Respiratory System PDF

The Respiratory System What is respiration? Cellular vs internal vs external respiration: 1. Cellular respiration refers to the set of biochemical reactions that occur within cells to convert energy from food into ATP, normally consuming O2 and releasing CO2 , and occurs all over t...

The Respiratory System What is respiration? Cellular vs internal vs external respiration: 1. Cellular respiration refers to the set of biochemical reactions that occur within cells to convert energy from food into ATP, normally consuming O2 and releasing CO2 , and occurs all over the body 2. Internal respiration refers to the exchange of O2 and CO2 between the capillary cellular interface, and occurs all over the body 3. External respiration refers to the exchange of O2 and CO2 between the environment , lungs, and alveolar capillary interface, and is enabled by the structure and function of the ‘ respiratory system General respiratory system function The respiratory system 1. Exchange respiratory gases ▪ O2 and CO2 exchange 2. Phonation (voice production) ▪ Vocal cords, glottis and larynx 3. Thermoregulation ▪ Nasal turbinates and panting 4. Acid-base balance ▪ CO2 , carbonic acid, bicarbonate, pH levels 5. Olfactory (sense of smell) ▪ Receptors high in the nasal passages Respiratory tracts The respiratory system can be separated according to the structures of the ‘upper respiratory tract’ and those of the ‘lower respiratory tract’ Upper Respiratory Tract Lower Respiratory Tract 1. Nose 1. Bronchi 2. Nasal passages 2. Bronchioles 3. Pharynx (throat) 3. Alveolar ducts 4. Larynx (voice box) 4. Alveoli 5. Trachea (windpipe) Upper Respiratory Tract Nose 1. The first structure of the respiratory system 2. The nares nostrils ) are the external openings and lead into the nasal passages Nasal passages 1. Located between the nares (nostrils) and the pharynx (throat) 2. The ‘ nasal septum ’ separates the left and right nasal passages 3. The ‘ hard and soft palates ’ separate the nasal passages (dorsal to the palate) from the mouth (ventral to the palate)  4. Lining the nasal passages are columnar epithelial cells with cilia that project up into a layer of mucus secreted by mucous glands) 5. Mucus functions to trap foreign particles 6. The cilia sweep the mucus down towards the pharynx where it can be swallowed 7. Beneath the epithelium lies an extensive complex of blood vessels 8. Nasal passage morphology is convoluted i.e. twists and turns) because of ‘ turbinates ’ (nasal conchae) that greatly increase the total surface area of the structure 9. Nasal passages ‘condition’ the inhaled air by: (1) warming it , (2) humidifying it , and (3) filtering it 10.Infection can lead to inflammatory secretions that ‘obstruct’ the cilia and inhibit their sweeping function (coughing and sneezing) 11. Nasal passages also house the olfactory receptors (sense of smell) Paranasal sinuses 1. Normally referred to just as the ‘ sinuses ’ 2. Outpouchings of the nasal passages, with the same kind of epithelial ciliated and mucous lining as the nasal passages 3. The function is unclear may simply help ‘ condition’ the inspired air Pharynx (throat) 1. Nasal passages lead into the pharynx 2. At the rostral end, the soft palate separates the pharynx into the (1) ‘nasopharynx’ (respiratory passageway) and the (2) ‘oropharynx’ (digestive passageway) 3. This then leads down to the main part of the pharynx, a passageway shared by both the respiratory system and the digestive system 4. At the caudal end, the pharynx opens dorsally into the esophagus and ventrally into the larynx and trachea 5. Pharynx and larynx cooperate in coordinating swallowing Larynx (voice box) 1. Connects the pharynx with the trachea 2. Segments of cartilage connect to one another and to the surrounding tissues 3. Segments of cartilage include the single epiglottis and the paired arytenoid cartilages (also present is the single thyroid cartilage and the single cricoid cartilage) 4. Epiglottis is leaf shaped and the most rostral of laryngeal cartilages. When breathing, epiglottis is normally tucked up behind the soft palate. When swallowing, muscle contractions pull larynx forward and fold epiglottis back over its opening to cover larynx and direct material into esophagus  5. Arytenoid cartilages attach to the vocal cords, parallel fibrous connective tissue bands that stretch across the lumen of the larynx. Muscles adjust the tension of the vocal cords by moving the cartilages. As air moves over the vocal cords, they