Lecture 15 Respiration 1 Flashcards
Steps of external respiration
1) ventilation/ gas exchange between atmosphere and alveoli (air sacs) in lungs
2) exchange of O2 and CO2 between air in alveoli and blood
3)transport of O2 and CO2 in blood to tissues
4)O2 and CO2 exchange between tissues and blood
Steps of internal respiration aka cellular respiration
Metabolic processes derive energy from nutrient molecules using O2 and produce CO2
Respiratory quotient (RQ)
- ratio of CO2 produced/O2 consumed
- varies depending on foodstuff consumed
Respiratory system
Airways - path to lungs
Lungs- organs of gas exchange
Upper resp tract: nasal passage/mouth
Pharynx, Larynx
Lower respiratory tract: Trachea
Bronchi, Bronchioles, Terminal bronchioles,Alveoli
Conduction zone and exchange surface
Trachea and bronchi: rigid tubes with rings of cartilage to prevent collapse
Bronchioles: no cartilage, walls contain smooth muscle (ANS controlled) sensitive to certain hormones and chemicals
Alveoli: thin walled inflatable sacs, site of gas exchange
Alveoli
Type l alveolar cells - 1 cell thick
Type ll alveolar cells - secrete surfactant
Pulmonary capillaries encircle each alveolus
Alveolar macrophages guard the lumen
Pores of Kohn: airflow between neighbouring alveoli - collateral ventilation
Good blood flow essential
Capillary network surrounds alveoli. Fusion of alveoli/capillary wall creates thin barrier. Large SA and thinness for gas exchange. 300x10⁶ alveoli per lung create 75m² SA that’s 75x the capacity of a hollow lung without alveoli
Thorax/chest is closed compartment
Pleural sacs enclose the lungs
Diaphragm
-skeletal muscle
- separated thoracic from abdominal cavity
Pleural sacs
- double walled, closed sac separating each lung from thoracic wall
- pleural cavity is interior of sac
- intrapleural fluid secreted by surfaces of the pleura allows smooth movement - reduces friction
4 primary functions of respiratory system
Exchange of gases between air and blood
Homeostatic regulation of body pH
Defences against inhaled pathogens/substances - cilia, mucus escalator, macrophages
Vocalisation
(Also water loss and heat release e.g. panting in dogs)
Ventilation and lung mechanics
Relative pressure in/outside lungs is important in ventilation
3 pressures to consider
- atmospheric (barometric) pressure
- intra-alveolar pressure (intrapulmonary pressure)
-intrapleural pressure (intrathoracic pressure)
Alveolar pressure < atmospheric air entering lungs
Alveolar pressure> atmospheric air flowing out of the lungs
Boyle’s law
At any constant temp. Pressure exerted by a gas varies inversely with the volume of gas V alpha 1/P
Change container size (lung dimensions) change pressure
Lung mechanisms
No muscle attached to lungs surface. Volume depends on difference in pressure between inside and outside of lungs and their stretchability (or compliance)
Pressure diff. Is called transpulmonary pressure -TP=Palv-Pip
Pressure inside lungs = air pressure inside alveoli (Palv)
Pressure outside lungs= pressure in intrapleural fluid (Pip)
Respiratory muscles attached to chest wall contract/relax, changing dimensions of chest causing changes in transpulmonary pressure thus changing lung volume
Inspiration : inspiratory muscles
Major inspiratory muscles
Diaphragm: innervated by phrenic nerve
Intercostal muscles - activated by intercostal nerve
75% of enlargement of thoracic cavity (quiet breathing) due to contraction and flattening of diaphragm
This expansion decreases intrapleural pressure. Lungs expand into this area of low pressure. Increase in lung vol lowers intra alveolar pressure below atmospheric pressure so air enters the lungs
(Accessory inspiratory muscles can further enlarge thoracic capacity)
Expiration
Starts by relaxation of inspiratory muscles
Relaxation of diaphragm and muscles of chest wall (plus the lasting recoil of alveoli) decrease size of chest cavity
Intrapleural pressure increases and lungs are compressed
Intra-alveolar pressure increases. When pressure increases above atmospheric pressure, air moves out - expiration occurs
Forced expiration can occur by contraction of expiratory muscles:
Abdominal wall muscles
Internal intercostal muscles
Lungs have elastic recoil
Compliance refers to effort needed to stretch lungs. Recoil due to highly elastic connective tissue in lungs and alveolar surface tension
Lung compliance
The change of volume due to given force or pressure -DV/DP
Ease with which chest volume can be changed
Reciprocal of elastance
Compliance high - chest expansion easy
Pressure volume curve closed loop (hysteresis)
Surface tension law
P=2T/R
If air pressure in large alveoli <smaller then small liable to collapse (air flows into larger alveoli)
Surfactant - produced by type ll alveolar cells is a phospholipid molecule that lowers surface tension of liquid lining alveoli so pressure needed to hold alveoli open reduced and smaller alveoli do not collapse
Pathology: new born respiratory distress syndrome - cortisol injection to mother before birth prevents this
Airway resistance
Upper airway diameter constant, resistance to airflow constant
Mucus accumulation can increase resistance.
Bronchioles: collapsible tubes, increase airway resistance
Bronchoconstriction/dilation can occur
Factor/affected by/mediated by
Length of system/constant/none
Viscosity of air- usually constant but humidity or altitude may alter it/none
Diameter of airways:
Upper airways/physical obstruction/ mucus and other factors
Bronchioles/
bronchoconstriction/PNS muscarinic receptors histamine and leukotrienes
Bronchodilation/ CO2 & epinephrine receptors
Spirometry
See diagram
Lung vol/capacity
Tidal vol (TV) vol of air breathed in 500ml
Inspiratory reserve (IRV) extra vol that can be max inspired (above TV) 3000ml
Inspiratory capacity IC=IRV+TV 3500ml
Expiratory reserve (ERV) extra vol tha t can be expired 1000ml
Residual vol (RV) min vol remaining in lungs after max expiration 1200ml
Functional residual capacity (FRC) vol of air in lungs at end of norm expiration (FRC=ERV+RV) 2200ml
Vital capacity (VC) max vol of air moved in single breath after max expiration.
VC=IRV+TV+ERV 4500ml
Total lung capacity (TLC) max vol lungs can hold TLC=VC+RV 5700ml
Forced expiratory volume in 1 second (FEV) vol of air that can be expired during first second of expiration in a VC determination
Anatomical dead space
Minute ventilation= tidal volume X respiratory rate
500ml each breath 10 breaths/min = 5000 ml/min available for respiration?
NO!!
Because there is dead space, conducting airways - larynx, trachea, bronchioles and terminal bronchioles
When no gas exchange occurs has a volume of 150ml
2200ml + 150ml remains in lung
Physiological dead space
Alveolar dead space present in normal individuals
-Inspired fresh air not used for gas exchange with the blood even though it reaches alveoli
- absence of blood flow to some alveoli e.g. if a vessel is blocked
Physiological dead space= anatomical dead space+alveolar dead space
Minute ventilation: vol air breathed in/out per min (ml/min)
Pulmonary ventilation= tidal volume X respiratory rate
Alveolar ventilation= (tidal volume - dead space) X respiratory rate
respiration and conduction zone
respiratory zone is where gas exchange takes place
the conduction zone is effectively the tube system that transports air to the alveoli
