Respiratory System Flashcards
Define external respiration
the exchange of CO2 and O2 between the external environment and the cells of the body
where does external respiration take place?
in the lungs
what is atmospheric pressure value at sea level?
760 mmHg
what is partial pressure?
the amount an individual gas contributes to overall air pressure
how can partial pressure of a gas be calculated?
fraction of air that the gas you are considering equates to x total air pressure
what do partial pressures define?
amount of o2 or other gas present in the lungs, blood or veins
What to PA, Pa and Pv stand for?
PA: Partial pressure in lungs/alveoli
Pa: Partial pressure in blood (arteries)
Pv: Partial pressure in veins
what factor must be considered when calculating partial pressures within the lungs?
water vapour is a gas so contributes to total atmospheric pressure
what is the partial pressure of water within the lungs?
47mmHg
what sort of muscle is the diaphragm formed from?
sheet of skeletal muscle
what two body cavities are separated by the diaphragm?
thoracic and abdominal
what nerve innervates the diaphragm?
phrenic nerve
when does the diaphragm contract (flatten)?
during inspiration
what is the chest wall formed from?
muscle and ribs
what do accessory muscles in the chest wall do?
lift ribs and sternum
name two accessory muscles in the chest wall
sternomastoid
scalene
what muscles contract during quiet inspiration?
diaphragm
external intercostals
what muscles contract during forceful inspiration?
diaphragm
external intercostals
accessory muscles
what muscles relax during quiet expiration?
diaphragm
external intercostals
what muscles are involved during forceful expiration?
diaphragm relaxes
internal intercoastals contract
abdominal muscles contract
what do change do chest movements lead to?
volume change
what happens to the chest volume during inspiration?
increases, leads to reduced pressure so air floods in
what happens to the chest volume during expiration?
reduced chest volume, increased pressure
what is the name of the membranes that covers the chest wall?
pleural membranes
what are the 2 types of pleural membranes?
parietal (chest wall)
visceral (lungs)
what fluid do membranes secrete?
intrapleural fluid to provide lubricaition
what are the 2 airway zones?
conducting zone
respiratory zone
what happens in the conducting zone?
movement of air into and out of lungs, no gas exchange
what happens in the respiratory zone?
gas exchange
what muscle is the airway made from?
smooth muscle
what changes resistance to airflow in the lungs?
changes in diameter of the conducting airways
what happens if the airway diameter dilates?
resistance to airflow will be reduced
what does contraction of airway smooth muscle cause?
narrowing (constriction) of airways
what body system is contraction and relaxation of airway smooth muscle influenced by?
autonomic nervous system
where within the lungs is most of the resistance to airflow?
upper airway (50-70%)
what are lungs held open by?
elasticity of lung tissue
what are the functional units of the lung?
alveoli
what are alveoli surrounded by?
sheet like capillaries
what type of cells is the alveolar wall formed of?
type 1 pneumocytes
what cells produce surfactant?
type 2 pneumocytes
what is the role of surfactant in lungs?
helps to stop the lung from collapsing and reduce the surface tension of fluid in the lungs
what is the driving force for the flow of air into and out of the lungs?
the difference between atmospheric pressure at the mouth and pressure within the alveoli
changes in which pressure determines the direction of airflow?
alveolar pressure
why does alveolar pressure determine the direction of airflow in and out of the lungs?
as atmospheric pressure is usually constant
in inspiration is the pressure greater in the lungs or the atmosphere?
greater in atmosphere
in expiration is the pressure greater in the lungs or the atmosphere?
greater in the lungs
what effect does movement of the ribs and diaphragm during inspiration have on the volume of the thoracic cavity?
increases
what effect does movement of the ribs and diaphragm during inspiration have on the intra-alveolar pressure?
decreases
why is inspiration phase active?
it requires muscles to achieve
what point must be reached to stop air flowing into the lungs
alveolar pressure reaches atmospheric pressure (PB)
what effect does movement of the ribs and diaphragm during expiration have on the volume of the thoracic cavity?
decreases
what effect does movement of the ribs and diaphragm during expiration have on the intra-alveolar pressure?
increases it
during quiet ventilation is the expiration phase passive or active?
passive
what does passive expiration depend on?
elastic recoil of lungs
when does air flowing out of lungs during expiration cease?
when alveolar pressure equals atmospheric pressure(PB)
is forceful ventilation active or passive?
active as it involves contraction of accessory expiratory muscles
what causes volume changes during respiration?
