Respiratory system 2 + 3 Flashcards
Air flow and pressure changes
respiratory pressure cycle
End of Expiration
Alveolar/ intra pulmonary pressure = atmospheric pressure
No air movement
Inspiration
Increased thoracic volume >
Increased alveolar volume
Decreased alveolar pressure
Atmospheric pressure > alveolar pressure
Air moves into lungs
End of Inspiration
Alveolar pressure = atmospheric pressure
No air movement
Expiration
Decreased thoracic volume
Decreased alveolar volume
Increased alveolar / intrapulmonary pressure
Alveolar pressure > atmospheric pressure
Air moves out of lungs
What is pleural pressure?
the pressure in the pleural cavity
Normally lower than alveolar pressure.
Suction effect - fluid removal by the lymphatic system
Negative pressure difference (lower pleural pressure than alveolar pressure) - role?
keeps the alveoli expanded
-ive pressure significance
Pulls the pleura away from the outside of the alveoli
Pressure on the alveoli is lower
Expansion is opposed by the tendency of the lungs to _____
recoil
Pneumothorax
Pleura pierced
Pneumothorax : Pleura pierced
Air introduced
Pleural pressure is not low enough to overcome lung recoil
Alveoli collapse
volume larger
more air sucked in
Inspiration
Active process(needs energy)
Signals from the respiratory centre in the medulla oblongata (brain stem) >
Contraction of the diaphragm and intercostal muscles leading to the diaphragm moving downward >
Transverse expansion of thoracic cavity
+
Vertical expansion of thoracic cavity
>
Lung volume increases and the intra-alveolar pressure decreases >
Air is sucked in (inhalation)
ExhalationPassive process - what kind of energy needed?
elastic potential energy
The process of exhalation:
A passive event due to elastic recoil of the lungs
Relaxation of diaphragm and external intercostal muscles
During forced expiration, ONLY there is contraction of abdominal, internal intercostal (accessory muscles)
Characteristics of
No inherent rhythm
Generate tension due to rhythmic pattern of neuron-induced action potentials activating them
Muscles attempt to overcome the resistance to airflow within the airways
When at rest, the thorax assumes the FRC (Functional Residual capacity) position
Respiratory Function: measurement
Spirometry is the process of measuring volumes of air that move into and out of the respiratory system
measure respiratory volumes: peak flow (info on health of lungs)
Volumes and Capacities
Respiratory volumes:
measures of the amount of air movement during different portions of ventilation,
Respiratory capacities
Sums of two or more respiratory volumes
How many litres does the total of volume of air contain in the respiratory system?
4-6L
Tidal Volume (VT)
The volume of gas expired/inspired in one breathing cycle
Also known as ‘resting’ or ‘quiet’ breathing
Inspiratory reserve volume
Inspiratory reserve volume is the amount of air that can be inspired forcefully beyond the resting tidal volume
Expiratory reserve volume
Expiratory reserve volume is the amount of air that can be expired forcefully beyond the resting tidal volume
Residual volume
Residual volume is the volume of air still remaining in the respiratory passages and lungs after maximum expiration
Without a residual volume, the lungs would completely collapse and the pressure required to generate inflation would be high
Total lung capacity (TLC)
The volume of gas in the lungs and airways at a position of full inspiration – therefore we are measuring how much air the lungs can actually hold
Lung expansion is limited at a point which defines TLC
Breathing out maximally does not mean you breathe ____ air out of lungs
ALL
Vital Capacity (VC)
The total volume of gas that can be expired from the lungs from a position of full inspiration/ the total volume of gas that can be inspired from a position of residual volume
This is similar to an FVC manoeuver except it is not forced
Inspiratory capacity
The tidal volume plus the inspiratory reserve volume
The amount of air a person can inspire maximally after a normal expiration
Functional Residual Capacity fluctuates between
lung recoil and chest wall
Limits of Spirometry
Cannot measure TLC, FRC, RV
Dynamic Lung Volumes
Rate at which air moved
Peak expiratory flow (PEF):
ameasure of how quickly youcan blow air out of yourlungs
What are capacity?
amount of air the lungs can hold IN TOTAL
peak flow properties?
