Lecture Notes: Cardiovascular and Respiratory Systems

Heart Orientation and Lung Anatomy

• 2/3 of the heart is oriented to the left of the midsternal line.
• The apex projects into the left lung's cardiac notch.
• Occupies space that could have been a third lobe in the left lung.
• Left lung has only two lobes and is smaller than the right lung.

Dalton's Law and Atmospheric Gases

• Atmospheric air is a mixture of gases with total pressure as the sum of partial pressures.
• Oxygen: 21% of atmospheric air, partial pressure = 21% of total.
• Nitrogen: 78% of atmospheric air, partial pressure = 78% of total.
• Carbon Dioxide: 1% completes the 100% of atmospheric air.

Pulmonary Ventilation

• Inspiration (active): Diaphragm contracts, external intercostal muscles elevate rib cage, increasing thoracic cavity volume.
  • Volume increase leads to a decrease in lung pressure, drawing air in.
• Expiration (passive): Diaphragm and external intercostal muscles relax, decreasing thoracic cavity volume.
  • Volume decrease increases lung pressure, expelling air out.
• Forced Expiration: Internal intercostal and abdominal muscles contract, further decreasing cavity volume and increasing lung pressure.

Types of Respiration

• External Respiration: Gas exchange between alveoli and pulmonary blood.
  • Driven by partial pressure differences.
  • Oxygen diffuses from alveoli to blood; carbon dioxide moves from blood to alveoli.
• Internal Respiration: Gas exchange between systemic capillaries and body tissues.
  • Oxygen diffuses from blood to tissues; carbon dioxide moves from tissues to blood.

Chemoreceptor Sensitivity and Breathing Regulation

• Chemoreceptors respond more to high carbon dioxide levels than low oxygen levels.
• High CO2 levels form carbonic acid, lowering blood pH, triggering increased breathing (hyperventilation).
• Hyperventilation: Excessive breathing reduces CO2, raises blood pH (respiratory alkalosis).
• Hypoventilation: Insufficient breathing increases CO2, lowers blood pH (respiratory acidosis).

Spirometry and Lung Volumes

• Tidal Volume (TV): Normal air breathed in/out (~500 mL).
• Inspiratory Reserve Volume (IRV): Additional air inhaled forcefully (~3000 mL).
• Expiratory Reserve Volume (ERV): Additional air exhaled forcefully (~1000 mL).
• Vital Capacity (VC): Total air expelled after maximum inhalation (TV + IRV + ERV ≈ 5000 mL).
• Residual Volume (RV): Air remaining post-ERV (~1200 mL).
• Total Lung Capacity (TLC): VC + RV.

Respiratory Control Centers and Breathing Regulation

• Located in the pons and medulla.
• Respond to changes in oxygen, carbon dioxide, blood pH.
• Eupnea: Normal breathing pattern.
• Apnea: Cessation of breathing, may lead to respiratory arrest.

Summary

• Breathing is regulated more by CO2 levels than oxygen.
• Various lung volumes and capacities regulate how much air is exchanged during different activities.
• The body's respiratory control centers adjust the rate and depth of breathing to maintain homeostasis.