Exam 3: Chapter 23: Respiratory System Flashcards by Makayla Lentz

*The ____ encloses the chamber for air inspiration.
*Although air can be inspired through the mouth, the mouth is part of the digestive system rather than the respiratory system

External Nose

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*The ______ is a cleaning, warming, and humidifying chamber for inspired air

Nasal Cavity

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*The _____ is commonly called the throat
*It serves as a common passageway for food and air

Pharynx

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*The _____ is frequently called the voice box
*Its rigid structure helps keep the airway constantly open, or patent

Larynx

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*The ____ is commonly known as the windpipe
*It serves as an air-cleaning tube to funnel inspired air to each lung

Trachea

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*The ____ are tubes that direct air into the lungs

Bronchi

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*Each _____ is a labyrinth of air tubes and a complex network of air sacs, called alveoli, and capillaries
*The air sacs are separated by walls of connective tissue containing both collagenous and elastic fibers
*Each air sac is the site of gas exchange between the air and the blood

Lungs

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*Breathing
*Gas exchange

Aspects of respiration

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Pulmonary ventilation
*Movement of air into and out of the lungs

Breathing

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*The diffusion of gases across membranes

Gas Exchange

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*The movement of gases between atmospheric air in the lungs and the blood

Pulmonary gas exchange

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*The movement of gases between the blood and the body’s cells

Tissue gas exchange

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Upper respiratory tract
Lower respiratory tract

Anatomical areas of respiratory tract

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*Includes the structures from the nose to the larynx

Upper Respiratory Tract

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*Includes the structures from the trachea through the alveoli in the lungs

Lower Respiratory Tract

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Conducting zone
Respiratory zone

Functional areas of the respiratory tract

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*Encompasses the structures from the nose to the smallest air tubes within the lungs and is strictly for pulmonary ventilation

Conducting Zone

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*Is solely within the lungs and includes some specialized small air tubes and the alveoli
*Gas exchange occurs within the _____

Respiratory Zone

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Pulmonary ventilation
Pulmonary gas exchange
Gas transport
Tissue gas exchange

Four processes necessary for gas exchange between the air and the cells of the body

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*This is what we more commonly refer to as breathing.
*Air moves into and out of the respiratory passages

Pulmonary Ventilation

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*At the terminal portion of the air tubes are tiny air sacs called alveoli
*O2 moves out of the alveolar air and into the blood
*At the same time, CO2 diffuses out of the blood and joins the air in the alveoli

Pulmonary gas exchange

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Carbon dioxide and O2 travel in the blood to and from cells

Gas transport

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*Gas exchange with the tissues involves the exit of O2 from the blood into cells, while CO2 exits cells to enter the blood

Tissue gas exchange

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Regulation of pH
Productions of chemical mediators
Voice production
Olfaction
Protection

Additional functions of the respiratory system

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*The respiratory system can alter blood pH by changing blood CO2 levels

Regulation of pH

*The lungs produce an enzyme called angiotensin-converting enzyme (ACE), which is an important component of blood pressure regulation

Productions of chemical mediators

Air moving past the vocal folds makes sound and speech possible

Voice production

*The sensation of smell occurs when airborne molecules are drawn into the nasal cavity

Olfaction

*The respiratory system provides protection against some microorganisms by preventing them from entering the body and removing them from respiratory surfaces

Protection

Nares Choanae Vestibule Hard Palate Nasal septum Chonchae Meatus Sinuses

Nasal cavity

oThe nasal cavity begins at the anterior external openings called the _____, or nostrils oIt extends to posterior openings into the pharynx

Nares

oThese openings are called _____ oInternal naris

Choanae

oJust inside each naris, in the anterior part of the nasal cavity, is a region called the _____ oThe ______ is lined with stratified squamous epithelium, which is continuous with the stratified squamous epithelium of the skin

Vestibule

oThe floor of the nasal cavity, which separates it from the oral cavity in the mouth, is called the ____ oThe _____ is formed by the palatine process of the maxillae and the palatine bone oWithin the nasal cavity, the ____ is covered by a highly vascular mucous membrane oIt is this mucous membrane that helps warm and humidify inspired air

Hard palate

oThe two halves of the nasal cavity are separated by a wall of tissue called the _____ oThe anterior part of the _____ is composed of cartilage, while the posterior part consists of the vomer bone and the perpendicular plate of the ethmoid bone

Nasal Septum

On each side of the nasal cavity, there are three lateral bony ridges called _______ oThe _____ used to be named the turbinate bones because they act as “wind turbines,” helping the air churn through the nasal cavity *The air passes through tunnels beneath each _____

Conchae

*Each of these tunnels is called a ______ oEach inferior ______ also contains the opening of a nasolacrimal duct for tear drainage from the surface of the eye

Meatus

oWithin the superior and middle meatuses are openings from the various paranasal ______

Sinuses

Passageway Cleans the air Humidifies and warms the air Olfaction Voice

Functions of Nasal Cavity

*The nasal cavity remains open even when the mouth is full of food

Passageway

*The vestibule is lined with hairs, which trap some of the large particles of dust in the air *The nasal septum and nasal conchae increase the surface area of the nasal cavity and make airflow within the cavity more turbulent, thereby increasing the likelihood that air will come into contact with the mucous membrane lining the nasal cavity *This mucous membrane consists of pseudostratified ciliated columnar epithelium wit goblet cells *The goblet cells secrete mucus, which traps debris in the air *The cilia on the surface of the mucous membrane sweep the mucus posteriorly to the pharynx, where it is swallowed and eliminated by the acidic secretions of the stomach

Cleans the Air

*Moisture is added to the air as it passes through the nasal cavity *There are two major sources for the moisture: 1.the mucous epithelium and 2.trars that drain into the nasal cavity through the nasolacrimal duct *Warm blood flowing through the mucous membrane warms the air within the nasal cavity before it passes into the pharynx, thus preventing damage to the rest of the respiratory passages due to cold air

Humidifies and Warms the Air

*The olfactory epithelium, the sensory organ for smell, is located in the most superior part of the nasal cavity

Olfaction

*The nasal cavity and paranasal sinuses are resonating chambers for speech

Voice

Nasopharynx Oropharynx Laryngopharynx

Regions of the Pharynx

*The ______ is the most superior portion of the pharynx *It is immediately posterior to the nasal cavity *Specifically, it is a continuation of the nasal cavity from the choanae *The ______ is superior to the soft palate *The nasopharynx is lined with a mucous membrane that traps debris such as dust, as well as microbes *This debris-laden mucus from the nasal cavity is moved through the ______ and swallowed *Any swallowed pathogens are likely killed by the acid in the stomach *The _______ is continuous with the middle ear through the auditory tubes to equalize air pressure between the atmosphere and the tympanic membrane *The posterior wall of the ______ houses the pharyngeal tonsil, or adenoids, which helps defend the body against infection

