Unit 8 - Respiratory Physiology Flashcards
Respiration
obtain O2 for use by body’s cells and to eliminate CO2
Two separate but related processes
Internal respiration(cellular respiration, intracellular metabolic processes) external respiration
External respiration
Breathing
Exchange of O2 and CO2 between air in alveoli and blood within the pulmonary capillaries
Transport of gases by the blood between lungs and tissue exchange of O2 and CO2 between tissues and blood
Getting smaller and smaller
tubes carry air between the atmosphere and alveoli
nasal passages -> pharynx -> trachea -> right and left bronchi to lungs-> lobar branches-> 2 respiratory bronchioles -> several alveoli for gas exchange
Structures of the pulmonary system
trachea, segmental bronchi, bronchioles, alveolar ducts
Trachea windpipe and larger bronchi
Non-muscular tubes with rings of cartilage preventing collapse
Bronchioles
no cartilage to hold them open
walls contain smooth muscle innervated by autonomic nervous system
alveoli
thin-walled inflatable sacs that function in gas exchange
walls consist of a single layer type I alveolar cells
pulmonary capillaries encircle each alveolus
epithelium contains type II alveolar cells (secrete pulmonary surfactant phospholipid)
lowers alveolar surface tension (increases pulmonary compliance, allows alveoli of different sizes to exist and remain open)
alveoli
alveolar macrophages guard lumen
pores of kohn permot airflow between adjacent alveoli collateral ventilation
the chest wall
outer chest wall thorax
12 pairs of ribs join sternum anteriorly and thoracic vertebrae posteriorly
protects lungs and heart
contains muscles that generate the pressure that causes airflow
pleural space
double-walled, closed sac separates each lung from thoracic wall
visceral(inner) layer covers lungs
parietal(outer) layer attached to chest wall
pleural cavity - interior of pleural sac
intrapleural fluid - secreted by surfaces of the pleura, lubricates pleural surfaces
respiratory mechanics
relationships among pressures inside and outside lungs important in ventilation
4 pressures
atmospheric/barometric pressure(Pb)
760mmHg
pressure exerted by weight of air in atmosphere on earths objects
Alveolar or intra-alveolar pressure(Palv)
pressure inside the alveolus
760mmHg when not breathing
negative (less than atmospheric) during inspiration and positive during expiration
Pleural or Intrapleural pressure (Pip)
pressure in pleural space
intra-pleural pressure= 756 (-4)
Transpulmonary/recoil pressure (Ptp=Palv-Pip)
pressure difference between alveolar pressure and pleural pressure
negative due to properties of lung and chest wall
lungs want to collapse
chest wall wants to expand
positive so keeps lungs and alveoli open
Step 1. Pulmonary ventilation main inspiratory muscles
external intercostal muscles(innervated by intercostal nerves)
diaphragm (dome-shaped sheet of skeletal muscle separates thoracic cavity from abdominal, innervated by phrenic nerve
accessory muscles
Expiratory muscles
expiration begins with relaxation of inspiratory muscles
relaxation of diaphragm and muscles of chest wall, plus the elastic recoil of the alveoli, decrease the size of the chest cavity
lungs are compressed intra-alveolar pressure increases
when pressure increases to level above atmospheric pressure, air is driven out - expiration occurs
factors influencing ventilation elastic recoil
how readily the lungs rebound after having been stretched
responsible for lungs returning to their pre-inspiratory volume when inspiratory muscles relax at end of inspiration
Factors influencing ventilation elastic recoil depends on two factors
Highly elastic connective tissue in the lungs
alveolar surface tension (thin liquid film lines each alveolus, reduces tendency of alveoli to recoil)
pulmonary surfactant(lipoprotein molecules secreted by type II alveolar cells, lowers alveolar surface tension)
(increases pulmonary compliance, reduces recoil presure of smaller alveoli, small and larger alveoli can co-exist, helps maintain lung stability)
factors influencing ventilation compliance
ability of lungs to stretch and expand
the less compliant the lungs are, more work required to produce a given degree of inflation
when compliance is high, lung is pliable and low elastic recoil
when compliance is low, lung is stiff and high elastic recoil
Air flow rate (F) depends on
difference between atmospheric and intra-alveolar pressure and the resistance of airways to airflow(R)
F = DeltaP/R
Controls contraction of smooth muscle in walls of bronchioles
ANS
During low O2 demands
PNS dominates when ventilatory demands are low
vagus nerve secretes Ach -> stimulates bronchiolar smooth -> decreases airways radii (bronchoconstriction)
High O2 demands
SNS dominates when ventilatory demand is increased
norepinephrine and epinephrine from adrenal medulla -> stimulates B2 receptors on bronchial smooth muscles -> increase airway radii (bronchodilation)
Pulmonary volumes and capacities
lung volume changes with different respiratory efforts
recorded by spirometer
forced expiratory volume in one second (volume of air that can be expired during 1st second of expiration)
Tidal volume (TV)
volume of air entering or leaving lungs during a single breath 500ml
inspiratory reserve volume (IRV)
extra volume of air that can be maximally inspired over and above the typical resting tidal volume 3000ml
Inspiratory capacity (IC)
Maximun volume of air that can be inspired at the end of a normal quiet expiration (IC=IRV + IV) 3500ml
Expiratory reserve volume (ERV)
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume 1000ml
Residual volume (RV)
Minimum volume of air remaining in the lungs even after a maximal expiration 1200ml
Functional residual capacity (FRC)
volume of air in lungs at end of normal passive expiration (FRC = ERV + RV) 2200ml
Vital capacity (VC)
Maximum volume of air that can be moved out during a single breath following a maximal inspiration (VC = IRV + TV + ERV) 4500ml
Total lung capacity (TLC)
Maximum volume of air that the lungs can hold (TLC = VC + RV) 5700ml
Forced expiratory volume in one second (FEV1)
Percentage of air expired during the first second of expiration >80%
Minute (Pulmonary) Ventilation
Volume of air breathed in and out in 1 minute
=Tidal volume X respiratory rate
= 500ml/breath X 12 breaths/min
= 6000ml/min
Anatomic dead space
not all lung tissues used for gas exchange not all air gets to alveoli; remains in conducting airways TV = 500ml but only 350 ml reach alveoli Alveolar ventilation = (TV - DPV) X respiratory rate = (500 - 150) X 12 breaths/min = 350 X 12 = 4200ml/min
the two steps in respiration
ventilation and perfusion
ventilation(V)
movement of air into alveoli
Perfusion(Q)
exchange of O2 and CO2
affected by body position due to gravity
minimal blood flow in apices of upright lung
maximal infusion into lung bases (25% of vessels perfused)
Ventilation-perfusion (V/Q) ratio
for adequate gas exchange between air in alveoli and blood in pulmonary capillaries need V and Q to match.
