Respiration Flashcards
What is the primary function of respiration?
Gas exchange
What is the pleural space?
A fluid filled sack wrapping around lungs connecting to ribcage
Describe the layers of the pleura getting closer and closer to the lungs
Parietal pleura
Intrapleural fluid
Visceral pleura
The pressure of the intrapleural space is (positive/negative)
Negative
How do lungs operate?
negative pressure pump (mechanical)
List the subdivisions of the airways
Trachea, bronchi, bronchioles, terminal bronchioles,
respiratory bronchioles, alveolar ducts, alveolar sacs
What are the 4 functions of the conducting pathways?
- Defense against bacterial infection/foreign particles (Mucociliary defense system)
- Warm and moisten air
- Sound/speech
- Regulation of air flow (smooth muscle can contract/relax to alter resistance)
What are the tyo circulations in the lungs?
Pulmonary circulation: brings mixed venous blood to the lungs allowing the blood to get oxygenated
Bronchial circulation: supplies oxygenated blood from the systemic circulation to the tracheobronchial tree (allows the airways to get oxygenated)
What are the three types of alveolar cells?
- Epithelial cells: Type I and II, Type II secretes surfactant, type I we have no idea
- Endothelial cells: Constitute the walls of the pulmonary capillaries (very thin)
- Alveolar macrophages (housekeeping/defense)
Name the 3 principal and 2 accessory muscles of inspiration
External intercostals
Parasternal intercartilaginous muscles
Diaphragm
Sternocleidomastoid
Scalenus
What muscles are involved in quiet expiration?
None (expiration results from passive recoil of lungs)
What are the 5 muscles involved in active expiration?
Internal intercostals (except for the parasternal intercartilaginous muscles) Abdominal muscles Rectus Abdominis External Oblique Internal Oblique Transversus Abdominis
What servical segments provide the phrenic nerves that innervate the diaphragm?
Segments 3, 4, and 5
What is tidal volume?
The volume that is expired during normal breathing
What is inspiratory reserve volume?
The distance from the maximum of tidal volume to the maximum possible inspiration
What is expiratory reserve volume?
The volume of air that can be expelled after expiring from tidal volume
What is residual volume?
The volume from 0 to the base of expiratory reserve volume
What is Vital capacity?
The amount of air from maximum inspiration to maximum expiration
What is functional residual capacity?
The amount of air in the lungs when expiring from tidal volume
What is inspiratory capacity?
The amound of air that could be inspired when expiring from tidal volume
What is total lung capacity?
The amount of oxygen from maximum inspiration to 0
How do you measure FRC?
Patient exhales and places mouth on tube connected to a container filled with radiolabelled gas
inspires labelled gas
You had the initial volume and concentration of the gas, you can calculate the final concentration of the gas, then use C1xV1 = C2xV2
FRC = (C1 x V1/C2) - V1
What is minute ventilation and how is it calculated?
The amount of air inspired (or expired) in one minute (V_E)
V_E = V_T x f
Where V_T is tidal volume and f is the numer of breaths per minute
Normally: V_T = 500 mL, f = 12 breaths/min
V_E = 6000 mL/min
What is anatomical dead space?
The amount of air that remains in conducting airways during respiration
Approximately 150 mL
What is Alveolar ventilation?
The amount of air that actuall reaches lungs
If tidal volume is typically 500 mL and frequency is typically 12 breaths /min And anatomical dead space is 150 mL, then V_A = (500-150) x 12 = 4200 mL/min
What is alveolar dead space? What causes it?
A pathological condition where inspired air reaches the respiratory zone but does not parttake in gas exchange
Caused by Decreased/no blood supply
How do you calculate physiological dead space?
V_D = Alveolar + anatomical Dead space
What happens to V_A and PaCO2 under normal ventilation?`
V_A matches CO2 and keeps PaCO2 at a constant level
What is the PO2 and PCO2 of air?
PO2 = 160 mmHg PCO2 = 0.3 mmHg
What is the PO2 and PCO2 of an alveoli?
PO2 = 105 mmHg PCO2 = 40 mmHg
What is the PO2 and PCO2 of the pulmonary vein and systemic arteries?
PO2 = 100 mmHg PCO2 = 40 mmHg
What is the PO2 and PCO2 of an aerobic cell?
PO2 < 40 mmHg
PCO2 > 46 mmHg
What is the PO2 and PCO2 of systemic and pulmonary veins?
