PHS 206: Respiratory System PDF

PHS 206: RESPIRATORY SYSTEM Mr. Soetan Olaniyi A  OUTLINE Physiologic anatomy of respiratory apparatus Pulmonary circulation Brief review of relevant gas laws Pulmonary ventilation – Mechanics of breathing – Lung Volumes and Capacities...

PHS 206: RESPIRATORY SYSTEM Mr. Soetan Olaniyi A  OUTLINE Physiologic anatomy of respiratory apparatus Pulmonary circulation Brief review of relevant gas laws Pulmonary ventilation – Mechanics of breathing – Lung Volumes and Capacities Exchange of oxygen and carbon Dioxide Transport of oxygen and carbon dioxide in blood and tissue fluids Regulation of respiration Effect of exercise on respiration Respiratory insufficiency- pathophysiology, diagnosis, treatment 2 PHYSIOLOGIC ANATOMY OF RESPIRATORY APPARATUS 3  PHYSIOLOGIC ANATOMY OF RESPIRATORY APPARATUS Objectives: The students are expected to be able to describe the anatomy of the nose, pharynx, larynx, trachea, bronchi and lungs. In addition, students would be able to identify the functions of each structures of respiratory system. 4  Introduction Basic function of the respiratory system is to supply the cells of the body with oxygen as well as removal of carbon dioxide. Also, the respiratory system exerts some non-respiratory functions e.g.? The respiratory system structures include - nose, - pharynx (throat), - larynx (voice box), - trachea (windpipe), - Bronchi, and - lungs. 5 Figure 1: Structures of the respiratory system 6  Classification of respiratory parts The parts of the respiratory system can be classified based on (a) Structure, and (b) Function. a. Structural classification Structurally, the respiratory system consists of two parts namely; i. Upper respiratory system, and ii. Lower respiratory system i. Upper respiratory system The structures that make up this part includes the nose, nasal cavity and pharynx 7  Classification of respiratory parts cont’d.. ii. Lower respiratory system The structures that make up this part includes the larynx, trachea, bronchi and lungs. b. Functional classification Functionally, the respiratory system consists of two important parts. Namely; i. The conducting zone ii. The respiratory zone 8  Classification of respiratory parts cont’d.. i. Conducting zone: The conducting zone consists of interconnecting cavities and tubes found outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. The primary function of the conducting zone is to filter, warm, moisten and conduct air into the lungs. ii. Respiratory zone This consists of tubes and tissues within the lungs where gas exchange occurs (i.e. site of gas exchange between air and blood). The structures that make up the respiratory zone includes the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli. 9  THE STRUCTURES OF RESPIRATION: i. Nose The nose is both an olfactory and respiratory organ. It consist of nasal skeleton which houses a cavity known as nasal cavity whose functions includes: 1. Warming and humidification of inspired air, 2. Removal and trapping of pathogenes and particulate matter from inspired air, 3. Smell sensation, 4. Drainage and clearance of the paranasal sinuses and lacrimal ducts. 10  THE STRUCTURES OF RESPIRATION: The nasal cavity This is the most superior part of the respiratory tract. It extends from the vestibule of the nose to the nasopharynx. The divisions of the nasal cavity are three. These are a. Vestibule: area surrounding the anterior external opening to the nasal cavity b. Respiratory region: this region is lined by ciliated psudeostratified epithelium, interspersed with goblet cell (mucus secreting cell). Figure 2: Sagittal c. Olfactory region: this region is located at the section of the nasal cavity apex of the nasal cavity, It is lined by 11 olfactory receptor cells.  THE STRUCTURES OF RESPIRATION: The nasal cavity merges anteriorly with external nose and communicates posteriorly with the pharynx through two openings called the internal nares. Projection from the lateral wall of the nasal cavity forms curved shelves of bone known as conchae. There are three conchae: inferior, middle and superior. The conchae projects into the cavity and creates four pathways (meatuses) for air to flow. The four meatuses are: Inferior, middle, superior, and spheno-ethmoidal recess. 12  THE STRUCTURES OF RESPIRATION: Note: The function of the conchae is to increase the surface area of the nasal cavity: this increases the amount of inspired air that comes into contact with the cavity walls. They also disrupt the fast, laminar flow of air, making it slow and turbulent. 