Lecture 9 Respiration (Human Anatomy & Physiology I) PDF

PHM 10402 HUMAN ANATOMY & PHYSIOLOGY I RESPIRATION LECTURER: DR.MOHD NUR NASYRIQ ANUAR (PhD) FACULTY OF PHARMACY, UniSZA Bachelor of Pharmacy (Honours) Year 1, Semester 1 Academic Session 2023/2024 Contents...

PHM 10402 HUMAN ANATOMY & PHYSIOLOGY I RESPIRATION LECTURER: DR.MOHD NUR NASYRIQ ANUAR (PhD) FACULTY OF PHARMACY, UniSZA Bachelor of Pharmacy (Honours) Year 1, Semester 1 Academic Session 2023/2024 Contents Aims Respiration 3. Exchange of gases and lung volume 1. Respiratory system anatomy Lung volumes and capacities 2. Pulmonary ventilation – Explain the difference between tidal 3. Exchange of gases and lung volume volume, inspiratory reserve volume, expiratory reserve volume, and residual 4. Control of respiration volume. 5. Exercise and respiration – Differentiate between inspiratory capacity, functional residual capacity, vital capacity, and total lung capacity. Aims Exchange of oxygen and carbon dioxide At the end of the lecture session, student will be able to: – Explain Dalton’s law and Henry’s law. 1. Respiratory system anatomy – Describe the exchange of oxygen and carbon dioxide in external and internal Describe the anatomy of the nose, pharynx, larynx, respiration trachea, bronchi, and lungs. 4. Control of respiration Identify the functions of each respiratory system structure. Explain how the nervous system controls breathing. 2. Pulmonary ventilation List the factors that can alter the rate and depth Describe the events that cause inhalation and of breathing exhalation. 5. Exercise and respiration Describe the effects of exercise on the respiratory system.  INTRODUCTION Functions of the respiratory system 1. Provides for gas exchange: intake of O2 for delivery to body cells and removal of CO2 produced by body cells. 2. Helps regulate blood pH. 3. Contains receptors for sense of smell, 4. Filters inspired air, 5. Produces vocal sounds (phonation) 6. Excretes small amounts of water and heat. 1. Respiratory System Anatomy Consists of the respiratory and conducting zones Conducting zone Respiratory zone – Provides rigid conduits for air to reach the – Site of gas exchange sites of gas exchange – Consists of bronchioles, alveolar – Includes all other respiratory structures (e.g., ducts, and alveoli nose, nasal cavity, pharynx, trachea) Respiratory muscles – diaphragm and other muscles that promote ventilation Major Functions To supply the body with oxygen and dispose of carbon dioxide Respiration – four distinct processes must happen – Pulmonary ventilation – moving air into and out of the lungs – External respiration – gas exchange between the lungs and the blood – Transport – transport of oxygen and carbon dioxide between the lungs and tissues – Internal respiration – gas exchange between systemic blood vessels and tissues The Nasal Cavity Structure of the Nose The nose is divided into two regions – The external nose, including the root, bridge, dorsum nasi, and apex – The internal nasal cavity Philtrum – a shallow vertical groove inferior to the apex The external nares (nostrils) are bounded laterally by the alae Function of the Nose The only externally visible part of the respiratory system that functions by: – Providing an airway for respiration – Moistening and warming the entering air – Filtering inspired air and cleaning it of foreign matter – Serving as a resonating chamber for speech – Housing the olfactory receptors Nasal Cavity Lies in and posterior to the external nose Divided by a midline nasal septum Opens posteriorly into the nasal pharynx via internal nares The ethmoid and sphenoid bones form the roof The floor is formed by the hard and soft palates Vestibule – nasal cavity superior to the nares Nasal cavities (NC) separated by the Nasal Septum (NS) – Vibrissae – hairs that filter coarse particles from inspired air Olfactory mucosa – Lines the superior nasal cavity – Contains smell receptors Respiratory mucosa – Lines the balance of the nasal cavity – Glands secrete mucus containing lysozyme and defensins to help destroy bacteria Inspired air is: – Humidified by the high water content in the nasal cavity – Warmed by rich plexuses of capillaries Ciliated mucosal cells remove contaminated mucus Nasal Cavity Superior, medial, and inferior conchae: – Protrude medially from the lateral walls – Increase mucosal