Mechanics of Breathing

This explanation of the physiology of breathing shows how our health improves through the conscious connected breathing that we do in Transformation Breathwork.

Humans need a continuous supply of oxygen for cellular respiration, and they must get rid of excess carbon dioxide, the poisonous waste product of this process.  Gas exchange supports this cellular respiration by constantly supplying oxygen and removing carbon dioxide.  The oxygen we need is derived from the Earth's atmosphere, which is 21% oxygen. This oxygen in the air is exchanged in the body by the respiratory surface. In humans, the alveoli in the lungs serve as the surface for gas exchange.

Gas exchange in humans can be divided into five steps:

  1. Breathing
  2. External Respiration
  3. Gas Transport
  4. Internal Respiration
  5. Cellular Respiration 

Other factors involved with respiration are:

  • Adaptations of Diving Mammals
  • Bohr Shift
  • Control of Breathing
  • Partial Pressure
  • Structure of Respiratory System

Structure of the Human Respiratory System

The Nose - Usually air will enter the respiratory system through the nostrils.  The nostrils then lead to open spaces in the nose called the nasal passages.  The nasal passages serve as a moistener, a filter, and to warm up the air before it reaches the lungs.  The hairs existing within the nostrils prevents various foreign particles from entering.  Different air passageways and the nasal passages are covered with a mucous membrane.  Many of the cells which produce the cells that make up the membrane contain cilia.  Others secrete a type a sticky fluid called mucus.  The mucus and cilia collect dust, bacteria, and other particles in the air.  The mucus also helps in moistening the air.  Under the mucous membrane there are a large number of capillaries.  The blood within these capillaries helps to warm the air as it passes through the nose.  The nose serves three purposes.  It warms, filters, and moistens the air before it reaches the lungs.  You will obviously lose these special advantages if you breath through your mouth.

Pharynx and Larynx - Air travels from the nasal passages to the pharynx, or more commonly known as the throat. When the air leaves the pharynx it passes into the larynx, or the voice box.  The voice box is constructed mainly of cartilage, which is a flexible connective tissue.  The vocal chords are two pairs of membranes that are stretched across the inside of the larynx.  As the air is expired, the vocal chords vibrate.  Humans can control the vibrations of the vocal chords, which enables us to make sounds.  Food and liquids are blocked from entering the opening of the larynx by the epiglottis to prevent people from choking during swallowing.

Trachea - The larynx goes directly into the trachea or the windpipe.  The trachea is a tube approximately 12 centimeters in length and 2.5 centimeters wide.  The trachea is kept open by rings of cartilage within its walls.  Similar to the nasal passages, the trachea is covered with a ciliated mucous membrane.  Usually the cilia move mucus and trapped foreign matter to the pharynx.  After that, they leave the air passages and are normally swallowed.  The respiratory system cannot deal with tobacco smoke very keenly. Smoking stops the cilia from moving.  Just one cigarette slows their motion for about 20 minutes.  The tobacco smoke increases the amount of mucus in the air passages.  When smokers cough, their body is attempting to dispose of the extra mucus.

Bronchi - Around the center of the chest, the trachea divides into two cartilage-ringed tubes called bronchi.  Also, this section of the respiratory system is lined with ciliated cells.  The bronchi enter the lungs and spread into a treelike fashion into smaller tubes calle bronchial tubes.  

Bronchioles - The bronchial tubes divide and then subdivide.  By doing this their walls become thinner and have less and less cartilage.  Eventually, they become a tiny group of tubes called bronchioles.

Alveoli - Each bronchiole ends in a tiny air chamber that looks like a bunch of grapes.  Each chamber contains many cup-shaped cavities known as alveoli.  The walls of the alveoli, which are only about one cell thick, are the respiratory surface.  They are thin, moist, and are surrounded by several numbers of capillaries.  The exchange of oxygen and carbon dioxide between blood and air occurs through these walls.  The estimation is that lungs contain about 300 million alveoli. Their total surface area would be about 70 square meters.  That is 40 times the surface area of the skin.  Smoking makes it difficult for oxygen to be taken through the alveoli.  When the cigarette smoke is inhaled, about one-third of the particles will remain within the alveoli.  There are too many particles from smoking or from other sources of air pollution which can damage the walls in the alveoli.  This causes a certain tissue to form.  This tissue reduces the working area of the respiratory surface and leads to the disease called emphysema.



