Control of Respiratory Function (PDF)

Control of Respiratory Function Part I Clinical Pharmacist Dr. Fatima Bani Salama ❑Outlines Anatomy & Physiology of RESPIRATORY system Function of the lung Lung volumes & capacities Exchange & transport of gases  Respiratory system consists of the air pa...

Control of Respiratory Function Part I Clinical Pharmacist Dr. Fatima Bani Salama ❑Outlines Anatomy & Physiology of RESPIRATORY system Function of the lung Lung volumes & capacities Exchange & transport of gases  Respiratory system consists of the air passages and lung Functionally and structurally, the air passages can be divided into two parts: ✓Conducting airway through which air moves as it passes into and out of the lung ✓ Respiratory tissues where gas exchange takes place  Conducting Airways o Consists of nasal, mouth, pharynx, larynx, trachea, bronchi, and bronchioles o Air is warmed, filtered, and humidified as it passes through these structure ❑ Wall of conducting airways is lined by epithelial cells which contains: 1. Mucus –secreting gland cells which form a layer called mucociliary blanket that entrap dust, bacteria and other foreign bodies (Protection) 2. Ciliated cell with hairlike protection to clear the lower airways and the alveoli; produce its optimal function with normal oxygen levels; smoking paralyze its motility 3. Serous glands that secrete a watery fluid containing antibacterial enzymes (moist & protection )  Air in the alveoli has the body temperature so contains considerably more water vapor than the atmospheric-temperature air During fever and increase RR, water vapor in the lung increase which causing withdrawal of moisture from its mucosal surface == thicken of secretion and diminishing of free cilia movement (can give expectorant) ✓ The functions of larynx -promoting speech (opening and closing of glottis) -protecting lungs from substances other than air during swallowing -the free edges of the epiglottis move downward to cover the larynx thus directing liquids and food into esophagus ✓ Walls of trachea -supported by C-shaped rings of hyaline cartilage which prevent it from collapse when pressure in the thorax become negative ✓ In the bronchioles, -there is no cartilage present and their walls are mainly composed of smooth muscle and elastic fibers The lung and respiratory airways ❑The functions of the lungs include: 1. Gas exchange function 2. Converting angiotensin I into angiotensin II 3. Heparin-producing cells which are abundant in the capillaries of the lung where small clots may be trapped 4. Promote Inactivating of vasoactive substances such as bradykinin  The lobules -are the functional units of the lung -consist of bronchioles (terminal bronchioles), alveoli, and pulmonary capillaries. - Here where gas exchange take place Pleura: a thin, transparent, double-layered serous membrane that encases the lung  Alveolar structure are composed of two types of cells: ✓ Type I; epithelial cells where gas exchange takes place ✓ Type II; produce surfactant: a lipoprotein substances that decrease the surface tension in the alveoli  Surface tension: it is the interface between the liquid film lined the alveoli and alveolar air The alveoli with the smallest radii would have the greatest pressure which cause them to empty into the larger alveoli, but that does not happen. Why??? Because of surfactant ❑Surfactant (largely lipoproteins and small amount of carbohydrates) interrupting the forces that create surface tension by attaching head of surfactant to liquid molecules and tail to the gas molecules ✓ It prevents alveolar collapse ✓ providing for stability and more distribution of ventilation ✓ helps in keeping the alveoli dry ✓ prevent pulmonary edema (with increase surface tension, capillaries pulled more water to the area. ) ❑ Ventilation and the mechanics of breathing The pressure of gas varies inversely with the volume of its container The movement of gases is always from the container with the greater pressure to the one with the lesser pressure During inspiration, the size of the chest cavity increases and the air moves into the lungs The degree to which the lungs inflate and deflate depends on: -the respiratory pressures inflating the lung -compliance of the lungs, -airway resistance ❑ Lung compliance Refers to the ease with which the lungs can be inflated Lug compliance is determined by : -the elastin and collagen fibers of the lung -its water content -the surface tension In lung diseases such as pulmonary fibrosis, the lung become stiff and noncompliance as the elastin fibers are replaced by scar tissue ❑ Lung Volumes Lung