area – Enhance air turbulence and help filter air Sensitive mucosa triggers sneezing when stimulated by irritating particles Functions of the Nasal Mucosa and Conchae Figure 22.3b During inhalation the conchae and nasal mucosa: – Filter, heat, and moisten air During exhalation these structures: – Reclaim heat and moisture – Minimize heat and moisture loss Paranasal Sinuses Sinuses in bones that surround the nasal cavity Sinuses lighten the skull and help to warm and moisten the air The Pharynx, Larynx and Trachea Pharynx Funnel-shaped tube of skeletal muscle that connects to the: – Nasal cavity and mouth superiorly – Larynx and esophagus inferiorly Extends from the base of the skull to the level of the sixth cervical vertebra It is divided into three regions Figure 22.3b – Nasopharynx – Oropharynx 2. Oropharynx – Laryngopharynx Extends inferiorly from the level of the soft palate to the epiglottis 1. Nasopharynx Opens to the oral cavity via an archway called the fauces Lies posterior to the nasal cavity, inferior to the sphenoid, Serves as a common passageway for food and superior to the level of the soft palate and air Strictly an air passageway The epithelial lining is protective Lined with pseudostratified columnar epithelium stratified squamous epithelium Closes during swallowing to prevent food from entering the Palatine tonsils lie in the lateral walls of nasal cavity the fauces The pharyngeal tonsil lies high on the posterior wall Lingual tonsil covers the base of the Pharyngotympanic (auditory) tubes open into the lateral tongue walls 3. Laryngopharynx Serves as a common passageway for food and air Lies posterior to the upright epiglottis Extends to the larynx, where the respiratory and digestive pathways diverge Larynx (Voice Box) Framework of the Larynx Attaches to the hyoid bone and opens into the laryngopharynx superiorly Continuous with the trachea posteriorly The three functions of the larynx are: – To provide a patent airway – To act as a switching mechanism to route air and food into the proper channels – To function in voice production Movements of Vocal Cords Trachea Flexible and mobile tube extending from the larynx into the mediastinum Composed of three layers – Mucosa – made up of goblet cells and ciliated epithelium – Submucosa – connective tissue deep to the mucosa – Adventitia – outermost layer made of Trachea structure C- shaped rings of hyaline cartilage Gross Anatomy of the Lungs Lungs Lungs occupy all of the thoracic cavity except the mediastinum Cardiac notch (impression) – cavity that accommodates the heart – Root – site of vascular and bronchial attachments Left lung – separated into upper and – Costal surface – anterior, lateral, and lower lobes by the oblique fissure posterior surfaces in contact with the ribs Right lung – separated into three – Apex – narrow superior tip lobes by the oblique and horizontal fissures – Base – inferior surface that There are 10 bronchopulmonary rests on the diaphragm segments in each lung – Hilus – indentation that contains pulmonary and systemic blood vessels Pleurae Thin, double-layered serosa Parietal pleura – Covers the thoracic wall and superior face of the diaphragm – Continues around heart and between lungs Visceral, or pulmonary, pleura – Covers the external lung surface Lung and Pleural Cavity – Divides the thoracic cavity into three chambers The central mediastinum Two lateral compartments, each containing a lung Respiratory Zone Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli Approximately 300 million alveoli: – Account for most of the lungs’ volume – Provide tremendous surface area for gas exchange Respiratory Membrane This air-blood barrier is composed of: – Alveolar and capillary walls – Their fused basal laminas Alveolar walls: – Are a single layer of type I epithelial cells Alveoli – Permit gas exchange by simple diffusion Surrounded by fine elastic fibers – Secrete angiotensin converting enzyme (ACE) Contain open pores that: Type II cells secrete surfactant – Connect adjacent alveoli – Allow air pressure throughout the lung to be equalized House macrophages that keep alveolar surfaces sterile Respiratory Membrane Conducting Zone: Bronchi The carina of the last tracheal cartilage marks the end of the trachea and the beginning of the right and left bronchi Air reaching the bronchi is: – Warm and cleansed of