Respiratory System Goals of respiration are to provide Oxygen to the tissues and to remove carbon dioxide 5-Dec-18 Respiratory System

Four major functions Pulmonary Ventilation Diffusion of oxygen and carbon dioxide between the alveoli and the blood Transport of O2 & CO2 in the Blood and Body Fluids to and from the body tissue cells Regulation of Ventilation 5-Dec-18 Respiratory System

Introduction Animal cells obtain energy by Therefore Oxidative breakdown of nutrients Therefore They must be continually supplied with oxygen Carbon dioxide must be removed 5-Dec-18 Respiratory System

Introduction In lower forms of life In mammals Simple diffusion is adequate In mammals Simple diffusion is not adequate Had to develop specialized system for Oxygen supply Carbon dioxide elimination 5-Dec-18 Respiratory System

Introduction To achieve this they use two systems Respiratory system Cardiovascular system Gas exchanger Fragile barrier between external & internal environment 5-Dec-18 Respiratory System

Introduction Fragile barrier protected against Trauma, dehydration, freezing Fragile membrane imposes Small barrier to gas exchange 5-Dec-18 Respiratory System

Respiratory System Respiration is the term used to include Internal respiration Gas exchange between blood and tissues External respiration Gas exchange between lungs and the atmosphere External respiration is the absorption of O2 from the external environment and the removal of CO2 from the body Internal respiration: utilization of O2 and the production of CO2 by the cells and the gaseous exchange between the cells and fluid medium 5-Dec-18 Respiratory System

Respiration System Respiratory system is made up of Gas exchange organ (lungs) The pump that ventilates the lungs which include Chest wall Respiratory muscles Respiratory center 5-Dec-18 Respiratory System

Respiration System At rest a normal human breathes 12 to 15 times per minute 500 mls of air per breath 6 to 8 liters of air inspired or expired per min 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea Gas exchange organ consists of 2 lungs Each divided into lobes The lungs comprise of 2 tree like structures Vascular tree made up of Arteries and veins Connected by capillaries Pleural space Bronchi Alveoli Diaphragm 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea Airway tree, embedded in elastic connective tissue Pleural space Bronchi Alveoli Diaphragm 5-Dec-18 Respiratory System

Structure of Lungs The trachea is divided into 2 main bronchi Conducting zone 1 The trachea is divided into 2 main bronchi The bronchi divides Many times to form bronchioles Between the trachea and alveolar sac Air ways divides 23 times (23 generations) Bronchi 2 3 4 17 Respiratory bronchiole 18 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea Conducting zone 1 The first 16 generation form Conducting zone of the airways Transport gas between exchange zone & exterior Made up of Bronchi Bronchioles Terminal bronchioles Bronchi 2 3 4 17 Respiratory bronchiole 18 Trachea, bronchi, bronchioles Warm & humidify air Distribute air to the depth of the lungs Part of the body’s defense system Removal of dust, bacteria, noxious gases from lungs 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea Conducting zone 1 The first 3 generations of conducting zone plus the trachea Contain cartilage to prevent airway collapse Bronchi 2 3 4 17 Respiratory bronchiole 18 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea Conducting zone 1 In the bronchioles Cartilage disappears The terminal bronchioles are the smallest airways in the conducting zone The bronchioles and terminal bronchioles are Suspended by elastic tissues in the lung parenchyma Bronchi 2 3 4 17 Respiratory bronchiole 18 The elasticity of the lung tissue help to keep these airways open The conducting zone has its own blood supply Originates from descending aorta Drains into pulmonary vein There is no gas exchange occurring in the conducting zone 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea The remaining 7 generations form the Transitional & respiratory zone Made up of Respiratory bronchioles Alveolar duct Alveoli Gas exchange takes place in this zone Conducting zone 1 Bronchi 2 3 4 17 Respiratory bronchiole 18 The respiratory zone has its own separate and blood supply Receives all the CO Blood flow is very high; low resistance RBC can pass through the capillary in <1 second 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Structure and Functions of Lungs Trachea The multiple divisions Greatly increase the cross sectional area of the airways 2.5 cm2 in the trachea 11,800 cm2 in the alveoli Hence the velocity of airflow Decline to very low values in small airways Conducting zone 1 Bronchi 2 3 4 17 Respiratory bronchiole 18 The respiratory zone has its own separate and blood supply Receives all the CO Blood flow is very high; low resistance RBC can pass through the capillary in <1 second 19 Respiratory zone 20 Alveolar duct 21 22 23 5-Dec-18 Respiratory System

