The Respiratory System

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

Respiratory System Anatomy • Nose • Pharynx = throat • Larynx = voicebox • Trachea = windpipe • Bronchi = airways • Lungs • Locations of infections • upper respiratory tract is above vocal cords • lower respiratory tract is below vocal cords

Pharynx • Muscular tube (5 inch long) hanging from skull • skeletal muscle & mucous membrane • 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

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

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

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 Tortora & Grabowski 9/e 2000 JWS

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

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

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

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

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 • How is this accomplished? • 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

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

Mechanics of Inspiration • Contraction of Respiratory Muscles • Passive Muscles – diaphragm goes • Active Muscles – external intercostals, pec minor, sternocleidomastoid, sclaneus Tortora & Grabowski 9/e 2000 JWS

Mechanics of Inspiration 2. Thoracic Cavity Expands: ribs move out & up 3. Lung Pleural Cavity Volume 4. Pleural Cavity Pressure 5. Alveolar Cavity Pressure 6. Air Rushes in for Equilibrium (Boyle’s Law) Tortora & Grabowski 9/e 2000 JWS

Mechanics of Expiration • Contraction of Respiratory Muscles • Passive Muscles – diaphragm goes • Active Muscles – internal intercostals, rectus abdominus, transverse abdominus Tortora & Grabowski 9/e 2000 JWS

Mechanics of Expiration 2. Thoracic Cavity Expands: ribs move down & in 3. Lung Pleural Cavity Volume 4. Pleural Cavity Pressure 5 Alveolar Cavity Pressure 6. Air Rushes in for Equilibrium (Boyle’s Law) Tortora & Grabowski 9/e 2000 JWS

Tortora & Grabowski 9/e 2000 JWS

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

Breathing Patterns • Eupnea = normal quiet breathing • Apnea = temporary cessation of breathing • Dyspnea =difficult or labored breathing • Tachypnea = rapid breathing • Diaphragmatic breathing = descent of diaphragm causes stomach to bulge during inspiration • Costal breathing = just rib activity involved

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 • 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

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

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 • Clinical application of Henry’s law • 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 Tortora & Grabowski 9/e 2000 JWS

Respiration • 4 distinct processes collectively called respiration must occur: Pulmonary Ventilation, External Respiration, Transport of Respiratory Gases, and Internal Respiration Tortora & Grabowski 9/e 2000 JWS

1. Pulmonary Ventilation • Movement of air into and out of the lungs so that the gases in the air sacs (alveoli) of the lungs are continuously changed and refreshed • The air movement is called ventilation Tortora & Grabowski 9/e 2000 JWS

2. External Respiration • Gas exchange (oxygen loading and carbon dioxide unloading) between the blood and the air-filled chambers of the lungs Tortora & Grabowski 9/e 2000 JWS

External Respiration • Gases diffuse from areas of high partial pressure to areas of low partial pressure • Exchange of gas between air & blood • Deoxygenated blood becomes saturated • 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 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

3. Transport of Respiratory Gases • Transport of oxygen and carbon dioxide between the lungs and tissue cells of the body • Accomplished by the cardiovascular system, which uses blood as the transporting fluid Tortora & Grabowski 9/e 2000 JWS

4. Internal Respiration • Gas exchanges (oxygen unloading and carbon dioxide loading) between the systemic blood and tissue cells Tortora & Grabowski 9/e 2000 JWS

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 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

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

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 • 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

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

Regulation of Respiratory Center • Cortical Influences • voluntarily alter breathing patterns • limitations are buildup of CO2 & H+ in blood • inspiratory center is stimulated by increase in either • if you hold breathe until you faint----breathing will resume

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

Types of Hypoxia • Deficiency of O2 at tissue level • Types of hypoxia • hypoxic hypoxia--low pO2 in arterial blood • high altitude, fluid in lungs & obstructions • anemic hypoxia--too little functioning Hb • hemorrhage or anemia • ischemic hypoxia--blood flow is too low • histotoxic hypoxia--cyanide poisoning • blocks metabolic stages & O2 usage

Respiratory Influences & Reflex Behaviors • Quick breathing rate response to exercise • input from proprioceptors • Inflation Reflex (Hering-Breurer reflex) • big deep breath stretching receptors produces urge to exhale • Factors increasing breathing rate • emotional anxiety, temperature increase or drop in blood pressure • Apnea or cessation of breathing • by sudden plunge into cold water, sudden pain, irritation of airway Tortora & Grabowski 9/e 2000 JWS

Exercise and the Respiratory System • During exercise, muscles consume large amounts of O2 & produce large amounts CO2 • Pulmonary ventilation must increase • moderate exercise increases depth of breathing, • strenuous exercise also increases rate of breathing • Abrupt changes at start of exercise are neural • anticipation & sensory signals from proprioceptors • impulses from motor cortex • Chemical & physical changes are important • decrease in pO2, increase in pCO2 & increased temperature Tortora & Grabowski 9/e 2000 JWS

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 Tortora & Grabowski 9/e 2000 JWS

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

The Respiratory System