Chapter 22: Respiratory System

functions of respiratory system

• Gas exchange
• Body tissues must be supplied with oxygen, CO2 waste must be disposed of
• Four processes involved with gas exchange:
• 1) Pulmonary ventilation
• 2) External respiration
• Gas exchange occurring in the lungs
• 3) Transport of respiratory gases to/from tissues**
• 4) Internal respiration**
• Gas exchange occurring in the tissues

**These are not in the respiratory system

anatomy of respiratory system

• Composed of two zones:
• 1) Conducting zone
• 2) Respiratory zone

conducting zone

• Respiratory passages leading from nose to the respiratory bronchioles
• Transports air to/from the lungs

respiratory zone

• Actual site of gas exchange
• Found in respiratory bronchioles, alveolar ducts, & alveoli

upper conducting zone

• 1) Nasal cavity
• 2) Pharynx

nasal cavity

• Air is warmed and humidified as it passes through this cavity
• How would breathing change without this function? Cold air decreases respiratory rate
• Mucous membranes of _____
• Respiratory mucosa: 2 cells types present
• 1) Goblet cells
• 2) Seromucous nasal glands
• Nerve endings in membrane → invading debris triggers a sneezing reflex
• Vascularization → capillaries and veins located superficially to help warm air as it passes through

goblet cells

Mucous-producing cells

seromucous nasal glands

• ”Mucous” portion traps particles & debris
• “Serous” portion secretes watery fluid containing lysozyme

pharynx

• Divided into 3 regions:
• 1) Nasopharynx
• 2) Oropharynx
• 3) Laryngopharynx

nasopharynx

• Contains pharyngeal tonsil & tubal tonsil
• Closes during swallowing by soft palate and uvula

oropharynx

• Meets oral cavity at isthmus of the fauces
• Contains palatine tonsils and lingual tonsils

laryngopharynx

Where respiratory and digestive passages split

lower conducting zone

• Divides the laryngopharynx from the respiratory passages
• Epiglottis → cartilage flap that closes off lower conducting zone
• What is the function of the epiglottis? Prevents fluids from entering the respiratory system
• 1) Larynx (voice box)
• 2) Trachea (windpipe)
• 3) Bronchi

larynx (voice box)

• Composed of cartilage
• Thyroid cartilage & cricoid cartilage
• _____ contains vocal cords for sound production
• Glottis: open passageway surrounded by vocal cords
• Vocal cords are ligaments composed of elastic fibers
• Fibers vibrate as we exhale to produce sound
• Sound pitch vs. sound loudness
• If chords are tense → higher pitch
• Air passed across chords with greater force → increases loudness
• Many sound properties created by other structures → tongue, lips, etc.

trachea (windpipe)

• Composed of elastic fibers and cartilage rings
• Elastic fibers provide flexibility → _____ can stretch/relax while breathing
• What is the importance of the cartilage rings? Allows _____ to remain open at all times
• Trachealis: smooth muscle tissue of _____
• What happens to the diameter of the ______ when this muscle contracts? How does it affect air movement? Becomes more narrow and forces air upward and out of the body
• Ex: coughing reflexes

bronchi

• Allow air to reach the respiratory zone
• Trachea branches to form 2 main _____
• _____ branch ~20-25 times, eventually form bronchioles
• Smallest of the _____ in conducting zone are terminal bronchioles

anatomy of respiratory zone

• Lungs
• Organ where external gas exchange occurs
• Each lung has a hilum → point at which the bronchi & any blood/nerve supply enter/leave the lung
• Lungs composed of air space and elastic connective tissue
• Why do the lungs need to be elastic in nature? They need to be able to contract easily

blood supply to lungs

• 1) Pulmonary circulation
• 2) Bronchial circulation

pulmonary circulation

• Pulmonary artery brings oxygen-poor blood to lungs
• Artery branches in a similar pattern as bronchi
• Pulmonary capillary network immediately surrounds alveoli
• Pulmonary vein moves oxygenated blood away from lungs

bronchial circulation

Bronchial arteries supply lung tissue with oxygenated systemic blood

innervation of lungs

• Nerve fibers enter lungs at pulmonary plexus
• Lungs have both parasympathetic & sympathetic fibers
• Parasympathetic causes the air tubes to contract
• Sympathetic causes the air tubes to dilate
• How does each influence breathing? Parasympathetic brings in less oxygen while sympathetic brings in more oxygen

