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88 Cards in this Set
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- Back
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Respiration and Respiratory System |
Respiration: can mean ventilation of the lungs (breathing) or the use of oxygen in cellular metabolism
Respiratory System: an organ system that rhythmically takes in air and expels it from the body, thereby supplying the body with oxygen and expelling carbon dioxide that it generates |
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Functions of the Respiratory System |
• Gas exchange: provides for oxygen and carbon dioxide exchange between the blood and air • Communication: serves for speech and vocalization (laughing/crying) • Olfaction: sense of smell • Acid-Base balance: By elimination CO2, it helps to control the pH of the body fluids • BP regulation: the lungs carry out a step in synthesizing angiotensin II, which helps to regulate blood pressure
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Functions of the Respiratory System Cont. |
• Blood and lymph flow: breathing creates pressure gradients between the thorax and abdomen that promote the flow of lymph and venous blood • Blood filtration: the lungs filter small blood clots from the bloodstream and dissolve them preventing clots from obstructing the more vital circulations • Valsalva maneuver: is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth, pinching one's nose shut while pressing out as if blowing up a balloon. |
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Principle Organs of the Respiratory System |
Nose, pharynx, laynx, trachea, bronchi, and lungs with a membrane (pleurae) to protect them.
Within the lungs, air flows along a dead end pathway consisting of bronchi→ bronchioles→ alveoli (millions of tiny, thin walled air sacs). Incoming air stops in the alveoli, exchanges gases with the bloodstream through the alveolar wall and then flows back out. |
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Divisions of the Respiratory System: Conducting Zone |
consists of a passageway of air that serves only for airflow- they warm, moisten, humidify and cleanse. Located in the nose, pharynx, larynx, trachea and bronchioles. The walls of these passages are too thick for adequate diffusion of oxygen from the air into the blood. |
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Divisions of the Respiratory System: Respiratory Zone |
· actual site of gas exchange that consists of alveoli and other gas exchange regions of the distal airway. It is composed of the respiratory bronchioles, alveolar ducts, and alveoli.
· The airway from the nose through the larynx is often called the upper respiratory tract (head and neck) and the regions from the trachea through the lungs is the lower respiratory tract (thorax organs)
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Nose Introduction |
warms, cleanses and humidifies inhaled air, detects odor and serves as a resonating chamber that amplifies the voice. It extends from anterior openings called the nostrils or anterior naris to a pair of posterior openings called the posterior nasal apertures or choanae
· The internal chamber of the nose is called the nasal cavity, which is divided into right and left halves called the nasal fossae. The dividing wall is a vertical plate, the nasal septum, that is composed of bone and hyaline cartilage.
· The paranasal sinuses and nasolacrimal ducts of the orbits drain into the nasal cavity
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Nasal Cavity |
begins with a chamber called the vestibule, which is lined with stratified squamous epithelium and has guard hairs or vibrissae that block insects and debris from entering the nose. The nasal cavity expands into a larger chamber where it occupies the superior, middle and inferior nasal conchae. |
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Conchae |
· The inferior conchae has a venous plexus called the erectile tissue (swell body)- erectile tissue on one side swells with blood and restricts airflow- air is then directed to the other nostril (switches off every hour). Beneath each concha is a narrow air passage called a meatus- helps to ensure that most air contacts the mucous membrane on its way through
· The conchae enables the nose to cleanse, warm and humidify the air more effectively
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Respiratory Epithelium of the Nose |
Epithelium that covers the rest of the nasal cavity and is ciliated pseudostratified epithelium. In the olfactory epithelium, the cilia are immobile and serve to bind odor molecules, but in the respiratory epithelium, they are mobile.
· Goblet cells secrete mucus and the ciliated cells propel the mucus posteriorly toward the pharynx- dust, pollen, bacteria and other foreign matter stick to the mucus are swallowed- they are either digested or pass through the digestive tract rather than contaminating the lungs
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Lamina Propria of the Nose |
· contains mucus glands and is well populated by lymphocytes and plasma cells that mount immune defenses against inhaled pathogens. It contains large blood vessels that help to warm the air
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The Pharynx and Nasopharynx |
a muscular funnel extending about 13 cm from the posterior nasal apertures to the larynx- it has three divisions: 1. Nasopharynx: receives the auditory tubes from the middle ears and houses the pharyngeal tonsil- inhaled air turns 90 degrees downward as it passes through the nasopharynx causing large particles to turn because of the inertia (normally cannot) - The large particles collide with the wall of the nasopharynx and stick to the muscosa near the tonsil, which is positioned to respond to airborne pathogens
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Oropharynx and Laryngopharynx |
1. Oropharynx: a space between the posterior margin of the solf palate and the epiglottis- houses the palatine and lingual tonsils
2. Laryngopharynx: lies mostly posterior to the larynx and extends to the cricoid cartilage- esophagus begins at this point
The nasopharynx passes only air and is lined by pseudostratified columnar epithelium, whereas the oropharynx and laryngopharynx pass air, food, and drink and are lined by stratified squamous epithelium
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The Larynx |
or voice box is a cartilaginous chamber where its primary function is to keep food and drink out of the airway but has also evolved the role of sound production (phonation) |
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The Epiglottis |
flap of tissue that guards the superior opening of the larynx. At rest, the epiglottis stands almost vertically, but when swallowing occurs, the extrinsic muscles of the larynx pull the larynx upward toward the epiglottis, the tongue pushes the epiglottis downward to meet it, and the epiglottis closes the airway and directs food and drink into the esophagus behind it
