Respiratory System
v Major Functions
v Gas exchange (external and internal exchange)
v Cleanse/Moisten/Warm Air
v Inspiration and expiration move air in and out of the lungs during breathing.
v Cellular respiration is the final destination where ATP is produced in cells.
Introduction
The respiratory tract
The Nose v The two nasal cavities are divided by a septum.
v They contain olfactory cells, receive tear ducts from eyes, and communicate with sinuses.
v The nasal cavities empty into the nasopharynx.
v Auditory tubes lead from the middle ears to the nasopharynx.
The path of air
The Pharynx v The pharynx (throat) is a passageway from the nasal
cavities to oral cavities and to the larynx.
v The pharynx contains the tonsils; the respiratory tract assists the immune system in maintaining homeostasis.
v The pharynx takes air from the nose to the larynx and takes food from the oral cavity to the esophagus.
The Larynx v The larynx is a cartilaginous structure lying between the
pharynx and the trachea.
v The larynx houses the vocal cords.
v A flap of tissue called the epiglottis covers the glottis, an opening to the larynx.
v In young men, rapid growth of the larynx and vocal cords changes the voice.
Placement of the vocal cords
15-8
The Trachea
v The trachea, supported by C-shaped cartilaginous rings, is lined by ciliated cells, which sweep impurities up toward the pharynx.
v Smoking destroys the cilia.
v The trachea takes air to the bronchial tree.
v Blockage of the trachea requires an operation called a tracheostomy to form an opening.
Cilia in the trachea
15-10
The Bronchial Tree v The trachea divides into right and left primary bronchi
which lead into the right and left lungs.
v The right and left primary bronchi divide into ever smaller bronchioles to conduct air to the alveoli.
v An asthma attack occurs when smooth muscles in the bronchioles constrict and cause wheezing.
The Lungs v Lungs are paired, cone-shaped organs that lie on either
side of the heart and within the thoracic cavity.
v The right lung has three lobes, and the left lung has two lobes, allowing for the space occupied by the heart.
v The lungs are bounded by the ribs and diaphragm.
The Alveoli v Alveoli are the tiny air sacs of the lungs made up of
squamous epithelium and surrounded by blood capillaries.
v Alveoli function in gas exchange, oxygen diffusing into the bloodstream and carbon dioxide diffusing out.
v Infant respiratory distress syndrome occurs in premature infants where underdeveloped lungs lack surfactant (thin film of lipoprotein) and collapse.
Gas exchange in the lungs
v During breathing, air moves into the lungs during inspiration (inhalation) from the nose or mouth, then moves out again during expiration (exhalation).
v A spirometer allows measurement of the components of air during breathing.
Mechanism of Breathing
Respiratory Volumes v Tidal volume (VT) the normal amount of air
moved in and out of the lungs when relaxed, is usually 500 ml.
v Inspiratory reserve volume is the maximum amount of forcibly inspired air.
v Expiratory reserve volume is the maximum amount of forcibly expired air.
v Vital capacity is the maximum amount of air moved in and out on deep breathing, and is the sum of tidal, inspiratory reserve, and expiratory reserve volumes.
v Air that remains in the lungs is residual volume.
Vital capacity
Inspiration and Expiration v There is a continuous column of air from the pharynx to
the alveoli, and the lungs lie within the sealed-off thoracic cavity.
v The thoracic cavity is bounded by the rib cage and diaphragm.
v Pleural membranes line the thoracic cavity and lungs and the intrapleural pressure is lower than atmospheric pressure, keeping the lobules of the lungs from collapsing.
v Minute Ventilation – The volume of inhaled and exhaled air in one minute.
Inspiration
v When we inhale (inspiration) impulses from the respiratory center in the medulla oblongata cause the rib cage to rise and the diaphragm to lower, causing the thoracic cavity to expand.
v The negative pressure or partial vacuum in the alveoli causes the air to come in.
v Changing amounts of blood of H+ and CO2 detected by chemoreceptors in the carotid arteries and aorta increase breathing rate.
O2 UPTAKE DURING EXERCISE
v VO2 - measured in ml/Kg/min
v VO2max - maximal oxygen uptake
v Metabolic Cart
v Predicted VO2max testing
v Astrand 6 min. test
v Balke Test
Nervous control of breathing
Inspiration
Expiration v When we exhale (expiration), lack of impulses from the
respiratory center allow the rib cage to lower and the diaphragm to resume a dome shape.
v Expiration is passive, while inspiration is active.
v The elastic recoil of the lungs causes expiration (gravity).
v A deep breath causes alveoli to stretch; stretch receptors then inhibit the respiratory center via the vagus nerve.
Expiration
Expiration: active
v Under extreme conditions, exhalation becomes dynamic.
v Internal intercostal muscles contract forcing the ribs down and inward.
v Tightening of the abdominal walls also pushes on the viscera which pushes the diaphragm and forces out even more air.
v FEV1 – the amount of air forcibly expired in one second. Reduced in patients with COPD
Spirometry
v External Respiration
v Individual gases exert pressure proportional to their portion of the total in a mixture of gases; this is called “partial pressure” (PO2). (Air - 21% O2, 0.04% CO2)
v External respiration is the diffusion of CO2 from pulmonary capillaries into alveolar sacs and O2 from alveolar sacs into pulmonary capillaries.
v Most CO2 is carried as bicarbonate ions.
v The enzyme carbonic anhydrase, in red blood cells, speeds up the conversion of bicarbonate and H+ to H2O and CO2; CO2 enters alveoli and is exhaled.
