BISC 307L 1st Edition Lecture 33 Current Lecture Functions of Respiratory System o o blood buffers bicarbonate o respiratory regulation of body pH is much slower than blood buffers but kidneys fastest Lungs and Thoracic Cavity o main body cavity divided into two by the diaphragm upper and lower o Upper is divided into 3 right pleural cavity pericardial cavity and left pleural cavity o Pleural cavity is where the lung sits and is lined with the pleural membranes o In the intrapleural space there is pleural fluid which is a slippery mucus used for breathing and movement prevents friction or damage o Muscles involved in inspirtartion external intercostal muscles diaphragm and scaines and sternociedomastoids o Expiration abdominal muscles and internal intercostal muscles Lung Lobules and Alveoli o o Be familiar with parts larynx to bronchi know are rigid tubes with cartilage o The bronchioles are collapsible with no cartilage but do have smooth muscle open and close with breathing movement can cause bronchiole constriction or dilation o Alveoli gas exchange only occurs here Cluster of grapes 2 types of epithelial cells lining Type 1 flat gas exchange Type 2 thicker secrete mucus containing surfactant to coat inside surrounded by capillaries distance about 0 1 1 5 micrometers from alveolar air to the RBC thin cells Properties of Gases o o o o o Partial pressure of oxygen is about 160mmHg at sea level The pressure of oxygen goes down as you go up in altitude But oxygen is always 21 of whatever the pressure is at that altitude Boyles Law pressure inversely proportional to volume If you change lung volume you will cange the pressure this is important for generating pressure gradients that drive air flow into and out of the lungs Pressure Changes in Quiet Breathing o o measuring the pressure in the alveoli difference between atmospheric pressure and alveolar pressure creates pressure gradient o Intrapleural pressure is the pressure in that tiny space o Time 0 just expired haven t inspired yet no air is going into or out of the system because there is no pressure gradient pressure in the alveolar but the intrapleural pressure is less than the atmospheric pressure so there is a pressure pushing air out of the lung the outside of the lung is stuck Intrapleural pressure is always negative below atmospheric pressure and alveolar pressure Thoracic cavity grows more than the lungs so when the lungs are fully inflated their volume is less than the cavity it occupies The lungs want to pull away from the wall so this is what creates the negative pressure in the intrapleural space o Inspiration diaphragm pushes down volume of the pleural cavity increases and the pressure falls creating a pressure gradient and air come in As it expands the lung expands too but because it is elastic is wants to recoil away from the wall but it cant The more you stretch the lungs the pleural pressure gets even more negative o Transpulmonary pressure alveolar pressure intrapleural pressure It goes up from time 0 to inspiration as the lung gets more stretched How strongly the outside of the lung is attached to the inside of the chest wall o Expiration usually passive exhale by ceasing to inhale because lungs are elastic and want to recoil diaphragm pushed back up Decrease in volume of pleural cavity pressure goes up and air goes out of the lungs As the lungs become less stretched the intrapleural pressure becomes more negative o Pneumothorax Air at atmospheric pressure being introduced to intrapleural space and the intrapleural pressure goes to zero and causes the lung to collapse Physical Properties of Lungs o o Pulmonary fibrosis Various causes due to poor compliance of lung what makes lung compliant is the elastic connective tissue between the alveoli combined with the surface tension this gets replaced with stiff collagen instead of elastin makes breathing very difficult o Elasticity Once you have a change in volume it goes back to former volume Elastin fibers and residual surface tension in alveolar fluid at surface of air water divide this forms surface tension due to hydrogen bonding Also causes alveolus to shrink Surfactants Interfere with surface tension at the sir water divide secreted by alveolar alveoli Reduce the surface tension making it possible for the alveoli to expand Do not reduce it down to zero Total residual surface tension is what contributes to the elasticity of the lung o Law of Laplace What the pressure of the air in the alveolus will be depending on surface tension and radius 2T r twice as much pressure in the one on the right we are wrong in assuming the surface tension is the same AS the alveolus decreases in size the surface tension also decreases there is a given amount of alveolar fluid in each alveoli so as it gets smaller the density of the surfactant molecules goes up making the surface tension less and less The more you inflate the alveoli the surface tension goes upimportant contributor to the elasticity of the lung Failure of surfactant to be secreted in newborns is the number 1 cause of respiratory distress surfactant is developed late in fetal life Diffusion and Solubility of Gases o o gases only move by diffusion o the rate of diffusion is proportional to the area concentration gradient and permeability but inversely so to the membrane thickness o amount of gas in air is determined by pressure but in fluids it is determined by concentration o At equilibrium then the partial pressure of O2 in water partial pressure of O2 in air so we give them both mmHg units o How much oxygen is in there depends on the pressure temperature 9higher the temperature the less gas and the solubility O2 is not very soluble in water CO2 is more so o Fish that need a lot of oxygen live in cold water o Because oxygen is not very soluble the oxygen carried in our blood is not soluble carried by hemoglobin