Respiratory System Functions

®   Gas exchange

®   To supply the body with oxygen and dispose of carbon dioxide

®   External respiration – gas exchange between the lungs and the blood

®   Transport – transport of oxygen and carbon dioxide between the lungs and tissues

®   Internal respiration – gas exchange between systemic blood vessels and tissues

®   Pulmonary ventilation

®   Moving air into and out of the lungs

®   Producing sound

®   Olfaction

Respiratory System

®   Consists of the respiratory and conducting zones

®   Respiratory zone:

®   Site of gas exchange

®   Consists of respiratory bronchioles, alveolar ducts, and alveoli

®   Conducting zone: 

®   Allows for air to reach the sites of gas exchange

®   Includes all other respiratory structures (e.g., nose, nasal cavity, pharynx, trachea)

®   Respiratory muscles – diaphragm and other muscles that promote ventilation

Respiratory System

Function of the Nose

® The only externally visible part of the respiratory system that functions by:

®  Providing an airway for respiration

®  Moistening and warming the entering air

®  Filtering inspired air and cleaning it of foreign matter

®  Serving as a resonating chamber for speech

®  Housing the olfactory receptors

Nasal Cavity

®    Inspired air is:

®   Humidified by the high water content in the nasal cavity

®   Warmed by rich plexuses of capillaries

®    Ciliated mucosal cells remove contaminated mucus

®    Superior, medial, and inferior conchae:

®   Protrude medially from the lateral walls

®   Increase mucosal area

®   Enhance air turbulence and help filter air

®    Sensitive mucosa triggers sneezing when stimulated by irritating particles

®    During inhalation the conchae and nasal mucosa:

®   Filter, heat, and moisten air

®    During exhalation these structures:

®   Reclaim heat and moisture

®   Minimize heat and moisture loss

Nasal Cavity

Pharynx

®   It is divided into three regions

®   Nasopharynx

®   Strictly an air passageway

®   Closes during swallowing to prevent food from entering the nasal cavity

®   Oropharynx

®   Serves as a common passageway for food and air

®   Laryngopharynx

®   Serves as a common passageway for food and air

Larynx (Voice Box)

® The three functions of the larynx are:

®  To provide an airway

®  To act as a switching mechanism to route air and food into the proper channels

®  To function in voice production

LARYNX

® Glottis

® Thyroid cartilage

® Cricoid

     cartilage

® Epiglottis

LARYNX

®   Arytenoid cartilage

®   Cuneiform cartilage

®   False vocal cords

®   Have no part in sound production

®   True vocal cords

®   Vibrate to produce sound as air rushes up from the lungs

Vocal Production

®   Speech – intermittent release of expired air while opening and closing the glottis

®   Pitch – determined by the length and tension of the vocal cords

®   Loudness – depends upon the force at which the air rushes across the vocal cords

®   The pharynx resonates, amplifies, and enhances sound quality

®   Sound is “shaped” into language by action of the pharynx, tongue, soft palate, and lips

TRACHEA

® Tracheal cartilages

® Annular ligaments

® Trachealis muscle

LUNGS

®   Pleural cavities

®   Rib cage, diaphragm, & mediastinum

®   Pleura

®   Parietal

®  Covers the thoracic wall

®   Visceral

®  Covers the external lung surface

®   Pleural fluid

LUNGS

® Lobes

®  Left lung – separated into upper and lower lobes by the oblique fissure

®  Superior, inferior

®  Right lung – separated into three lobes by the oblique and horizontal fissures

®  Superior, middle, inferior

®  Cardiac notch

®  Cavity that accommodates the heart

Organs in the Thoracic Cavity

Bronchial Tree

®   Primary bronchi

®   Air reaching the bronchi is:

®   Warm and cleansed of impurities

®   Saturated with water vapor

®   Primary bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs

®   Secondary bronchi

®   As conducting tubes become smaller, structural changes occur

®   Cartilage support structures change

®   Amount of smooth muscle increases

®   Tertiary bronchi

®   Bronchopulmonary
segment

®   Bronchioles

®   Have a complete layer of circular smooth muscle

l   Bronchodilation

l   Bronchoconstrction

®   Lack cartilage support and mucus-producing cells

®   Terminal bronchiole

Conducting Zones

Respiratory Zone

®   Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles

®   Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli

®   Approximately 300 million alveoli:

®   Account for most of the lungs’ volume 

®   Provide tremendous surface area for gas exchange

ALVEOLI  

® Alveolar duct

® Alveolar sacs

® Alveoli

®  Capillaries

®  Elastic tissue

ALVEOLI

® Alveolar walls

®  Are a single layer of type I epithelial cells

®  Permit gas exchange by simple diffusion

® Alveolar macrophage

®  Keep alveolar surfaces sterile

® Type II cells

®  Secrete surfactant

®  Surface tension

®  Respiratory distress syndrome (RDS)

