The Respiratory System Biology 1612 Lecture Outline K. Donaldson, M.S. Georgia Perimeter College

INTRODUCTION The two systems that cooperate to supply O2 and eliminate CO2 are the cardiovascular and the respiratory system. The respiratory system provides for gas exchange. The cardiovascular system transports the respiratory gases. Failure of either system has the same effect on the body: disruption of homeostasis and rapid death of cells from oxygen starvation and buildup of waste products. Respiration is the exchange of gases between the atmosphere, blood, and cells. It takes place in three basic steps: ventilation (breathing), external (pulmonary) respiration, and internal (tissue) respiration.

The Respiratory System Cells continually use O2 & release CO2 Respiratory system designed for gas exchange Cardiovascular system is what transports gases in blood Failure of either system leads to rapid cell death from O2 starvation

Respiratory System Anatomical Terms Nose Pharynx = throat Larynx = voice box Trachea = windpipe Bronchi = airways Lungs Terms to indicate locations of respiratory infections: upper respiratory tract is above vocal cords lower respiratory tract is below vocal cords The conducting system consists of a series of cavities and tubes - nose, pharynx, larynx, trachea, bronchi, bronchiole, and terminal bronchioles - that conduct air into the lungs. The respiratory portion consists of the area where gas exchange occurs - respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

External Nasal Structures Skin, nasal bones, & cartilage lined with mucous membrane Openings are called external nares or nostrils

External Anatomy The external portion of the nose is made of cartilage and skin and is lined with mucous membranes. Openings to the exterior are the external nares or nostrils. The external portion of the nose is made of cartilage and skin and is lined with mucous membranes. The bony framework of the nose is formed by the frontal bone, nasal bones, and maxillae.

Internal Anatomy The interior structures of the nose are specialized for warming, moistening, and filtering incoming air; receiving olfactory stimuli; and serving as large, hollow resonating chambers to modify speech sounds. The internal portion of the nose communicates with the paranasal sinuses and nasopharynx through the internal nares. The inside of both the external and internal nose is called the nasal cavity. It is divided into right and left sides by the nasal septum. The anterior portion of the cavity is called the vestibule.

Nasal Polyps Nasal polyps are outgrowths of the mucous membranes which are usually found around the openings of the paranasal sinuses. They are soft, noncancerous (benign) growths that develop on the lining of your nose or sinuses. Small nasal polyps usually cause few problems, but larger ones can affect your breathing and diminish your sense of smell. Sometimes they may cause dull headaches or snoring, and in rare cases, massive nasal polyps can alter the shape of your face. Nasal polyps result from chronic inflammation in the lining of your nose or sinuses, but just what triggers the inflammation isn't always clear. Although nasal polyps can affect anyone, they're more common in people older than 40 and in adults and children with conditions such as asthma, chronic sinus infections, hay fever and cystic fibrosis.

Nose -- Internal Structures Large chamber within the skull Roof is made up of the ethmoid bone and floor is hard palate Internal nares (choanae) are openings to pharynx In the lateral walls of either fossa are three shell-like concavities: the superior, middle and inferior conchae. Air passages or meatuses connect the conchae. The nostrils (external nares) open anteriorly into the nasal cavity and the choanae (posterior nares) communicate posteriorly with the nasopharynx. Nasal septum is composed of bone & cartilage.

Functions of the Nasal Structures Specialized columnar epithelium called olfactory epithelium lines the upper medial portion of the nasal cavity and responds to odors. Pseudostratified ciliated columnar epithelium with goblet cells lines nasal cavity. The function is to: warms air due to high its high vascularity mucous moistens air & traps dust, pollens, smoke and other airborne particles cilia move mucous towards pharynx where it can be removed Paranasal sinuses open into nasal cavity: The four paranasal sinuses are the ethmoid, sphenoid, frontal & maxillary sinuses. Their function is to lighten the overall weight of the skull and to act as sound chambers for voice resonance.

Rhinoplasty Rhinoplasty (“nose job”) is a surgical procedure in which the structure of the external nose is altered for cosmetic or functional reasons (fracture or septal repair) Procedure: local and general anesthetic nasal cartilage is reshaped or removed by entering through nostrils bones fractured and repositioned internal packing & splint while healing

Pharynx - Overview The pharynx (throat) is a muscular tube lined by a mucous membrane. The anatomic regions are the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx functions in respiration. Both the oropharynx and laryngopharynx function in digestion and in respiration (serving as a passageway for both air and food).