chest movements
what are the muscles of inspiration?
external intercostals
diaphragm
what is the diaphragm shaped like?
a parachute/dome
what shape does the diaphragm become on contraction?
flat
when the diaphragm flattens on inspiration what effect does this have on the thoracic and abdominal (visceral) cavity?
increases thoracic volume
displaces viscera caudally (downwards)
what are the 2 types of intercostal muscle?
external and internal
what are the two major accessory muscles of breathing?
scalene (within the neck) abdominal muscles (pressurize abdomen)
what are the 4 pressures that need to be considered during the breathing cycle?
atmospheric
intra-alveolar
intrapleural
transmural
what is intra-alveolar pressure?
pressure in lungs
what is intrapleural pressure?
pressure between lungs and chest wall
what is transmural pressure?
the difference between intra-alveolar and intrapleural pressure
when is lung tissue stretched?
at all times even after full expiration
is the chest wall compressed or stretched at resting lung volumes?
compressed
what are the opposing forces which contribute to intrapleural pressure?
outward recoil of chest
inward recoil of ‘elastic’ lungs
why do outward recoil of chest and inward recoil of ‘elastic’ lungs oppose each other?
because lungs and chest wall are attached
how is negative pressure in the pleural space produced?
force of elastic recoil of lung and chest wall oppose creating negative pressure in intrapleural spacethat exerts force on both.
define vital capacity
amount of air that can be expelled from lungs after full inhalation
what is functional residual capacity?
volume in lung remaining at the end of normal expiration
what are capacities the sum of?
two or more volumes
how is the work of breathing minimised?
when the lung volume at the end of expiration equals functional residual capacity
why is the lung volume at the end of expiration equal to functional residual capacity?
at FRC the inward force of lungs equals the outward force of chest
what quality aids the expansion of lungs during stretching?
high compliance (easy to distend)
what is the ‘collapse’ of lungs aided by when the stretching force is removed?
elasticity
for what 2 reasons does inspiration require energy?
stretch the lungs and chest wall
overcome the resistance of airways
what process recovers some of the energy stored as elastic recoil?
expiration
what can an increase in lung compliance be caused by?
emphysema (loss of elastic tissue so easier to stretch)
ageing
what can a decrease in lung compliance be caused by?
fibrosis (lung becomes stiffer)
pulmonary oedema
deficiency of surfactant
what does lung stretching (inspiration) increase within the lung?
tension
what does tension in the lung pull on and increase the size of?
airways and blood vessels
what effect does increasing the diameter of airways and blood vessels have?
reduces pulmonary vascular resistance
reduces airway resistance
what must breathing overcome within the fluid lining alveoli?
surface tension
what creates surface tension in the alveoli?
fluid lining
is pressure caused by surface tension greater in smaller or larger alveoli?
smaller
where do surfactent molecules sit in the lung?
between water molecules in alveoli
what effect does the presence of surfactant molecules in the alveoli have?
reduces surface tension
what is pressure in the small and large alveoli equalised by?
presence of surfactant
what effect does surfactant have on pulmonary compliance?
increases it and so reduces the work of inflating the lungs
what effect does surfactant have on the tendency of lungs to recoil?
reduces it so they do not collapse so readily
what is the name of the pulmonary surfactant?
dipalmitoyl phosphotidyl choline
what is the pulmonary surfactant formed from?
phospholipids
where does the pulmonary surfactant originate from?
type II alveolar cells (pneumocytes)
what is the function of pulmonary surfactant?
reduces surface tension
what is the release of pulmonary surfactant stimulated by?
during inspiration (stimulated by stretch)
what must airway resistance be overcome by?
the action of inspiratory muscles that create the air to alveolar pressure gradient
how can airflow be calculated?
pressure gradient (air -alveolar pressure) divided by resistance of airway
what diseases increase resistance of airways?
COPD (encompasses bronchitis and emphysema
oedema (fluid restricts airflow)
asthma (increased constriction of smooth muscle and increased mucus secretion and inflammation)
what is anatomical deadspace within the lungs?
volume in airways that does not support gas exchange
how many ml per kg is there of dead space within the average human?
