REsp Flashcards
What is Resp
: Metabolic processes in which oxygen (O2) is used to oxidize nutrients to produce energy in the form of ATP, generating carbon dioxide (CO2) at the cellular level…
The transport of oxygen from the ambient air to the tissue cells and the transport of CO2 in the opposite direction
a combination of airflow, and gas exchange (followed by blood flow and gas exchange).
Name the stages of resp
- Stage 1 Ventilation from the ambient air into the lung (pulmonary) alveoli
- Stage 2 Pulmonary gas exchange from the alveoli into the pulmonary capillaries
- Stage 3 Gas transport from the pulmonary capillaries to the peripheral (tissue) capillaries
- Stage 4 Peripheral gas exchange from the tissue capillaries into the cells (mitochondria)
- Stage 5 …and CO2 back again, though this is not usually considered to be one of the stages…
What causes gas flow for resp to happen
A pressure gradient is established between the atmosphere and the lung, and gas flows in response to it
What is pressure
Force/Area
What is flow
Flow = Rate of change of volume or Volume/unit time
As Gas moves down the airway what happens to the cross sectional area
It Increases
What happens to pressure and velocity when the cross sectional area increases
pressure reduces and velocity reduces
What factor is necessary for Gas molecules to move
Force
What kind of flow does air flow occur by
Bulk flow
Resistance to air flow is caused by the folloeing properties:
a function of the shape of the conduit (that which it flows through)
the properties of the substance (that which flows).
In gas exchange from the airway to blood, the properties of the interface also affect resistance to flow.
Lung functions
GAS exchange(conduction of air) Diffusion of Gas
Transport
Metabolism
Defense
Filters unwanted substances from circulation
How is the chest wall coupled with the pleural membrane
The movement of the chest wall is mechanically coupled through the plural membranes.
The lung-thorax system has a single orifice at the trachea that functions as a ?
Reciprocal pump.
sucks in air in response to negative pressure generated by the muscle of the chest wall.
How much negative pressure is needed for gas flow to happen in the lungs
2cm of water generates 1L/sec of flow by bulk flow
What happens on inspiration
the diaphragm contracts and descends, and the intercostal muscles raise the ribs and spread them apart. This increases volume of the thoracic cavity and decreases intrathoracic pressure, which ‘sucks’ air into the lungs. The air travels through the conducting apparatus.
What’s the relationship between Vol and Intrathoracic pressure upon inspiration
Increase thoracic cavity volume
Decrease Intrathoracic Pressure
The Conducting Apparatus consists of
trachea, bronchi(Segmental)
bronchioles(Nonrespiratory)
terminal bronchioles (smallest airways without alveoli).
Together, they conduct inspired air into the gas exchanging regions of the lung.
The components of the conducting zone take no part in gas exchange, and constitute the anatomic Dead Space, with a volume of about 150 ml in each breath.
respiratory zone is made up of?
Gas excnahging regions of the lungs.
respiratory bronchioles (which have occasional alveoli budding from their walls)
and
2.alveolar ducts: are completely lined with alveoli.
3.ALveolar Sac.
The respiratory zone makes up most of the lung volume, about 2.5 to 3 liters during rest
where is the narrowest part of the airway and greatest resistance to airflow
Trachea
Whats the relation between velocity of flow and area
this is Inversely related
In the alveolus what happens to air velocity
its so slow that it comes to a standstill.
Whats the benefit of the velocity of air flow slowing down when it reaches the alveolus
Rapid diffusion of gases hapens here.
During which cycle of Respiration does gaseous exchange happen
During Expiration
The airway becomes shorter and numerous as it gets further into the Lungs True or false
T
From 17th generation we have a combined function of transitional and respiratory zones
The alveolocapillary membrane Consist of?
The alveolocapillary membrane is the thin structure dividing air from blood.
It is only 0.5µM thick. It consists
the alveolar epithelium on the ‘air’ side,
the endothelium on the ‘capillary’ side, and
the interstitium which lies between the two membranes
Is the flow fast or slow in conducting Zone?
Fast
The alveolar epithelium has 2 types of cells
: Type 1 cells (sunny side up, or pavement cells), and the
Type 2 pneumocytes which secrete a surface active material (or surfactant) into the alveoli
. The alveolar epithelial cells secrete the Angiotensin Converting Enzyme, which is necessary to convert Angiotensin I to Angiotensin II, an important vasoconstrictor which is necessary for sodium retention and maintenance of intravascular volume in salt and water-depleted states.