Pharynx

Pharynx Muscular tube (5 inch long) hanging from skull composed of skeletal muscle and mucous membranes. Extends from internal nares to cricoid cartilage Functions: passageway for food and air resonating chamber for speech production tonsil (lymphatic tissue) in the walls protects entryway into body Distinct regions -- nasopharynx, oropharynx and laryngopharynx

Nasopharynx From choanae to soft palate Passageway for air only openings of auditory (Eustachian) tubes from middle ear cavity adenoids or pharyngeal tonsil in roof Passageway for air only pseudostratified ciliated columnar epithelium with goblet

Oropharynx From soft palate to epiglottis fauces is opening from mouth into oropharynx palatine tonsils found in side walls, lingual tonsil in tongue Common passageway for food & air stratified squamous epithelium

Laryngopharynx Extends from epiglottis to cricoid cartilage Common passageway for food & air & ends as esophagus inferiorly stratified squamous epithelium

Larynx - Overview The larynx (voice box) is a passageway that connects the pharynx with the trachea. It contains the thyroid cartilage (Adam’s apple); the epiglottis, which prevents food from entering the larynx; the cricoid cartilage, which connects the larynx and trachea; and the paired arytenoid, corniculate, and cuneiform cartilages. Voice Production: The larynx contains vocal folds (true vocal cords), which produce sound. Taunt vocal folds produce high pitches, and relaxed vocal folds produce low pitches. Other structures modify the sound.

Cartilages of the Larynx Thyroid cartilage forms Adam’s apple Epiglottis---leaf-shaped piece of elastic cartilage during swallowing, larynx moves upward epiglottis bends to cover glottis Cricoid cartilage---ring of cartilage attached to top of trachea Pair of arytenoid cartilages sit upon cricoid many muscles responsible for their movement partially buried in vocal folds (true vocal cords)

Larynx Cartilage & connective tissue tube Anterior to C4 to C6 Constructed of 3 single & 3 paired cartilages

Vocal Cords False vocal cords (ventricular folds) found above vocal folds (true vocal cords) True vocal cords attach to arytenoid cartilages

The Structures of Voice Production True vocal cord contains both skeletal muscle and an elastic ligament (vocal ligament) When 10 intrinsic muscles of the larynx contract, it moves the cartilages & stretches the vocal cord tight When air is pushed past tight ligament, sound is produced (the longer & thicker vocal cord in male produces a lower pitch of sound) The tighter the ligament, the higher the pitch To increase volume of sound, push air harder.

Movement of Vocal Cords Opening and closing of the vocal folds occurs during breathing and speech

Speech and Whispering Speech is modified sound made by the larynx. Speech requires pharynx, mouth, nasal cavity & sinuses to resonate that sound Tongue & lips form words Pitch is controlled by tension on vocal folds pulled tight produces higher pitch male vocal folds are thicker & longer so vibrate more slowly producing a lower pitch Whispering is forcing air through almost closed rima glottidis -- oral cavity alone forms speech

Laryngitis Laryngitis is an inflammation of the larynx that is usually caused by respiratory infection or irritants.

Trachea The trachea (windpipe) extends from the larynx to the primary bronchi. It is composed of smooth muscle and C-shaped rings of cartilage and is lined with pseudostratified ciliated columnar epithelium. The cartilage rings keep the airway open. The cilia of the epithelium sweep debris away from the lungs and back to the throat to be swallowed.

Trachea Size is 5 in long & 1in diameter Extends from larynx to T5 anterior to the esophagus and then splits into bronchi Layers mucosa = pseudostratified columnar with cilia & goblet submucosa = loose connective tissue & seromucous glands hyaline cartilage = 16 to 20 incomplete rings open side facing esophagus contains trachealis m. (smooth) internal ridge on last ring called carina adventitia binds it to other organs

Trachea and Bronchial Tree Full extent of airways is visible starting at the larynx and trachea

Histology of the Trachea Ciliated pseudostratified columnar epithelium Hyaline cartilage as C-shaped structure closed by trachealis muscle

Airway Epithelium Ciliated pseudostratified columnar epithelium with goblet cells produce a moving mass of mucus.

