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Mechanism of Breathing, Transport of Gases, Role of Respiratory Pigments in Humans

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Mechanism of Breathing in Humans

Breathing is a procedure in which fresh air containing more oxygen is pumped into the lungs and air with more concentration of CO2 is pumped out of the lungs. To put it simply breathing is a mechanical procedure including two stages, inspiration or inhalation and expiration. During inhalation, fresh air moves in and in expiration air with low O2 and high CO2 concentration vacates the lungs.

During rest, the breathing rate is rhythmically at the frequency of 15 to 20 times per minute in humans. To understand the system of breathing we should keep in mind three elements related to lungs and associated structures.

  1. Lungs are spongy in nature. The lungs themselves neither pull air in nor can they press it out. During inspiration, passive expansion of flexible lungs happens and expiration is due to a passive contraction of the lungs.
  2. The floor of the chest cavity is the diaphragm, which is a muscular sheet. The shape of the diaphragm is more domelike when its muscles are relaxed. On the other hand, when the muscles of the diaphragm contract its shape becomes less domelike.
  3. Walls of the chest cavity are composed of ribs and intercostal muscles. When muscles between the ribs contract, the ribs are elevated and when muscles in between ribs are relaxed the ribs settle down.
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Inspiration

Throughout inspiration, the space inside the chest cavity is increased in two ways. Firstly, the muscles of ribs contract and raise the ribs upwards and forwards and secondly, the muscles of the diaphragm also contract and diaphragm end up being less domelike.

This downward motion of the diaphragm and external and upward movement of the ribs causes a boost in the chest cavity and decreases pressure. When the pressure from the lungs is removed, they broaden. With the expansion of the lungs, vacuum is created inside the lungs in which the air rushes from the outside due to higher air pressure. This is called inspiration.

Inspiration-expiration

Expiration

Throughout expiration the muscles of ribs are relaxed and the ribs move downward and inward. In this way from the sides of the chest cavity, space becomes less. At the same time, the muscles of the diaphragm also relax becoming more domelike and the chest cavity is also lowered from the floor. This reduction in space of the chest cavity applies pressure on the lungs. When lungs have pressed the air inside the lungs moves out of the lungs and this is expiration.

Transport of Respiratory Gases

Consumption of oxygen and release of carbon dioxide by blood travelling through capillaries of alveoli is brought about by the following factors.

  1. Diffusion of oxygen in and CO2 out occurs because of the difference in partial pressures of these gases.
  2. Within the rich network of blood vessels surrounding the alveoli, blood is distributed in incredibly thin layers and, therefore, exposed to the big alveolar surface area.
  3. Blood in the lungs is separated from the alveolar air by incredibly thin membranes of the capillaries and alveoli.
Transportation of Oxygen

In humans the respiratory pigment is haemoglobin. It is present in red blood cells. Haemoglobin easily integrates with oxygen to form bright red oxyhaemoglobin. Oxyhaemoglobin is unstable and splits into the typical purple-red coloured haemoglobin and oxygen in the conditions of low oxygen concentration and less pressure.

Carbonic anhydrase enzyme present in R.B.C. facilitates this activity. In this way haemoglobin acts as an efficient oxygen carrier. A small percentage of oxygen likewise gets dissolved in the blood plasma.

Haemoglobin can take in optimal oxygen at the water level. The maximum quantity of oxygen which normal human blood takes in and brings at the sea-level is about 20ml/100ml of blood. This is the maximum capability of haemoglobin for oxygen when it is completely oxygenated. Under normal conditions, the blood of alveoli of the lungs is not totally oxygenated. When an oxygen tension is 115mm mercury, haemoglobin is 98 percent saturated and, therefore, includes 19.6 ml of oxygen per 100ml of blood.

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This indicates that haemoglobin can be almost completely oxygenated by an oxygen pressure of 100 mm mercury, which exists in the lungs. Any higher oxygen pressure would have the very same outcome.

When oxygen pressure falls below 60 mm mercury, as in numerous cells and tissues, the oxygen saturation of haemoglobin decreases very greatly. This leads to the release of large quantities of oxygen from haemoglobin. In this way in the tissue where the oxygen tension is low oxyhaemoglobin dissociates rapidly.

There are 3 essential elements which affect the capacity of haemoglobin to integrate with oxygen.

  1. Carbon dioxide

When CO2 pressure increases, the oxygen tension reduces, the capability of haemoglobin to hold oxygen becomes less. In this way, increased CO2 tension favours the greater liberation of oxygen from the blood to the tissue.

  1. Temperature

The rise in temperature level also triggers a reduction in the oxygen-carrying capability of the blood, e.g., in the increased muscular activity.

