cgier 28 Flashcards
The gases in the alveoli come into equilibrium with the blood by — across the —– and —–
- diffusion ( from difference in partial pressure between the alveoli and the blood )
- pulmonary epithelium and capillary walls
The pressure exerted by an individual gas in a mixture is known as its
partial pressure
at — level the —- typically supports column mercury 760nm high
- sea level
- barometric pressure
oxygen’s share of that pressure can be calculated as:
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 )
*Fick’s law of diffusion states ,The amount of oxygen or carbon dioxide that diffuses across the membrane of an alveolus depends on the
-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
There is a gradient of PO2 from dry inspired air to alveolar air, from 160 to 104 due to
due to an increase in partial pressure of water vapour
O2 present in blood in two forms:
1- physical : dissolved in the plasma
2- chemical combination: >98 bound to haemoglobin in the blood
O2 in arterial blood — and in tissues ( at rest )
- 100 mm hg
- 40 mm hg
-Oxygen diffuses out of the —– and into the tissues.
capillaries
When arterial blood reaches tissue capillaries, the gradient is
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.
02 has poor solubiltiy in the — which is insufficient
- 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)
each haemoglobin molicule can bind to — o2 molecules and — % of 02 in the blood is bounded to heamoglobin
- 4 02 molecules
- 89.5%
when the oxygen concentration increases , there is a — in binding to haemoglobin and its highest in
increase , pulmonary capillaries
in the OXYGEN-HAEMOGLOBIN DISSOCIATION CURVE the relationship is not linear but is
- sigmoid due to the cooperative binding of 02 to haemoglobin
maximum amount of oxygen that haemoglobin can transport is
Oxygen-carrying capacity
actual amount of oxygen bound to haemoglobin is
Oxygen content
ratio of oxygen content to oxygen-carrying capacity
oxygen saturation
- The ability of haemoglobin to bind and release oxygen is influenced by several factors in addition to percent oxygen saturation as:
pH, carbon dioxide concentration, and temperature these factors result in shift in the curve
right shifts indicates
- 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
left shift leads to
- increased affinity for 02
- can bind easily
- low h
- low temp
Displacement of the oxygen-haemoglobin dissociation curve by a change in pH is known as the
bohrs effect
Carbon dioxide produced in respiring tissue reacts with water in the plasma to form
carbonic acid, H2CO3.
Oxyhaemoglobin unloads oxygen more readily in an
- 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
Binding of H+ ions to specific amino acid residues on the globin chain stabilises
haemoglobin in a low affinity state and promotes release of oxygen
released from active muscles also lowers blood pH and has a similar effect on the oxygen-haemoglobin dissociation curve
lactic acid
UTILIZATION COEFFICIENT
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
Carbon dioxide is much more soluble in blood
blood than oxygen thus there is usually more in simple solution
Carbon dioxide is transported in the blood in three ways
(i) dissolved in solution (approx. 10% in plasma)
(ii) bound to proteins, (particularly haemoglobin, 20%) (iii) as bicarbonate ions (HCO3-) (approx. 70%)
CO2 can be carried within erythrocytes by two mechanisms
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)
CHLORIDE SHIFT
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.
Bicarbonate is transported out by a transport protein in exchange for a chloride ion (Cl–). This is called the
chloride shift
REVERSE OF CHLORIDE SHIFT
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.
HALDANE EFFECT
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
— effect helps lungs release carbon dioxide from haemoglobin
Haldane effect
— effect helps oxygen release from oxyhaemoglobin
bohrs effect