Tracheostomy and Intubation Reestablishing airflow past an airway obstruction crushing injury to larynx or chest swelling that closes airway vomit or foreign object Tracheostomy is incision in trachea below cricoid cartilage if larynx is obstructed Intubation is passing a tube from mouth or nose through larynx and trachea

Bronchi The trachea divides into the right and left pulmonary bronchi. The bronchial tree consists of the trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, and terminal bronchioles. Walls of bronchi contain rings of cartilage. Walls of bronchioles contain smooth muscle.

Bronchi and Bronchioles Primary bronchi supply each lung Secondary bronchi supply each lobe of the lungs (3 right + 2 left) Tertiary bronchi supply each bronchopulmonary segment Repeated branchings called bronchioles form a bronchial tree

Histology of Bronchial Tree Epithelium changes from pseudostratified ciliated columnar to nonciliated simple cuboidal as pass deeper into lungs Incomplete rings of cartilage replaced by rings of smooth muscle & then connective tissue sympathetic NS & adrenal gland release epinephrine that relaxes smooth muscle & dilates airways asthma attack or allergic reactions constrict distal bronchiole smooth muscle nebulization therapy = inhale mist with chemicals that relax muscle & reduce thickness of mucus.

Pleural Membranes & Pleural Cavity Visceral pleura covers lungs --- parietal pleura lines ribcage & covers upper surface of diaphragm Pleural cavity is potential space between ribs & lungs

Lungs - Overview Lungs are paired organs in the thoracic cavity; they are enclosed and protected by the pleural membrane . The parietal pleura is the outer layer which is attached to the wall of the thoracic cavity. The visceral pleura is the inner layer, covering the lungs themselves. Between the pleurae is a small potential space, the pleural cavity, which contains a lubricating fluid secreted by the membranes. The pleural cavities may fill with air (pneumothorax) or blood (hemothorax). A pneumorthorax may cause a partial or complete collapse of the lung. The lungs extend from the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly.

Lungs - Overview The lungs almost totally fill the thorax. The right lung has three lobes separated by two fissures; the left lung has two lobes separated by one fissure and a depression, the cardiac notch. The secondary bronchi give rise to branches called tertiary (segmental) bronchi, which supply segments of lung tissue called bronchopulmonary segments. Each bronchopulmonary segment consists of many small compartments called lobules, which contain lymphatics, arterioles, venules, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Gross Anatomy of Lungs Base, apex (cupula), costal surface, cardiac notch Oblique & horizontal fissure in right lung results in 3 lobes Oblique fissure only in left lung produces 2 lobes

Mediastinal Surface of Lungs Blood vessels & airways enter lungs at hilus Forms root of lungs Covered with pleura (parietal becomes visceral)

Structures within a Lobule of Lung Branchings of single arteriole, venule & bronchiole are wrapped by elastic CT Respiratory bronchiole simple squamous Alveolar ducts surrounded by alveolar sacs & alveoli sac is 2 or more alveoli sharing a common opening

Alveoli Alveolar walls consist of type I alveolar (squamous pulmonary epithelial) cells, type II alveolar (septal) cells, and alveolar macrophages (dust cells). Type II alveolar cells secrete alveolar fluid, which keeps the alveolar cells moist and which contains a component called surfactant. Surfactant lowers the surface tension of alveolar fluid, preventing the collapse of alveoli with each expiration. Respiratory Distress Syndrome is a disorder of premature infants in which the alveoli do not have sufficient surfactant to remain open. Gas exchange occurs across the alveolar-capillary membrane.

Histology of Lung Tissue Photomicrograph of lung tissue showing bronchioles, alveoli and alveolar ducts.

Details of Respiratory Membrane

Cells Types of the Alveoli Type I alveolar cells simple squamous cells where gas exchange occurs Type II alveolar cells (septal cells) free surface has microvilli secrete alveolar fluid containing surfactant Alveolar dust cells wandering macrophages remove debris

Alveolar-Capillary Membrane Respiratory membrane = 1/2 micron thick Exchange of gas from alveoli to blood 4 Layers of membrane to cross alveolar epithelial wall of type I cells alveolar epithelial basement membrane capillary basement membrane endothelial cells of capillary Vast surface area = handball court

Details of Respiratory Membrane Find the 4 layers that comprise the respiratory membrane

Double Blood Supply to the Lungs Deoxygenated blood arrives through pulmonary trunk from the right ventricle Bronchial arteries branch off of the aorta to supply oxygenated blood to lung tissue Venous drainage returns all blood to heart Less pressure in venous system Pulmonary blood vessels constrict in response to low O2 levels so as not to pick up CO2 on there way through the lungs

Clinical Applications Nebulization, a procedure for administering medication as small droplets suspended in air into the respiratory tract, is used to treat many different types of respiratory disorders. In the lungs vasoconstriction in response to hypoxia diverts pulmonary blood from poorly ventilated areas to well ventilated areas. This phenomenon is known as ventilation – perfusion coupling.