Measured inlitres/minute(l/min)
“Normal” will depend on age, height and gender
Record in a peak flow diary and compare against “best”
Can be used for diagnosis of asthma or to predict oncoming asthma attack
Forced (Expiratory) Vital Capacity
Rate at which lung volume changes during direct measurement of the vital capacity.
FEV1 forced expiratory volume amount of air you can force from your lungs in one second
Important pulmonary test
FORCED vital capacity
individual inspires maximally and then exhales maximally as rapidly as possible into a spirometer:
records volume of air expired per s
What conditions can be identified where vital capacity might not be affected but the expiratory flow rate is reduced?
Asthma - contraction of the smooth muscle in the bronchioles increases the resistance to airflow
Emphysema - changes in the lung tissue result in the destruction of the alveolar walls, collapse of the bronchioles, and decreased elasticity of the lung tissue.
increase the resistance to airflow
FEV1 – Forced Exhaled Volume in 1 Second = Key Parameters
Amount of air exhaled in 1 second
Affected by airway diameter
Predict ‘healthy’ values by age, gender and height
FVC – Forced Vital Capacity Definition
Key parameters
Total amount of air that can be exhaled
FVC + Residual Volume = Lung Capacity
Predict ‘healthy’ values by age, gender and height
FEV1 / FVC ratio
= key parameters
Does not require tables, FEV1 values adjusted to FVC
Ratio <0.7 indicates airway obstruction
Basic gas exchange
- Ventilation – we need to be able to get air to the alveoli for gases to exchange
- Perfusion – the circulatory system needs to ensure blood gets to the alveolar
Gas Exchange
Between air and blood occurs at the respiratory membranes
Alveoli
Some in the respiratory bronchioles and
alveolar ducts
Not in conducting zone - the bronchioles, bronchi, and trachea.
The volume of these = anatomical dead space
Pathology such as emphysema can increase this
What effects gas exchange?
- Thickness of the membrane
- O2 diffuses through the respiratory membrane less easily than does CO2
- O2 diffuses through the respiratory membrane less easily than does CO2 - Total surface area of the respiratory membrane
- reducing reduces gas exchange - Partial pressure of gases across the membrane
- pressure excreted by a specific gas in a mixture of gases
PO2, PCO2
- gases in the air dissolve in liquid
- until partial pressure in liquid pressure in air
- gases in liquid and air diffuse from areas of higher partial pressure toward area of lower. partial pressure until equal
- Blood from tissues
Blood from tissues has a lower Po2 and a higher Pco2 compared to alveolar air
O2 diffuses from the alveoli into the pulmonary capillaries
Po2 in the alveoli > in the pulmonary capillaries
CO2 diffuses from pulmonary capillaries into the alveoli
Pco2 pulmonary capillaries > alve
- Venous ends of the capillaries:
Pressures equal because of diffusion
The blood carries O2 away by bulk flow to the
tissues where O2 is required
- Mixing with deoxygenated blood = PO2 levels?