impurities – Saturated with water vapor Bronchi subdivide into secondary bronchi, each supplying a lobe of the lungs Air passages undergo 23 orders of branching in the lungs Bronchial Tree Conducting Zone: Bronchial Tree Tissue walls of bronchi mimic that of the trachea As conducting tubes become smaller, structural changes occur – Cartilage support structures change – Epithelium types change – Amount of smooth muscle increases Bronchioles – Consist of cuboidal epithelium – Have a complete layer of circular smooth muscle – Lack cartilage support and mucus-producing cells 2. Pulmonary ventilation The process of gas exchange in the body, Pressure changes during pulmonary called respiration, has three basic steps: ventilation 1.Pulmonary ventilation (pulmon- = lung), or Inhalation breathing, is the inhalation (inflow) and exhalation (outflow) of air and involves the Breathing in is called inhalation (inspiration). exchange of air between the atmosphere and Just before each inhalation, the air pressure inside the the alveoli of the lungs. lungs is equal to the air pressure of the atmosphere, which at sea level is about 760 millimeters of mercury 2. External (pulmonary) respiration is the (mmHg), or 1 atmosphere (atm). exchange of gases between the alveoli of the For air to flow into the lungs, the pressure inside the lungs and the blood in pulmonary capillaries alveoli must become lower than the atmospheric across the respiratory membrane. In this pressure. process, pulmonary capillary blood gains O2 and loses CO2. This condition is achieved by increasing the size of the lungs. 3.Internal (tissue) respiration is the exchange Differences in pressure caused by changes in lung of gases between blood in systemic capillaries volume force air into our lungs when we inhale and out and tissue cells. In this step the blood loses O2 when we exhale. and gains CO2. Within cells, the metabolic For inhalation to occur, the lungs must expand, which reactions that consume O2 and give off CO2 increases lung volume and thus decreases the pressure during the production of ATP are termed in the lungs to below atmospheric pressure. cellular respiration. The first step in expanding the lungs during normal quiet inhalation involves contraction of the main muscles of inhalation, the diaphragm and external intercostals Ref: Principles of Anatomy and Physiology/ Tortora GJ, Derrickson BH. — 12 ed. Boyle’s law. Pressure changes during pulmonary ventilation Inhalation The pressure of a gas in a closed container is inversely proportional to the volume of the container. This means that if the size of a closed container is increased, the pressure of the gas inside the container decreases, and that if the size of the container is decreased, then the pressure inside it increases. This inverse relationship between volume and pressure, called Boyle’s law. Exhalation Breathing out, called exhalation (expiration), is also due to a pressure gradient, but in this case the gradient is in the opposite direction: The pressure in the lungs is greater than the pressure of the atmosphere. Normal exhalation during quiet breathing, unlike inhalation, is a passive process because no muscular contractions are involved. Instead, exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched. Two inwardly directed forces contribute to elastic recoil: (1) the recoil of elastic fibers that were stretched during inhalation and (2) the inward pull of surface tension due to the film of alveolar fluid. Pressure changes during pulmonary ventilation Exhalation Exhalation starts when the inspiratory muscles relax. As the diaphragm relaxes, its dome moves superiorly owing to its elasticity As the external intercostals relax, the ribs are depressed. These movements decrease the vertical, lateral, and anteroposterior diameters of the thoracic cavity, which decreases lung volume. In turn, the alveolar pressure increases to about 762 mmHg. Air then flows from the area of higher pressure in the alveoli to the area of lower pressure in the atmosphere. 