ALVEOLI

® Respiratory membrane

®  Air-blood barrier is composed of

®  Alveolar wall

®  Epithelial basement membrane

®  Capillary basement membrane

®  Endothelium of
capillary

® Diffusion is rapid

Respiratory Physiology

® Pulmonary ventilation

®  Alveolar ventilation

® Breathing, or pulmonary ventilation, consists of two phases

®  Inspiration – air flows into the lungs

®  Expiration – gases exit the lungs

® Pulmonary ventilation is a mechanical process that depends on volume changes in the thoracic cavity

RESPIRATION

®   Atmospheric pressure

®   Boyle’s law

®   The relationship between the pressure and volume of gases

®   P = 1/V

®   Gases flow from high pressure to low pressure

®   Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure

Pressure Relationships in the Thoracic Cavity

®   Intrapulmonary pressure (P_pul) – pressure within the alveoli

®   Intrapleural pressure (P_ip) – pressure within the pleural cavity

®   Intrapulmonary pressure and intrapleural pressure fluctuate with the phases of breathing

®   Intrapulmonary pressure always eventually equalizes itself with atmospheric pressure

®   Intrapleural pressure is always less than intrapulmonary pressure and atmospheric pressure

Pressure Relationships

RESPIRATION

® Diaphragm

® External intercostals

® Accessory muscles

®  Sternocleidomastoid

®  Scalenes

®  Pectoralis minor

®  Abdominal muscles

®  Internal intercostals

Inspiration

® The diaphragm and external intercostal muscles (inspiratory muscles) contract and the rib cage rises

® The lungs are stretched and intrapulmonary volume increases

® Intrapulmonary pressure drops below atmospheric pressure (-1 mm Hg)

® Air flows into the lungs, down its pressure gradient, until intrapleural pressure = atmospheric pressure

Inspiration

Expiration

® Inspiratory muscles relax and the rib cage descends due to gravity

® Thoracic cavity volume decreases

® Elastic lungs recoil passively and intrapulmonary volume decreases

® Intrapulmonary pressure rises above atmospheric pressure (+1 mm Hg)

® Gases flow out of the lungs down the pressure gradient

Expiration

Lung Collapse

® Caused by equalization of the intrapleural pressure with the intrapulmonary pressure

®  Pneumothorax

RESPIRATION

® Compliance

®  The ease with which lungs can be expanded

®  Connective tissue

®  Surfactant

®  A detergent-like complex, reduces surface tension and helps keep the alveoli from collapsing

®  Thoracic mobility

® Airway Resistance

Airway Resistance

® As airway resistance rises, breathing movements become more strenuous

® Severely constricted or obstructed bronchioles:

®  Can prevent life-sustaining ventilation

®  Can occur during acute asthma attacks which stops ventilation

® Epinephrine release via the sympathetic nervous system dilates bronchioles and reduces air resistance

Respiratory Volumes

® Tidal volume (TV) – air that moves into and out of the lungs with each breath (approximately 500 ml)

® Inspiratory reserve volume (IRV) – air that can be inspired forcibly beyond the tidal volume (2100–3200 ml)

® Expiratory reserve volume (ERV) – air that can be evacuated from the lungs after a tidal expiration (1000–1200 ml)

® Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml)

Respiratory Capacities

®   Inspiratory capacity (IC) – total amount of air that can be inspired after a tidal expiration (IRV + TV)

®   Functional residual capacity (FRC) – amount of air remaining in the lungs after a tidal expiration
(RV + ERV)

®   Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV)

®   Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in males)

RESPIRATION

®   Tidal volume (V_T)

®   Respiratory rate

®   Minute ventilation

_®       MV = Rate * V_T

®   Alveolar ventilation

®   Measures the flow of fresh gases into and out of the alveoli during a particular time

®   Anatomic dead space (V_D)

®   Volume of the conducting respiratory passages (150 ml)

®   V_A = Rate * (V_T – V_D)

®   V_A is more important than MV

Gas Laws

®    Dalton’s Law

®   Partial pressures

®   P_O2 ~ 159 mm
Hg

®    Henry’s Law

®    The amount of gas that will dissolve in a liquid also depends upon its solubility:

®   Carbon dioxide is the most soluble

®   Oxygen is 1/20th as soluble as carbon dioxide

®   Nitrogen is practically insoluble in plasma

®    The atmosphere is mostly oxygen and nitrogen, while alveoli contain more carbon dioxide and water vapor

