Respiratory Physiology Flashcards
Functions of Respiratory System X4
- Gas exchange –Oxygen added to the blood from the air, carbon dioxide removed from the blood into the air.
- Acid base balance –regulation of body pH
- Protection from infection
- Communication via speech
Cellular/Internal respiration
A biochemical process that releases energy from glucose either via Glycolysis or Oxidative Phosphorylation. Latter requires oxygen and depends on EXTERNAL RESPIRATION
External Respiration
movement of gases between the air and the body’s cells, via both the respiratory and cardiovascular systems.
systemic vs pulmonary ventilation
pulmonary delivers CO2(to the lungs) and collects O2(from the lungs)
while the systemic circulation delivers O2 to peripheral tissues and collects CO2.
The pulmonary artery carries deoxygenated blood away from heart
while the pulmonary vein carries oxygenated blood.
net volume of gas exchanged in the lungs per unit time
250ml/min O2; 200ml/min CO2
URT
nose
pharynx - throat
larynx- voice box
LRT
trachea
bronchi
alveoli cell structures
type 1- gas exchange
type 2- surfactant production
macrophages
alveoli type 1 cells are always next to
cappilaries
tidal volume
500-600ml
(5-6L)
residual lung volume
1200ml
prevents alveolar collapse and allows gas exchange outside inspiration
vital capacity
full volume of air that can be forced in and out
4600ml
functional residual capacity
volume of air left in lungs after relaxed expiration
all muscles used in breathing x6
DIAPHRAGM
internal intercostals
external intercostals
abdominal muscles
scalenes
sternocleidomastoids
internal intercostal rib movement
down and in
external intercostal rib movement
up and out
accessory muscles of expiration
abdominal
internal intercostals
inter inter cancels out si makes expiration
accessory muscles of inspiration
external intercostals
scalenes and
sternocleidomastoids
lung contraction is controlled by
phrenic nerve
Intra-thoracic (Alveolar) Pressure (PA):
pressure inside the thoracic cavity, (essentially pressure inside the lungs). May be negative or positive compared to atmospheric pressure.
always negative to pleural
Intra-pleural Pressure (Pip):
pressure inside the pleural cavity, typically negative compared to atmospheric pressure (in healthy lungs at least!)
Transpulmonary pressure (PT):
difference between alveolar pressure and intra-pleural pressure. Almost always positive because Pip is negative (in health).
PT=
Palv–Pip
Between breaths at the end of an unforced expiration Patm =
alveolar pressure- no air movement
what does surfactant do
- Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
- Increases lung compliance (distensibilty)
- Reduces lung’s tendency to recoil
- Makes work of breathing easier
- Is more effective in small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated
law of laplace
when surfactant is low, the smaller alveoli collapse and push air into the bigger ones which makes them bigger
decreasing SA ratio making them less effective and harder to keep open- requires more pressure
compliance definition
change in volume relative to change in pressure i.e. how much does volume change for any given change in pressureI t represents
the stretchability of the lungs - how easy it is to get the air in
HIGH COMPLIANCE
large increase in lung volume for small decrease in ip pressure- less efort
LOW COMPLIANCE =
small increase in lung volume for large decrease in ip pressure
Anatomical dead space volume is
150 mL
Pulmonary (Minute) ventilation=
total air movement into/out of lungs (relatively insignificant in functional terms)
Alveolar ventilation=
fresh air getting to alveoli and therefore available for gas exchange (functionally much more significant!)
pulmonary and alveolar ventilation is measured in
L/min
pumonary ventilation =
resp rate X air coming in- tidal volume
alveolar volume =
tidal volume minus dead space
why is dead space important
it wont change
but amount of air getting in and out can - tidal volume and resp rate
so it can take up a different proportion of that, leading to hypo / hyper ventilation
hypo ventilation
shallow fast breathing
hyperventilation
deep slow breathing
PP of O2 in lungs
100mmHg
13kPa
PP CO2 in lungs
40mmHg
5.3kPa
Alveolar ventilation declines
with height from base to apex of an upright lung due to changes in compliance
PP of arterial blood =
PP of alveolar
100mmHg O2 40mmHg CO2
PP of venous blood =
PP of peripheral tissues
40mmHg/ 5.3 kPa O2
46mmHg/ 6.3kPa CO2
diffusion in lungs
CO2 diffuses more rapidly because of its greater solubility.
