What Distinguishes Cellular from Pulmonary Respiration Illustration

What Distinguishes Cellular from Pulmonary Respiration?

by | Updated: Dec 14, 2023

Understanding the intricacies of the human body means diving into the subtle distinctions between processes that, at a glance, may seem similar.

Two such processes are cellular and pulmonary respiration.

Both are fundamental to our survival and energy production, but they function at different levels of our biological system and for distinct purposes.

Grasping the difference between them is crucial for anyone looking to delve deeper into human physiology.

What Distinguishes Cellular from Pulmonary Respiration?

The primary factor that distinguishes cellular respiration from pulmonary respiration is where diffusion takes place. Cellular respiration occurs in cells, converting glucose into energy (ATP) via the mitochondria. Pulmonary respiration refers to the gas exchange process in the lungs where oxygen is inhaled and carbon dioxide is exhaled, facilitating oxygenation of the blood.

What is Cellular Respiration?

Cellular respiration is a set of metabolic processes and reactions that take place within the cells of organisms.

It allows cells to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

The reactions involved in cellular respiration are catabolic, meaning they break down large molecules into smaller ones, releasing energy in the process.

Cellular Respiration Vector Illustration

There are three primary stages of cellular respiration:

  1. Glycolysis: This process occurs in the cytoplasm and breaks down glucose, a six-carbon sugar molecule, into two molecules of a three-carbon compound called pyruvate. This results in a net gain of two ATP molecules.
  2. Krebs Cycle (Citric Acid Cycle): This cycle occurs in the mitochondria. Each pyruvate molecule produced in glycolysis is further broken down, producing ATP, carbon dioxide (which is expelled as a waste product), and high-energy molecules like NADH and FADH2.
  3. Electron Transport Chain (ETC) and Oxidative Phosphorylation: Also located in the mitochondria, the ETC uses the high-energy molecules from the Krebs Cycle to produce a gradient across the mitochondrial membrane. This gradient powers the synthesis of ATP. Oxygen acts as the final electron acceptor in this chain, forming water when it combines with electrons and protons.

In the presence of oxygen, cells undergo aerobic respiration, which includes all three stages mentioned above.

However, in the absence of oxygen, cells may undergo anaerobic respiration or fermentation, which can produce energy without the electron transport chain.

In total, cellular respiration can generate up to 36-38 ATP molecules from one glucose molecule in eukaryotic cells, although the number can vary in prokaryotic cells.

What is Pulmonary Respiration?

Pulmonary respiration, more commonly referred to simply as “respiration” in the context of physiology, is the process of breathing – the inhalation and exhalation of air.

This process involves the exchange of gases between the atmosphere and the blood through the lungs.

Pulmonary respiration ensures that oxygen from the atmosphere gets into the bloodstream, while carbon dioxide, a waste product of cellular metabolism, is expelled from the body.

Pulmonary Respiration Vector Illustration

Here’s a brief breakdown of the process:

  1. Inhalation (Inspiration): Air containing oxygen is drawn into the body through the nose or mouth and travels down the trachea. It then divides into the bronchi and bronchioles and finally reaches the alveoli, tiny air sacs in the lungs.
  2. Gas Exchange in the Alveoli: Within the walls of the alveoli, oxygen diffuses into the surrounding capillaries and binds to hemoglobin in red blood cells. This oxygenated blood is then transported to the body’s cells for cellular respiration. Simultaneously, carbon dioxide, a waste product from cellular respiration, diffuses from the blood into the alveoli.
  3. Exhalation (Expiration): Carbon dioxide-rich air is expelled from the alveoli, traveling up and out of the lungs and body.

Pulmonary respiration is essential because it replenishes the body’s oxygen supply and removes carbon dioxide, maintaining the necessary conditions for cellular respiration and the proper functioning of cells and tissues.

Remember: While “cellular respiration” and “pulmonary respiration” both use the term “respiration,” they refer to distinct, albeit interconnected, biological processes.

Cellular Respiration vs. Pulmonary Respiration

Cellular respiration and pulmonary respiration are both fundamental processes in living organisms, but they operate at different levels and serve unique functions.

Here’s a comparative breakdown:

Cellular Respiration

  • Level of Occurrence: Takes place within the cells, specifically in the mitochondria for aerobic respiration.
  • Primary Function: To convert biochemical energy from nutrients (mainly glucose) into adenosine triphosphate (ATP), the cell’s primary energy currency. This process releases waste products.
  • Stages: Comprises Glycolysis (in the cytoplasm), Krebs Cycle (in the mitochondria), and the Electron Transport Chain (in the mitochondrial inner membrane).
  • End Products: Depending on the process (aerobic or anaerobic), end products can include ATP, water, carbon dioxide, lactic acid, or ethanol.
  • Oxygen Dependency: Aerobic cellular respiration requires oxygen. However, cells can also produce energy through anaerobic processes (like fermentation) without oxygen.
  • Waste Product: Carbon dioxide, which needs to be expelled from the body.

Pulmonary Respiration

  • Level of Occurrence: Involves the respiratory system, particularly the lungs and associated pathways.
  • Primary Function: To facilitate the exchange of gases between the atmosphere and the bloodstream. Oxygen is inhaled and delivered to cells, while carbon dioxide, a waste product of cellular metabolism, is exhaled.
  • Stages: Comprises inhalation (drawing oxygen-rich air into the lungs) and exhalation (expelling carbon dioxide-rich air out of the lungs).
  • End Products: This process doesn’t produce ATP or other energy molecules. Its primary outputs are oxygenated blood and the removal of carbon dioxide.
  • Oxygen Dependency: The process revolves around oxygen intake and carbon dioxide output, so oxygen is crucial.
  • Waste Product: While pulmonary respiration itself doesn’t produce waste in the form of molecules, it’s responsible for expelling the carbon dioxide waste generated by cellular respiration.

