notes part 2

Question 1

Discuss the ventilation differences between different lung regions

Answer 1

At apex: the intrapleural pressure is more -ve than the base less air is moved into & out of alveoli during inspiration.
So, ventilation at base is higher than apex of the lung

Question 2

Discuss the perfusion differences between different lung regions.

Answer 2

Due to gravity,: blood flow to the base of the lungs is more than apex in upright posture
→ more perfusion to base
In supine position: blood flow to posterior part of lung is more than anterior parts
In exercise : ↑ apical & basal blood flow
In Hemorrhage → underperfusion of the apex

Question 3

Describe the consequences of the physiological mismatching between ventilation and perfusion at the lung apex and at the lung base

Answer 3

Lung apex:
- High VA/ Q ratio
- ↑ O2 & ↓CO2
- Wasted ventilation (physiological dead space)
Lung base:
- Low VA/ Q ratio
- ↓ O2 & ↑CO2
- Wasted blood
(venous admixture) 
(physiological shunt)

Question 4

Give an account on the physiologic dead space.

Answer 4

Definition; wasted ventilation
(air doesn’t share in gas exchange)
= Anatomical + Alveolar dead space
in upright posture (↓ blood flow to upper parts of lungs)

Question 5

Give an account on the physiologic shunt (venous admixture)

Answer 5

wasted perfusion

blood leaves the lungs without oxygenation

Question 6

Discuss the physiologic compensatory mechanisms that minimize the ventilation/perfusion mismatching

Answer 6

1- Higher VA/ Q ratio (More air than blood)
- ↑ local alveolar PO2→vasodilatation of pulmonary vessels → ↑ blood flow
- ↓local alveolar PCO2→ bronchoconstriction → local ↓ in ventilation
2- Low VA/ Q ratio(More blood than air)
- ↓ local alveolar PO2→ vasoconstriction of pulmonary vessels → ↓ blood flow
- ↑local alveolar PCO2→ bronchodilatation → local ↑ in ventilation

Question 7

List the pressure differences responsible for oxygen and carbon dioxide diffusion in the body

Answer 7

1- O2 diffusion:
by down pressure gradient , From alveolar air (PO2 = 100 mmHg) to pulmonary capillary blood (PO2 = 40mmHg)
2- CO2 diffusion:
by down pressure gradient, From pulmonary capillary blood (PCO2 46mmHg) to alveolar air (PCO2 40mmHg)

Question 8

Alveolar PO2 remains constant because:

Answer 8

New O2 arrives to the alveoli is EQUAL to O2 leaves the alveoli into the blood

Question 9

Gas exchange between alveolar air (air) & pulmonary capillaries (blood) occurs by…………………………………………

Answer 9

simple diffusion

from areas of high partial pressure to areas with low partial pressure

Question 10

Mention the layers and the characters of the respiratory membrane

Answer 10

اسكيمة ال 6 ليرز 
F , 2A , IF , 2C
 1) Fluid lining alveoli & surfactant
2) Alveolar epithelium
3) Alveolar basement membrane
4) Interstitial space &fluid
5) Capillary basement membrane
6) Capillary endothelium
Thickness = 0.5 u 
Surface area = 50-100 m2

Question 11

Describe the factors affecting diffusion of gases through the respiratory membrane.

Answer 11

1) Pressure gradient
2) Surface area of the pulmonary membrane
3) Thickness of the respiratory system
4) Diffusion coefficient of the gas

Question 12

the diffusion rate of CO2 is 20 times faster than

O2 because………………

Answer 12

The solubility of CO2 is much more than O2 by 24 times

Question 13

Respiratory diseases affect …………diffusion more than ………………..diffusion

Answer 13

O2 diffusion more than CO2 diffusion

Question 14

Define the diffusion capacity. List the values of O2 and CO2 diffusion capacity during rest and during exercise.

