Blood supply, gas exchange, ventilation + perfusion Flashcards
State the 2 circuations that occur at the lungs
Bronchial circulation (nutritive) Pulmonary circulation ( gas exchange)
Describe bronchial circulation ( nutritive)
- supplies oxygenated blood(horemones, nutrients) to airway SM, nerves + lung tissue.
- via bronchial arteries originating from systemic circulation
Describe pulmonary circulation ( gas exchange)
- Supplies deoxygenated blood to capillary network surrounding alveoli + returns oxygenated blood to the left atrium via the pulmonary vein.
- via L+R pulmonary arteries originating from right ventricle.
State the features of the rate of diffusion across the membrane
- directly proportional to the partial pressure gradient.
- directly proportional to gas solubility
- directly proportional to the available surface area
- inversely proportional to the thickness of the membrane
- most rapid over short distances.
Blood flow and ventilation at base of lungs
- blood flow is higher than ventilation because arterial pressure is higher than alveolar pressure, which compresses alveoli
Blood flow and ventilation at apex of lungs
blood flow is low because arterial pressure is less than alveolar pressure, which compresses arterioles.
When both ventilation and blood flow declines
Blood flow declines faster than ventilation, so BF>ventilation at the base and ventilation>BF at apex
What happens when ventilation decreases
Decreased ventilation will cause PCO2 to increase and PO2 to decrease+ the blood flowing past the alveoli doesn’t get oxygenated
-decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting bood to a better ventiated alveoli
Effect of increased PCO2
causes mild bronchodilation
What is a shunt?
- when the passageway of blood through areas of the lung is poorly ventiated.
- ventilation
What is alveolar dead space?
- Alveoli that is ventilated but not perfused
- Ventilation>perfusion
- caused by pulmonary embolism
What is physiological dead space?
alveolar DS + anatomical DS
What is PaO2?
-partial pressure of arterial blood and referss to O2 in soution in the plasma
What is PaO2 determined by?
O2 solubiity and the partial pressure of O2 in the gaseous phase that is driving O2 into solution
Is PP gradient the same as the concentration gradient? Explain your answer.
PP gradient is not equal to the concentration gradient due to the concentration gradient being dependent on the phase ( liquid/gaseous)
Do gases travel as gaseous/liquid phase in plasma?
Gases travel as liquid phase. If it travels in gaseous phase in the plasma, it will lead to bubbles in the blood > air embolism.
Solubility of O2 in plasma/H20
O2 has a low soubility in plasma/H2O
Describe the structure of HbA
Consists of 4 polypeptide subunits ( 2 alpha + 2 beta chains) each with an FE containing haeme group.
What reaction takes place when O2 binds to haemoglobin?
Oxygenation reaction takes place when haemoglobin binds to O2.
Describe the structure of HbA2
2 alpha subunits and 2 delta units(δ)
Describe the structure of HbF (foetal haemoglobin)
2 alpha units and 2 gamma units(y)
Types of glycosylated Hb
HbA1a, HbA1b, HbA1c
Types of Haemoglobin chains
Globin chains: alpha, beta, delta, gamma and glycosylated
What are the main types of Hb in RBC?
HbA ( 92%) the rest (8%)
Describe the relationship between Hb + O2 transport in relation to the equilibrium
Hb removes O2 from the plasma thus also maintaing a partial pressure gradient that continues to suck O2 out of the alveoli until the Hb becomes satureated with O2.
How can we determine how much O2 binds to Hb?
PP in the plasma
Describe the affinities of HbF and myoglobin
- Myoglobin and HbF have a higher haemoglobin compared to adult Hb.
- This will allow them to extract maternal/arterial blood
- Myoglobin>Foetal
What is anaemia?
Condition whereby the oxygen carrying capacity is compromised.
- iron deficiency, haemorrhage, Vit B12 deficiency can cause this
What factors shifts the oxyhaemoglobin dissociation curve to the right ?