3. Exchange of gases and lung Residual volume volume Even after the expiratory reserve volume is exhaled, considerable air remains in the lungs Tidal volume because the subatmospheric intrapleural  While at rest, a healthy adult averages 12 pressure keeps the alveoli slightly inflated, and breaths a minute, with each inhalation and some air also remains in the noncollapsible exhalation moving about 500 mL of air airways. into and out of the lungs. This volume, which cannot be measured by  The volume of one breath is call the tidal spirometry, is called the residual volume and volume (VT). The minute ventilation (MV) amounts to about 1200 mL in males and 1100 mL – the total volume of air inhaled and in females. exhaled each minute – is respiratory rate Inspiratory reserve volume and expiratory multiplied by the tidal volume: reserve volume MV = 12 breaths/min X 500 mL/breath By taking a very deep breath, you can inhale a good deal more than = 6 liters/min 500 mL. This additional inhaled air, called the inspiratory reserve volume, is about 3100 mL in an average adult male and 1900 mL  A lower-than-normal minute in an average adult female. ventilation usually is a sign of Even more air can be inhaled if inhalation follows forced pulmonary malfunction. exhalation.  The apparatus commonly used to If you inhale normally and then exhale as forcibly as possible, you measure the volume of air exchanged should be able to push out considerably more air in addition to the during breathing and the respiratory 500 mL of tidal volume. The extra 1200 mL in males and 700 mL in rate is a spirometer or respirometer. females is called the expiratory reserve volume. The FEV1.0 is the forced expiratory volume in 1 second, the  The record is called a spirogram. volume of air that can be exhaled from the lungs in 1 second with  Inhalation is recorded as an upward maximal effort following a maximal inhalation. deflection, and exhalation is recorded as Typically, chronic obstructive pulmonary disease (COPD) greatly a downward deflection. reduces FEV1.0 because COPD increases airway resistance.  Lung capacities  Combination of specific lung volumes.  Inspiratory capacity: the sum of tidal volume and inspiratory reserve volume capacity (500 mL + 3100 mL = 3600 mL, male), (500 mL + 1900 mL = 2400 mL, Female).  Functional residual capacity: the sum of residual volume and expiratory reserve volume (1200 mL + 1200 mL = 2400 mL, male), (1100 mL + 700 mL = 1800 mL, female).  Vital capacity: the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume (4800 mL, male and 3100 mL, female).  Total Lung Capacity: the sum of vital capacity and residual volume (4800 mL + 1200 mL = 6000 mL, males and 3100 mL + 1100 mL = 4200 mL, females) Spirogram of lung volumes and capacities Ref: Principles of Anatomy and Physiology/ Tortora GJ, Derrickson BH. — 12 ed. Distinguish between Dalton’s law and Henry’s law Henry’s law The exchange of O2 and CO2 between alveolar air and pulmonary blood occurs via passive diffusion, which is Henry’s law helps explain how the governed by the behavior of gases as described by two solubility of a gas relates to its diffusion. gas laws, Dalton’s law and Henry’s law. Henry’s law states that the quantity of a gas that will dissolve in a liquid is Dalton’s law proportional to the partial pressure of the gas and its solubility. Dalton’s law is important for understanding how gases move down their pressure differences by diffusion. In body fluids, the ability of a gas to stay in solution is greater when its partial According to Dalton’s law, each gas in a mixture of gases pressure is higher and when it has a high exerts its own pressure as if no other gases were present. solubility in water. The higher the partial pressure of a gas The pressure of a specific gas in a mixture is called its over a liquid and the higher the solubility, partial pressure (Px); the subscript is the chemical formula the more gas will stay in solution. of the gas. Dalton’s law Henry’s law External and internal respiration The left ventricle pumps oxygenated blood into External respiration or pulmonary the aorta gas exchange is the diffusion of O2 from and through the systemic arteries to systemic air in the alveoli of the lungs to blood in capillaries. pulmonary capillaries and the diffusion The exchange of O2 and CO2 between systemic of CO2 in the opposite direction. capillaries and tissue cells is called internal respiration or systemic gas exchange. External respiration in the lungs converts deoxygenated blood (depleted of some O2) As O2 leaves the bloodstream, coming from the right side of the heart into oxygenated blood is converted into oxygenated blood (saturated with O2) that deoxygenated blood. returns to the left side of the heart. Unlike external respiration, which occurs only in the lungs, internal respiration occurs in tissues As blood flows through the pulmonary throughout the body. capillaries, it picks up O2 from alveolar air and unloads CO2 into alveolar air. Although this process is commonly called an “exchange” of gases, each gas diffuses independently from the area where its partial pressure is higher to the area where its partial pressure is lower. Exchange of gases Summary of chemical reactions that occur during gas exchange.  