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Chapter 23

Respiratory System

23-2

Respiration• Ventilation: Movement of air into and out

of lungs• External respiration: Gas exchange

between air in lungs and blood• Transport of oxygen and carbon dioxide in

the blood• Internal respiration: Gas exchange between

the blood and tissues

23-3

Respiratory System Functions • Gas exchange: Oxygen enters blood and carbon

dioxide leaves• Regulation of blood pH: Altered by changing

blood carbon dioxide levels• Voice production: Movement of air past vocal

folds makes sound and speech• Olfaction: Smell occurs when airborne

molecules drawn into nasal cavity• Protection: Against microorganisms by

preventing entry and removing them

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Respiratory System Divisions• Upper tract

–Nose, pharynx and associated structures

• Lower tract–Larynx,

trachea, bronchi, lungs

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Nose and Pharynx• Nose–External nose–Nasal cavity

• Functions–Passageway for air–Cleans the air–Humidifies, warms air–Smell–Along with paranasal

sinuses are resonating chambers for speech

• Pharynx–Common opening

for digestive and respiratory systems

–Three regions• Nasopharynx• Oropharynx• Laryngopharynx

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Larynx

• Functions–Maintain an open passageway for air

movement–Epiglottis and vestibular folds prevent

swallowed material from moving into larynx

–Vocal folds are primary source of sound production

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Vocal Folds

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Trachea

• Windpipe• Divides to

form–Primary

bronchi

Insert Fig 23.5 all but b

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Tracheobronchial Tree• Conducting zone

–Trachea to terminal bronchioles which is ciliated for removal of debris

–Passageway for air movement–Cartilage holds tube system open and

smooth muscle controls tube diameter• Respiratory zone

–Respiratory bronchioles to alveoli–Site for gas exchange

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Tracheobronchial Tree

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Bronchioles and Alveoli

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Lungs• Two lungs: Principal

organs of respiration–Right lung: Three lobes–Left lung: Two lobes

• Divisions–Lobes,

bronchopulmonary segments, lobules

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Ventilation• Movement of air into and out of

lungs• Air moves from area of higher

pressure to area of lower pressure• Pressure is inversely related to

volume

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Alveolar Pressure Changes

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Changing Alveolar Volume• Lung recoil

– Causes alveoli to collapse resulting from • Elastic recoil and surface tension

– Surfactant: Reduces tendency of lungs to collapse

• Pleural pressure– Negative pressure can cause alveoli to expand– Pneumothorax is an opening between pleural

cavity and air that causes a loss of pleural pressure

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Normal Breathing Cycle

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Compliance

• Measure of the ease with which lungs and thorax expand– The greater the compliance, the easier it is for a

change in pressure to cause expansion– A lower-than-normal compliance means the

lungs and thorax are harder to expand• Conditions that decrease compliance

– Pulmonary fibrosis– Pulmonary edema– Respiratory distress syndrome

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Pulmonary Volumes• Tidal volume

– Volume of air inspired or expired during a normal inspiration or expiration

• Inspiratory reserve volume– Amount of air inspired forcefully after inspiration of normal tidal

volume

• Expiratory reserve volume– Amount of air forcefully expired after expiration of normal tidal

volume

• Residual volume– Volume of air remaining in respiratory passages and lungs after the

most forceful expiration

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Pulmonary Capacities• Inspiratory capacity

– Tidal volume plus inspiratory reserve volume

• Functional residual capacity– Expiratory reserve volume plus the residual volume

• Vital capacity– Sum of inspiratory reserve volume, tidal volume, and expiratory

reserve volume

• Total lung capacity– Sum of inspiratory and expiratory reserve volumes plus the tidal

volume and residual volume

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Spirometer and Lung Volumes/Capacities

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Minute and Alveolar Ventilation• Minute ventilation: Total amount of air moved

into and out of respiratory system per minute• Respiratory rate or frequency: Number of

breaths taken per minute• Anatomic dead space: Part of respiratory

system where gas exchange does not take place• Alveolar ventilation: How much air per minute

enters the parts of the respiratory system in which gas exchange takes place

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Physical Principles of Gas Exchange

• Partial pressure– The pressure exerted by each type of gas in a mixture– Dalton’s law– Water vapor pressure

• Diffusion of gases through liquids– Concentration of a gas in a liquid is determined by its

partial pressure and its solubility coefficient– Henry’s law

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Physical Principles of Gas Exchange

