Respiratory System Explained

• Chapter 23 is about the Respiratory System

Function of the Respiratory System

• Puts O2 in, and removes CO2

Collective Processes of Respiration (Resp)

• Pulmonary ventilation: Governs the intake and output of gas in the lungs
• External respiration: Manages the exchange of gas between the lungs and blood
• Gas transport: This is between the lungs and tissues, via blood vessels
• Internal respiration: Governs gas exchange between tissue and blood

Respiratory Zone

• This is the site of gas exchange
• Alveoli are structures in this zone

Conducting Zone

• Rigid conduits allow air to reach lungs

Nasal Cavity

• Vibrissae are nose hairs

Boundaries of the Nasal Cavity

• Roof: Sphenoid and ethmoid
• Floor: Maxilla, palatine, and palate

Conchae

• These protrude medially
• Their function is to increase surface area

Mucosal Linings

• Olfactory mucosa lies on the superior nasal conchae
• Respiratory mucosa: The surface of conchae with mucus that contains defenses, lysozymes to destroy bacteria
  • Irritation here leads to a sneeze

Functions of Conchae and Mucosa

• These filter/warm/moisten the air

Paranasal Sinuses

• These sinuses are spaces in bones surrounding the nasal cavity
• Bones include frontal, sphenoid, ethmoid, and maxillary

Functions of Paranasal Sinuses

• Lighten the skull
• Warm and moisten air

Vocal Folds

• The larynx is positioned above the vocal folds

Trachea

• Rigid conduits allow air to reach lungs
• The trachea contains cartilage rings

Bronchi and Bronchioles

• Carina is the most inferior section of the trachea cartilage, highly embedded with nerves
• Primary bronchi: One on the left and one on the right
• Secondary bronchi: Two on the left, three on the right

Bronchioles

• Have cuboidal ET and complete layer of smooth muscle but no cartilage
• Pulmonary arteries supply oxygenation to the lungs
• Bronchial arteries provide nourishment to lung tissue

Respiratory Zone

• Order of flow: Terminal bronchiole to respiratory bronchiole, to alveolar duct

Respiratory Membrane

• Air-blood barrier: Fused walls of alveoli & capillaries
• Alveolar walls
  • Type 1 cells Simp squamous ET
  • Permit gas exchange through simple diffusion
• Surfactant: Type II cells are scattered in alveoli to keep them open
  • Features: Smooth muscle, elastic fibers, alveolar pores, and macrophages

Pleural Cavity

• Parietal pleura and visceral pleura

Muscles of Respiration

• Sternocleidomastoid, scalenes, pectoralis minor, external intercostals, and diaphragm
• Abdominal muscles and internal intercostals assist in expiration

Pressure Relationships

• Atmospheric pressure (Patm) is 760 mm Hg at sea level
  • Respiratory pressures are relative to Patm
  • Negative respiratory pressure < Patm
  • Positive respiratory pressure > Patm
  • Zero respiratory pressure = Patm
• Intrapulmonary pressure: Pressure in alveoli, fluctuates with breathing, always eventually equalizes with Patm

Forces Acting on Lungs

• Forces promoting lung collapse: Elasticity of lungs and surface tension of alveolar
• Forces promoting lung expansion: Elasticity of chest wall and low intrapleural pressure
• Pressure in pleural space < pressure in lungs which acts like a vacuum
• Hemothorax is blood in the lung cavity
• Pneumothorax means collapsed lung
  • Also known as Atelectasis
  • Pressure differential is removed

Physical Principles of Gas Exchange

• Dalton’s law: Total pressure = sum of pressures of each gas
• Henry’s Law: Concentration of gas in liquid is determined by its partial pressure and solubility
• Diffusion of gases through respiratory membrane
  • Depends on membrane thickness; the thicker it is, the lower the diffusion rate
• Diffusion coefficient of gas measures how easily a gas diffuses through a liquid or tissue
• Surface area in the lungs: Alveolar SA = 40m^2
• Partial pressure differences: Partial pressure of oxygen is higher in alveoli than in blood
  • It's usually true that the partial pressure of carbon dioxide is opposite
  • Partial Pressure O2 increases in alveoli and decreases in blood
  • Partial Pressure CO2 decreases in alveoli and increases in blood

Gas Exchange

• External respiration: Driven by pressure gradients
• -Ventilation = amount of gas reaching the alveoli --Perfusion = amount of blood flow circulating by alveoli --Ventilation-Perfusion coupling is tightly regulated to maintain efficient gas exchange
• Internal respiration: Driven by pressure gradients

Ventilation and Perfusion

• Pulmonary arterioles constrict
  • This is when there is a decrease in ventilation, an increase in perfusion, an increase in PCO2 and decrease in PO2
• Pulmonary arterioles dilate
  • This is when there is increase in ventilation, decrease in perfusion, a decrease in PCO2 and increase in PO2

Oxygen Transport

• Hemoglobin carries 98.5% of O2 in the blood
• The remaining O2 is dissolved in plasma
• Factors affecting Hb’s affinity for O: What stimulates O2 release PO2 - 25% of the O2 bound to Hb is released
• Temperature: increased body temperature decreases affinity of Hb for O2 which promotes O2 release
• Blood pH - decreased pH (Bohr effect) decreased PH affinity
  • O2 allowed release to increase PH
  • PCO2 - increased CO2 partial pressure to active tissue increases affinity
  • BPG concentration is increased by BPG affinity
  • Cigarette smoking

CO2 Transport

• It is picked up in tissues and transported in the blood in 3 forms:
  • Dissolved in plasma which is 10% (1.5% O2), and bound to hemoglobin at 20% (98% O2
  • As bicarbonate ion in plasma makes up 70% with HCO3 in plasma - RBC - H2CO3 - split CO2 + H2O - diffuse to alveoli
• At lungs:
  • Bicarbonate ions move into RBCs and bind with hydrogen ions to from carbonic acid
  • Carbonic acid is split by carbonic anhydrase to release carbon dioxide and water
  • Then CO2 diffuses from blood to alveoli