Respiratory System - topic 3

respiratory system main functions

• pulmonary ventilation

• gaseous exchange

Blood consistency

55% plasma - 45% blood cells

tidal volume

 volume of air inspired or expired per breath measured in ml or litres. Average = 500 ml

inspiratory reserve volume

the maximum amount of additional air you can forcibly inhale into your lungs after a normal tidal volume

expiratory reserve volume

the maximum amount of additional air that can be forcefully exhaled from the lungs after a tidal volume out

residual volume

the amount of air that remains in the lungs after a maximal, forceful exhalation

vital capacity

the maximum amount of air a person can exhale after taking the deepest possible breath

functional residual volume

 the amount of air left in the lungs after a normal, passive exhalation

total lung capacity

 the maximum volume of air the lungs can hold after a maximum inhalation

minute ventilationbre

the volume of air inspired or expired per minute in ml or litres

breathing frequency

represents the number of breaths taken per minute.

minute ventilation equation

Minute ventilation (L/min) = frequency x tidal volume

factors affecting tidal volume

• Depth of breathing

• Frequency of breathing

• Exercise intensity

how to measure tidal volume

spirometer

effect on tidal volume due to exercise intensity

as exercise intensity increases, tidal volume proportionally increases, until we reach maximum frequency of breaths ( 50 - 70 per minute )

effect on breathing rate due to exercise intensity

as exercise intensity increases, breathing rate proportionally increases until maximum frequency of breaths is reached.

effect on minute ventilation due to exercise intensity

 anticipatory rise, then a rapid rise due to depth and frequency of breathing , then a further gradual increase , then a gradual decrease during recovery.

tidal volume figures

untrained rest - 0.5 l

untrained exercise - 2-2.5 l

trained rest - 6 l

trained exercise - 2.5-3 l

breathing frequency figures

untrained rest - 12-15/min

untrained exercise - 40-50 /min

trained rest - 10-12/min

trained exercise - 40-55/min

minute ventilation figures

untrained rest - 6-8 L/min

untrained exercise- 90 - 120 L/min

trained rest - 5-7 L/min

trained exercise - 150-200 + L/min

inspiration at rest

active

inspiration at rest process

• The diaphragm contracts and flattens

• External intercostal muscles contract

• Rib cage moves up and out

• Volume of the thoracic cavity increases

• Pressure of thoracic cavity decreases

• Air moves from high pressure to low pressure in the lungs so air is pulled in.

expiration at rest

passive

expiration at rest process

• The diaphragm relaxes and returns to a dome shape

• External intercostal muscles relax

• Rib cage moves down and in

• Volume of thoracic cavity decreases

• Pressure of thoracic cavity increases, air moves form higher pressure inside to lower pressure outside lungs

 

inspiration at exercise

active

inspiration at exercise process

• Diaphragm contracts and flattens more than at rest

• External intercostal muscles contract more than at rets

• Additional muscles are recruited e.g. sternocleidomastoid, scalenes, and pectoralis minor

• Rib cage moves up and out further than in rest

• Volume of thoracic cavity increases more than at rest

• Pressure of thoracic cavity increases more than at rest which decreases the pressure more than at rest

• More air moves form higher pressure outside to lower pressure inside.

 

expiration at exercise

active

expiration at exercise process

• The diaphragm relaxes

• External intercostal muscles relax

• Additional muscles are recruited

• Rectus abdominal , external obliques, internal obliques contract

• Rib cage moves down and in further than at rest

• Volume of the thoracic cavity decreases more than at rest

• Pressure of the thoracic cavity increases more than at rest

• More air moves from higher pressure outside to lower pressure in the lungs

respiratory control centre

located in medulla oblongata

inspiration centre at rest

active

phrenic nerve

stimulates diaphragm

intercostal nerve

stimulates external intercostals

expiration centre at rest

passive - doesnt engage

inspiration centre at exercise

During exercise, the body requires more oxygen and produces more carbon dioxide. This leads to:

• Increased blood CO₂

• Decreased pH (more acidic blood)

• Increased muscle/chemoreceptor stimulation

These changes are detected by:

• Chemoreceptors – detect CO₂ and pH

• Proprioceptors – detect movement

• Thermoreceptors - inform of increased blood temperature

 

Signals from these receptors are sent to the RCC.

This gets the lungs to contract with more force - by recruiting extra additional muscles -> breathing can be quicker and deeper and faster.

