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What does the conducting zone consist of?
Bronchi:
Secondary Bronchi
Tertiary Bronchi
Bronchioles
And Terminal Bronchioles
Describe the Secondary Bronchi
Three on right side to three lobes of right lung
Two on left side to two lobes of left lung
Describe the Tertiary Bronchi
20–23 orders of branching
Describe the Bronchioles
Less than 1 mm in diameter
Functions of the conducting zone
Air passageway: 150 mL in volume (dead space)
It increases air temperature to body temperature and humidifies air
Epithelium of the conducting zone include…
Goblet cells (secrete mucous), ciliated cells (cilia moving particles toward mouth) and mucus escalator
Functions of the respiratory zone
Exchange of gases between air and blood via diffusion
Structures of the respiratory zone include…
Respiratory bronchioles,Alveolar ducts, Alveolar sacs, Alveoli
What are the site of gas exchange called?
Alveoli
How many alveoli are there in the lungs and what are their size in total?
300 million alveoli with a size of a tennis court
Alveoli contain a ____, having capillaries form sheet over alveoli
Rich blood supply
Type I alveolar cells…?
make up wall of alveoli and are single layer of epithelial cells
Type II alveolar cells…?
secrete surfactant
Epithelium of the respiratory zone is the…
respiratory membrane
The respiratory membrane consists of…
Epithelial cell layer of alveoli (type I) and Endothelial cell layer of capillaries
it is 0.2 μm thick
The role of alveolar macrophages is
scavenging microbes such as viruses, bacteria, fungi, inhaled environmental particles like coal, silica, asbestos, tissue debris, and cancer cells
Air moves in and out of lungs by…?
Bulk flow
What drives flow in lungs?
The pressure gradient, where air moves from high to low pressure
Inspiration:
pressure in lungs less than atmospheric pressure
intra-alveolar pressure is negative (less than atmospheric)
Expiration:
pressure in lungs greater than atmospheric pressure
intra-alveolar pressure is positive (less than atmospheric)
Describe atmospheric pressure - pulmonary pressures
It is 760 mm Hg at sea level and decreases as altitude increases
It Increases under water
Other lung pressures are given relative to atmospheric pressure (set Patm = 0 mm Hg)
Describe Intra-alveolar pressure (Palv) - pulmonary pressures
It is the pressure of air in alveoli given relative to atmospheric pressure
Describe Intrapleural pressure (Pip) - pulmonary pressures
Pressure inside pleural sac, always negative under normal conditions and always less than Palv
At rest, Pip is….
-4 mm Hg
Why is Pip negative at rest?
due to elasticity in lungs and chest wall
Lungs recoil inward as chest wall recoils outward
opposing forces pull on intrapleural space
Surface tension of intrapleural fluid prevents wall and lungs from pulling apart
Transpulmonary pressure
= Palv – Pip
it is the distending pressure across the lung wall
Increase in transpulmonary pressure….
increases distending pressure across lungs, which causes lungs (alveoli) to expand, increasing volume
What does mechanics of breathing describe
describes mechanisms for creating pressure gradients
Movement of air in and out of lungs occurs due to ________
pressure gradients
force for flow = pressure gradient
What remains constant during breathing cycle?
Atmospheric pressure remains constant (during breathing cycle), thus alveolar pressure changes affect gradients
Describe Boyle’s law
pressure is inversely related to volume
If amount of gas is the same and container size is reduced, pressure will increase So pressure (P) varies inversely with volume (V)
P1V1 = P2V2
Factors determining intra-alveolar pressure
Quantity of air in alveoli and Volume of alveoli
What happens when lungs expand?
alveolar volume increases
Palv decreases
Pressure gradient drives air into lungs
What happens when lungs recoil?
alveolar volume decreases
Palv increases
Pressure gradient drives air out of lungs
What muscles increase the volume of the thoracic cavity?
Inspiratory muscles; Diaphragm and External intercostals
What muscles decrease the volume of the thoracic cavity?
Expiratory muscles; Internal intercostals and Abdominal muscles
What takes place during inspiration?
