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The Respiratory System

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1 The Respiratory System
Chapter 22

2 The Respiratory System
Processes of Respiration: Pulmonary Ventilation – movement of air into and out of the lungs External Respiration – gas exchange at the lungs; O2 from lungs to blood, CO2 from blood to lungs Respiratory gas transport – use of blood to deliver O2 to the tissues and deliver CO2 to the lungs Internal Respiration – gas exchange at the tissues; O2 from blood to tissues, CO2 from tissues to blood Figure 22.1

3 The Respiratory System
Anatomy of Respiration: Conducting zone – the group of respiratory passages that provide passage of air to the lungs. Includes nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles Respiratory zone – the microscopic lung structures where gas exchange occurs. Includes any structure with air sacs, called alveoli. Figure 22.1

4 The Nasal Cavity Nasal Cavity - air passage that warms, moistens, and filters air, and also contains olfactory receptors. Medially divided by the nasal septum. External nares - the visible ‘nostrils’ that are the entrances into the nasal cavity Conchae - bony protrusions into the nasal cavity that cause the air to flow turbulently through the nasal cavity Figure 22.3b

5 The Nasal Cavity Respiratory mucosa – PSCCE with mucous and serous glands, producing a watery mucus rich in lysozymes, enzymes that break down bacteria Internal nares - the exits from the nasal cavity into the pharynx, located at the posterior side of the nasal cavity Paranasal sinuses - hollow spaces in the certain skull bones, lined with mucous membrane. This mucus drains into the nasal cavity Rhinitis – inflammation of the nasal mucosa Sinusitis – inflammation of the paranasal sinuses Figure 22.3b

6 The Pharynx The Pharynx - air and food passage that connects the nasal cavity and mouth to the larynx and esophagus. Commonly called the throat, divided into 3 regions: Nasopharynx – posterior to nasal cavity, air only, lined with PSCCE Oropharynx – posterior to oral cavity, air and food, lining is stratified squamous Laryngopharynx – posterior to the epiglottis, air and food, lining is stratified squamous Figure 22.3b

7 The Larynx The Larynx - air passage that connects the pharynx to the trachea, composed of individual cartilages, mostly hyaline. Commonly called the voice box for its additional function of voice production Epiglottis - the only elastic cartilage, blocks entrance to the larynx during swallowing, ensuring food only enters the esophagus Figure 22.4a, b

8 The Larynx Vocal Ligaments – elastic connective tissues in the lumen of the larynx. The glottis is the opening between these ligaments. Lining epithelium switches from stratified squamous to PSCCE below these ligaments. Vocal folds (true vocal cord) – vibrate to produce sound Vestibular folds (false vocal cords) - superior to vocal folds. Help close the glottis when swallowing Laryngitis – inflammation of the vocal ligaments Figure 22.5

9 The Trachea The Trachea - air passage from the larynx to the bronchi, commonly called the windpipe Trachealis muscle - smooth muscle on the posterior side of the trachea, used in coughing Trachea Layers in cross section: Mucosa – PSCCE with goblet cells. Cilia sweep debris toward throat for swallowing. Submucosa – connective tissue layer containing mucous glands Hyaline Cartilage – c-shaped to support air passage while also allowing esophagus expansion Adventitia - connective tissue to anchor trachea into surrounding tissues Figure 22.6

10 The Bronchial Tree Bronchial Tree – the series of branching air passages leading to lung compartments Conducting zone structures: Primary bronchi – branch from trachea, one for each lung Secondary bronchi – branch from primary once inside the lung, one for each lung lobe Tertiary bronchi - branch from secondary Bronchioles – when the air passage diameter is <1mm Terminal bronchioles – when the diameter is <0.5mm Figure 22.7

11 The Bronchial Tree Respiratory zone structures:
Respiratory bronchioles – bronchioles with scattered alveoli Alveolar duct – blind-ended passage lined by alveoli Alveolar sac – a cluster of alveoli at the end of a duct Alveoli – the individual lung compartments where gas exchange with blood occurs Figure 22.8

12 The Respiratory Membrane
Respiratory Membrane – the fusion of alveolar and capillary walls, creating a 5µm thick membrane for gas exchange between air and blood Figure 22.9a, b