Nasopharynx

*The _____ is an incomplete partition composed of muscle and connective tissue *It separates the nasopharynx from the middle portion of the pharynx, the oropharynx *The extension of the ______ is called the uvula *The _____ prevents swallowed materials from entering the nasopharynx and nasal cavity *It pushes food and other materials toward the back of the pharynx

Soft Palate

*The ______ is a continuation of the nasopharynx *The ______ is the middle portion of the pharynx *It is immediately posterior to the mouth and begins at the soft palate *From there, it descends to the superior portion of the larynx *A region called the fauces joins the mouth’s oral cavity and the _____ *Thus, air, food, and drink all pass through the _______ *Moist stratified squamous epithelium lines the ______ and protects it against abrasion *Two groups of tonsils, called the palatine tonsils and the lingual tonsil, are located near the fauces

Oropharynx

*The ______ is a continuation of the oropharynx *The _______ spans the posterior length of the larynx: from the most superior larynx structure, the epiglottis, to the esophagus *Food and drink pass through the _________ to the esophagus *Although most air passes from the _______ into the larynx, a small amount of air may be swallowed with food and drink *The ________ is lined with moist stratified squamous epithelium

Laryngopharynx

The ______ is commonly known as the voice box *It is located in the anterior part of the laryngopharynx and extends from the base of the tongue to the trachea *The ______ is held in place by membranes and muscles superior to the hyoid bone *The rigid walls of the ____ maintain an open passageway between the pharynx and the trachea *Its rigidity is due to an outer casing of nine cartilages connected to one another by muscles and ligaments

Larynx

*The _______ is the largest of the cartilages *It is a single shield-shaped piece of cartilage, which is also known as the Adam’s apple

Thyroid Cartilage

Anchors larynx to trachea *The _____ forms the base of the larynx *It is a single piece of cartilage upon which the other cartilages rest

Cricoid Cartilage

Flap that covers the glottis during swallowing *The ____ is a single piece of cartilage that is attached to the thyroid cartilage and projects superiorly *The _____ is unique among the larynx cartilages because it is a freely movable flap and is constructed of elastic cartilage rather than hyaline cartilage *It helps divert food away from the trachea opening during swallowing

Epiglottic

Arytenoid cartilages Corniculate cartilages Cuneiform cartilages

Three pairs of small cartilage that forms walls of larynx

The paired ______ articulate with the superior border on the posterior of the cricoid cartilage

Arytenoid Cartilages

The paired ______ are attached to the superior tips of the arytenoid cartilages

Corniculate Cartilages

The paired ______ are contained in a mucous membrane anterior to the corniculate cartilages

Cuneiform Cartilages

*The ______, or true vocal cords, contain the inferior ligaments *At the junction of the ______ is an opening; this opening, in combination with the ______, is called the glottis *The epithelium covering the vestibular and ______ is stratified squamous

Vocal Folds (Inferior Folds)

*The ______, or false vocal cords, contain the superior pair of ligaments that extend from the anterior surface of the arytenoid cartilages to the posterior surface of the thyroid cartilage

Vestibular Folds (Superior Folds)

1.intrinsic muscles 2.extrinsic muscles

The Larynx Wall Contains Two Sets of Skeletal Muscles

Attach to the arytenoid and corniculate cartilages and aid in closing and opening the glottis

Intrinsic Muscles

Include the sternohyoid and the sternothyroid, which elevate the larynx during swallowing

Extrincis Muscles

*Maintains an open passageway for air movements *Prevents swallowed materials from entering the larynx and lower respiratory tract *Produces sound for speech *Protects the lower respiratory tract from foreign materials

Functions of Larynx

*The ____ is commonly known as the windpipe *It allows air to flow into the lungs *The _____ is a membranous tube attaches to the larynx and consists of dense regular connective tissue and smooth muscle *The _____ is reinforces with 15-20 C-shaped pieces of hyaline cartilage called ______ rings *The ______ rings support the trachea and prevent it from collapsing *The cartilages support the anterior and lateral sides of the ____ to protect it while maintaining a patent passageway for air *The ____ has an inside diameter of 12mm and a length of 10-12cm, descending from the larynx to the level of the fifth thoracic vertebra *The ______ rings are incomplete circles with the thickest portion of cartilage at the anterior wall of the ____ *The posterior wall of the ____ is devoid of cartilage and contains an elastic ligamentous membrane and bundles of smooth muscle *The smooth muscle, called the trachealis muscle, can narrow the diameter of the _____by contracting, which aids in coughing *Narrowing the _____ diameter causes air to move forcefully through the _____, helping to expel mucus and foreign objects during coughing *A mucous membrane lines the ____ *The membrane’s goblet cells produce mucus, which traps inspired dust, bacteria, and other foreign matter *The ciliated epithelium then moves the mucus and foreign matter into the larynx *From the larynx the foreign matter enters the pharynx and is swallowed

Trachea

*The trachea divides to form smaller tubes called ______, or primary bronchi, each of which extends to a lung

Main Bronchi

*At the location where the trachea divides into the two main bronchi is a ridge of cartilage called the ______ *The ______ is an important landmark for reading x-rays *In addition, the mucous membrane of the _____ is very sensitive to mechanical stimulation *If foreign matter is inspired to the level of the _____, it stimulates a powerful cough reflex *Materials in the air passageways beyond the _____ do not usually stimulate a cough reflex

Carina of Trachea

*The _____ consists of the trachea and the network of air tubes in the lungs *The trachea divides to from a left and right main bronchus, each of which divides to form smaller and smaller bronchi *The smaller bronchi continue getting smaller until they terminate in microscopic tubes and sacs *The right main bronchus is larger in diameter and more directly in line with the trachea than the left main bronchus *Because the right main bronchus is more in line with the trachea, an inspired object is more likely to become lodged in it than the left main bronchus *The main bronchi have cartilage rings like those in the trachea *Within each lung, there are four main classes of passageways *Overall, approximately 16 generations of branching occur from the trachea to the smallest air tubes *The walls of each class of air passageway are supported by cartilage and smooth muscle, giving way to all smooth muscle in the smallest air passageways *In addition, each class of air passageway is lined with a type of ciliated epithelium, which functions as a mucus-cilia escalator, trapping debris from the air and moving it to the larynx