How does gas exchange happen
Across the alveolar capillary membrane by diffusion
Ficks Law
The volume of gas that flows across a sheet of tissue is proportional to the area of the sheet, and inversely proportional to its thickness, and pressure gradient across the sheet.
Thus V* (Volume of gas/unit time) is proportional to (Area /Thickness) x (P1-P2), but also depends on the properties of the gas (mainly solubility and molecular mass)
The rate of diffusion of a gas across a permeable membrane depends on:
- The nature of the membrane
- The surface area of the membrane (A)
- The thickness of the membrane (T)
- the partial pressure gradient of the gas across the membrane (DP)
- The diffusion coefficient of the gas (D)
when is diffusion most efficient
It follows that diffusion is most efficient when the blood gas interface has a large surface area, and is very thin.
How does the blood gas interface Surface area get large and thin
This is achieved by wrapping the capillaries around minute air sacs called alveoli. There are 300 million alveoli in the human lung, with a surface area of 85 square meters.
In addition, the pulmonary capillaries are of very small caliber (7µM), squeezing the Red Blood Cells (RBCs) close to the vessel wall, and decreasing the distance for diffusion.
Blood flow in the lungs comprises of
pulmonary circulation and bronchial circulation
Components of alveoli
Type 1 and 2 alveolar cells
surfactant
ALveola macrophage
Respiratory brochiole components
Mucus layer
Ciliated cell
nerve
Bronchiole component
Mucus layer
ciliated cell
Basement membrane
Trachea and Bronchus
Mucus layer
Serous cell
Goblet cells
ciliated cells
Diffusion in the lung
In the normal lung:
300 million alveoli
Barrier between blood and air is less than 1mm
Capillaries are very small so almost all RBC in contact
CO2 diffuses about 20X faster than O2
Diffusion constant
solubility/
square root of MW
The ALveolus has 2 types of cells
Type 1 and type 2 pneumocytes
Relationship between Alveolo capillary membrane and diffusion
Alveolo-capillary membrane is usually very thin (0.3 – 0.5 mm) but can thicken in various disease states which can reduce oxygen diffusion….this may increase with disease.
Interstitial space gets thicker….u have to be sicker to be able to mess this up.
Diffusion of CO2 usually not impacted but can be by very serious disease states.
What are Macrophages used for
Defence in the Lungs
TRansport:
Components of pulmonary circulation
1.The lung is a reservoir for blood
Receives almost all cardiac output
2.Low resistance circuit
Pressure=Flow x resistance and since resistance is low, the pressure gradient can also be low to get good flow (F=(P)/R)
3.The alveoli are essentially “bathed in blood “: efficient gas exchange
Low pressure circuit
Explain blood flow and gas exchage in the capillary
As pulmonary vascular resistance is so low, a mean pulmonary arterial pressure of only 20 cm water (15 mmHg) is needed for a flow of 6L/min, which is the Cardiac Output, and also the RV output into the lung, as the 2 systems are in series. (Fig. 5.)
Blood flows rapidly into the pulmonary capillaries, which form a dense network in the walls of the alveoli. The branches are so short, that they virtually form a pool of blood, bathing the alveoli. This provides a very efficient milieu for gas exchange
Factors affecting the caliber of pulmonary vessels or pulmonary Vascular resistance /pulmonary circulation
1.pressure around them:
As the lung expands extra alveolar vessels are pulled open by the traction of expanding lung parenchyma.
their resistance fall with inflation
2.Alveolar vessels(capillaries)resistance increase at High volume as the lungs expands because they are compressed by the high pressure generated because of the lung expansion.
Increase vol=Inc alveolar vessel Resistance
- At low lung volumes, the extra alveolar vessel resistance increases significantly Because pressure is up.. If a lung is completely collapsed, pulmonary artery pressure has to be raised to several cms. above downstream pressure before any flow will occur; this is called the critical opening pressure.
Pulm vascular resistance is reduced by inc blood flow
During Exercise when CO and pulm blood is increased.
- Pulmonary vascular resistance increases with alveolar hypoxia, due to constriction of small pulmonary arteries
- Pulmonary vascular resistance can be decreased with Nitric Oxide, which is a powerful selective pulmonary vasodilator, and is used to treat pulmonary hypertension. Useful in neonatal pulmonary hypertension due to prematurity
Acid base status: Alkalemia is a pulmonary vasodilator
What is critical opening pressure
. If a lung is completely collapsed, pulmonary artery pressure has to be raised to several cms. above downstream pressure before any flow will occur
PVR maybe reduced by
Increased blood flow.
this is called recruitment
this is occurs because of capillary distention
and opening of capillaries which are normally ‘closed’: no blood flows through them at rest.