PULMONARY VENTILATION Respiration occurs in three basic steps: pulmonary ventilation, external respiration, and internal respiration. Inspiration (inhalation) is the process of bringing air into the lungs. The movement of air into and out of the lungs depends on pressure changes governed in part by Boyle’s law, which states that the volume of a gas varies inversely with pressure, assuming that temperature is constant.

Breathing or Pulmonary Ventilation Air moves into lungs when pressure inside lungs is less than atmospheric pressure How is this accomplished? Air moves out of the lungs when pressure inside lungs is greater than atmospheric pressure Atmospheric pressure = 1 atm or 760mm Hg

Boyle’s Law As the size of closed container decreases, pressure inside is increased The molecules have less wall area to strike so the pressure on each inch of area increases.

Dimensions of the Chest Cavity Breathing in requires muscular activity & chest size changes Contraction of the diaphragm flattens the dome and increases the vertical dimension of the chest

Inspiration The first step in expanding the lungs involves contraction of the main inspiratory muscle, the diaphragm. Inhalation occurs when alveolar (intrapulmonic) pressure falls below atmospheric pressure. Contraction of the diaphragm and external intercostal muscles increases the size of the thorax, thus decreasing the intrapleural (intrathoracic) pressure so that the lungs expand. Expansion of the lungs decreases alveolar pressure so that air moves along the pressure gradient from the atmosphere into the lungs. During forced inhalation, accessory muscles of inspiration (sternocleidomastoids, scalenes, and pectoralis minor) are also used.

Quiet Inspiration Diaphragm moves 1 cm & ribs lifted by muscles Intrathoracic pressure falls and 2-3 liters inhaled

Expiration Expiration (exhalation) is the movement of air out of the lungs. Exhalation occurs when alveolar pressure is higher than atmospheric pressure. Relaxation of the diaphragm and external intercostal muscles results in elastic recoil of the chest wall and lungs, which increases intrapleural pressure, decreases lung volume, and increases alveolar pressure so that air moves from the lungs to the atmosphere. There is also an inward pull of surface tension due to the film of alveolar fluid. Exhalation becomes active during labored breathing and when air movement out of the lungs is impeded. Forced expiration employs contraction of the internal intercostals and abdominal muscles.

Quiet Expiration Passive process with no muscle action Elastic recoil & surface tension in alveoli pulls inward Alveolar pressure increases & air is pushed out

Labored Breathing Forced expiration Forced inspiration abdominal mm force diaphragm up internal intercostals depress ribs Forced inspiration sternocleidomastoid, scalenes & pectoralis minor lift chest upwards as you gasp for air

Intrapleural Pressures Always subatmospheric (756 mm Hg) As diaphragm contracts intrathoracic pressure decreases even more (754 mm Hg) Helps keep parietal & visceral pleura stick together

Summary of Breathing Alveolar pressure decreases & air rushes in Alveolar pressure increases & air rushes out

Alveolar Surface Tension Thin layer of fluid in alveoli causes inwardly directed force = surface tension water molecules strongly attracted to each other Causes alveoli to remain as small as possible Detergent-like substance called surfactant produced by Type II alveolar cells lowers alveolar surface tension insufficient in premature babies so that alveoli collapse at end of each exhalation

Compliance of the Lungs Ease with which lungs & chest wall expand depends upon elasticity of lungs & surface tension Some diseases reduce compliance tuberculosis forms scar tissue pulmonary edema --- fluid in lungs & reduced surfactant paralysis

Airway Resistance Resistance to airflow depends upon airway size increase size of chest airways increase in diameter contract smooth muscles in airways decreases in diameter

Breathing Patterns Eupnea is normal variation in breathing rate and depth. Apnea refers to breath holding. Dyspnea relates to painful or difficult breathing. Tachypnea involves rapid breathing rate. Costal breathing requires combinations of various patterns of intercostal and extracostal muscles, usually during need for increased ventilation, as with exercise. Diaphragmatic breathing is the usual mode of operation to move air by contracting and relaxing the diaphragm to change the lung volume. Modified respiratory movements are used to express emotions and to clear air passageways.

