Respiratory Physiology
#AnimalPhysio2015
•
What is respiration?
–
Respiration = the series
of exchanges that leads
to the uptake of oxygen
by the cells, and the
release of carbon
dioxide to the lungs
Step 1 = ventilation
–
Inspiration &
expiration
Step 2 = exchange
between alveoli
(lungs) and
pulmonary
capillaries (blood)
–
Referred to as
External
Respiration
Step 3 = transport of
gases in blood
Step 4 = exchange
between blood and
cells
–
–
Cough
Sneeze
Sound
Referred to as
Internal
Respiration
Cellular respiration =
use of oxygen in ATP
synthesis
Pulmonary circulation
Schematic View of Respiration
Basics of the Respiratory System
General Functions
• Exchange of gases
• Directionality depends on gradients!
– Atmosphere to blood
– Blood to tissues
• Regulation of pH
– Dependent on rate of CO2 release
• Protection
• Vocalization
• Synthesis
Basics of the Respiratory System
Control of Respiration
• Respiratory neurons in brain stem
– sets basic drive of ventilation
– descending neural traffic to spinal cord
– activation of muscles of respiration
• Ventilation of alveoli coupled with perfusion
of pulmonary capillaries
• Exchange of oxygen and carbon dioxide
Basics of the Respiratory System
Control of Respiration
Respiratory Control System
Cerebral Cortex
Mechanoreceptors
Respiratory center-Medulla
Chemoreceptors
Nerve Impulses
Spinal Cord
Force,
displacement
Nerve Impulses
Respiratory Muscles
Lung & Chest Wall
Ventilation
Respiratory membrance
Diffusion
Perfusion-----> Blood
Pco2, Po2, pH
Basics of the Respiratory System
Respiratory centers
• Located in brain stem
– Dorsal & Ventral Medullary group
– Pneumotaxic & Apneustic centers
• Affect rate and depth of ventilation
• Influenced by:
– higher brain centers
– peripheral mechanoreceptors
– peripheral & central chemoreceptors
Basics of the Respiratory System
Muscles of Ventilation
• Inspiratory muscles– increase thoracic cage volume
• Diaphragm, External Intercostals, SCM,
• Ant & Post. Sup. Serratus, Scaleni, Levator Costarum
• Expiratory muscles– decrease thoracic cage volume
• Abdominals, Internal Intercostals, Post Inf. Serratus,
Transverse Thoracis, Pyramidal
Basics of the Respiratory System
Ventilation-Inspiration
• Muscles of Inspiration-when contract
 thoracic cage volume
– diaphragm
• drops floor of thoracic cage
– external intercostals
– sternocleidomastoid
– anterior serratus
– scaleni
– serratus posterior superior
– levator costarum
– (all of the above except diaphragm lift rib cage)
Ventilation-expiration
• Muscles of expiration when contract pull
rib cage down  thoracic cage volume
(forced expiration
•
•
•
•
•
•
•
rectus abdominus
external and internal obliques
transverse abdominis
internal intercostals
serratus posterior inferior
transversus thoracis
pyramidal
– Under resting conditions expiration is passive
and is associated with recoil of the lungs
Movement of air in/out of lungs
• Considerations
– Pleural pressure
• negative pressure between parietal and visceral
pleura that keeps lung inflated against chest wall
• varies between -5 and -7.5 cmH2O (inspiration to
expiration
– Alveolar pressure
• subatmospheric during inspiration
• supra-atmospheric during expiration
– Transpulmonary pressure
• difference between alveolar P & pleural P
• measure of the recoil tendency of the lung
• peaks at the end of inspiration
Basics of the Respiratory System
Functional Anatomy
• What structural aspects must be considered in the process of
respiration?
– The conduction portion
– The exchange portion
– The structures involved with
ventilation
• Skeletal & musculature
• Pleural membranes
• Neural pathways
• All divided into
– Upper respiratory tract
• Entrance to larynx
– Lower respiratory tract
• Larynx to alveoli (trachea
to lungs)
Basics of the Respiratory System
Functional Anatomy
• Bones, Muscles & Membranes
Basics of the Respiratory System
Functional Anatomy
• Function of these Bones, Muscles & Membranes
– Create and transmit a pressure gradient
• Relying on
– the attachments of the
muscles to the ribs
(and overlying tissues)
– The attachment of the
diaphragm to the base
of the lungs and associated
pleural membranes
– The cohesion of the parietal
pleural membrane to the
visceral pleural membrane
– Expansion & recoil of the lung
and therefore alveoli with the
movement of the overlying
structures
Basics of the Respiratory System
Functional Anatomy
• What is the function of the upper respiratory
Raises
tract?
– Warm
– Humidify
– Filter
– Vocalize
incoming air to
37 Celsius
Raises
incoming air to
100% humidity
Forms
mucociliary
escalator
Basics of the Respiratory System
Functional Anatomy
• What is the function of the lower respiratory tract?
– Exchange of gases …. Due to
• Huge surface area = 1x105 m2 of type I alveolar cells (simple
squamous epithelium)
• Associated network of pulmonary capillaries
– 80-90% of the space between alveoli is filled with blood in
pulmonary capillary networks
• Exchange distance is approx 1 um from alveoli to blood!