- In infants, the epiglottis is high in the throat so infants are able to chew and breathe at the same time- by age 2, it descends to a lower positions where this action becomes impossible |
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Cartilages of the Larynx |
Cartilage is the primary structure and has bad blood supply 1. Epiglottic cartilage: most superior in the epiglottis 2. Thyroid cartilage: largest- covers the anterior and lateral aspects of the larynx. The adams apple is called the laryngeal prominence which is stimulated by testosterone during growth 3. Cricoid cartilage: inferior to the thyroid cartilage (constitute the voice box) 4. Two arytenoid cartilages: posterior to the thyroid cartilage 5. Two corniculate cartilages: attached to arytenoid cartilage 6. Two cuneiform cartilages: between the arytenoids and epiglottis |
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Intrinsic Ligaments of the Larynx |
contained entirely within the larynx and link its nine cartilages to each other- include ligaments of the vocal cords and vestibular folds- intrinsic muscles control the vocal cords by pulling on corniculate and arytenoid cartilages causing them to pivot. The arytenoid cartilage abducts or adducts the vocal cords causing air to be forced between them and the vocal cords to vibrate, producing a high-pitched sound |
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Vestibular Folds of the Larynx |
• The inferior wall of the larynx has two folds on each side: superior vestibular folds: play no role in speech but close the larynx during swallowing and are supported by the vestibular ligaments • The inferior vocal cords (folds) produce sound when air passes between them and contain the vocal ligaments- they are covered with stratified squamous epithelium to endure vibration and contact between the cords • The vocal cords and the opening between them are called the glottis
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Extrinsic Ligaments of the Larynx |
thyrohyoid and cricotracheal ligament- links the larynx to other organs- connect it to they hyoid bone and elevate the larynx during swallowing: called the infrahyoid group |
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The Trachea |
“windpipe” is a rigid tube anterior to the esophagus that is supported by 16-20 C shaped rings of hyaline cartilage. The trachea is named for the texture imparted by these rings. The rings reinforce the trachea and keep it from collapsing when you inhale Two primary divisions: 1. C shaped rings made from hyaline cartilage 2. The open part of the C is spanned by smooth muscle called the trachealis- the gap in the C allows room for the esophagus to expand as swallowed food passes by. The trachealis muscle contracts and relaxes to adjust airflow |
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Inner Layer of Trachea |
made up on pseudostratified columnar epithelium composed of goblet cells (produce mucus), ciliated cells and short basal stem cells
• Mucociliary escalator: the mucus traps inhaled particles and the upward beating of the cilia drives the debris toward the pharynx where it is swallowed. Mechanism to remove debris • The connective tissue beneath the tracheal epithelium contains lymphatic nodules, mucous and serous glands and tracheal cartilages. The outermost layer is called the adventitia and is composed of fibrous CT that blends into other adventitia of other organs in the mediastinum • The trachea forks into the right and left main bronchi
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Lungs |
The broad costal surface is pressed against the rib cage and the convex/smaller mediastinal surface faces medially. The mediastinal surface exhibits a slit called the hilium through which the lung receives the main bronchus, blood vessels, lymphatics, and nerves- these structures constitute the root of the lung |
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Characteristics of Lungs |
• On the medial surface, the left lung has an indentation called the cardiac impression where the heart presses against it • The right lung has three lobes: superior, middle and inferior- the horizontal fissure separates the superior and middle lobes and the oblique fissure separates the middle and inferior lobes. The left lung has only a superior and inferior lobe and a single oblique fissure |
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The Bronchial Tree |
branching system of air tubes in each lung • Primary bronchi: arises from the fork in the trachea, outside of the lungs, similar to the trachea- made of elastic CT- supported by C shaped rings of hyaline cartilage • The primary bronchus gives off three branches: superior, middle and inferior secondary bronchi to the right lung and superior and inferior lobar bronchi to the two lobes of the left lung • The lobar bronchi branch into tertiary bronchi- each one ventilates a functionally independent unit of lung tissue called the bronchopulmonary segment- the secondary and tertiary bronchi are supported by irregular cartilaginous plates • All divisions of the bronchial tree have a substantial amount of elastic CT which contributes to the recoil that expels air from the lungs
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Bronchioles |
continuations of the airway that lack supportive cartilage and are about 1 mm or less in diameter- portion of the lung ventilated by one bronchiole is called a pulmonary lobule. Bronchioles have ciliated cuboidal epithelium and a well-developed layer of smooth muscle in their walls |
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Terminal Bronchioles |
• Each bronchiole divides into 50-80 terminal bronchioles, which are the final branches of the conducting division. They measure .5 mm or less in diameter and have no mucous glands or goblet cells. They do have cilia so that the mucous draining into them can be driven back by the mucociliary escalator |
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Respiratory Bronchioles |
• Each terminal bronchiole gives off two or more smaller respiratory bronchioles, which have alveoli budding from their walls. They are considered the beginning of the respiratory division because their alveoli participate in gas exchange. Each respiratory bronchiole divides into elongated, thin passages called alveolar ducts • The ducts end in alveolar sacs: clusters of alveoli arrayed around a central space called the atrium. |
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Summery of Airflow |
The first several passages belong to the conducting division where there are no alveoli and the tissue is too thick for any significant exchange of oxygen or CO2 with the blood: nasal cavityàpharynxà tracheaà main bronchusàlobar/secondary bronchusà segmental/tertiary bronchusàbronchioleàterminal bronchioleà begin respiratory division