Exchange of O2 and CO2 in pulmonary capillaries (external respiration) o As CO2 is exhaled, hemoglobin (Hb) inside red blood cells in pulmonary capillaries unloads CO2 and picks up O2 from alveolar air. o Binding of O2 to Hb—H releases hydrogen ions (H+). o Bicarbonate ions (HCO3-) pass into the RBC and bind to released H+, forming carbonic acid (H2CO3). o The H2CO3 dissociates into water (H2O) and CO2, and the CO2 diffuses from blood into alveolar air. o To maintain electrical balance, a chloride ion (Cl-) exits the RBC for each HCO3- that enters (reverse chloride shift). Pulmonary capillary blood gains O2 and loses CO2 Summary of chemical reactions that occur during gas exchange.  Exchange of O2 and CO2 in systemic capillaries (internal respiration) o CO2 diffuses out of tissue cells that produce it and enters red blood cells, where some of it binds to hemoglobin, forming carbaminohemoglobin (Hb—CO2). o This reaction causes O2 to dissociate from oxyhemoglobin (Hb— O2). o Other molecules of CO2 combine with water to produce bicarbonate ions (HCO3-) and hydrogen ions (H+). o As Hb buffers H+, the Hb releases O2 (Bohr effect). o To maintain electrical balance, a chloride ion (Cl-) enters the RBC for each HCO3- that exits (chloride shift). Systemic capillaries blood loses O2 and gains CO2 4. Control of respiration Respiratory center The respiratory center is composed of neurons in the medullary rhythmicity area in the medulla oblongata the pneumotaxic and apneustic areas (pontine respiratory center) in the pons. Medullary rhythmicity area in the medulla oblongata Function: to control the basic rhythm of respiration. Inspiratory area  dorsal respiratory group (DRG) Expiratory area  ventral respiratory group (VRG) Control of respiration During quiet breathing, inhalation lasts for about 2 seconds and exhalation lasts for about 3 seconds. Nerve impulses generated in the inspiratory area establish the basic rhythm of breathing. While the inspiratory area is active, it generates nerve impulses for about 2 seconds. The impulses propagate to the external intercostal muscles via intercostal nerves and to the diaphragm via the phrenic nerves. When the nerve impulses reach the diaphragm and external intercostal muscles, the muscles contract and inhalation occurs. Even when all incoming nerve connections to the inspiratory area are cut or blocked, neurons in this area still rhythmically discharge impulses that cause inhalation. The neurons of the expiratory area remain inactive At the end of 2 seconds, the inspiratory during quiet breathing. However, during forceful breathing area becomes inactive and nerve nerve impulses from the inspiratory area activate the expiratory impulses cease. With no impulses area. arriving, the diaphragm and external intercostal muscles relax for about 3 Impulses from the expiratory area cause contraction of the seconds, allowing passive elastic recoil of internal intercostal and abdominal muscles, which the lungs and thoracic wall. Then, the decreases the size of the thoracic cavity and causes forceful cycle repeats. exhalation. How does the medullary rhythmicity area regulate respiration? How are the apneustic and pneumotaxic areas related to the control of respiration? pneumotaxic area in the pons helps coordinate the transition between inhalation and exhalation. transmits inhibitory impulses to the inspiratory area. The major effect of these nerve impulses is to help turn off the inspiratory area before the lungs become too full of air. – the impulses shorten the duration of inhalation. When the pneumotaxic area is more active, breathing rate is more rapid. Apneustic area in the pons. coordinates the transition between inhalation and exhalation Sends stimulatory impulses to the inspiratory