Answer 14

Definition: the volume of a gas diffusion from alveoli to pulmonary capillary blood through the respiratory
membrane/ min/ 1 mmHg pressure difference

1- O2 diffusion capacity
At rest :
20mL/ min/ 1 mmHg 
In exercise:
 60-70mL/ min/ 1 mmHg 

2- CO2 diffusion capacity
At rest :
400 mL/min/ 1 mmHg
In exercise:
1600 mL/min/ 1 mmHg

Question 15

Outline the factors affecting diffusion capacity

Answer 15

- ↑ in exercise due to:
 ↑ Number of opened capillaries & ↑ alveolar expansion → ↑ surface area & ↓ thickness
- ↓ in
↑ Thickness of respiratory membrane
↓ surface area of respiratory membrane

Question 16

Mention the conditions that increase Thickness of respiratory membrane

Answer 16

• Fibrosis

- Oedema

Question 17

Mention the conditions that decrease surface area of respiratory membrane

Answer 17

• Collapse
• Emphysema
• VA/Q imbalance

Question 18

Describe the methods of O2 transport in blood.

Answer 18

O2 in blood transported in 2 forms:
1- In physical solution 1.5%
-Dissolved in water of plasma & RBCs
- It cannot satisfy the demands of tissues
2- In chemical combination 98.5%
- Binds to the ferrous iron of heme of hemoglobin
- Tissues depend on it

Question 19

Define: O2 content, O2 carrying capacity, and the % saturation of hemoglobin with O2

Answer 19

O2 content:-
- Total O2 carried in blood
O2 carrying capacity of blood:-
- Maximal O2 carried by Hb when Hb is fully saturated with O2.
% saturation of Hb with O2:-
- It is a measure of the extent of Hb combination with O2

Question 20

Define O2-hemoglobin curve. Discuss its physiological importance.

Answer 20

A curve showing the relation between PO2 & % saturation of Hb
- Sigmoid (S-Shaped) has 2 parts:
1) Steep part (at low PO2)
Represent what happens at tissues
It is important for normal adequate supply of O2 to tissues in normal conditions & in exercises
2) Plateau part (at high PO2)
Represents what happens in the lungs
This part of the curve is a safety factor against changes in PO2

Question 21

. List the factors that cause right shift of O2- hemoglobin curve = ↓ affinity of Hb to O2 & ↑ O2release

Answer 21

لما التيشو يكون محتاج اكسجين اكتر 
 ↑ PCO2 (Bohr effect)
 ↑ temperature
 ↑ H+(↓ pH = acidosis)
 ↑ 2.3 DPG
 ↓ PO2

Question 22

List the factors that cause left shift of O2- hemoglobin curve.= ↑ affinity of Hb to O2 & ↓ O2 release

Answer 22

 ↓ PCO2
 ↓ temperature
 ↓ H+(↑ pH = alkalosis)
 ↓2.3 DPG
 ↑ PO2

Question 23

Define P50 and mention its importance.

Answer 23

PO2 at which 50% of Hb saturated with O2
Normal: P50 =27 mmHg
- It is an index of Hb affinity to O2
- P50 is inversely related to Hb affinity to O2

Question 24

Describe the Bohr’s effect on O2-Hb curve at the tissues and at the lungs.

Answer 24

At tissues: 
-↑ PCO2 & H+ → shift to right
- O2 release from Hb
At lungs: 
- ↓ PCO2 & H+ → shift to left 
- O2 uptake by Hb

Question 25

Give an account on CO poisoning

Answer 25

CO Binds to Hb at the same O2 binding site → carboxy Hb (COHb) [or carbon monoxyHb]

Question 26

explain why Very small amount of CO Bind to a large amount of Hb ( Interfere with O2 binding to Hb)

Answer 26

Affinity of Hb to CO is 240 times more than its affinity to O2

Question 27

2,3 DBG can not act on fetal Hb because………………………………………….

Answer 27

it normally acts on B chains , and fetal Hb contains 2 Alpha and 2 Gamma ( no Beta )

Question 28

One myoglobin molecule carries one O2 only

because ……………………………….

Answer 28

it has only one ferrous

Question 29

Myoglobin acts as O2 store, it releases its O2 to

muscles only in ………………………….

Answer 29

serve exercise (marked ↓ in PO2)

Question 30

Mean pulmonary arterial pressure =

Answer 30

13mmHg