Respiratory System Physiology “Breathing”

Pulmonary Ventilation Inspiration- in Expiration- out Breathing occurs because of a pressure gradient between the lungs and exterior environment Respiratory muscles control the size of the thoracic cavity setting up the gradient

Inspiration When the diaphragm contracts it increases size of thoracic cavity Intercostal muscles aid in expanding size of rib cage

Expiration Is aided by elastic recoil, tendency of thorax and lungs to return to shape When muscles relax it causes a decrease in size of thorax Compliance is the ability of lungs to relax or stretch

Breathing Patterns Eupnea- normal quiet breathing Hyperpnea- increased breathing rate and depth to meet need for O2 Hyperventilation- increased breathing rate and depth with out need for O2 Hypoventilation- slowed breathing Dyspnea- difficult labored breathing Apnea- cessation of breathing

Exchange of Gases O2 and CO2 move across pressure gradients from the atmosphere into the lungs Alveolar and capillary surface area is extremely large with thin walls Capillaries in lungs have a diameter one cell thick

Transport of O2 Hemoglobin greatly increases the amount of O2 that can be dissolved in the blood

Transport of CO2 A small amount of CO2 binds amino acid groups onto hemoglobin Most of the CO2 in blood associates with H2O to form carbonic acid H2CO3 (bicarbonate) H2CO3 once catalyzed by carbohydrate anhydrase (enzyme) dissociates into H+ and HCO3- Increased CO2 in the blood causes a decrease in blood pH/increase in acidity

Systemic Gas Exchange As oxygenated blood enters tissues it has high Po2 and low Pco2 relative to the tissue O2 is pulled off the hemoglobin and CO2 binds temporary to hemoglobin to form carbaminohemoglobin

Respiratory Control Centers Ventilation is the rate and depth of breathing Ventilation is controlled by the medullary rhythmicity centers of the brain The apneustic center stimulates the inspiratory center thus increasing respiration The pneumotaxic center inhibits the apneustic center in the brain

Factors that influence Breathing Chemoreceptors in the medulla measure levels of CO2 Low levels of CO2 will decrease rate and depth of breathing High levels of CO2 increase rate and depth of breathing pH plays a small role in controlling breath Blood levels of O2 seem to have little effect on breathing rate

Breathing Reflexes Hering-Breuer reflex maintains normal breath depth Once tidal volume is reached, inhalation stretch receptors trigger inhibitory impulses to the inspiratory centers of the brain

Breathing Reflexes Breathing can be controlled voluntarily to a certain extent You cannot hold your breath till you die, CO2 is too strong a stimulant Sudden stimulation - reflex apnea Sudden cold stimuli - reflex apnea Stimulation of pharynx or larynx causes choking reflex Breathing can be affected by emotions

Breathing Reflexes Cough reflex- caused by stimulation Sneeze reflex- air is forced out nose and mouth(100 mph) Hiccup- caused by a spasm of diaphragm Yawn- slow and deep breath with similar function to a stretch