Tracheobronchial Tree

*The ____, or secondary bronchi, arise directly from the main bronchi *In the _____, the C-shaped cartilage rings are replaced with cartilage plates *Smooth muscle forms a layer between the cartilage and mucous membrane *The _____ are lines with pseudostratified ciliated columnar epithelium, which slowly changes as the tubes get smaller and smaller *In the left lung, there are two ____ *In the right lung, there are three _____ *Each _____ supplies its own section of each lung, which are called lobes

Lobar Bronchi (Secondary Bronchi)

*The ______, or tertiary bronchi, supply subdivisions within each lung lobe, which are called bronchopulmonary segments *As the bronchi become smaller, the cartilage become sparse, and smooth muscle becomes more abundant

Segmental Bronchi (Tertiary Bronchi)

*The _____ result from continued branching of the segmental bronchi *Are less than 1mm in diameter and have less cartilage and more smooth muscle *The larger _____ are lines with ciliated simple columnar epithelium

Bronchioles

*The _____ arise from several subdivisions of bronchioles *The ______ have no cartilage in their walls, but the smooth muscle layer is prominent *The _______ are lines with ciliated simple cuboidal epithelium

Terminal Bronchioles

Occurs when the smooth muscle relaxes, making the bronchiole diameter larger

Bronchodilation

Occurs when the smooth muscle contracts, making the bronchiole diameter smaller

Bronchoconstriction

*Sight of gas exchange between atmospheric air and blood oThe sites of pulmonary gas exchange are the ____ oAre small, air-filled chambers where the air and the blood come into close contact with each other oFrom the terminal bronchioles to the ______, there are approximately seven generations of branching

Alveoli

Respiratory bronchioles Alveolar ducts Alveolar sacs

Branches of Bronchioles

The ______ have a few attached alveoli *As the _____ divide to form smaller _____, the number of attached alveoli increases

Respiratory Bronchioles

The ____ arise from the respiratory bronchioles *The ______ are like long, branching hallways with many open doorways *The “doorways” open into the alveoli *Eventually, the number of alveoli becomes so large that the wall of the _____ becomes just a series of alveoli

Alveolar Ducts

Are chambers connected to two or more alveoli at the end of an alveolar duct

Alveolar Sacs

Type I pneumocytes Type II pneumocytes

Cells that Form Alveolar Wall

 Are thin squamous epithelial cells that form 90% of the alveolar surface Most of the gas exchange between alveolar air and the blood takes place through these cells

Type I Pneumocytes

Are round or cube-shaped secretory cells that produce surfactant, which makes it easier for the alveoli to expand during inspiration

Type II Pneumocytes

oThe alveolar walls and surrounding pulmonary capillaries form the _____ in the lungs oThe ______ is the location of pulmonary gas exchange oIt is where O2 enters the blood and CO2 exits the blood oTo facilitate diffusion of gases, the ______ is extremely thin; it is thinner than a sheet of tissue paper oAssociated with each of the three components are secreted fluids and basement membranes, which fuse together o If any of these components were to increase in thickness, the rate of gas diffusion could be appreciably changed

Respiratory Membrane

Alveolar cell layer Capillary endothelial layer Space between the two cell layers

Respiratory Membrane Contains

A thin layer of alveolar fluid The alveolar epithelium, which is a single layer of simple squamous epithelium The basement membrane of alveolar epithelium A thin interstitial space The basement membrane of the capillary endothelium The capillary endothelium, which is a single layer of simple squamous cells

The Individual Layers of the Respiratory Membrane Are

*The ____ are the primary organs of gas exchange *Based on their volume, they are among the largest organs of the body *Each _____ is conical in shape and extends from the diaphragm to a point approximately 2.5cm superior to the clavicle *The portion of the ____ in contact with the diaphragm is the base *The portion of the _____ that extends above the clavicle is called the apex *The right ____ is larger than the left and weighs an average of 620g, whereas the left ____ weighs an average of 560g

Lungs

*All the structures passing through the hilum are referred to as the root of the ____ *The right ____ has three large sections called lobes, while the left ____ has two lobes *The ____ lobes are separated by deep, prominent fissures on the surface of the ____ *Each _____ lobe is supplied by a lobar bronchus *The left ____ also has a medial indentation called the cardiac notch *This structural arrangement provides room for the heart to lie between the _____ *The ____ lobes are further subdivided into bronchopulmonary segments *Each bronchopulmonary segment is supplied by the segmental bronchi *There are 9 bronchopulmonary segments in the left ___ and 10 in the right ____ *The bronchopulmonary segments are separated from each other by connective tissue partitions, which are not visible as surface fissures *Individual diseased bronchopulmonary segments can be surgically removed because major blood vessels and bronchi do not cross the connective tissue partitions *This leaves the rest of the _____ relatively intact *The bronchopulmonary segments are even further subdivided into lobules by partial walls of connective tissues

Lungs

*Bronchioles supply each lobule *Occupy entire thoracic cavity *Right ____ has 3 lobes, 2 fissures *Left ____ has 2 lobes, 1 fissure *The major route takes deoxygenated blood to the alveoli in the _____, where it is oxygenated *To get to the alveoli, the deoxygenated blood flows through pulmonary arteries to pulmonary capillaries *In the capillaries, the blood becomes oxygenated and returns to the heart through pulmonary veins *The second route takes oxygenated blood to the tissues of the bronchi down to the respiratory bronchioles *The oxygenated blood flows from the thoracic aorta through bronchial arteries to capillaries, where O2 is released *Deoxygenated blood from the proximal part of the bronchi returns to the heart through the bronchial veins and the azygos venous system *More distally, the venous drainage from the bronchi enters the pulmonary veins *Thus, the oxygenated blood returning from the alveoli in the pulmonary veins is mixed with a small amount of deoxygenated blood returning from the bronchi *The _____ have two lymphatic supplies: 1.the superficial lymphatic vessels and 2.the deep lymphatic vessels *The superficial lymphatic vessels are deep to the connective tissue that surrounds each lung, called the visceral pleura *These vessels drain lymph from the superficial ____ tissue and the visceral pleura *The deep lymphatic vessels follow the bronchi *These vessels drain lymph from the bronchi and associated connective tissues *There are no lymphatic vessels located in the walls of the alveoli

Lungs

Is an indentation on the medial surface of the lung *The ____ is where structures, such as the main bronchus, blood vessels, nerves, and lymphatic vessels, enter or exit the lung

Helium of Lung

*The lungs are contained within the thoracic cavity *There are two pleural cavities within the thoracic cavity *Each pleural cavity houses one lung *The pleural cavities are lined with a serous membrane *The serous membrane that covers the inner thoracic wall, the superior surface of the diaphragm, and the mediastinum is called the parietal ____ *At the hilum, the parietal ____ is continuous with the visceral ____, which covers the surface of the lung *Each lung is located in a pleural cavity *Pleural cavity is lined with parietal _____ *Visceral ____ covers each lung *____ fluid fills cavity and provides lubrication