• Diffusion of gases through the respiratory membrane– Depends on membrane’s thickness, the diffusion coefficient

of gas, surface areas of membrane, partial pressure of gases in alveoli and blood

• Relationship between ventilation and pulmonary capillary flow– Increased ventilation or increased pulmonary capillary blood

flow increases gas exchange– Physiologic shunt is deoxygenated blood returning from

lungs

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Oxygen and Carbon Dioxide Diffusion Gradients

• Oxygen– Moves from alveoli into

blood. Blood is almost completely saturated with oxygen when it leaves the capillary

– P02 in blood decreases because of mixing with deoxygenated blood

– Oxygen moves from tissue capillaries into the tissues

• Carbon dioxide– Moves from tissues

into tissue capillaries

– Moves from pulmonary capillaries into the alveoli

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Changes in Partial Pressures

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Hemoglobin and Oxygen Transport

• Oxygen is transported by hemoglobin (98.5%) and is dissolved in plasma (1.5%)

• Oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated when P02 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen.

• A shift of the curve to the left because of an increase in pH, a decrease in carbon dioxide, or a decrease in temperature results in an increase in the ability of hemoglobin to hold oxygen

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Hemoglobin and Oxygen Transport

• A shift of the curve to the right because of a decrease in pH, an increase in carbon dioxide, or an increase in temperature results in a decrease in the ability of hemoglobin to hold oxygen

• The substance 2.3-bisphosphoglycerate increases the ability of hemoglobin to release oxygen

• Fetal hemoglobin has a higher affinity for oxygen than does maternal

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Oxygen-HemoglobinDissociation Curve at Rest

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Oxygen-HemoglobinDissociation Curve during Exercise

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Shifting the Curve

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Transport of Carbon Dioxide

• Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%)

• Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect)

• In tissue capillaries, carbon dioxide combines with water inside RBCs to form carbonic acid which dissociates to form bicarbonate ions and hydrogen ions

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Transport of Carbon Dioxide

• In lung capillaries, bicarbonate ions and hydrogen ions move into RBCs and chloride ions move out. Bicarbonate ions combine with hydrogen ions to form carbonic acid. The carbonic acid is converted to carbon dioxide and water. The carbon dioxide diffuses out of the RBCs.

• Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels

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Carbon Dioxide Transportand Chloride Movement

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Respiratory Areas in Brainstem

• Medullary respiratory center– Dorsal groups stimulate the diaphragm– Ventral groups stimulate the intercostal and

abdominal muscles• Pontine (pneumotaxic) respiratory group

– Involved with switching between inspiration and expiration

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Respiratory Structures in Brainstem

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Rhythmic Ventilation• Starting inspiration

– Medullary respiratory center neurons are continuously active– Center receives stimulation from receptors and simulation from parts of

brain concerned with voluntary respiratory movements and emotion– Combined input from all sources causes action potentials to stimulate

respiratory muscles• Increasing inspiration

– More and more neurons are activated• Stopping inspiration

– Neurons stimulating also responsible for stopping inspiration and receive input from pontine group and stretch receptors in lungs. Inhibitory neurons activated and relaxation of respiratory muscles results in expiration.

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Modification of Ventilation

• Cerebral and limbic system– Respiration can be

voluntarily controlled and modified by emotions

• Chemical control– Carbon dioxide is

major regulator• Increase or decrease

in pH can stimulate chemo- sensitive area, causing a greater rate and depth of respiration

– Oxygen levels in blood affect respiration when a 50% or greater decrease from normal levels exists

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Modifying Respiration

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Regulation of Blood pH and Gases

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Herring-Breuer Reflex

• Limits the degree of inspiration and prevents overinflation of the lungs– Infants

• Reflex plays a role in regulating basic rhythm of breathing and preventing overinflation of lungs

– Adults• Reflex important only when tidal volume large as in

exercise

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Ventilation in Exercise• Ventilation increases abruptly

– At onset of exercise– Movement of limbs has strong influence– Learned component

• Ventilation increases gradually– After immediate increase, gradual increase occurs

(4-6 minutes)– Anaerobic threshold is highest level of exercise

without causing significant change in blood pH• If exceeded, lactic acid produced by skeletal muscles

23-42

Effects of Aging

• Vital capacity and maximum minute ventilation decrease

• Residual volume and dead space increase• Ability to remove mucus from respiratory

passageways decreases• Gas exchange across respiratory membrane

is reduced