ensure air is delivered to lung regions where blood is going and vice versa.
Normal ratio of V/Q is 0.8 (4/5L)
affected by disorders in ventilation, perfusion or both
matching of air and blood
air in alveoli must patch blood in capillary
alveolar dead space + anatomic dead space = physiological dead space
shunts
some alveoli are perfused but not ventilated
alveolar dead space
some alveoli are ventilated but not perfused
small in healthy lungs
Step 2
exchange of O2 and CO2 between air in alveoli and blood in pulmonary capillaries
step 4
exchange of O2 and CO2 between cells and blood
Exchange in steps 2 and 4 takes place by
process of simple diffusion
down the partial pressure gradient
Step 3
transport of gases by the blood between lungs and cells
Diffusion of gases depends on
partial pressure of gas across membrane
resistance to diffusion of gas across membrane
Factors that affect the rate of gas exchange
as partial pressure gradient increases, rate of diffusion increases
as surface area increases, the rate of diffusion increases
increases in thickness of barrier separating air and blood decreases rate of gas exchange
Step 2: gas exchange in lungs
oxygen diffusion PO2 in alveoli = 100mmHg
PO2 in pulmonary capillary = 40mmHg
O2 diffuses from area of high alveoli to low partial pressure(pulmonary capillaries) until PO2 blood equilibrates with PO2 alveoli
Carbon dioxide diffusion
PCO2 in pulmonary capillary = 46mmHg
PCO2 in alveoli = 40mmHg
CO2 diffuses from area of high (pulmonary capillary) to low (alveoli) until PCO2 blood equilibrates with PCO2 alveoli
Step 4 gas exchange at cell level oxygen diffusion
PO2 in systemic capillary = 100mmHg
PO2 in cell = 40mmHg
O2 diffuses from area of high (capillary to low partial pressure (cell) until PO2 blood equilibrates with PO2 cell
Step 4 gas exchange at cell level carbon dioxide diffusion
CO2 partial pressure in systemic capillary = 40mmHg
CO2 partial pressure in cell = 46 mmHg
CO2 diffuses from area of high (cell) to low (alveoli) until PCO2 blood equilibrates with PCO2 cell
Step 3 transport in the blood oxygen transport
- 5% combined with Hgb inside erythrocyte
1. 5% dissolved in plasma
Step 3 transport in the blood carbon dioxide combines with water to form carbonic acid
dissociates into hydrogen ions and bicarbonate ion (the enzyme carboninc anhydrase) 80-90% bound to hemoglobin as bicarbonate (HCO3-) The reverse (bicarbonate ions forming CO2) in lungs
Hemoglobin
Binds with oxygen in blood
fully saturated - all 4 Hg binding sites bound to oxygen & no sites available
Partially saturated - some binding sites bound to oxygen and some sites available
Unsaturated - no sites bound to oxygen and all sites available
Control of respiration
Pons and medulla
Control of respiration by central receptors
generating inspiratory/expiratory rhythm, rate & depth of breathing
modifying respiratory activites
medulla respiratory centre
Dorsal respiratory group DRG
inspiratory neurons fire-> cell bodies and axons in spinal cord dire->inspiration
stop firing->expiration
Ventral respiratory group VRG
for active inspiration and expiration
project directly onto and activate other muscles (tongue, upper airway)
Two types of peripheral receptors
mechanical and chemical
Mechanical receptors
lung and chest wall receptors that detect changes in pressure, flow, or displacement of a structure
Chemical receptors
peripheral chemoreceptors signal in aorta and carotid bodies impact medulla respiratory centre
Decreased arterial PO2
increased arterial PCO2
H+
peripheral chemoreceptors
carotid bodies located in carotid sinus
aortic bodies located in aortic arch
respond to specific changes in chemical content of arterial blood
Non-gas exchange factors that influence ventilation
sneezing/coughing
inhaling noxious agents may trigger cessation of breathing
pain reflex stimulates respiratory centre
various emotional states
respiratory centre reflex inhibited during swallowing
Tension pneumothorax
traumatic origin from penetrating (stab wounds, GSW) or non-penetrating injury (rib fractures)
also from iatrogenic causes CPR
air enters pleural space during inspiration but cannot escape during exhalation
air builds up in pleural space
lung on ipsilateral same side collapses and forces mediastinum toward contralateral opposire side
decreses venous return and cardiac output