  1. pH

The pH of blood also influences the degree to which oxygen binds to haemoglobin. As the pH of the blood declines, the amount of oxygen bound to haemoglobin likewise declines. This occurs because decreased pH results from a boost in hydrogen ions, and the hydrogen ions combine with the protein part of the haemoglobin particles, triggering a decrease in the ability of haemoglobin to bind oxygen. On the other hand, a boost in blood pH leads to an increased capability of haemoglobin to bind oxygen.

Transport of Carbon Dioxide

Carbon dioxide is more soluble than oxygen and dissolves easily in the tissue fluid surrounding the cells. From the tissue fluid, dissolved CO2 passes to the plasma within the blood capillaries. Carbon dioxide is transported in the blood in a number of different states.

  1. Some of the CO2 (about 20%) is brought as carboxyhaemoglobin. Carboxyhaemoglobin is formed when carbon dioxide integrates with the amino group of haemoglobin.
  2. Other plasma proteins likewise carry about 5% carbon dioxide from the body fluids to the capillaries of lungs.
  3. About 70% of carbon dioxide is carried as bicarbonate ion combined with sodium in the plasma. As carbon dioxide from tissue fluid enters the blood vessels it combines to form carbonic acid.

breathing-carbonic

The carbonic acid divides rapidly and ionizes to produce hydrogen ions and bicarbonate ions.

HCO3

When blood leaves the capillary most of the carbon dioxide remains in the kind of bicarbonate ions. All these reactions are reversible. In the lung’s bicarbonate ions combine with hydrogen ions to form carbonic acid which splits into water and CO2. It is this carbon dioxide which diffuses out from the blood vessels of the lungs into the space of alveolar sac.

co2-h2o

  1. A small amount of CO2 is likewise carried by corpuscles combined with potassium.
Carbon Dioxide Concentration

In Arterial and Venous Blood, it has been discovered that arterial blood consists of about 50 ml of carbon dioxide per 100 ml of blood whereas venous blood has 54 ml of carbon dioxide per 100 ml of blood. In this way, every 100 ml of blood uses up simply 4 ml of CO2 as it passes through the tissues and gives of 4 ml of CO2 per 100 ml of blood as it passes through the lungs.

Role of Respiratory Pigments

Numerous types of respiratory pigments exist in different animals. The pigment combines with oxygen reversibly and increases the oxygen carrying capacity of the blood.

Haemoglobin is the most crucial protein present in numerous animals including humans. Haemoglobin in man increases the oxygen carrying capability of the blood to about 75 times.

Haemoglobin

Myoglobin is haemoglobin-like iron-containing protein pigment taking place in muscle fibres. Myoglobin is likewise called muscle haemoglobin. It works as an intermediate substance for the transfer of oxygen from haemoglobin to aerobic metabolic procedures of the muscle cells. It can also store some oxygen.

Myoglobin includes simply one polypeptide chain associated with an iron-containing ring structure which can bind with one molecule of oxygen. The affinity of myoglobin to integrate with oxygen is much greater as compared to haemoglobin.

Multiple-Choice Questions with Answers:

