The Explainer | How does the Body Controls Breathing?

The three physiological functions that are responsible for adequate tissue and cellular oxygenation are:

  1. Pulmonary gas exchange
  2. Oxygen delivery
  3. Oxygen consumption

The respiratory system helps gas exchange through the process of ventilation, diffusion and perfusion for the uptake of oxygen and helps with the removal of carbon dioxide from the body. Functionally the respiratory system consists of the functional zones and the conducting zones, namely the upper and the lower respiratory portions.

The conducting portions

  • Nasal Cavities
  • Pharynx
  • Larynx
  • Trachea

The purpose of the conducting Zones is to

  • Filter
  • Humidify
  • Warm
  • Allow the passage of air to the lower respiratory zones

The respiratory Zone Site of gas exchange containing

  • Bronchioles
  • Alveolar ducts
  • Alveolar

The main function of the respiratory system is supplying the body with oxygen and eliminate carbon dioxide. In addition to this main function, the respiratory system plays a part in the following functions

  • Acid-base regulation – This is done through the process of ventilation; the lungs remove CO2 and regulates the PH of the body. Regulation of PH is accomplished through the removal of volatile acids.
  • Blood reservoir– The lungs receive venous blood from the right ventricle. Due to the ability of the pulmonary circulation to receive blood, the lungs act as a reservoir from which the left side of the heart takes blood from.
  • Filtering mechanism – The lungs also constantly filter the air we breathe and removes the trapped particles through the mucociliary clearance mechanism and the lymphatic system. The Lungs also act as a filtering mechanism for the blood by removing particles such as gas bubbles, small blood clots aggregates of platelets and WBC and other pieces of cellular debris.
  • Metabolism – The Lungs also produce chemicals that are responsible for vasodilation, blood clotting and maintenance of lung structural stability. Some chemical passing through the lungs are converted to there active forms, chemicals such as angiotensin I produced by the kidneys which are converted into angiotensin II which is potent vasoconstrictor.

 

Control of Respiration

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Breathing is usually involuntary, but voluntary breathing is also very important when an individual is doing other activities such as walking, talking or singing etc.

In this instance, the haemostatic imbalances in the ventilatory mechanism are adjusted by the nervous system to maintain a normal gas exchange.

The lungs are innervated by the autonomic nervous system. Fibres of the sympathetic division of the nervous system branch from the upper thoracic and cervical ganglia of the spinal cord, while the fibres from the parasympathetic division travel to the vagus nerve. Which is important in the control of ventilation.

The respiratory centres of the brain stem control involuntary ventilation by transmitting impulses to the respiratory muscles causing them to contract and relax.

The pneumotaxic centres in the upper pons functions to maintain rhythmic respiration. It stimulates the expiratory centre, which then sends inhibitory signals to the inspiratory centres. Inspiration ends, and expiration begins.

Strong stimuli from the pneumotaxic centres result in shorter inspiration and mild stimulation results in longer ones.

Pathologies

Chronic obstructive pulmonary disease

COPD refers to chronic obstructive bronchitis and emphysema. The two condition often occurs together. COPD and emphysema both limit the flow of air in and out of the lungs which makes it difficult for an individual to breathe. COPD usually gets worse with time.

Bronchial tubes which carry air in and out of the lungs are constantly inflamed in the individual with COPD. Constant irritation of the bronchioles causes the growth of cells that make mucus, the extra mucus leads to a lot of coughing. Over time the irritation causes the walls of the bronchioles to thicken and develop scars. COPD only happens when the airways become thickened to the point it limits the flow of air to and from the lungs.

Emphysema 

The lung tissue gets weak, and the walls of the air sacs break down. The ruined air sacs mean that less oxygen gets to pass into the blood, this then causes shortness of breath wheezing and coughing.

NOTE

 The rate of emphysema among women has increased by 5 percent in recent years but has decreased among men. And more women have died from COPD than men every year since 2000. Researchers are trying to understand why. Cigarette smoking, a main cause of COPD, has increased among women. One theory is that cigarette smoke is more damaging to women than to men.

 

Sources

Calverley, P. M. A. (2005). Control of breathing. European respiratory monograph31, 44.

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