Respiratory system III Flashcards
Ventilation
- Air to the alveoli for gases to
exchange
Perfusion
- The circulatory system needs to ensure blood gets to the
alveolar
Gas Exchange
- Respiratory membranes are between air and blood
- Respiratory bronchioles and alveolar ducts and alveoli
- Perfusion for those that have emphysema
Gas exchange
Thickness of membrane
- O2 exchange affected before CO2
- O2 diffuses through the respiratory membrane less easily than does CO2
Gas exchange
Total surface area of the respiratory membrane
- Less surface area reduces gas exchange
Gas exchange
Partial pressure of gases across the membrane
- Pressure exerted by a specific gas in a mixture of gases PO2, PCO2
- Gases in the air dissolve in the liquid
- Until partial pressure in liquid = to the partial pressure in air
- Gases in liquid and air diffuse from areas of higher partial pressure toward areas of lower partial pressure until equal
step 1
Process of gas exchange
tissues to alveoli
- Blood from tissues has a lower Po2 and a higher Pco2 compared to alveolar air
- O2 diffuses from the alveoli into the pulmonary capillaries
- CO2 diffuses from pulmonary capillaries into the alveoli
Step 2
Process of gas exchange
venous end of 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 =
lower PO2 than in capilaries
Step 3
Process of gas exchange
Diffusion to cells
- Oxygen diffuses out of the blood and
into the interstitial fluid then into cells - Carbon dioxide diffuses from cells into
the interstitial fluid and from the interstitial fluid into the blood and equalibrium is reached
How is oxygen stored in the body
- As a gas in the lungs
- Dissolved in tissue fluids
- As oxyhaemoglobin in blood
- As oxymyoglobin in muscle
Oxyhaemoglobin
Dissociation Curve
- Hemoglobin to bind to O2
depends on the Po2 - High Po2, haemoglobin binds to
O2 - Low Po2, hemoglobin releases
O2 - In the lungs the ppO2 is usually high heam holds most O2
- At tissues the ppO2 is usually low heam relases the O2
Factors that effect Oxyhaemoglobin
Dissociation Curve
- Low Po2,
*high Pco2
*low pH
*high temperature
*Physical Exercise
Transport of Carbon Dioxide
- Transported as CO2 dissolved in the plasma
- Transported bound to blood proteins, primarily haemoglobin
- 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 - Increase uptake of CO2 by red blood cells
Gas exchange in tissues
- Capillaries of the lung 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
pH importance of carbon dioxide
- CO2 levels increase, the blood pH decreases
because CO2 reacts with H2O to form H2CO3 - H+ that results from the dissociation of H2CO3 is responsible for the decrease in pH
- Blood levels of CO2 decline, the blood pH increases
Regulation of pH
- Chemical acid base buffer system
- The respiratory centre - lungs
- Kidney which takes hours
Control of Respiration
- Rate of breathing dependant on number of times repiratory muscles are stimulated
- Spontaneously initiated within the central nervous system
- Increase in the depth of breathing is dependant on more stimulation and stronger contractions of muscle fibre
Rhythmic breathing
Starting inspiration
- Neurons are continually active stimulating the repiratory centre caused by blood gas lavels muscle movement
- When threashold is reached somatic nervous system neurons stimulate respiratory muscles and inspiration starts
Rhythmic breathing
Increasing inspiration
- Increase in neurone activation therefore stonger stimulation of respiratory muscles which last 2s
Rhythmic breathing
Stopping inspiration
- Neurones that stimulate inspiratory muscles also stimulate medullary neurones that stop inspiration
- Receive input from the pontine respiratory neurons stretch receptors in the lungs
- When inputs exceed threashold levels it causes neurone respiratory muscles to be inhibited
- Leads to relaxation and expiration
Key functions of Respiration
- Maintainance through involantary controls through regular rhythmic breathing
- Tidal volume and breathing frequency so that ventilation is mantained for gas exchange
- Adjust breathing pattern depending on activity
Pons
- Pontine respiratory group
- Controls switches between inspiration
and expiration
Medulla Dorsal respiratory group
Diaphragm
Medulla Ventral respiratory group
- Intercostals
- Abdominals
- Inspiratory and expiratory
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
- Inhibition of respiratory centres causes expiration
Chemical control of breathing
- Increase of CO2 in the blood urgue to breath increases with CO2
3 Control pathways
- PCO2 is the principle pathway, controlling the rate and depth of breathing on a breath-by-breath basis
- Acclimatization to altitude, the PO2 pathway can override the PCO2 pathway
- Allows talking, swallowing and coughing to break through the normal pattern of breathing and try to match breathing to the expected voluntary or behavioural activity
Central chemoreceptors
- PaCO2 rises causing a rapid increase in H+ ions
- Causes the pH level to fall
- Causes the central chemoreceptors to transmit a signal to increase ventilation
- PaCO2 and CO2 decrease and when balance is
restored, ventilation will decrease
Types of chemoreceptors
- Central Medulla oblongata
- Peripherally Carotid bodies and Aortic bodies
Controlling the breathing rate
- CO2 levels of the blood decrease causing the pH to increase - Medullary chemoreceptors signal decrease inbreathing rate keeps CO2 in the blood
- Increase CO2 in the blood causes H+ levels to increase and blood pH decreases
Globullar innervation
Airways
- Innervated by the vagus nerve –
Parasympathetic causing bronchoconstriction
Respiratory muscle innervation
- Intercostal (motor) nerves
- Phrenic nerve innervates the diaphragm
Parasympathetic nervous system
- Acetylcholine is the effector neurotransmitter
- The muscarinic M1 to M5
- Most important receptor M3 for airways
Muscarinic receptors
- Stimulation causes the contraction of bronchial smooth muscle
- Muscarinic receptors located in many glands help to stimulate secretion
Sympathetic nervous system
- Noradrenaline effector with adrenergic receptors
- Beta1 receptors – Heart Stimulation increases rate and force
- Beta2 receptor smooth muscle of bronchioles stimulation (Agonist) causes relaxation