Gas Transport & Exchange

2 ways to transport oxygen

Dissolved in Plasma

Attached to haemoglobin

What oxygen exerts a partial pressure

Only oxygen dissolved in plasma

(oxygen in Plasma has a Partial Pressure - all the Ps)

Is oxygen soluble

Only very slightly

Why can’t we just rely on oxygen dissolved in plasma for our oxygen requirement

We need haemoglobin to supply the other 235ml O2 needed

For every 1g of haemoglobin (Hb) how many ml of O2 is it carrying

1.34 ml

How much Hb is in 100ml of blood

Hb 15 g Hb/100 ml

How much oxygen is in 100ml of blood

20.1mlO2

When CO is 5L how many ml of oxygen being delivered (ml/min)

1005ml/min

When CO is 30L how many ml of oxygen being delivered (ml/min)

6030 ml/min

How many oxygens does haemoglobin generally give up at rest

1

Generally 3/4 molecules are still attached

O2 capacity of blood formula

O2 saturation of Hb formula

Oxygen content in blood / (oxygen-carrying capacity of Hb (1.34 mL) x Hb conc. in blood)

How much O2 is Hb carrying / How much is possible for it to carry

O2 saturation of Hb in mixed venous blood

75% saturated (so up to 75% of O2 supply to tissues is in reserve

(this would make sense - Hb only usually gives out 1 of 4 O2s so 75% would be left)

name this curve

Oxygen dissociation curve

What is an oxygen dissociation curve

For a given PO2 what percentage of haemoglobin is going to be saturated

(PaO₂ represents the amount of dissolved O₂ in plasma , not in RBCs. e.g. this would be high in the lungs)

(Think of PaO₂ as the pressure pushing oxygen into:

• Hemoglobin (to bind it),

• Tissues (to deliver it).)

Explain the shape of the graph

Flat upper portion: For a big drop in PO2 you only get a small drop in haemoglobin saturation

Much sharper decrease

The first oxygen is difficult to give up. The oxygens become easier to lose after that

if the oxygen dissociation curve moves right what does this mean

Any time we need more oxygen to be released from haemoglobin for use in cells the graph moves to the right.

E.g. during exercise we need haemoglobin to be less saturated as we need it to give up oxygen more easily to the muscle

The temperature goes up - it goes up during exercise

Space under the graph = oxygen bound to Hb. Space over the graph = oxygen given up to tissues (if we move the graph right we decrease the area under the graph (O2 bound to Hb) and increase area above the graph (O2 given to tissues) which is what we want during exercise!)

If the oxygen dissociation curve moves left what does this mean

e.g. foetal haemoglobin

(BPG binds to deoxygenated haemoglobin (Hb) and reduces its affinity for oxygen, which helps haemoglobin release oxygen to tissues)

Polycythaemia

Overproduction of red blood cells

(from cancer or high altitudes)

(Poly = many. Cyto = cell. Haemia = blood)

Effect of anaemia and polycythaemia on oxygen concentration curve

Doesn’t change the shape of the curve

People with anaemia (Hb = 10) have a lower oxygen concentration despite the same oxygen saturation as those with higher Hb levels.

People with polycythaemia (Hb = 20) have higher oxygen concentration despite the same oxygen saturation as those with lower Hb levels.

4 types of hypoxia & what are they

(Hypo- = low, -oxia = oxygen, 👉 So: Hypoxia = low oxygen (in tissues))

Hypoxic Hypoxia - Low Arterial PO2 (Pulmonary Disease)(not enough O2 entering the blood from the lungs)

Anaemic Hypoxia - Decreased ability to Carry O2 (Anaemia or CO Poisoning)(low iron → low Hb → low O2)

Circulatory Hypoxia (Stagnant Hypoxia) - Slow blood flow - pools in legs (Shock, Local Obstruction) (Good O2, Good Hb, Bad delivery - low blood volume / clot / heart failure)

Histotoxic Hypoxia - Toxic Substance Stops Tissue Using Available O2 (cyanide)(oxygen is there, delivery is fine, but cells can’t use it due to poisoning)

(4 places for problems:

• Lungs → Blood

• Blood Plasma → Hb

• Hb → Cells

• Cells use of O2)

How is CO2 transported

70% is transported as carbonic acid (H2CO3) - dissociates into H+ and bicarbonate (HCO3-)

23% is bound to amino globular proteins in Hb molecule forming carbaminohemoglobin

7% is transported as CO2 dissolved in plasma - CO2 has a higher solubility coefficient than O2

What happens when CO2 enters red blood cells from respiring tissues and combines with water

Role of chloride ion transport in & out

Keeps electrical neutrality

In respiratory physiology, work = (formula)

In respiratory physiology, work = pressure x volume.

Lungs opening easily isn’t always a good thing, why?

In emphysema are highly compliant - doesn’t mean person is healthy

(High compliance in emphysema = lungs too floppy → can't recoil → air trapping + poor gas exchange.)

Compliance formula

Tidal volume in ml

approx. 500ml

Patient inhales 500 mL of air from a spirometer with a starting pressure of -5 cmH2O ending at -10 cmH2O. Calculate compliance

Compliance normal value

100ml/ cm of water

How does compliance change throughout the lungs

Alveoli at the bottom are easy to open - very small - easier to expand before they reach their maximum size

Alveoli at the top are hardest to open

What significance does compliance change throughout the lungs have

Pneumonia in the bottom of the lungs will be a bigger problem than something affecting the top of the lungs.