pleurae

• Thin, double-layered serous membrane
• Parietal pleura: covers thoracic wall & upper portion of diaphragm
• Visceral pleura: covers external lung features
• Produces pleural fluid → fills cavity between visceral & parietal layers
• Each lung has its own _____ → creates chambers for each lung
• Benefits:
• 1) As organs move/shift with breathing, etc. → pleural layers “slide over” one another
• 2) Prevents spread of infection from one organ to another

respiratory bronchioles

• Branch from the terminal bronchioles of the conducting zone
• Lead into alveolar sacs composed of multiple individual alveoli
• Walls of alveoli are simple squamous epithelia
• Alveoli are covered with capillary beds
• Gas exchange occurs via diffusion
• Individual alveoli connected to “neighbors” via alveolar pores

types of alveolar cells

• Alveoli have 3 cell types:
• A) Type I alveolar cells
• B) Type II alveolar cells
• C) Alveolar macrophage

type I alveolar cells

• Squamous epithelial cells
• Function: create walls of alveoli → where gas exchange occurs

type II alveolar cells

• Cuboidal cells scattered among Type I cells
• Functions:
• 1) Secrete surfactant → detergent-like substance
• Why is surfactant production important? Prevents walls of alveoli from sticking together
• 2) Secrete antimicrobial proteins → innate immunity

alveolar macrophage

• Mobile cells
• Function: consume debris, pathogens, etc. → protect internal alveolar surfaces

physiology of respiratory system

• 2 processes involved with respiratory physiology:
• 1) Pulmonary ventilation
• 2) Gas Exchange
• 3 gas laws influence these 2 processes:
• 1) Boyle’s Law
• 2) Dalton’s Law of Partial Pressures
• 3) Henry’s Law

pulmonary ventilation

• The flow of air into and out of the lungs
• Air flows according to a pressure gradient
• Air flows from high pressure to low pressure

gas exchange

• The exchange of respiratory gases across the alveolar wall
• Respiratory gases can move from air space in lungs to blood, or from blood to air space in lungs

Boyle’s Law and ventilation

• The volume of a gas is inversely proportional to the pressure exerted by the gas on the walls of its container
• If you change the volume of a container filled with a gas, the pressure within the container will change
• If the volume of the container increases, what happens to the pressure? It decreases
• Why? Molecules are bouncing off walls less frequently
• If the volume of the container decreases, what happens to the pressure? It increases
• Why? Molecules are bouncing off walls more frequently
• Boyle’s Law is important for pulmonary ventilation
• Inhalation and exhalation changes the volume of the lungs!
• Changing the volume of the lungs will change the pressure of air inside the lungs
• Pressure in the lungs always described relative to atmospheric pressure
• At sea level → atmospheric pressure (Patm) = 760 mm Hg

intrapulmonary pressure (Ppul)

• Pressure in the alveoli
• Changes as you inhale or exhale
• But → always equalizes Patm at some point

inspiration

• Initiated by contraction of inspiratory muscles:
• 1) Diaphragm*: during contraction, diaphragm flattens
• What happens to the size of the thoracic cavity when the diaphragm flattens? It becomes larger
• 2) Intercostal muscles: during contraction,
external intercostal muscles pull ribs up & outward
• What happens to the size of the thoracic cavity when this occurs? It becomes larger
• Why is the change in the size of the thoracic
cavity important for respiration? It allows for respiration to occur
• As thorax increases in size during inhalation,
lungs are naturally pulled outward
• Volume of the lungs increases
• What happens to intrapulmonary pressure when the lungs increase in size? It decreases
• Result: Air flows into lungs along the pressure gradient
• _____ ends when Ppul = Patm
• Why??? Molecules can’t move anywhere

expiration

• _____ mostly due to lung elasticity
• Respiratory muscles relax & return to resting length
• Elastic fibers of lungs recoil → lungs become smaller in size
• Lungs recoil, pull thorax wall inward with → thoracic and intrapulmonary volume decrease
• What happens to the volume of the lungs? How does this affect intrapulmonary pressure? Volume decreases and pressure increases
• Air flows out of lungs along the pressure gradient
• _____ ends when Ppul = Patm

respiratory volumes

• The amount of air that can be pushed into/out of lungs during ventilation
• Types of _____:
• 1) Tidal volume (TV)
• 2) Inspiratory reserve volume (IRV)
• 3) Expiratory reserve volume (ERV)
• 4) Residual (reserve) volume (RV)

tidal volume (TV)