All of the following passages have alveoli along their walls and engage in gas exchange: Respiratory bronchioleà alveolar ductà atriumà alveolus
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Alveoli and Alveolus |
Alveoli: each human lung is a spongy mass composed of 150 million little sacs, which provide about 70 meters squared of surface for gas exchange Alveolus: is a pouch about .2 to .5 mm in diameter- capillary network that facilitates the exchange |
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Alveolus and Respiratory Membrane |
• Each alveolus is surrounded by a web of blood capillaries supplied by small branches of the pulmonary artery. The barrier between the alveolar, air and blood is called the respiratory membrane: consists only of squamous alveolar cell, the squamous endothelial cell of the capillary, and their shared basement membrane • Important to keep low capillary blood pressure and to keep fluid from accumulating in the alveoli |
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Squamous and Great Alveolar Cells |
Squamous (Type I) alveolar cells: cover majority of the alveolar surface area- their thinness allows for rapid gas diffusion between the air and blood Great (Type II) alveolar cells: the rest is covered by rounded cuboidal cells- although they cover less surface, they outnumber the squamous alveolar cells. Functions: 1. Repair the alveolar epithelium when the squamous cells are damaged 2. Secrete pulmonary surfactant: a mixture of phospholipids and protein that coats the alveoli and smallest bronchioles and prevent the bronchioles from collapsing when one exhales and decreases surface tension |
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Alveolar Macrophages |
(dust cells): most numerous cells in the lung- wander the lumens of the alveoli and the CT between them and keep the alveoli free of debris by phagocytizing dust particles that escape mucus in the higher respiratory tract |
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Visceral and Parietal Pleura |
double layered membrane on the lungs
• Visceral pleura or pulmonary: surface of the lung that consists of a serous membrane which extends into the fissures • Parietal pleura: at the hilum, the visceral pleura turns back on itself and forms the parietal which adheres to the mediastinum, inner surface of the rib cage and superior surface of the diaphragm |
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Pleural Cavity and Functions of Pleura and Pleural Fluid |
• Pleural cavity: the space between the parietal and visceral pleura. Does not contain a lung, but wraps around it. It contains nothing but a film of slippery pleural fluid that acts as a lubricant Functions of the Pleurae and pleural fluid: 1. Reduction of friction: fluid acts a lubricant that enables the lungs to expand and contract with minimal friction 2. Creation of pressure gradient: in the creation of a pressure gradient that expands the lungs when one inhales 3. Compartmentalization: the pleurae, mediastinum, and pericardium compartmentalize the thoracic organs and prevent infections of one organ from spreading easily to neighboring organs |
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Pulmonary Ventilation: Quiet and Forced |
or breathing consists of a repetitive cycle of inspiration (inhaling) and expiration (exhaling)- one complete breath, in and out is called a respiratory cycle • Quiet respiration: refers to relaxed, unconscious, automatic breathing (not thinking about breathing) • Forced respiration: unusually deep or rapid breathing- possibly in state of exercise or blowing up a balloon |
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Pulmonary Ventilation Cont. |
• The lungs do not ventilate themselves- the smooth muscle in the walls of the bronchi and bronchioles adjusts the diameter of the airway and affects the speed of airflow, but the skeletal muscles of the trunk ventilate the lungs
• Air flows down a pressure gradient from high to low- the act of the respiratory muscles is to increase the volume and lower the pressure in the thoracic cavity (so air flows in and inversely air flows out) |
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Respiratory Muscles: Diaphragm |
Principle muscles of the respiratory system are the diaphragm and the intercostal muscles
Diaphragm alone produces 2/3 of the pulmonary airflow- when relaxed, it bulges upward, pressing against the base of the lungs: lungs at minimum volume. When the diaphragm contracts, it tenses and flattens, dropping about 1.5 cm in relaxed inspiration and as much as 12 cm in deep breathing and also pushes outward on the sternum and ribs • Enlargement of the thoracic cavity lowers its internal pressure and produces an inflow of air. When diaphragm relaxes, it bulges upward again, compresses the lungs, and expels air. |
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Intercostal Muscles and Scalenes |
Intercostal muscles: serve as synergists to the diaphragm- primary function is to stiffen the thoracic cage during respiration and prevent it from caving inward when the diaphragm descends. They also contribute to enlargement and contraction of the thoracic cage and add about 1/3 of the air that ventilate the lungs
Scalenes: during quiet breathing, muscles of the neck hold ribs 1 and 2 stationary while the external intercostal muscles pull the other ribs upward- they swing upward and thrust the sternum forward. These actions increase the transverse (left/right) and anteroposterior diameters of the chest. Scalenes also elevate the upper ribs during forced respiration |
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Muscles That Aid in Forced Respiration |
considered accessory muscles: erector spinae, sternocledomastoids, scalenes of neck, pectoralis minor, pectoralis major, external/internal obliques, seratus, and the intercartilaginous part of the internal intercostals |
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Normal Expiration |
an energy saving passive process achieved by the elasticity of the lungs and thoracic cage- the bronchial tree, attachments of the ribs, tendons of the diaphragm and other respiratory muscles spring back when the muscles relax. The thoracic cage diminishes in size, the air pressure in the lungs rises above the atmospheric pressure outside and the air flows out. The muscles relax gradually rather than abruptly, making the transition from inspiration to expiration smoother. |
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Forced Expiration |
the rectus abdominis pulls down the sternum and lower ribs while the internal intercostals pulls the other ribs downward. These actions reduce the chest dimensions and expel air more rapidly than usual. Other lumbar, abdominal, and pelvic muscles contribute to forced expiration.