2.2 ml per kg
where is anatomical deadspace found?
conducting zone (permits movement of air in and out of the lungs
what is alveolar dead space?
where the alveoli is ventilated but not perfused, so not involved in gas exchange
is there alveolar dead space in a healthy adult human?
no
what is physiological dead space?
anatomical dead space + alveolar dead space
in a healthy lung what is physiological dead space?
anatomical dead space only as there should not be any alveolar dead space
where is there most and least resistance to airflow in the lungs?
most: trachea and primary bronchi
least: terminal bronchiole and alveoli
what are the 3 influences on airway diameter and resistance?
physical factors affecting airflow
chemical influences on airways
autonomic control of airways
how are lung tissues connected to bronchioles?
by lung parenchyma
how does increased airway diameter affect resistance to airflow?
reduces resistance to airflow
what are the 4 types of chemical influences on airways?
nervous
hormonal
chemical
physical
give an example of a nervous bronchoconstrictor and bronchodilator
constrictor: cholinergenic
dilator: adregenic
what receptor to adrenogenic bronchodilators act on?
alpha and beta adrenoreceptors
give an example of a hormonal bronchoconstrictor and bronchodilator
constrictor: acetylcholine
dilator: norepinephrine
what receptor do norepinepherine bronchodilators act on?
alpha and beta adrenoreceptors
give an example of 3 chemical bronchoconstrictors and 2 bronchodilator
bronchoconstrictors: histemine, SRS-A, prostaglandin F-2alpha
bronchodilator: CO2
give an example of 3 physical bronchoconstrictors
smoke
dust
SO2
what does the diameter of the conducting airways determine?
resistance to airflow
how can ANS influence resistance and airflow?
constricting/dilating airways
what effect do beta-receptor agonists have on airways?
act to dilate airways
what system is airway resistance (bronchomotor tone) increased by?
parasympathetic nervous system
what nerve processes causes bronchoconstriction?
parasympathetic neurons release acetylcholine that activate muscarinic receptors which causes contraction of muscle and bronchoconstriction
How does the nervous system cause bronchodilation?
sympathetic nervous system release of adrenaline acts on beta 2 receptors and causes bronchodilation
describe the process of the cough reflex
irritant receptors - sensory receptors - vagal afferents - medulla oblongata respiratory centres - vagal efferent - effector/target organs (bronchioles leading to vasoconstriction)
describe the process of the hering-breuer reflex
lung stretch receptors - sensory receptors - vagal afferents - medulla oblongata respiratory centres - vagal efferent - effector/target organs (bronchioles leading to vasodilation also termination of inspiration)
what is the energy in respiration used to overcome?
to stretch the lung
overcome the resistance of the airways
how can disease alter compliance and resistance?
compliance increase: emphysema
compliance decrease: pulmonary fibrosis/oedema
resistance increase: asthma
what are the 3 ways the lung function can be measured?
static volumes (breathing cycle) dynamic volumes (change with time) CO2 in expired air (over time)
what equipment is used to measure static volumes?
spirometry
what equipment is used to measure dynamic volumes?
vitalograph
what equipment is used to measure CO2 in expired air?
capnography
what are static volumes a measure of?
capacity and volume
what is forced vital capacity (FVC)?
total volume of air expired from lungs
what is FEV1?
forced expiratory volume in 1 second
how do lung volumes change with reduced compliance?
air leaves faster but less is expelled
how do lung volumes change with increased airway resistance?
it is harder to move air into and out of the lungs so volume is reduced
what principle is capnography based on?
inspired air contains zero CO2 and expired air contains lots
where is capnography often used?
anesthesia
what is the usual mean BP in the pulmonary circulation?
15 mmHg
what is the usual mean BP in the systemic circulation?
100 mmHg
what are the two types of circulation in the lungs?
pulmonary and bronchial
what does the bronchial circulation in the lungs provide?
arterial blood to the lung tissue
what is the right to left anatomical shunt?
inclusion of some deoxygentated blood in the left atrium
by how much does the venous blood from the bronchial and coronary systems reduce the partial pressure of oxygen in the aorta?
5-15 mmHg
what can the measure of the A-a gradient be useful for?
in determining causes of hypoxaemia (low blood O2)
what is the A-a gradient?
difference between partial pressure of O2 in the alveoli (PAO2) and the arteries (PaO2)
what is the alveolar air equation?
