cgier 28 Flashcards

1
Q

The gases in the alveoli come into equilibrium with the blood by — across the —– and —–

A
  • diffusion ( from difference in partial pressure between the alveoli and the blood )
  • pulmonary epithelium and capillary walls
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2
Q

The pressure exerted by an individual gas in a mixture is known as its

A

partial pressure

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3
Q

at — level the —- typically supports column mercury 760nm high

A
  • sea level
  • barometric pressure
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4
Q

oxygen’s share of that pressure can be calculated as:

A

Air = 760mm Hg, Oxygen 21% in Air 0.21 X 760 = 160mm Hg
( since oxygen makes up 21%)
and co2 can be done similarly ( 0.004% x 760 )

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5
Q

*Fick’s law of diffusion states ,The amount of oxygen or carbon dioxide that diffuses across the membrane of an alveolus depends on the

A

-differences in partial pressure on the two sides of the membrane & on the surface area of the membrane.
- gas diffuses faster if the difference in pressure or surface area increases
- rate of diffusion = K x A x ( p2-p1 / d)
k: diffusion constant
a : area
d: distance
p: difference in pp

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5
Q

There is a gradient of PO2 from dry inspired air to alveolar air, from 160 to 104 due to

A

due to an increase in partial pressure of water vapour

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6
Q

O2 present in blood in two forms:

A

1- physical : dissolved in the plasma
2- chemical combination: >98 bound to haemoglobin in the blood

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7
Q

O2 in arterial blood — and in tissues ( at rest )

A
  • 100 mm hg
  • 40 mm hg
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8
Q

-Oxygen diffuses out of the —– and into the tissues.

A

capillaries

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9
Q

When arterial blood reaches tissue capillaries, the gradient is

A

reversed
-Because PO2 is lower in the cells, oxygen diffuses the pressure gradient into the cells. Returning venous blood will now have the same PO2 as the cells it just passed.

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10
Q

02 has poor solubiltiy in the — which is insufficient

A
  • blood
  • so the remaining 98% will combine reversely w/ haemoglobin and increases the 02 transport
    -Blood contains a large concentration of haemoglobin (140 - 180 g/L for men, 120 to 160 g/L for women)
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11
Q

each haemoglobin molicule can bind to — o2 molecules and — % of 02 in the blood is bounded to heamoglobin

A
  • 4 02 molecules
  • 89.5%
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12
Q

when the oxygen concentration increases , there is a — in binding to haemoglobin and its highest in

A

increase , pulmonary capillaries

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13
Q

in the OXYGEN-HAEMOGLOBIN DISSOCIATION CURVE the relationship is not linear but is

A
  • sigmoid due to the cooperative binding of 02 to haemoglobin
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14
Q

maximum amount of oxygen that haemoglobin can transport is

A

Oxygen-carrying capacity

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15
Q

actual amount of oxygen bound to haemoglobin is

A

Oxygen content

16
Q

ratio of oxygen content to oxygen-carrying capacity

A

oxygen saturation

17
Q
  • The ability of haemoglobin to bind and release oxygen is influenced by several factors in addition to percent oxygen saturation as:
A

pH, carbon dioxide concentration, and temperature these factors result in shift in the curve

18
Q

right shifts indicates

A
  • low oxygen affinity to heaomglbin
  • difficult to bind
  • requires higher pp of 02
  • makes it easy for haemoglobin to release o2 bound to it
  • increase temp
  • increase h
  • low ph
19
Q

left shift leads to

A
  • increased affinity for 02
  • can bind easily
  • low h
  • low temp
20
Q

Displacement of the oxygen-haemoglobin dissociation curve by a change in pH is known as the

A

bohrs effect

21
Q

Carbon dioxide produced in respiring tissue reacts with water in the plasma to form

A

carbonic acid, H2CO3.

