Respiratory System Lecture Notes PDF

Respiratory system (呼吸系统) NUR1019 – Lecture 1 Dr. Wilson Leung 1 Learning Outcomes 1. The Respiratory System 2. Mechanism of Breathing 3. Gas Exchange and Transport 2 The Respiratory System 3 Intr...

Respiratory system (呼吸系统) NUR1019 – Lecture 1 Dr. Wilson Leung 1 Learning Outcomes 1. The Respiratory System 2. Mechanism of Breathing 3. Gas Exchange and Transport 2 The Respiratory System 3 Introduction Major function: gas exchange (氣體交換) that allows oxygen from the air to enter the blood and carbon dioxide from the blood to exit into the air 1. Inspiration / inhalation (i.e., breathing in): air is conducted toward from the lungs by a series of cavities, tubes, and openings. 2. Expiration / exhalation (i.e., breathing out): air is conducted away from the lungs by a series of cavities, tubes, and openings. 4 Introduction Works with the cardiovascular system to accomplish: Pulmonary ventilation (breathing) – the entrance and exit of air into and out of lungs External respiration – the exchange of gases between air and blood Internal respiration – the exchange of gases between blood and tissue fluid Transport of gases – to and from the lungs and the tissues Reason for the respiratory events – provide oxygen for and remove carbon dioxide waste from cellular respiration in order to produce ATP 5 The Respiratory Tract (上呼吸道) (鼻腔) (咽) (聲門) (喉) (下呼吸道) (氣管) (支氣管) (細支氣管) (肺) (橫隔膜) 6 The Respiratory Tract The path of air from the nose to the lungs Air is cleansed, warmed and moistened (潤濕) by our respiratory tract. - Cleansed by nasal hairs, cilia, and mucus - Lysozyme in the mucus helps to kill bacteria - Mucociliary escalator: - In the trachea and other airways, the cilia beat upward, carrying mucus, dust, and other trapped contaminants into the pharynx. - Warmed by warm blood flowing through blood Mucociliary vessels close to the airway surface escalator - Moistened by the mucous membrane 7 The Nose The only external portion of the respiratory system Air enters through the nostrils (鼻孔) 2 nasal cavities - Separated by a septum (隔膜) (bone and cartilage) - Lined by a mucous membrane - Nasal conchae increase the surface area for moistening and warming inhaled air - Odor receptors (氣味受體) located in the olfactory epithelium 8 The Nose Paranasal sinuses Olfactory epithelium 9 The Nose Tears empty into the nasal cavities by way of the nasolacrimal canals (鼻淚管) - Crying produces a runny nose (流鼻涕) Paranasal sinuses (鼻竇) - Air-filled spaces - Reduce the weight of the skull - Act as resonating chambers for the voice The nasal cavities are separated from the oral cavity by the palate (齶) - A partition that has two portions, hard palate and soft palate 10  The Nose (Maxilla and palatine bones) 11 The Pharynx (Throat) Funnel (漏斗)-shaped passageway that connects the nasal and oral cavities to the larynx Three parts: 1. Nasopharynx (鼻咽) 2. Oropharynx (口咽) 3. Laryngopharynx (喉咽) Tonsils (扁桃體) contain lymphocytes (B cells and T cells) (淋巴細胞) that protect against invasion of inhaled pathogens Passageway for both food and air 12 The Larynx (Voicebox) Cartilaginous passageway for air between the pharynx (咽) and trachea (氣管) A triangular box whose apex (頂尖), the Adam’s apple, is located at the anterior neck Houses the vocal cords (聲帶) – supported by elastic ligaments - When air is expelled (驅逐) past the vocal cords through the glottis, the vocal cords vibrate, producing sound. 13 The Larynx (Voicebox) Voice pitch (音高) regulated by the tension (緊張) on the vocal cords and opening of glottis (聲門) - The greater the tension, as the glottis becomes more narrow, the higher the pitch - Loudness depends on the amplitude (振幅) of the vibrations - How much the vocal cords vibrate At puberty, the growth of the larynx and vocal cords is much faster and accentuated (強調) in males than in females - A more prominent Adam’s apple (喉結) - Deeper voices (longer vocal cords) The epiglottis (會厭) prevents food from entering the larynx - A flat elastic cartilage 14 The Trachea (Windpipe氣管) Connects the larynx to the primary bronchi (支氣管) Anterior (前) to esophagus Held open by about twenty C-shaped cartilaginous rings - Creates a patent airway - Allows for expansion of the esophagus Mucociliary escalator - Epithelial cilia sweep mucus produced by goblet cells - Smoking is known to destroy these cilia. 