PAO2 = PIO2 - (PaCO2/respiratory ratio)
what is the respiratory ratio?
ratio of CO2 to O2
what effect does hypoventilation have on PaO2?
reduces
what effect does hyperventilation have on PaCO2?
reduces
when does a physiological shunt occur in the lungs
when perfusion continues but alveoli is not ventilated
what is an effect of a physiological shunt?
increased venous admixture (more deoxygenated/poorly oxygenated blood in the left atrium)
what effect does a physiological shunt have on oxygenation?
reduced - similar to anatomical but larger
what medical conditions can cause a physiological shunt to be observed?
pulmonary oedema
pneumonia
foreign body entry
obstructions
what is the result of physiological shunt?
less oxygen in the blood
what is PaO2 determined by?
average PO2 of all blood leaving the left side of the heart (including the venous blood from lungs and heart)
what does pulmonary pressure prevent?
oedema
what happens to pulmonary resistance at high arterial pressure?
distention of opened capillaries and recruitment of closed ones to reduce resistance
what effect does the greater compression of alveolar capillaries at larger lung volumes have?
increases resistance
what effect does greater tension in tissue at larger lung volumes have?
dilates extra-alveolar vessels and so reduces resistance
does alveolar pressure rise or fall with increased lung volume?
rise
does extra alveolar pressure rise or fall with increased lung volume?
fall
what happens to pulmonary artery resistance while PAO2 falls?
rises which diverts blood away from the poorly ventilated regions of the lung
what conditions in the body cause vasoconstriction?
hypoxia
hypercapnia
decreased pH
angiotensin II
what substances can cause vasodilation?
adenosine
bradykinin
histamine
vasopressin
what are vasodilators of the lung dependant on?
receptors in the endothelium and nitric oxide enzymes
what is pulmonary hypertension caused by?
reduced perfusion, leading to less nitric oxide produced which leads to vasoconstriction
what is the dominant effect of the sympathetic nervous system on the lungs?
vasoconstriction
what receptor is sympathetic vasoconstriction in the lungs managed by?
alpha 1 adrenoreceptor (reduces pulmonary blood flow by 30%)
what receptor is sympathetic vasodilation in the lungs managed by and stimulated by?
alpha 2 and beta 2 receptors on endothelium stimulated by adrenaline
what effect does the PNS have on the lungs?
vasodilation
what effect does VIP and CGRP have on the lungs?
dilate
is pulmonary vascular resistance lower or higher than systemic?
lower
what are the main deternimants of PVR?
capillaries
what influences PVR (pulmonary vascular resistance)?
control by sympathetic and parasympathetic nervous systems
hypoxia
lung volume and alveolar pressure
is the perfusion in lungs uniform and why?
no - increases down the lung due to the effect of gravity
is the blood flow in lungs uniform and why?
no - blood vessels are more open lower down the lung and resistance is lower
is ventilation of the lungs uniform and where does most take place?
no - in the base of the lung
what ratio is PaO2 determined by?
ratio of ventilation to perfusion
what must happen to ventilation and perfusion for optimal gas exchange?
must be matched (~5 litres/min at rest)
what should VA/Q be equal to?
1
what is happening in the lungs when V greater than 1?
ventilation is normal or elevated, perfusion is reduced
what is happening in the lungs when V is equal to 1?
ventilation and perfusion are normal
what happens when V is less than one?
ventilation is reduced, perfusion is reduced
what are the consequences of V-Q mismatch?
hypoxia (low blood O2)
hypercapnia (high blood CO2)
why may hypercapnia not be seen in mild to moderate V-Q mismatch?
hypoxia drives increased ventilation. so functioning alveoli are able to blow off more CO2 keeping PaCO2 normal
what can areas with low VQ (shunt effect due to poor ventilation)|be caused by?
blocked airways
what can areas with high VQ (poor perfusion dead space effect) be caused by?
loss of capillaries
is the effect of gravity more pronounced in?
ventilation
what is diffusion dependent on?
distance
surface area
permeability
what Law is diffusion determined by?
Fick’s Law
what is diffusion in alveoli driven by?
partial pressures
how many alveoli are there approximately in the human?
~300 million
what is the formula used to calculate the diffusion of volume of a gas?
lung area x diffusion constant x pressure gradient divided by thickness of alveolar membrane
how thick are the alveolar membranes?
