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Anatomy and Physiology, Seventh Edition

Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

Chapter 23Chapter 23

Lecture OutlineLecture Outline**

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Chapter 23

Respiratory System

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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

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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

are drawn into nasal cavity• Protection: Against microorganisms by preventing

entry and removing them from respiratory surfaces.

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Respiratory System Divisions

• Upper tract: nose, pharynx and associated structures

• Lower tract: larynx, trachea, bronchi, lungs and the tubing within the lungs

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Nose and Nasal Cavities• External nose• Nasal cavity

– From nares to choanae– Vestibule: just inside nares– Hard palate: floor of nasal

cavity– Nasal septum: partition

dividing cavity. Anterior cartilage; posterior vomer and perpendicular plate of ethmoid

– Choanae: bony ridges on lateral walls with meatuses between. Openings to paranasal sinuses and to nasolacrimal duct

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Functions of Nasal Cavity

• Passageway for air• Cleans the air• Humidifies, warms air• Smell• Along with paranasal sinuses are

resonating chambers for speech

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Pharynx• Common opening for digestive and

respiratory systems• Three regions

– Nasopharynx: pseudostratified columnar epithelium with goblet cells. Mucous and debris is swallowed. Openings of Eustachian (auditory) tubes. Floor is soft palate, uvula is posterior extension of the soft palate.

– Oropharynx: shared with digestive system. Lined with moist stratified squamous epithelium.

– Laryngopharynx: epiglottis to esophagus. Lined with moist stratified squamous epithelium

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Larynx

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Larynx• Unpaired cartilages

– Thyroid: largest, Adam’s apple– Cricoid: most inferior, base of larynx– Epiglottis: attached to thyroid and has a flap near base of

tongue. Elastic rather than hyaline cartilage

• Paired– Arytenoids: attached to cricoid– Corniculate: attached to arytenoids– Cuneiform: contained in mucous membrane

• Ligaments extend from arytenoids to thyroid cartilage– Vestibular folds or false vocal folds: prevent food and

liquids from entering larynx during swallowing– True vocal cords or vocal folds: sound production.

Opening between is glottis

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Functions of Larynx

• Maintain an open passageway for air movement: thyroid and cricoid cartilages

• Epiglottis and vestibular folds prevent swallowed material from moving into larynx

• Vocal folds are primary source of sound production. Greater the amplitude of vibration, louder the sound. Frequency of vibration determines pitch. Arytenoid cartilages and skeletal muscles determine length of vocal folds and also abduct the folds when not speaking to pull them out of the way making glottis larger.

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Vocal Folds

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Trachea• Membranous tube of dense regular

connective tissue and smooth muscle; supported by 15-20 hyaline cartilage C-shaped rings open posteriorly. Posterior surface is elastic ligamentous membrane and bundles of smooth muscle called the trachealis. Contracts during coughing.

• Inner lining: pseudostratified ciliated columnar epithelium with goblet cells. Mucus traps debris, cilia push it superiorly toward larynx and pharynx. Divides to form– Left and right primary bronchi– Carina: cartilage at bifurcation.

Membrane of carina especially sensitive to irritation and inhaled objects initiate the cough reflex

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Tracheobronchial Tree and

Conducting Zone

• Trachea to terminal bronchioles which is ciliated for removal of debris. – Trachea divides into two primary

bronchi. – Primary bronchi divide into

secondary bronchi (one/lobe) which then divide into tertiary bronchi.

– Bronchopulmonary segments: defined by tertiary bronchi.

– Tertiary bronchi further subdivide into smaller and smaller bronchi then into bronchioles (less than 1 mm in diameter), then finally into terminal bronchioles.

• Cartilage: holds tube system open; smooth muscle controls tube diameter.

• As tubes become smaller, amount of cartilage decreases, amount of smooth muscle increases

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Respiratory Zone: Respiratory Bronchioles to Alveoli

• Respiratory zone: site for gas exchange– Respiratory bronchioles

branch from terminal bronchioles. Respiratory bronchioles have very few alveoli. Give rise to alveolar ducts which have more alveoli. Alveolar ducts end as alveolar sacs that have 2 or 3 alveoli at their terminus.

– No cilia, but debris removed by macrophages. Macrophages then move into nearby lymphatics or into terminal bronchioles.

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The Respiratory Membrane

• Three types of cells in membrane.– Type I pneumocytes. Thin squamous

epithelial cells, form 90% of surface of alveolus. Gas exchange.