Summary: While both processes are intertwined and essential for life, cellular respiration is about producing energy at the cellular level, and pulmonary respiration is about facilitating the gas exchange necessary to support this energy production. Pulmonary respiration ensures cells receive the oxygen they need and helps to remove the carbon dioxide they produce, thus setting the stage for efficient cellular respiration.

FAQs About Cellular and Pulmonary Respiration

How Does Air Flow into the Lungs?

Air flows into the lungs due to a difference in pressure between the atmosphere and the inside of the chest cavity. When we inhale, the diaphragm contracts and moves downward, while the rib cage expands.

This increases the volume inside the thoracic cavity, decreasing the pressure.

As a result, air from the atmosphere, which is at a higher pressure, rushes into the lungs through the nose or mouth, down the trachea, and into the bronchi and bronchioles, ultimately filling the alveoli.

What Force Moves Oxygen and Carbon Dioxide Across the Respiratory Membrane?

The primary force that drives the exchange of oxygen and carbon dioxide across the respiratory membrane is simple diffusion.

This process is based on the principle that molecules move from areas of higher concentration to areas of lower concentration.

In the lungs, oxygen in the alveoli has a higher concentration than in the blood in surrounding capillaries, so it diffuses into the blood.

Conversely, carbon dioxide is more concentrated in the blood than in the alveoli, prompting it to diffuse out of the blood and into the alveoli, ready for exhalation.

What is the Exchange of Oxygen and Carbon Dioxide Called?

The exchange of oxygen and carbon dioxide between the air in the lungs and the blood is called external respiration or pulmonary gas exchange.

Additionally, the exchange of these gases between the blood and tissues in the body is referred to as internal respiration or tissue gas exchange.

Both processes are crucial components of the respiratory system’s function.

Which Findings Would Indicate That the Patient’s Breathing Is Adequate?

Several clinical indicators suggest that a patient’s breathing is adequate:

  • Normal Respiratory Rate: For adults, a typical respiratory rate ranges from 12 to 20 breaths per minute. Values within this range often indicate effective breathing, although individual needs can vary.
  • Regular Rhythm of Breathing: An even and consistent pattern without sudden pauses or rapid sequences indicates adequate breathing.
  • Adequate Chest Movement: Symmetrical and noticeable chest rise with each breath ensures proper lung inflation.
  • Normal Breath Sounds: When listening with a stethoscope, clear and consistent breath sounds in all lung fields without wheezing, crackles, or other abnormal noises are positive signs.
  • Oxygen Saturation: A pulse oximeter measures the percentage of hemoglobin in blood that’s saturated with oxygen. Values between 95% to 100% are generally considered normal for healthy individuals.
  • Absence of Cyanosis: The skin, especially around the lips and fingertips, should appear pink and not blue or gray, which can indicate decreased oxygen levels.

What Is the Difference Between Ventilation, Respiration, and Inspiration?

  • Ventilation: Refers to the mechanical process of moving air in and out of the lungs. It consists of two phases – inspiration (inhaling) and expiration (exhaling). Ventilation ensures fresh air reaches the alveoli for gas exchange.
  • Respiration: A broader term that encompasses several processes. Pulmonary respiration refers to the exchange of gases in the lungs, while cellular respiration refers to the metabolic processes in cells that produce energy from nutrients. Respiration, in a general context, may also be used to describe the entire process of breathing and gas exchange.
  • Inspiration: Specifically refers to the act of inhaling or drawing air into the lungs. During inspiration, the diaphragm contracts and the thoracic cavity volume increases, leading to a decrease in pressure inside the lungs. As a result, air flows in.

What is the Difference Between Cellular Respiration and Breathing?

  • Cellular Respiration: A metabolic process occurring at the cellular level where glucose and other molecules are broken down to produce ATP, the cell’s primary energy source. This process requires oxygen and produces carbon dioxide as a waste product. It takes place within the mitochondria of cells.
  • Breathing: Also known as pulmonary respiration, this refers to the physical act of inhaling (taking in oxygen) and exhaling (releasing carbon dioxide). It is a mechanical process involving the respiratory system, specifically the lungs and the associated pathways, and serves to refresh the body’s oxygen supply while expelling carbon dioxide produced during cellular respiration.

Final Thoughts

While both cellular and pulmonary respiration are vital for our existence, they serve very different roles in our body.

Cellular respiration harnesses the energy stored in glucose at a microscopic level, turning it into usable energy for our cells. In contrast, pulmonary respiration ensures that oxygen reaches our cells by exchanging gases in the lungs.

Recognizing these distinctions is essential for a comprehensive understanding of human energy processes.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Manoj KM. Aerobic Respiration: Criticism of the Proton-centric Explanation Involving Rotary Adenosine Triphosphate Synthesis, Chemiosmosis Principle, Proton Pumps and Electron Transport Chain. Biochem Insights. 2018 Dec 25.
  • Powers KA, Dhamoon AS. Physiology, Pulmonary Ventilation and Perfusion. [Updated 2023 Jan 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Recommended Reading