Breathing consists of two phases,  inspiration and expiration.  During inspiration,  the diaphragm and the intercostal muscles contract.   The diaphragm moves downwards increasing the volume of the thoracic (chest) cavity, and the intercostal muscles pull the ribs up expanding the rib cage and further increasing this volume.  This increase of volume lowers the air pressure in the alveoli to below atmospheric pressure.  Because air always flows from a region of high pressure to a region of lower pressure, it rushes in through the respiratory tract and into the alveoli.  This is called negative pressure breathing,  changing the pressure inside the lungs relative to the pressure of the outside atmosphere.  In contrast to inspiration, during expiration the diaphragm and intercostal muscles relax.  This returns the thoracic cavity to it's original volume, increasing the air pressure in the lungs, and forcing the air out.

External Respiration

When a breath is taken, air passes in through the nostrils, through the nasal passages, into the pharynx, through the larynx, down the trachea, into one of the main bronchi, then into smaller bronchial tubules, through even smaller bronchioles, and into a microscopic air sac called an alveolus.  It is here that external respiration occurs.  Simply put, it is the exchange of oxygen and carbon dioxide between the air and the blood in the lungs.   Blood enters the lungs via the pulmonary arteries.  It then proceeds through arterioles and into the alveolar capillaries.  Oxygen and carbon dioxide are exchanged between blood and the air.  This blood then flows out of the alveolar capillaries, through venuoles, and back to the heart via the pulmonary veins.  For an explanation as to why gasses are exchanged here, see partial pressure.


Gas Transport

If 100mL of plasma is exposed to an atmosphere with a pO2 of 100mm Hg, only 0.3mL of oxygen would be absorbed.  However,  if 100mL of blood is exposed to the same atmosphere, about 19mL of oxygen would be absorbed.  This is due to the presence of haemoglobin, the main means of oxygen transport in the body. The respiratory pigment haemoglobin is made up of an iron-containing porphyron, haem, combined with the protein globin.  Each iron atom in haem is attached to four pyrole groups by covalent bonds.  A fifth covalent bond of the iron is attached to the globin part of the molecule and the sixth covalent bond is available for combination with oxygen.  There are four iron atoms in each hemoglobin molecule and therefore four heam groups.

Oxygen Transport

In the loading and unloading of oxygen, there is a cooperation between these four haem groups.  When oxygen binds to one of the groups, the others change shape slightly and their attraction to oxygen increases.  The loading of the first oxygen, results in the rapid loading of the next three (forming oxyhemoglobin).  At the other end, when one group unloads it's oxygen, the other three rapidly unload as their groups change shape again having less attraction for oxygen.  This method of cooperative binding and release can be seen in the dissociation curve for hemoglobin.  Over the range of oxygen concentrations where the curve has a steep slope, the slightest change in concentration will cause hemoglobin to load or unload a substantial amount of oxygen.   Notice that the steep part of the curve corresponds to the range of  oxygen concentrations found in the tissues. When the cells in a particular location begin to work harder, e.g. during exercise, oxygen concentration dips in that location, as the oxygen is used in cellular respiration.  Because of the cooperation between the haem groups, this slight change in concentration is enough to cause a large increase in the amount of oxygen unloaded.

As with all proteins, hemoglobin's shape shift is sensitive to a variety of  environmental conditions.  A drop in pH lowers the attraction of hemoglobin to oxygen,  an effect known as the Bohr shift.  Because carbon dioxide reacts with water to produce carbonic acid, an active tissue will lower the pH of it's surroundings and encourage hemoglobin to give up extra oxygen, to be used in cellular respiration.  Hemoglobin is a notable molecule for it's ability to transport oxygen from regions of supply to regions of demand.