Valsalva maneuver: consists of taking a deep breath, holding it by closing the glottis, and then contracting abdominal muscles to raise abdominal pressure and push the organ contents out. Ex. childbirth, urination, vomiting
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Neural Control of Breathing |
the lungs do not have an autorhythmic pacemaker for respiration- we know that breathing depends on repetitive stimuli from the brain. Two reasons for this dependence on the brain: 1. Skeletal muscles cannot contract without nervous stimulation
2. Breathing involves the well orchestrated action of multiple muscles – requires a central coordinating mechanism |
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Brainstem Respiratory Centers |
breathing is controlled at two levels of the brain- one is cerebral and conscious, enabling us to inhale or exhale at will and the other is unconscious or automatic Automatic, unconscious cycle controlled by 3 pairs of respiratory centers in the reticular formation of the medulla oblongata and pons: 1. Ventral Respiratory Group 2. Dorsal Respiratory Group 3. Pontine Respiratory Group
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Ventral Respiratory Group and I Neurons |
is the primary generator of the respiratory rhythm. It is located in the medulla with two webs of neurons: 1. Inspiratory (I) neurons- in quiet breathing (eupnea) the I neuron circuit fires for about 2 seconds at a time, signaling nerve signals to integrating centers in the spinal cord. Output from the spinal centers travels to the intercostal muscles- contraction of these muscles enlarges the thoracic cage and causes inspiration. |
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Ventral Respiratory Group and E Neurons |
As long as I neurons are firing, E neurons are inhibited. Eventually I neurons cease firing because of fatigue or and outside source- the E neurons begin firing, inhibiting the I neurons further, allowing the inspiratory muscles to relax. Relaxed expiration normally lasts about 3 seconds. Then the E neuron activity wanes and the I neurons resume firing and the cycle repeats · The alternating between the I neuron and the E neuron circuits produces a respiratory rhythm of about 12 breaths per minute. – DRG will influence VRG |
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Dorsal Respiratory Group |
the VRG is subject to influence from other sources causing breathing to be slower, shallower, deeper than normal- the DRG is an integrating center that receives input from several sources: a respiratory center in the pons, a chemosensitive center of the anterior medulla oblongata, chemoreceptors in certain major arteries, and stretch irritant receptors in the airway - The DRG issues output to the VRG that modifies the respiratory rhythm to adapt to varying conditions- modifies rate/depth of breathing |
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Pontine Respiratory Group |
located on each side of the pons that modifies the rhythm of the VRG. It receives input from higher brain centers including the hypothalamus, limbic system, and cerebral cortex and issues output to both the VRG and DRG. By acting on those centers in the medulla, it delays the transition from inspiration to expiration, adapting breathing to different circumstances (exercise, sleep, crying, etc.) |
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Central and Peripheral Input to the Respiratory Centers |
respiratory centers of the medulla and pons receive input from several other levels of the nervous system and respond to the body’s physiological needs
multiple sensory receptors also provide info to the respiratory centers: central chemoreceptors, peripheral chemoreceptors, stretch receptors, irritant receptors |
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Central and Peripheral Chemoreceptors |
- Central chemoreceptors: brainstem neurons that respond to changes in the pH of the cerebrospinal fluid- they are located bilaterally in the medulla (brainstem). The pH of the CSF reflects the CO2 level in the blood, so by regulating respiration to maintain stable pH, the respiratory centers also ensure a stable blood CO2 level. - Peripheral chemoreceptors: located in the carotid and aortic bodies- they respond to the O2 and CO2 content of the blood, but most of all to pH. The carotid bodies communicate w/ brainstem by glossopharyngeal nerves and the aortic bodies by vagus nerves. |
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Stretch and Irritant Receptors |
• Stretch receptors: located in the SM of the bronchi and bronchioles in the visceral pleura- they respond to inflation of the lungs and signal the DRG by way of the vagus nerves. Excessive inflation triggers the Hering breuer reflex: occurs with excessive inflation and is a protective somatic reflex that strongly inhibits the I neurons to stop inspiration
• Irritant receptors: nerve endings surrounding the epithelial cells of the airway- they respond to smoke, dust, pollen, chemical fumes, cold air, and excess mucus. They transmit signals by way of vagus nerves to the DRG and the DRG signals to the respiratory and bronchila muscles, resulting in protective reflexes (shallower breathing, breath holding, coughing) |
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Voluntary Control of Breathing |
important in singing speaking, breath holding- such control originates in the motor cortex of the cerebrum (frontal lobe) and the output neurons send impulses down the corticospinal tracts to integrating centers in the spinal cord and bypassing the brainstem centers.
