The Respiratory System

Respiratory System Functions Pulmonary ventilation movement of air into and out of lungs “breathing” External respiration movement of O2 and CO2 between blood and lungs Transport of respiratory gases transport of O2 and CO2 between tissue and lungs Internal respiration movement of O2 and CO2 between blood and tissue Olfaction

Respiratory System Upper respiratory system Lower respiratory system Conducting Zone Respiratory Zone Respiratory mucosa Respiratory defense system (adaptive or innate?)

Upper Respiratory External nares Nasal cavity Warm, moisten & filter air (Nasal conchae, surface area) Detect smell (olfactory epithelium) Modifying sounds by resonance Pharynx both respiratory & digestive pathway

Larynx Provide an open airway to route air and food properly Produce a voice

Sound Production Phonation Articulation

Trachea “windpipe” Lined in mucosa with cilia that propel debris laden mucus to the pharynx (destroyed by smoking, use coughing instead)

Lungs

Lungs Lobes Superior, middle, inferior Superior, inferior Oblique fissures Cardiac notch

Bronchial Tree Primary bronchi Secondary bronchi Tertiary bronchi Bronchopulmonary segment Bronchioles Bronchodilation Bronchoconstrction Terminal bronchiole

Pulmonary lobule Lymph vessel, arteriole, and venule Respiratory bronchioles

Alveoli Alveolar duct Alveolar sacs Alveoli Capillaries Elastic tissue

Alveoli Type I alveolar cells Alveolar macrophage Type II alveolar cells (septal cells) Surfactant Surface tension Respiratory distress syndrome (RDS) Type I alveolar cells – simple single layer of thin squamous epithelium that line the alveoli Alveolar macrophage (dust cells) – use ameboid motion to move around over the epithelial surface – they use phagocytosis to absorb any pathogens or dust that might have gotten into the lungs Septal cells – aka type II cells – cuboidal epithelial cells that produce an surfactant (phosopholipids and lipoproteins) Secretes alveolar fluid which contains surfactant which are secreted into the alveoli forming a superficial coating over a thin layer of water Reduces surface tension Surface tension = force of attraction between water molecules (polar molecules) at an air-liquid boundary Draws liquid molecules close together Resists forces that try to increase surface area of the liquid Deep breaths stimulate the septal cells to release surfactant Why a water strider can “walk” on water, why water beads up on a surface ST of water exerts an inward pressure which keeps the alveoli small. The air coming into the lungs counteracts that pressure. Since the walls of the alveoli are thin, they will collapse due to the surface tension on the water Surfactant interferes with polar bonds of water molecules to decrease the surface tension. Example is what soap can do to a bead of water. Pressure greater in small alveoli than large ones and can become so great they can collapse This inward force exerted by surface tension of water helps to force air out of your lungs when you exhale, but as the alveoli get smaller with exhalation, they would collapse Even if they didn’t collapse, if they were lined with water, they would require a lot of force to reinflate them. Surfactant molecules get in between the water molecules to decrease the attraction between them and REDUCES surface tension Respiratory distress syndrome – if you don’t produce enough surfactant, you have to use a lot more force to overcome the inward pressure produced by surface tension to inflate the lungs This is a serious problem in premature births. Oxygen has to be delivered using positive airpressure or surfactant is administered directly to lungs.

Respiratory Physiology Pulmonary ventilation “breathing” Inhalation Exhalation External (pulmonary) respiration Internal (tissue) respiration Problems Hypoxia Ventilation-perfusion coupling Anoxia

Respiratory Gas Laws

Boyle’s Law: P=1/V

Inhalation (inspiration) Requires changes in air pressure. At sea level air pressure is 1 atmosphere (atm) or 760mmHg. During inhalation pressure must drop below 1 atm. Gas particles move from an area of high pressure to an area of low pressure (diffusion). Increasing the volume of a quantity of gas leads to a drop in pressure—an inverse relationship.