– Protection
• Free alveolar macrophages (dust cells)
• Surfactant produced by type II alveolar cells (septal cells)
Basics of the Respiratory System
Functional Anatomy
• Characteristics of exchange membrane
– High volume of blood through huge capillary
network results in
• Fast circulation through lungs
– Pulmonary circulation = 5L/min through lungs….
– Systemic circulation = 5L/min through entire body!
• Blood pressure is low…
– Means
» Filtration is not a main theme here, we do not want a net
loss of fluid into the lungs as rapidly as the systemic
tissues
» Any excess fluid is still returned via lymphatic system
Basics of the Respiratory System
Functional Anatomy
• Sum-up of functional anatomy
– Ventilation?
– Exchange?
– Vocalization?
– Protection?
Effect of Thoracic Cage on Lung
• Reduces compliance by about 1/2 around
functional residual capacity (at the end of a
normal expiration)
• Compliance greatly reduced at high or low
lung volumes
Work of Breathing
• Compliance work (elastic work)
– Accounts for most of the work normally
• Tissue resistance work
– viscosity of chest wall and lung
• Airway resistance work
• Energy required for ventilation
– 3-5% of total body energy
Patterns of Breathing
• Eupnea
– normal breathing (12-17 B/min, 500-600 ml/B)
• Hyperpnea
–  pulmonary ventilation matching  metabolic
demand
• Hyperventilation ( CO2)
–  pulmonary ventilation > metabolic demand
• Hypoventilation ( CO2)
–  pulmonary ventilation < metabolic demand
Patterns of breathing (cont.)
• Tachypnea
–  frequency of respiratory rate
• Apnea
– Absense of breathing. e.g. Sleep apnea
• Dyspnea
– Difficult or labored breathing
• Orthopnea
– Dyspnea when recumbent, relieved when
upright. e.g. congestive heart failure, asthma,
lung failure
Pleural Pressure
• Lungs have a natural tendency to collapse
– surface tension forces 2/3
– elastic fibers 1/3
• What keeps lungs against the chest wall?
– Held against the chest wall by negative pleural
pressure “suction”
Collapse of the lungs
• If the pleural space communicates with the
atmosphere, i.e. pleural P = atmospheric P the lung
will collapse
• Causes
– Puncture of the parietal pleura
• Sucking chest wound
– Erosion of visceral pleura
– Also if a major airway is blocked the air trapped distal to
the block will be absorbed by the blood and that segment
of the lung will collapse
Pleural Fluid
• Thin layer of mucoid fluid
– provides lubrication
– transudate (interstitial fluid + protein)
– total amount is only a few ml’s
• Excess is removed by lymphatics
– mediastinum
– superior surface of diaphragm
– lateral surfaces of parietal pleural
– helps create negative pleural pressure
Pleural Effusion
• Collection of large amounts of free fluid in
pleural space
• Edema of pleural cavity
• Possible causes:
– blockage of lymphatic drainage
– cardiac failure-increased capillary filtration P
– reduced plasma colloid osmotic pressure
– infection/inflammation of pleural surfaces which
breaks down capillary membranes
Surfactant
• Reduces surface tension forces by forming a
monomolecular layer between aqueous fluid
lining alveoli and air, preventing a water-air
interface
• Produced by type II alveolar epithelial cells
• complex mix-phospholipids, proteins, ions
– dipalmitoyl lecithin, surfactant apoproteins, Ca++
ions
Static Lung Volumes
• Tidal Volume (500ml)
– amount of air moved in or out each breath
• Inspiratory Reserve Volume (3000ml)
– maximum vol. one can inspire above normal
inspiration
• Expiratory Reserve Volume (1100ml)
– maximum vol. one can expire below normal
expiration
• Residual Volume (1200 ml)
– volume of air left in the lungs after maximum
expiratory effort
Static Lung Capacities
• Functional residual capacity (RV+ERV)
– vol. of air left in the lungs after a normal expir.,
balance point of lung recoil & chest wall forces
• Inspiratory capacity (TV+IRV)
– max. vol. one can inspire during an insp effort
• Vital capacity (IRV+TV+ERV)
– max. vol. one can exchange in a resp. cycle
• Total lung capacity (IRV+TV+ERV+RV)
– the air in the lungs at full inflation
Pulmonary Flow Rates
• Compromised with obstructive conditions
– decreased air flow
• minute respiratory volume
– RR X TV
• Forced Expiratory Volumes (timed)
– FEV/VC
• Peak expiratory Flow
• Maximum Ventilatory Volume
Airways in lung
• 20 generations of branching
– Trachea (2 cm2)
– Bronchi
• first 11 generations of branching
– Bronchioles (lack cartilage)
• Next 5 generations of branching
– Respiratory bronchioles
• Last 4 generations of branching
– Alveolar ducts give rise to alveolar sacs which
give rise to alveoli
• 300 million with surface area 50-100 M2
Dead Space
• Area where gas exchange cannot occur
• Includes most of airway volume
• Anatomical dead space (=150 ml)
– Airways
• Physiological dead space
– = anatomical + non functional alveoli
• Calculated using a pure O2 inspiration and
measuring nitrogen in expired air (fig 37-7)
– % area X Ve
Alveolar Volume
• Alveolar volume (2150 ml) = FRC (2300 ml)dead space (150 ml)
• At the end of a normal expiration most of the
FRC is at the level of the alveoli
• Slow turnover of alveolar air (6-7 breaths)
• Rate of alveolar ventilation
– Va = RR (Vt-Vd)