• There are limits to voluntary control- holding one’s breath raises the CO2 level of the blood until a breaking point is reached when automatic controls override and forces a person to resume breathing even if they have lost consciousness |
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Pressure and Flow |
the flow of a fluid is directly proportional to the pressure difference between two points and inversely proportional to resistance: F=Change in P/R - differences between atmospheric and intrapulmonary pressure Pressure: the pressure that drives respiration is atmospheric pressure: the weight of the air above us- at sea level, averages about 760 mmHg or 1 atm. • Intrapulmonary pressure: internal pressure of lungs- pressure within alveoli- rises and falls as one breathes (4 mL Hg)• To change the pressure of an enclosed gas, one can change the volume (Boyle's Law) |
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Boyle's Law |
states that at a constant temperature, the pressure of a given quantity of gas is inversely proportional to its volume. • Ex. if the lungs contain a quantity of gas and lung volume increases, their internal (intrapulmonary pressure) will decrease or if the intrapulmonary pressure falls below the atmospheric pressure, air tends to flow down its pressure gradient into the lungs and if the intrapulmonary pressure rises above atmospheric pressure, air flows out •Measure respiratory pressures in centimeters of water (cm H20) |
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Inspiration |
the flow of air into the lungs- at the beginning of the respiratory cycle, there is no movement of the thoracic cage or difference between the air pressure within the lungs and external to the body • When the thoracic cage expands: the diaphragm flattens, the pleura of the lung surface cling to each other, the chest wall tends to expand outward while the lungs and chest wall are pulled in opposite directions- creates a slightly negative intrapleural pressure between the parietal and visceral pleurae |
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Inspiration Cont. |
When the ribs swing up and out during inspiration, the partietal pleura follows, reducing the intrapleural pressure a little more. As the visceral pleura is pulled outward, it stretches the alveoli just below the surface of the lung- alveoli are linked to deeper ones which also stretch. The entire lung expands with the thoracic cage. • When the respiratory muscles stop contracting, the inflowing air quickly achieves an intrapulmonary pressure equal to atmospheric pressure and flow stops. |
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Charle's Law |
The intrapulmonary alveolar pressure drops because of the increase in volume causing a pressure gradient. Another force that expands the lungs is the warming of the inhaled air.
Charle's law: the volume of a given quantity of gas is directly proportional to its absolute temp. Inhaled air is warmed to 37 degrees celcius by the time is reaches the alveoli- the thermal expansion will contribute to the inflation of the lungs. |
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Expiration |
a passive process where the muscles relax and elastic lung tissue causes elastic recoil of the thoracic cage. The recoil compresses the lungs and raises the intrapulmonary pressure, causing air to flow down the pressure gradient and out of the lungs. • Pneumothorax: the presence of air in the pleural cavity- without the negative intrapleural pressure to keep the lungs inflated, they recoil and collapse. The collapsed part of the lungs is called atelectasis • Respiratory braking: involves the phrenic nerve- stimulates diaphragm at reduced level producing braking method so lung doesn’t contract too suddenly- smooths out transition. |
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Resistance To Airflow: Diameter of Bronchioles |
Another determinant of airflow is resistance- the greater the resistance, the slower the flow. Resistance is inversely proportional to airflow. Two factors: 1. Diameter of bronchioles: An increase in the diameter of a bronchus or bronchiole is called bronchodilation, which is stimulated by sympathetic nerves like epinephrine and norepinephrine and increase airflow and a reduction in diameter is called bronchoconstriction, which is stimulated by histamine, parasympathetic nerves (acetylcholine), cold air, and chemical irritants. |
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Resistance To Airflow: Pulmonary Compliance and Surface Tension |
Pulmonary Compliance: the ease in which the lungs expand or the change in lung volume relative to a given pressure change. Compliance is reduced by degernative lung diseases (tuberculosis, black lung disease) in which the lungs are stiffened by scar tissue causing the thoracic cage to expand normally but the lungs to expand little.
Surface tension: a limitation on pulmonary compliance is a thin film of water on the respiratory epithelium- the film is necessary for gas exchange, but creates a potential problem for pulmonary ventilation. Water molecules are attracted to each other by hydrogen bonds, creating surface tension. Such force draws the walls of the airway inward toward the lumen causing parts of the airway to collapse and resist reinflation |
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The Solution To Surface Tension Problem |
• The solution to this problem is the alveolar cells and their surfactant: an agent that disrupts the hydrogen bonds of water and reduces surface tension. The pulmonary surfactants are composed of amphipathic proteins, T cells and phospholipids.