13 The Respiratory Membrane
Type 1 cells – squamous cells of the alveolar wall, fuse to endothelial cells Type 2 cells - cuboidal cells that secrete surfactant, which reduces the surface tension of water to prevent alveolar collapse Alveolar macrophages - move amongst the respiratory membrane engulfing cells and debris Alveolar pores - small holes that connect adjacent alveoli Figure 22.9c, d

14 The Lungs Lungs - Paired organs that are highly compartmentalized into small air sacs Right Lung - divided into upper, middle, and lower lobes by the horizontal fissure and oblique fissure respectively Left Lung - divided into upper and lower lobes by the oblique fissure, also has the cardiac notch – an indentation for the heart’s apex Figure 22.10a

15 The Pleurae The Pleurae - a double layer of serous membrane producing serous fluid to reduce friction during lung ventilation/movement Visceral pleura - the serous membrane layer that clings to the lung surface Parietal pleura - the serous membrane that is separated from the lungs, clings to the internal surface of the thoracic body wall Pleural cavity - the space between the parietal and visceral layers, filled with serous fluid Figure 22.10c

16 Mechanics of Breathing
Pulmonary Ventilation - the movement of air into and out of the lungs based on the interactions of pressures in and around the body Inspiration - the movement of air into the lungs Expiration - the movement of air out of the lungs Figure 22.12

17 Mechanics of Breathing
Involved pressures: Atmospheric pressure (Patm)- pressure exerted by the air around the body, 760 mmHg Intrapulmonary pressure (Ppul) - the air pressure within the alveoli, rises and falls ( mmHg) but eventually equalizes with Patm Intrapleural pressure (Pip) - the pressure in the pleural cavity (756 or -4 mmHg), 4 mmHg less than Ppul (must be a negative pressure to prevent lung collapse) Transpulmonary pressure – the difference between intrapleural and intrapulmonary pressures, (Ppul - Pip)… 760 – 756 = 4 mmHg

18 Mechanics of Breathing
Boyle’s law : P1V1 = P2V2 When the volume of a chamber increases, the pressure inside that chamber decreases. When the volume of a chamber decreases, the pressure inside that chamber increases Figure 22.13

19 Mechanics of Breathing
Inspiration: Contraction of diaphragm and external intercostal muscles increases the volume of the thoracic cavity and lungs Volume increase lowers the Ppul to 759 mmHg (-1 mmHg) Air moves down its pressure gradient, into the lungs, until the Ppul equalizes with the Patm Figure 22.13a

20 Mechanics of Breathing
Expiration: Relaxation of the inspiratory muscles decreases volumes of thoracic cavity and lungs Volume decrease raises Ppul to 761 mm Hg (+1 mmHg) Air moves down its pressure gradient, out of the lungs, until the Ppul equalizes with the Patm again Figure 22.13b

21 Mechanics of Breathing
When Ppul is less than the Patm , inspiration occurs and lung volume increases As the lung volume increases, so does pressure, eventually equalizing with Patm When Ppul is greater than the Patm , expiration occurs and lung volume decreases As the lung volume decreases, so does pressure, eventually equalizing with Patm Figure 22.14

22 Factors Affecting Ventilation
Airway Resistance – friction of air on walls of respiratory passages, is insignificant in a healthy person Alveolar surface tension – cohesion of water molecules would cause alveolar collapse. Surfactant from type 2 cells reduces this IRDS – infant respiratory distress syndrome – an inability to produce surfactant in premature births Lung compliance – the ability of the lungs to stretch as the thoracic cavity expands Figure 22.15

23 Respiratory Volumes and Capacities
Tidal volume - The volume of air ventilated during resting breathing (0.5 L) Inspiratory reserve volume - additional air that can be forcefully inhaled beyond tidal (2-3L) Expiratory reserve volume - additional air that can be forcefully exhaled beyond tidal ( mL) Residual volume - volume of air always in lungs, prevents lung collapse (1.2L) Figure 22.16a

24 Respiratory Volumes and Capacities
Vital Capacity - total amount of exchangeable air ( L) Total Lung Capacity - total air volume in lungs (4.2-6 L) Dead spaces – areas where air is not involved in gas exchange Anatomical dead space – volume of conducting zone structures (150 mL) Alveolar dead space – volume of any nonfunctional alveoli Figure 22.16a

25 Measuring Ventilation
Spirometry – the measurement of lung volumes and capacities Alveolar ventilation rate (AVR) - measure of air volume flowing into and out of alveoli AVR = Breath frequency x (Tidal volume – dead space) AVR = 12 breaths/min x (500mL – 150 mL) AVR = 4,200 mL/min

