Chapter 22 - The Respiratory System

Describe the structure and functions of the upper and lower respiratory tracts - nasal cavity, pharynx, larynx, trachea, and bronchi.

The combination of 3 processes is required for respiration to occur: ventilation (breathing), external (pulmonary) respiration (exchange of O2 and CO2), and internal (tissue) respiration (exchange between tissue cells and capillary blood)

Structurally, the components of the respiratory system are divided into 2 parts: upper respiratory and lower respiratory system

• Upper respiratory: nose, pharynx (throat), and associated structures

• Lower respiratory: larynx, trachea, bronchi, lungs

Functionally, the components of the respiratory system are divided into 2 parts: conducting zone and respiratory zone

Nasal cavity

• Nasal meatuses: superior, middle, inferior

• Nasal conchae: superior, middle, inferior

  • Create bigger surface contact within nose to catch bacteria on pseudostratified, mucous membrane

• Humidify, warm, filter for inspired air

Pharynx

• Functions as a passageway for air and food

• Provides a resonating chamber for speech sounds and houses the tonsils, which participate in immunological reactions against foreign invaders

• 3 regions of the pharynx: nasopharynx, oropharynx, laryngopharynx

Larynx

• Voice box; passageway that connects the pharynx and trachea

  • Contains vocal folds, which produce sound when they vibrate (air passes the glottis, causing vibrations)

• Has different types of cartilage: epiglottis, corniculate cartilage, thyroid cartilage (adam’s apple), cricoid cartilage, tracheal cartilage

Trachea

• Extends from the larynx to the primary bronchi

• Contains C-shaped cartilage, meaning the posterior side (made of trachealis muscle instead of cartilage) allows expansion so bigger things can pass through esophagus if necessary

Bronchi

• At the superior border of the 5th thoracic vertebrae, the trachea branches into a right primary bronchus that enters the right lung and left primary bronchus that enters the left lung

• Trachea → main bronchi → lobar bronchi → segmental bronchi → bronchioles → terminal bronchioles

• Bronchioles carry air to small sacs in the lungs (alveoli), which perform gas exchange

Follow the flow of air from the nasal cavities to the alveoli, identifying every structure through which the air passes

Vestibules → nasal conchae → nasal meatuses → nasopharynx → laryngopharynx → larynx → trachea → primary bronchi → secondary bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveoli

Describe the structure of the lungs, bronchial tree, bronchioles, and alveoli. Discuss the alveolar membrane and its role in gas exchange.

Lungs

• Paired organs in the thoracic cavity, enclosed and protected by the pleural membrane

  • Pleural membrane is a serous membrane in the thoracic cavity with a visceral and parietal layer

  • Right lung has two fissures: horizontal and oblique

  • Left lung has one fissure: oblique

Bronchial tree

• Trachea → main bronchi → lobar bronchi → segmental bronchi → bronchioles → terminal bronchioles

Alveoli

• When the conducting zone ends at the terminal bronchioles, the respiratory zone begins

• The respiratory zone terminates at the alveoli, the “air sacs” found within the lungs (respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli)

  • There are 2 kinds of alveolar cells, Type I and Type II

    • Type I: make up most of the alveolar wall

    • Type II: produces surfactant, which helps decrease surface tension between molecules

• The respiratory membrane is composed of…

  • Layer of type I and type II alveolar cells and associated alveolar macrophages that constitutes the alveolar wall

  • Epithelial basement membrane underlying the alveolar wall

  • Capillary basement membrane that is often fused to the epithelial basement membrane

  • Capillary endothelium

Discuss the mechanism of breathing and outline the sequence of events and pressure changes for normal quiet inspiration and expiration. Name respiratory muscles, passive and active phases of breathing. Explain Boyle’s Law.