Modified Respiratory Movements Coughing deep inspiration, closure of rima glottidis & strong expiration blasts air out to clear respiratory passages Hiccuping spasmodic contraction of diaphragm & quick closure of rima glottidis produce sharp inspiratory sound

LUNG VOLUMES AND CAPACITIES Air volumes exchanged during breathing and rate of ventilation are measured with a spiromometer, or respirometer, and the record is called a spirogram. Among the pulmonary air volumes exchanged in ventilation are tidal (500 ml), inspiratory reserve (3100 ml), expiratory reserve (1200 ml), residual (1200 ml) and minimal volumes. Only about 350 ml of the tidal volume actually reaches the alveoli, the other 150 ml remains in the airways as anatomic dead space. Pulmonary lung capacities, the sum of two or more volumes, include inspiratory (3600 ml), functional residual (2400 ml), vital (4800 ml), and total lung (6000 ml) capacities. The minute volume of respiration is the total volume of air taken in during one minute (tidal volume x 12 respirations per minute = 6000 ml/min).

Lung Volumes and Capacities Tidal volume = amount air moved during quiet breathing MVR= minute ventilation is amount of air moved in a minute Reserve volumes ---- amount you can breathe either in or out above that amount of tidal volume Residual volume = 1200 mL permanently trapped air in system Vital capacity & total lung capacity are sums of the other volumes

EXCHANGE OF OXYGEN AND CARBON DIOXIDE To understand the exchange of oxygen and carbon dioxide between the blood and alveoli, it is useful to know some gas laws. According to Dalton’s law, each gas in a mixture of gases exerts its own pressure as if all the other gases were not present.

Dalton’s Law Each gas in a mixture of gases exerts its own pressure as if all other gases were not present partial pressures denoted as p Total pressure is sum of all partial pressures atmospheric pressure (760 mm Hg) = pO2 + pCO2 + pN2 + pH2O to determine partial pressure of O2-- multiply 760 by % of air that is O2 (21%) = 160 mm Hg

What is Composition of Air? Air = 21% O2, 79% N2 and .04% CO2 Alveolar air = 14% O2, 79% N2 and 5.2% CO2 Expired air = 16% O2, 79% N2 and 4.5% CO2 Observations alveolar air has less O2 since absorbed by blood mystery-----expired air has more O2 & less CO2 than alveolar air? Anatomical dead space = 150 ml of 500 ml of tidal volume

EXCHANGE OF OXYGEN AND CARBON DIOXIDE The partial pressure of a gas is the pressure exerted by that gas in a mixture of gases. The total pressure of a mixture is calculated by simply adding all the partial pressures. It is symbolized by P. The partial pressures of the respiratory gases in the atmosphere, alveoli, blood, and tissues cells are shown in the text. The amounts of O2 and CO2 vary in inspired (atmospheric), alveolar, and expired air.

Henry’s Law Henry’s law states that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility coefficient (its physical or chemical attraction for water), when the temperature remains constant. Nitrogen narcosis and decompression sickness (caisson disease, or bends) are conditions explained by Henry’s law.

Henry’s Law Quantity of a gas that will dissolve in a liquid depends upon the amount of gas present and its solubility coefficient explains why you can breathe compressed air while scuba diving despite 79% Nitrogen N2 has very low solubility unlike CO2 (soda cans) dive deep & increased pressure forces more N2 to dissolve in the blood (nitrogen narcosis) decompression sickness if come back to surface too fast or stay deep too long Breathing O2 under pressure dissolves more O2 in blood

Hyperbaric Oxygenation A major clinical application of Henry’s law is hyperbaric oxygenation. Use of pressure to dissolve more O2 in the blood treatment for patients with anaerobic bacterial infections (tetanus and gangrene) anaerobic bacteria die in the presence of O2 Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O2 Used to treat heart disorders, carbon monoxide poisoning, cerebral edema, bone infections, gas embolisms & crush injuries

Respiration

External Respiration O2 and CO2 diffuse from areas of their higher partial pressures to areas of their lower partial pressures. Diffusion depends on partial pressure differences Compare gas movements in pulmonary capillaries to tissue capillaries