vibrate and produce sound (slack = lower pitch, taut = higher pitch) 6. Glottis is the opening between the vocal cords. Fine adjustments control airflow. Complete closure occurs to generate the initial pressure for a cough, and for non respiratory functions that involve straining (micturition, defecation, parturition) so that abdominal compression can occur a nd prevent air flow out of the lungs Trachea (windpipe) 1. Wide tube extending from the larynx, down the neck, into the thorax, where it divides (‘ bifurcation of the trachea ’) into the two main bronchi that enter the lungs 2. The trachea is composed of fibrous tissue, and is held open by c-shaped cartilage rings along its length, with smooth muscle bridging the gap in the cartilage rings 3. The trachea is lined with the same kind of epithelial ciliated and mucous lining as the nasal passages, with cilia that sweep the mucus up towards to pharynx where it can be swallowed  4. Mucus accumulation stimulates coughing to clear the airway Lower respiratory tract Bronchial tree ( bronchi bronchioles alveolar ducts) 1. Bronchial tree includes the air passageways that extend from the main bronchi, along the numerous and successive subdivisions, to the alveolar sacs 2. The main bronchi (singular is bronchus ) enter the lungs, where they subdivide into smaller and smaller bronchi, and finally into bronchioles… 3. The bronchioles themselves subdivide into smaller and smaller bronchioles, and finally into the microscopic alveolar ducts… 4. The alveolar ducts end in groups of alveoli called alveolar sacs 5. Smooth muscle fibers in the wall of the bronchial tree allow for adjustment of lumen diameter (under autonomic control) 6. At rest, smooth muscle partially contracts reducing the size of the air passageways, eliciting partial bronchoconstriction (irritants in inhaled air can bring about severe bronchoconstriction and asthma) 7. During exercise, smooth muscle relaxes increasing the size of the air passageways, bronchodilation Alveoli 1. Gas exchange of O2 and CO2 occurs at the terminal alveoli singular is alveolus) 2. Alveoli are microscopic, thin walled sacs, surrounded by a network of capillaries 3. The alveolar wall is composed of simple squamous epithelium, and the capillary wall is also composed of simple squamous epithelium thus, the barrier for O2 and CO2 diffusion is minimal! 4. Each alveolus is lined with a thin fluid containing surfactant , which reduces surface tension and prevents collapse The lungs 1. Base, apex, convex lateral surface 2. Base of lungs lies directly against the diaphragm (thin sheet of muscle that separates the thoracic and abdominal cavities) 3. Convex lateral surface lies against the inner surface of thoracic wall 4. In most domestic species, left lung has three lobes ( cranial, middle, caudal lobes ) and right lung has four lobes cranial, middle, caudal lobes and a small accessory lobe  5. Each lung has a small well defined area on its medial side called the ‘hilum’ / ’hilus’ where the main bronchi, major blood vessels, lymph vessels and nerves enter and exit the lung 6. Blood supply to and from the lungs is called the ‘ pulmonary circulation 7. Blood enters via pulmonary arteries ( O2 & CO2 ) and exits via pulmonary veins ( O2 & CO2) 8. Within the lungs, the blood vessels basically follow and subdivide along with the bronchial tree 9. Blood from the ‘ pulmonary arterioles ’ enters the capillary network, which wraps around the alveoli, allowing exchange of O2 & CO2 , before exiting along the ‘ pulmonary venules ’ … back to the heart 10.The fetal lung is non functional and is entirely filled with fluid 11. At birth, the fluid clears, and the lungs fill with air Thoracic cavity 1. Contains the heart, lungs, large blood vessels, nerves, trachea, esophagus, lymphatic vessels, lymph nodes 2. The pleura is the thin membrane that covers the organs and structures within the thorax (visceral layer) and lines the inside of the thoracic cavity (parietal layer) 3. Between visceral layer and parietal layer is a lubricating pleural fluid , ensuring the lungs slide smoothly against the thorax during breathing  4. Slight negative pressure exists within the thorax to keep the lungs partially inflated and pulled up against the thoracic wall 5. The diaphragm is a thin sheet of muscle that separates the thoracic and abdominal cavities and acts as an important respiratory muscle Breathing 1. Breathing (pulmonary ventilation) requires the effective movement of air into and out of the lungs at a