of blood flow through pulmonary capillaries.
• Matching required for efficient gas exchange. Controlled by local autoregulation mechanisms (e.g., changes in Po2 or Pco2 affecting arteriolar or bronchiolar diameters).

Respiratory Centers in the Brain Stem

• Control breathing rate and depth.
• Respond to chemical stimuli (O2, CO2, pH) and neural input.
• Include Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG).

Neural and Chemical Influences on Respiratory Centers

• Other receptors and stimuli (emotional stimuli, pain, receptors in muscles and joints). Peripheral and central chemoreceptors detect changes in Po2, Pco2, and pH.

Factors Influencing Breathing Rate and Depth

• Chemical factors: arterial Pco2, Po2, and pH.
• Influence of Po2 is less powerful than Pco2 in influencing breathing rate and depth. pH also affects respiratory rate and depth, though not as directly as CO2.

Test your knowledge on the principles of respiratory physiology, including Boyle's Law, gas exchange, and the mechanics of breathing. This quiz covers the role of pressure changes in the thoracic cavity, as well as oxygen and carbon dioxide transport mechanisms in the body.