26 Properties of Gases Dalton’s Law - total pressure from a mixture of gases is the sum of the partial pressures of each individual gas; this partial pressure is proportional to the percentage of that gas in the mixture. Example: Patm = PO2 + PCO2 + PN2 Henry’s Law – when a mixture of gases is exposed to a liquid, the gases will dissolve in proportion to their partial pressures 

27 Gas Exchange External Respiration :
The PO2 of the air in the alveoli is greater than the PO2 of the blood arriving at the alveoli Oxygen moves down its pressure gradient from the alveoli into the blood The PCO2 of the blood arriving at the alveoli is greater than the PCO2 of the air in the alveoli Carbon dioxide moves down its pressure gradient from the blood into the alveoli Figure 22.17

28 Gas Exchange Oxygen moves from the alveoli into the blood until the partial pressures equalize, taking about 0.25 sec Figure 22.18

29 Gas Exchange Ventilation–Perfusion coupling –
Areas of lung tissue whose alveoli are well supplied with air experience dilation of local blood vessels Areas with relatively unventilated alveoli experience local vasoconstriction Figure 22.19

30 Gas Exchange Internal Respiration :
The PO2 of the blood arriving at the tissues is greater than the PO2 of the tissues Oxygen moves down its pressure gradient from the blood into the tissues The PCO2 of the tissues is greater than the PCO2 of the blood arriving at the tissues Carbon dioxide moves down its pressure gradient from the tissues into the blood Figure 22.17

31 Oxygen Transport 1.5% of oxygen is transported by being dissolved in the blood’s plasma 98.5% of oxygen is transported by being bound to hemoglobin Hemoglobin is 100% saturated with oxygen upon leaving the lungs, and is still 75%saturated after delivering to the tissues Bohr effect – increased PCO2 weakens the bond between hemoglobin and oxygen Hypoxia – inadequate oxygen delivery to body tissues Figure 22.20

32 Carbon Dioxide Transport
7-10% of carbon dioxide is transport by being dissolved in plasma 20% of carbon dioxide is transported by being bound to hemoglobin 70% of carbon dioxide is transported as bicarbonate ions (HCO3-) Dissolved carbon dioxide reacts with water to form carbonic acid (H2CO3) which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). Therefore, CO2 levels in the blood affect blood pH by affecting H+ levels Figure 22.22a

33 Carbon Dioxide Transport
Carbonic acid-bicarbonate ion buffer system – the chemical reaction involving carbon dioxide is reversible, allowing the prevention of drastic changes of blood pH Haldene effect - blood can transport more carbon dioxide when the PO2 is lower Figure 22.22b

34 Control of Respiration
Medullary Respiratory Centers – nuclei in the medulla that regulate breathing rate and depth Ventral respiratory group – generates the breathing rhythm, inspiratory nerves from here control the inspiratory muscles Dorsal Respiratory group – regulates the breathing rhythm with information from chemoreceptors in the blood Pontine respiratory group – regulates smooth transitions between inhalation and exhalation Figure 22.24

35 Control of Respiration
Factors Affecting Breathing: Chemoreceptors – receptors for CO2, O2 and H+ in the medulla and major arteries. If carbon dioxide levels increase (decreasing pH), breathing rate and depth should increase Higher brain centers – emotions can affect breathing rate. The cerebral cortex allows us to voluntarily control breathing. Hyperpnea – increased breathing rate due to metabolic need, as in during exercise Other receptors – irritants or excessive stretch inhibits ventilation Hyperventilation – increased breathing rate beyond body needs. Leads to vasoconstriction of cerebral blood vessels and can lead to fainting Figure 22.25

36 Respiratory Disorders
Chronic Obstructive Pulmonary Disorder (COPD) – any condition involving a decreased ability to expel air from the lungs. Symptoms include dyspnea (labored breathing), coughing, and hypoventilation Chronic bronchitis – excessive mucous production in the respiratory passages leading to frequent infections Emphysema – a progressive loss of the respiratory membrane and decreased lung elasticity Tuberculosis- bacterial infection spread through aerosols; treated with 1 year course of antibiotics Cystic fibrosis – genetic disease causing excessive, thick mucus production causing major infections Figure 22.28

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