physiology 2/2 Flashcards
what circulation provides nutrients to the lungs & where from
the Bronchial circulation which is from the systemic circulation to supply smooth muscle, nerves and tissue
what is important about the pulmonary circulation
HIGH flow
LOW pressure
what is the O2 and CO2 concentration of the alveoli
PO2 = 100mmHg
PCO2 - 40mmHg
what is special about the alveoli gas pressures
they become the systemic arterial pressures
how do the gasses diffuse across the membrane
down the partial pressure gradient
what is the de oxygenated bloods gas pressure
PO2 = 40mmHg
PCO2 = 46mmHg
what is the oxygenated blood gas pressure
PO2 = 100mmHg
PCO2 = 40mmHg
what is the symbol V(with a squiggle on top)
mixed venous blood
how much blood passes through systemic/pulmonary circulation
5 litres
what are the 2 factors that tranaport across a membrane are proportional too
- partial pressure gradient
- directly proportional to gas solubility
at what rate do CO2 and O2 move down their partial pressure gradients
CO2 = 200ml/min
O2 = 250ml/min
which gas has a grater partial pressure gradient why is it not bigger
Oxygen
CO2 is more soluble
why is the gap between alveoli and capillary so small
the alveoli and capillary have fused basement membranes
what are the 4 lung diseased related to gas exchange
emphysema
fibrotic lung disease
pulmonary oedema
asthma
what is the ideal ventilation-perfusion rate
ideally matching each other
what happens to blood flow and ventilation as you move up the lung - why
it decreases
FRC is bigger in alveoli so compresses capillaries
which declines at a faster rate with height
blood flow
what is the ventilation-blood flow rate at the bottom vs the apex
blood>ventilation
it then switches
ventilation>blood flow
what does the problem of ventilation>blood flow
alveolar dead space
what is the problem with blood flow>ventilation
shunt
how is shunt combated
vasoconstriction of the vessel adjacent to the alveoli with reduced ventilation
what is physiological dead space
alveolar dead space + anatomical dead space
how much O2 is dissolved in the plasma
3ml per litre of plasma
how much O2 is carried in the haemoglobin
197ml per litre
200ml /L in total plasma and Hb
what is arterial partial pressure of O2 referring too
its referring to the oxygen in solution this means you can have a normal PaO2 and have low haemoglobin saturation meaning you have low O2 concentration
what is the PaO2 value
what is this known as
100mmHg
aka oxygen tension
how much arterial O2 is needed and extracted by peripheral tissue at rest
250ml/min
this is only 25% of the arterial O2 created
what determines the saturation of haemoglobin
PaO2
the partial pressure of O2 in the blood
how many O2 molecules bind two 1 haemoglobin group
4
what is the reaction that is occurring when O2 binds to Haemoglobin
oxygenation (tinder shag)
NOT
oxidation (marriage)
what is the most prominent form of Haemoglobin in red blood cells
92% of haemoglobin is HbA
how long does Hb saturation take
normally 0.25s out of the 0.75 seconds of contact time
what role does Hb play at the alveoli
it binds to O2 in the plasma keeping the [atrial pressure gradient across the alveoli until the Hb and plasma are saturated
in order of highest affinity what is the order of Hb
what does this mean
myoglobin
foetal Hb
normal HB
they require less partial pressure of oxygen
what is the saturation of Hb when PaO2= 60mmHg
Hb saturation = 90%
what is the normal venous PO2 , what is the Hb reserve saturation at this level
40mmHg
Hb saturation = 75%
what is the definition of anaemia
any condition where the oxygen carrying capacity of the blood is compromised
what are some causes of anaemia
Iron deficiency, haemorrhage, vitamin B12 deficiency
what effect does pH have on Haemoglobins affinity for O2
alkalosis (7.6) increases O2 affinity
acidosis decreases affinity - exercise muscle releases lactic acid - lower affinity - releases more O2
what is the pH of normal blood
pH 7.2 so slightly alkali
what effect does temperature have on Haemoglobins affinity for O2
the higher the temperature the less the affinity for O2 as bond between Hb and O2 becomes denatured
AND VISE VERSA
what effect dose an increase in PCO2 have
it decreases the affinity of O2 as the increased CO2 produces H+ ions which have the same effect as acidosis
AND VISE VERSA
what is 2,3 - DPG
what effect dose it have on O2 affinity
it is a intermediate in glycolysis found in RBCs when there is inadequate O2 supply
added 2,3,DPG = less affinity for O2 meaning more is realised to the peripheral tissue when needed
what is CO affinity to Hb in relation to O2
CO has a affinity of 250 times greater than O2
what is the problem once CO is dissolved in the circulation
it disassociates from the Hb very slowly
what are the symptoms of CO poisoning
CHERRY RED SKIN, Hypoxia and anaemia, nausea and headaches
what is the respiration rate in someone who has Co poisoning
normal due to normal arterial CO2 levels
what is the definition of hypoxia
inadequate supply of O2 to the tissues
what are the 5 main types of hypoxia
Hypoxemic Hypoxia - most common - due to bad O2 diffusion at lungs
Anaemic Hypoxia - reduction in O2 carrying capacity
Stagnant Hypoxia - blood not reaching lungs and tissue
histotoxic hypoxia – poison prevents cells using O2 - CARBON MONOXIDE
metabolic hypoxia - O2 not enough for tissue
what are the 3 forms of CO2 transport through the blood - what percentage?
