QUESTIONS FOR REVIEW

1)A patient is unable to produce surfactant .To inhale a normal tidal volume ,will her

intrapleural pressure have to be more or less subatmospheric during inspiration,relative to a

healthy person?

ANSWER

Her intrapleural pressure must be made more subatmospheric than usual during inspiration to

achieve lung expansion .This requires more vigorous contraction of the diaphragm and

inspiratory intercostal muscles. This person needs to breathe shallowly and must breathe at a

higher frequency to inspire an adequate volume of air.

In addition: insufficient surfactant levels can cause the lungs to be less compliant,

therefore a greater transpulmonary pressure is required to expand the lungs.

2)A person’s alveolar membranes have become thickened enough to moderately decrease the

rate at which gases diffuse across them at any given partial pressure differences .Will this

person necessarily have a low arterial PO2 at rest? During exercise?

This person will have a low arterial PO2 at rest because decreased alveolar ventilation will

increase the alveolar Pco2 because there is less inspired fresh air to dilute the carbon dioxide

entering the alveoli from the blood .Increased production of carbon dioxide will also increase

the alveolar Pco2.

During exercise ,these capillaries open and receive blood,thereby enhancing gas exchange.The

pulmonary circulation at rest is at such a low blood pressure that the pressure in these apical

capillaries is inadequate to keep them open ,but the increased cardiac output of exercise raises

pulmonary vascular pressures which opens these capillaries .During exercise there is increased

PO2.

If the membranes are thickened to cause only a moderate decrease in the diffusion rate of

gases then the person would not necessarily have a low arterial PO2 at rest. The

equilibration of alveolar air and pulmonary capillary blood is rapid and occurs long

before the end of the capillaries. Therefore even though diffusion may be retarded, there

may still be enough time for equilibration to be reached. With respect to exercise, the time

for equilibration is decreased. Failure to equilibrate may result in a lowered arterial PO2

3)Why does an inspired O2 of 100 percent increase arterial PO2 much more in a patient with

ventilation perfusion mismatch than in a patient with pure anatomical shunt.

Ventilation perfusion mismatch is when there are incorrect proportions amounts of alveolar air

flow and capillary blood flow to the alveolus,SHUNT is when there may be blood flowing

through areas of lung that have no ventilation due to collapsed alveoli.

An inspired O2 of 100 percent increased arterial PO2 is much more in a patient with ventilation

–perfusion mismatch than in a patient with pure anatomical shunt because the alveoli are

capable of receiving carbon dioxide from and supplying oxygen to the pulmonary capillary

blood whilst with the pure anatomical shunt there may be ventilated alveoli with no blood

supply at all due to blood clot or collapsed alveoli.

In pure anatomical shunt, blood passes through the lung without exposure to any alveolar

air. Therefore, increases in alveolar PO2 caused by increased inspired O2 will not affect

the PO2 of the shunt blood. In ventilation-perfusion mismatch some blood still flow

through a region of the lung. Therefore an increase in PO2 in the alveoli can increase the

PO2 in this blood.

4)Describe the ways in which CO2 is transported in the blood.

10 percent of CO2 entering the blood dissolves in the plasma and erythrocytes .

30 percent CO2 react reversibly with the amino groups of hemoglobin to form carbamino

hemoglobin

CO2+Hb HbCO2

This reactions shows that deoxyhemoglobin has a greater affinity for CO2 than does

oxyhemoglobin.

60 percent of the carbon dioxide molecules entering the blood in tissues is converted to

bicarbonate ions

CO2+H2O H2CO3 HCO3-+H+

The enzyme catalyzing the first reaction is carbonic anhydrase the products are carbonic acid

and bicarbonate.

5)Draw and label a diagram of the oxygen dissociation curve .What is the biological

significance of it’s shape.

6)Explain how the curve might respond to changes in

a)Temperature

b)Ph

c)2,3diphosphoglycerate

ANSWER

With an increase (of temperature, pH, DPG) the curve responds by shifting to the right ,PO2

is given off ,hemoglobin has less affinity for oxygen ,a decrease in any of these factors causes

the curve to shift to the left ,such that at any given PO2 ,hemoglobin has a greater affinity for

oxygen.

Also include diagrams of the curves of each of the factors as seen in the text

7)WHAT ARE BOHR AND HALDANE EFFECTS.