Tag: physiology of the respiratory system

Physiology of the Respiratory System

Physiology of the respiratory system refers to the act of respiration, also known as breathing or pulmonary ventilation. Pulmonary ventilation involves repetitive cycles of inhalation and exhalation, in which movement of oxygen happens from the outside environment to the cells within tissues, followed by the removal of carbon dioxide in the opposite direction. A pressure difference between air pressure within the lungs and the air outside of the body causes air to flow in and out of the lungs.

Common Respiratory Terms:

  • Eupnoea: respiratory rate at rest
  • Bradypnoea: decreased respiratory rate
  • Tachypnoea: increased respiratory rate
  • Apnoea: temporary cessation of breathing
  • Dyspnoea: difficulty breathing
  • Orthopnoea: difficulty breathing when laying down
  • Respiratory Arrest: permanent breathing cessation
  • Hyperventilation: fast breathing rate in which Carbon Dioxide is expelled faster than it is produced, lowering the Carbon Dioxide level in the blood leading to an increase in the blood pH
  • Hypoventilation: slow breathing rate in which Carbon Dioxide in the blood is increased due to not expelling it at the same rate as it is produced

Normal Respiratory Rates:

  • Adults: 12-20 breaths per minute
  • Children: 18-30 breaths per minute
  • Infants (up to 1 year): 30-60 breaths per minute
Retrieved from https://www.physio-pedia.com/Muscles_of_Respiration on 23rd April 2021

Respiratory muscles used in quiet inspiration:

  • Diaphragm – lowers to increase the thoracic cavity depth
  • External Intercostal Muscles – elevate the ribs leading to widening of the thoracic cavity

Respiratory muscles used in forced inspiration:

  • Sternocleidomastoids and Pectoralis Minor – elevate the sternum and ribs leading to the widening of the thoracic cavity
  • Scalenes – elevate ribs 1 and 2 leading to the widening of the thoracic cavity
  • Internal Intercostals (part of) – elevate the ribs leading to widening of the thoracic cavity

Respiratory muscles used in quiet expiration:

  • Diaphragm
  • Thoracic Cage
  • Lung Elasticity

Respiratory muscles used in forced expiration:

  • Internal Intercostals (part of)
  • Rectus Abdominis
  • Internal and External Obliques
  • Transversus Abdominis
Retrieved from https://teachmephysiology.com/respiratory-system/ventilation/mechanics-of-breathing/ on 23rd April 2021

Neural Breathing Control

Breathing happens through repetitive brain stimuli within the medulla oblongata:

Inspiratory neurons activate during quiet and forced inspiration, firing impulses leading to the diaphragm (through the phrenic nerve) and the external intercostal muscles (through the intercostal nerves) contracting. The inspiratory muscles relax when the inspiratory neurons stop firing, causing expiration.

Expiratory neurons activate during forced expiration.

The Respiratory Rate is affected by the Respiratory Centres, namely:

  • Central Chemoreceptors – found in the medulla oblongata
  • Peripheral Chemoreceptors – found in major blood vessels

These respond to the changes in Oxygen, Carbon Dioxide levels and pH of the blood. For example, if there is a decrease in Oxygen level, an increase in Carbon Dioxide level and a decrease in the blood pH, the Respiratory Rate is automatically increased so as to compensate for the lack of Oxygen.

Breathing can be manipulated through the cerebral cortex, which sends impulses to the diaphragm and intercostal muscles, bypassing the medulla oblongata and pons in the process. However, an increase in Carbon Dioxide level reduces the ability to control breathing manipulation.

The Pressure Gradient

The pressure gradient is the difference between the atmospheric pressure (pressure of the outside air) and the intrapulmonary pressure (pressure within the lungs). Pressure and resistance work together in determining airflow.

During inspiration, the rib cage elevates and the diaphragm depresses and flattens, leading to an increase in the thoracic volume, causing the intrapulmonary pressure to fall when compared to atmospheric pressure. Thus, air flows into the lungs.