13  THE STRUCTURES OF RESPIRATION: Openings into the nasal cavity There are many openings into the nasal cavity through which drainage occurs. These are: a. Paranasal sinuses b. Nasolacrimal ducts c. Auditory tube 14  Openings into the nasal cavity a. Paranasal Sinuses These are cavities in certain cranial and facial bones, lined with mucous membranes that are continuous with the lining of the nasal cavity. Skull bones containing the paranasal sinuses are frontal, sphenoid, ethmoid and maxillae. Therefore, the sinuses includes sphenoid sinuses, frontal, maxillary, middle and anterior ethmoidal sinuses). At birth, the paranasal sinuses are small or absent but usually increases in size during two periods of facial enlargement– (a) during eruption of the teeth and (b) at the onset of puberty. 15  Openings into the nasal cavity cont’d.. Functions of paranasal sinus It allows the skull to increase in size without a change in the mass of the bone. It increases the surface area of the nasal mucosa (increases mucus production that helps to moisten and cleanse inhaled air). It serves as resonating chambers within the skull that intensify and prolong sounds, thereby enhancing the quality of the voice (effect more prominent when an individual is having cold). Figure 3: Openings into the nasal cavity 16  Openings into the nasal cavity cont’d.. b. Nasolacrimal duct: This acts to drain tears from the eye. It opens into the inferior meatus. c. Auditory tube: It is also known as Eustachian tube. It opens into the nasopharynx at the level of the inferior meatus. It allows the middle ear to equalize with the atmospheric air pressure. Clinical relevance of auditory tube Since it connects the middle ear and upper respiratory tract, it serves as path by which infection spread from upper respiratory tract to the ear. 17 Blood supply to the nose The nose has a very rich vascular supply. This readily allows for effective change of humidity and temperature of inspired air. The nose receives blood from both internal and external carotid arteries. Branches of Internal carotid arteries that supply the nose are the anterior ethmoidal artery and posterior ethmoidal artery. Figure 4: arterial supply to the nose 18 Blood supply to the nose cont’d.. Branches of the external carotid artery that supplies the nose are sphenopalatine artery, greater palatine artery, superior labial artery and lateral nasal arteries. Note: The arteries form anastomosis (prevalent in the anterior region) with one another. Figure 4: arterial supply to the nose 19 Venous drainage in the nose The veins of the nose follow the arteries and drains into the pterygoid plexus, facial vein or cavernous sinus. In some individuals, few nasal veins joins with sagittal sinus and thus represents means by which infection spreads from the nose to the cranial cavity. 20  Structures of respiratory system cont’d.. ii. Pharynx The pharynx, also known as throat is a funnel-shaped tube about 13cm long that starts at the internal nares and extends to the level of the cricoid cartilage (the most inferior cartilage of the larynx). It lies posterior to the nasal and oral cavities and superior to the larynx, and just anterior to the cervical vertebrae. The wall of the pharynx is composed of skeletal muscle and is lined with mucous membrane. 21  Structures of respiratory system cont’d.. Noteworthy, when the skeletal muscle contracts, it keeps the pharynx open and vice versa. Anatomical regions of the pharynx The pharynx has three important regions. - Nasopharynx, - Oropharunx, and - Laryngopharynx. 22  Structures of respiratory system cont’d.. Nasopharynx: It lies posterior to the nasal cavity and extends to the soft palate. The wall is lined with pseudostratified ciliated columnar epithelium. The nasopharynx exchanges small amount of air with the auditory tubes to equalize air pressure between the middle ear and the atmosphere. Oropharynx: This part has both respiratory and digestive functions. In particular, it serves as a passage way for air, food and drink. The wall is lined with nonkeratinized stratified squamous epithelium (protects against abrasion by food particles). 23  Structures of respiratory system cont’d.. Laryngopharynx: This begins at the level of the hyoid bone. At its inferior end, it opens into the esophagus posteriorly and the larynx anteriorly. Like the oropharynx, the laryngopharynx wall is lined by nonkeratinized stratified squamous epithelium. Functions of pharynx: The pharynx functions as passage way for air and food, It promotes resonating chamber for speech sounds, and Houses tonsil which participate in immunological reactions against foreign invasion. 