Respiration Pressure measurements Atmospheres (atm)  pressure at sea level 760mm Hg / torr = 1atm 1033.6cm H20 = 1 atm 15 PSI = 1 atm

Respiration Atmospheric pressure Intrapulmonary pressure Intrapleural pressure

Muscles of inspiration Diaphragm External intercostals During forceful breathing Sternocleidomastoid Scalenes Pectoralis minor

Muscles of expiration Relaxation of inspiratory muscles During forceful expiration Internal intercostals Abdominals

Respiratory Volumes Tidal Volume  each breath. Inspiratory Capacity  biggest inhale Expiratory Reserve  biggest exhale Vital Capacity  maximum volume Residual Volume air left after exhale VD anatomical dead space

Respiratory Capacities TLC VC IC FRC

Spirogram of lung volumes

Inhalation and exhalation summary

Other factors affecting ventilation Compliance Elasticity Surface tension Thoracic mobility Airway resistance Airway diameter Contraction and relaxation of smooth muscles ANS input Greatest resistance is in medium bronchi Obstruction or collapse of airways

Gas exchange: Dalton’s Law Dalton’s law—each gas exerts its own pressure Atm=PN2+PO2+PH2O+PCO2+Pother gases Inhaled air PO2 = 159 mmHg PCO2= 0.3 mmHg Alveolar air PO2 = 105 mmHg PCO2= 40 mmHg Exhaled air is a mixture of inhaled and alveolar air

Gas exchange: Henry’s Law Henry’s law—the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas AND the solubility each gas. CO2 is 20X more soluble than O2

Gas Exchange Partial pressure differences Small distance Molecular weight and solubility of gases Large surface area Coordinated blood- and airflow

Ventilation-perfusion coupling Necessary for efficient gas exchange Ventilationthe amount of gas reaching the alveoli Perfusion blood flow in the capillaries

Oxygen transport Red blood cells Hb + O2 « HbO2 Hemoglobin saturation and affinity PO2 of blood Blood pH PCO2 of blood Temperature Metabolism in RBC’s

Hemoglobin and PO2 Oxygen-hemoglobin saturation curve Shape of Hb changes as O2 binds Cooperativity Oxygen reserve Oxygen “bars” Carbon monoxide

Hemoglobin and pH Normal blood—pH = 7.4 Active tissues are acidic Bohr Effect interaction between hemoglobin's affinity for oxygen and its affinity for hydrogen ions

Hemaglobin and PCO2 CO2 + H2O « H2CO3 « H+ + HCO3-

Hemaglobin and Temperature Normal blood has temperature = 37ºC Active tissues have higher temps

Hemaglobin and BPG Biphosphoglycerate (BPG) found in RBCs decreases the affinity of Hb for O2 Glycolysis produces lactic acid and BPG BPG binds reversibly to Hb and is required for Hb to release O2

Fetal Hemoglobin Higher affinity for O2 than adult Hb

CO2 Transport Dissolved CO2 Carbamino compounds Bicarbonate ions Carbaminohemoglobin Bicarbonate ions CO2 + H2O « H2CO3 « H+ + HCO3- Chloride shift Haldane effect

Summary

Haldane effect O2 effects on CO2 transport in blood

Nervous Control Respiratory center Medullary rhythmicity area Ventral respiratory group responsible for pattern generation of breathing Pontine respiratory group (Pneumotaxic area)

Chemical Control PCO2 PO2

Respiratory Reflexes Chemoreceptors Central Peripheral Aortic and carotid bodies Hypercapnia Involuntary hyperventilation Hypocapnia Voluntary hyperventilation

Homeostatic Imbalances Rhinitis Hyperventilation Hyperapnea COPD Dyspnea Emphysema Bronchitis Asthma TB Lung Cancer Cystic Fibrosis

Resources Interactive Respiratory Physiology Function of the Respiratory System