• Normal volume of air that moves into and out of lungs during normal breathing
• In healthy individuals → ~500 ml air

inspiratory reserve volume (IRV)

• Amount of air that can be inspired forcibly past the tidal volume
• ~2100-3000 ml air

expiratory reserve volume (ERV)

• Amount of air that can be forced from lungs after a normal tidal volume expiration
• ~1000-1200 ml air

residual (reserve) volume (RV)

• Amount of air left in the lungs after forced expiration
• ~1200 ml air
•**The lungs are NEVER empty of air!!!**

respiratory capacities

• The sum of two or more respiratory volumes
• _____
• 1) Inspiratory capacity (IC)
• 2) Functional residual capacity (FRC)
• 3) Vital capacity (VC)
• 4) Total lung capacity (TLC)

inspiratory capacity (IC)

• Total amount of air that can be inspired after a normal tidal volume expiration
• IC = TV + IRV

functional residual capacity (FRC)

• Amount of air remaining in the lungs after a normal tidal volume expiration
• FRC = RV + ERV

vital capacity (VC)

• Total amount of exchangeable air
• VC = TV + IRV + ERV
• What volume does not contribute to VC? Why? RV because there is always air left in the lungs

total lung capacity (TLC)

• The total amount of air the lungs can hold after a maximum inhalation
• TLC = IRV + TV + ERV + RV

dead space

• Air that fills the conducting zone, but never contributes to gas exchange
• Anatomical dead space
• Alveolar dead space
• Total dead space = anatomical dead space + alveolar dead space
• “Non-useful volumes”

anatomical dead space

• _____ for a healthy individual is ~150 ml air
• 1 ml of air per pound of ideal body weight
• Remember: TV is ~500 ml
• What is the total volume of air used for gas exchange? ~350 mL

alveolar dead space

• Another source of “dead space” is in the respiratory zone
• _____ → air reaches the alveoli, but no gas exchange occurs
• Due to localized damage or collapse of alveoli
• Examples: blockage from mucus during illness, damage due to smoking

Dalton’s Law and gas exchange

• The total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture
• In other words: total atmospheric pressure is the sum of the pressures of the different gases that makes up air that we breathe
• Nitrogen (79%) and oxygen (20.9%) account for ~99% of Patm
• Small amounts of CO2, water vapor, and other gases make up remaining

partial pressure (PP)

• The pressure of each individual gas in the mixture is the _____
• The _____ of one gas is independent of the _____ of a different gas in the mixture
• Importance: If we know _____ of each gas, we can see pressure gradients that drive diffusion into or out of the blood

Henry’s Law and gas exchange

• A gas will dissolve in a liquid in proportion to its partial pressure
• Higher PP = more gas dissolves in liquid
• Gases dissolve in liquid best under high pressure, low temperature, and high solubility
• Is the partial pressure of oxygen greater in the alveolar space (gas) or in the blood (liquid)? Blood
• Will oxygen move into or out of the liquid? Out of the blood

gas exchange: external respiration

• Gas exchange that occurs in the alveoli
• 3 factors affecting rate at which gas exchange occurs between alveoli and capillaries:
• 1) Partial Pressure Gradients & Gas Solubility
• PO2 in alveoli > PO2 in lung capillaries → oxygen moves from alveoli & into blood
• What direction does carbon dioxide move? Out of blood
• Equal amounts of CO2 and O2 are exchanged
• 2) Thickness & surface area of respiratory membrane
• The respiratory membrane is exceptionally thin → gas exchange occurs quickly
• The greater the surface area, the greater amount of gas that can diffuse in a given amount of time
• Alveolar surface area is HUGE!
• 3) Ventilation-Perfusion Coupling