dissolved in plasma (7%)
CO2 + Hb (23%)
CO2 + water to form carbonic acid - then disassociates to get H+ IONS (70%)
what can the creation of carbonic acid by CO2 do
control the pH of the extracellular fluid
how is normal pH maintained
because ALL CO2 produced is eliminated in expelled air
what does hypoventilation cause
CO2 retention leading to more [H+ ] and respiratory acidosis
what does hyperventilation cause
blowing off more C)2 leading to decreased [H+] and respiratory alkalosis
what muscle type/muscles are stimulated during ventilation
skeletal muscles, diaphragm and intercostal muscles
what nerves are stimulated during ventilation
phrenic nerves and intercostal nerves
where is the origin of the phrenic nerve
C3,4,5 keep the diaphragm alive
where is ventilation controlled
in the respiratory centres
where are the respiratory centres
in the pons and medulla
what is the respiratory system modulated by (4)
Emotion - via limbic system (brain)
Voluntary over-ride
Mechano-sensory input (from thorax)
chemical input into CHEMORECEPTORS
what is the role of the respiratory centres
set an autonomic rhythm of breathing and adjust in response to stimuli (CO2, pH …)
what are the two types of chemo receptors
peripheral and central
what is the role of peripheral chemoreceptors
carotid and aortic bodies
respond to plasma [H+] (INDIRECT) and PO2
secondary ventilatory drive
what is the role of central chemoreceptors
in the medulla
respond directly to [H+] in the CSF which directly reflects (PCO2)
PRIMARY ventilatory drive
what is the name for raised PCO2
Hypercapnia
what can/cannot cross the blood-brain barrier
CAN - gas and some nutrients
CANNOT - ions
how do central chemoreceptors respond to [H+] if ions cannot cross the blood-brain barrier
CO2 is able to diffuse through the barrier into the CSF where it forms carbonic then bicarbonate ant H+ ions
these then interact with the central chemoreceptors on the medulla
what is hypoxic drive
what patients with COPD develop due to chronically elevated levels of PCO2
use secondary ventilatory drive (PO2)
when do the peripheral chemoreceptors activate
when a significant change in arterial PO2 (PaO2 so in plasma) is recorded
what overrides voluntary control of ventilation (i.e. holding breath and voluntary hypoventilation)
cant override involuntary stimuli - to get rid of PaCO2
or by a increase in PaO2 (hypoventilation - takes longer)
when is respiration inhibited - why
during swallowing to avoid aspiration of food or fluid
what happens after swallowing
a expiration occurs to get small particles (that might have got past the epiglottis) out
what do opioids to the respiratory centre
suppress it and death occurs due to respiratory failure
what dose nitric oxide (NO) do to the respiratory system
suppresses the peripheral chemoreceptors to PaO2 - DANGEROUS in HYPOXIC DRIVE (don’t give hypoxic drive)
what happens when you get a decrease in PCO2
mild bronchial constriction
what happens when you get a increase in alveolar PO2
pulmonary vasodilation
what is O2 solubility in water - why is this important
0.03ml/L/mmHg
as we have 3ml of O2 in the plasma it that gives a pressure of 100mmHg
what is the major factor that determines haemoglobin saturation
the partial pressure of oxygen in arterial blood
what is the O2 reserve capacity at normal Venous PO2
75%
at PO2 = 40mmHg
where fires the signals to the respiratory muscles
DRG (DORSAL respiratory group of neurons)
VRG (ventral respiratory group of neurons)
what causes a raise in H+
a raise in PCO2 = hypercapnia
what crosses the blood brain barrier
CO2 - which is then converted in to H+
