Gaseous diffusion and transport Flashcards

1
Q

Factors affecting O2 carriage

A

pO2 is proportional to conc dissolved in blood. Hb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How to calculate O2 carrying capacity of normal blood

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

O2 saturation of blood entering pulmonary capillaries and leaving

A

enter=75% leave=97-100%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the haem group

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When does 2,3 DPG increase

A

hypoxia, anaemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is anaemia and what causes it

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How is Hb association curve affected in anaemia? sketch

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the negative effects of CO binding to Hb

A

reduces amount of O2 bound to Hb

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Sketch O2 dissociation curve for CO poisoning

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

HbF binds DPG more or less than HbA

A

less

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Cyanosis what is it

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

2 types of cyanosis

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

At which point is cyanosis observable

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are CO2 carried and state the proportions

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

CO2+H2OH2CO3H+ +HCO3- describe

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do carbamino compound form

A

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

17
Q

How are various forms of CO2 unloaded in lung

A

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

18
Q

What is the haldane effect and why does it occur

A

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-

19
Q

Sketch CO2 dissociation curve and note key points

A

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

20
Q

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

A

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

pKa=-log(dissociation constant of H2CO3)

21
Q

What is the relationship between alveolar pCO2 and alveolar ventilation

A

Inversely proportional. If one doubles, other halves

22
Q

How to measure O2 consumption

A

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

23
Q

What is the respiratory quotient

A

CO2 produced: O2 utilised

24
Q

What is hyper and hypoventilation

A

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

25
Q

Why does hyperventilation not equate to increased ventilation

A

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

26
Q

What does hyperventilation lead to

A

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

27
Q

Hyperventilation cause

A

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

28
Q

What are the consequences of hyperventilation

A

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

29
Q

What does hypoventilation cause and what is it caused by

A

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

30
Q

Consequences of increased PCO2 due to hypoventilation

A

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

31
Q

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

A

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%

32
Q

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

A

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