Factors That Influence Compliance

Posture

Age - Compliance often ↑

High standing Diaphragm - Pregnancy, Obesity, Scoliosis

Lung Disease

• If lung is unventilated for long period (C↓)

• ↑ surface tension within alveoli (C↓)

• Lung engorged with blood (↑pulmonary venous pressure) (C↓)

Pneumothorax - Trauma, diving, underlying lung pathologies

Effect of fibrosis on compliance

You need a huge increase in pressure to open lungs - very low compliance

Name 3 restrictive disorders that decrease compliance and therefore increase stiffness & work needed to inflate lungs

Pneumonia

Toxicity

Fibrosis

Name a disease that increases compliance, reducing stiffness and work needed to inflate lungs

COPD

(Emphysema & chronic bronchitis)

Compliance is dependant on what 3 things

Distensibility - ease to stretch/deflate – Elastin

Elasticity - Collagen (Without elasticity, lungs enlarge with every breath. Compliance would eventually become zero - Not compatible with life)

Surface Tension

What are the 2 determinants of lung compliance at an alveolar level

What produces surfactant

Type II alveolar cells

What stimulates Type II alveolar cells to produce surfactant

Cortisol plays a key role in stimulating surfactant production in Type II alveolar cells.

What happens to infants without enough surfactant

Infant Respiratory Distress Syndrome (low compliance)

How is Infant Respiratory Distress Syndrome treated

Exogenous surfactant

Does surfactant increase/decrease surface tension

↓Surface Tension

Does surfactant increase/decrease lung compliance

↑ Lung compliance

Other roles of surfactant

↑ Stability of the alveoli

↓Small alveoli emptying into larger ones

Helps to keep alveoli dry because the “surface tension” of the alveolus liquid layer would tend to draw water into the alveolus

What does the Law of Laplace show

Smaller alveoli have higher pressure inside

(it is la place of pressure)

is surfactant hydrophillic/hydrophobic/amphipathic

amphipathic

Surfactants are composed of approximately ___% lipids and ___% proteins

approximately 90% lipids and 10% proteins

These Surfactant specific proteins are hydrophobic/phillic

SP-A

SP-B

SP-C

SP-D

SP-B and SP-C are two small hydrophobic proteins

SP-A and SP-D are large hydrophilic proteins

Most abundant neutral lipid in surfactant

Cholesterol

responsible for generating a near-zero surface tension at the air–liquid interface of the alveoli during compression

DPPC (lipid)

(REALLY long name!)

The effect of DPPC is stronger in higher/lower alveolar volumes

lower

Role of Surfactant Protein A (SP-A)

Immune defence

Role of Surfactant Protein B (SP-B)

Reduces Surface Tension (B chill - no tension)

Antibacterial (Ban Bacteria)

Which surfactant protein is only found in the lung

SB-C

(You only C it in the lung)

Explain the Pressure-Volume Curve

Early in inspiration there is a small change in volume for a large pressure change

At this time the slope (V/P) is small and compliance is low

As inspiration continues the slope is steeper indicating an increase in compliance

The V/P relationship during expiration is different than during inspiration - hysteresis

Volume at any pressure is greater for deflation than inflation

Most of the hysteresis and also most of the compliance of the lung appears due to the surface tension within of the alveoli

How would the addition of saline to the lung affect the lines on this graph

(Inflation of the lung with saline eliminates air-liquid interface and surface tension)

It is much easier to inflate lung with saline as elastic recoil of the lung is diminished due to lack of surface tension

Also not much difference between inflation and deflation – no hysteresis

Why does hysteresis happen

Changes in Surfactant activity: Surface tension greater in inspiration

Stress relaxation: Inherent property of elastic tissues (crinkled structure of collagen in the lung)

Redistribution of gas: fast and slow alveoli

Lung compliance formula

Change in lung vol / change in transpulmonary press

Chest wall compliance formula

Change in lung vol / change in transchestwall press

Total compliance within the respiratory system in ml / cmH2O

Approx. 100 ml / cmH2O

Flow formula

Flow = Pressure/Resistance

Factors That Effect Flow

1) Diameter(radius)

2) Velocity

3) Anatomy

4) Lung volume

5) Inspiration

6) Expiration

What does resistance depend on

Whether flow is laminar or turbulent

Airway dimension

Viscosity of the gas.

What is the Major Site of Airway Resistance

Most Resistance in Medium Sized Bronchi

What is a Site of low Airway Resistance

Terminal Bronchioles Offer Very Little Resistance

How does innervation cause a decrease in airway diameter

The vagus nerve innervates the smooth muscle of the airways.

It releases acetylcholine (ACh) which constricts airways

How does innervation cause an increase in airway diameter

Activation of Adrenergic Receptors

Adrenaline, Isoprenaline, β2-Adrenergic Agonists

Diseases in which airway narrowing occurs

COPD, asthma - increase airway resistance

which is resistance & which is conductance

Does resistance increase/decrease above FRC

Decrease - increased airway diameter

Effect of Decrease Lung Volume below FRC to RV

Airway Resistance

Airway Diameter

Decrease Lung Volume below FRC to RV causes

• Increased Airway Resistance

• Decreased Airway Diameter

Small Airways (Base of Lung) May Close Completely

what is this called & what does it represent

Which of these are normal & what is wrong with the rest