PO2 = 40 mmHg PCO2 = 46 mmHg
What happens to PO2 and PCO2 during hyperventilation?
PO2: increases
PCO2: decreases
What happens to PO2 and PCO2 during hypoventilation?
PO2: decreases
PCO2: increases
According to Fick’s Law, what does diffusion depend on?
Proportional to surface area
Proportional to partial pressure gradient
Inversely proportional to thickness
To diffuse through a liquid a gas must be ____ in that liquid
Soluble
CO2 is more or less soluble than O2 in water? What is a consequence of this?
Why does that not really matter? ( i mean it does but)
Much more (20 times)
Because of this it diffuses much faster than O2
HOWEVER the difference in PCO2 is 10 times smaller than that for PO2, so they diffuse in almost exactly the same amount of time
In what ways (3) does the pulmonary circulation differ from systemic circulation?
- The RIGHT ventricle develops a pressure of 25 mmHg (compared to 120 mmHg in the LEFT)
- Blood pressure in the pulmonary circulation is LOWER than in systemic circulation
- The blood vessels are THINNER and contain less smooth muscle in pulmonary circulation compared to systemic circulation
How do you calculate flow?
Flow = Pressure / Resistance
What is the total pressure drop from pulmonary artery to left atrium?
10 mmHg
What determines the low vascular resistance in pulmonary circulation?
The thin walls of the vascular system
*The low vascular resistance and high compliance of the pulmonary circulation allows the LUNG to accept the whole cardiac output at ALL TIMES
What are two ways the pulmonary circulation can accommodate 2- to 3-fold increases in cardiac output with little change in resistance?
Recruitment (opening more vessels)
Distension (dilating already open vessels)
Which drugs cause contraction of smooth muscle, and what is a consequence of this?
Serotonin, histamine, norepinephrine
Increased pulmonary resistance
Which drugs cause relaxation of smooth muscle and what is a consequence of this?
Acetylcholine and Isoproteranol
Decreased pulmonary resistance
What is reflex vasoconstriction?
regions in the lungs that are poorly oxygenated will contract automatically
True/False? Pulmonary blood flow is affected by gravity
True (test performed by injecting radioactive xenon in a peripheral vein)
What are West’s 3 zones and which receive blood flow?
Top, middle, bottom of lungs
Top receives little blood flow (PA > Pa > Pv)
Middle receives some blood flow (Pa > PA > Pv)
Bottom receives most blood flow (Pa > Pv > PA)
What happens to vascular resistance above FRC?
Alveoli increase in size, alveolar vessels stretch longitudinally
Longitudinal stretch causes decrease in diameter, which increases resistance
What happens to vascular resistance below FRC?
Alveoly shrink, extra-alveolar vessels collapse because they are not stretched by pulmonary tissues (resistance still increases)
True/False? Gravity does not affect the distribution of ventilation
False
In an upright lung at rest, in normal gravity, the alveoli at the top of the lungs are more opened than the bottom ones (think of a slinky)
Can be measured with inhalation of radiolabelled gas
What happens to Blood flow and ventilation as you move from the bottom of the ribs to the top?
They decrease (at different rates, sweet spot around rib #3)
What is the average value for VA/Q?
1
O2 consumption per minute (VO2dot)) is ___ the O2 taken up by the blood in the lungs in one minute
EQUAL
Describe the structure of hemoglobin
Each molecule contains 4 subunits bound together
Each subunit is made up of heme joined to a globin
Heme contains Fe++ which can bind one molecule of O2
True/False? Hb binds irreversibly to O2
False
What is the total amount of O2 bound to Hb? at PO2 of 100 mmHg
19.5% vol
Does O2 contribute to PO2 once bound to Hb?
No (but the PO2 of plasma determines the amount of O2 bound to Hb)
What does the O2 dissociation curve show?
The amount of O2 carried by Hb at a given partial pressure of O2
How does Oxygen “know how to” bind Hb in alveoli and dissociate near aerobic cells?
At low PO2, O2 dissociates from Hb
At high PO2, O2 associates to Hb
Why is the O2 dissociation curve a curve and not linear?
Once the first O2 binds, it increases the affinity of the second heme (cooperative binding)
What O2 binding molecule is found in skeletal muscle? How is it different from hemoglobin and what is a result of this difference?
Myoglobin, only binds one O2
O2 myoglobin curve is hyperbolic, only releases O2 at very low PO2 (safety measure)
What is the Bohr effect? What is a result of it?