volumes can be divided into: ✓ Tidal volume (TV) (500 ml): amount of air that moves into and out of the lung during normal breath ✓ Inspiratory reserve volume (IRV) (3100): the maximum amount of air that can be inspired in excess of the normal TV ✓ Expiratory reserve volume (ERV) (1200): the maximum amount of air that can be exhaled in excess of the normal TV ✓ Residual volume (RV) (1200): amount of air remains in the lungs after forced expiration 19 ❑ Lung Capacities Lung capacities include two or more lung volumes: ✓Vital Capacity (VC) = IRV + TV + ERV ✓Inspiratory Capacity (IC) = IRV + TV ✓Functional residual capacity (FRC) = RV + ERV ✓Total lung capacity = the sum of all the volumes in the lungs ❑ Exchange and transport of gases Pulmonary gas exchange is divided into three processes: ✓ Ventilation ✓ Perfusion ✓ Diffusion Efficiency of gas exchange requires that alveolar ventilation occur adjustment to perfused pulmonary capillaries ❑ Ventilation It is the movement of air between the atmosphere and lung There are two types: ✓Pulmonary ventilation: the total exchange of gases between the atmosphere and lung ✓ Alveolar ventilation: ventilation in the gas exchange portion of the lungs ❑ Perfusion Flow of blood through the pulmonary capillary bed Primary function of pulmonary circulation is to provide blood flow to gas exchange portion Other functions include filtration all blood and remove mot of the thromboemboli that may form Distribution of pulmonary blood flow is affected by body position and gravity ❑ Hypoxia Hypoxia produce marked vasoconstriction in the blood vessels when alveolar oxygen level drop below 60 mmHg There are two types: ✓ Regional hypoxia occurs with a localized airway obstruction; directing blood flow away from the hypoxic regions of the lungs ✓ Generalized hypoxia produce generalized vasoconstriction with person with chronic hypoxia caused by lung disease; lead to pulmonary hypertension and increased workload on right heart ❑ Diffusion Refers to movement of gases in the alveoli and across the alveolar-capillary membrane Is influenced by four factors: -Surface area available for diffusion (removal of one lung decrease diffusion) -Thickness of the alveolar-capillary membrane (pulmonary edema) -Differences in the partial pressure of the gases on either side of the membrane (administration of high conc. of oxygen increase pressure difference between two side and increase diffusion) -Characteristics of gases (molecule weight and solubility) == (CO2 diffuse 20 times more rapidly than O2 because of its great solubility in respiratory membrane )  Matching of ventilation and perfusion The efficiency of gas exchange requires matching of ventilation and perfusion so that equal amounts of gas and blood enter respiratory portion of the lungs Two factors interfere with this matching and do not contribute to gas exchange: 1. Dead air space 2. Shunt ❑Dead air space (alveolar dead space) results from alveoli that are ventilated but not perfused ❑Shunt -results from blood moving through unventilated parts of the lung refers to blood moves from the right to the left side of the circulation without being oxygenated ❑ Oxygen and Carbon Dioxide Transport Blood carries O2 and CO2 as : -dissolved gases -in combination with hemoglobin Arterial blood is used for measuring blood gases: ✓ Normal value of partial pressure of O2 (PO2) is above 80 mmHg ✓ Normal value of PCO2 is between 35 to 45 mmHg Normally, arterial blood gases are the same or nearly the same as the partial pressure of the gases in the alveoli ==increase in alveolar partial of gases reflect an increase in arterial partial pressure of gases ❑Oxygen is transformed in two forms: 1. In chemical combination with hemoglobin (98-99%) 2. Physically dissolved in plasma (PO2) (1-2%) Hemoglobin the main transporter and highly efficient carrier of oxygen and carries about 98 to 99% of oxygen in the blood Hemoglobin saturation is approximately 95 to 97% as the blood leaves the left side of heart; hemoglobin is almost completely saturated with O2 during the short time it spends in pulmonary capillaries  PO2 represents the level of dissolved oxygen in plasma o Although the amount of O2 that carries in this way is small, it can become a lifesaving mode of transport in case of CO2 poisoning when most sites of hemoglobin are occupied by CO2  Carbon Dioxide Transport CO2 is carried in three forms: 1) Attached to hemoglobin (30%) 2) Dissolved CO2 in plasma (10%) 3) As bicarbonate Most of CO2 diffuse into red blood cells where it forms carbonic acid (H2CO3) or combines to hemoglobin CO2 + H2O H2CO3 H+ HCO3-