15 Mucociliary escalator in the Trachea 16 The Bronchial Tree The trachea divides into the right and left primary bronchi (支 氣管) that lead into the right and left lungs The primary bronchi branch into secondary bronchi - Three for the right lung (3 lobes) - Two for the left lung (2 lobes) – allow room for the heart The secondary bronchi divide into tertiary bronchi - Supported by smaller plates of cartilage Bronchioles (細支氣管) are the smallest conducting airways - No cartilage support - Possess a ciliated epithelium and a well-developed smooth muscle layer Each bronchiole leads to air sacs called alveoli (肺泡) (singular: alveolus) Where oxygen is exchanged for carbon dioxide 17 The Lungs Paired, cone (錐體)-shaped organs - Right lung: 3 lobes - Left lung: 2 lobes – allow room for the heart Each lobe is divided into lobules - Each lobule has a bronchiole and pulmonary arteries / arterioles / capillaries that serve many alveoli 18 The Lungs Enclosed by a double layer of serous membrane (漿膜) called the pleurae (胸膜) (singular: pleura) The visceral pleura adheres to the surface of the lung The parietal pleura lines the inside of the thoracic cavity Produces a lubricating serous fluid that also creates surface tension (表面張力) between the layers → allows the 2 pleural layers to cling together, thus holding the lungs open against the chest wall 19 The Alveoli With each inhalation, air passes through the bronchial tree to the alveoli. Alveolar sac (肺泡囊) surrounded by extensive pulmonary capillaries (肺微血管) Gas exchange (氣體交換) occurs between the air in the alveoli and the blood in the capillaries Oxygen into and carbon dioxide out the bloodstream Each alveolus is lined with an extremely thin layer of water-based tissue fluid. Gas exchange takes place across moist (濕) cellular membranes. The attractive force created by the fluid’s surface tension (表面張力) helps the distended (膨脹的) lung tissue to return to its resting position when a person exhales. Normal alveoli are lined with surfactant (i.e., a film of lipoprotein that lowers surface tension to an acceptable level): prevent the alveoli from completely collapsing Dust cells: white blood cells to defend us against any debris or pathogens we might inhale 20 Gas exchange in the lungs - The pulmonary artery and arteriole carry oxygen-poor blood (blue), while the pulmonary vein and venule carry oxygen-rich blood (red). 21 Respiratory membrane Facilitates rapid gas exchange Alveolar epithelium and the capillary endothelium layered together Extremely thin Large surface area (50-70m2) Same as the area of the alveoli The red blood cells within the capillaries are pressed up against the narrow capillary wall, and little plasma is present. Facilitate the rate of gas exchange 22 Mechanism of Breathing 23 Ventilation The lungs lie within the sealed-off thoracic cavity (封閉胸腔). As the respiratory muscles actively expand the volume of the entire thorax, the balloon-like lungs passively expand. - The surface tension between the visceral and parietal pleura creates intrapleural pressure (i.e., the pressure between pleura) - Less than atmospheric pressure - Help to keep the lungs inflated (膨脹) A continuous column of air extends from the pharynx to the alveoli of the lungs. 24 Ventilation - Inspiration/Inhalation (吸氣) Active phase of ventilation (i.e., muscular effort involved) Diaphragm (橫膈膜) contracts and flattens. External intercostal muscles (外肋間肌) contract. The rib cage (肋骨籃) moves upward (向上) and outward (向外). Thoracic cavity volume (胸腔容積) increases, causing the lungs to increase in volume – because the lung adheres to the wall of the thoracic cavity. Air pressure within the alveoli (i.e., intrapulmonary pressure) decreases. Air flows from an area of higher pressure (atmospheric pressure) to an area of lower pressure (within the lungs) until pressures are equal. 25 Ventilation - Expiration/Exhalation (呼氣) Usually the passive phase of ventilation (i.e., no muscular effort required) The diaphragm relaxes and resumes its dome shape. The external intercostal muscles relax and the rib cage moves down and in. The volume of the thoracic cavity decreases and the lungs recoil (縮). - Due to the elastic tissue built into the lung’s walls and the slight alveolar surface tension Lung volume decreases and the intrapulmonary pressure increases. Since intrapulmonary pressure is now greater than atmospheric pressure, air will flow out of the lungs until pressure are equal. 26 27 Maximum Inspiratory Effort (最大吸氣力度) Maximum expansion of the lungs Help increase the size of the thoracic cavity larger than normal Allows more air to be inspired Involves the accessory muscles of respiration - Muscle of the back (Erector spinae 豎脊肌) - Chest muscle (Pectoralis minor 胸小肌) - Anterior neck muscle (Scalene 斜角肌 and sternocleidomastoid muscles) 28 Forced Expiration (用力呼氣) During heavy exercise, singing, blow air into a trumpet (喇叭), or blow out birthday candles (生日蠟燭) Increased pressure in the thoracic cavity by: Contraction of internal intercostal muscles (內肋間肌) to force the rib cage (肋骨籃) to move downward and inward Contraction of the abdominal wall muscles (腹肌) to push on the abdominal organs and compress upward against the diaphragm 29 Measurement of Ventilation Spirometer (肺量計) – instrument that records the volume of air exchanged during breathing Spirogram (肺活量圖) – shows the measurements recorded by a spirometer 30 Respiratory Volumes and Capacities 31 Respiratory Volumes and Capacities 1. Tidal volume - Normal, relaxed breathing - About 500 mL 2. Vital capacity - Maximum volume of air that can be inhaled plus the maximum volume of air that can be exhaled - i.e., the sum of the tidal, inspiratory reserve, and expiratory reserve volumes - Depends on: a. Inspiratory reserve volume - Forced inspiration - Increases the volume of air beyond the tidal volume by about 3,000 mL b. Expiratory reserve volume - Forced expiration - About 1,200 mL 3. Residual volume - Amount of air remaining in the lungs (alveoli) after a forced expiration - About 1,000 mL 4. Dead air space - Only 70% of the tidal volume does reach the alveoli, but 30% remains the airways. 