Ventillation And Diffusion

Question 1

Describe the structure of the conducting airways?

Answer 1

Made of cartilage, few smooth muscles
- will rarely collapse

Question 2

what is alveolar ventilation?

what is pulmonary ventilation?

Answer 2

• Alveolar ventilation is the exchange of gas between the alveoli and the external environment
• Pulmonary ventilation is the process of air flowing into the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation) – about 500ml of air inhaled and expired on each breath
• Pulmonary ventilation includes the gas used in gas exchange, and the anatomic dead space air that fills up the respiratory system, but isn’t used in gas exchange

Question 3

Describe the structure of the respiratory and alveolar ducts?
Are the susceptible to collapse??

Answer 3

• no cartilage, lots of smooth muscle
• susceptible to collapse during expiration

Question 4

How much air is there in anatomical dead space?

At what generation does the dead space turn into respiratory area?

Answer 4

250mls
Generation 17

Question 5

How much alveoli do humans have?
&
Across what surface area?

Answer 5

Humans have around 300 million alveoli in a cross sectional area that increases from 2.5cm2 at trachea to around 100m2

Question 6

Why does airflow velocity decrease?

At what number of airway generations/divisions does aggregate cross-sectional area start to rapidly increase?

Where will this area be around?

Answer 6

• Airflow velocity decreases to allow adequate time for diffusion once the air reaches the capillaries
• At about 12-14 airway generations/divisions, the aggregate cross-sectional area starts to rapidly increase
• The area will be around the respiratory bronchioles, as this area is where alveoli start to appear

Question 7

What are the primary functions of the respiratory and cardiovascular systems?

Answer 7

• transport O2 from the lungs to all tissues in the body.
• remove CO2 from the tissues to the lungs
• lungs will expire this CO2 to the atmosphere

Question 8

How are Oxygen and CO2 able to move by diffusion?

Where is Oxygen and CO2 partial pressure high and low?

How does partial pressure change affect diffusion of gas?

What is this principle the basis of?

Answer 8

• Oxygen and CO2 can diffuse (passive) as both gases move by diffusion down their partial pressure gradients (also down their concentration gradients)
• Oxygen partial pressure is high in the air, and low in the tissues
  CO2 partial pressure is high in the tissues and low in the air
• These both allow the gases to move down their partial pressure gradient
• If the partial pressure in the liquid becomes greater than in the air, the gas will diffuse out of the liquid, and vice versa, due to gases flowing down partial pressure gradients
• This is the basis for O2 moving into the blood from the lungs, whereas C02 moves out of the blood into the lungs

Question 9

Describe the movement in concentration gradient for both CO2 and O2

Answer 9

Both gases move down their concentration gradient.

O2 goes down concentration gradient as it moves from air to the tissues

CO2 moves down the concentration gradient as it moves from tissues to air.

Question 10

What is Daltons Law?

Answer 10

“Total pressure (Ptotal) of a mixture of gases is the sum of their individual partial pressures (Px)”

Question 11

what is the value for atmospheric pressure?

Answer 11

atmospheric pressure at sea level is 760mmHg or 101.325 kPa

Question 12

if atmospheric pressure changes …

is proportion of gas changes …

Answer 12

if atmospheric pressure changes then partial pressure changes

is proportion of gas changes its partial pressure changes

Question 13

what is Henry’s law?

Answer 13

• states that the concentration of O2 dissolved in water (O2(dis)) is proportional to the partial pressure (PO2) in the gas phase

(O2) dis= s x PO2

where s = solubility of O2 in water

Question 14

How soluble is CO2, O2, and N2 in blood at atmospheric pressure?

Why do we need haemoglobin?

Answer 14

• CO2 is the most soluble in blood plasma
• O2 is about 1/20th as soluble as CO2
• This means the blood can carry far more dissolved CO2 than O2
• This is why we need haemoglobin as a special oxygen carrier, otherwise we wouldn’t have enough oxygen in the blood
  N2 is barely soluble in blood at atmospheric pressure

Question 15

What happens to alveolar air?

