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Flashcards in Control of Breathing Deck (26):

What is required for gas diffusion?

1) Large surface area for gas exchange.
2) Large partial pressure gradients.
3) Gases with advantageous diffusion properties.
4) Specialised mechanisms for transporting O 2 and CO 2 between lungs and tissues.


Partial pressure defintion

Sum of the partial pressures (mmHg) or tensions (torr) of a gas must be equal to total pressure.


Partial pressure equation

Partial pressure of gas (Pgas) = fraction of gas (Fgas) in gas mixture x barometric pressure
Pgas = Fgas x Pb


How is oxygen transported in the blood?

1. Dissolved
2. Bound to haemoglobin (Hb)


What makes up a haemoglobin (Hb)?

Four heme (iron porphyrin compounds) groups joined to globin protein (two α chains and two β chains polypeptide chains)
Each heme group contains iron in the reduced ferrous form (Fe+++)


What is the job of the reduced ferrous form in the heme group?

Site for O2 binding


How many O2 groups bind a heme groups

4 O2 molecules


What is the oxyhemoglobin dissociation curve?

Curve illustrates relationship between PO2 in blood and number of O2 molecules bound to Hb


CO2 Production

Normal healthy conditions:
- 200 ml CO2 / min produced
- 80 molecules CO2 expired by lung for every 100 molecules of O2 entering.
Ratio of expired CO2 to O2 uptake – Respiratory Exchange Ratio.
In normal conditions, respiratory exchange ration = 0.8 (80 CO2 to 100 O2).


How is CO2 carried around in the blood?

i) 7% dissolved- other 93% diffuses into red blood cells
ii) 23% (of 93%) bound to haemoglobin (Hb).
iii) 70% (of 93%) converted to bicarbonate and hydrogen ions(created by enzyme carbonic anhydrase)


What are mechanoreceptors?

how body detects how much muscles are moving per breath
Sleep, Phonation, Emotion, Cardiovascular, Temperature, Exercise- other variables that effect the brain


What is chemoreceptors?

Chemoreceptors are sensory receptors that detect chemical changes in the surrounding environment.
In respiratory system chemoreceptors detect changes in PO2, PCO2 and pH in blood.


What are peripheral chemoreceptors?

Peripheral chemoreceptors are small, highly vascularised bodies in region of aortic arch and carotid sinuses (internal and external carotid artery)


How is information from peripheral chemoreceptors sent to the brain?

Information sent via the glossopharyngeal and vagus nerves to the nucleus in brainstem called NTS


What is the vagus nerve?

Main nerve in the brain


What is the glossopharyngeal nerve?

Another carotid nerve


What do peripheral chemoreceptors respond to?

- Respond to decreases in PO 2 (hypoxia).
- Reduction in arterial PO 2
- Peripheral chemoreceptors stimulated.
- Neural signals sent from carotid and aortic bodies to NTS in brainstem.
- Ventilation increases to restore PO 2 levels.


What happens if PO2 is less than 60 mmHg

Progressive hyperventilation


What are central chemoreceptors?

Clusters of neurones in the brainstem that are activated when PCO 2 is increased (hypercapnia) or pH decreased


Where does hypercapnia response occur?

Central chemoreceptors in brainstem


What is hypercapnia involved in?

Plays a major role in movement to movement control of breathing


What are mechanoreceptors?

Sensory receptors that detects changes in pressure, movement and touch
In respiratory system detect movement of lungs and chest wall


What neurones generate rhythm of breathing?

Respiratory neurones


What do brainstem neurones produce?

Rhythmic neural signals sent to spinal cord


Where does the phrenic nerve exit the spinal cord?

Level 3-5


What do nerves exiting the thoracic spinal cord do?

Innervate intercostal muscles