Nevertheless the overall rates of equilibrium between O2& CO2 are similar because of the greater pressure gradient for O2
diseases causing diffusion problems
emphysema
pulmonary edema
diseases causing ventilation problems
fibrotic lung disease
asthma
emphysema
normal alveolar O2
low artery O2
reduced alveolar SA due to damage
less elastic recoil- harder to breath out
Increased compliance
pulmonary edema
normal alveolar O2
low artery O2
increased ISF distance
CO2 normal- dissolves more easily
fibrotic lung disease
normal alveolar O2
low arterial O2
thick alveoli walls slows gas exchange
decreased compliance
too much connective tissue
asthma
low alveoli O2
low arterial O2
increased CO2
constricted bronchioles
obstructive vs restrictive lung disease
obstructive: obstruction of air flow
effects exhalation
Restrictive: Restriction of lung expansion
effects inhalation
obstructive lung diseases
asthma
COPD
restrictive lung diseases
Fibrosis
Infant Respiratory Distress Syndrome
Oedema
Pneumothorax
loss of compliance causes
difficulty inhaling
can’t expand to let in
increase of compliance causes
difficulty exhaling
can’t squeeze out
types of spirometry
Static–where the only consideration made is the volume exhaled
Dynamic–where the time taken to exhale a certain volume is what is being measured
volumes not measured by spirometery
anything that uses residual volume
inc. total lung capacity and expiratory reserve volume
FEV1
Forced expiratory volume in 1 second
FVC
Forced vital capacity
FVC volume
5l
FEV1/FVC normal ratio
80%
obstructive lung disease and FEV1/FVC
decreases ratio
restrictive lung disease and FEV1/FVC
stays same - both FEV and FVC decrease
less can get in less can get out
perfusion means
blood distribution
distribution of ventilation and blood flow in lungs
Both blood flow and ventilation decrease with height across the lung- apex lower
apex blood flow/ventilation ratio
both lower than base
but more ventilation than blood flow
base blood flow/ventilation ratio
both more than apex
more blood flow than ventilation
what happens when blood flow > ventilation
shunt
happens at base
shunt
deoxygentaed blood that didn’t get oxygenated by faulty alveoli gets shunted into oxygenated blood diluting it
increases CO2 in alveoli and decreases O2 in both
how shunt is fixed
vasoconstricting blood vessels- diverts passed faulty alveoli
when ventilation > blood flow
alveolar dead space
happens at apex
gets O2 fine but can’t perfuse it well
how alveolar dead space is fixed
vasodilation
what does RSA do
keep perfusion-ventilation match during breathing by changing heart beat
through vagus nerve
how O2 and CO2 is distributed
3ml O2 dissolved per litre plasma
197ml per L in haemoglobin in red blood cells
Bulk (77%) of CO2is transported in solution in plasma, 23% is stored within haemoglobin
what is The major determinant of the degree to which haemoglobin binds (is saturated with) oxygen
partial pressure of oxygen in the blood.
PP of O2 only refers to
O2 dissolves in plasma
What would happen to PO2in anaemia?
nothing- Po2 is only the stuff dissolved in plasma- not heamoglobin
what causes decreased haemoglobin affinity for O2
decrease in pH
an increase in PCO2
increase in temperature
binding 2,3-diphosphoglycerate (2,3-DPG)
found in areas of low O2 like heart disease to max O2
what causes increased haemoglobin affinity for O2
a rise in pH or a fall in PCO2, or temperature
will take up lots of O2 but wont give away to tissues
oxygen disassociation in different types of Hb
HbF and myoglobin have a higher affinity for O2
where is myoglobin found
cardiac and skeletal muscle
5 types of hypoxia
- Hypoxaemic Hypoxia: most common. Reduction in O2diffusion at lungs either due to decreased PO2atmos or tissue pathology.
- Anaemic Hypoxia: Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency).
- Stagnant Hypoxia: Heart disease results in inefficient pumping of blood to lungs/around the body
- Histotoxic Hypoxia: poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide
- Metabolic Hypoxia: oxygen delivery to the tissues does not meet increased oxygen demand by cells
respiratory centre has its rhythm controlled by
- Emotion (via limbic system in the brain)
- Voluntary over-ride (via higher centres in the brain)
- Mechano-sensory input from the thorax (e.g. stretch reflex).
- Chemical composition of the blood (PCO2, PO2and pH) –detected by chemoreceptors
where are central chemoreceptors found
medulla
where are peripheral chemoreceptors found
carotid and aortic bodies
cental chemoreceptors function
- Detect changes in [H+] in CSF around brain
- Cause reflex stimulation of ventilation following rise in [H+]
peripheral chemoreceptor function
Detect changes in arterial PO2and [H+]
•Cause reflex stimulation of ventilation following significant fall in arterial PO2
(not O2 content- doesnt take Hb into account)
hypoxic drive
Individuals become desensitised to PCO2and instead rely on changes in PaO2to stimulate ventilation
if plasma pH falls ([H+] increases) ventilation will be
stimulated (acidosis)
if plasma pH increases ([H+] falls) e.g.vomiting (alkalosis), ventilation
will be inhibited
Hypoventilation leads to
causing CO2 retention, leads to increased [H+] bringing about respiratory acidosis.
Hyperventilation leads to
blowing off more CO2, lead to decreased [H+] bringing about respiratory alkalosis
how to calculate alveolar volume
(tidal volume - dead space) X resp rate
PAO2 is
alveolar
PaO2 is
arterial
how to calculate pack years
(number of cigarettes a day/ 20)
X
years of smoking
Hb affinity for O2 is decreased by
decrease in pH
increase in PCO2
Increase in temp
binding of 2,3- DPG
means Hb gives oxygen to tissues more regularly- like during exercise
what makes Hb curve move right
decrease in pH
increase in PCO2
Increase in temp
e.g in asthma attack
what increases Hb affinity for O2
rise in Ph
fall in PCO2
fall in temp
oxygen unloading is more difficult but keep oxygen up in pulmonary circulation
what makes Hb curve move left
rise in Ph
fall in PCO2
fall in temp
caused by alkalosis
foetal haemoglobin is shifted to the ____ on the Hb curve
left
when is 2,3-DPG found
when O2 supply isn’t enough:
heart/lung disease
living at high altitude