At what instances does recruitment occur and what happens
During Exercise when CO and pulm blood is increased.
How does pulmonary veins impact Bronchial Circ
Carries deoxygenated blood away from the lungs
Which pneumocytes produce surfactant
type 2 pneumocytes which line the alveoli
surfactant and function
Surfactant decreases surface tension in less expanded lungs, enhancing alveolar stability, and preventing collapse at low lung vol
Produced by type II pneumocytes Reduces surface tension Effect is greatest at low lung volumes Contributes to hysteresis Lack results in RDS in premature babies
PVR is a sum of Which 2 components and what happen in each components as lung expands
Extra-alveola and alveola resistance.
As the alveoli expand the large extra-alveolar vessels are stretched:
Resistance goes down
As the alveoli expand the thin alveolar blood vessels get thinner: Resistance goes up
What is surface tension
Surface tension: The elastic tendency of a fluid surface which makes it acquire the least surface area possible
Surface tension exerts a force that would tend to collapse the alveoli at low lung volume
Treatment of persistent Pulmonary hypertension of the newborn
nitric oxide diffuses into pulmonary vascular bed relaxing pulmonary arteries,then rapidly binds to hgb and is inactivated .
Effects are thereby limited to the pul vasculature.
Lung metabolism involves
Metabolism of vasoactive substances: Produces Angiotensin Converting Enzyme (ACE), which generates vasoconstrictor Angiotensin II
Metabolizes bronchoactive substances such as leukotrienes (which cause bronchospasm)
Is an important reservoir of several cytochrome P450 enzymes (CYPs) and plays a role in the metabolism of xenobiotics.
Contains mast cells which produce the anticoagulant heparin…stops clots from getting bigger when formed in the lungs
which lung part has most alveoli
Alveolar duct
What happens during inspiration
Diaphragm contract and descend/ribs are raised
Components of resp zone
resp bronchioles.
alveolar duct
alveolar sac
Whats the chief mode of ventilation after velocity of gas becomes small when it gets to the resp zone
Gaseous diffusion
The Whole output of the right heart hoes to the lungs t/f
T
What secretes mucus in the lungs
mucous glands and Globet cells in the bronchial wall and swept away by the cilia.The alveoli have no mucus cells and particles there are engulfed by the macrophages
The foreign material is then removed from the lung via the lymphatics or the blood flow
The mucociliary escalator protects the lung from inhaled particles
Can be overcome as in black lung
Production of IgA – Important first line of defense
What causes air to move
Inspiration is active
The diaphragm moves down, the ribs move forward, upward and outward
Volume in the chest increases
P decreases
Air flows into the lung down a pressure gradient
Is Expiration active or passive
Passive Due to elastic recoil of the chest wall V in the chest decreases so P increases Air flows out passively down the pressure gradient
Examples of Active Expiration
Wind instrument
Asthma
Uses the muscles of the abdomen and internal intercostal muscles
Whats the main factor producing inspiration during normal breathing
Contracttion of the diaphragm
What is characteristics of bulk flow
depends on pressure gradient, size and resistance of the conduit and the nature of the fluid
Characteristics of Laminar flow
Smooth, high velocity, streamlined
Charcateristics of Turbulent flow
: Branch points, increased airway resistance – asthma – velocity is reduced and more pressure is required to drive flow
Transitional flow
Less axial velocity than laminar flow
More work to drive flow
Reducing the density of the gas can reduce work
Heliox: Helium:Oxygen 80:20 can convert turbulent flow to laminar flow
Used to treat upper airway obstruction: Croup and Asthma
This makes the gas less dense
It follows that when velocity of flow is high, as occurs in the trachea during exercise, turbulence increases
Transitional flow
At branch points
When radius is Halved what happens to resistance
Increases 16fold
Flow falls 16 fold if pressure is constant
Reduce gas density
Heliox: He:O2 - 80:20 for a child in croup.
Doubling the lenght does what to the resistance
Doubles the resistance and flow falls one half
What are the factors affecting airway resistance
Lung volume: Greater the volume, the less the AWR
Similar to effect of lung volume on extra-alveolar vessels
Airways pulled open as lung expands.