0.5 micrometres
why is it so crucial that alveolar membranes are so thin?
to reduce the thickness and so distance gas must travel by diffusion
what is the diffusion gradient in the lungs created by?
partial pressure of gases
is the difference in partial pressure greater in oxygen or carbon dioxide?
oxygen
what is the diffusion constant determined by?
solubility and molecular weight
what does the diffusion constant measure?
how quickly gases diffuse
how many more times more soluble in the blood is CO2 than O2?
up to 25 times
What is transit time/
the time blood takes to move along capillary
what is rate of gas uptake across the alveolar membrane limited by?
gas diffusion and blood perfusion
which gases cross the alveolar membrane quickly?
nitrus oxide
what is gas uptake limited by in gases which cross the alveolar membrane quickly?
perfusion - there is not enough blood in the capillaries to meet gas uptake
why does CO appear to cross the membrane slowly even when it diffuses quickly?
is bound to haemoglobin so that partial pressure remains low
what is diffusion limited gas exchange limited by?
rate of diffusion
how is oxygen transfer normally limited?
by perfusion
when can diffusion limited transfer happen in oxygen uptake?
if diffusion is impaired by thickening of alveolar wall
what is the effect of diffusion limited transfer on A-a gradient?
increases it
why does exercise in some species result in low PaO2 but high PAO2?
diffusion is limited as blood moves through the capillaries too quickly
what is right to left shunt the result of?
blood passing through lungs without respiratory gas exchange and venous blood draining from bronchial circulation
what level must PO2 in lungs remain at and why?
high to drive diffusion and match demand by tissues
what are the 2 ways oxygen is transported in the blood?
dissolved in solution
bound to haemoglobin (Hb)
what does the solubility coefficient determine?
how much oxygen dissolves in plasma
how many ml of O2 per litre is present in the blood?
3ml/litre
when saturated how much oxygen can 1g of haemoglobin transport?
1.39ml
what is most of the O2 content of the blood bound to?
haemoglobin
does gas that is bound (not in free solution) contribute to the partial pressure of that gas?
no
what is blood PO2 a measure of?
the portion of O2 that is dissolved in the blood
what is gas dissolved in a liquid determined by?
pressure and solubility of the gas
what is the partial pressure of gas in liquid proportional to?
the partial pressure of the gas at the surface
what does the partial pressure gradient determine?
movement between gas (air) and liquid (blood)
does a bound gas exert partial pressure?
no
what is the role of haemoglobin?
binds O2 to increase partial pressure gradient
what does each alpha and beta polypeptide chain of haemoglobin contain?
a haem group
how many haem groups are there in a single RBC?
4
how is binding energy of oxygen to haem reduced?
allosteric effect of O2 binding
In what sort of environment does Hb have low affinity for O2?
acidic environement
why is oxygen released at tissues?
more CO2, lower pH, acidic
why is oxygen taken up at lungs?
less CO2, higher pH, alkaline
what is fully saturated oxygen known as?
oxyhaemoglobin
how many oxygen molecules is oxyhaemoglobin carrying?
4
what is haemoglobin with a single oxygen molecule known as?
deoxyhaemoglobin
what does the high affinity for O2 and high pH at the lungs encourage?
uptake of O2
what does the lower affinity for O2 and lower pH at the tissues encourage?
release of O2
what is the oxygen dissociation curve relationship known as?
sigmoidal relationship
what happens in anaemia?
Hb is reduced (can be up to by 50%)
what is the Bohr shift?
for a given PO2 more oxygen is given up at the tissues. Affinity of Hb for O2 is lower
how does increased temperature during skeletal muscle contractions affect oxygen dissociation?
causes reduced O2 affinity that aids unloading of oxygen
what are the 5 reasons we need erythrocytes?
holds a high concentration of Hb which decreases blood viscosity
Provides an environment for DPG
Encapsulates and concentrates carbonic anhydrase (CO2 transport)
Prevents Hb loss via filtration in the kidneys
Concave shape aids passage through tight spaces
how is carbon dioxide transported in the blood?
chemically in the form of HCO3-
combined with haemoglobin
dissolved in solution
what percentage of CO2 is directly dissolved into the blood?
~5% of total
what is the solubility coefficient of CO2?
0.3 mmol of CO2 per L blood per mmHg
in what form is CO2 bound to haemoglobin?
carbaminohaemaglobin
what percentage of CO2 is reversibly bound to Hb?
~30% of total
what percentage of CO2 is bicarbonate?
~65% of total
what is the chloride shift in red blood cells?
HCO3- is formed in RBC and diffuses into plasma via facilitated diffusion carrier in exchange for chloride (both negative, no charge difference)
what enzyme is needed to form HCO3- in RBC?
carbonic anhydrase
why is there no saturation of CO2 in blood as there is for oxygen?