– Type II pneumocytes. Round to cube-shaped secretory cells. Produce surfactant. (Discuss later)

– Dust cells (phagocytes)• Layers of the respiratory membrane

– Thin layer of fluid lining the alveolus– Alveolar epithelium (simple squamous

epithelium– Basement membrane of the alveolar

epithelium– Thin interstitial space– Basement membrane of the capillary

endothelium– Capillary endothelium composed of

simple squamous epithelium• Tissue surrounding alveoli contains elastic

fibers that contribute to recoil.

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Lungs

• Two lungs: Principal organs of respiration– Base sits on diaphragm, apex

at the top, hilus on medial surface where bronchi and blood vessels enter the lung. All the structures in hilus called root of the lung.

– Right lung: three lobes. Lobes separated by fissures

– Left lung: Two lobes• Divisions

– Lobes (supplied by secondary bronchi), bronchopulmonary segments (supplied by tertiary bronchi and separated from one another by connective tissue partitions), lobules (supplied by bronchioles and separated by incomplete partitions).

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Thoracic WallsMuscles of Respiration

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Thoracic Wall

• Thoracic vertebrae, ribs, costal cartilages, sternum and associated muscles

• Thoracic cavity: space enclosed by thoracic wall and diaphragm

• Diaphragm separates thoracic cavity from abdominal cavity

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Inspiration and Expiration• Inspiration: diaphragm, external intercostals, pectoralis minor,

scalenes– Diaphragm: dome-shaped with base of dome attached to inner

circumference of inferior thoracic cage. Central tendon: top of dome

• Quiet inspiration: accounts for 2/3 of increase in size of thoracic volume. Inferior movement of central tendon and flattening of dome. Abdominal muscles relax

– Other muscles: elevate ribs and costal cartilages allow lateral rib movement

• Expiration: muscles that depress the ribs and sternum: abdominal muscles and internal intercostals.

• Quiet expiration: relaxation of diaphragm and external intercostals with contraction of abdominal muscles

• Labored breathing: all inspiratory muscles are active and contract more forcefully. Expiration is rapid

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Effect of Rib and Sternum

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Pleura• Pleural cavity surrounds each lung and is formed by the pleural membranes. Filled with pleural fluid.

• Visceral pleura: adherent to lung. Simple squamous epithelium, serous.

• Parietal pleura: adherent to internal thoracic wall.

• Pleural fluid: acts as a lubricant and helps hold the two membranes close together (adhesion).

• Mediastinum: central region, contains contents of thoracic cavity except for lungs.

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Blood and Lymphatic Supply• Two sources of blood to lungs:

– Pulmonary artery brings deoxygenated blood to lungs from right side of heart to be oxygenated in capillary beds that surround the alveoli. Blood leaves via the pulmonary veins and returns to the left side of the heart.

– Oxygenated blood travels to the tissues of the bronchi. Bronchial arteries (branches of thoracic aorta) to capillaries. Part of this now deoxygenated blood exits through the bronchial veins to the azygous; part merges with blood of alveolar capillaries and returns to left side of heart.

– Blood going to left side of heart via pulmonary veins carries primarily oxygenated blood, but also some deoxygenated blood from the supply of the walls of the conducting and respiratory zone.

• Two lymphatic supplies: superficial and deep lymphatic vessels. Exit from hilus– Superficial drain superficial lung tissue and visceral pleura– Deep drain bronchi and associated C.T.– No lymphatics drain alveoli

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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• General Gas Law: PV = nRT, where P = pressure, V =

volume, n = #gram-molecules of gas, R = gas constant, T = temperature.

• Pressure is proportionate to number of molecules and temperature

• P = nRT/V Pressure is inversely proportionate to volume• F = P1-P2/R where F = air flow, P1 and P2 are pressures in

two different places, and R = resistance to flow.• If barometric pressure is greater than alveolar pressure, then

air flows into the alveoli.• If diaphragm contracts, then size of alveoli increases.

Remember P is inversely proportionate to V; so as V gets larger (when diaphragm contracts), then P in alveoli gets smaller.

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Alveolar Pressure Changes

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Changing Alveolar Volume: Lung Recoil

• Causes alveoli to collapse resulting from – Elastic recoil: elastic fibers in the alveolar walls– Surface tension: film of fluid lines the alveoli. Where

water interfaces with air, polar water molecules have great attraction for each other with a net pull in toward other water molecules. Tends to make alveoli collapse.