The shift in HbO2 dissociation curve to the right when blood CO2 or temperature increases (or when blood pH decreases)
Occurs during exercise
eg. for a given drop in PO2, an additional amount of O2 is released from Hb into the aerobic tissues (releases O2 at higher concentrations)
Why is carbon monoxide poisioning a threat?
CO has an extremely high affinity for the O2 binding sites in hemoglobin
Reduces amount of O2 bound to Hb
Shifts O2Hb curve to the left
Doesn’t stimulate increased ventilation because PaO2 remains normal
What is the main product of oxidative processes taking place in the body?
CO2
What are the three forms of CO2 found in blood?
Straight up CO2 (disolved in blood) 10%
Combined with Hb to form HbCO2 11% (no competition between O2)
As Bicarbonate 79%
How is bicarbonate formed?
CO2 + H2O -> H2CO3
H2CO3 -> HCO3- + H+
How is CO2 transported in tissue capillaries? In pulmonary capillaries?
CO2 enters RBC from plasma
Forms Bicarbonate + H+
Cl- enters cell to maintain charge balance
(bicarbonate circulates in plasma)
Reverse for Pulmonary capis
Why doesn’t CO2 compete with O2 in Hemoglobin?
CO2 binds gloin, whereas O2 binds heme
What is the Haldane effect?
In tissue capillaries, O2-free Hb may combine with H+
H+ + HbO2 -> HHb + O2
This occurs because reduced Hb is less acidic than HbO2 (Hb acts as a buffer)
Bottom line: For a given PCO2, more CO2 is carried in deoxygenated blood than oxygenated blood
What is the main symptom of respiratory failure? What are the three ways this can happen?
Failure of the respiratory system to do its job
Due to failure in:
- gas exchanging capabilities of the lungs
- Neurol control of ventilation
- Neuromuscular breathing apparatus
What are the 5 general causes of hypoxia?
Inhalation of low PO2 (eg low altitude)
Hypoventilation
Ventilation/Perfusion imbalance in the lungs
Shunts of blood across lungs (venous blood bypasses gas exchanging region of lungs)
O2 diffusion impairment (eg thickening of capillary membrane, or edema)
Which parts of the brain control voluntary breathing? which control involuntary breathing?
Voluntary: Cerebral hemispheres
Involuntary: brainstem (pons/medulla)
What is the breaking point of respiration?
When arterial PCO2 reaches 50 mmHg and PO2 reaches about 70 mmHg, the voluntary control of respiration is overridden
What are the two sensors for respiratory control?
Pulmonary receptors (info about lung volume) Chemoreceptors (info about O2 and CO2 content)
What is the controller of respiratory control?
The brainstem (pons and medulla) Gathers info from sensors and integrates them
What are the effectors of respiratory control?
Respiratory muscles
What are the two respiratory groups of the medulla? What happens if this medullary center is lysed?
Ventral: generates basic rhythm (pacemakers)
Dorsal: receives sensory inputs
Ventral and Dorsal groups talk to each other to determine the afferent rhythm of respiration
Cutting these centres leads to irregular breathing
What do cells in the rostral (upper) pons do in relation to breathing? What happens if these pneumotaxic centers are lysed?
They “turn off” breathing, leading to smaller tidal volume and increased breathing frequency
Cutting these centres leads to deep, slow breathing (same effect as cutting vagus nerves which bring afferent information)
What happens if you remove the influence of the upper pons and the vagus nerves?
Apneuses (tonic inspiratory activity interrupted by short expirations)
Seen in severe brain injuries
What do cells in the apneustic centre (lower pons) do in relation to breathing? what happens if these apneustic centres are lysed?
Send exitatory impulses to respiratory groups of medulla, promotic inspiration
What are sensed by chemoreceptors?
PO2, PCO2, and pH in arterial blood
Changes in these cause a change in ventilation
(activity proportional to respiration)
What are the two types of chemoreceptors?
Central and peripheral
Where are central chemoreceptors located? What do they detect? Where do they detect it?
Located in Ventral surface of medulla
Detect pH of cerebrospinal fluid (CSF) surrounding them *PCO2 and pH are influenced by those of arterial blood
What is the term given to elevated CO2 in blood?
Hypercapnia
Where are peripheral chemoreceptors located? What do they detect? Where do they detect it?