• These molecules are partially hydrophobic so they spread out over the surface of the water film. As the small airways deflate, the surfactants are squeezed closer together. The physical structure of the surfactants resists compression and as they become crowded in a small area and resist layering, they retard and then halt the collapse of the airway. Deep breathing spreads pulmonary surfactant throughout the small airways. (crucial for patients right out of surgery) • La Place gas law: F=2T/r |
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Measures of Pulmonary Ventilation and Respiratory Volumes |
Respiratory volumes: tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume •TV: amount of air inhaled and exhaled in one cycle- in quiet breathing, it averages about 500 mL •IRV: amount of air in excess of tidal volume that can be inhaled with max effort- averages about 3000 mL •ERV: amount of air in excess of TV that can be exhaled with max effort- av. About 1200 mL •RV: amount of air remaining in the lungs after max expiration- the amount that can never voluntarily be exhaled- av. 1300 mL |
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Measures of Pulmonary Ventilation and Respiratory Capacities |
obtained by adding two or more of the respiratory volumes •Vital capacity: the maximum ability to ventilate the lungs in one breath ERV+TV+IRV •Inspiratory capacity: TV+IRV •Functional residual capacity: RV+ERV •Total lung capacity: RV+VC
Forced expiratory volume (FEV): the volume of air or the percentage of the vital capacity that can be exhaled in a given time interval Minute respiratory volume: the amount of air inhaled per minute- largely determines the alveolar ventilation rate |
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Alveolar Ventilation |
air that actually enters the alveoli becomes available for gas exchange- a portion of the alveoli fills the conducting division of the airway which cannot exchange gases with the blood- called the anatomical dead space. The sum of the anatomical dead space and any pathological alveolar dead space is called physiological (total) dead space |
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Respiratory Rhythm |
• Eupnea: relaxed, quiet breathing with a tidal volume of about 500 mL and a respiratory rate of about 12-15 breaths/minute (can change with aerobic condition) • Apnea: temporary cessation of breathing (one or more skipped breaths) and then breathe abruptly • Dyspnea: labored, grasping breathing- shortness of breath- increased rate and depth of breathing • Hyperpnea: increased rate and depth of breathing in response to exercise, pain, or other conditions • Hyperventilation: Increased pulmonary ventilation in excess of metabolic demand- expels CO2 faster than it is produced, which lowers the blood CO2 concentration and raising the blood pH • Hypoventilation: reduced pulmonary ventilation- leads to an increase in blood CO2 concentration if ventilation is insufficient to expel CO2 as fast s it is produced |
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Composition of Air and Dalton's Law |
air consists of nitrogen, oxygen and carbon dioxide (most to least in that order) as well as several minor gases (argon, neon, helium, methane, ozone) and water vapor.
• The total atmospheric pressure is a sum of the contributions of these individual gases- principle called dalton’s law: the total pressure of a gas mixture is equal to the sum of the partial pressures of its individual gases • The separate contribution of each gas mixture is symbolized with a P followed by the formula of the gas- Ex. PN2 +PO2+PH2O+PCO2→ 597+159+3.7+0.3 (N2= 78.6% air→ .786 x 760 mmHg= 597 |
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Composition of Air in the Alveoli |
They differ because of three influences:
1. It is humidified by contact with the mucous membranes- PH20 is more than 10 times higher than the of the inhaled air 2. Freshly inspired air mixes with residual air left the previous respiratory cycle- causing oxygen to be diluted and enriched with CO2 3. Alveolar air exchanges O2 and CO2 with the blood causing the PO2 is lower and the PCO2 is significantly higher |
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Alveolar Gas Exchange |
For oxygen to get into the blood, it must dissolve in the water that the alveolus is in contact with that covers the alveolar epithelium and pass through the respiratory membrane separating air from the bloodstream. For CO2 to leave the blood it must pass the other way and diffuse out of the water film into the alveolar air – this back and form traffic of O2 and CO2 across the respiratory membrane is called alveolar gas exchange. · -Each gas diffuses down its own partial pressure gradient whenever air and water are in contact with each other- continues to diffuse until the partial pressure of each gas in the air is equal to its partial pressure in the water |
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Alveolar Gas Exchange and Henry's Law |
states that at the air-water interface, the amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in the air (assuming constant temp)- at the alveolus, the blood is said to unload CO2 and load O2- each gas behaves independently
• Both O2 loading and CO2 unloading involve erythrocytes- efficiency of process depends on how long a RBC spends in alveolar capillary compared to how long it takes for each gas to be fully loaded or unloaded (reach equilibrium concentrations in the capillary blood) |
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Variables that affect the efficiency of alveolar gas exchange: Pressure Gradients of Gases |
o PO2: about 104 mmHg in alveolar air and 40 mmHg in blood arriving at an alveolus- oxygen diffuses from the air into the blood where it reaches a PO2 of 104 mmHg. When the blood is leaving the lungs, it drops to about 95 mmHg because there is mixing of oxygen rich pulmonary blood with oxygen poor systemic blood o PCO2: about 40 mmHg in alveolar air and 46 mmHg in blood arriving at the alveolus- CO2 then diffuses from the blood into the alveoli (up the concentration gradient) |
