Chapter 16: Respiratory System - Ventilation Flashcards
internal vs external respiration
- external respiration refers to the exchange of oxygen and carbon dioxide between the atmosphere and body tissues
- internal respiration is the gas exchange between the blood and the tissue
major organs of the respiratory system
- lungs
- upper airways
- respiratory tract
what are the upper airways?
- refers to air passages in the head and neck
- this includes the nasal cavity and oral cavity which lead to the pharynx
what is the respiratory tract?
- includes all air passageways from the pharynx to the lungs
- has two components:
(1) conducting zone (upper part)
(2) respiratory zone (lower part)
what is the difference between the conducting zone and respiratory zone?
conducting zone:
- is the the upper part of the respiratory tract
- functions in conducting air from the larynx to the lungs
respiratory zone:
- the lowermost part of the respiratory tract
- contains the sites of gas exchange within the lungs
–> the main difference between the conducting and respiratory zones in the lungs is the thickness of the walls around the air spaces. gas exchange happens only in air spaces with thin walls.
components of the conducting zone
- larynx = voice box that air passes through
- trachea = windpipe, connects larynx to bronchi
- bronchi = main airway branching off trachea supplying each lung
- secondary bronchi = 3 on right, 2 on the left
- tertiary bronchi = supplies speicifc regions of the lungs
- bronchioles = tiny air passageways
- terminal bronchioles = final and smallest components
3 functions of the conducting zone
1) to provide a passageway for air to enter and exit the respiratory zone (where gas exchange occurs)
2) increase air temperature to adjust to body temperature
3) humidify air to keep the respiratory tract moist
what specialized cells line the conducting zone of the respiratory system?
- epithelium lines the conducting zone
- contains goblet cells
- contains ciliated cells
–> the goblet cells secrete mucus that coats the airway and traps foreign particles within inhaled air
–> cilia of the ciliated cells beat in a whiplike fashion the process the mucus up the throat where it can be swallowed
–> this is called the mucus elevator which prevents mucus from accumulating in airways and decreasing likelihood of infections
what changes occur to tissues within the conducting zone?
- cartilage is abundant in the walls of the trachea and bronchi but decreases in amount as bronchi diameter reduces.
- there’s no cartilage in bronchioles.
- smooth muscle is sparse in the trachea and bronchi but increases as airways become smaller.
- bronchioles lack cartilage and have more smooth muscle, enabling them to change diameter and regulate air flow resistance.
components of the respiratory zone
- respiratory bronchioles
- alveolar ducts
- alveolar sacs
- alveoli
functions of the respiratory zone
- allow for exchange between air and blood via diffusion
what are alveoli?
- balloon-shaped air sacs located at the end of the respiratory zone
- they facilitate the exchange of oxygen and carbon dioxide
- they expand during inhalation, taking in oxygen, and shrink during exhalation, expelling carbon dioxide
characteristics of alveoli
- alveoli are not independent structures, they are connected via alveolar pores
- type I alveolar cells form the respiratory membrane, consisting of a thin, single layer of epithelial cells.
- type II alveolar cells secrete surfactant, which reduces surface tension and prevents alveolar collapse
- also contain macrophages that engulf particles and pathogens inhaled into the lungs
what is the respiratory membrane?
- endothelial cell layer of capillaries and epithelial cell layer of alveoli alveolar fuse to form a thin barrier
- it separates air from the blood
- the thinness helps with gas exchange
structures of the thoracic cavity
- the chest wall:
(1) ribcage
(2) sternum
(3) thoracic vertebrae
(4) internal and external intercostal muscle
(5) the diaphragm - the pleura
- pleural sac around each lung
- intrapleural space with intrapleural fluid
what forces drive pulmonary ventilation?
- air moves into and out of lungs by bulk flow
- bulk flow is driven by a pressure gradient between the alveoli and the outside air (atmosphere)
- air moves from high to low pressure
inspiration vs expiration
- inspiration = pressure in the lungs is less than the pressure in the atmosphere, so air moves into the alveoli
- expiration = pressure in the lung exceeds the pressure in the atmosphere, so air leaves the alveoli
4 pressures associated with ventilation
1) atmospheric pressure
2) intra-alveolar pressure
3) intrapleural pressure
4) transpulmonary pressure
what is atmospheric pressure?