(decreases the affinity of haemoglobin for O2)
- decrease in pH
- Increase in PCO2
- increase in temperature
- increased 2, 3-DPG (diphosphoglycerate)
What factors shifts the oxyhaemoglobin dissociation curve to the left? ( increases the affinity for haemoglobin for O2)
- increase in pH
- decrease in PCO2
- decrease in temperature
- CO
What synthesises 2,3-DPG and under which circumstances will it be produced?
erythrocytes synthesises 2,3-DPG during circumstances where there is inadequate O2 + will help maintain O2 release in the tissues.
Describe the effect of CO on haemoglobin
CO binds to Hb to form carbaminohaemoglobin and has a 250x higher affinity for O2 than normal Hb. O2 binds quicly, greatly but released slowly
-Dissociation curve moves to LHS
The effect of anaemia on dissociation curve
- does not shift dissociation curve unless ( 2, 3- DPG_
State the symptons of carbon monoxide poisoning
Hypoxia, anaemia, nausea, headaches + cherry skin and muscous membranes.
The effect of CO on RR
RR=unchanged as normal arterial PCO2 ( determines RR)
State the types of hypoxia + give the definition of each
Hypoxaemic hypoxia: Decrease in O2 difusion at lungs due to decreased PO2(atmos)/tissue pathology
Anaemic hypoxia: Decrease in O2 carrying capacity of blood due to anaemia (RBC loss/iron deficiency)
Stagnant Hypoxia: heart disease results in inefficient pumping of blood to lungs/around the body
Histotoxic hypoxia: poisoning prevents cells utilising O2 delivered to them (CO/cyanide)
Metabolic hypoxia:O2 delivery to tissues does not meet increase O2 demand by cells
Describe CO2 transport
PERIPHERAL TISSUES
CO2 molecules diffuses from tissues ( via capillaries) into blood. 7% remains in the dissolved plasma + 23% enters erythrocytes + combines with deoxyhaemoglobin to form carbamino compounds. The remaining 70% will combine with water to form carbonic acid which dissociates(carbonic anhydrase) to yield bicarbonate and H+ ions and CO2 will be transported as bicarbonate.
-Bicarbonate levels increase in the erythrocyte and moves down its conc gradient > plasma. The shift in charge is balanced by facilitated diffusion ( ionic exchange of HCO3- + Cl-) aka chloride shift. Cl- enters RBC as HCO3- enters the plasma.
LUNGS
- In the lungs, due to there being a high PO2 + low PCO2, more O2 will dissolve into the RBC’s + binds to Hb at the haeme group. This alters the shape of Hb, thus reducing the Hb affinity for CO2 + H+.
- Now, there is a rise in H+ + HCO3-, it renters the RBC from plasma down its conc gradient into the RBC. The excess CO2 continues to increase so causes PCO2 to be high and drives diffusion down the PP gradient from RBC>plasma>alveoli where PCO2 is 40mmH.
Write out the acid-base balance
CO2 + H2O ↔ H2CO3 ↔ HCO3 + H+
What can cause respiratory acidosis?
- Failure of the respiratory system
- causes CO2 retention, leading to increased [H+]
Describe what happens when H+ increase/decrease in terms of the acid-base balance
When H+ decreases: equilibrium will fav our the RHS to produce more HCO3- & H+
When H+ increases: Equilibrium will favour the LHS so HCO3- binds with H+ to form carbonic acid (H2CO3) which will split into CO2 & H2O
What happens when perfusion>ventilation ( shunt)
- PaCO2 increases since alveoli is still getting good blood flow and less CO2 diffuses out of the blood>alveoli
- PaO2 decreases since less O2 is getting into the blood from the alveoli
What occurs when ventiation>perfusion ( alveolar dead space)
- PACO2 decreases since CO2 isn’t diffusing from the blood into the alveoli
- PAO2 increases since O2 can’t deposit O2 into the bood
Why is ventilation and blood flow higher at the base of the lung?
the weight of intrapleural fluid increases intrapleural pressure @ base of lungs to a less negative value…..
-perfusion is greater at the base due to gravity
What is a shunt?
describes passage of blood through areas of lung that is poorly ventilated
What is physioogical dead space
Alveolar DS + Anatomical DS
