Gaseous diffusion and transport

Question 1

Factors affecting O2 carriage

Answer 1

pO2 is proportional to conc dissolved in blood. Hb

Question 2

How to calculate O2 carrying capacity of normal blood

Answer 2

max O2 1g of Hb can combine with x normal blood Hb concentration=Oxygen capacity of normal blood

Question 3

O2 saturation of blood entering pulmonary capillaries and leaving

Answer 3

enter=75% leave=97-100%

Question 4

What is the haem group

Answer 4

iron porphyrin compound attached via histidine N to globin. O2 binding is oxygenation, iron remains in Fe2+ strate after O2 released

Question 5

When does 2,3 DPG increase

Answer 5

hypoxia, anaemia

Question 6

What is anaemia and what causes it

Answer 6

when there is reduced content of functional Hb in blood. Caused by defect Hb production or red cell numbers. O2 carrying capacity reduced

Question 7

How is Hb association curve affected in anaemia? sketch

Answer 7

venous pO2 will be lower so tissue pO2 also low. Extraction of O2 during exercise limited

Question 8

What are the negative effects of CO binding to Hb

Answer 8

reduces amount of O2 bound to Hb

shifts O2 binding curve to left, increases O2 affinity of remaining binding site decreasing unloading of O2

Question 9

Sketch O2 dissociation curve for CO poisoning

Answer 9

tissues still remove 5mldl-1 of blood. Venous PO2 even lower (2kPa)=tissue PO2

Question 10

HbF binds DPG more or less than HbA

Answer 10

less

Question 11

Cyanosis what is it

Answer 11

If supply of O2 to tissues is deficient, content of de-oxyHb in tissue capillary increases because of hypoxia. De-oxy Hb has blue-ish tinge causing discolourisation of tissues

Question 12

2 types of cyanosis

Answer 12

Peripheral-reduced blood flow to region resulting in hypoxic tissue causing blue-ish tinge in extremities. Cause=cardiovascualr shock, low temp, reduced CO, poor arterial supply
central=arterial hypoxaemia, buccal mucosa and lips used to spot.
Cause=chronic respiratory disease e.g. COPD (~8kPa), right to lef shunt reduces O2 sat

Question 13

At which point is cyanosis observable

Answer 13

Arterial blood containing >1.5-2g/dl of deoxyHb, canosis is observable even in well-perfused tissues. OCcurs when O2 sat <85% if [Hb] is normal

Question 14

How are CO2 carried and state the proportions

Answer 14

HCO3-=60%
Hb-CO2=30%
Dissolved CO2

Question 15

CO2+H2OH2CO3H+ +HCO3- describe

Answer 15

Reaction 1: slow in plasma but fast in RBC because of presene of carbonic anhydrase
Reaction 2 aided by buffering o f {H+] by deooxy-Hb. Bicarbonate formed by reaction 2 diffuses out down its conc grad via antiporter into plasma in exchange for Cl- (chloride shift)

Question 16

How do carbamino compound form

Answer 16

RNH2+CO2->RNHCOOH (lysine, arginine side chains)
Mostly formed with deoxy-Hb in red cell, a little with plasma proteins. Oxygenation of Hb inhibits reaction and aids CO2 being breathed out

Question 17

How are various forms of CO2 unloaded in lung

Answer 17

CO2 dissolved in plasma: diffuses down partial pressure grad
carbamino compound: CO2 comes off assisted byy oxygenation of Hb and diffuses into alveoli
HCO3- from plasma: taken back into RBC, combines with H+ which comes off as O2 binds to Hb forming H2 CO3. H2 CO3 dissociates into CO2 via carbonic anhydrase

Question 18

What is the haldane effect and why does it occur

Answer 18

at any given PCO2, CO2 quantity carried is greater in deoxygenated than oxygenated
Cause:
1. Hb forms carbamino compounds easier when deoxygenated
2. Hb binds to H+ better when deoxygenated which favours formation HCO3-

Question 19

Sketch CO2 dissociation curve and note key points

Answer 19

not sigmoidal, no plateau, approx linear over physiological range.
More total CO2 carrying capacity than O2. Haldane effect. mixed venous CO2 content-mixed arterial=amount of CO2 produced at rest for 100ml blood passing

Question 20

What is the Henderson-Hasselbach equation and what is pKa of

Answer 20

pH=pKa+log([HCO3-]/[CO2])

pKa=-log(dissociation constant of H2CO3)

Question 21

What is the relationship between alveolar pCO2 and alveolar ventilation

Answer 21

Inversely proportional. If one doubles, other halves

Question 22

How to measure O2 consumption

Answer 22

1) FIck principle: O2 consumption by tissues=COx(arterial-venous O2 content)
2) respiratory measurements:
CO2 produced in tissues=COx(venous-arterial CO2 content)

Question 23

What is the respiratory quotient

Answer 23

CO2 produced: O2 utilised

Question 24

What is hyper and hypoventilation

Answer 24

Hyper: over ventilation in proportion to metabolism leading to lower arterial PCO2 below normal values
Hypo: under ventilation in proportion to metabolism results in higher arterial PCO2 levels

Question 25

Why does hyperventilation not equate to increased ventilation

Answer 25

e.g. exercise increases ventilation but so does metabolic rate so arterial PCO2 remains relatively constant

Question 26

What does hyperventilation lead to

Answer 26

Hypocapnia=low arterial PCO2->reduces [H+] causes respiratory alkalosis

Question 27

Hyperventilation cause

Answer 27

anxiety, pain, excessive mechanical ventilation, diseases contribiting to metabolic acidosis

Question 28

What are the consequences of hyperventilation

Answer 28

1) low PaCO2->cerebral vasoconstriction->cerebral hypoxia resulting in dizziness 2) alkalosis-> decrease plasma free [Ca2+] (more binds to proteins)->increase exitable cells (VGCC open at lower threshold potentials)->disturbed sensation and unwanted muscle contractions

Question 29

What does hypoventilation cause and what is it caused by

Answer 29

hypercapnia=high arterial PCO2->increases {H+] causes respiratory acidosis. Caused by head injury impairing respiration, anaesthetic drugs, chronic lung disease

Question 30

Consequences of increased PCO2 due to hypoventilation

Answer 30

Increasing arterial PCO2 causes peripheral vasodilation, flushed skin, full pulse, extra systoles Very high PCO2 depresses CNS function causing drowsiness, coma and death

Question 31

What are the normal values of: PAO2, PaO2, arterial O2 content, Arterial Hb saturation, Mixed venous PO2, mixed venous O2 content, mixed venous Hb saturation

Answer 31

PAO2=13.3kPa/100mmHg PaO2=12.5kPa/94mmHg, arterial O2 content=200ml/l, Arterial Hb saturation=97%, M ixed venous PO2=5.3kPa/40mmHg, mixed venous O2 content=150ml/l, mixed venous Hb saturation=~75%

Question 32

What are the normal values for: PACO2, PaCO2, arterial CO2 content, Mixed venous PCO2, mixed venous CO2 content, arterial pH, arterial [HCO3-]

Answer 32

PACO2=4.7-6.1kPa/35-45mmHg, PaCO2=4.7-6.1kPa/35-45mmHg, arterial CO2 content=480ml per litre, Mixed venous PCO2=6.1kPa/46mmHg, mixed venous CO2 content=520ml/litre, arterial pH=7.44-7.36, arterial [HCO3-]=21-27mmol/litre