area that activate it and prolong inhalation. The result is a long, deep inhalation. When the pneumotaxic area is active, it overrides signals from the apneustic area. The control of respiration (ventilation) by the respiratory center of the brain The ventral respiratory group (VRG) and the dorsal respiratory group (DRG) within the medullary rhythmicity area cooperate to establish the pattern for spontaneous ventilation and basal rate of ventilation which may be adjusted by impulses from related respiratory control centers in the pons; the VRG contains both inspiratory and expiratory neurons; – the autorythmic inspiratory neurons stimulate the diaphragm and external intercostals for approximately 2 seconds to cause inspirations and then the antagonistic expiratory neurons fire for approximately 3 seconds to permit passive or stimulate active expirations; – thereby inspiratory and expiratory neurons cooperate in a negative feedback control relationship, setting the basic rhythm of respiration (spontaneous ventilation, resting or tidal breathing (eupnea)); the DRG neurons are involved in altering the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance; – these neurons stimulate neurons in the VRG to achieve those effects; – they are responsive to sensory information from chemoreceptors and mechanoreceptors. How do the cerebral cortex, levels of CO2 and O2, proprioceptors, inflation reflex, temperature changes, pain, and irritation of the airways modify respiration? The basic rhythm of respiration set and coordinated by the inspiratory area can be modified in response to inputs from other brain regions, receptors in the peripheral nervous system, and other factors.  Regulation of the respiratory center: cerebral cortex  Cortical influences on respiration o Because the cerebral cortex has connections with the respiratory center, we can voluntarily alter our pattern of breathing. – We can even refuse to breathe at all for a short time. – Voluntary control is protective because it enables us to prevent water or irritating gases from entering the lungs. – The ability to not breathe, however, is limited by the buildup of CO2 and H+ in the body. – When PCO2 and H+ concentrations increase to a certain level, the inspiratory area is strongly stimulated, nerve impulses are sent along the phrenic and intercostal nerves to inspiratory muscles, and breathing resumes, whether the person wants it to or not. – It is impossible for small children to kill themselves by voluntarily holding their breath, even though many have tried in order to get their way. – If breath is held long enough to cause fainting, breathing resumes when consciousness is lost. o Nerve impulses from the hypothalamus and limbic system also stimulate the respiratory center, allowing emotional stimuli to alter respirations as, for example, in laughing and crying. Regulation of the respiratory Chemoreceptors center: levels of CO2 and O2 Chemoreceptor regulation of respiration Central o Certain chemical stimuli modulate chemoreceptors how quickly and how deeply we are located in or near the medulla breathe. oblongata in the o The respiratory system functions to maintain CNS. proper levels of CO2 and O2 are very responsive to changes in the levels of these gases in body fluids. o Chemoreceptors in two locations of the respiratory system monitor levels of CO2, H+, and O2 and provide input to the respiratory center. o Central chemoreceptors o They respond to changes in H+ Peripheral chemoreceptors concentration or PCO2, or both, in are located in the aortic cerebrospinal fluid. bodies, clusters of o Peripheral chemoreceptors chemoreceptors located in the wall of the arch of the o These chemoreceptors are aorta, and in the carotid part of the PNS and are bodies, which are oval sensitive to changes in PO2, nodules in the wall of the left and right common carotid H+, and PCO2 in the blood. arteries where they divide into the internal and external carotid arteries. Regulation of the respiratory center Chemoreceptor regulation of respiration (cont..)  Because CO2 is lipid-soluble, it easily diffuses into cells where, in the presence of carbonic anhydrase, it combines with water (H2O) to form carbonic acid (H2CO3).  Carbonic acid quickly breaks down into H+ and HCO3-.  