24  Structures of respiratory system cont’d.. iii. The larynx Also known as the voice box, is a short passageway that connects laryngopharynx with the trachea. It lies in the midline of the neck anterior to the esophagus and the fourth through sixth cervical vertebrae. The wall of the larynx superior to the vocal fold is nonkeratinized stratified squamous epithelium while the wall inferior to the vocal fold is lined by psudostratified ciliated columnar epithelium that consist of ciliated columnar cells, goblet cells and basal cells. 25  Structures of respiratory system iv. The trachea cont’d.. The trachea is also known as windpipe. It is a tubular passage for air that is about 12cm long and 2.5cm in diameter. It is located anterior to the esophagus and extends from the larynx to the superior border of the fifth thoracic vertebra where it divides into right and left primary bronchi. The branching of the bronchi is illustrated below. The layer of the trachea wall from deep to superficial layer includes mucosa, submucosa, hyaline cartilage and adventitia.26  Structures of respiratory system cont’d.. v. The Bronchi The trachea divides into a right and left main bronchus which enters the right and left lungs respectively. The right main bronchus is more vertical, shorter and wider than the left. 27  Structures of respiratory system cont’d.. Consequently, an aspirated object has tendency to enter and lodge in the right main bronchus than the left one. Like the trachea, the bronchi consist of incomplete ring of cartilage lined by pseudostratified ciliated columnar epithelium. Note: There is an internal ridge known as carina at the point of division of trachea. The mucous membrane of the carina is highly sensitive and plays important role in cough reflex. 28  Structures of respiratory system cont’d.. vi. Lung The lungs are paired cone-shaped organs in the thoracic cavity. Each lung is enclosed and protected by a double layered serous membrane called pleural membrane. The superficial layer that lines the wall of the thoracic cavity is known as parietal pleura while the deep layer which covers the lung is known as viscera pleura. Figure 5: Characteristic features of the lung. One or two fissures divide each lung into The space between the parietal and lobes. Both lungs have an oblique fissure viscera pleura is known as pleural cavity. which extends inferiorly and anteriorly (this divides the lung into different lobes; superior and inferior lobes). The right lung has horzintal fissure (this creates a third29 lobe known as middle lobe).  Structures of respiratory system cont’d.. Lung Parenchyma The portion of the lung that contains alveolus and participates in gas exchange is known as the lung parenchyma. Each alveolus in the lung parenchyma opens directly into alveolar duct. Lobule of the lung Small compartments of each bronchopulmonary segment of the lung. 30  Figure 6: Portion of the lobule of lung Lobule of the lung is wrapped in elastic connective tissue and contains a lymphatic vessel, an arteriole, a venule and a branch from a terminal bronchiole 31  Structures of respiratory system cont’d.. The alveoli of the lung An alveolus is a cup-shaped sac at the end of the bronchioles. The wall of the alveoli consists of two important type of cell known as alveolar epithelial cells. These are: a. Type 1 alveolar cell: There are more of these type of cells than the second. It is a squamous pulmonary epithelial cell that forms a nearly continuous lining of the alveolar walls. It is the main site of gas exchange. 32  Structures of respiratory system cont’d.. b. Type II alveolar cell: Type II cells are known as septa cells. Unlike the type I, type II cells are only few and they are found usually between type I alveolar cells. Their function is secretion of alveolar fluid, including surfactant, a complex mixture of phospholipids and lipoproteins that lowers the surface tension of alveolar fluid and therefore prevents the lung from collapsing. Note: The alveoli also contains macrophages (small in number; know the source??) that serves important function of protecting the host against invading organisms. 33  THE RESPIRATORY MEMBRANE The respiratory membrane is the portion through which gas exchange occurs. It has four layers; their arrangements from the alveolar air space to the blood plasma are: a. Layer of type I and type II alveolar cells and associated alveolar macrophages b. An epithelial basement membrane that underlies the alveolar wall c. A capillary basement membrane that is often fused to the epithelial basement membrane d. The capillary endothelium. 