• Surfactant: Reduces tendency of lungs to collapse by reducing surface tension. Produced by type II pneumocytes.

• Respiratory distress syndrome (hyaline membrane disease). Common in infants with gestation age of less than 7 months. Not enough surfactant produced.

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Pleural Pressure

• Negative pressure can cause alveoli to expand

• Alveoli expand when pleural pressure is low enough to overcome lung recoil

• 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: deposition of inelastic fibers in lung (emphysema)

– Pulmonary edema– Respiratory distress syndrome– Increased resistance to airflow caused by airway

obstruction (asthma, bronchitis, lung cancer)– Deformities of the thoracic wall (kyphosis, scoliosis)

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Pulmonary Volumes and Capacities• Spirometry: measures volumes of air that move into and

out of respiratory system. Uses a spirometer• Tidal volume: amount of air inspired or expired with each

breath. At rest: 500 mL• Inspiratory reserve volume: amount that can be inspired

forcefully after inspiration of the tidal volume (3000 mL at rest)

• Expiratory reserve volume: amount that can be forcefully expired after expiration of the tidal volume (100 mL at rest)

• Residual volume: volume still remaining in respiratory passages and lungs after most forceful expiration (1200 mL)

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Pulmonary Capacities

• The sum of two or more pulmonary volumes• Inspiratory capacity: tidal volume plus

inspiratory reserve volume• Functional residual capacity: expiratory reserve

volume plus 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 tidal volume and residual volume.

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Spirometer, Lung Volumes, and Lung Capacities

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Minute Ventilation and Alveolar Ventilation

• Minute ventilation: total air moved into and out of respiratory system each minute; tidal volume X respiratory rate

• Respiratory rate (respiratory frequency): number of breaths taken per minute

• Anatomic dead space: formed by nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles

• Physiological dead space: anatomic dead space plus the volume of any alveoli in which gas exchange is less than normal.

• Alveolar ventilation (VA): volume of air available for gas exchange/minute

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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: in a mixture of gases, the percentage of each gas is proportionate to its partial pressure

– Water vapor pressure: pressure exerted by gaseous water in a mixture of gases

– Air in the respiratory system contains humidity because of mucus lining system

• Diffusion of gases through liquids– Henry’s Law: Concentration of a gas in a liquid is

determined by its partial pressure and its solubility coefficient

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Physical Principles of Gas Exchange

• Diffusion of gases through the respiratory membrane depends upon three things

1. Membrane thickness. The thicker, the lower the diffusion rate

2. Diffusion coefficient of gas (measure of how easily a gas diffuses through a liquid or tissue). CO2 is 20 times more diffusible than O2, surface areas of membrane, partial pressure of gases in alveoli and blood

3. Surface area. Diseases like emphysema and lung cancer reduce available surface area

4. Partial pressure differences. Gas moves from area of higher partial pressure to area of lower partial pressure. Normally, partial pressure of oxygen is higher in alveoli than in blood. Opposite is usually true for carbon dioxide

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Relationship Between Ventilation and Pulmonary Capillary Flow

• Increased ventilation or increased pulmonary capillary blood flow increases gas exchange

• Shunted blood: blood that is not completely oxygenated• Physiologic shunt is deoxygenated blood returning from lungs.

Two sources:– Blood returning from bronchi bronchioles– Blood from capillaries around alveoli

• Regional distribution of blood flow determined primarily by gravity, but can also be determined by alveolar PO2. – Low PO2 causes arterioles to constrict so that blood is

shunted to a region of the lung where the alveoli are better ventilated.

– In other tissues of the body, low PO2 causes arterioles to dilate to deliver more blood to the tissues.

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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

– PO2 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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Gas Exchange

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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: describes the percentage of hemoglobin saturated with oxygen at any given PO2

• Oxygen-hemoglobin dissociation curve at rest shows that hemoglobin is almost completely saturated when PO2 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen.

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Curve During Exercise

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Bohr Effect

• Effect of pH on oxygen-hemoglobin dissociation curve: as pH of blood declines, amount of oxygen bound to hemoglobin at any given PO2 also declines

• Occurs because decreased pH yields increase in H+ that combines with hemoglobin changing its shape and oxygen cannot bind to hemoglobin

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Effects of CO2 and Temperature

• Increase in PCO2 causes decrease in pH• Carbonic anhydrase causes CO2 and water

to combine reversibly and form H2CO3 which ionizes to H+ and HCO3

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• Increase temperature: decreases tendency for oxygen to remain bound to hemoglobin, so as metabolism goes up, more oxygen is released to the tissues.