®   These differences result from:

®   Gas exchanges in the lungs – oxygen diffuses from the alveoli and carbon dioxide diffuses into the alveoli

®   Humidification of air by conducting passages

®   The mixing of alveolar gas that occurs with each breath

Gas Exchange

®   Partial pressure differences

®   Small distance

®   Lipid-soluble gases

®   O₂ and CO₂ have limited solubility

®   Large surface area

®   Coordinated blood- and airflow

Gas Pickup

®   O₂ and CO₂ have limited solubility

®   Molecular oxygen is carried in the blood:

®   Bound to hemoglobin (Hb) within red blood cells

®   Dissolved in plasma

®   Red blood cells

_®      Hb + O₂ --> HbO₂

®   Each Hb molecule binds four oxygen atoms in a rapid and reversible process

®   The hemoglobin-oxygen combination is called oxyhemoglobin (HbO₂)

Hemoglobin Saturation and Affinity

® Saturated hemoglobin – when all four hemes of the molecule are bound to oxygen

® Partially saturated hemoglobin – when one to three hemes are bound to oxygen

® The rate that hemoglobin binds and releases oxygen is regulated by:

®  P_O2, temperature, blood pH, P_CO2, and the concentration of BPG (an organic chemical)

®  These factors ensure adequate delivery of oxygen to tissue cells

Hb and P_O2

® Oxygen-hemoglobin saturation curve

® Shape of Hb changes as O₂ binds

®  Cooperativity

® Carbon monoxide

Other Factors Influencing Hemoglobin Saturation

®   Temperature, H⁺, P_CO2, and BPG

®   Modify the structure of hemoglobin and alter its affinity for oxygen

®   Increases of these factors:

®  Decrease hemoglobin’s affinity for oxygen

®  Enhance oxygen unloading from the blood

®   Decreases act in the opposite manner

®   These parameters are all high in systemic capillaries where oxygen unloading is the goal

Factors That Increase Release of Oxygen by Hemoglobin

®   As cells metabolize glucose, carbon dioxide is released into the blood causing:

®   Increases in P_CO2 and H⁺ concentration in capillary blood

®   Declining pH (acidosis), which weakens the hemoglobin-oxygen bond (Bohr effect)

®   Metabolizing cells have heat as a byproduct and the rise in temperature increases BPG synthesis

®   All these factors ensure oxygen unloading in the vicinity of working tissue cells

Other Factors Influencing Hemoglobin Saturation

Fetal Hb

® Higher affinity for O₂ than adult Hb

CO₂ Transport

® Carbon dioxide is transported in the blood in three forms

_®     Dissolved CO₂

®  Dissolved in plasma – 7 to 10%

®  Carboamino compounds

®  Chemically bound to hemoglobin – 20% is carried in RBCs as carbaminohemoglobin

®  Bicarbonate ions

®  Bicarbonate ion in plasma – 70% is transported as bicarbonate (HCO₃^–)

Transport and Exchange of Carbon Dioxide

® Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H₂CO₃), which quickly dissociates into hydrogen ions and bicarbonate ions

® In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid

Transport and Exchange of Carbon Dioxide

®   At the tissues:

®   Bicarbonate quickly diffuses from RBCs into the plasma

®   The chloride shift – to counterbalance the outrush of negative bicarbonate ions from the RBCs, chloride ions (Cl^–) move from the plasma into the erythrocytes

Transport and Exchange of Carbon Dioxide

®    At the lungs, these processes are reversed

®   Bicarbonate ions move into the RBCs and bind with hydrogen ions to form carbonic acid

®   Carbonic acid is then split by carbonic anhydrase to release carbon dioxide and water

®   Carbon dioxide then diffuses from the blood into the alveoli

Respiratory Control

® Respiratory rhythmicity centers

®  Medullary rhythmicity area

®  Inspiratory area

®  Expiratory area

®  Pneumotaxic area

®  Apneustic area

Respiratory Reflexes

®   Chemoreceptor

®   Central

®   Peripheral

®  Aortic and carotid bodies

®   Hypercapnia

®   Hypocapnia

®   Baroreceptor reflex

®   Hering-Breuer (Inhalation) Reflex

®   Stretch receptors in the lungs are stimulated by lung inflation

®   Protective reflexes

®   Apnea

Depth and Rate of Breathing: P_CO2

®   Changing P_CO2 levels are monitored by chemoreceptors of the brain stem

®   Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated

®   Resulting carbonic acid dissociates, releasing hydrogen ions

®   P_CO2 levels rise (hypercapnia) resulting in increased depth and rate of breathing