34  PULMONARY CIRCULATION The blood is supplied to the lung through two sets of arteries (pulmonary and bronchial arties). The pulmonary trunk (divides into right and left pulmonary artery) and conveys deoxygenated blood to the lung. The bronchial arteries, a branch from aorta delivers oxygenated blood to the lung. Blood supplied to the lung mostly return to the heart via pulmonary vein. Some blood drains into bronchial veins, branches of the azygos system and returns to the heart via superior vena cava. 35 RELEVANT GAS LAWS 36  Introduction The atmosphere from where we derive oxygen and release carbon dioxide into contains a mixture of gases. Atmospheric air is a mixture of the following gases Nitrogen 78.6%, Oxygen 20.9%, Water 0.04%, CO2 0.004%, OTHERS 0.0006% Gas movement and interaction with molecules such as water is dependent on physical and/or chemical attributes of the gases which have been demonstrated by various gas laws. 37  Gas laws The important gas laws are: i. Boyle’s law, ii. Charle’s law, iii. Gaylusac’s law, iv. Dalton’s law, v. Henry’s law vi. Ideal gas law (PV = nRT) i. Boyle’s Law Boyle’s law describe the relationship (*inverse) between pressure and volume – Boyle’s law/Boyle–Mariotte law states that at a constant temperature, the pressure is inversely proportional to volume 38  Boyle’s Law cont’d.. i.e. P alpha 1/V - where alpha = proportional to Thus, for the same gas under different conditions at the same temperature, p1v1= p2v2 Application: Inspiration and expiration event that occurs in the lung follows boyle’s law. Further, the law can be used to describe the effect of altitude on gases in closed cavity within the body. 39  Boyle’s Law cont’d.. Notably volume increases with decreasing pressure that as seen during sea level to the sky movement. Report from an artificial pneumothorax model shows that a 40ml pneumothorax increase in volume by about 16% at 1.5km (approx.. 5000 feet) above sea level. In human, expansion of about 30% can be seen after ascending from sea level to an altitude of 2.5km (approx.. 8200 feet). 40  Boyle’s Law cont’d.. Example:  A patient with a simple pneumothorax (volume =1500ml (101.3 kPa) at sea level), that is transferred to a local hospital via helicopter that reaches altitude of 1km (90 kPa) would have a final volume of x? X = 1688 41  Charle’s law: Although not relevant in respiration since temperature of the body is kept at a relatively constant level, describe relationship (*direct) between gas volume and temperature. It states that the volume of an ideal gas is directly proportional to absolute temperature at constant pressure. i.e. V alpha T = k or V/T = k 42  Charle’s law cont’d.. Charle’s law is apparent in gas thermometer, where the change in gas volume (e.g. hydrogen) is used to indicate temperature change. Also, the law is demonstrated by reduction in the volume of a balloon filled with gas after placing it into a freezer. It has been demonstrated that warming from 20 degree C (273 degrees K) to 37 degree C (310K) will cause an increase in volume of inspired gases. 43  Charle’s law cont’d.. In particular, an adult tidal breath of 500ml of air at room temperature increases to a volume of 530 ml when it reaches the site of gas exchange as a result of warming by the body temperature. 44  Gay-Lussac’s Law This law describes the relationship between pressure and temperature. According to the law, increase temperature is followed by a corresponding increase in gas pressure. Since most physiological processes occur at 37 degree C, there are only few clinical application of Gay-Lussac’s law. 45  Dalton’s law: Describe relationship between different gases that make up a mixture of gases. It states that a specific gas type in a mixture exerts its own pressure (i.e. partial pressure) which is proportional to its percentage in the total. Therefore, the total pressure Oxygen percentage exerted by a mixture of gases is composition in air = 21% the sum of the partial pressures of the gases. Partial pressure = 21% of 760 = 160mmHg 46  Henry’s Law This law describes the relationship between pressure and solubility of gases. According to the law, an increase in pressure is followed by a corresponding increase in solubility. Henry’s law has shown benefits in the understanding of decompression sickness that divers undergo if they surface too quickly. 