Why is this important?

How is this affected on a cold day?

Answer 15

• Alveolar air is warmed and humidified by adding water vapour to it
• This is important alveolar cells are sensitive to pressure/temperature
• When the air is cold, the humidity in the air is decreased, so the air becomes dry
• There is not enough time to warm this air, so it dries out the respiratory system

Question 16

what is the partial pressure for water vapour?

Answer 16

Water vapour also has a partial pressure, so when we breath gases in and add water vapour, we have to subtract the partial pressure of water vapour from the partial pressure of these gases that make up atmospheric pressure

The partial pressure of water vapour is 47mmHg

Question 17

what is s for blood plasma?
(s= solubility of O2 in water)

Answer 17

s= 0.0013 mM/mmHg at 37 degrees celsius so

so (O2)dis= 0.0013 x 100 mmHg = 0.13 mM (arterial blood)

(O2) dis = 0.0013 x 40 mmHg = 0.05 mM (mixed venous blood)

Question 18

Is oxygen or co2 more soluble?

Answer 18

CO2 is the most soluble, O2 is about 1/20th as soluble and N2 is barely soluble at atmospheric pressure.

Question 19

for there to be gas exchange between alveolar and blood, what does O2 have to do?

Answer 19

O2 has too:
- dissolve in an aqueous environment
- diffuse across the membranes
- enter the blood

Question 20

what is the equation for flow?

Answer 20

Question 21

what is the rate of difussion proportional to?

Answer 21

• partial pressure difference
• solubility area
• solubility (D, diffusion coefficient)
• molecular mass
• inversely proportional to tissue thickness (T)

Question 22

describe the surface structure/size of the lungs?

Answer 22

• surface area of lungs is large (50-100m2)
• large number of alveoli (around 500million)
• thin walls (0.2-0.5um)

Question 23

what is the concentration gradient across the lungs?

Answer 23

PO2 alveolar air= 100mmHg
PO2 of venous blood = 40mmHg

diffusion is rapid
(molecular mass is insignificant, but solubility is very important, with CO2 diffusing 20x more rapidly than O2

Question 24

what is the difference between rest and exercise for the time is takes for blood to pass through the capillaries?

Answer 24

at rest = 0.75-1 second for blood to pass through pulmonary capillaries

• O2 equilibrium only takes about 0.25 secs (so not normally diffusion limited)

in exercise, capillary transit time can be reduced to as little as 0.3 secs (so not it is diffusion limited)

This can decrease how saturated each blood cell is with oxygen, leading to an incomplete O2 equilibrium.

Question 25

describe the direction of movement of CO2 in the blood capillary? across what concentration gradient?

Answer 25

CO2 moves in the opposite direction to O2 from blood capillary into alveoli - against smaller concentration gradient: - alveolar PCO2 is 40mmHg - venous PCO2 is 45 mmHg however, there is a greater solubility, so CO2 will diffuse 20x more rapidly than O2 as the same amount of gas moves.

Question 26

when are there diffusion limitations?

Answer 26

- in oedema - emphysema - pulmonary fibrosis - mucus, inflammation of airway, tumours, reduced gas entry (gas exchange reduced)

Question 27

how does edoema effect flow?

Answer 27

because T (thickness of barrier) increases - the transit time through capillary may not be suffiecnt to complete full gas exchange, therefore - gas exchange is reduced - more marked effect on O2 than CO2, due to greater solubility of CO2

Question 28

how does emphysema effect flow?

Answer 28

in emphysema, A is reduced (breakdown of tissue in alveolar sac) - gas exchange will be reduced

Question 29

how does pulmonary fibrosis effect flow?

Answer 29

in pulmonary fibrosis, T is increased due to deposition of fibrotic tissue - gas exchange is reduced

Question 30

what is the effect of altitude?