volume and rate sufficient for the body’s immediate requirement for O 2 and CO 2 exchange 2. Breathing in is termed ‘inspiration’, breathing out is termed ‘expiration’ Inspiration: 1. Process of drawing air into the lungs (i.e. inhalation) 2. Inspiratory muscles activate and enlarge the thoracic cavity volume 3. Lungs passively follow the enlargement and air is drawn in through the respiratory passageways 4. Main inspiratory muscles are the ‘diaphragm’ and the external intercostal muscles 5. The diaphragm , at the base of the lungs, changes from an ‘upward dome shape’ to a ‘flat shape’ when activated , pushing down on the abdominal organs, increasing thoracic volume, and inflating the lungs 6. The external intercostal muscles , located at the external portion of the spaces between the ribs, have oblique oriented  fibers that rotate the ribs upward and forward when activated , increasing thoracic volume, and inflating the lungs Expiration: 1. Process of pushing air out of the lungs ( i.e. exhalation) 2. Normally, a mostly passive process achieved through relaxation of the inspiratory muscles 3. Under exertion, the main expiratory muscles are the internal intercostal muscles ’ and the abdominal muscles 4. The internal intercostal muscles , located at the internal portion of the spaces between the ribs, rotate the ribs backward when activated, decreasing thoracic volume, compressing the lungs 5. The abdominal muscles , push abdominal organs against the diaphragm when activated, decreasing thoracic volume, compressing the lungs Functional measures of respiration 1. Tidal volume (mL or L): ▪ Volume of air displaced during inspiration and expiration (one breath) 2. Respiratory rate (min-1) ▪ Number of breaths per minute 3. Minute ventilation (mL min-1 or L min-1) ▪ Volume of air inspired and expired every minute, varies depending on the body’s requirements for O2 and CO2 exchange e.g. 450 mL × 10 min-1 = 4500 mL min-1 or 4.5 L min-1 Gas exchange at alveolar capillary interface 1. Atmospheric air contains ~21% O2 (PO2 is ~160 mmHg at sea level) and 0.04% CO2 (PCO2 is ~0.25 mmHg at sea level) 2. O2 and CO2 gas molecules diffuse passively down their respective partial pressure gradients 3. O2 diffuses from the alveolar air (high PO2 , ~100 mmHg) into the ‘entering’ capillary blood (low PO2 , ~40 mmHg) 4. CO2 diffuses from the ‘entering’ capillary blood (high PCO2, ~46 mmHg ) into the alveolar air (low PCO2 , ~40 mmHg 5. These O2 and CO2 partial pressure gradients stay fairly constant at the alveolar capillary interface because of the continuous renewal of air and the continuous supply of blood Control of breathing 1. Breathing (pulmonary ventilation) is under the default autonomic control of the so called ‘ respiratory center ’ (but can be consciously overridden) contained within the medulla oblongata and the pons of the brainstem 2. The respiratory center is comprised of individual control centers for inspiration and expiration that alternate in their activity 3. The primary immediate stimulus for breathing is CO2 (not O2) 4. The body has two main feedback systems that signal back to the respiratory center to control patterns of breathing: (1) mechanical control and (2) chemical control Mechanical control: 1. Stretch receptors in the lungs determine routine (resting) breathing patterns by setting limits on routine inspiration and expiration 2. When lungs inflate to a preset level, nerve impulse is sent to the respiratory center signaling the lungs are full, then the respiratory center sends out nerve impulses to stop inspiratory muscle contractions and to commence expiratory muscle contractions 3. When lungs deflate to another preset level, another nerve impulse is sent to the respiratory center signaling the lungs are sufficiently empty, then the respiratory center sends out  nerve impulses to stop expiration and to commence inspiration Chemical control: 1. Chemical receptors in the brainstem and in specific blood vessels (viz. aortic and carotid bodies) affect breathing patterns when the homeostatic balance is disturbed by responding to perturbations in blood (1) CO2 , (2) pH, and (3) O2 2. If blood CO2 , pH , or O2 varies from preset limits, the chemical control signals the respiratory center to modify breathing patterns until normal levels are once again achieved 3. Clinically, if a patient is mechanically ‘over’ ventilated, too much CO2 can be removed from the body, inducing a temporary apnea, until the pH balance is restored, and normal breathing resumes