Mainly sensitive to changes in PO2, but stimulated by increased PCO2 and decreased pH
They are located in carotid bodies and in aortic bodies
Increasing PCO2 ____ ventilation at any given PO2
Increases (due to chemoreceptor function)
What are the three types of receptors in the lung that respond to mechanical stimuli? How do these impulses travel? what is the result of vagotomy?
Pulmonary stretch receptors
Irritant receptors
Juxta-capillary or J-receptors (C-fibres)
All afferent fibers travel in vagus nerves, vagotomy results in slow, deep breathing
Where are pulmonary stretch receptors located?
When do they discharge?
What reflex stimulates them?
Located in smooth muscles of trachea down to terminal bronchioles
Discharge in response to distension of the lung
Main reflex effect is the Hering-Breuer Inflation Reflex (Decrease in respiratory frequency due to prolonged expiratory time)
Where are irritant receptors located?
When are they stimulated?
What does their stimulation lead to?
Located between airway epithelial cells in trachea down to respiratory bronchioles
Stimulated by noxious gases, cigarette smoke, histamine, cold air, etc
Stimulation leads to cronchoconstriction and hyperpnea (increased breathing depth)
*may be important in reflex bronchoconstriction triggered by histamine release during allergic asthmatic attack
Where are Juxta-Capillary receptors located?
When are they stimulated?
What does their stimulation lead to?
Located in alveolar wall close to capillaries
NONMYELENATED FIBRES
Stimulated by increase in interstitial fluid in lungs
Stimulation leads to rapid and shallow respiration (intense stimulation causes apnea)
May play a role in dypsnea (difficulty breathing)
How do you measure the static properties of the lungs?
Elastic properties - recoil pressure
Lung volumes - spirometry
Pressures - manometers
“negative pressure” means below atmospheric
Esophageal pressure is approximately equal to what pressure? Why? How can you measure this?
Pleural pressure, because it is located between the two pleural spaces
Measured by inflating a balloon in the esophagus
What is compliance and how is it calculated?
The ease at which a structure can be distended
C = dV/dP
Typically measured with static pressure-volume curve
How does compliance change as pressure increases?
It gets harder to distend lungs as pressure increases (the slope levels off)
What happens to compliance during Emphysema? During Fibrosis?
Emphysema: compliance is greatly increased (very little increase in pressure reaches TLC)
Fibrosis: Compliance is greatly decreased (huge increase in pressure to reach TLC)
What is elastance?
1/compliance
What happens to the compliance of the chest wall at a) 60% VC? b) 0% VC? c) 100% VC?
a) 0 mmHg (at rest)
b) -40 mmHg (wants to expand outwards)
c) ~15 mmHg (wants to recoil inwards)
What happens to pressure at FRC?
Pressure is zero:
The inwards recoil of the lungs is balanced by the outward recoil of the chest wall
How is flow calculated in an alveoli?
What happens to these pressures during inspiration? During Expiration?
F = (Palv - Patm)/R
Inspiration: Palv < Patm (F < 0 alvioli expands)
Expiration: Palv > Patm (F >0 alveoli shrink)
What prevents you from inspiring indefinitely?
Palv becomes = to Patm, no more flow
How are flow and alveolar pressure plotted on a graph?
Sinusodial, IN PHASE
Which pressures must be different to have gas flow through airways?
Pao (airway opening) and Palv (alveolar)
How do you calculate resistance of an aiway to gas flow (Raw)?
Raw = (Palv - Pao)/Flow
Describe the dyanmic compression of airways when a subject inspires to TLC and expires to RV? What is universal about this curve?
During expiration, flow rises very rapidly to a high value then declines over the rest of expiration
The descending portion of the flow/volume curve is independent of effort because the comprassion of the airways is by intrathoracic pressure
Describe the various changes to Paw, Ppl and Palv during inspiration to forced expiration
Before inspiration: Paw = 0, Ppl =-5 cm H2O
During inspiration: Ppl and Paw fall
At the end of inspiration, Paw is 0 and the airway transmural pressure is 8 cm H2O
During forced expiration, Ppl and Palv are increased
Because of the pressure drop along the airways as flow begins, there is a point at which there is a positive pressure tending to close the airways
How is flow altered during an Obstructive disease such as Emphysema? During a restrictive disease such as Fibrosis?
Obstructive: lung volume shifted to left, FRV slightly smaller than TLC of normal patient, “scooped out” shape, greatly decreased peak flow
Restrictive: TLC slightly larger than normal FRV, FRVs similar, greatly decreased peak flow, “bulgy” appearance