Co2 is hugely soluble in plasma
what is the Haldane effect?
difference between venous and arterial blood. It enhances the unloading of CO2 from tissues into the blood
at low PO2 what does haemoglobin have a higher affinity for?
CO2
why is the curve for venous blood (on CO2 dissociation curve) to the left and above that for arterial blood?
venous blood contains more CO2 at any given value of PCO2 than does arterial blood
what does increased CO2 (due to ventilation) result in in terms of blood pH?
respiratory acidosis
what does decreased CO2 (due to ventilation) result in in terms of blood pH?
respiratory alkalosis
what is normal arterial blood pH?
~7.4
what is ventilation normally closely matched to?
metabolic requirements
what effect does increased ventilation have on PACO2?
reduced
what relationship is there between PACO2 and alveolar ventilation?
inverse
what effect can hyperventilation have on PaCO2?
<40mmHg
what effect can hypoventilation have on PaCO2?
> 45mmHg
what causes hyperventilation?
inducible: high anxiety and pain
altitude
what does hyperventilation lead to?
hypocapnia
respiratory alkalosis
what are the effects on the body of hyperventilation?
cerebral vasoconstriction muscle cramps (low calcium in muscles)
how can hyperventilation be compensated for?
hypoventilation or re breathing exhaled air
what causes hypoventilation?
chest injury
obstruction (COPD)
impaired respiratory drive
what does hypoventilation lead to?
hypercapnia
respiratory acidosis
hypoxia
what are the effects of hypoventilation?
peripheral vasodilation
confusion
drowsiness
coma
how can hypoventilation be compensated for?
hyperventilation
what are the 2 types of respiratory chemoreceptors?
peripheral
central
where are peripheral chemo receptors located?
carotid sinus and aortic arch
where are central chemo receptors located?
within the medulla oblongata
define hypoxia
low O2 levels
define anoxia
no O2
define asphyxia
low O2 and high CO2
define hypercapnia
high CO2
define hypocapnia
low CO2
define hyperventilate
excessive breathing
define hypoventilate
shallow/inadequate breathing
define apnoea
no breathing
define dyspnoea
sensation of breathlessness
describe the reflex control system of breathing
CNS monitoring homeostasis of blood gases - motor efferent - effector/target organ: altered function of respiratory pump muscles (change in rate/depth of ventilation) - feedback - chemo (sensory) receptors - sensory afferent - CNS
what nerve is innervated by the carotid peripheral chemoreceptors?
sinus nerve
what nerve is innervated by the aortic peripheral chemoreceptors?
aortic nerve
which nerve does the sinus nerve join?
glossopharyngeal nerve
which nerve does the aortic nerve join?
vagus nerve
where do both the glossopharyngeal and vagus nerves terminate?
nucleus tractus solitarii (NTS) in the medulla oblongata
what is signalling from carotid body chemoreceptors stimulated by?
reduced PaO2
what does the CNS equate repeat firing of carotid body chemoreceptors with?
hypoxia
which cell releases the neurotransmitter to signal the chemoreceptor afferent ending
type 1 glomus cell
what stimulates peripheral chemoreceptors?
hypoxia hypercapnia haemmorrhage acidosis increased sympathetic activity sodium cyanide (during experiments)
what is the most effective stimulant of peripheral chemoreceptors?
combination of hypoxia and hypercapnia
how quick is peripheral chemoreceptor response time?
fast! within 1 breath
what surface of the medulla oblongata are the chemo-sensitive regions located?
ventral
what is the CNS indirectly sensitive to?
PaCO2
what is the effect of increased H+?
increases ventilation, reduces PaCO2
what is the effect of reduced H+?
decreases ventilation
can H+ cross the blood brain barrier?
not well
does CO2 cross blood brain barrier?
yes
once in the CSF what happens to CO2?
converted to H+ and bicarbonate by carbonic anhydrase
why is the response of central chemoreceptors slow?
due to delay in creation of H+ and bicarb in CSF as H+ cannot pass blood brain barrier
describe the ventilatory response to hypoxia
as PaO2 reduces respiration rate increases until it reaches peak respiratory response. there is then depression of nervous activity of the brain which eventually leads to apnoea due to no driving of ventilation by brain
what percentage of the bodies receptors is the ventilatory response to hypercapnia mediated by?
