Transcript Respiration
BIO 238 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Body cells require Constant supply of oxygen Constant removal of carbon dioxide Both respiratory and cardiovascular systems contribute to fulfilling this requirement Respiration is the overall process of gas exchange between atmosphere and body cells Respiration involves four events Movement of air in and out of the lungs, which is call ventilation 1. External respiration Gas exchange between air and blood in lungs by diffusion O2 from Air CO2 from blood 2. Transport of gases between lungs and body cells (cardiovascular system) 3. Internal respiration Gas exchange between blood and body cells by diffusion O2 from blood CO2 from cells Organs of the Respiratory System Subdivisions Upper respiratory system Portion not located in the thorax Lower respiratory system Portion located in the thorax Alveoli Alveoli ~300 million per lung Surface area ~75m2, holding ~6,000ml of air Site of respiratory gas exchange Filled with watery fluid to aid diffusion Surfactant prevents alveolar collapse during exhalation Reduces attraction between water molecules Breathing Process that exchanges air between atmosphere and alveoli Air moves along a pressure gradient Air moves from high pressure region to low pressure region Three important breathing pressures 1. 2. 3. Atmospheric pressure Pressure of air surrounding earth 760 mmHg at sea level Decreases at higher elevations Intra-alveolar (intrapulmonary) pressure Air pressure within the lungs Intrapleural pressure Pressure within the pleural cavity Normally 756 mmHg Called “negative pressure” Keeps lungs pressed against thorax walls during breathing If it equals atmosphere pressure, lungs would collapse Inspiration Process of breathing air into lungs Air pressure in lungs must be reduced to less then atmospheric air pressure Begins with muscle contraction Diaphragm Contraction pulls the diaphragm downward and flattens it External intercostal muscles Contraction lifts the ribs upward and outward Contractions increase volume of thoracic cavity Air moves into lungs Expiration Diaphragm and external intercostal muscles relax Thoracic cavity and lungs to return to normal size Aided by abundant elastic tissue in lungs and thoracic wall Air is pushed out until intra-alveolar pressure and atmospheric pressure are equalized Forceful expiration Contraction of internal intercostal muscles Contraction of abdominal muscles Pull ribs down and inward Force abdominal viscera and lungs upward Further decreases volume of lungs Increases air pressure in lungs, causing more air to flow out Respiratory Volumes Average adult: 10 to 20 quiet breathing cycles per minute Breathing cycle: one inspiration followed by one expiration Volume of air inhaled during quiet or forceful breathing cycle varies Size, age, sex, physical condition Volumes 80% or less than normal average indicate respiratory disease Spirometers are used to determine respiratory volumes Produces a spirogram, a graphic record of air volumes being exchanged Respiratory Center Control is through neurons of the respiratory center Located in both the medulla and the pons of the brain stem Many other factors can also influence breathing Factors That Influence Breathing • Chemicals – Important chemical factors include • CO2 • H+ ions (formed from ↑ levels of CO2) • O2 – Chemoreceptors detect changes in these chemicals • Respiratory center • Carotid bodies • Aortic Bodies Inflation Reflex Stretch reflex that prevents over inflation of the lungs Higher Brain Centers Voluntarily generated When a person chooses to alter the normal pattern of quiet breathing Limited in their control Involuntary impulses Emotional experiences and chronic pain increase breathing rate Sudden emotional experience, sharp pain, or sudden cold stimulus can cause apnea Body Temperature Increase temperature, increase breathing rate Decrease temperature, decrease breathing rate Disorders of the Respiratory System Disorders are grouped into Inflammatory disorders Noninflammatory disorders Inflammatory Disorders Chronic obstructive pulmonary disease (COPD) Long-term obstruction Chronic bronchitis Emphysema Bronchitis Inflammation of bronchi accompanied by excessive mucus production partially obstructing air flow Acute bronchitis: viral or bacterial infection Chronic bronchitis: chronic asthmatics and smokers Emphysema Due to long term exposure to airborne irritants Effects Large spaces form when alveoli rupture Air blocked in alveoli due to excess mucus production Reduces respiratory surface area and impairs gas exchange Asthma Characterized by wheezing and dyspnea (difficult breathing) Due to contraction of bronchiole smooth muscle Causes Allergic reactions Hypersensitivity to pathogens infecting the bronchial tree Common cold Viral infections Involves rhinitis, laryngitis, sinusitis Causes excessive mucus production, sneezing, and congestion Influenza Caused by flu virus Symptoms include fever, chills, headache, muscle aches True influenza viruses do not infect the digestive system – there is not such thing as a “stomach flu.” Laryngitis Inflammation of mucus membrane of the larynx Thickens the vocal cords, deepening the voice Caused by viruses and bacteria Rhinitis Inflammation of mucus membrane in nasal cavity Main symptom is increased mucus secretion Causes can be viral, bacterial, or allergens Sinusitis Inflammation of the sinuses Symptoms include increased mucus secretion and pressure in sinuses Causes can be viral, bacterial, or allergens Pleurisy Inflammation of pleural membranes Can have two effects Decreases serous fluid production, Causes sharp pains during breathing Increase serous fluid production, Causes increase in pressure on lungs Impairs their expansion Pneumonia Acute inflammation of alveoli caused by virus or bacteria Alveoli become filled with fluid, pathogens, and WBCs Reduces gas exchange space, resulting in low blood oxygen levels Tuberculosis Inflammation caused by bacteria Mycobacterium tuberculosis Transmitted by inhaling the bacteria Destroyed lung tissue is replaced by fibrous connective tissue Reduces lung elasticity Retards gas exchange Effective medical therapies are available Noninflammatory Disorders Lung cancer Due to long term exposure to irritants, such as cigarette smoke Metastasizes rapidly and spreads quickly to other body areas Treatments include surgery and anti-cancer therapy Pulmonary edema Accumulation of fluid in the lungs Due to excessive fluid passing from blood into alveoli Symptoms include labored breathing and suffocation feeling Treatments include oxygen therapy, diuretics, and mechanical ventilation Pulmonary embolism Blood clot or gas bubble that blocks a pulmonary artery and Prevents blood from reaching that lung portion No gas exchange possible in affected area Massive embolism can cause a cardiac arrest Respiratory distress syndrome (RDS) Disease of newborn infants, usually those prematurely born Due to insufficient surfactant production in alveoli Causes alveolar collapse Without surfactant, alveoli collapse after every expiration Requires a lot of energy to perform each inhalation