In pulmonary ventilation, air flows between the atmosphere and the alveoli of the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles (inhalation, exhalation)

3 basic steps of respiration

1. At rest, when the diaphragm is relaxed, alveolar pressure is equal to atmospheric pressure and there is no air flow

2. During inhalation (active phase), the diaphragm contracts and external intercostals contract

   • Chest cavity expands → alveolar pressure drops below atmospheric pressure

   • Air flows in the lungs in response to the pressure gradient and the lung volume expands

   • During deep inhalation, the scalene and sternocleidomastoid muscles expand the chest further, causing a greater drop in alveolar pressure

3. During exhalation (passive phase), the diaphragm relaxes and the external intercostals relax

   • Chest and lungs recoil, chest cavity contracts, and the alveolar pressure increases above the atmospheric pressure

   • Air flows out of the lungs in response to the pressure gradient, and the lung volume decreases

   • During forced exhalation, the internal intercostals and the abdominal muscles contract, thereby reducing the size of the chest cavity further → greater increase in alveolar pressure

Muscles of inhalation: sternocleidomastoid, scalenes, external intercostals, diaphragm

Muscles of exhalation: internal intercostals, abdominal muscles (external oblique, internal oblique, transervus abdominus, rectus abdominus)

Eupnea: quiet breathing/resting respiratory rate (12-18 breaths/min)

Boyle’s Law: the volume of a gas varies inversely with its pressure

Identify the differences between atmospheric and alveolar pressures during breathing.

Inhalation

• Alveolar pressure < atmospheric pressure

  • Diaphragm contracts → enlarged thorax (lung volume increases, so air pressure inside decreases)

  • Atmospheric pressure outside is greater than pulmonary pressure inside → air moves into lungs

Exhalation

• Alveolar pressure > atmospheric pressure

  • Diaphragm relaxes → thorax gets smaller (lung volume decreases, so air pressure inside increases)

  • Pulmonary air pressure is greater than atmospheric pressure → air moves out of the lungs

Intrapulmonary (intra-alveolar) pressure: in relaxed breathing, the different between atmospheric pressure and intrapulmonary pressure is small

Intrapleural pressure: pressure in space between parietal and visceral pleura; remains below atmospheric pressure throughout the respiratory cycle

Discuss the primary factors that influence the respiratory control center and its control of respiratory rate and depth.

Surface tension: inwardly directed force in the alveoli which must be overcome to expand the lungs during each inspiration

Elastic recoil: decreases the size of the alveoli during expiration

Compliance: ease with which the lungs and thoracic wall can be expanded - depends on the stretchability of elastic fibers within lungs and surface tension inside alveoli

Identify and explain how CO2, O2, and pH changes can affect breathing. Identify primary stimulus for breathing.

Changes in CO2, O2, and pH levels in the blood influence the activity of chemoreceptors, which send signals to the brain to adjust breathing rate and depth.

CO2 levels

• Most significant regulator of breathing

• Increased CO2 levels cause blood to become more acidic → stimulates central chemoreceptors in the medulla (brainstem) to increase breathing rate and depth to expel excess CO2

• Decreased CO2 levels decreases respiratory drive (slower breathing)

O2 levels

• Peripheral chemoreceptors detect low O2 levels

• If O2 drops significantly, these receptors signal the brain to increase breathing rate to enhance oxygen intake

• Under normal conditions, O2 levels do not strongly affect breathing

pH levels

• Directly linked to CO2 levels

• Increased H+ (low pH, more acidic) stimulates the central and peripheral chemoreceptors to increase ventilation

• Higher pH (more alkaline) → decreased breathing to retain CO2 and restore balance

Describe the Hering-Breuer reflex.

Stretch receptors in the pleurae and airways are stimulated by lung inflation.

• Send inhibitory signals to the medullary respiratory centers to end inhalation and allow expiration

• May act as a protective response more than as a normal regulatory mechanism

Describe and give normal values for the following lung volumes: total lung capacity (TLC), tidal volume (V), vital capacity (VC), and residual volume (RV).

