Human Anatomy: Respiratory Volumes & Capacities

Respiratory Volumes

• Tidal volume (TV) is the amount of air that normally enters the lungs during quiet breathing.
• The average tidal volume is approximately 500 mL.
• Expiratory reserve volume (ERV) is the extra volume of air that can be expired with maximum effort beyond the normal, quiet expiration.
• The average expiratory reserve volume for men is approximately 1100 mL, while for women it is approximately 800 mL.
• Inspiratory reserve volume (IRV) is the extra volume of air that can be inspired with maximal effort after reaching the end of a normal, quiet inspiration.
• The average inspiratory reserve volume is approximately 3000 mL.
• Residual volume (RV) is the volume of air remaining in the lungs after maximal exhalation.
• Residual volume helps prevent the alveoli from collapsing, making breathing easier.

Respiratory Capacities

• Respiratory capacity is the combination of two or more respiratory volumes.
• Total lung capacity (TLC) is the sum of all the lung volumes (TV, ERV, IRV, and RV).
• The average TLC is approximately 6000 mL for men and 4200 mL for women.
• Vital capacity (VC) is the total amount of air exhaled after maximal inhalation.
• VC is the sum of TV, ERV, and IRV.
• The average VC is between 4000-5000 mL.
• Inspiratory capacity (IC) is the maximum amount of air that can be inhaled past a normal tidal expiration.
• IC is the sum of TV and IRV.
• Functional residual capacity (FRC) is the amount of air that remains in the lung after a normal tidal expiration.
• FRC is the sum of ERV and RV.

Pulmonary Function Tests

• Pulmonary function tests measure the volume and flow of air in the lungs.
• Spirometry measures the volume of air that can be inhaled and exhaled.
• Forced vital capacity (FVC) is the volume of air exhaled after maximum inhalation.
• Forced expiratory volume (FEV) is the volume of air exhaled in one breath.
• Forced expiratory flow is the rate of air flow during exhalation.
• Peak expiratory flow (PEF) is the fastest rate of exhalation.
• Maximum voluntary ventilation (MVV) is the volume of air that can be inspired and expired in one minute.
• Slow vital capacity (SVC) is the volume of air that can be slowly exhaled after inhaling past the tidal volume.
• Total lung capacity (TLC) is the volume of air in the lungs after maximum inhalation.
• Functional residual capacity (FRC) is the volume of air left in the lungs after normal expiration.
• Residual volume (RV) is the volume of air in the lungs after maximum exhalation.
• Blood gas analyzers measure the concentration of oxygen and carbon dioxide in the blood.

Dead Space

• Dead space is the volume of ventilated air that does not participate in gas exchange.
• Anatomical dead space is the volume of air that fills the conducting zone of respiration (nose, trachea, bronchi).
• Anatomical dead space is approximately 30% of normal tidal volume, or 150 mL.
• Physiologic dead space is the sum of anatomical dead space and alveolar dead space.
• Alveolar dead space is the volume of air in the respiratory zone that does not take part in gas exchange.
• In a healthy adult, alveolar dead space is negligible.

Respiratory Rate and Control of Ventilation

• The respiratory rate (RR) is the number of breaths per minute.
• The normal RR in adults is 12 to 20 breaths per minute.
• The respiratory rate is controlled by the respiratory center in the medulla oblongata of the brain.
• The respiratory center responds primarily to changes in carbon dioxide, oxygen, and pH levels in the blood.

Ventilation Control Centers

• The control of ventilation is a complex process involving multiple regions in the brain.
• The medullary respiratory center sets the basic rhythm of breathing.
• The ventral respiratory group (VRG) generates the breathing rhythm and integrates data coming into the medulla.
• The dorsal respiratory group (DRG) integrates input from stretch receptors and chemoreceptors in the periphery.
• The pontine respiratory group (PRG) modifies the medulla oblongata's functions, including the pneumotaxic and apneustic centers.
• The aortic body monitors blood PCO2, PO2, and pH.
• The carotid body monitors blood PCO2, PO2, and pH.
• The hypothalamus monitors emotional state and body temperature.
• Cortical areas of the brain control voluntary breathing.
• Proprioceptors send impulses regarding joint and muscle movements.
• Pulmonary irritant reflexes protect the respiratory zones of the system from foreign material.
• The inflation reflex protects the lungs from over-inflating.

Respiratory Centers of the Brain

• Neurons that innervate the muscles of the respiratory system control and regulate pulmonary ventilation.
• The major brain centers involved in pulmonary ventilation are the medulla oblongata and the pontine respiratory group.
• The medulla oblongata contains the dorsal respiratory group (DRG) and the ventral respiratory group (VRG).
• The DRG maintains a constant breathing rhythm by stimulating the diaphragm and intercostal muscles to contract, resulting in inspiration.
• The VRG is involved in forced breathing by stimulating the accessory muscles involved in forced breathing to contract, resulting in forced inspiration.
• The pontine respiratory group, located within the pons, consists of the apneustic and pneumotaxic centers.
• The apneustic center stimulates neurons in the DRG, controlling the depth of inspiration, especially during deep breathing.
• The pneumotaxic center inhibits the activity of neurons in the DRG, allowing relaxation after inspiration, and thus controlling the overall rate of breathing.

Factors Affecting Respiratory Rate and Depth

• Multiple systemic factors stimulate the brain to produce pulmonary ventilation.
• The major factor stimulating the medulla oblongata and pons is the concentration of carbon dioxide (CO2) in the blood.
• Increased CO2 levels result in increased H+ levels, decreased pH and stimulate central chemoreceptors in the brain and brainstem.
• Peripheral chemoreceptors, located in the carotid arteries and aortic arch, also sense changes in CO2 and H+ levels.
• Systemic arterial concentrations of H+ influence respiratory activity.
• Peripheral chemoreceptors sense acidic pH levels and stimulate increased ventilation to remove CO2 and increase pH.
• Blood O2 levels affect respiratory rate, but only large changes in blood O2 levels stimulate peripheral chemoreceptors.
• The hypothalamus and limbic system regulate breathing in response to emotions, pain, and temperature.

This quiz covers key concepts related to respiratory volumes and capacities, such as tidal volume, expiratory and inspiratory reserve volumes, and residual volume. Understand the significance of these measurements in human anatomy and how they aid in efficient breathing.