ventilation-perfusion coupling

• Optimal gas exchange results from equal amounts of gas reaching alveoli (via ventilation) and blood supply to pulmonary capillaries (via perfusion)
• Respiratory gases affect perfusion or ventilation
• Perfusion: flow of blood through blood vessels
• 1) Influence of PO2 on perfusion (occurring at the lungs)
• 2) Influence of PCO2 on ventilation

influence of PO2 on perfusion

• If local PO2 is low → local arterioles to those alveoli constrict
• Why? This decreases blood flow
• Blood is redirected to respiratory areas with high PO2
• Importance: Ensures adequate O2 uptake
• If local PO2 is high → local arterioles to those alveoli dilate
• Why? This increases blood flow
• Area is flooded with blood → takes up maximum amount of O2

influence of PCO2 on ventilation

• If local PCO2 levels are high, bronchioles dilate
• CO2 eliminated by the body faster
• Importance: Increased CO2 affects blood pH!
• If local PCO2 levels are low, bronchioles constrict

composition of alveolar gases

• Atmospheric gases mostly N2 and O2
• Alveolar gases mostly CO2 and water vapors
• Why are they different?
• 1) Gas exchange is occurring in alveoli → O2 diffuses into blood, CO2 diffuses into alveoli
• 2) Conducting passages humidify air → creates water vapor
• 3) Mixture of air in alveoli → inspiration brings in new gases, but there is still gases left over (reserve volume)

gas exchange: internal respiration

• Gas exchange that occurs in the body tissues
• PCO2 in tissues > PCO2 in blood
• What direction does CO2 travel? Enters blood in tissues and leaves blood in lungs
• PO2 in blood > PO2 in tissues
• What direction does O2 travel? Enters blood in lungs and leaves blood in tissues
• What can be said about partial pressures and diffusion gradients between internal and external respiration? Gases move in opposite directions

oxygen transport

• Oxygen transported primarily by Hb (4 O2 molecules per Hb molecule)
• Binding first O2 molecule facilitates binding of other 3
• Unloading first O2 molecule facilitates unloading of remaining 3
• Why is this beneficial? Tissue cells receive oxygen faster
• Arterial blood is 98% saturated
• Venous blood is 75% saturated
• Why is this not 0%? How is this beneficial to us? Tissue cells will never use 100% of O2 so if respiration stops, blood can circulate many times before O2 depletes

carbon dioxide transport

• CO2 is transported 3 ways:
• 1) Dissolved in plasma
• 2) Bound to Hb
• CO2 does not bind heme, it binds amino acids of globulin
• Why do we not want CO2 to bind to heme/Fe+? If CO2 binded heme, O2 would not be able to bind as well
• 3) As bicarbonate ions (HCO3-) in plasma***
• When CO2 diffuses into erythrocyte it combines with H2O to form carbonic acid (H2CO3)
• Carbonic acid split to form H+ and HCO3- (bicarbonate)
• The reaction: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

influence of CO2 on blood pH

• Conversion of CO2 to bicarbonate causes release of H+
• Normally, this is buffered by red blood cells → maintains 7.35-7.45 pH of blood
• An increase in CO2 in the blood causes blood pH to decrease
• Respiratory acidosis
• Caused by: slow, shallow breathing
• A decrease in CO2 in the blood causes blood pH to increase
• Respiratory alkalosis
• Caused by: rapid, deep breathing

CNS control

• 1) Medullary Respiratory Center
• 2) Pontine respiratory center (PRC)

medullary respiratory center

• Two areas that set the normal respiratory rhythm
• 1) Ventral respiratory group (VRG)
• 2) Dorsal respiratory group (DRG)

ventral respiratory group (VRG)

Some neurons in this group fire during inspiration, others fire during expiration → but they cannot fire at the same time!

dorsal respiratory group (DRG)

• Modifies rhythm set by VRG
• Integrates information from other structures (chemoreceptors, etc.), delivers it to VRG

pontine respiratory center (PRC)