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Effect of BPG

• 2,3-bisphosphoglycerate (BPG): released by RBCs as they break down glucose for energy

• Binds to hemoglobin and increases release of oxygen

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Shifting the Curve

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Fetal Hemoglobin• Fetal hemoglobin picks up oxygen from maternal hemoglobin

for several reasons• Concentration of fetal hemoglobin is 50% greater than

concentration of maternal hemoglobin.• Oxygen-hemoglobin dissociation of fetal hemoglobin is left of

maternal; i.e., fetal can bind oxygen better than maternal• BPG has little effect on fetal hemoglobin. Does not cause it to

release oxygen• Movement of carbon dioxide out of fetal blood causes the fetal

oxygen-hemoglobin dissociation curve to shift to the left. Simultaneously, movement of carbon dioxide into mother’s blood causes maternal oxygen-hemoglobin dissociation curve to shift to the right: double Bohr effect

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Transport of Carbon Dioxide

• Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%: primarily hemoglobin) 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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Carbon Dioxide Transport and Chloride Movement

(a) Tissue capillaries: as CO2 enters red blood cells, reacts with water to form bicarbonate and hydrogen ions. Chloride ions enter the RBC and bicarbonate ions leave: chloride shift. Hydrogen ions combine with hemoglobin. Lowering the concentration of bicarbonate and hydrogen ions inside red blood cells promotes the conversion of CO2 to bicarbonate ion.

(b) Pulmonary capillaries: CO2 leaves red blood cells, resulting in the formation of additional CO2 from carbonic acid. The bicarbonate ions are exchanged for chloride ions, and the hydrogen ions are released from hemoglobin.

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

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Respiratory Structures 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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Rhythmic Ventilation: a Possible Explanation

• 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

• Apnea. Cessation of breathing. Can be conscious decision, but eventually PCO2 levels increase to point that respiratory center overrides

• Hyperventilation. Causes decrease in blood PCO2 level. Peripheral vasodilation causes decrease in BP. Fainting. Problem before diving.

• Cerebral and limbic system. Respiration can be voluntarily controlled and modified by emotions

• Chemical control– Carbon dioxide is major

regulator, but indirectly through pH change

• 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

• CO2. – Hypercapnia: too much CO2

– Hypocapnia: lower than normal CO2

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Modifying Respiration

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Chemical Control of Ventilation• Chemoreceptors: specialized neurons that respond

to changes in chemicals in solution– Central chemoreceptors: chemosensitive area of the

medulla oblongata; connected to respiratory center– Peripheral chemoreceptors: carotid and aortic bodies.

Connected to respiratory center by cranial nerves IX and X

• Effect of pH: chemosensitive area of medulla oblongata and carotid and aortic bodies respond to blood pH changes– Chemosensitive areas respond indirectly through

changes in carbon dioxide– Carotid and aortic bodies respond directly to pH changes

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Chemical Control of Ventilation• Effect of Carbon Dioxide: small change in carbon

dioxide in blood triggers a large increase in rate and depth of respiration– Hypercapnia: greater-than-normal amount of carbon

dioxide– Hypocapnia: lower-than-normal amount of carbon

dioxide

• Chemosensitive area in medulla oblongata is more important for regulation of PCO2 and pH

• Carotid bodies respond rapidly to changes in blood pH because of exercise

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Chemical Control of Ventilation

• Effect of oxygen: carotid and aortic body chemoreceptors respond to decreased PO2 by increased stimulation of respiratory center to keep it active despite decreasing oxygen levels

• Hypoxia: decrease in oxygen levels below normal values

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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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Effect of Exercise on Ventilation• 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: highest level of exercise without causing significant change in blood pH. If exceeded, lactic acid produced by skeletal muscles

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Other Modifications of Ventilation

• Activation of touch, thermal and pain receptors affects respiratory center

• Sneeze reflex, cough reflex

• Increase in body temperature yields increase in ventilation

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Respiratory Adaptations to Exercise

• Athletic training– Vital capacity increases slightly; residual volume

decreases slightly– At maximal exercise, tidal volume and minute

ventilation increases– Gas exchange between alveoli and blood increases at

maximal exercise– Alveolar ventilation increases– Increased cardiovascular efficiency leads to greater

blood flow through the lungs

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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