Pleura

Diaphragm External intercostals Pectoralis minor Scalene muscles

Muscles of Inspiration

*Downward movement of the _____ upon contraction is responsible for approximately two-thirds of the thoracic volume increase *The _____ is dome-shaped, and the base of the dome attaches to the inner circumference of the inferior thoracic cage *The top of the dome is a flat sheet of connective tissue called the central tendon *In normal, quiet inspiration, contraction of the _____ causes the central tendon to move downward *This downward movement is facilitated by relaxation of the abdominal muscles, which moves the abdominal organs out of the way *As the depth of inspiration increases, the abdominal organs prevent the central tendon from moving inferiorly *Continued contraction of the ______ causes it to flatten as the lower ribs are elevated

Diaphragm

*Increase thoracic volume by elevating the ribs *As the ribs are elevated, the costal cartilages allow lateral rib movement and lateral expansion of the thoracic cavity *The ribs slope inferiorly from the vertebrae to the sternum, and elevation of the ribs also increases the anterior-posterior dimension of the thoracic cavity

External Intercostals

Pectoralis Minor

Scalene Muscles

Internal intercostals Transverse thoracis Abdominal muscles

Muscles of Expiration

*During quiet pulmonary ventilation, expiration is a passive process due to significant amounts of elastic tissue in the thorax wall and the lungs *When tension is removed, the thorax wall and the lungs spring back into a smaller, relaxed state *In addition, the diaphragm relaxes, which causes it to move upward *Also, the external intercostals relax and the ribs move downward

Internal Intercostals

Transverse Thoracis

*Contractions of ____ also cause the thoracic cavity volume to decrease and push the abdominal organs upward into the diaphragm, which moves it superiorly

Abdominal Muscles

Movement of air into and out of the respiratory tract

Ventilation

1.Actions of muscles of respiration 2.Air pressure gradients

Two Aspects Important to Ventilation

Air moves from areas of high pressure to areas of lower pressure

Behavior of Gases

*P=k/V oP is gas pressure oK is a constant for a given temperature oV is the volume of the container *Explains why, upon inspiration, the air pressure within the thoracic cavity decreases *Upon expiration, the air pressure within the thoracic cavity increases because the volume of the thoracic cavity decreases *Pressure is inversely proportional to volume *Change volume through contraction and relaxation of muscles of respiration

Boyle's Law

Thoracic cavity volume increases as diaphragm contracts *During _____, air flows into the lungs down its pressure gradient

Inspiration

Thoracic cavity volume decreases as diaphragm relaxes *During _____, air flows out of the lungs down its pressure gradient

Expiration

*The tidal volume is the normal volume of air inspired and expired with each breath *At rest, quiet pulmonary ventilation results in a _____ of approximately 500 mL

Tidal Volume (TV)

*Is the amount of air that can be inspired forcefully after a normal inspiration (approximately 3000 mL at rest)

Inspiratory Reserve Volume (IRV)

*Is the amount of air that can be forcefully expired after a normal expiration (approximately 1100 mL at rest)

Expiratory Reserve Volume (ERV)

*Is the volume of air still remaining in the respiratory passages and lungs after the most forceful expiration (approximately 1200 mL)

Residual Volume (RV)

*Are the sum of two or more pulmonary volumes

Pulmonary Capacities

*Is the tidal volume plus the inspiratory reserve volume *It is the amount of air a person can inspire maximally after a normal expiration (approximately 3500 mL at rest)

Inspiratory Capacity

*Is the sum of the inspiratory reserve volume, the tidal volume, and the expiratory reserve volume *It is the maximum volume of air a person can expel from the respiratory tract after a maximum inspiration (approximately 4600 mL)

Vital Capacity (VC)

*Is the sum of the inspiratory and expiratory reserve volumes plus the tidal volume and the residual volume (approximately 5800 mL)

Total Lung Capacity

Volume of air moved each minute; TV x respiratory rate * Tidal Volume x Respiratory Rate= Minute Volume *The ______ is a measure of the amount of air moved through the respiratory system per minute *The _____ can be calculated by multiplying the tidal volume by the respiratory rate *Although ______ measures the amount of air moving into and out of the respiratory system per minute, it is not a measure of the amount of air available for gas exchange *Is clinically important because it is an indication of CO2 levels, an important physiological parameter

Minute Volume

1.anatomical dead space 2.physiological dead space

There are two types of dead space within the respiratory system

*The _____ areas include all the structures of the upper respiratory tract, and structures of the lower respiratory tract to the terminal bronchioles *These are all of the conducting zone areas *The volume of air in the ______ is approximately 1 mL per pound of an individual’s ideal body weight

Anatomical Dead Space

*Is a combination of the anatomical dead space and the volume of any alveoli with lower than normal gas exchange

Physiological dead space

Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture *According to _____, the total pressure of a gas is the sum of the individual pressures of each gas

Dalton's Law

Pressure exerted by each gas is its _______ and is proportional to its percentage in the total gas mixture *The individual pressure of each gas is called the _______ *To determine the_____ of each gas, its percentage is multiplied by the total pressure 1.Example: air is 70% nitrogen, 20% oxygen, 9% carbon dioxide; pressure is 760 mmHg; the partial pressure of oxygen is equal to 20% of 760 mmHg or 152 mmHg

Partial Pressure

1.Air entering the respiratory system is humidified 2.O2 diffuses from the alveoli into the blood, while CO2 diffuses from the blood into the alveoli 3.The alveolar air is only partially replaced with atmospheric air during each inspiration

Three factors cause differences in the composition among alveolar air, expired air, and atmospheric air

*Gas molecules move from the air into a liquid, or from a liquid into the air, down their partial pressure gradients *Gases move from a higher partial pressure to a lower partial pressure *When partial pressures of gases are equal between the air and a liquid, they are in equilibrium *To calculate the amount of gas in a liquid, the partial pressure alone is not sufficient *The amount of gas is also dependent on how readily a gas dissolves in the liquid, which is called the solubility coefficient

Diffusion of Gases into and out of Liquids

When a gas is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure *At a given temperature, _______ describes the concentration of a gas at equilibrium in a liquid *Concentration of dissolved gas= Pressure of gas x Solubility coefficient

Henry's Law

Gas will move from areas of high pressure to areas of lower pressure

Movement of oxygen and carbon dioxide between the alveoli and blood depends on partial pressure differences