The greater the volume, the lower is the resistance, as expanding lung parenchyma exert radial traction on the airways, increase radius and thus decrease resistance. Conversely, as the lung collapses, airway resistance increases, and may even close down airways, especially at the base
Airway Generation: Most resistance occurs upto the 7th generation (determined experimentally)(highest resistance in the 7th gen)
Bronchial Smooth Muscle contraction will increase resistance. Contraction occurs in response to β2 adrenergic blockers, parasympathetic activity, acetylcholine and histamine.
b2-adrenergic agonists cause smooth muscle relaxation
b2 receptor agonists treat asthma
Terbutaline, albuterol
Density and viscosity of inspired gas During deep sea diving, the density of the gas increase, and airway resistance at the medium sized bronchi, where flow is turbulent, increases. The reverse occurs with a low density Helium O2 mixture (Heliox)
Pre-inspiration the pressure in the potential space is -5 cmH2O
Pressure difference from the airways to the intra-pleural space is always positive during normal breathing, keeping the airways open
During forced expiration, flow is determined by alveolar pressure-plural pressure (not mouth pressure) and so is independent of effort.
- The dimensions and content of the airways
- The structure and quality of tissue
- The degree of vascular distension
- The composition (viscosity and density) of the inspired air
- The mechanical properties of the chest wall
How does conductance relate to airway resistance
Conductance is inverse of AWR but increases linearly
During forced Expiration what determines the flow
Flow during dynamic compression is determined by the gradient between alveolar pressure and pleural pressure, not mouth pressure, as the airway is compressed
What impacts pulmonary compliance
Compliance of the lung and compliance of the chest wall together impact upon pulmonary compliance.
Whats Lung compliance
The term compliance refers to the distensibility of the lung, or the change in volume for a given change in pressure
also said to be ease with which u can change a volume for a given pressure.
Factors that affect Lung compliance
Volume: Compliance increases with decreasing lung volume.
- Hysteresis: The phenomenon by which the lung demonstrates different compliance curves during inspiration and expiration. Lung volume at any given pressure is higher during deflation than during inflation.
- Elasticity of the lung, or its tendency to return to resting position after inflation, leads to a negative pressure surrounding the lung, compared to atmospheric pressure. This elasticity is attributed to fibers of elastin and collagen in the alveolar walls, around vessels and bronchi.
4
Surfactant reduces surface tension at low lung volumes, keeping the alveoli open.
It increases compliance of the lung, promotes stability of alveoli, keeps alveoli dry. Surfactant prevents reduction of hydrostatic pressure in tissue around capillaries, prevents capillary transudation of fluid into alveoli.
5.
5. Vascular Distension: Engorgement of the lung causes increased stiffness, ie decreased compliance
conditions that increase compliance
Aging
Emphysema
Conditions that decrease compliance
Pulmonary Fibrisis Alveolar Edema Hypoventilated lung Increased pulmonary venous pressure Atelectasis
Pneumothorax characteristics and treatment
Stab wound allowing air to enter
Loss of mechanical linkage between chest and lung
Lung collapses
Lung cannot be inflated by forced respiration
Let air out of the pleural space with a chest tube and vacuum.
Relationship between FRC and and airway pressure.
At volumes above FRC, the airway pressure is positive. The chest wall tends to expand at volumes upto 75% of vital capacity.
At volumes below FRC, airway pressure is negative, and hence air is sucked into the lung, to maintain FRC.
What is FRC and application
The volume of the lung at which the elastic recoil of the lung pulling it inwards, and the tendency for the chest wall to spring out, are balanced
The volume in the lung, which stays there, keeps the lung open and acts as a bank to supply O2 when needed
Keeps the lung ‘open’, keeps intra-pleural pressure negative
Applied : Incentive Spirometry maximizes FRC, prevents lung collapse
Tye 1 pneumocytes and function
Large, flattened, non replicating
Involved in gas exchange
Diffiuse Alveolar Disease (DAD) seen in SARS epidemic
Type II Pneumocytes is the( biochemical engine of the lungs)
can differentiate into Type I but not vice versa
Compare Apex and BAse pressure and volume during ventilation
Apex volume is large
Apex pressure is low
Not much room for expansion
However,
Base pressure is high
Base volume is decreased
Thus ventilation/unit volume is increased at the base vs apex
What happens with Baseline ventilation of Apex
Apex is aerated better at baseline, as surrounding intrapleural pressure is more negative at the apex