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Pressure Gradients of Gases At Different Elevations |
• Compared to the oxygen gradient at sea level, the gradient is less steep at high elevation because the PO2 of the atmosphere is lower- oxygen loading of the pulmonary blood is slower (reduced gradient= slower O2 diffusion)
• In a hyperbaric chamber with 100% oxygen, the gradient from air to blood is very steep and oxygen loading is rapid (henry's law) |
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Variables that affect the efficiency of alveolar gas exchange: Solubility of Gases |
gases differ in their ability to dissolve in water- CO2 is 20 times more soluble than oxygen and oxygen and twice a soluble as nitrogen. This causes equal amount of the two gases to exchange because CO2 is much more soluble and diffuses more rapidly even though the pressure gradient of O2 is much greater than CO2 |
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Variables that affect the efficiency of alveolar gas exchange: Membrane Thickness and Membrane Area |
Membrane thickness: the respiratory membrane between the blood and alveolar air is fairly thin so it normally presents little obstacle for diffusion, but if there is a heart condition, it can cause the respiratory membranes to become thickened causing the gases to travel farther between the blood and air- cannot equilibrate fast enough to keep pace with blood flow • Blood leaving the lungs would have high PCO2 and low PO2
Membrane area: in good health, each lung has about 70 meters squared of respiratory membrane available for gas exchange- alveolar capillaries contain total of 100 mL of blood at one time so it is spread thinly. If one has a pulmonary disease, it decreases the surface area and leads to low blood PO2 • For diffusion one needs a large surface area |
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Variables that affect the efficiency of alveolar gas exchange: Ventilation Perfusion Coupling |
need good ventilation of the alveoli but also good perfusion of their capillaries for gas exchange- VPC refers to physiological responses that match airflow to blood flow and vice versa • Ex: If part of lung was poorly ventilated (causing low PO2 in that region) it stimulates local vasoconstriction, rerouting the blood to better-ventilated areas of the lung where it can pick up more oxygen. Increased ventilation raises the local blood PO2 and this stimulates vasodilation, increasing blood flow to that region to take advantage of the oxygen availability • These reactions of the pulmonary arteries are opposite from the reactions of the systemic arteries (dilate in response to hypoxia)- changes in the blood flow to a region of a lung stimulate bronchoconstriction or dilation, adjusting ventilations so that air is directed to the best perfused parts of the lung |
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Gas Transport: Oxygen |
Gas transport is process of carrying gases from the alveoli to the systemic tissues and carrying gases from systemic tissues to the alveoli
Arterial blood carries about 20 mL of oxygen/deciliter- about 98.5% is bound to hemoglobin in the RBCs and 1.5% is dissolved in blood plasma. Hemoglobin is specialized for oxygen transport. It consists of 4 protein chains, each with one heme group. Each heme group can bind 1 O2, thus 1 hemoglobin molecule can carry up to 4 O2. • If one or more molecules of O2 are bound to hemoglobin, it is called oxyhemoglobin, where hemoglobin with no oxygen bound to it is called deoxyhemoglobin (O and desaturated). 4 O2 on molecule= 100% saturated, 3 O2=75% saturated, 2 O2=50% saturated • Each gram of hemoglobin can carry 1.34 mL of oxygen. Males have about 15 g Hb/dL of blood: 1.34 x 15=20 ml O2/dl. Per liter= 200 mL and per blood volume= 1000 mL O2 • Arterial blood is 95-98% saturated and venous blood is 70% saturated |
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Gas Transport: Oxygen and the Oxyhemoglobin Disassociation Curve |
not a simple linear relationship- at low PO2, the curve rises slowly and then there is a rapid increase in oxygen loading as PO2 rises further. When hemoglobin loads oxygen, the first heme group binds to O2 causing hemoglobin to change shape that facilitates the uptake of another heme group and then a third and fourth • As it passes through the alveolar capillaries where the PO2 is high, hemoglobin becomes saturated with oxygen and as it passes through the systemic capillaries the PO2 is low, it typically gives up oxygen |
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Gas Transport: Carbon Dioxide |
Transported in three forms: • Carbonic acid: about 90% of the CO2 is hydrated (reacts with water) to form carbonic acid, which then disassociates into bicarbonate and hydrogen ions- CO2+H2O→ H2CO3→ HCO3-+ H+ It is catalyzed by enzyme carbonic anhydrase • Chemically bound to hemoglobin: About 5% binds to AA of plasma proteins and hemoglobin to form carbaminohemoglobin: Hb+CO2→HbCO2 Carbon dioxide does not compete with oxygen because CO2 and O2 bind different sites on the hemoglobin molecule (oxygen to heme and CO2 to the polypeptide chains) • Dissolved in blood plasma: the remaining 5% of CO2 is carried in the blood as dissolved gas • The amounts of CO2 exchanged between the blood and alveolar air differ from the percentages given: 70% exchanged CO2 comes from carbonic acid, 23% from carbaninohemogloin, and 7% from dissolved gas. |
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Systemic Gas Exchange: CO2 Loading |
CO2 loading: Aerobic respiration produces a molecule of CO2 for every molecule of O2 It consumes- the tissue therefore contains a high PCO2 in the tissues as long as one is alive. The CO2 gradient is normally 46→ 40 mmHg from tissue fluid to blood. o CO2 diffuses into the bloodstream where most of it reacts with water to produce bicarbonate and hydrogen ions. This reaction occurs slowly in the blood plasma but much faster in the RBCs, where it is catalyzed by enzyme carbonic anhydrase o Chloride shift: the chloride bicarbonate exchanger then pumps most of the bicarbonate of the RBC in exchange for Cl- from the blood plasma. Cl- goes into the cell to balance the outrush of the negative bicarbonate ions |