- the pressure of outside air
- at sea level = 760 mmHg
- at altitudes higher than sea level, atmospheric decreases
- at altitudes lower than sea level, atmospheric pressure increases
what is intra-alveolar pressure (Palv)
- the pressure of air within the alveoli
- intra-alveolar pressure varies during the phases of ventilation
- the difference in intra-alveolar pressure and atmospheric pressure drives ventilation
–> when atmospheric pressure > intra-alveolar pressure (is negative) = inspiration occurs
–> when intra-alveolar pressure (is positive) > atmospheric pressure = expiration
what is intrapleural pressure?
- is the pressure inside the pleural sac
- pressure is always negative and less than intra-alveolar pressure
- pressure varies through phases of respiration
- at rest is -4mmHg
why is intrapleural pressure always negative?
- the lung and chest wall are both elastic, so if they are stretched out of their natural position they can recoil back
- at rest, the chest walls tends recoil outwards and the lungs recoil inward
- these opposing forces would normally move the chest wall and lungs apart, but they are kept together by the surface tension of the intrapleural fluid
- as a result, the chest wall pulls outward on the intrapleural space, while the lungs pull inward, creating a negative intrapleural pressure
what happens if intrapleural pressure isn’t maintained?
- if the pleural sac isn’t airtight and the the sac is broken, the negative pressure is lost
- the lungs will recoil and collapse while the chest wall expands
- this allows air to enter the intrapleural space, which is called pneumothorax
what is transpulmonary pressure?
- is the difference between the intrapleural pressure and the intra-alveolar pressure
- transpulmonary pressure gradient keeps the airways and alveoli open
when intraalveoli > intrapleural pressure = increase in transpulmonary pressure = increased pressure across the lungs = lungs/alveoli expand = increase volume
what mechanism allows people to breathe?
- breathing is driven by a pressure gradients that the muscles of respiration create by changing the volume of the lungs
- the driving force for air movement is the difference between atmospheric and intra-alveolar pressure. since atmospheric pressure is constant, changes in alveolar pressure determine the direction of air movement
what is boyles law?
- an inverse relationship between pressure and volume
–> if the volume of the container increases, the pressure exerted by the gas falls
–> if the volume of container decreases, the pressure of the gas rises
what factors determine intra-alveolar pressure?
1) the quantity of air in the alveoli
2) the volume of alveoli
–> when lungs expand, alveolar volume increases = intra-alveolar pressure decreases = pressure gradient drives air into lungs
–> when lung recoil, alveolar volume decreases = intra-alveolar pressure increases = pressure gradient drives air out of lungs
what muscle are involved in respiration?
inspiratory muscles increase volume of thoracic cavity = lungs expand:
- diaphragm
- external intercostals
expiratory muscles decrease volume of thoracic cavity = lungs recoil
- internal intercostals
- abdominal muscles
how does inspiration occur?
- initiated by neural stimulation of the inspiration muscles via the release of acetylcholine
- the diaphragm contracts which causes it to flatten and move downward
- at the same time, the external intercostals causes the ribs to pivot upward and outward therefore expanding the chest wall
- colelctively, the volume of the thoracic cavity increases
–> expansion of the chest wall causes an outward pull on the pleura = decrease in intrapleural pressure = increase in transpulmonary pressure = the lungs/alveoli expand = decreases intra-alveolar pressure below atmospheric pressure = air flows into the alveoli via bulk flow
how does expiration occur?
- expiration is a passive process because it doesn’t require muscle contraction
- after inspiration, the muscles relax and the chest wall and lungs recoil to their resting positions
- as this happens, the volume of the lungs decrease = causing alveolar pressure to increase higher than atmospheric pressure = air flows out of the alveoli
what happens during active expiration?
- active expiration requires expiratory muscles to be contracted
- contraction of muscles produces a faster and greater decrease in thoracic cavity volume = increase intra-alveolar pressure = greater pressure gradient for air to flow out of the alveoli
what factors affect pulmonary ventilation?
1) lung compliance
2) airway resistance
what is lung compliance?