47  Henry’s Law cont’d.. Notably, as diving depth increases, the partial pressure of each gas inspired increases and thus causes higher concentration of nitrogen to dissolve in the blood. Such a high amount of nitrogen dissolved in the blood is usually not a problem at depth but can pose serious problem if regular stops are not made during ascent. – Implication of rapid ascent is the formation of bubbles due to the nitrogen release and eventual development of decompression sickness. 48 PULMONARY VENTILATION 49  Introduction Respiration which is the process of gas exchange in the body has three basic steps. These are: a) Pulmonary ventilation b) External respiration c) Internal respiration. Pulmonary ventilation: also known as breathing is the inhalation and exhalation of air. It involves exchange of air between the atmosphere and the lung alveoli. External respiration: also known as pulmonary respiration is the exchange of gas between the lung alveoli and the blood in the pulmonary capillaries across the respiratory membrane. Internal respiration: Also known as tissue respiration is the exchange of gases between the blood in systemic capillaries and tissue cells. It involves oxygen removal from the blood and release of waste product of cellular respiration (i.e. carbon dioxide) into the blood. 50  PULMONARY VENTILATION In pulmonary ventilation,  Air flows between the atmosphere and the alveoli of the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles.  The rate of airflow and the amount of effort needed for breathing are also influenced by: a. Alveolar surface tension b. Compliance of the lungs, and c. Airway resistance. 51  Pulmonary Ventilation (Mechanics of Breathing) There are two phases of breathing: 1. Inspiration (inhalation) the increase and decrease 2. Expiration (Exhalation) in thorax and lung volumes makes breathing possible. for example, Lung expansion/stretch is required for inspiration to occur. Conversely, reduction in lung volume ( lung recoil/contraction) is required for expiration. 52  Pulmonary Ventilation (Mechanics of Breathing) cont’d.. Events that favors lung expansion and contraction and hence change in lung volumes are a. The upward and downward movement of the diaphragm ( useful in quiet breathing) b. Elevation and depression of the rib (increases and decreases the anteroposterior diameter of the chest cavity). 53  Pulmonary Ventilation (Mechanics of Breathing) Effect of the upward and downward movement of the diaphragm ( useful in quiet breathing). The diaphragm is the main muscle of inspiration. In contracted state, the diaphragm moves downward and vice versa during relaxation. Such downward movement pulls the lower surface of the lung downwards to favor inspiration. Upward movement of the diaphragm however favors lung recoil and hence expulsion of air (during quiet breathing). 54 Pulmonary Ventilation (Mechanics of Breathing) Effect of elevation and depression of the rib It increases (necessary for inspiration) and decreases (necessary for expiration) the anteroposterior diameter of the chest cavity. Muscles that elevate the rib cage are known as inspiration muscle. E.g. external intercostal, sternocleidomastoid, anterior serrati and scalene muscles. Muscles that depresses the rib cage are known as expiration muscle e.g. abdnominal recti and internal intercostal muscles. 55  Pressure changes during pulmonary ventilation Remember Boyle’s law??? – Inverse relationship between volume and pressure. How is boyle’s law related to pulmonary ventilation??? During inspiration, – increase lung volume = decrease intrapleural pressure = decrease alveoli pressure= air inflow. 56  Pressure changes during pulmonary ventilation Just before each inhalation, it has been shown that pressure inside the lung is equal to the atmospheric pressure (at sea level = 760mm Hg/ 1 atm). For air to flow in, the pressure inside the lung (i.e. intrapulmonary pressure) falls below atmospheric.  Note: – The intrapleural pressure is usually subatmospheric (allows for lung expansion). – During normal quiet breathing diaphragm descends about 1 cm to produce pressure difference of 1-3 mm Hg that 57 drives 500mL of air inflow.  