Respiratory system


Respiratory system

The taking in of oxygen and removal of carbon dioxide.

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Lung volumes

The movement of air into (inhalation) and moving out of (expiration) the lungs. 

  • Tidal volume- the volume of air inspired or expired per breath (0.5 litres) 
  • Minute ventilation- the volume of air inspired or expired per minute. Can be calculated by: Number of breaths (per minute- approx.12) x Tidal volume  
  • Inspiratory reserve volume- the volume of air forcibly inspired after a normal breath
  • Expiratory reserve volume- the volume of air that can be forcibly expired after a normal breath
  • Residual volume- the amount of air that remains in the lungs after maximal expiration. 

Change during exercise:

  • Tidal volume- Increases
  • Minute ventilation- Large increase 
  • Inspiratory reserve volume- Decreses
  • Expiratory reserve volume- Slight decrease
  • Residual volume- Remains the same

Easy mistake to make that beacuse breathing rate increases, IRV and ERV increases... BUT THEY DECREASE!

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Gaseous Exchange

Gaseous Exchange- the movement of oxygen from the air into the blood, and carbon dioxide from the blood into the air. 

Partial Pressure- the pressure exerted by an individual gas when it exists within a mixture of gases

Diffusion- the movement of gas molecules from an area of high concentration or partial pressure to an area of low concentration or partial pressure. 

Since gases flow from an area of high pressure to an area of high pressure to an area of low pressure, it is important that as air moves from the alveoli to the blood and then to the muscle, the partial pressure of oxygen of each is successively lower.


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Gaseous Exchange at the alveoli

Gaseous exchange at the alveoli

The alveoli are responsible for the exchange of gases between the lungs and the blood, and their structure is designed to help gaseous exchange.

  • One cell thick- short diffusion pathway.
  • Surrounded by capillaries- excellent blood supply
  • Large surface area- allows greater uptake of oxygen

The partial pressure of oxygen in the alveoli is higher than the partial pressure in the capillary blood vessels because oxygen has been removed by the working muscles so its concentraion of blood is lower = lower partial pressure

The difference in partial pressure is reffered to as the concentration/diffusion gradient (high to low). The bigger the gradient, the faster the diffusion.Oxygen will diffuse from the alveoli into the blood until the pressure is equal in both. 

Carbon dioxide follows the same sequence but in reserve order. Partial pressure of carbon dioxide in the blood entering the alveoli cappiliaries is higher than in the alveoli, so carbon dioxide diffuses into the alveoli from the blood until the pressure is equal.

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Gaseous Exchange at the muscles

The partial pressure of oxygen has to be lower at the tissues than in the blood for diffusion to occur. 

The lower partial pressure in the capillary membranes surrounding the muscles than in the blood.

This allows oxygen to diffuse from the blood into the muscles until equilibruim is reached 

Conversely, the partial pressure of carbon dioxide in the blood is lower than in the tissues so diffusion occurs and the carbon dioxide moves into the blood to be transported into the lungs.

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Respiratory centre

An increased concentration of carbon dioxide in the blood stimulates the respiratory centre to increase respiratory rate. The respiratory centre has two main areas:

  • The inspiratory centre is responsible for inspiration and expirartion
  • The expiratory centre stimulates the expiratory muscles during exercise

The inspiratory centre sends out nerve impulses to the diaphragm and external intercostals to cause them to contract. This stimulation lasts for 2 seconds and passive expiration occurs due to the recoil of the lungs.

The respiratory centre responds mainly to the changes in blood chemistry. During exercise, blood acidity increases due to an increase of carbon dioxide and latic acid production. These changes detected by the chemoceptors send impulses to the inspiratory centre to increase ventilation until the blood acidity has returned to normal. 

To achieve this, the respiratory centre sends impulses to stimulate the inspiratory muscles. As a result, the rate and depth of breathing increases.

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Role of proprioceptors and baroreceptors in PV

  • Proprioceptors- detect increase in muscle movemnts and provide feedback to the respiratory centre to increase breathing during exercise
  • Baroreceptors- decrease in blood pressure detected by baroreceptors in the aorta and carotid arteries results in an increase in breathing rate.

Order of neural/chemical control for increased inspiration during exercise is:

  • Receptors -> medulla oblongata -> phrentic nerve -> inspiratory muscles (diaphragm, external intercostals) 

Order of neutral/chemical control for expiration during exercise is:

  • Receptors -> medulla oblongata -> intercostal nerve -> abdominals and internal intercostals
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Hormonal regulation of PV during exercise

Adrenaline increases breathing rate in preparation for exercise and the demand to take in more oxygen and remove more carbon dioxide. 

The anticipatory rise is the mind’s response to the body’s need to prepare for exercise.

Subconsciously, the body knows it is about to exercise and therefore the brain sends several signals in the form of nhormones (e.g. adrenaline) to the heart. When these chemicals reach the heart they signal for a reduction in parasympathetic drive  and small increase in sympathetic drive  resulting in an increased heart rate.

The increase in heart rate is important because it leads to an increase in cardiac output (the amount of blood pumped out of the left side of the heart in one minute).

This is turn results in an increased blood supply to the body. At the same time the body begins redirecting the blood supply to the parts of body that will require it during the exercise (vascular shunt). This increased blood supply brings with it oxygen and an increased ability to produce energy in the muscles, which will be used to as fuel for exercise.

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Impact of poor lifestyle choices on the respirator

Smoking affects oxygen transport because the carbon monoxide from cigarettes combines with haemoglobin in red blood cells much more readily than oxygen.

This reduces the oxygen-carrying capacity of the blood, which increases breathlessness during exercise.

Smoking can also cause:

  • irration of the trachea and bronchi 
  • reduced lung function and swelling/narrwoing of the lungs airways
  • build up of excess mucus in the lungs- results in smokers cough 
  • reduction in the efficiency of gasous exchange, which can increase the risk of COPD
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