 

expiration centre at exercise

Because the breathing rate needs to increase:

• Baroreceptors inform the RCC of increased lung inflation

• The expiratory centre becomes active (it is not active at rest)

• It sends nerve impulses via the intercostal nerve

• To the internal intercostal muscles and abdominals

• Causing contraction +  active expiration (forced breathing out)

This:

• Speeds up the removal of CO₂

• Allows faster breathing cycles so inspiration can happen again quic

association

combining of oxygen and haemoglobin to from oxyhaemoglobin

disassociation

release of oxygen from oxyhaemoglobin for respiration

oxyhaemoglobin

a molecule formed when oxygen binds to haemoglobin, the protein in red blood cells that transports oxygen from the lungs to the body's tissues

saturation

the extent to which haemoglobin in the blood is bound with oxygen

external respiration

the process of exchanging gases between the alveoli in the lungs and the blood

internal respiration

 the exchange of gases, between the body's tissue cells and the blood

partial pressure

the pressure exerted by an individual gas held in a mixture of gases

diffusion

 movement of gases across a membrane down a gradient from an area of high concentration to an area of low concentration

diffusion gradient

the difference in areas of pressure from one side of a membrane to the other.

what are the partial pressures breathed in from the air

PO₂ ≈ 105 mmHg, PCO₂ ≈ 40 mmHg

What are the partial pressures in the alveoli?

PO₂ ≈ 100 mmHg, PCO₂ ≈ 40 mmHg ( 5 lost in the trachea)

Why does oxygen diffuse from alveoli into the blood?

Alveoli have higher PO₂ (105 mmHg) than pulmonary capillaries (40 mmHg).

Why does carbon dioxide diffuse from the blood into the alveoli?

Blood has higher PCO₂ (45 mmHg) than alveoli (40 mmHg).

Why does oxygen diffuse from blood into tissues?

Blood has higher PO₂ (100 mmHg) than tissues (40 mmHg).

Why does carbon dioxide diffuse from tissues into the blood?

Tissues have higher PCO₂ (50 mmHg) than blood (40 mmHg).

What are the partial pressures in veins returning to the heart?

PO₂ ≈ 40 mmHg, PCO₂ ≈ 45 mmHg

process at rest

• Deoxygenated blood arrives at the lungs with low PO₂ (~40 mmHg) and high PCO₂ (~45 mmHg).

• In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses into the alveoli due to steep partial pressure gradients.

• Blood leaves the lungs oxygenated with high PO₂ (~100 mmHg) and low PCO₂ (~40 mmHg).

• Oxygenated blood is transported to body tissues via systemic arteries.

• In tissues, oxygen diffuses from the blood into cells where it is used in respiration.

• Respiring tissues produce carbon dioxide, increasing PCO₂ (~50 mmHg).

• Carbon dioxide diffuses from tissues into the blood.

• Deoxygenated blood returns to the lungs to repeat the cycle.

process at exercise

• During exercise, blood arriving at the lungs has very low O₂ (~20–30 mmHg) and high CO₂ (~50–60 mmHg) due to increased muscle respiration.

• Increased ventilation keeps alveolar air at high O₂ (~105 mmHg) and low CO₂ (~35–40 mmHg).

• Steep partial pressure gradients cause rapid diffusion: O₂ into the blood and CO₂ into the alveoli (external respiration).

• Blood leaving the lungs remains high in O₂ (~100 mmHg) and low in CO₂ (~38–40 mmHg).

• In active muscles, O₂ diffuses rapidly from blood to tissues and CO₂ diffuses from tissues to blood (internal respiration).

• Blood returning to the heart again has very low O₂ and high CO₂, completing the cycle.

how many molecules of oxygen can haemoglobin carry

4

oxygen dissociation curve

in lungs , partial pressure s approximately 100 mm hg , at this pressure, haemoglobin has a high affinity to 02 and is 98% saturated

in other tissues/ organs, partial pressure is around 40 mmhg so haemoglobin has a lower affinity to 02 and offloads it to the tissues.

oxygen dissociation at rest

approximately 25% of Oxygen has dissociated

It has now become available for diffusion into the muscle cells.

75% remains associated with haemoglobin in the blood stream

oxygen dissociation at exercise

pO2 lowers in the muscle cells as exercise intensity increases

approximately 75% of Oxygen has dissociated

It has now become available for diffusion into the muscle cells.

The Bohr shift

The curve shifts to the right

Bohr Shift factors

Increase in temperature

Increase in CO2 (raising pCO2)

Increases production of lactic acid and carbonic acid (lowers pH)

MCCOAT

muscle activity increases during exercise

curve shifts right

carbon dioxide increases

oxygen decreases

acidity increases

temperature increases

importance of warming up

• A warm-up increases muscle activity and respiration, producing more CO₂.

• Increased CO₂ lowers blood pH (more acidic conditions).

• Lower pH causes the Bohr shift, reducing haemoglobin’s affinity for oxygen.

• Oxyhaemoglobin dissociates more easily, releasing more O₂ to muscles.

• This improves oxygen delivery at the start of exercise, enhancing performance and delaying fatigue.

recovery

During recovery the OXYHAEMOGLOBIN CURVE shifts back to the left

This returns haemoglobin saturation with oxygen to its original relationship

This allows a greater uptake or association of oxygen to haemoglobin at the alveoli –oxygenating the blood stream to flush waste