lower PO2 than in capillaries
- Oxygen diffuses out of the blood and into the interstitial fluid then into cells
Po2 in interstitial fluid < capillary
Po2 in cells < than interstitial fluid
Carbon dioxide diffuses from cells into the interstitial fluid and from the interstitial fluid into the blood
- Equilibrium
equal pressure
Transport of Oxygen
Oxygen is stored in the body in four forms -
As a gas in the lungs
Dissolved in tissue fluids
As oxyhaemoglobin in blood
As oxymyoglobin in muscle
Haemoglobin - structure:
red blood cell
no nucleus so more haemoglobin can fit in
cytoplasm with large amount of haemoglobin
shape gives large surface area to pass oxygen through
Gases can dissolve & diffuse between the ___ and the ________ system
lungs
circulatory
oxygen diffuses into
red blood cells
carbon dioxide diffuses into
alveolus
Haemoglobin – Structure
- Consists of 4 myoglobin units joined together
- Each has one polypeptide chain and one heam group
- Haem contains central Iron (Fe2+ )atom
Iron atom binds to one oxygen as blood travels between lungs and tissues - one Hb molecule can bind 4 O2 molecules
Oxyhaemoglobin Dissociation Curve
Ability of hemoglobin to bind to O2 depends on the Po2
- oxy-Hb dissociation curve
- High Po2, haemoglobin binds to O2
- Low Po2, hemoglobin releases O2
lungs, Po2 normally high - hemoglobin holds as much O2 as it can
- In the tissues, Po2 is lower
hemoglobin releases O2
Oxyhaemoglobin Dissociation Curve
Amount of O2 released from oxyhemoglobin (reduced affinity) is increased by
low Po2,
high Pco2
low pH
high temperature
Physical Exercise
Transport of Carbon Dioxide
Carbon dioxide diffuses from cells into the blood.
Transported by:
1. 7% is transported as CO2 dissolved in the plasma
- 23% is transported bound to blood proteins, primarily haemoglobin
- 70% as bicarbonate ions
Gas exchange in Tissues
CO2 diffuses into plasma and RBC
Forms carbonic acid catalysed by carbonic anhydrase found inside RBC and on capillary epithelium
Carbonic anhydrase increases the rate at which carbonic acid generated in tissue capillaries
promotes the uptake of CO2 by red blood cells.
Gas Exchange in Lungs
Capillaries of the lungs
the process is reversed
CO2 diffuses from RBC to alveoli
HCO3−dissociates to produce H2CO3
Carbonic anhydrase catalyses formation of CO2 and H20 from H2CO3
The CO2 diffuses into the alveoli and is expired
What does CO2 and water form?
carbonic acid
H2CO3
How is pH regulated?
Chemical acid-base buffer system of bodies fluids - (seconds)
The respiratory centre – minutes
The kidneys - hours-days
Control of Respiration
Normal rate of breathing in adults
Between 12 and 20 breaths per minute
rate of breathing determined by the number of times respiratory muscles are stimulated
Breathing is spontaneously initiated within the central nervous system (CNS)
Medulla oblongata (brainstem)
An increased depth of breathing results from
stronger contractions of the respiratory muscles caused by recruitment of muscle fibres
increased frequency of stimulation of muscle fibres
Rhythmic Breathing
It takes more effort and time to fill the lungs than it takes to exhale, when the diaphragm simply relaxes to push out the air. Rhythmic breathing can make us more aware of the need for a longer time to inhale the oxygen needed for high-intensity exercise like running.
- Starting inspiration.
Neurons in the medullary respiratory center that promote inspiration - continuously active
stimulation from
blood gas levels, movements of muscles and joints, voluntary respiratory movements
When the inputs reach a threshold level
somatic nervous system neurons stimulate respiratory muscles ( via action potentials)
inspiration starts
- Increasing inspiration
Once inspiration begins, more and more neurons are activated
Progressively stronger stimulation of the respiratory muscles, lasts for approximately 2 seconds
- Stopping inspiration
Neurons stimulating muscles of inspiratory muscles also stimulate medullary neurons that stop inspiration
- These also receive input from the pontine respiratory neurons
- Stretch receptors in the lungs
When the inputs to these neurons exceed a threshold level,
they cause the neurons stimulating respiratory muscles to be inhibited.
Relaxation of respiratory muscles leads to in expiration (3 s).