Thus, an increase in CO2 in the blood causes an increase in H+ inside cells, and a decrease in CO2 causes a decrease in H+. Normally, the PCO2 in arterial blood is 40 mmHg. If even a slight increase in PCO2 occurs—a In addition, the peripheral chemoreceptors (but not the condition called hypercapnia or hypercarbia— central chemoreceptors) respond to a deficiency of O2. the central chemoreceptors are stimulated and When PO2 in arterial blood falls from a normal level respond vigorously to the resulting increase in H+ of 100 mmHg but is still above 50 mmHg, the level. peripheral chemoreceptors are stimulated. The peripheral chemoreceptors also are Severe deficiency of O2 depresses activity of the stimulated by both the high PCO2 and the rise in central chemoreceptors and inspiratory area, H+. which then do not respond well to any inputs and send fewer impulses to the muscles of inhalation. As the breathing rate decreases or breathing ceases altogether, PO2 falls lower and lower, establishing a positive feedback cycle with a possibly fatal result. Regulation of the respiratory center (conti..) Chemoreceptor regulation of respiration (conti..) The chemoreceptors participate in a negative feedback system that regulates the levels of CO2, O2, and H+ in the blood. As a result of increased PCO2, decreased pH (increased H+), or decreased PO2, input from the central and peripheral chemoreceptors causes the inspiratory area to become highly active, and the rate and depth of breathing increase. Rapid and deep breathing, called hyperventilation, allows the inhalation of more O2 and exhalation of more CO2 until PCO2 and H+ are lowered to normal. If arterial PCO2 is lower than 40 mmHg—a condition called hypocapnia or hypocarbia—the central and peripheral chemoreceptors are not stimulated, and stimulatory impulses are not sent to the inspiratory area. As a result, the area sets its own moderate pace until CO2 accumulates and the PCO2 rises to 40 mmHg. The inspiratory center is more strongly stimulated when PCO2 is rising above normal than when PO2 is falling below normal. If even a slight increase in PCO2 occurs the central chemoreceptors are stimulated and respond vigorously to the resulting increase in H+ level. the peripheral chemoreceptors also are stimulated by both the high PCO2 and the rise in H+. the peripheral chemoreceptors (but not the central chemoreceptors) respond to a deficiency of O2. When PO2 in arterial blood falls from a normal level of 100 mmHg but is still above 50 mmHg, the peripheral chemoreceptors are stimulated. As a result of increased PCO2, decreased pH (increased H+), or decreased PO2, input from the central and peripheral chemoreceptors causes the inspiratory area to become highly active, and the rate and depth of breathing increase. Rapid and deep breathing, called hyperventilation, allows the  inhalation of more O2 and  exhalation of more CO2  until PCO2 and H+ are lowered to normal. Regulation of the respiratory center: Regulation of the respiratory center: proprioceptors inflation reflex Proprioceptor stimulation of respiration The inflation reflex  As soon as you start exercising, your rate and Similar to those in the blood vessels, stretch- depth of breathing increase, even before changes sensitive receptors called baroreceptors or in PO2, PCO2, or H+ level occur. stretch receptors are located in the walls of bronchi and bronchioles.  The main stimulus for these quick changes in respiratory effort is input from proprioceptors, When these receptors become which monitor movement of joints and muscles. stretched during overinflation of the lungs, nerve impulses are sent along  Nerve impulses from the proprioceptors the vagus (X) nerves to the inspiratory stimulate the inspiratory area of the medulla and apneustic areas. oblongata. In response, the inspiratory area is inhibited  At the same time, axon collaterals directly, and the apneustic area is inhibited (branches) of upper motor neurons that from activating the inspiratory area. originate in the primary motor cortex (precentral gyrus) also feed excitatory As a result, exhalation begins. As air leaves the impulses into the inspiratory area. lungs during exhalation, the lungs deflate and the stretch receptors are no longer stimulated. Thus, the inspiratory and apneustic areas are no longer inhibited, and a new inhalation begins. How do the temperature changes, How do the limbic system pain, and irritation