*Air pressure in the alveoli is called intra-alveolar pressure *When a person inspires, the intro-alveolar pressure decreases because the alveolar volume has increased *When a person expires, the intra-alveolar pressure increases because the alveolar volume has decreased *It is the pressure difference between atmospheric pressure and intra-alveolar pressure that results in air movement during one respiratory cycle

Mechanisms of Alveolar Ventilation

*At the end of expiration, before the next respiratory cycle starts, atmospheric pressure and intra-alveolar pressure are equal and no air moves into or out of the lungs

Alveolar Pressure Equals Atmospheric Pressure

Alveolar pressure decreases as thoracic volume increases *Alveolar pressure is less than atmospheric pressure *As _____ begins, contraction of inspiratory muscles increases thoracic volume, which results in expansion of the lungs and an increase in alveolar volume *The increased alveolar volume causes a decrease in intra-alveolar pressure below atmospheric pressure to approximately -1mm Hg. *Air flows into the lungs because atmospheric pressure is greater than intra-alveolar pressure

Inhalation

Alveolar pressure again equals atmospheric pressure *At the end of inspiration, the thorax stops expanding, the alveoli stop expanding, and the intra-alveolar pressure becomes equal to atmospheric pressure because of airflow into the lungs *No movement of air occurs after intra-alveolar pressure becomes equal to atmospheric pressure, but the volume of the lungs is larger than it was at the end of expiration

End of Inhalation

*Alveolar pressure is greater than atmospheric pressure as thoracic volume decreases *During _______, the volume of the thorax decreases as the diaphragm relaxes, and the thorax and lungs recoil *Because thoracic volume determines alveolar volume, the smaller thoracic volume results in a corresponding decrease in alveolar volume *Thus, intra-alveolar pressure rises over atmospheric pressure to approximately +1mm Hg *Because intra-alveolar pressure is greater than atmospheric pressure, air flows out of the lungs *As expiration ends, the decrease in thoracic volume stops, and the alveoli stop changing size *The process repeats, beginning at step 1

Exhalation

*The determining factor of gas movement direction is the _______ for each gas *If the _______ of a gas is higher in the alveolus, it will diffuse across the respiratory membrane into the blood *If the partial pressure of a gas is higher in the blood, it will diffuse across the respiratory membrane into the alveolus *When the partial pressure of a gas is greater on one side of the respiratory membrane than on the other side, net diffusion occurs from the higher to the lower partial pressure *Normally, the partial pressure of oxygen (P O2) is greater in the alveoli than in the blood of the pulmonary capillaries, and the partial pressure of carbon dioxide (P CO2) is greater in the blood than in the alveolar air

Partial Pressure Gradients

*The partial pressure gradient for O2 is into the blood from the alveoli *Once in the blood, the partial pressure gradient for O2 is into the body’s cells from the blood

Oxygen Partial Pressure Gradients

*The P O2 of alveolar air averages approximately 104 mm Hg *The P O2 in the pulmonary capillaries is approximately 40mm Hg *Thus, because the P O2 is higher in the alveolar air, O2 diffuses into the pulmonary capillaries, down its partial pressure gradient *Even if a person is exercising, by the time blood reaches the venous ends of the pulmonary capillaries, an equilibrium has been achieved and the P O2 in the blood is 104mm Hg *There is a slight decrease in the P O2 of blood in the pulmonary veins to about 95mm Hg *This slight decrease is due to mixing of deoxygenated blood from the bronchial veins with the blood leaving the pulmonary capillaries *The P O2 of arterial blood as it arrives in the tissues is still 95mm Hg compared to the P O2 of the interstitial fluid, which is 40mm Hg *The P O2 in individual tissue cells is around 20mm Hg *Thus, O2 diffuses out of the capillaries into the interstitial fluid and across the plasma membrane of individual cells *The individual cells then use the O2 to produce ATP, which releases CO2 as a by-product *By the time blood has reached the venous end of a capillary network, it has achieved equilibrium with the cells and interstitial fluid

Steps of the specific partial pressures for O2 as it moves toward the body's cells

*The partial pressure gradient for CO2 is the opposite that for O2 *Carbon dioxide moves out of the body’s cells and into the blood *Once in the blood, the partial pressure gradient for CO2 is out of the blood into the alveoli

Carbon Dioxide Partial Pressure Gradients

*As cells produce CO2, the intracellular P CO2 increases to approximately 46mm Hg and the interstitial fluid P CO2 is approximately 45mm Hg *The P CO2 of arterial blood as it arrives in the tissues is 40mm Hg *Thus, CO2 diffuses out of the cells, into the interstitial fluid and into the blood, down its partial pressure gradient *By the time blood has reached the venous end of the capillary network, it has achieved an equilibrium with the interstitial fluid and has a P CO2 of 45 mm Hg *The P CO2 of the blood when it returns to the arterial end of the pulmonary capillaries is still 45mm Hg, compared to a P CO2 of 40mm Hg in the alveoli *Thus, at the alveoli, Co2 diffuses out of the blood down its partial pressure gradient *At the venous end of the pulmonary capillaries, P CO2 has achieved an equilibrium with the alveoli and has decreased to 40mm Hg

Steps of partial pressures for CO2 as it moves away from the body's cells toward the alveoli (reverse of steps for O2)

*Increasing the thickness of the respiratory membrane decreases the rate of gas diffusion *The thickness of the respiratory membrane normally averages 0.6 µm, but diseases increase its thickness *A twofold or threefold thickness increase markedly decreases the rate of gas exchange *The most common cause of increased ________ is an accumulation of fluid in the alveoli, known as pulmonary edema *Alveolar fluid accumulation is usually caused by failure of the left side of the heart *Left-side heart failure increases venous pressure in the pulmonary capillaries and causes fluid to accumulate in the alveoli *Conditions that result in inflammation of the lung tissues, such as with tuberculosis or pneumonia, can also cause fluid accumulation within the alveoli

Respiratory Membrane Thickness

*In a healthy adult, the total surface area of the respiratory membrane is approximately 70m^2 (approximately one-fourth of the size of a tennis court or the floor area of a 25-by-30-foot room) *Several respiratory diseases, including emphysema and lung cancer, cause a decrease in the surface area of the respiratory membrane *Even small decreases in this surface area adversely affect the respiratory exchange of gases during strenuous exercise *When the total surface area of the respiratory membrane is decreased to one-third or one-fourth of normal, the exchange of gases is significantly restricted, even under resting conditions *A decreased surface area for gas exchange can also result from the surgical removal of lung tissue, the destruction of lung tissue by cancer, the degeneration of the alveolar walls by emphysema, or the replacement of lung tissue by connective tissue due to tuberculosis *More acute conditions that cause the alveoli to fill with fluid also reduce the surface area for gas exchange because the increased thickness of the respiratory membrane caused by the fluid accumulation makes the alveoli nonfunctional *This may occur in pneumonia or in pulmonary edema resulting from failure of the left ventricle