Next inspiration step 1
Control of Respiration
The system must perform three key functions:
- Maintain, through involuntary controls, a regular rhythmic breathing pattern
- Adjust the tidal volume (VT) and breathing frequency (fb) such that alveolar ventilation is sufficient to meet the demands for gas exchange at cellular level
- Adjust the breathing pattern to be consistent with other activities using the same muscles, such as speech
Some conscious control
Respiratory control system
Central control system
> output > effectors > sensors [chemoreceptors, lungs and other rreceptors] > input back to CCS
Respiratory control centres
Major groups of neurones in respiratory centre which control respiration:
Pons
Pontine respiratory group
Controls switches between inspiration and expiration
Medulla
Dorsal respiratory group (DRG)
Diaphragm (inspiratory)
Ventral respiratory group (VRG)
Intercostals
Abdominals
Inspiratory and expiratory
Nervous Control of Breathing
Some voluntary control
Most autonomic
Several reflexes, such as sneeze and cough reflexes, can modify breathing
The Hering- Breuer reflex
- limits the extent of inspiration
- As the muscles of inspiration contract the lungs fill with air
- Sensory stretch receptors located in the lungs are stimulated
- Action potentials sent to the medulla oblongata
Here they inhibit the respiratory centre neurons and cause expiration
- In infants important role in regulating the basic rhythm of breathing and over inflation
- In adults when the tidal volume is large - during heavy exercise
Chemical control of Breathing
Level of CO2 (not O2), in the blood is the major driving force
Even a small increase in the CO2 level (hypercapnia) results in a powerful urge to breathe
Breathing is controlled so finely that the PaO2 and PaCO2 are kept within normal limits
the system has three control pathways – to control of breathing
The PCO2 is the principle pathway, controlling the rate and depth of breathing on a breath-by-breath basis
Under certain circumstances, such as acclimatization to altitude, the PO2 pathway (the second pathway) can override the PCO2 pathway.
3rd pathway is required to allow all other actions e.g. talking/swallowing/coughing to break through the normal pattern of breathing and try to match breathing to the expected voluntary or behavioural activity
Central chemoreceptors
An increase in H+ ions increases ventilation and vice versa as follows:
PaCO2 rises causing a rapid increase in H+ ions > causes pH to fall (increase acidity) > central chemoreceptors to transmit a signal to increase ventilation > PaCO2 and CO2 decrease and when balance is restored, ventilation will decrease
Chemoreceptors
Centrally;
Medulla oblongata
Peripherally
Carotid bodies
Aortic bodies
Chemical control
pH that accompanies an increase in CO2 levels
Chemoreceptors
Medulla oblongata
chemoreceptors H+ concentration
pH CO2
If blood CO2 levels decrease, pH increase > medullary chemoreceptors signal a decreased breathing rate > retains CO2 in the blood
More CO2 in the blood causes H+ levels to increase, > blood pH to decrease to normal levels
Carotid and Aortic bodies:
pH, > Co2, > O2
Increased breathing
Global Innervation
Airways
Innervated by the vagus nerve – Parasympathetic
Dominant
Bronchoconstriction
Innervated by the Sympathetic nerve chain
Respiratory Muscles
Innervated by the intercostal (motor) nerves
Phrenic nerve innervates the diaphragm
Autonomic Nervous System Physiology
Parasympathetic nervous system
Neurotransmitter (effector) – Acetylcholine (Ach)
Receptors – muscarinic / cholinergic receptors
M1 to M5
Airways: M1 M2 M3 present. M3 most important
Muscarinic receptors
Stimulation causes the contraction of bronchial smooth muscle
Muscarinic receptors located in many glands help to stimulate secretion e.g. mucus and saliva
Sympathetic nervous system - types of receptors
Neurotransmitter (effector) – Noradrenaline (NA)
Receptors – adrenergic receptors
alpha, beta1 and beta2
Beta1 receptors – heart
Stimulation increases rate and force e.g.
adrenaline/epinephrine
Beta2 receptors – smooth muscle of bronchioles
Stimulation (Agonist) causes relaxation e.g. salbutamol
