Control of Respiration PDF

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Control of respiration Chong Ho Phin (Ph.D.) [email protected]...

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Control of respiration Chong Ho Phin (Ph.D.) [email protected] 1  Subtopics and learning outcomes Subtopics: 1. Physiology of the respiratory system Learning outcomes: Students should be able to: Describe the role of respiratory center in respiration Explain the regulations of respiratory center Discuss the nervous control on smooth muscle of the lungs 2  Respiratory center The respiratory center is located bilaterally in the medulla and pons Three major centers contribute to respiratory regulation: dorsal respiratory center, ventral respiratory center, pneumotaxic center The dorsal respiratory center is mainly responsible for inspiration, the ventral respiratory center is responsible for both expiration and inspiration, and the pneumotaxic center helps control the breathing rate and pattern 3  Respiratory center The size of the thorax is altered by the action of the respiratory muscles, which contract and relax as a result of nerve impulses These nerve impulses are sent from clusters of neurons located in the medulla oblongata and pons of the brain stem This widely dispersed group of neurons, collectively called the respiratory center, can be divided into three areas on the basis of their functions: 1) The medullary rhythmicity area 2) The pneumotaxic area 3) The apneustic area 4  Respiratory center: Medullary rhythmicity area The function of the medullary rhythmicity area is to control the basic rhythm of respiration There are inspiratory and expiratory areas within the medullary rhythmicity area 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 5  Respiratory center: Medullary rhythmicity area Inhalation 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 Exhalation At the end of 2 seconds, the inspiratory area becomes inactive and nerve impulses cease With no impulses arriving, the diaphragm and external intercostal muscles relax for about 3 seconds, allowing passive elastic recoil of the lungs and thoracic wall Then, the cycle repeats 6  Roles of the medullary rhythmicity area Roles of the medullary rhythmicity area in controlling: (a) Basic rhythm of respiration (b) Forceful breathing 7  Respiratory center: Pneumotaxic Area The pneumotaxic area 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 In other words, the impulses shorten the duration of inhalation When the pneumotaxic area is more active, breathing rate is more rapid 8  Respiratory center: Apneustic Area This area 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 9  Nerves used in respiration Phrenic nerves The nerves that stimulate the activity of the diaphragm They are composed of two nerves, the right and left phrenic nerve, which pass through the right and left side of the heart respectively They are autonomic nerves Vagus nerve Innervates the diaphragm as well as movements in the larynx and pharynx It also provides parasympathetic stimulation for the heart and the digestive system It is a major autonomic nerve Posterior thoracic nerves These nerves stimulate the intercostal muscles located around the pleura They are considered to be part of a larger group of intercostal nerves that stimulate regions across the thorax and abdomen. They are somatic nerves. 10  Regulation of respiratory center The basic rhythm of respiration set and coordinated by the inspiratory area The rhythm of respiration can be modified in response to inputs from other brain regions, receptors in the peripheral nervous system, and other factors Regulation of respiration is controlled by 1) Cortical influences 2) Chemoreceptor regulation 3) Proprioceptor regulation 4) Inhalation reflex 11  Cortical influences on respiration 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 12 Cortical influences on respiration 13  Nerve signals trigger contraction of inspiratory muscles 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 14  Chemoreceptor regulation of respiration Chemoreceptors in two locations monitor levels of CO2-, H+, and O2- and provide input to the respiratory center Central chemoreceptors are located in or near the medulla oblongata in the central nervous system They respond to changes in H+ concentration or pCO2-, or both, in cerebrospinal fluid Peripheral chemoreceptors are located in the aortic bodies, and in the carotid bodies 15  Chemoreceptor regulation of respiration These chemoreceptors are part of the peripheral nervous system and are sensitive to changes in pO2, H, and PCO2 in the blood Axons of sensory neurons from the aortic bodies are part of the vagus (X) nerves, and those from the carotid bodies are part of the right and left