of the airways stimulation, stretching the anal modify respiration? sphincter muscle, and blood Temperature pressure modify respiration? An increase in body temperature, as Limbic system stimulation occurs during a fever or vigorous muscular exercise, increases the rate Anticipation of activity or emotional anxiety of respiration. A decrease in body may stimulate the limbic system, which then temperature decreases respiratory sends excitatory input to the inspiratory area, rate. increasing the rate and depth of ventilation. A sudden cold stimulus (such as plunging Stretching the anal sphincter muscle into cold water) causes temporary apnea (an This action increases the respiratory rate and is absence of breathing). sometimes used to stimulate respiration in a Pain newborn baby or a person who has stopped breathing. A sudden, severe pain brings about brief apnea, but a prolonged somatic pain Blood pressure increases respiratory rate. The carotid and aortic baroreceptors that Visceral pain may slow the rate of respiration. detect changes in blood pressure have a small effect on respiration. Irritation of airways A sudden rise in blood pressure decreases the Physical or chemical irritation of the pharynx rate of respiration, and a drop in blood pressure or larynx brings about an immediate increases the respiratory rate. cessation of breathing followed by coughing or sneezing. 5. Exercise and respiration When muscles contract during exercise, they consume large amounts of O2 and produce large The effects of exercise on the respiratory amounts of CO2. system During vigorous exercise, O2 consumption and pulmonary The respiratory and ventilation both increase dramatically. cardiovascular systems make adjustments in response to both At the onset of exercise, an abrupt increase in the intensity and duration of pulmonary ventilation is followed by a more exercise. gradual increase. As cardiac output rises, the blood With moderate exercise, the increase is due mostly to an flow to the lungs, termed pulmonary increase in the depth of ventilation rather than to increased perfusion, increases as well. breathing rate. In addition, the O2 diffusing capacity, The more gradual increase in ventilation during moderate a measure of the rate at which O2 exercise is due to chemical and physical changes in the can diffuse from alveolar air into the bloodstream, including blood, may increase three-fold (1) slightly decreased PO2, due to increased O2 consumption; during maximal exercise because more pulmonary capillaries become (2) slightly increased PCO2, due to increased CO2 production maximally perfused. by contracting muscle fibers; and As a result, there is a greater (3) increased temperature, due to liberation of more heat as surface area available for diffusion more O2 is utilized. of O2 into pulmonary blood capillaries. When exercise is more strenuous, the frequency of breathing also increases. During strenuous exercise, HCO3- buffers H+ released by lactic acid in a reaction that liberates CO2, which further increases PCO2. The effects of exercise on the respiratory system (cont..) The abrupt increase in ventilation at the start of exercise is due to neural changes that send excitatory impulses to the inspiratory area in the medulla oblongata. These changes include (1) anticipation of the activity, which stimulates the limbic system (2) sensory impulses from proprioceptors in muscles, tendons, and joints; and (3) motor impulses from the primary motor cortex (precentral gyrus).  At the end of an exercise session, an abrupt decrease in pulmonary ventilation is followed by a more gradual decline to the resting level.  The initial decrease is due mainly to changes in neural factors when movement stops or slows; the more gradual phase reflects the slower return of blood chemistry levels and temperature to the resting state.  References 1. Principles of Anatomy and Physiology/ Tortora GJ, Derrickson BH. — 12 ed. 2. Color Atlas of Physiology/ Despopoulos — 5th ed. 3. Guyton and Hall Textbook of Medical Physiology/ Hall JE — 11 ed. 4. Essentials of anatomy and physiology/ValerieC. Scanlon, Tina Sanders. — 5th ed. 5. https://www.apsubiology.org/anatomy/2020/2020_Exam_Reviews/Exam_3/CH22_ANS_Control_of_Br eathing.htm 6. Lecture note, Anatomy of respiratory system, Mr. Masro Bin Mohamad (MBM), Faculty of Pharmacy, CUCMS