Rate of Diffusion of Gases Depends upon partial pressure of gases in air p O2 at sea level is 160 mm Hg 10,000 feet is 110 mm Hg / 50,000 feet is 18 mm Hg Large surface area of our alveoli Diffusion distance (membrane thickness) is very small Solubility & molecular weight of gases O2 smaller molecule diffuses somewhat faster CO2 dissolves 24X more easily in water so net outward diffusion of CO2 is much faster disease produces hypoxia before hypercapnia lack of O2 before too much CO2

Internal Respiration Exchange of gases between blood & tissues Conversion of oxygenated blood into deoxygenated Observe diffusion of O2 inward at rest 25% of available O2 enters cells during exercise more O2 is absorbed Observe diffusion of CO2 outward

Oxygen Transport In each 100 ml of oxygenated blood, 1.5% of the O2 is dissolved in the plasma and 98.5% is carried with hemoglobin (Hb) inside red blood cells as oxyhemglobin (HbO2). Hemoglobin consists of a protein portion called globin and a pigment called heme. The heme portion contains 4 atoms of iron, each capable of combining with a molecule of oxygen.

Hemoglobin and Oxygen Partial Pressure The most important factor that determines how much oxygen combines with hemoglobin is PO2. The greater the PO2, the more oxygen will combine with hemoglobin, until the available hemoglobin molecules are saturated.

Hemoglobin and Oxygen Partial Pressure Blood is almost fully saturated at pO2 of 60mm people OK at high altitudes & with some disease Between 40 & 20 mm Hg, large amounts of O2 are released as in areas of need like contracting muscle

Oxygen Transport in the Blood Oxyhemoglobin contains 98.5% chemically combined oxygen and hemoglobin inside red blood cells Does not dissolve easily in water only 1.5% transported dissolved in blood Only the dissolved O2 can diffuse into tissues Factors affecting dissociation of O2 from hemoglobin are important Oxygen dissociation curve shows levels of saturation and oxygen partial pressures

Hemoglobin and Oxygen Partial Pressure Blood is almost fully saturated at pO2 of 60mm people OK at high altitudes & with some disease Between 40 & 20 mm Hg, large amounts of O2 are released as in areas of need like contracting muscle

Other Factors Affecting Hemoglobin Affinity for Oxygen In an acid (low pH) environment, O2 splits more readily from hemoglobin. This is referred to as the Bohr effect. Low blood pH (acidic conditions) results from high PCO2. Within limits, as temperature increases, so does the amount of oxygen released from hemoglobin. Active cells require more oxygen, and active cells (such as contracting muscle cells) liberate more acid and heat. The acid and heat, in turn, stimulate the oxyhemoglobin to release its oxygen. BPG (2, 3-biphosphoglycerate) is a substance formed in red blood cells during glycolysis. The greater the level of BPG, the more oxygen is released from hemoglobin.

Acidity & Oxygen Affinity for Hb As acidity increases, O2 affinity for Hb decreases Bohr effect H+ binds to hemoglobin & alters it O2 left behind in needy tissues

pCO2 & Oxygen Release As pCO2 rises with exercise, O2 is released more easily CO2 converts to carbonic acid & becomes H+ and bicarbonate ions & lowers pH.

Temperature & Oxygen Release As temperature increases, more O2 is released Metabolic activity & heat More BPG, more O2 released RBC activity hormones like thyroxine & growth hormone

Oxygen Affinity & Fetal Hemoglobin Differs from adult in structure & affinity for O2 When pO2 is low, can carry more O2 Maternal blood in placenta has less O2

Review

Fetal Hemoglobin Fetal hemoglobin has a higher affinity for oxygen because it binds BPG less strongly and can carry more oxygen to offset the low oxygen saturation in maternal blood in the placenta. Because of the strong attraction of carbon monoxide (CO) to hemoglobin, even small concentrations of CO will reduce the oxygen carrying capacity leading to hypoxia and carbon monoxide poisoning.

Carbon Monoxide Poisoning CO from car exhaust & tobacco smoke Binds to Hb heme group more successfully than O2 CO poisoning Treat by administering pure O2

Carbon Dioxide Transport CO2 is carried in blood in the form of dissolved CO2 (7%), carbaminohemoglobin (23%), and bicarbonate ions (70%). The conversion of CO2 to bicarbonate ions and the related chloride shift maintains the ionic balance between plasma and red blood cells.