- refers to the change in lung volume that results from a change in transpulmonary pressure
- it is the ease at which the lungs can be stretched
–> the more compliant a lung is, the less pressure (easier it is) to change the volume
–> the less compliant a lung, the more pressure (harder it is) to change the volume
how does lung compliance affect pulmonary ventilation?
- lung compliance affects the ability of the lungs to expand during inspiration
- larger lung compliance makes it easier to inspire
- this is because a less (transpulmonary) pressure is needed to bring in a given volume in air = less work/muscle contraction is needed
- when lung compliance decreases = respiratory muscles work harder to expand the lungs to a given volume.
what factors affect lung compliance?
1) elasticity of the lungs
- the lungs are elastic due to the presence of elastic fibers in the connective tissue
- greater elasticity = the lungs resist being stretched more = lower compliance = harder for lungs to contract
2) surface tensions of lungs
- surface tension is the force that causes alveoli to collapse or resist expansion
- alveoli are lined with a thin layer of fluid where surface tension arises due to attractions between water molecules.
- greater surface tension leads = less compliance because it opposes the expansion of the alveoli = harder to expand alveoli
how to overcome surface tension?
- a surfactant is released from type II cells
- a surfactant is a detergent that decreases surface tension by interfering with the h-bonding between water molecules
- it increases lung compliance and makes inspiration easier
how does airway resistance affect pulmonary ventilation?
- airway resistance is determined by the radius of the airway
–> as radius decreases = resistance increases
what is airway resistance like in normal lungs?
- resistance to air flow into and out of lungs are low
- as the diameter of airways decrease, the number of smaller tubes increase due to the extensive branching
- therefore the overall resistance in the conducting zone is low
factors affecting airway resistance
1) contractile activity of smooth muscle
2) mucus secretion
how does the contractile activity of smooth muscle affect resistance?
the smooth muscle of the bronchioles is influenced by the ANS
- bronchoconstriction: smooth muscle contracts = causing radius to decrease
- bronchodilation: smooth muscle relaxes = causing
radius to increase
–> the contractile state of bronchiolar smooth muscle under
extrinsic and intrinsic control
extrinsic control of brionchiole radius
the autonomic nervous system plays a role:
- sympathetic = relexation of smooth muscle (bronchodilation)
- parasypathietc = contraction of smooth muscle (bronchoconstriction)
- the release of epinephirne can also cause bronchodilation
intrinsic control of bronchiole radius
- the release of histamine causes bronchoconstriction and the buildup of mucus within airways
- CO2 levels affect the radius:
–> when CO2 levels are high = bronchioles dilate
–> when CO2 levels are low = bronchioles constrict
how does mucus affect resistance?
- mucus can build up and block airways and physically obstruct airflow
- this makes ventilation more difficult
what is spirometry?
- it measures the volumes of inspired and expired air using a spirometer
- an individual inserts a mouthpiece that is attached to an invert bell filled with air or oxygen
- when they breathe air in and out it will mark a paper calibrated to record the volume of air moved in/out of lungs.
how does spirometry work?
- when the patient inhales, the volume of air in the bell decreases, and the bell descends deeper into the water.
- when the patient exhales, the volume of air in the bell increases, and the bell rises in the water.
- the bell is connected via a pulley system to a pen that moves up and down when the bell moves up and down which writes on paper
4 types of lung volumes
1) tidal volume (TV)
2) inspiratory reserve volume (IRV)
3) expiratory reserve volume (ERV)
4) residual volume (RV)
4 types of lung capacities
1) inspiratory capacity (IC)
2) vital capacity (VC)
3) functional residual capacity (FRC)
4) total lung capacity (TLC)
what are the clinical applications of lung volumes?
- provides information about lung capacity and compliance
- helps distinguish a diagnosis between obstructive or restrictive pulmonary disorders
–> low FVC = restrictive pulmonary disorder = indicating reduced lung capacity
–> low FEV = obstructive pulmonary disorder = indicating impaired airflow during exhalation
what is forced vital capacity?
the maximum amount of air a person can forcefully inhale followed by an exhale as fast as possible
what is forced expiratory volume?
the percentage of the forced vital capacity that can be exhaled within a certain time frame