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Systemic Gas Exchange: O2 Unloading |
When H+ binds to oxyhemoglobin, it reduces the affinity of hemoglobin for O2 and makes hemoglobin release it. Oxygen consumption by respiring tissues keeps the PO2 of tissue fluid low- pressure gradient of 95→40 mmHg of oxygen from the arterial blood to the tissue fluid. This causes the liberated oxygen to diffuse into the tissue fluid. |
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O2 Unloading: Utilization Coefficient and Venous Reserve |
o Utilization coefficient: blood arrives at systemic capillaries with oxygen concentration of 20 mL/dL and hemoglobin 97% saturated, but as it leaves capillaries, oxygen concentration is about 15 mL/dL and hemoglobin is 75% saturated (22% unloaded) o Venous reserve: oxygen remaining in the blood after it passes through the capillary bed- able to sustain life for 4-5 minutes even in the event of respiratory arrest
o The reactions that happen in the lungs (alveolar gas exchange) is essentially the reverse of systemic gas exchange
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Adjustment To Metabolic Needs of Individual Tissue: Ambient PO2 |
hemoglobin adjusts unloading based on needs of the tissue (does not unload same amount of oxygen to all tissues). Ex. in exercising skeletal muscles, the utilization coefficient may be as high as 80% Four factors adjust the rate of oxygen unloading to the metabolic rates of different tissue: 1. Ambient PO2: since an active tissue consumes oxygen rapidly, the PO2 of its tissue fluid remains low- from the oxyhemogloin disassociation curve, it shows that’s that at low PO2, hemoglobin releases more oxygen
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Adjustment To Metabolic Needs of Individual Tissue: Temperature and Bohr Effect |
2. Temperature: when temp rises the oxyhemoglobin disassociation curve shifts to the right- meaning elevated temperature promotes oxygen unloading. Active tissues are warmer than less active ones, thus extracting more oxygen from the blood passing through them 3. Bohr effect: active tissues generate extra CO2, which raises H+ concentration and lowers the pH of the blood. Hydrogen ions weaken the bond between hemoglobin and oxygen, which promotes oxygen unloading. On the oxyhemoglobin disassociation curve, it shows a drop in the pH shifts the curve to the right- pH has little effect on pulmonary oxygen loading, but is more pronounced in the systemic capillaries where PO2 is lower. |
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Adjustment To Metabolic Needs of Individual Tissue: BPG |
4. BPG: By product of RBC metabolism (no mitochondria so use anaerobic fermentation) that binds hemoglobin and promotes oxygen unloading. An elevated body temp, thyroxine, growth hormone, testosterone, and epinephrine stimulate the BPG synthesis and therefore promote oxygen unloading in the tissues |
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Haldane Effect |
the rate of CO2 loading is adjusted to varying needs of the tissues - a low level of oxyhemoglobin (HBO2) enables the blood to transport more CO2. This occurs because oxyhemoglobin does not bind CO2 as well as deoxyhemoglobin and deoxyhemoglobin binds more hydrogen ions than oxyhemoglobin does - A high metabolic rate keeps oxyhemoglobin levels low and allow more CO2 to be transported by these two mechanisms |
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Blood Gases and Respiration |
Normally the systemic arterial blood has a PO2 of 95 mmHg, a PCO2 of 40 mmHg and a pH of 7.35-7.45. The rate and depth of breathing are adjusted to maintain these values. This is possible because of the brainstem respiratory centers receiving input from central/peripheral chemoreceptors.
•The most potent stimulus for breathing is pH, followed by CO2, and the least significant is O2.
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Response To Carbon Dioxide |
at the beginning of exercise, the rising blood CO2 level may directly stimulate the peripheral chemoreceptors and trigger an increase in ventilation more quickly then the central chemoreceptors do. (Increase in ventilation and indirectly related to pH levels) |
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Response To Oxygen |
the partial pressure of oxygen usually has little effect on respiration - the hemoglobin is 97% saturated with O2, so little can be added by increasing pulmonary ventilation (hemoglobin saturation fairly constant). Arterial PO2 affects respiration only if it drops below 60 mmHg. This causes stimulation of the peripheral chemoreceptors and causes the hemoglobin level to fall and bind more H+ which raises the blood pH and inhibits respiration (hypercapnia)- counteracts the effect of low PO2 |
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Response To Hydrogen Ions |
pulmonary ventilation is adjusted to maintain the pH of the brain - H+ does not cross the blood-brain barrier very easily, but CO2 does and once it is in the CSF, it reacts with water to produce carbonic acid which disassociates into bicarbonate and hydrogen ions. The high H+ in the CSF stimulates central and peripheral chemoreceptors |
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Hydrogen Ions: pH Imbalances |
• Acidosis: a blood pH lower than 7.35 • Alkalosis: a blood pH greater than 7.45 • Hypocapnia: A PCO2 less than 37 mmHg (normal range is 37-43) and the most common cause of alkalosis • Hypercapnia: a PCO2 greater than 43 mmHg and most common cause of acidosis • The corrective homeostatic response to acidosis is hyperventilation or “blowing off” CO2 faster than the body produces it. As CO2 is eliminated from the body, the carbonic acid reaction shifts to the left: CO2+H2O← H2CO3← HCO3-+H+. The H+ on the right is consumed and as H+ concentration declines, the pH rises and returns the blood from the acidotic range to normal • The corrective response to alkalosis is hypoventilation: allows CO2 to accumulate in the body fluids faster than we exhale it. Hypoventilation shifts the reaction to the right, raising the H+ concentration and lowering the pH to normal. |
