Chapter 15 – The Respiratory System (Essentials of Anatomy & Physiology, 8th Ed.)

Respiratory System – Key Functions

• Works with cardiovascular system
• Supplies $O<em>2$, removes $CO</em>2$
• Enables speech, smell, taste
• Helps maintain acid–base balance

Upper Respiratory Tract (URT)

• Nose & nasal cavities: warm, moisten, filter air; olfactory receptors
• Conchae ↑ mucosal surface area
• Paranasal sinuses (frontal, sphenoid, ethmoid, maxillary): lighten skull, voice resonance
• Pharynx:
  • Nasopharynx – air only; connects to eustachian tubes
  • Oropharynx – air & food; palatine tonsils
  • Laryngopharynx – opens to larynx (front) & esophagus (back)
• Larynx (voice box): 9 cartilages (thyroid largest, epiglottis uppermost); vocal cords flank glottis

Lower Respiratory Tract (LRT)

• Trachea: 4–5 in, $16!–!20$ C-shaped cartilage rings; ciliated mucosa
• Bronchial tree:
  • Primary bronchi → secondary → tertiary bronchi → bronchioles → alveolar ducts → alveoli
• Lungs:
  • Right: 3 lobes, horizontal & oblique fissures
  • Left: 2 lobes, oblique fissure
  • Hilus: entry of primary bronchus, pulmonary vessels
• Pleurae: parietal (thoracic wall), visceral (lung surface); serous fluid ↓ friction
• Alveoli: type I cells (gas exchange), type II cells (pulmonary surfactant); elastic CT maintains recoil

Ventilation (Breathing)

• Driven by pressure gradients
  • Atmospheric pressure ($P_{atm}$)
  • Intrapleural pressure < P_{atm}
  • Intrapulmonic (alveolar) pressure varies with breathing
• Inspiration:
  • Medulla → phrenic nerve (diaphragm) & intercostal nerves (external intercostals)
  • Diaphragm ↓, ribs ↑/out → $P<em>{intra\,pulm} < P</em>{atm}$ → air in
• Expiration (passive): muscles relax, elastic recoil ↑ $P_{intra\,pulm}$ → air out

Pulmonary Volumes (approx.)

• Tidal volume $\approx 500\,\text{mL}$
• Inspiratory reserve $\approx 2000!–!3000\,\text{mL}$
• Expiratory reserve $\approx 1000!–!1500\,\text{mL}$
• Vital capacity = TV + IRV + ERV
• Forced expiratory volume ↓ in COPD (e.g., emphysema)
• Dead space: anatomic (airways) vs physiological (non-functional alveoli)

Gas Exchange

• External respiration (alveoli ↔ pulmonary capillaries)
  • $P<em>{O</em>2}$ high in alveoli → $O_2$ into blood
  • $P<em>{CO</em>2}$ high in blood → $CO_2$ into alveoli
• Internal respiration (systemic capillaries ↔ tissues)
  • Reverse gradients drive diffusion

Gas Transport

• $O_2$: ~98% bound to hemoglobin (Hb); requires iron
  • Hb–$O<em>2$ affinity ↓ with ↑ $P</em>{CO<em>2}$, ↓ pH, ↑ T → more $O</em>2$ released
• $CO_2$:
  • ~20% as carbaminohemoglobin
  • Majority as $HCO_3^-$ in plasma (via carbonic anhydrase)

Regulation of Respiration

• Nervous control
  • Medulla: basic rhythm & motor output; stretch receptors limit inflation
  • Pons: apneustic (prolongs insp.) & pneumotaxic (promotes exp.) centers
  • Cortex: voluntary control (speech, breath-holding)
• Chemical control
  • Chemoreceptors (medulla, carotid, aorta) monitor $P<em>{CO</em>2}$, $P<em>{O</em>2}$, pH
  • Hypoxia ↑ rate & depth; hypercapnia ↑ ventilation to blow off $CO_2$
• Protective reflexes: cough, sneeze, hiccup

Acid–Base & ABGs

• Normal arterial ranges: $pH\,7.35!–!7.45$, $P<em>{O</em>2}\,85!–!100\,\text{mmHg}$, $P<em>{CO</em>2}\,35!–!45\,\text{mmHg}$, $HCO_3^-\,22!–!26\,\text{mEq/L}$
• ROME mnemonic: Respiratory—Opposite (pH ↑, $P<em>{CO</em>2}$ ↓ = alkalosis); Metabolic—Equal (pH ↑, $HCO_3^-$ ↑ = alkalosis)

Breathing Patterns & Terms

• Dyspnea: difficult breathing
• Apnea: cessation
• Tachypnea: rapid rate
• Hyperventilation vs hypoventilation: ↑ vs ↓ rate & depth
• Orthopnea: difficulty lying flat
• Biot’s, Cheyne–Stokes, Kussmaul: abnormal patterns

Common Respiratory Disorders (high-yield)

• Emphysema (COPD): alveolar wall destruction, air trapping, barrel chest
• Asthma: inflammatory bronchoconstriction → wheeze, dyspnea; triggers allergens/infection
• Pneumonia: infection of lung tissue (viral, bacterial, etc.); mucus/pus blocks diffusion; ↓ compliance

Key Clinical Values

• Normal respirations: $12!–!20\,\text{breaths/min}$
• $SpO_2$ norm ≈ $97\%$
• Diseases lowering lung compliance: pneumonia, emphysema, tuberculosis