Gas Exchange
Partial Pressures
Hemoglobin Structure
v Hemoglobin (Hb) takes up oxygen from alveoli and becomes oxyhemoglobin (HbO2).
v 4 globular proteins (globin) & 4 heme units.
v (64 000 daltons)
Internal Respiration v Internal respiration is the diffusion of O2 from systemic
capillaries into tissues and CO2 from tissue fluid into systemic capillaries.
v Oxyhemoglobin gives up O2, which diffuses out of the blood and into the tissues because the partial pressure of O2 of tissues fluid is lower than that of the blood.
v After CO2 diffuses from tissue cells into the blood, it enters red blood cells where a small amount is taken up by hemoglobin, forming carbaminohemoglobin.
Internal Respiration Cont. v Most of the CO2 combines with water to form
carbonic acid (H2CO3), which dissociates to release hydrogen ions (H+) and bicarbonate ions (HCO3
-); the enzyme carbonic anhydrase speeds this reaction.
v The globin portion of hemoglobin combines with excess hydrogen ions to become reduced hemoglobin or HHb; this helps maintain a normal blood pH.
v Blood leaving capillaries is a dark maroon color because red blood cells contain reduced hemoglobin.
External and Internal Respiration
External and Internal Respiration
External
v Hb + O2 à HbO2
v HbCO2 à Hb + CO2
v H+ + HCO3- à H2CO3
à CO2 + H2O
Internal
v HbO2 à Hb + O2
v CO2 + H2O à H2CO3 à H+ + HCO3
-
v Hb + CO2 à HbCO2
v H+ + Hb à HHb
v HCO3- dissolves in
plasma
Chemical Equation Summary
Respiratory Centre • located in the medulla oblongata
• stimulated by the presence of CO2 and H+ ions.
• neurons send automatic rhythmic discharge that triggers breathing
• the signals travel to the diaphragm and the intercostal muscles via the phrenic nerve.
v Low O2 in blood registered by carotid and aortic bodies
v Communication with respiratory centre
v Increase in minute ventilation occurs
v Hemoglobin has 200X affinity for CO than O2
Respiratory Centre Cont.
Hemoglobin Saturation (SO2)
v Lungs: 98-100% saturated
v Tissues: 60-70% saturated
v Conditions affecting Saturation:
v Partial Pressure of O2 – incr. é SO2
v pH – incr. pH é SO2
v Temperature – incr. temp ê SO2
v Exercise – increases temperature and decreases pH causing a decrease in arterial oxygen saturation (SaO2)
Oxyhaemoglobin Dissociation Curve
v Common Respiratory System Diseases:
v Asthma
v COPD
v Chronic Bronchitis
v Emphysema
v Pleurisy
v Cancer
v Influenza
v Sinusitis
Respiration and Health
Sites of upper respiratory infections
Sinusitis v Sinusitis is infection of the cranial sinuses within the
facial skeleton that drain into nasal cavities.
v It occurs when nasal congestion blocks the sinus openings and is relieved when drainage is restored.
v Pain and tenderness over the lower forehead and cheeks, and toothache, accompany this condition.
Lower respiratory tract disorders
COPD Chronic Bronchitis
v Long-term cough with mucus
Emphysema
v A breakdown of the alveoli walls.
Causes, Risk Factors, Symptoms v Smoking
v Exposure to gases and fumes, cooking fire
v Cough, Fatigue, many R.T.I, Wheezing
Asthma v Muscle lining small airways becomes irritated
v Causes a narrowing of airway passages
v Steroids or bronchodilators can be used to prevent constriction
Lung Cancer v Lung cancer follows this sequence of events: thickening of
airway cells, loss of cilia on the lining, cells with atypical nuclei, tumor development, and finally metastasis.
v Removal of a lobe or lung, called pneumonectomy, may remove the cancer.
v Smoking, whether active or passive, is a major cause of lung cancer.
Normal lung versus cancerous lung
15-47
Chapter Summary v Air passes through a series of tubes before gas exchange
takes place across an extensive moist surface in the alveoli of the lungs.
v Respiration comprises breathing, external and internal respiration, and cellular respiration.
v During inspiration, the pressure in the lungs decreases and air comes rushing in; during expiration, increased pressure in the thoracic cavity causes air to leave the lungs.
Chapter Summary Cont. v External respiration occurs in the lungs where oxygen
diffuses into the blood and carbon dioxide diffuses out of the blood.
v Internal respiration occurs in the tissues where oxygen diffuses out of the blood into tissue cells and carbon dioxide diffuses into the blood.
v Spirometry is the measurement of lung capacities and can be used to diagnose certain respiratory conditions such as COPD.
Chapter Summary Cont. v The respiratory pigment hemoglobin transports
oxygen from the lungs to the tissues and aids in the transport of carbon dioxide from the tissues to the lungs.
v Hemoglobin’s oxygen affinity is affected by pH, temp and PO2
v The respiratory tract is especially subject to disease because it is exposed to infectious agents; also, cigarette smoking contributes to two major lung disorders—emphysema and cancer.