glossopharyngeal (IX) nerves 16  Chemoreceptor regulation of respiration 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 17  Chemoreceptor regulation of respiration Normally, the pCO2 in arterial blood is 40 mmHg If even a slight increase in pCO2 occurs a condition called hypercapnia The peripheral chemoreceptors also are stimulated by both the high pCO2 and the rise in H In addition, 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 Severe deficiency of O2 depresses activity of the central chemoreceptors and inspiratory area 18  Chemoreceptor regulation of respiration The central chemoreceptors and inspiratory area 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 (cardiac arrest, organ dysfunction, etc) The chemoreceptors regulate the levels of CO2, O2, and H in the blood As a result of increased CO2, 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 19  Chemoreceptor regulation of respiration If arterial CO2 is lower than 40 mmHg a condition called hypocapnia 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 As a result, people who hyperventilate voluntarily and cause hypocapnia can hold their breath for an unusually long period 20  Chemoreceptor regulation of respiration Swimmers are encouraged to hyperventilate just before diving in to compete However, this practice is risky because the O2 level may fall dangerously low and cause fainting before the pCO2 rises high enough to stimulate inhalation If you faint on land you may suffer bumps and bruises, but if you faint in the water you could drown 21  Proprioceptor stimulation of respiration As soon as you start exercising, your rate and depth of breathing increase, even before changes in pO2, PCO2, or H level occur The main stimulus for these quick changes in respiratory effort is input from proprioceptors, which monitor movement of joints and muscles Nerve impulses from the proprioceptors stimulate the inspiratory area of the medulla oblongata 22  The inhalation reflex Similar to those in the blood vessels, stretch-sensitive receptors called baroreceptors or stretch receptors are located in the walls of bronchi and bronchioles When these receptors become stretched during over inflation of the lungs, nerve impulses are sent along the vagus (X) nerves to the inspiratory and apneustic areas In response, the inspiratory area is inhibited directly, and the apneustic area is inhibited from activating the inspiratory area As a result, exhalation begins As air leaves the 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 This reflex, referred to as the inflation reflex, is mainly a protective mechanism for preventing excessive inflation of the lungs 23  Other influences on respiration Limbic system stimulation: Anticipation of activity or emotional anxiety may stimulate the limbic system, which then sends excitatory input to the inspiratory area, increasing the rate and depth of ventilation Temperature: An increase in body temperature, as occurs during a fever or vigorous muscular exercise, increases the rate of respiration Pain: A sudden, severe pain brings about brief apnea, but a prolonged somatic pain increases respiratory rate. Visceral pain may slow the rate of respiration Stretching the anal sphincter muscle: This action increases the respiratory rate and is sometimes used to stimulate respiration in a newborn baby or a person who has stopped breathing 24  Other influences on respiration Irritation of airways: Physical or chemical irritation of the pharynx or larynx brings about an immediate cessation of breathing followed by coughing or sneezing Blood pressure: The carotid and aortic baroreceptors that detect changes in blood pressure have a small effect on respiration A sudden rise in blood pressure decreases the rate of respiration, and a drop in blood pressure increases the respiratory rate 25  Nervous control on smooth muscle of the lungs During exercise, activity in the sympathetic division of the autonomic nervous system (ANS) increases and the adrenal medulla releases the hormones epinephrine and norepinephrine; both of these events cause relaxation of smooth muscle in the bronchioles, which dilates the airways Because air reaches the alveoli more quickly, lung ventilation improves The parasympathetic division of the ANS and mediators of allergic reactions such as histamine have the opposite effect, causing contraction of bronchiolar smooth muscle, which results in constriction of distal bronchioles 26  Subtopics and learning outcomes Subtopics: 1. Physiology of the respiratory system Learning outcomes: Students should be able to: Describe the role of respiratory center in respiration Explain the regulations of respiratory center Discuss the nervous control on smooth muscle of the lungs 27 Thank you! Have a great day! Questions? 28