Carbon Dioxide Transport 100 ml of blood carries 55 ml of CO2 Is carried by the blood in 3 ways dissolved in plasma combined with the globin part of Hb molecule forming carbaminohemoglobin as part of bicarbonate ion CO2 + H2O combine to form carbonic acid that dissociates into H+ and bicarbonate ion

Summary of Gas Exchange and Transport in Lungs and Tissues CO2 in blood causes O2 to split from hemoglobin. Similarly, the binding of O2 to hemoglobin causes a release of CO2 from blood.

Summary of Gas Exchange & Transport

Respiratory Center The area of the brain from which nerve impulses are sent to respiratory muscles is located bilaterally in the reticular formation of the brain stem. This respiratory center consists of a medullary rhythmicity area (inspiratory and expiratory areas), pneumotaxic area, and apneustic area.

Role of the Respiratory Center Respiratory mm. controlled by neurons in pons & medulla 3 groups of neurons medullary rhythmicity pneumotaxic apneustic centers

Medullary Rhythmicity Area The function of the medullary rhythmicity area is to control the basic rhythm of respiration. The inspiratory area has an intrinsic excitability of autorhythmic neurons that sets the basic rhythm of respiration. The expiratory area neurons remain inactive during most quiet respiration but are probably activated during high levels of ventilation to cause contraction of muscles used in forced (labored) expiration.

Medullary Rhythmicity Area Controls basic rhythm of respiration Inspiration for 2 seconds, expiration for 3 Autorhythmic cells active for 2 seconds then inactive Expiratory neurons inactive during most quiet breathing only active during high ventilation rates

Pneumotaxic Area The pneumotaxic area in the upper pons helps coordinate the transition between inspiration and expiration. The apneustic area sends impulses to the inspiratory area that activate it and prolong inspiration, inhibiting expiration.

Regulation of Respiratory Center Cortical Influences voluntarily alter breathing patterns Cortical influences allow conscious control of respiration that may be needed to avoid inhaling noxious gasses or water. Voluntary breath holding is limited by the overriding stimuli of increased [H+] and [CO2]. inspiratory center is stimulated by increase in either if you hold breathe until you faint----breathing will resume

Chemoreceptor Regulation of Respiration A slight increase in PCO2 (and thus H+), a condition called hypercapnia, stimulates central chemoreceptors. As a response to increased PCO2, increased H+ and decreased PO2, the inspiratory area is activated and hyperventilation, rapid and deep breathing, occurs. If arterial PCO2 is lower than 40 mm Hg, a condition called hypocapnia, the chemoreceptors are not stimulated and the inspiratory area sets its own pace until CO2 accumulates and PCO2 rises to 40 mm Hg. Severe deficiency of O2 depresses activity of the central chemoreceptors and respiratory center.

Chemical Regulation of Respiration Central chemoreceptors in medulla respond to changes in H+ or pCO2 hypercapnia = slight increase in pCO2 is noticed Peripheral chemoreceptors respond to changes in H+ , pO2 or PCO2 aortic body---in wall of aorta nerves join vagus carotid bodies--in walls of common carotid arteries nerves join glossopharyngeal nerve

Negative Feedback Regulation of Breathing Negative feedback control of breathing Increase in arterial pCO2 Stimulates receptors Inspiratory center Muscles of respiration contract more frequently & forcefully pCO2 Decreases

Control of Respiratory Rate Proprioceptors of joints and muscles activate the inspiratory center to increase ventilation prior to exercise induced oxygen need. The inflation (Hering-Breuer) reflex detects lung expansion with stretch receptors and limits it depending on ventilatory need and prevention of damage. Other influences include blood pressure, limbic system, temperature, pain, stretching the anal sphincter, and irritation to the respiratory mucosa. Table 23.2 summarizes the changes that increase or decrease ventilation rate and depth.

Regulation of Ventilation Rate and Depth

Hypoxia Hypoxia refers to oxygen deficiency at the tissue level and is classified in several ways. Hypoxic hypoxia is caused by a low PO2 in arterial blood (high altitude, airway obstruction, fluid in lungs). In anemic hypoxia, there is too little functioning hemoglobin in the blood (hemorrhage, anemia, carbon monoxide poisoning). Stagnant hypoxia results from the inability of blood to carry oxygen to tissues fast enough to sustain their needs (heart failure, circulatory shock). In histotoxic hypoxia, the blood delivers adequate oxygen to the tissues, but the tissues are unable to use it properly (cyanide poisoning).