Respiratory Zone Alveoli are Alveolar capillary membrane is Surrounded by pulmonary capillaries Alveolar capillary membrane is Very thin < 0.5 m & comprised of Alveolar epithelium Interstitial fluid Capillary endothelium Branch of pulmonary artery Branch of pulmonary vein Respiratory bronchiole The alveolar capillary membrane Very thin Composed of alveolar membrane, interstitial fluid, capillary endothelium Air is brought to one side of the interface by ventilation Blood is brought to the other side of the interface by the pulmonary circulation Alveolus with capillary network Alveolus (from Hassen Taha Sherrif ) 5-Dec-18 Respiratory System

Respiratory Zone There are 300 millions alveoli in human Total SA of alveolar wall in contact with capillary = 75 m2 (cf skin SA = 1.8 m2) Branch of pulmonary artery Branch of pulmonary vein Respiratory bronchiole Alveolus with capillary network Alveolus (from Hassen Taha Sherrif ) 5-Dec-18 Respiratory System

Alveolar Capillary Membrane Basement membrane Capillary endothelium Made up of Capillary endothelium Single layer endothelial cells Basement membrane Elastic collageneous tissue Alveolar epithelium Single layer epithelial cells Alveolar epithelium Surface lining Diameter of RBC = 7.5 m Alveolar diameter = 300 m Alveolar capillary membrane (0.2 m) 5-Dec-18 Respiratory System

Alveolar Capillary Membrane Basement membrane Capillary endothelium Alveolar capillary membrane thickness can increase if Basement membrane is distended with fluid Pulmonary oedema Fluid accumulates in the alveolar space Alveolar epithelium Surface lining Diameter of RBC = 7.5 m Alveolar diameter = 300 m Alveolar capillary membrane (0.2 m) 5-Dec-18 Respiratory System

Surface Tension Any air – liquid interface develop surface tension When water forms interface with air Water molecules on the surface of the water have strong attraction force for one another Water surface attempt to contract 5-Dec-18 Respiratory System

Surface Tension the lungs are filled with air, this forms an interface between the air and the alveoli Thus the water on the inner side of alveoli tend to contract This causes alveoli to try to collapse The net effect is to cause an elastic contractile force of the entire lungs which is called Surface tension elastic force 5-Dec-18 Respiratory System

Laplace’s law P = (2T)/R In the alveoli P = pressure exerted by surface tension of bubble T = surface Tension R = radius of the bubble (alveolus) In the alveoli During expiration R decreases P increases tendency to collapse increases 5-Dec-18 Respiratory System

Surfactant and its effect on surface tension Is a surface active agent in water which greatly reduces surface tension Synthesized by type II alveolar cells (granular pneumonocytes) It is a complex mixture of Phospholipids (Dipalmitoylphosphatidylcholine) Proteins (surfactant apoproteins) Calcium ions 5-Dec-18 Respiratory System

Surfactant Phospholipids Responsible for reducing the surface tension Does not dissolve uniformly in the water lining the alveolar surface One portion of molecule is hydrophilic Dissolves in water The other portion is hydrophobic Oriented towards air 5-Dec-18 Respiratory System

Surfactant Thus a hydrophobic surface is exposed to the air Has a much lower ST The amount of reduction of ST by surfactant Proportional to concentration of surfactant on the surface 5-Dec-18 Respiratory System

Surfactant During inspiration Volume of alveolar space increases With fixed amount of surfactant Conc of surfactant on surface decreases Increases ST Prevent further increase in surface of alveoli 5-Dec-18 Respiratory System

Surfactant During expiration Volume of alveolar space decreases Conc of surfactant on the surface increases Decreases ST Decrease the tendency to collapse 5-Dec-18 Respiratory System

Surfactant Thus Stabilizing the alveoli against tendency to collapse Diminish the force required for expansion of the lung Reduces the work of breathing 5-Dec-18 Respiratory System