Neural stimulation of inspiratory muscles → Diaphragm contraction causes it to flatten and move downward → Contraction of external intercostals makes ribs pivot upward and outward, expanding the chest wall
a passive process (12-20 breaths/min); When inspiratory muscles stop contracting, recoil of the lungs and chest wall to their original positions decreases the volume of the thoracic cavity
What happens as a result of inspiration?
thoracic cavity volume increases
Outward pull on pleura decreases intrapleural pressure, which results in an increase in transpulmonary pressure
Alveoli expand, decreasing alveolar pressure
Air flows into alveoli by bulk flow
Events in the process of inspiration
increase in neural input →
inspiratory muscles contract →
chest wall expands →
increase pull on intrapleural fluid → decrease intrapleural pressure → increase transpulmonary pressure →
increase alveoli volume → decrease alveolar pressure → increase atmospheric pressure - alveolar pressure → increase flow of air into alveoli → increase in alveolar pressure
The pressure gradient for ventilation is represented as
atmospheric pressure - alveolar pressure
______ requires expiratory muscles (30-40 breaths/min)
Active expiration
Contraction of expiratory muscles creates a _____________ in the volume of the thoracic cavity
greater and faster decrease
What are the factors affecting pulmonary ventilation
lung compliance and airway resistance
What is lung compliance?
Ease with which lungs can be stretched
Smaller change in transpulmonary pressure needed to bring in a given volume of air
Larger lung compliance means
Easier to inspire
Factors affecting lung compliance
Elasticity (elastic recoil, ability to resist stretch: thick rubber ballon compared to thin rubber balloon)
Surface tension of lungs (force for alveoli to collapse or resist expansion)
How does Elasticity affect lung compliance
More elastic → less compliant
How does Surface tension affect lung compliance
Thin layer of fluid lines alveoli
Surface tension arises due to attractions between water molecules;
Greater tension → less compliant
How are the affects of surface tension on lung compliance overcomed
Surfactant is secreted from type II cells, which is a detergent that decreases surface tension
This then increases lung compliance, making inspiration easier
Airway resistance - as airways get _____ in diameter, they _____ in number, keeping overall resistance low
smaller; increase
Pressure gradient is needed for air flow, so resistance is normally _____
low, roughly 1 mm Hg
Does a decrease or increase to the resistance (airway resistance) happen to make it harder to breathe?
Increase in resistance makes it harder to breathe
Pressure gradient needed for air flow: > 1 mm Hg
What are the factors affecting airway resistance?
1. Contractile activity of smooth muscle
2. Mucus secretion
What is the role of the bronchiolar smooth muscle in airway resistance?
Bronchoconstriction and Bronchodilation
Bronchoconstriction
smooth muscle contracts, causing radius to decrease
Bronchodilation
smooth muscle relaxes, causing radius to increase
Describe the extrinsic control of bronchiole radius in the sympathetic nervous system
Relaxation of smooth muscle
Bronchodilation via Beta 2 receptors
Describe the extrinsic control of bronchiole radius in the parasympathetic nervous system
Contraction of smooth muscle
Bronchoconstriction via muscarinic receptors
Describe the extrinsic control of bronchiole radius in terms of hormonal control
Epinephrine, Relaxation of smooth muscle/Bronchodilation
Describe the intrinsic control of bronchiole radius in terms of hormonal control
Histamine causing bronchoconstriction
Histamine is released during asthma and allergies, which also increases mucus secretion
CO2 causes bronchodilation
Total lung volume is divided into a series of ___ volumes and ____capacities useful in diagnosing problems
4; 4
Tidal Volume (TV)
Amount of air taken in during inhalation (~500 mL)
350 mL enters alveoli + ~150 mL remains in conducting passageways (Anatomic dead space - VD)
Respiratory Rate (f) + ?