During exhalation, the rib cage descends and the diaphragm rises in the form of a dome. Lungs recoil to a smaller volume, which causes the intrapulmonary pressure to increase when compared to atmospheric pressure. Thus, air flows out of the lungs.

Resistance to airflow depends on:

  • Thoracic Wall Compliance – if the thoracic wall tissues are non-compliant, the thoracic cavity doesn’t increase, which inhibits the lungs to increase in size during inhalation
  • Bronchial Diameter – bronchoconstriction causes resistance to airflow
  • Alveolar Surface Tension – alveoli walls are lined by a thin film of water that creates tension at their surface

Respiratory Volumes

Tidal Volume (TV) is the volume of air inspired or expired in a normal respiratory cycle.

Inspiratory Reserve Volume (IRV) is the maximum volume of air that can be inspired during forced respiration. This does not include the tidal volume (forced inspiration amount).

Expiratory Reserve Volume (ERV) is the maximum volume of air that can be expired during forced respiration. This does not include the tidal volume.

Residual Volume (RV) is the volume of air left in the lungs following forced expiration. RV allows gas exchange to happen between respiratory cycles, allowing the alveoli to stay inflated.

Respiratory Capacity refers to the combination of more than one volume.

Total Lung Capacity (TLC) is the combination of all lung volumes:

Tidal Volume + Expiratory Reserve Volume + Inspiratory Reserve Volume + Residual Volume = Total Lung Capacity

Vital Capacity (VC) is the amount of air an individual can move in or out of the lungs:

Tidal Volume + Expiratory Reserve Volume + Inspiratory Reserve Volume = Vital Capacity

Inspiratory Capacity (IC) is the total amount of air that can be inhaled:

Tidal Volume + Inspiratory Reserve Volume = Inspiratory Capacity

Functional Residual Capacity (FRC) is the amount of air remaining in the lung following a normal tidal expiration:

Expiratory Reserve Volume + Residual Volume = Functional Residual Capacity

A PEFR measures Forced Expiratory Volume (FEV), which is the maximum amount of air that can be forcefully exhaled in one second.

Below you can find a collection of videos that can help provide a more visual approach to the physiology of the respiratory system.

Physiology of the Respiratory System – Animation

https://www.youtube.com/watch?v=kacMYexDgHg

Physiology of the Respiratory System – Animation

Lung Anatomy & Physiology

Breathing Control

Gas Exchange

Respiratory Volumes – Spirometry

Special thanks to the creators of the featured videos on this post, specifically Youtube Channels Alila Medical Media and RegisteredNurseRN.

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Anatomy of the Respiratory System

When looking into the anatomy of the respiratory system, one needs to take a look at all the components involved in breathing. Through respiration, lungs experience ventilation (breathing), an exchange of gases happens between air and blood and between blood and cells, which cause oxygen perfusion throughout the whole body on a cellular level.

Respiratory System Functions:

  • provides the body with an oxygen supply
  • eliminates carbon dioxide
  • allows gas exchange
  • provides a path to and from the alveoli
  • provides a sense of smell through the olfactory system
  • acts as a humidifier by warming incoming air
  • maintains a balanced pH in the body
  • allows expulsion of abdominal content (such as during childbirth)

The respiratory system can be divided into the following sub-categories:

Upper Respiratory Tract:

Accessed from https://www.physio-pedia.com/Upper_respiratory_airways on 23rd February 2021
  • Nose: includes nostrils (nares), guard hairs (vibrissae, which help prevent insects and large particles from entering the nose), posterior nasal apertures (choanae), nasal cavity, nasal septum (composed of bone and cartilage), nasal fossae, nasal conchae, hard palate, soft palate, paranasal sinuses (which help decrease weight of skull due to its air content), goblet cells, respiratory epithelium of ciliated pseudostratified columnar type, and olfactory epithelium; functions include warming, humidifying and cleansing the inhaled air, providing a sense of smell, and helping in voice amplification.
  • Pharynx: a muscular structure about 5 inches long that acts as a common passageway for food and air consisting of the nasopharynx (lined with pseudostratified columnar epithelium), oropharynx and laryngopharynx (both lined with stratified squamous epithelium, making it a hard surface to be able to tolerate abrasion caused by the swallowing of food); includes an auditory tube, pharyngeal tonsil, palatine tonsils and lingual tonsils (tonsils help combat infection).
  • Larynx: plays an important role in speech through the vocal cords; comprises of 9 rigid hyaline cartilages with a flap of elastic cartilage known as the epiglottis that helps lead air and food into their appropriate pathways.
Accessed from https://sen842cova.blogspot.com/2015/08/pharynx-and-larynx-anatomy.html on 23rd February 2021

Lower Respiratory Tract:

Assessed from https://www.therespiratorysystem.com/category/lower-respiratory-tract/ on 23rd February 2021
  • Trachea: contains c-shaped hyaline cartilage rings that help support it (open parts of ‘c’ face the oesophagus to allow expansion whilst swallowing; lined with ciliated pseudostratified columnar epithelium with a lot of goblet cells that cause mucus production; mucus traps any debris, pushing it upwards through the mucociliary escalator towards the pharynx to be swallowed.
  • Bronchi: formed by the division of the trachea, just beneath the carina; supported by hyaline cartilage with a smooth muscle layered wall. These are further divided into secondary bronchi, one for every lobe within the lungs.
  • Bronchioles: the smallest of all bronchi, which end up with alveolar sacs; do not contain cartilage but are supported by smooth muscle, making them able to dilate or contract to cause bronchodilation or bronchoconstriction.
  • Alveoli: comprised of a single thin layer of squamous alveolar cells that facilitate gas exchange; contain alveolar macrophages (white blood cells) that engulf any bacteria or other debris; great alveolar cells produce a lipid molecule ‘surfactant‘ which coats the alveolar surfaces, preventing the alveoli walls from sticking together, thus allowing them to inflate easily during inhalation; air that enters the alveoli becomes available for gas exchange.
  • Lungs: found within the thoracic cavity; the stroma, which is made of elastic connective tissue, allows the lungs to recoil passively during exhalation; contain the visceral pleura (which ‘hugs’ the lungs), the parietal pleura (the outer layer), both encasing the pleural cavity which contains fluid that helps reduce friction between the lungs and the ribcage while they expand and contract); the two lungs are separated by the mediastinum which is the space found between the two lungs containing the heart, oesophagus and the major blood vessels. The right lung has 2 fissures, forming the superior lobe, middle lobe and inferior lobe. The left lung has 1 fissure, forming the superior lobe and the inferior lobe. The left lung also has the ‘cardiac notch‘, which is the area that houses the heart.

THE CONDUCTING ZONE forms a continuous passageway for air to move in and out of the lungs:

Nose > Pharynx > Larynx > Trachea > Bronchi > Bronchioles > Terminal Bronchioles

THE RESPIRATORY ZONE forms a passageway in which air is exchanged:

Respiratory bronchioles > Alveolar ducts > Alveolar sac

The respiratory membrane consists of squamous alveolar cell, squamous endothelial cell that lines the capillary, and a shared thin basement membrane, all of which help facilitate gas exchange.

Below you can find a collection of videos that can help provide a more visual approach to the anatomy of the respiratory system.

Anatomy of the respiratory System – Animation

https://www.youtube.com/watch?v=kacMYexDgHg

Overview of the Respiratory System – Animation

Lung Anatomy

The Respiratory System

Respiratory System Physiology

Special thanks to the creators of the featured videos on this post, specifically Youtube Channels Alila Medical Media, Registered Nurse RN, KhanAcademyMedicine and Professor Dave Explains.

Did you find the above nursing information useful? Follow us on Facebook and fill in your email address below to receive new blogposts in your inbox as soon as they’re published 🙂