• Interacts with medullary respiratory centers to “smooth” the respiratory pattern
• Transition from inspiration to expiration (& vice versa)

how CNS determines breathing rate and depth

• CNS measures 2 factors to determine breathing rate and depth:
• 1) CO2 is the most potent and most closely controlled
• Hypercapnia
• Hypocapnia
• 2) PO2 of arterial blood
• PO2 must drop substantially to stimulate increased ventilation
• Remember: venous reservoir of saturated Hb (~75%) → body can use this if PO2 drops slightly
• If PO2 drops substantially → respiratory centers are stimulated
• Ventilation increases → O2 levels increase

hypercania

• An increase in PCO2 levels in blood
• What happens to blood pH with _____? It decreases
• How does CNS change breathing rate and depth to correct this? VRG will increase respiratory rate and depth

hypocania

• A decrease in PCO2 levels in blood
• What happens to blood pH with _____? It increases
• How does CNS change breathing rate and depth to correct this? VRG will decrease respiratory rate and depth

higher brain center influence

• 1) Hypothalamic control
• 2) Cortical controls

hypothalamic controls

• Strong emotion & pain send information from hypothalamus & limbic system to respiratory centers
• Ex: excitation stimulates respiratory rate
• Ex: substantial drop in temperature can cause apnea

cortical controls

• We can override the respiratory centers to control our own breathing depth/rate
• Cerebral motor cortex sends impulses to motor neurons that stimulate respiratory muscles
• This only goes so far
• Ex: you cannot hold your breath forever
• Why? Medulla and pons will eventually override _____

respiratory adjustments

• Some activities/conditions require alteration of the normal pattern of respiration:
• Exercise: adjustments made based on intensity and duration of physical exertion
• Active muscles need large amounts of oxygen & produce large amounts of waste
• Hyperpnea: ventilation increases 10-20x during exercise
• Ventilation and perfusion during exercise are still balanced
• Respiration increases at beginning of exercise, then plateaus
• This is most likely due to rate of CO2 delivery to the lungs

homeostatic imbalances of respiration

• 1) Chronic Obstructive Pulmonary Disease (COPD)
• 2) Asthma
• 3) Tuberculosis
• 4) Sleep apnea

chronic obstructive pulmonary disease (COPD)

• Group of conditions characterized by a physiological inability to expel air from the lungs
• This condition is irreversible
• Features/shared characteristics: labored breathing, coughing, pulmonary infection, etc.
• 1) Emphysema
• 2) Chronic bronchitis

emphysema

• Permanent enlargement of the alveoli & eventual destruction of their walls
• Lungs lose elasticity
• Bronchioles collapse during expiration → trap air in alveoli
• Hyperinflation of alveoli leads to “barrel chest”
• Damage to alveoli results in damage to pulmonary capillaries

chronic bronchitis

• Chronic production of excess mucous due to inhaled irritants
• Lower respiratory passages become inflamed over time & eventually fibrose
• Ventilation decreases
• This mucous is not removed from the lungs
• Bacteria & microorganisms thrive in stagnant mucous → infection is frequent

asthma

• Some similarities to COPD, but _____ is temporary bronchospasm attacks followed by symptom-free periods
• Allergic asthma is most common form → allergen causes inflammation of airways
• Inflammation caused by IgE antibodies
• Inflammation persists between attacks → airways become hypersensitive
• Subsequent attacks can be very severe
• Treatment: inhaled corticosteroids and/or bronchodilators

tuberculosis

• Bacterial disease spread (primarily) by inhaled air
• Mostly affects lungs, but can spread to other organs
• 33% of world population is infected
• BUT, it’s not active in most
• Immune response contains bacteria to hardened nodules in lungs → bacteria cannot cause infection
• If active, symptoms include fever, night sweats, weight loss, racking cough, coughing up blood

sleep apnea

• Characterized by temporary cessation of breathing during sleep
• People with _____ must wake up during sleep due to this condition
• Can be as high as ~30 times/hour
• Constant fatigue usually results → leads to increased susceptibility to hypertension, heart disease, stroke, etc.
• Common forms:
• A) Obstructive sleep apnea
• B) Central sleep apnea

obstructive sleep apnea

• Occurs when upper airways collapse during sleep
• Muscles associated with pharynx relax during sleep → airway sags and closes
• Most common in men, made worse by obesity
• Treatment: CPAP machine → blows air into passages constantly to prevent collapse

central sleep apnea

Respiratory centers of the brain “slack” during sleep → breathing rhythm/rate not maintained