Total lung capacity (TLC): 6,000 mL

Tidal volume (V): 500 mL

Vital capacity (VC): 3,000 - 5,000 mL

Residual volume: 1,000 - 1,200 mL

Explain the role of surfactant in maintaining alveolar stability.

Surfactant is produced by type II alveolar cells.

• Reduces surface tension, making it easier for alveoli to remain open during exhalation

  • Increases lung compliance (ability to expand) as surfactant reduces the effort needed for inhalation

Describe the manner and forms in which O2 and CO2 are carried in the blood. Explain how concentration (partial pressure of O2 and CO2) can change blood pH.

External respiration: oxygen diffuses from alveoli → pulmonary capillaries; CO2 moves in the opposite direction

Internal respiration: oxygen diffuses from systemic capillaries → tissue; CO2 moves in the opposite direction

Oxygen

• 98.5% of the oxygen is carried by hemoglobin (Hb)

• 1.5% of the oxygen is dissolved in the plasma

Carbon dioxide

• 70% of the CO2 is transported as bicarbonate ions (HCO3)

  • Occurs primarily in the RBCs, where enzyme carbonic anhydrase reversibly and rapidly catalyzes the reaction of CO2 combining with water

  • Chloride shift: outrush of HCO3 from RBCs is balanced as Cl- moves into RBCs from plasma

• 23% of CO2 is carried by Hb inside RBCs as caraminohemoglobin

• 7% of the CO2 is dissolved in the plasma

Describe the principle of partial pressures of gases and its importance in explaining gas movements between alveoli and blood.

Principle of Partial Pressure (Dalton’s Law): total pressure of a gas mixture (such as air) is the sum of the partial pressures of each individual gas

• Partial pressure of a gas is the pressure it would exert if it were alone in a mixture

• Movement of gases in the body follow partial pressure gradients - gases diffuse from areas of higher partial pressure to areas of lower partial pressure

• Since alveolar oxygen partial pressure is higher than capillary oxygen partial pressure, oxygen moves from alveoli → blood

  • Ensures oxygenation of blood before it’s transported to the tissues

• Capillary CO2 partial pressure is higher than the alveolar CO2 partial pressure

  • Ensures CO2 diffuses from the blood into the alveoli, where it is expelled during exhalation

Discuss gas exchange in alveoli between the capillary blood and alveoli.

The respiratory system is responsible for the movement of gases involved in cellular metabolism.

• O2 is used up and CO2 is generated during the aerobic breakdown of glucose and other fuel molecules in order to produce ATP

External respiration

• Ventilation brings air, rich in O2, in the alveolar spaces in the lung

  • Air in the alveolar space is high in O2 and low in CO2

  • Blood in the pulmonary capillary compartment (entering lungs) has low O2 and high CO2

• Diffusion of gases is dependent on the partial pressure of the gases

• O2 moves from the alveolar compartment to the capillary compartment

• Blood leaving the lungs and flowing to the body is well oxygenated

  • CO2 moves from the capillary compartment to the alveolar compartment and is removed from the body at the next respiration

Discuss gas exchange in the tissues between capillary blood and the cells.

Internal respiration

• Blood, high in O2 and low in CO2, circulates past tissue cells

• Blood near tissues has high O2 and low CO2

• Each cell in the tissue compartment has low O2 and high CO2

• Diffusion of gases is dependent on the partial pressure of the gases → O2 moves from the capillary blood department to the cell department; CO2 moves from the cell compartment to the capillary department

Describe the characteristics of the following types of respiration: apnea, dyspnea, tachypnea, and bradypnea.

Apnea: cessation of breathing

Dyspnea: labored or difficult breathing

Tachypnea: abnormally fast breathing

Bradypnea: abnormally slow breathing

Hypercapnia: slight increase in PCO2 (thus H+) → stimulates central chemoreceptors

Hypoxia: oxygen deficiency at the tissue level, caused by low PO2 in arterial blood due to high altitude, airway obstruction, or fluid in the lungs