EXERCISE AND THE RESPIRATORY SYSTEM The respiratory system works with the cardiovascular system to make appropriate adjustments for different exercise intensities and durations. As blood flow increases with a lower O2 and higher CO2 content, the amount passing through the lung (pulmonary perfusion) increases and is matched by increased ventilation and oxygen diffusion capacity as more pulmonary capillaries open. Ventilatory modifications can increase 30 times above resting levels, in an initial rapid rate due to neural influences and then more gradually due to chemical stimulation from changes in cell metabolism. A similar, but reversed, effect occurs with cessation of exercise. Smokers have difficulty breathing for a number of reasons, including nicotine, mucous, irritants, and that fact that scar tissue replaces elastic fibers.

Smokers Lowered Respiratory Efficiency Smoker is easily “winded” with moderate exercise nicotine constricts terminal bronchioles carbon monoxide in smoke binds to hemoglobin irritants in smoke cause excess mucus secretion irritants inhibit movements of cilia in time destroys elastic fibers in lungs & leads to emphysema trapping of air in alveoli & reduced gas exchange

The time line for development of the respiratory system 6 – 16 weeks the basic structures are formed 16 – 26 weeks vascularization and the development of respiratory bronchioles, alveolar ducts and some alveoli begins 26 weeks to birth many more alveoli develop By 26 – 28 weeks there is sufficient surfactant for survival.

Aging & the Respiratory System Respiratory tissues & chest wall become more rigid Vital capacity decreases to 35% by age 70. Decreases in macrophage activity Diminished ciliary action Decrease in blood levels of O2 Result is an age-related susceptibility to pneumonia or bronchitis

Disorders of the Respiratory System Asthma Chronic obstructive pulmonary disease Emphysema Chronic bronchitis Lung cancer Pneumonia Tuberculosis Coryza and Influenza Pulmonary Edema Cystic fibrosis

Pneumothorax Pleural cavities are sealed cavities not open to the outside Injuries to the chest wall that let air enter the intrapleural space causes a pneumothorax collapsed lung on same side as injury surface tension and recoil of elastic fibers causes the lung to collapse

DISORDERS OF THE RESPIRATORY SYSTEM Asthma is characterized by the following: spasms of smooth muscle in bronchial tubes that result in partial or complete closure of air passageways; inflammation; inflated alveoli; and excess mucus production. A common triggering factor is allergy, but other factors include emotional upset, aspirin, exercise, and breathing cold air or cigarette smoke. Chronic obstructive pulmonary disease (COPD) is a type of respiratory disorder characterized by chronic and recurrent obstruction of air flow, which increases airway resistance. The principal types of COPD are emphysema and chronic bronchitis. Bronchitis is an inflammation of the bronchial tubes, the main symptom of which is a productive (raising mucus or sputum) cough.

DISORDERS OF THE RESPIRATORY SYSTEM In bronchogenic carcinoma (lung cancer), bronchial epithelial cells are replaced by cancer cells after constant irritation has disrupted the normal growth, division, and function of the epithelial cells. Airways are often blocked and metastasis is very common. It is most commonly associated with smoking. Pneumonia is an acute infection of the alveoli. The most common cause in the pneumococcal bacteria but other microbes may be involved. Treatment involves antibiotics, bronchodilators, oxygen therapy, and chest physiotherapy. Tuberculosis (TB) is an inflammation of pleurae and lungs produced by the organism Mycobacterium tuberculosis. It is communicable and destroys lung tissue, leaving nonfunctional fibrous tissue behind. Coryza (common cold) is caused by viruses and usually is not accompanied by a fever, whereas influenza (flu) is usually accompanied by a fever greater than 101oF.

DISORDERS OF THE RESPIRATORY SYSTEM Pulmonary edema refers to an abnormal accumulation of interstitial fluid in the interstitial spaces and alveoli of the lungs. It may be pulmonary or cardiac in origin. Cystic fibrosis is an inherited disease of secretory epithelia that affects the respiratory passageways, pancreas, salivary glands, and sweat glands. Asbestos related diseases develop as a result of inhaling asbestos particles. Diseases such as asbestosis, diffuse pleural thickening, and mesothelioma may result. Sudden infant death syndrome (SIDS) is the sudden unexpected death of an apparently healthy infant. Peak incidence is ages two to four months. The exact cause is unknown. Severe acute respiratory syndrome (SARS) is an emerging infectious disease.