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(1)

Transport of oxygen and carbon dioxide in

blood and body fluids

July 13th, 2011

Ann Raddant, B.S.

(2)

Pressures of gases in water and tissues

• Henry’s Law

• Solubility coefficient depends on physical and chemical attraction or repulsion to water molecules

Molecule Solubility coefficient

Oxygen 0.024

Carbon dioxide 0.57

More soluble = lower partial pressure

Blood P

O2

: 100mmHg

(3)

Today’s Topics

• Diffusion of respiratory gases from the alveolus to the level of the systemic capillary and back to the lung

• The two mechanisms by which oxygen in carried in the blood: dissolved and bound to hemoglobin

• Oxygen-hemoglobin dissociation curve

• The three forms by which carbon dioxide is carried in the blood

• The basics of acid-base control using the Henderson-Hasselbach equation and Davenport diagrams for

(4)
(5)

Uptake of oxygen by pulmonary blood

• PO2 gradient between alveolus

and pulmonary capillary • RBC transit time

– Safety factor

• Increased flow during exercise is easily accommodated

• Pathological thickening of

membranes can limit O2 transfer

– Fick’s Law (increased surface area) – Decreased rate of diffusion

(6)

P

O2

in arterial blood

Of blood entering the left heart:

(7)

Oxygen: from blood to cell: 2 step process

Diffusion of oxygen from capillaries to the interstitial fluid

• PO2 capillary = 95

• PO2 interstitial fluid = 40

Increased blood flow will increase interstitial fluid PO2

(8)

Oxygen: from blood to cell: 2 step process

Diffusion of oxygen from interstitial fluid to cells

• PO2 interstitial fluid = 40

• PO2 intracellular = 5 – 40 (shown as 23 here)

(9)

CO2 diffusion from peripheral tissues back to alveoli

CO

2

is a waste product of many metabolic reactions

• P

CO2

intracellular = 46

• P

CO2

interstitial = 45

(10)

CO2 diffusion from peripheral tissues back to alveoli

• ΔP can be lower for CO

2

than O

2

because it

diffuses so much faster than O

2

• Increased blood flow will reduce venous P

CO2
(11)
(12)

Transport of O

2

in the blood

1. Dissolved oxygen – 3%

– Low solubility limits the concentration of O2 that can be transported dissolved in blood

2. Hemoglobin (Hb) – 97%

– Contained within red blood cells (RBC’s) – Each Hb molecule contains 4 chains

(13)

Oxygen capacity

• ~ 20 ml O

2

/100ml blood

• O

2

capacity is affected in diseases such as anemia

and polycythemia

– anemia: decreased number of RBC’s or

decreased amount of Hb in blood

(14)
(15)

Volumes per cent:

common expression of

a solution’s concentration

(16)

Volumes per cent:

common expression of

a solution’s concentration

Saturated blood: 20% O2

15 grams Hb per 100ml blood

1.34 ml O2 per 1g Hb

(17)

Oxygen-Hemoglobin Dissociation Curve

Small change in PO2 here won’t impair Hb loading

(18)

Utilization coefficient

• Percentage of blood that gives up its

oxygen as it passes through the tissue

capillaries

(19)

Utilization coefficient

Arterial blood Venous

blood

5ml O2 per 100ml

blood

5ml O2 per 100ml of blood used 20ml O2 = starting amount

(20)

Utilization coefficient

Arterial blood

Venous blood during exercise

15ml O2 per 100ml

blood

15ml O2 per 100ml of blood used 20ml O2 = starting amount

(21)

Factors that shift the

Oxygen-Hemoglobin dissociation curve

P

O2

%

H

b

S

at

u

ra

ti

o

n

The Bohr Effect:

CO

2

and H

+

ions interact with Hb

and reduce its affinity for O

2

• Shifting the curve to the right enhances the release of O2

– Lower saturation at the same PO2

• Shifting the curve to the left enhances loading of O2

(22)

R: release

L: loading

(23)

R: release

L: loading

(24)

Factors which can shift the curve to the

right

• Decreased pH

– Increased [H

+

]

• Increased CO

2

• Increased temp

• Increased DPG

• Exercise

(25)

DGP: 2,3-diphosphoglycerate

Conditions of low tissue O

2

lead

to generation of more DGP

• High altitude

• Airway obstruction

(26)

Factors which can shift the curve to the

left

• Increased pH

– Decreased [H

+

]

(27)

Transport of CO

2

in the blood

1. Dissolved carbon dioxide – 7%

– Obeys Henry’s law, by CO2 is 20x more soluble than O2

2. Bicarbonate (HCO

3-

) – 70%

– carbonic anhydrase - CA

3. Carbamino compounds – 23%

(28)

The chloride shift

• HCO

3-

diffuses out of RBC down its

concentration gradient

• Cl

-

moves into RBC in order to balance total

(29)
(30)

CO

2

dissociation curve

(31)

The Haldane Effect

• Binding of O

2

with hemoglobin tends to displace

CO

2

from the blood

– Opposite of Bohr effect

(32)

The Haldane Effect

In peripheral tissues

(top):

• Reduced Hb (no O

2

) is a

better proton acceptor –

binds H

+

, shifts CO

2

-

(33)

The Haldane Effect

In the lungs

(bottom):

• O

2

-Hb is a bad proton

acceptor – promotes H

+

release, shifts CO

2

-

(34)

Displacement of O

2

by CO

• Hemoglobin has a

much higher binding

affinity for CO then

oxygen – small

(35)

Respiratory exchange ratio

Transported in every 100ml of blood:

• 5ml O2

• 4ml CO2

R changes in response to metabolism

• Carbs: R = 1.0

• Fat: R = 0.7

(36)

Acid Base Balance

Lung excretes 10,000 mEq/day of carbonic acid every day

Bicarb buffer is critical for maintenance of blood pH

(37)
(38)
(39)

Take home points

• Oxygen and carbon dioxide move

between blood to tissue based on partial pressure gradients

• Most oxygen is transported bound to

hemoglobin, while most carbon dioxide is transported as bicarbonate

• Many factors can affect the binding of oxygen to hemoglobin

Referensi

Garis besar

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