Pressure changes during pulmonary ventilation In strenuous breathing, the diaphragm may descend to about 10 cm to produce a pressure difference of 100 mmHg and inhalation of about 2-3 L of air. QUICK TEST: Inhalation is referred to as active process. Why do you think this is so? 58  Pressure changes during pulmonary ventilation Like inhalation, exhalation is also due to pressure gradient but the condition is a reverse of what was seen during inhalation. During exhalation, the pressure inside the alveoli (762mm Hg) is more than the atmosphere Noteworthy, there are no contraction of muscle involved in exhalation (passive process). Instead, lung and chest wall recoil occurs and promotes the expiration process. Exhalation becomes active only during forceful breathing when the abdominal and internal intercostal muscles contracts. To increase pressure in the abdominal region and thorax. 59  Changes in lung volume and pressures during normal breathing Note; Transpulmonary pressure = pressure difference between alveolar pressure and pleural pressure. Also known as recoil 60 pressure.  Other factors that affects pulmonary ventilation Apart from the effect of pressure gradients and muscular relaxation, other factors that affects pulmonary ventilation includes: a) Surface tension of the alveolar fluid b) Compliance of the lung, and c) airway resistance 61  Other factors that affects pulmonary ventilation cont’d.. a. Surface tension An increase surface tension prevent expansion of the lung. The surfactants secreted by the alveolar cell however reduces the surface tension. The phospholipids in particular Surfactant is a complex are responsible for reducing the mixture of several surface tension by not phospholipids, proteins and dissolving completely in the ions. alveolar fluid. - components includes: phospholipid dipalmitoyl 62 phosphatidylcholinne, surfactant apoproteins and calcium ions.  Other factors that affects pulmonary ventilation cont’d.. b. Compliance It is the extent to which the lung will expand for each unit increase in transpulmonary pressure if enough time is allowed to reach equilibrium. High compliance means the chest wall and lung expands easily and vice versa for low compliance. Normal value in adult is about 200 ml of air /cm of water transpulmonary pressure. 63 Compliance cont’d.. Inspiratory compliance curve and expiratory compliance curve showing relationship between lung volume and pleural pressure… 64 Compliance cont’d.. Elastic forces of the lung (elastic forces of the lung tissue and surface tension of fluid in the lung) determines compliance. 65  Other factors that affects pulmonary ventilation cont’d.. c. Airway resistance: The walls of the airways, especially the bronchioles offer some resistance to normal flow of air into and out of lung. – This is usually achieved by alteration in the diameter of the airway as a result of smooth muscle contraction and relaxation. – Signals from the sympathetic nervous system causes relaxation of the smooth muscle and subsequent bronchodilation. 66  Lung volumes and capacities Measurement of the volume of air entering and living the lung can be recorded to study pulmonary ventilation. This recording is done using an equipment known as a spirometer. The method of taking such recording is known as spirometry. 67  Lung volumes and capacities cont’d.. The spirometer consists of a drum which is inverted over a chamber of water. The drum (contains air or oxygen) is counterbalanced by a weight. A tube with a mouth piece is usually connected to the gas chamber. A subject can thus breath into and out of the gas chamber through the mouth piece. 68  Lung volumes and capacities cont’d.. Breathing into and out of the gas chamber usually cause the drum to rise or fall This in turn draws appropriate mark on the recording drum as illustrated in the diagram 69  Lung Volumes 1. Tidal volume (TV; 500ml): Volume of gas inspired/expired during normal breathing. 2. Inspiratory reserve volume (IRV; 3000ml): Maximum volume that can be inspired during forced breathing other than tidal volume. 3. Expiratory reserve volume (ERV; 1300ml): Maximum volume of gas that can be expired during forced breathing other than tidal volume 4. Forced expiratory volume (FEV): Amount of gas that can be expired forcefully in 1s, 2s, 3s. (e.g. FEV1) 5. Residual volume (RV; 1200ml): Volume of gas remaining in the lungs after vital capacity expiration. Cannot be measured by spirometry. 70  Lung Capacity 1. Vital capacity (VC; 4700ml): Maximum air that can be expired after a maximum inspiration (the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume). 2. Total lung capacities (TLC; 6000ml): The sum of vital capacity and residual volume 3. Inspiratory capacity (IC; 3600ml): The sum of tidal volume and respiratory reserve volume 4. Functional residual capacity (FRC; 2400ml): Volume of air that remains in the lung at the end of each normal expiration. FRC= sum of residual volume and expiratory reserve volume. Measurement of FRC is by indirect spirometry (helium dilution method???). 