80% central chemoreceptors
20% peripheral chemoreceptors
what is the synergistic effect of response to hypercapnia?
sensitivity to PACO2 is high when PAO2 is low
what effect do hypoxia and hypercapnia have on the nervous system?
increased sympathetic nerve activity
increase in release of adrenaline from adrenal medulla
what is the hypocapnic braking response to hypoxia?
hypoxia drives ventilation increase less when PCO2 starts to fall. PaCO2 stimulates central chemoreceptors and a fall in PaCO2 will depress or ‘brake’ the response to low PO2
what is hyperventilation driven by peripheral hypoxia reduced by?
subsequent central hypocapnia
what is the advantage of a gas transport system based on haemoglobin?
blood O2 content can be relatively independent of the O2 content of inspired air due to the ability for saturation
why is th eclose regulation of blood CO2 necessary?
to regulate blood pH
why is the regulation of both blood CO2 and blood O2 not possible?
increased ventilation required to compensate for hypoxia would blow off blood CO2 and cause respiratory alkalosis
what areas of the brain command the patterns of breathing?
brainstem and spinal cord
what do afferent cranial nerves receive information from?
chemoreceptors and stretch receptors
what do efferent cranial nerves send information to
bronchial muscles which control resistance
where is the central control of ventilation located?
pons and medulla are only areas of the brain required to develop rhythm of ventilation (brainstem)
where is the rhythm of breathing generated?
pons
where is the pattern of breathing generated?
medulla
what are PaCO2, PaO2 and pH levels monitored by?
central chemoreceptors
peripheral chemorecptors
pulmonal mechanoreceptors
mechanosensors in joints, tendons and muscles
what are the types of sensory information which regulate breathing?
mechanoreceptors
chemoreceptors
what nerve contains the afferent fibres of pulmonary mechanoreceptors?
vegus nerve
what type of receptors are pulmonary mechanoreceptors?
slowly adapting stretch receptors
wht are pulmonary mechanoreceptors stimulated by?
lung stretch and bronchoconstriction
what effect does stimulation of pulmonary mechanoreceptors have?
terminates inspiration
prolongs expiration
activates expiritory muscles
bronchodilation
what are 2 other vagal afferent receptors?
rapidly adapting stretch receptors (cough reflex)
juxtapulmonary capillary receptors (leads by oedema)
what are 3 factors which drive breathing?
decrease in arterial PO2
increase in arterial PCO2
increase in H+ concentration
what type of receptors are the factors which drive breathing monitored by?
peripheral and central chemoreceptors
what is the venous partial pressure of oxygen?
40 mmHg
what is the arterial partial pressure of CO2?
40 mmHg
where are peripheral chemoreceptors located?
carotid bodies at carotid bifarcation
aortic bodies
what are the carotid bodies activated by?
mainly decreased PaO2
increased PaCO2
decreased pH
what are the integrated responses to breathing regulation?
chemoreceptor feedback (interaction between CO2 and O2. Interaction between CO2 and H+) feedforward regulation
what is the central response to CO2 via/
pH
what is CSF pH determined by?
arterial PCO2 and CSF concentration of H+
what do central chemoreceptors not detect?
hypoxia/PO2
in healthy breathing where does drive to breathe come from?
central chemoreceptors (PCO2 via H+), dependant on pH
if PCO2 is constant at what point will PO2 produce drive to breathe in the brain?
<60 mmHg
how can the pH set point change over time due to prolonged hypercapnia?
prolonged hypercapnia means CO2 removal is impaired leading to compensatory changes in HCO3- transport in CSF. The CSF pH is returned to normaleven though blood pH is still low due to elevated PCO2.
when central drive via CO2 is reduced by prolonged hypercapnia where must the chemoreceptive drive come from?
O2- hypoxic drive in peripheral chemoreceptors
what receptors does an increase in H+ stimulate?
peripheral chemo receptors
why are central chemo receptors not stimulated by an increase in H+?
H+ does not cross blood brain barrier
what is the effect of stimulation of peripheral chemo receptors but chemoreceptors not stimulated?
increase in ventilation reduced PaCO2 and reduces brain pH. This reduces the ability of both peripheral and central chemoreceptors
describe the route to increased ventilation in the respiratory system
PCO2 increased stimulates peripheral and central chemo receptors. Peripheral chemo receptor afferents stimulate the respiratory centre via NTS. Central chemo receptor cell bodies in medulla which increase the output of pre-motor neurons. Leads to increased ventilation
what factors can depress respiratory reflexes?
sleep opiates GA Alcohol Bacterial toxins Stress/pain/fever