Carbon Dioxide Transport - Out of the carbon dioxide released from respiring cells, 7% dissolves into the plasma, 23% binds to the multiple amino groups of hemoglobin (Caroxyhemoglobin), and 70% is carried as bicarbonate ions.  Carbon dioxide created by respiring cells diffuses into the blood plasma and then into the red blood cells, where most of it is converted to bicarbonate ions.  It first reacts with water forming carbonic acid, which then breaks down into H+ and CO3-.  Most of the hydrogen ions that are produced attach to hemoglobin or other proteins. 



Internal Respiration

The  body tissues need the oxygen and have to get rid of the carbon dioxide, so the blood carried throughout the body exchanges oxygen and carbon dioxide with the body's tissues.  Internal respiration is basically the exchange of gasses between the blood in the capillaries and the body's cells.

Control of Breathing

The respiratory center is gray matter in the pons and the upper Medulla, which is responsible for rhythmic respiration. This center can be divided into an inspiratory center and an expiratory center in the Medulla, an apneustic center in the lower and midpons and a pneumotaxic center in the rostral-most part of the pons. This respiratory center is very sensitive to the pCO2 in the arteries and to the pH level of the blood.  The CO2 can be brought back to the lungs in three different ways; dissolved in plasma, as carboxyhemoglobin, or as carbonic acid. That particular form of acid is almost broken down immediately by carbonic hydrase into bicarbonate and hydrogen ions.  This process is then reversed in the lungs so that water and carbon dioxide are exhaled. The Medulla Oblongata reacts to both CO2 and pH levels which triggers the breathing process so that more oxygen can enter the body to replace the oxygen that has been utilized.  The Medulla Oblongata sends neural impulses down through the spinal chord and into the diaphragm. The impulse contracts down to the floor of the chest cavity, and at the same time there is a message sent to the chest muscles to expand causing a partial vacuum to be formed in the lungs.  The partial vacuum will draw air into the lungs.      

There are two other ways the Medulla Oblongata can be stimulated. The first type is when there is an oxygen debt (lack of oxygen reaching the muscles), and this produces lactic acid which lowers the pH level.  The Medulla Oblongata is then stimulated.  If the pH rises it begins a process known as the Bohr shift.  The Bohr shift is affected when there are extremely high oxygen and carbon dioxide pressures present in the human body.  This factor causes difficulty for the oxygen and carbon dioxide to attach to hemoglobin.  When the body is exposed to higher altitudes the oxygen will not attach to the hemoglobin properly, causing the oxygen level to drop and the person will black out.  This theory also applies to divers who go to great depths, and the pressure of the oxygen becomes poisonous.  These pressures are known as pO2 and pCO2, or partial pressures.  The second type occurs when the major arteries in the body called the aortic and carotid bodies, sense a lack of oxygen within the blood and they send messages to the Medulla Oblongata.   

Adaptations of Diving Mammals

Various marine mammals have been found to have adapted special abilities which help in their respiratory processes, enabling them to remain down at great depths for long periods of time.  The Weddell seal possesses some amazing abilities.  It only stores 5% of its oxygen in its lungs, and keeps the remaining 70% of its oxygen circulating throughout the blood stream. Humans are only able to keep a small 51% of their oxygen circulating throughout the blood stream, while 36% of the oxygen is stored in the lungs. The explanation for this is that the Weddell seal has approximately twice the volume of blood per kilogram as humans. As well, the Weddell seal's spleen has the ability to store up to 24L of blood.  It is believed that when the seal dives the spleen contracts causing the stored oxygen enriched blood to enter the blood stream.  Also, these seals have a higher concentration of a certain protein found within the muscles known as myoglobin, which stores oxygen.  The Weddell seal contains 25% of its oxygen in the muscles, while humans only keep about 12% of their oxygen within the muscles.

Not only does the Weddell seal store oxygen for long dives, but they consume it wisely as well.  A diving reflex slows the pulse, and an overall reduction in oxygen consumption occurs due to this reduced heart rate.  Regulatory mechamisms reroute blood to where it is needed most (brain, spinal cord, eyes, adrenal glands, and in some cases placenta) by constricting blood flow where it is not needed (mainly in the digestive system).  Blood flow is restricted to muscles during long dives and they rely on oxygen stored in their myoglobin and make their ATP from fermentation rather then from respiration.