71  MORE DEFINITIONS a. The minute ventilation (MV): – is the total volume of air inhaled and exhaled each minute. – Can be obtained by multiplying respiratory rate by tidal volume (i.e. MV= 12 breaths/min x 500ml/breath = 6 L/min). b. Anatomic dead space: the conducting airways with air that does not undergo respiratory exchange. c. Alveolar ventilation: the volume of air per minute that actually reaches the respiratory zone. 72 Exchange of Oxygen and Carbon dioxide 73  Exchange of Oxygen and Carbon dioxide The means by which gases are exchanged is via diffusion; an event which usually follows pulmonary ventillation (as in external respiration). Diffusion can be affected by factors like 1. concentration gradient and 2. partial pressure Thus represents important determinants of gas exchange between air and alveoli, alveoli and blood and blood and tissues. 74  Exchange of Oxygen and Carbon dioxide cont’d.. Molecular basis of gas diffusion Gas molecules are continually in motion ( random; except at absolute zero temperature). Energy required for motion = kinetic energy. According to the law of diffusion, the net diffusion of gas that occurs is determined by concentration gradient. – Usually, gas move from region of high concentration to low.  Remember that Concentration is related to pressure 75  Exchange of Oxygen and Carbon dioxide cont’d.. Partial pressure and gas diffusion A mixture of gas containing different gases, will have concentration which is proportional to pressure. Concentration/pressure of Gas mixture = sum of partial pressure of gases that make up the mixture (what law?). Since gas move from more concentrated to less concentrated region, partial pressure of gas is directly proportional to the rate of diffusion. – Noteworthy, partial pressure of Oxygen in a mixture of gas (at sea level) containing 21% oxygen = (21/100) x 760 mmHg = 160 mmHg. 76  Partial pressure and gas diffusion Dissolved gases also exert partial pressure!!! When dissolved in fluid, gases also exert pressure which is determined by concentration and solubility coefficient as follows. According to Henry law:  Partial pressure = solubility = concentration of gas in fluid Therefore, solubility coefficient = concentration of dissolved gas/partial pressure. 77  Exchange of Oxygen and Carbon dioxide cont’d.. Using the formula: Partial pressure = (concentration of dissolved gas/ solubility coefficient) The solubility coefficient of oxygen, carbon dioxide, nitrogen, helium and Carbon monoxide can be calculated when partial pressure is expressed in 1 atm and concentration expressed in volume of gas dissolved in each volume of water. Solubility coefficient of some gases are:  0.024 (for oxygen), 0.57 (CO2) and 0.012 (N) 78  Exchange of Oxygen and Carbon dioxide cont’d.. Partial pressure of gases in alveolar air, blood and tissues 79 Changes in partial pressure of oxygen and carbon dioxide 80 during external and internal respiration  Diffusion through respiratory membrane The respiratory gases can readily pass through membrane lipids therefore their diffusion is determined by the partial pressure. Other factors that determines gas diffusion through respiratory membrane are i. Thickness of the membrane, ii. surface area of the membrane, and iii. diffusion coefficient of the gas Note: diffusion coefficient for each gas is a function of the gas solubility in the 81 membrane, and inversely proportional to the square root of the molecular weight factors that determines gas diffusion through respiratory membrane cont’d.. 1. Thickness of the respiratory membrane  Increased thickness (common) = decrease diffusion.  Common causes: edema, pulmonary diseases e.g. fibrosis of lung 2. Surface area (SA) of respiratory membrane: usually a decrease in SA is associated with decrease diffusion. Common causes: removal of entire lung, emphysema 3. Diffusion coefficient: high value is indicative of high diffusion rate. It can be affected by gas solubility and molecular weight of gas. 82  Diffusion capacity of respiratory membrane Diffusion capacity of the respiratory membrane This is the volume of a gas that diffuses through the membrane per minute for a partial difference of 1mmHg. Note: diffusion capacity of the respiratory membrane can be affected by factors that affects diffusion. 