32 Control of Ventilation 12-20 ventilations per minute (adults) Controlled by 2 respiratory centers in the medulla oblongata (延腦) and pons of the brainstem - The phrenic nerve carries impulses to the diaphragm. - The intercostal nerves stimulate the external intercostal muscles to contract. - Functioning together, these 2 centers allow normal, quiet breathing (eupnea) - Medulla only: respiration is short, irregular, and gasping 喘氣 33 Control of Ventilation Influenced by nervous input and chemical input Nervous input - Input from cerebral cortex (大腦皮層), limbic system, hypothalamus (下丘脑), and other brain centers - E.g., Increase when you are angry or frightened (hyperpnea: faster-than- normal respiration) - E.g., Decrease in the soundest stage of sleep - Hering-Breuer reflex – prevents overexpansion of the lungs - When inspiratory depth increases, the stretch receptors (mechanoreceptors) in bronchi, bronchioles, and the walls between the adjacent alveoli are stimulated - In turn, they produce inhibitory (抑制性) nerve signals that travel from the inflated lungs to the respiratory center and causes the center to stop sending out nerve signals 34 Control of Ventilation Chemical input: The respiratory center is extremely sensitive to the levels of carbon dioxide and hydrogen ions. When they rise due to increased cellular respiration during exercise, the center increases respiratory rate and depth. Chemoreceptors (化學感受器) located in the carotid arteries ( 頸動脈) (“carotid bodies”) and aorta (主動脈) (“aortic bodies”) are sensitive to blood oxygen levels. When oxygen concentration decreases, these receptors communicate with the respiratory center, and the rate and depth of breathing increase. 35 Gas Exchange and Transport 36 External Respiration Exchange of gases in the lungs Gases are exchanged between the alveolar air (肺泡氣) and the pulmonary capillary blood (肺微血管血). Oxygen - Higher concentration in the alveoli - Diffuses from the alveoli into the blood Carbon dioxide - Higher concentration in the blood - Diffuses from the blood in the pulmonary capillaries to the alveoli 37 Internal Respiration Exchange of gases in the tissues Gases are exchanged between the blood in systemic capillaries and the tissue fluid. Oxygen - Higher concentration in the blood - Cells are continually consuming O2 during cellular respiration. - Diffuses from the blood into the tissue fluid Carbon dioxide - Higher concentration in the tissue fluid - CO2 is an end product of cellular respiration. - Diffuses from the tissue fluid into the blood 38 External and Internal Respiration 39 Gas Transport – Oxygen Transport 97-98% transported by hemoglobin in the red blood cells - Combined with oxygen – oxyhemoglobin - Released oxygen – deoxyhemoglobin - Increased blood carbon dioxide, acidity, and temperature all increase the amount of oxygen that oxyhemoglobin releases (especially in tissues). Small amount (2-3%) transported in the plasma - Oxygen is not very soluble in water 40 Gas Transport – Carbon Dioxide Transport 1. As a dissolved gas in blood plasma and in the cytoplasm of red blood cells – 10% 2. Combine with protein (globin) portion of hemoglobin (carbaminohemoglobin) – 30% 3. Most combines with water, forming carbonic acid (H2CO3) – 60% - Carbon dioxide combines with water to form carbonic acid (H2CO3) - CO2 + H2O → H2CO3 - Carbonic acid dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-) - H2CO3 → H+ + HCO3- - This reaction is catalyzed by an enzyme, carbonic anhydrase (abundant in red blood cells) - Bicarbonate ions diffuse out of red blood cells into the plasma in exchange for chloride ions - Chloride shift: to maintain the electrical balance between the plasma and the red blood cells - Carbonic acid splits into CO2 and H2O, and the CO2 diffuses out of the blood into the alveoli. 41 Gas Transport 42 Respiratory Control of Blood pH The respiratory system helps to regulate pH. Bicarbonate/Carbonic acid buffer system is altered by breathing - Hypoventilation = increased CO2 = decreased pH (high [H+])= acidosis (pH less than 7.35) - ↑CO2 + H2O → ↑H2CO3 ↑ H+ + HCO3- - Hyperventilation = decreased CO2 = increased pH (Low [H+])= alkalosis (pH greater than 7.45) - ↓CO2 + H2O → ↓ H2CO3 ↓ H+ + HCO3- - Both acidosis and alkalosis can be fatal because they interfere with cell enzyme functions. 43 Reference Longenbaker, S. N. (Ed.) (2020). Mader’s Understanding Human Anatomy and Physiology (10th ed.). McGraw-Hill. 44