Answer 30

- at a high altitude, atmospheric pressure will be reduced, hence PO2 is reduced

Question 31

what is the effect on partial pressure by simple being in Denver Colorado?

Answer 31

Denver is 1620m above sea level. - Pb is 632 (down from 760mmHg) - inspired PO2is 125 (down from 149 mmHg) - alveolar PO2 is 84 (down from 104 mmHg) - alveolar PCO2 is 34 (down from 40mmHg

Question 32

what are the 2 physiological adaption to altitude?

Answer 32

acute hypoxia adaptive hypoxia

Question 33

acute hypoxia?

Answer 33

- hypoxia is sensed by peripheral chemoreceptors - ventilatory drive increases initially but blunted by central chemoreceptors that respond to decreased PaCO2 due to increased ventilation - CO increases due to suppression of the cardioinhibitory centre

Question 34

adapt hypoxia?

Answer 34

- central chemoreceptors adapt so ventilation rate continuous to increase - PaCO2 drops leading to respiratory alkalosis, kidneys compensate by reducing acid excretion blood Ph normalises - alkalosis stimulates 2,3 DPG production leading to righforward shift of O2 dissociation curve

Question 35

what happens to the: blood vasculature cardiopulmonary system during acclimation

Answer 35

Blood: - erythropoietin release stimulated - Hb concentration increases to 200 g/L from 150 g/L Vasculature: - hypoxia stimulates angiogenesis - capillary density increases throughout the body Cardiopulmonary system: - vascular and ventricular remodelling - smooth muscle growth increases vascular wall thickness - right ventricle hypertrophies

Question 36

what happens to the atmospheric pressure while diving? what are the effects of depth?

Answer 36

it will increase by 760 mmHg (1atmosphere) every 10m depth. effects of depth: - increase in partial pressure, N2 and O2 dissolve into blood at lethal excess - volume decreases

Question 37

how can gas become toxic during diving?

Answer 37

* N2 narcosis = partial pressure of N2 (40m and below) rises and starts to dissolve in body tissues *02 poisoning = tightly regulated at sea level and system essentially saturated * at higher pressure O2 dissolves in blood in excess of the buffering capacity of the Hb * helix = N2 replaced by helium and percentage of O2 is tailored to reduce harm * helium is less readily dissolved in body tissues and less narcotic.

Question 38

In what 3 steps is N2 narcosis caused? How can N2 narcosis be avoided?

Answer 38

N2 narcosis steps: 1) At 40m of depth and below, the partial pressure of N2 rises, which leads to N2 dissolving into the blood and distributed into the circulation, preferentially partitioning in fat tissue 2) If we resurface too quickly, the high N2 partial pressure that forced N2 into the blood returns to normal, and the N2 comes out of the blood too quickly, which forms pure N2 bubbles 3) The presence of bubbles in the blood stream causes decompression sickness, or “the bends. – a painful process N2 narcosis can be avoided by resurfacing slowly, which allows N2 partial pressure to slowly equilibrate and N2 to move out of the blood slowly

Question 39

What is oxygen toxicity/poisoning? How is it normally caused? How does it affect the lungs? How soon can it appear? How is O2 poisoning at depth caused?

Answer 39

- Oxygen toxicity/poisoning is organ system/tissue damage that occurs from breathing in too much extra (supplemental) oxygen - Extended exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes, leading to the collapse of the alveoli in the lungs. - Pulmonary effects can present as early as within 24 hours of breathing pure oxygen - At higher atmospheric pressures due to depth, partial pressure of oxygen increases, which forces more oxygen to dissolve in the blood, causing hyperoxia - This O2 dissolves in blood in excess of the buffering capacity of Hb, leading to blood alkalosis

Question 40

How can N2 Narcosis and oxygen poisoning be avoided?

Answer 40

- N2 narcosis and oxygen poisoning can be avoided by replacing N2 with helium and tailoring the oxygen to reduce harm - This mixture is known as Heliox (Helium and Oxygen) - Helium (He) less readily dissolves in body tissues and is less narcotic