83  Diffusion capacity of respiratory membrane Diffusion capacity of oxygen: normal value in man at rest = 21ml/min/mm Hg. Thus for mean oxygen pressure difference of about 11mm Hg, a total of about 230ml of oxygen diffuses through the respiratory membrane per minute. An increase in oxygen diffusion capacity is usually seen during exercise as well as other Diffusion capacities conditions that causes increase blood flow to the lung. Contributing factors are many and includes: a. extra dilation of the pulmonary capillaries/opening of new ones 84 b. Improved pulmonary ventilation perfusion ratio (VA /Q) Diffusion capacity of respiratory membrane cont’d.. Pulmonary ventilation perfusion ratio (VA /Q) and concept of Physiological shunt and physiological dead space.  When (VA /Q) is below normal = Physiological shunt (calculated using the formula: Qps/Qt = (CiO2 – CAO2)/(CiO2 – CVO2) Where, Qps = Physiological shunt, Qt = cardiac output per mins, CiO2 = concentration of oxygen in arterial blood under normal condition, CAO2 = concentration of measured oxygen in the artery, and CVO2 = concentration of oxygen in the mixed venous blood  Higher than normal VA /Q is causes physiological dead space 85 Oxygen and Carbon dioxide Transport 86  Oxygen and Carbon dioxide Transport The transport of the respiratory gases is determined by a. Diffusion, and b. Flow of blood Note:  Uptake is far more than flow rate under normal condition.  Thus, increased flow rate during exercise is accompanied by an increase in oxygen uptake 87 Oxygen and Carbon dioxide Transport cont’d.. Transport of a gas (e.g. Oxygen) from one region/vessel to another is accompanied by changes in the partial pressure of the gas. Noteworthy, partial pressure of Oxygen is Changes in partial pressure of oxygen in the determined by rate of capillary, systemic arterial, systemic capillary transport and rate of and systemic venous circulation utilization by the tissues 88 Changes in partial pressure cont’d.. a b 89  Hemoglobin(Hb) and Oxygen transport About 97% of oxygen from the lung is transported in combination with Hb. The rest is transported in dissolved state in the water of the plasma and blood cells.  Hb consist of 4 polypeptides: 2alpha and 2 beta chains  Each chain contains a heme group with ferrous ion (Fe2+) that bind loosely with oxygen molecule 90 91 Oxygen-Hemoglobin dissociation curve Demonstrates a progressive increase in the percentage of hemoglobin bound with oxygen as blood oxygen partial pressure increases. Note, 100ml of human blood contains 15g of Hemoglobin and 1g of Hb is capable of combining with 1.34ml of oxygen. Therefore 100ml blood can carry 15 x 1.34ml = 20.1 ml (oxygen carrying capacity) N.B: 5ml of oxygen is usually released to tissues in normal state. This value can increase to by a factor of 3 during strenuous exercise. 92  THE BOHR EFFECT Effect of carbon dioxide and hydrogen ions on oxygen dissociation curve…  shift curve to right (Implication?) 93 Effect of carbon monoxide on oxygen carrying capacity of Hb? CO binds to same point as oxygen but with a much greater affinity (about 250 times that of oxygen). CO poisoning is dangerous; blood remains bright red, PO2 may be normal; hence exert no effect on respiratory feedback. Intervention: administration of pure Oxygen or 5% CO2. 94  Transport of Carbon dioxide Like Oxygen, CO2 is also transported by the blood. – 100ml of blood transports about 4ml of CO2 from tissue to the lungs. – 2.7ml/dl is transported in dissolved form at 45mmHg blood pressure ; 2.4ml/dl is transported in dissolved form at 40 mm Hg blood pressure. – Therefore 0.3ml is transported to the lung. 95  Transport of Carbon dioxide Majority of CO2 is transported in a reversible form with water in red blood cell (contains carbonic anhydrase). – CO2 + water = H2CO3 = HCO3 + H – H* is buffered by Hb – HCO3 is transported out of cell via bicarbonate-chloride transporter (an antiport) Also, CO2 reacts with amine radicals of Hb to form carbaminohemoglobin (CO2Hgb). Assignment – READ HALDANE EFFECT 96 REGULATION OF RESPIRATION 97  Introduction Oxygen is important for life; hence the need to obtain from the atmosphere… Similarly, carbon dioxide excretion is important for life. Factors from within and in the environment as well as activities carried out by man, can readily alter the concentrations of these gases to create imbalance (harmful to life). Like all other functions in human, respiratory process and subsequent changes in gas concentration and/or supply to the tissues are well regulated. 98  Introduction cont’d.. Usually the control of respiration is basically directed at the need of the body. 99 THANKS FOR YOUR ATTENTION 100