Respiratory Membrane Surface Area

*Once O2 diffuses through the respiratory membrane into the blood, it is transported to all cells of the body *Approximately 98.5% of O2 is transported reversibly bound to hemoglobin within red blood cells, and the remaining 1.5% is dissolved in the plasma *Cells use O2 in aerobic cellular respiration to synthesize ATP 1.Only 3% of oxygen in blood is dissolved gas, rest is bound to hemoglobin 2.Binding of oxygen to hemoglobin shows cooperativity, after binding of first oxygen to first heme, subsequent binding is easier; allows for rapid uptake of oxygen at lungs

Transport of O2

*Carbon dioxide is formed as a by-product of the breakdown of glucose when cells use O2 to produce ATP *The CO2 diffuses out of individual cells into the blood *The blood concentration of CO2 needs to be very tightly regulated because too much CO2 in the blood causes the blood to become acidic *There are three ways CO2 is transported in the blood: 1.Dissolved in the plasma, 2.Bound to hemoglobin, and 3.converted to bicarbonate ion (HCO3-)

Transport of CO2

*About 7% of CO2 dissolves directly in the plasma as it diffuses out of the cells and into the blood *The remaining CO2 diffuses into the red blood cells, where it either binds to hemoglobin or is converted to HCO3-

Transport of CO2 in the Plasma

*Approximately 23% of CO2 is transported bound to hemoglobin *Many CO2 molecules bind in a reversible fashion to the α- and β-globin chains of hemoglobin molecules *Carbon dioxide’s ability to bind to hemoglobin is affected by the amount of O2 bound to hemoglobin *The smaller the amount of O2 bound to hemoglobin, the greater the amount of CO2 able to bind to it, and vice versa *This relationship is called the Haldane effect *In tissues, as hemoglobin binds to CO2, the affinity of hemoglobin for O2 is reduced *This is beneficial because tissues with higher levels of CO2 demand more O2 in order to continue aerobic cellular respiration, our cell’s most efficient means of producing ATP

Transport of CO2 by Hemoglobin

*About 70% of blood CO2 is transported in the form of HCO3-, dissolved in either the cytoplasm of red blood cells or the plasma of the blood *Within red blood cells, an enzyme called carbonic anhydrase catalyzes a reversible reaction *Carbonic anhydrase catalyzes the production of carbonic acid (H2CO3) from CO2 and H2O *The H2CO3 then dissociated into H+ and HCO3- *As CO2 levels increase, more H+ is produced *Higher concentrations of H+ cause the pH to decrease and the solution becomes acidic *Because this is a reversible reaction, if CO2 levels decrease, carbonic anhydrase creates H2CO3 upon the combining of H+ and HCO3- *The H2CO3 then dissociates to form CO2 and H2O, which lowers H+ concentration, and pH increases into a more basic (alkaline) range *At the tissues, where CO2 levels are higher, HCO3- is removed from the red blood cell by and HCO3-/Cl- antiporter *This process is called the chloride shift *In the chloride shift, HCO3- diffuses out of the red blood cell while Cl- diffuses in through the antiporter *This exchange maintains electrical neutrality in the red blood cells and plasma *Removing HCO3- from inside the red blood cells also promotes greater CO2 transport *As HCO3- concentrations decrease within the red blood cell, more CO2 reacts with water to form additional HCO3- and H+ *Although elevated H+ levels usually create an acidic environment, there are mechanisms within the red blood cells that dampen the effect of increased H+ *Hemoglobin serves as a buffer within the red blood cell cytoplasm *Hemoglobin binds to H+, preventing an increase in H+ concentration 1.7% transported as dissolved gas 2.23% bound to hemoglobin (globin chain) 3.70% transported as bicarbonate ion

Transport of CO2 as Bicarbonate Ions

Effect of P O2 Bohr Effect Effect of Temperature Effect of BPG

Physiological Factors Affecting Gas Transport

*The relationship between O2 and hemoglobin is similar to that of a ligand and its receptor in that hemoglobin has specific binding sites for O2 *These binding sites are the heme groups of the hemoglobin *Hemoglobin is 100% saturated with O2 when four O2 molecules are bound to each hemoglobin molecule in the red blood cells *When there is an average of two O2 molecules bound to each hemoglobin molecule, hemoglobin is 50% saturated *The oxygen-hemoglobin dissociation curve describes the percent saturation of hemoglobin in the blood at different blood PO2 values *The degree of hemoglobin saturation is determined by many factors that affect the “attraction” of hemoglobin for O2 *This attraction is called affinity *Normally, the PO2 in the blood leaving the lungs is 104 mm Hg. *At that partial pressure, hemoglobin is 98% saturated *Decreases in the PO2 in the pulmonary capillaries have a relatively small effect on hemoglobin saturation, as shown by the fairly flat shape of the upper part of the oxygen-hemoglobin dissociation curve *Even if the blood PO2 decreases from 104mm Hg to 60mm Hg, hemoglobin is still 90% saturated *Because the affinity of hemoglobin for O2 is stable over a wide range of PO2 levels, hemoglobin is effective at picking up O2 in the lungs even if the PO2 drops significantly *23% of the O2 picked up in the lungs is released from hemoglobin *Oxygen the diffuses into the cells of the tissues *The 75% of O2 still bound to the hemoglobin is an O2 reserve, which can be released if blood PO2 decreases further *In the tissues, at lower PO2 levels, a relatively small change in blood PO2 results in a relatively large change in hemoglobin saturation *As tissues use more O2, hemoglobin releases more O2 to those tissues

Effect of P O2

*The effect of pH on the oxygen-hemoglobin dissociation curve is called the _____ *An increase in PCO2 also decreases hemoglobin’s ability to bind to O2 due to the effect of CO2 on pH *Changes in CO2 levels indirectly produce a______ by altering pH *In addition, CO2 can directly affect hemoglobin’s ability to bind to O2 *When CO2 binds to the α- and β-globin chains of hemoglobin, hemoglobin’s affinity for O2 is reduced *The ______ is beneficial to tissues when they are in high demand for O2

