Respiratory System Physiology

Physiology of The Respiratory System FOR STUDENTS IN COLLEGE OF PHARMACY

2009-2010

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Respiration Ventilation: Movement of air into

and out of lungs External respiration: Gas exchange between air in lungs and blood Transport of oxygen and carbon dioxide in the blood Internal respiration: Gas exchange between the blood and tissues

Respiratory System Functions Gas exchange: Oxygen enters blood

and carbon dioxide leaves Regulation of blood pH: Altered by changing blood carbon dioxide levels Voice production: Movement of air past vocal folds makes sound and speech Olfaction: Smell occurs when airborne molecules drawn into nasal cavity Protection: Against microorganisms by preventing entry and removing them

Respiratory System Divisions Upper tract Nose, pharynx and associated structures Lower tract Larynx, trachea, bronchi, lungs 

Nose and Pharynx Pharynx

Nose External nose Nasal cavity Functions

1.Passageway for air 2.Cleans the air 3.Humidifies, warms air 4.Smell 5.Along with paranasal sinuses are resonating chambers

Common opening

for digestive and respiratory systems Three regions  Nasopharynx  Oropharynx  Laryngopharynx

Larynx Functions 1.Maintain an open passageway for air movement 2.Epiglottis and vestibular folds prevent swallowed material from moving into larynx 3.Vocal folds are primary source of

Tracheobronchial Tree Conducting zone

1.Trachea to terminal bronchioles which is ciliated for removal of debris 2.Passageway for air movement 3.Cartilage holds tube system open and smooth muscle controls tube diameter Respiratory zone

1.Respiratory bronchioles to alveoli 2.Site for gas exchange

Lungs

Two lungs:

Principal organs of respiration Right lung:

Three lobes Left lung: Two lobes

Divisions Lobes, bronchopulm onary segments, lobules

Pleura Pleural fluid

produced by pleural membranes

Acts as lubricant Helps hold parietal

and visceral pleural membranes

Ventilation Movement of air into and

out of lungs Air moves from area of higher pressure to area of lower pressure Pressure is inversely related to volume

Changing Alveolar Volume Lung recoil Causes alveoli to collapse resulting from  Elastic recoil and surface tension  Surfactant: Reduces tendency of lungs to collapse

Pleural pressure Negative pressure can cause alveoli to

expand Pneumothorax is an opening between pleural cavity and air that causes a loss of pleural pressure

Normal Breathing Cycle

Compliance Measure of the ease with which lungs

and thorax expand The greater the compliance, the easier it is for a change in pressure to cause expansion A lower-than-normal compliance means the lungs and thorax are harder to expand Conditions that decrease compliance Pulmonary

fibrosis Pulmonary edema Respiratory distress syndrome

Pulmonary Volumes Tidal volume Volume of air inspired or expired during a normal inspiration or expiration Inspiratory reserve volume Amount of air inspired forcefully after inspiration of normal tidal volume Expiratory reserve volume Amount of air forcefully expired after expiration of normal tidal volume Residual volume Volume of air remaining in respiratory passages and lungs after the most forceful expiration

Pulmonary Capacities Inspiratory capacity Tidal volume plus inspiratory reserve volume Functional residual capacity Expiratory reserve volume plus the residual volume Vital capacity Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume Total lung capacity Sum of inspiratory and expiratory reserve volumes plus the tidal volume and residual volume

Spirometer and Lung Volumes/Capacities

Minute and Alveolar Ventilation Minute ventilation: Total amount of air

moved into and out of respiratory system per minute Respiratory rate or frequency: Number of breaths taken per minute Anatomic dead space: Part of respiratory system where gas exchange does not take place Alveolar ventilation: How much air per minute enters the parts of the respiratory system in which gas exchange takes place

Physical Principles of Gas Exchange Partial pressure The pressure exerted by each type of gas in

a mixture Dalton’s law Water vapor pressure Diffusion of gases through liquids Concentration of a gas in a liquid is

determined by its partial pressure and its solubility coefficient Henry’s law 

Physical Principles of Gas Exchange Diffusion of gases through the respiratory

membrane

Depends on membrane’s thickness, the

diffusion coefficient of gas, surface areas of membrane, partial pressure of gases in alveoli and blood

Relationship between ventilation and

pulmonary capillary flow

Increased ventilation or increased

pulmonary capillary blood flow increases gas exchange Physiologic shunt is deoxygenated blood returning from lungs

Oxygen and Carbon Dioxide Diffusion Gradients Oxygen Moves from alveoli into blood. Blood is almost completely saturated with oxygen when it leaves the capillary P02 in blood decreases because of mixing with deoxygenated blood Oxygen moves from

Carbon dioxide Moves from

tissues into tissue capillaries Moves from pulmonary capillaries into the alveoli

Hemoglobin and Oxygen Transport Oxygen is transported by hemoglobin

(98.5%) and is dissolved in plasma (1.5%) Oxygen-hemoglobin dissociation curve shows that hemoglobin is almost completely saturated when P02is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen. A shift of the curve to the left because of an increase in pH, a decrease in carbon dioxide, or a decrease in temperature

Hemoglobin and Oxygen Transport A shift of the curve to the right because

of a decrease in pH, an increase in carbon dioxide, or an increase in temperature results in a decrease in the ability of hemoglobin to hold oxygen The substance 2.3-bisphosphoglycerate increases the ability of hemoglobin to release oxygen Fetal hemoglobin has a higher affinity for oxygen than does maternal

Oxygen-Hemoglobin Dissociation Curve at Rest

Bohr effect

Temperature effects

Shifting the Curve

Transport of Carbon Dioxide Carbon dioxide is transported as

bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%) Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect) In tissue capillaries, carbon dioxide combines with water inside RBCs to form carbonic acid which dissociates to form bicarbonate ions and hydrogen

Transport of Carbon Dioxide In lung capillaries, bicarbonate ions and

hydrogen ions move into RBCs and chloride ions move out. Bicarbonate ions combine with hydrogen ions to form carbonic acid. The carbonic acid is converted to carbon dioxide and water. The carbon dioxide diffuses out of the RBCs. Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels

Respiratory Areas in Brainstem Medullary respiratory center Dorsal groups stimulate the

diaphragm Ventral groups stimulate the intercostal and abdominal muscles Pontine (pneumotaxic) respiratory group Involved with switching between inspiration and expiration

Modification of Ventilation Cerebral and limbic

system

Respiration can be

voluntarily controlled and modified by emotions

Chemical control Carbon dioxide is

major regulator  Increase or

decrease in pH can stimulate chemo- sensitive area, causing a greater rate and depth of respiration

Oxygen levels in

blood affect respiration when a 50% or greater decrease from

Modifying Respiration

Herring-Breuer Reflex Limits the degree of inspiration and

prevents overinflation of the lungs Infants Reflex plays a role in regulating

basic rhythm of breathing and preventing overinflation of lungs

Adults Reflex important only when tidal volume large as in exercise

Ventilation in Exercise Ventilation increases abruptly At onset of exercise Movement of limbs has strong

influence Learned component Ventilation increases gradually After immediate increase, gradual increase occurs (4-6 minutes) Anaerobic threshold is highest level of exercise without causing significant change in blood pH If exceeded, lactic acid produced by

Effects of Aging Vital capacity and maximum minute

ventilation decrease Residual volume and dead space increase Ability to remove mucus from respiratory passageways decreases Gas exchange across respiratory membrane is reduced