12-20 breaths per min
Minute ventilation (VE) = ?
f x TV
“# of breaths x volume of each breath”
~6 L/min
Alveolar Ventilation (VA) = ?
f x (TV – VD)
“# of breaths x (amount – dead space)”
= 12 x (500 – 150) = 4.2 L/min
Inspiratory Reserve Volume (IRV)
maximum air inspired at the end of a normal inspiration
~3000 mL
Expiratory Reserve Volume (ERV)
maximum air expired at the end of a normal expiration
~1000 mL
Residual Volume
Air left in the lungs after a maximal exhalation
~1200 mL
Hyperpnea
increase in respiratory rate/volume due to increase in metabolism
Hyperventilation
increase in respiratory rate/volume without increase metabolism
Hypoventilation
decrease in respiratory rate/volume, increase alveolar ventilation
Dyspnea
shortness of breath (difficulty breathing)
Apnea
cessation of breathing
Respiratory Capacities
Lung Capacities (4)
sums of 2 or more volumes
What is inspiratory capacity (IC)?
Maximum amount of air that can be inspired at the end of expiration
TV + IRV = 500 mL + 3000 mL = 3500 mL
What is Vital Capacity?
Maximum amount of air that can be exhaled following a max inhalation
VC = IRV + TV + ERV
= 3000 mL + 500 mL + 1000 mL = 4500 mL
OR
VC = IC + ERV
= 3500 mL + 1000 mL = 4500 mL
What is Functional Residual Capacity
Amount of air remaining at the end of normal expiration (~2300 ml)
ERV (1000 mL) + RV (1200 mL) = ~2200 mL
What is Total Lung Capacity?
Volume of air in lungs at the end of a maximum inspiration
TLC = TV + ERV + IRV + RV (or VC + RV or FRC + IC)
= 500 mL + 1000 mL + 3000 mL + 1200 mL = 5700 mL
Pulmonary Function Tests - Forced vital capacity (FVC) =
maximum-volume inhalation followed by exhalation as fast as possible
What does a low Forced vital capacity indicate?
indicates restrictive pulmonary disease
Pulmonary Function Tests - • Forced expiratory volume (FEV) =
percentage of FVC that can be exhaled within certain time frame
FEV1 =
percentage of FVC that can be exhaled within 1 second
What is a normal FEV1 percentage
80%
If FVC = 4000 mL…
should expire 3200 mL in 1 se
What does FEV1 < 80% indicate
indicates obstructive pulmonary disease
Total Pulmonary Ventilation = ?
ventilation rate x tidal volume
also known as minute ventilation (VE)
Total Pulmonary Ventilation calculation
ventilation rate x tidal volume;
12 breaths/min x 500 mL/breath = 6000 mL or 6 L/min
Some inspired air does not enter alveoli, which is known as the…
anatomical dead space, ~150 mL of air
What is Alveolar Ventilation (VA)?
movement of air into and out of the alveoli
ventilation rate x (tidal volume – dead space)
Alveolar Ventilation (VA) Calculation
ventilation rate x (tidal volume – dead space);
12 breaths/min x (500 – 150 mL/breath) = 4200 mL/min or 4.2 L/ min
What can drastically alter alveolar ventilation
Rate or depth of breathing can
What is Maximum Voluntary Ventilation?
Breathing as deeply and quickly as possible
What may happen as a result of Maximum Voluntary Ventilation?
May increase total pulmonary ventilation to ~170 L/ min
Alveoli During Breathing
Hypoventilation, Ventilation is inadequate, ↑ CO2
Hyperventilation, over breathing, ↓ CO2
Arterial blood O2 and CO2 levels remain relatively ____
constant
___ moves from alveoli to blood at the same rate it is consumed by cells
Oxygen
___ moves from blood to alveoli at the same rate it is produced by cells
CO2
What is the composition of Air?
Nitrogen (N2) ~79.04%
Oxygen (O2) ~20.93%
Carbon dioxide (CO2) ~0.03%
Dalton’s Law of Partial Pressures
Each gas contributes to the total pressure in proportion to its number of molecules Partial Pressure = total pressure x fraction of a gas
At sea level with dry air (total 760 mmHg) - PN2
= 760 mmHg x 0.7904 = 600.7 mmHg