Bohr Effect

*An increase in temperature also decreases O2’s tendency to remain bound to hemoglobin *Therefore, elevated temperatures resulting from increased metabolism increase the amount of O2 released into the tissues by hemoglobin *In less metabolically active tissues in which the temperature is lower, less O2 is released from hemoglobin *When hemoglobin’s affinity for O2 decreases, the oxygen-hemoglobin dissociation curve is shifted to the right, and hemoglobin releases more O2 *During exercise, when CO2 and acidic substances accumulate and the temperature increases in the tissue spaces, the oxygen-hemoglobin curve shifts to the right *Under these conditions, as much as 75-85% of the O2 is released from the hemoglobin *In the lungs the curve shifts to the left because of the lower CO2 levels, lower temperature, and lower acid levels *Therefore, hemoglobin’s affinity for O2 increases, and it becomes easily saturated *During resting conditions, approximately 5mL of O2 are transported to the tissues in each 100mL of blood, and cardiac output is approximately 5000mL/min *Consequently, 250mL of O2 are delivered to the tissues each minute *During exercise, this value can increase up to 15 times *Oxygen transport can be increased threefold because of a greater degree of O2 release from hemoglobin in the tissue capillaries, and the rate of O2 transport is increased another five times because of the increase in cardiac output *Consequently, the volume of O2 delivered to the tissues can be as high as 3750mL/min *Highly trained athletes can increase this volume to as high as 5000mL/min

Effect of Temperature on O2 Transport

*Typically, when body temperature increases, the rate of ATP production is increased *Thus, more CO2 enters the blood and eventually is converted into H+ and HCO3-, lowering the pH *The response is often an increased respiratory rate, which removes excess CO2 from the body

Effect of Temperature on CO2 Transport

*As red blood cells metabolize glucose for energy, they produce a by-product called 2,3-bisphosphyoglycerate *BPG binds to hemoglobin, which reduces its affinity for O2 *Thus, hemoglobin release more O2 *A potent trigger for increased BPG production is low blood O2 *BPG helps increase O2 delivery to tissues because higher levels of BPG increase the release of O2 in tissues (the oxygen-hemoglobin dissociation curve shifts to the right) *When blood is removed from the body and stored in a blood bank, the BPG levels in the stored blood decrease *As BPG levels decrease, the blood becomes unsuitable for transfusion after approximately 6 weeks because the hemoglobin releases less O2 to the tissues *Banked blood is, therefore, discarded after 6 weeks of storage

Effect of BPG on O2 Transport

*BPG enhances the Haldane effect because hemoglobin with less O2 bound can transport more CO2

Effect of BPG on CO2 Transport

*Normally, resting pulmonary ventilation provides the body with all the O2 it needs to maintain homeostasis *This is because there are many alveoli, each of which is supplied with ample blood *The flow of blood to the alveoli through pulmonary is called pulmonary capillary perfusion *The relationship between ventilation of the alveoli and blood flow to the alveoli is called ventilation-perfusion coupling *There are certain conditions that disrupt normal ventilation-perfusion coupling *Even with normal ventilation-perfusion coupling, not 100% of cardiac output is fully saturated with O2 *Blood that is not completely oxygenated is called shunted blood *Blood that passes through pulmonary capillaries without becoming fully oxygenated is also shunted blood

Local Control

1.An anatomical shunt 2.A physiological shunt

There are two types of shuts in the lungs

*Due to deoxygenated blood from the bronchi and bronchioles mixing with blood in the pulmonary veins

Anatomical Shunt

*The combination of the anatomical shunt and incompletely oxygenated blood from the alveoli *Normally the ______ makes up 1-2% of cardiac output

Physiological Shunt

1.If there is insufficient blood flow to the alveoli 2.If there is insufficient air flow to the alveoli *Sometimes alveolar ventilation is sufficient, but blood flow to the alveoli has been reduced *Another factor that influences differences in blood flow to different areas of the lung is body position *When a person is standing, greater blood flow and pulmonary ventilation occur in the base of the lung than in the top of the lung because gravity tends to pull the blood down toward the base of the lungs *Thus, when standing, more gas exchange occurs at the base of the lungs *In other instances, alveolar ventilation is severely reduced and the blood in the pulmonary capillaries does not become fully oxygenated *This happens during an asthma attack when bronchioles become constricted

There are two main situations that can cause normal ventilation-perfusion coupling to be disrupted

*In pneumonia or pulmonary edema, a buildup of fluid in the alveoli results in poor gas diffusion and less oxygenated blood *Although gravity is the major factor affecting regional blood flow in the lung, under certain circumstances alveolar PO2 can also have an effect *In most tissues, low PO2 results in increased blood flow through the tissues *However, in the lung, low PO2 has the opposite effect *Low PO2 causes arterioles to constrict, which reduces blood flow *This response helps keep gas exchange in the lungs efficient *Blood is routed away from areas of low O2 toward parts of the lung that are better oxygenated *Because the function of the lungs is to acquire O2 for the body, it is more efficient to avoid low O2 areas in the lungs

There are two main situations that can cause normal ventilation-perfusion coupling to be disrupted

*Regulation of pulmonary ventilation is surprisingly complex *Pulmonary ventilation can be regulated voluntarily such as when speaking or chewing food; yet, during sleep or when focused on other tasks, pulmonary ventilation is regulated involuntarily *The brainstem is the site of automatic regulation of pulmonary ventilation *However, unlike regulation of the heart, which involves a specific set of pacemaker cells, there is not a known single set of neurons functioning as the pacemaker for pulmonary ventilation *The respiratory center is a complex network of neurons *The brainstem neurons control the basic rhythm of pulmonary ventilation through stimulation of the muscles of ventilation *The recruitment of muscle fibers and the more frequent stimulation of muscle fibers result in stronger muscle contractions and increased depth of pulmonary ventilation *The rate of pulmonary ventilation is determined by how frequently the respiratory muscles are stimulated

Neural Control

1.The ventral respiratory group 2.The dorsal respiratory group

The medullary respiratory center in the medulla oblongata consists of two sets of neurons

*Forms a longitudinal column of cells located in the ventral part of each half of the medulla oblongata *The VRG is responsible for generating the normal, involuntary rhythm of breathing, called eupnea *In addition, within the VRG is a collection of neurons that are active during both inspiration and expiration *A part of the VRG, the pre-Bötzinger complex, is believed to establish the basic rhythm of pulmonary ventilation

Ventral Respiratory Group (VRG)

*Forms a longitudinal column of cells in the dorsal part of each half of the medulla oblongata *The DRG receives sensory input from chemoreceptors and mechanoreceptors as well as other sources *The DRG integrates this information and then communicates with the VRG for any modifications to the respiratory rhythm

Dorsal Respiratory Group (DRG)