22
Q

Oxyhaemoglobin unloads oxygen more readily in an

A
  • acidic rather than normal ph environment
  • his has the beneficial effect of delivering more oxygen to tissues where CO2 levels are rising due to increased metabolism.This is due to deoxyhaemoglobin binding H+ ions more actively than oxyhaemoglobin
23
Q

Binding of H+ ions to specific amino acid residues on the globin chain stabilises

A

haemoglobin in a low affinity state and promotes release of oxygen

24
Q

released from active muscles also lowers blood pH and has a similar effect on the oxygen-haemoglobin dissociation curve

A

lactic acid

25
Q

UTILIZATION COEFFICIENT

A

This is the fraction of the blood that gives up its oxygen as it passes through the capillary bed
* Arterial blood contains approx. 20ml oxygen/ 100 ml blood.
* Under normal conditions, 5 ml of oxygen per 100 ml blood will be
released to the tissue.
* Therefore only 25% of O2 present in the blood is utilized by the tissue.
Hence venous blood still contains approx. 15 ml O2/ 100 ml.
* During strenuous exercise, some 15ml O2/100ml blood or 75% of the carrying capacity can be delivered (increased release of oxygen due to the drop in partial pressure of O2 in cells), this is three times normal delivery

26
Q

Carbon dioxide is much more soluble in blood

A

blood than oxygen thus there is usually more in simple solution

26
Q

Carbon dioxide is transported in the blood in three ways

A

(i) dissolved in solution (approx. 10% in plasma)
(ii) bound to proteins, (particularly haemoglobin, 20%) (iii) as bicarbonate ions (HCO3-) (approx. 70%)

27
Q

CO2 can be carried within erythrocytes by two mechanisms

A

1- As carbaminohaemoglobin - 20% approx.
* CO2 bind haemoglobin at a different location than O2
* Reversible reaction – when the red blood cells reach the lower CO2 concentration of the lungs, CO2 is released from carbaminohaemoglobin and diffuses into the alveoli
2- 2. As bicarbonate - 75%
In plasma, carbon dioxide slowly combines with water to form carbonic
acid
* This reaction proceeds much more rapidly inside RBCs as a result of
CO2 + H2O –> H2CO3 (carbonic acid) the action of the enzyme carbonic anhydrase
* Carbonic acid is an unstable intermediate molecule and quickly dissociates
into hydrogen ions and bicarbonate ions
H2CO3 –> H+ + HCO3- (bicarbonate ion)

28
Q

CHLORIDE SHIFT

A

CO2 quickly converted into bicarbonate ions, this reaction allows for continued uptake of CO2 into the blood, therefore allows large amount of CO2 to be transported as bicarbonate
* It also results in the production of H+ ions. If too much H + is produced, it can alter blood pH. Most hydrogen ions released from the carbonic acid combine with haemoglobin, which is a very effective buffer, thus limiting shifts in pH
* Carbon dioxide and water diffuse freely into the red blood cell but H+ and HCO3- ions do not pass through cell membranes.
* Bicarbonate is transported out by a transport protein in exchange for a chloride ion (Cl–). This is called the chloride shift.

29
Q

Bicarbonate is transported out by a transport protein in exchange for a chloride ion (Cl–). This is called the

A

chloride shift

30
Q

REVERSE OF CHLORIDE SHIFT

A

When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion.
* The H+ ion dissociates from the haemoglobin and binds to the bicarbonate ion.
* This produces the carbonic acid intermediate, which is converted back into carbon
dioxide through the enzymatic action of Carbonic Anhydrase.
* The carbon dioxide produced is expelled through the lungs during exhalation.
Cl– HCO3– Bicarbonate
* In the alveolar capillaries, CO2 diffuses out of the plasma and into the alveoli.
* Bicarbonate ions diffuse from the plasma into the RBCs.
H Bicarbonate
Cl–
H2CO3 H+
Carbonic acid
Hemoglobin
Alveoli
CO2
CO2 + H2O H2O CO2
CO2
CO2
released
from haemoglobin
Pulmonary capillary wall
* H+
combines with bicarbonate ions, producing carbonic acid.
* Carbon dioxide produced from the carbonic acid diffuses out of the blood and into the alveoli.

31
Q

HALDANE EFFECT

A

The binding of oxygen with the haemoglobin tends to displace carbon dioxide from the blood.
* This is called the Haldane effect
* This doubles the release of CO2 in the lungs and the uptake of CO2 in the tissues.
* The cause is increased release of H+ ions from the haemoglobin when it combines with oxygen.
* The increased H+ will combine with HCO3- to produce additional CO2 for release to the alveoli
* Conversely, deoxygenation of the blood increases its ability to carry carbon dioxide

32
Q

— effect helps lungs release carbon dioxide from haemoglobin

A

Haldane effect

33
Q

— effect helps oxygen release from oxyhaemoglobin

A

bohrs effect