*Communication occurs between the two halves of the medulla within a respiratory group so that respiratory movements are symmetrical *Communication also occurs between the dorsal and ventral respiratory groups *Intercommunication among the VRG, DRG, and pontine respiratory group work to modify the rate and depth of breathing

Role of DRG and VRG

1.An inspiratory phase 2.A postinspiratory phase 3.An expiratory phase

Eupnea has three distinct phases

The pre-Bötzinger complex drives the continuous inspiratory rhythm, which last about 2 seconds The fundamental action of this ______ is generation of action potentials in the phrenic and intercostal nerves to drive contraction of the diaphragm and external intercostal muscles The pre-Bötzinger complex appears to also coordinate other groups of neurons in order to adjust the rate of inspiration based upon conditions in the body such as levels of CO2 or O2

Inspiratory Phase

During this phase, which is transient, the extrinsic laryngeal muscle contraction ceases and the contraction of the diaphragm is prolonged to prevent elastic recoil of the thorax This is beneficial for gas exchange because the length of time air stays in the lungs is increased The ______ is related to lung mechanoreceptor and pontine group functions

Postinspiratory Phase

A group of expiratory neurons within the VRG drive this phase, which lasts about 3 seconds These neurons inhibit the inspiratory neurons of the VRG, resulting in relaxation of the diaphragm and external intercostal muscle Expiration occurs due to elastic recoil of the thorax

Expiratory Phase

*Carbon dioxide is the principal regulator of respiratory rate *Changes in PO2 can also affect pulmonary ventilation *A decrease in O2 below its normal values is called hypoxia *If PO2 levels in the arterial blood are markedly reduced while the pH and PCO2 are held constant, an increase in pulmonary ventilation rate occurs *Within a normal range of PO2 levels, the effect of O2 on the regulation of pulmonary ventilation is small *Only after arterial PO2 decreases to approximately 50% of its normal value does it begin to have a large stimulatory effect on respiratory movements *At any PO2 above 80mm Hg, nearly all of the hemoglobin is saturated with O2 *If PO2 levels decrease below 80mm Hg, the oxygen-carrying capacity of the blood is significantly reduced *When PO2 levels are low, the carotid and aortic body chemoreceptors stimulate the respiratory center *This keeps it active despite decreasing O2 levels *If PO2 decreases sufficiently, the respiratory center can fail, resulting in death

Effect of PO2 on Respiratory Rate

*Blood CO2 levels are a major regulator of pulmonary ventilation during both resting conditions and intense exercise *Even a small increase in CO2 in the bloodstream triggers a large increase in the rate and depth of pulmonary ventilation *A greater than normal amount of CO2 in the blood is called hypercapnia and a lower-than-normal CO2 level is called hypocapnia *Hypocapnia results in periods when the pulmonary ventilation rate is reduced or does not occur at all *The chemoreceptors in the chemosensitive area of the medulla oblongata and in the carotid and aortic bodies respond to changes in CO2 primarily because of the effects of CO2 on blood pH *The chemosensitive area in the medulla oblongata is far more important in regulating PCO2 and pH than either the carotid or the aortic body *The carotid and aortic bodies are responsible for, at most, 15-20% of the total response to changes in PCO2 or pH *During intense exercise, however, the carotid bodies respond more rapidly to changes in blood pH than does the chemosensitive area of the medulla

Effect of PCO2 on Respiratory

*The central chemoreceptors in the medulla oblongata detect changes in blood pH due to changes in CO2 *The carotid and aortic bodies detect changes in pH due to changes in H+ concentrations *Because H+ does not easily cross the blood-brain barrier or the blood-cerebrospinal fluid barrier, the central chemoreceptors detect changes in blood pH through changes in blood CO2 *Carbon dioxide easily diffuses across the blood-brain barrier and the blood-cerebrospinal fluid barrier *The lower pH then stimulates the respiratory center, resulting in a greater rate and depth of pulmonary ventilation reducing CO2 levels, and blood pH increases to normal levels *Maintaining body pH levels within normal limits is necessary for the proper functioning of cells *Because changes in CO2 levels can change pH, the respiratory system plays an important role in acid-base balance

Effect of pH on Respiratory Rate

*The rate and depth of pulmonary ventilation is controlled both voluntarily and involuntarily by the cerebral cortex *During exercise, respiratory rate changes are controlled through various inputs to the respiratory center *Initially, there is a very rapid increase that occurs too quickly to be accounted for by changes in metabolism *After the initial immediate increase in respiratory rate, there is a gradual increase that levels off within 4-6 minutes *The highest level of exercise that can be performed without causing a significant change in blood pH is called the anaerobic threshold *If the exercise intensity is high enough the exceed the anaerobic threshold, blood pH drops *The drop in pH stimulates the carotid bodies, which increases pulmonary ventilation *Pulmonary ventilation can increase so much that arterial PCO2 decreases below resting levels and arterial PO2 increases above resting levels *Apnea is the absence of pulmonary ventilation *A person may stop breathing voluntarily *As the period of voluntary apnea increases, a greater and greater urge to breathe develops *That urge is primarily due to high PCO2 levels in the arterial blood *The PCO2 reaches levels that cause the respiratory center to override the conscious influence from the cerebrum *Occasionally, people are able to hold their breath until the blood PCO2 declines to a level low enough that they lose consciousness *After consciousness is lost, the respiratory center resumes its normal automatic control of pulmonary ventilation *On the other hand, voluntary hyperventilation decreases blood PCO2 levels far enough, which causes vasodilation of the peripheral blood vessels and a corresponding drop in blood pressure *Dizziness or a giddy feeling can result because the decreased blood pressure results in a decreased rate of blood flow to the brain, and therefore less O2 is delivered to the brain *Emotions acting through the limbic system of the brain can also affect the respiratory center

Cerebral and Limbic System Control of Respiratory Rate

*Higher brain centers control the respiratory system when touch, thermal, or pain receptors are activated *An increase in body temperature can stimulate increased pulmonary ventilation because metabolism is elevated and more CO2 is produced, which then needs to be expelled from the body

Other Modifications of Pulmonary Ventiliation

A.Medulla and pons are involved in regulating respiration B.Chemical factors affect breathing rate

Note on Regulating Respiration and Breathing

1.Partial pressure of carbon dioxide 2.Partial pressure of oxygen

Chemical Factors That Affect Breathing Rate

Most powerful stimulant; affects CNS; increases in carbon dioxide results in decrease in blood pH, will cause an increase in the breathing rate

Partial Pressure of Carbon Dioxide

Affects PNS; substantial decrease in oxygen is needed to affect breathing rate

Partial Pressure of Oxygen

Exam 3: Chapter 23: Respiratory System Flashcards

(170 cards)