  1. What is the main function of the diaphragm during inspiration?
    • a) To relax the chest cavity
    • b) To raise the ribs
    • c) To decrease chest cavity pressure
    • d) To contract the lungs
    • Answer: c) To decrease chest cavity pressure
  2. What causes the movement of air into the lungs during inspiration?
    • a) Contraction of intercostal muscles
    • b) Relaxation of the diaphragm
    • c) Expansion of the chest cavity
    • d) Relaxation of ribs
    • Answer: c) Expansion of the chest cavity
  3. During expiration, what happens to the diaphragm?
    • a) Contracts and becomes less domelike
    • b) Relaxes and becomes more domelike
    • c) Expands and contracts rapidly
    • d) Remains stationary
    • Answer: b) Relaxes and becomes more domelike
  4. How is the transportation of oxygen and carbon dioxide facilitated in blood vessels?
    • a) Active transport
    • b) Diffusion
    • c) Osmosis
    • d) Filtration
    • Answer: b) Diffusion
  5. What is the primary respiratory pigment in humans?
    • a) Chlorophyll
    • b) Hemoglobin
    • c) Myoglobin
    • d) Carotene
    • Answer: b) Hemoglobin
  6. What is the product when oxygen combines with hemoglobin in the blood?
    • a) Oxyhaemoglobin
    • b) Carboxyhaemoglobin
    • c) Myoglobin
    • d) Hematocrit
    • Answer: a) Oxyhaemoglobin
  7. How does carbon dioxide mainly get transported in the blood?
    • a) As dissolved gas
    • b) As bicarbonate ions
    • c) As carboxyhaemoglobin
    • d) As myoglobin
    • Answer: b) As bicarbonate ions
  8. What happens to the oxygen-carrying capacity of blood when pH decreases?
    • a) Increases
    • b) Decreases
    • c) Remains unchanged
    • d) Fluctuates randomly
    • Answer: b) Decreases
  9. What is the function of myoglobin in muscle cells?
    • a) Transport of carbon dioxide
    • b) Storage of oxygen
    • c) Production of oxygen
    • d) Transport of nutrients
    • Answer: b) Storage of oxygen
  10. Which factor influences the capacity of hemoglobin to bind with oxygen when CO2 pressure increases?
    • a) Increase in oxygen tension
    • b) Decrease in oxygen tension
    • c) Increase in temperature
    • d) Increase in pH
    • Answer: b) Decrease in oxygen tension
  11. What is the primary mechanism of breathing in humans?
    • a) Active contraction of lungs
    • b) Passive expansion and contraction of the lungs
    • c) Movement of the ribs
    • d) Contraction of the diaphragm
    • Answer: b) Passive expansion and contraction of the lungs
  12. What happens during inspiration?
    • a) Chest cavity decreases
    • b) Air moves out of the lungs
    • c) Diaphragm relaxes
    • d) Chest cavity pressure increases
    • Answer: d) Chest cavity pressure increases
  13. What causes a decrease in the chest cavity during expiration?
    • a) Contraction of intercostal muscles
    • b) Elevation of ribs
    • c) Relaxation of the diaphragm
    • d) Contraction of the diaphragm
    • Answer: a) Contraction of intercostal muscles
  14. Which enzyme facilitates the formation of oxyhaemoglobin from haemoglobin and oxygen?
    • a) Amylase
    • b) Catalase
    • c) Carbonic anhydrase
    • d) Protease
    • Answer: c) Carbonic anhydrase
  15. What is the maximum capacity of haemoglobin for oxygen at sea level?
    • a) 10 ml/100ml of blood
    • b) 15 ml/100ml of blood
    • c) 20 ml/100ml of blood
    • d) 25 ml/100ml of blood
    • Answer: c) 20 ml/100ml of blood
  16. How does a decrease in blood pH affect the binding of oxygen to hemoglobin?
    • a) Increases oxygen binding
    • b) Decreases oxygen binding
    • c) No effect on oxygen binding
    • d) Enhances oxygen dissociation
    • Answer: b) Decreases oxygen binding
  17. What percentage of carbon dioxide is carried as bicarbonate ions in the plasma?
    • a) 20%
    • b) 50%
    • c) 70%
    • d) 90%
    • Answer: c) 70%
  18. Which respiratory pigment increases the oxygen-carrying capacity of blood in humans?
    • a) Chlorophyll
    • b) Hemoglobin
    • c) Myoglobin
    • d) Melanin
    • Answer: b) Hemoglobin
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Frequently Asked Questions (FAQs) related to the Tutorial

  1. Q: What are the key stages involved in the mechanism of breathing in humans?
    • A: The mechanism of breathing involves inspiration (inhalation) and expiration. During inspiration, fresh air with higher oxygen concentration is drawn into the lungs, while during expiration, air with low oxygen and high CO2 concentration is expelled.
  2. Q: How does inspiration occur during the breathing process?
    • A: Inspiration is facilitated by the contraction of muscles, including the diaphragm and ribs. This causes an increase in the chest cavity, creating a vacuum that draws air into the lungs.
  3. Q: What role does the diaphragm play in breathing?
    • A: The diaphragm, a muscular sheet at the floor of the chest cavity, contracts during inspiration, becoming less domelike. This contraction contributes to the expansion of the chest cavity, leading to the inhalation of air.
  4. Q: How is expiration different from inspiration?
    • A: Expiration involves the relaxation of muscles, including the diaphragm and ribs. This results in a decrease in the chest cavity, applying pressure on the lungs and causing the expulsion of air.
  5. Q: What factors contribute to the transport of respiratory gases in the blood?
    • A: The transport of respiratory gases is influenced by factors such as diffusion based on partial pressures, exposure to the alveolar surface area, and the thin membranes of capillaries and alveoli.
  6. Q: What is the primary respiratory pigment in humans, and how does it function?
    • A: Haemoglobin, present in red blood cells, is the primary respiratory pigment. It easily binds with oxygen to form oxyhaemoglobin, enhancing oxygen transport. Carbonic anhydrase enzyme facilitates this process.
  7. Q: What is the maximum oxygen-carrying capacity of haemoglobin at sea level?
    • A: The maximum amount of oxygen that haemoglobin can carry at sea level is approximately 20 ml per 100 ml of blood when fully oxygenated.
  8. Q: How does the concentration of carbon dioxide affect the oxygen-carrying capacity of haemoglobin?
    • A: An increase in CO2 pressure reduces the oxygen tension, diminishing haemoglobin’s capacity to hold oxygen. This favors the release of oxygen to the tissues.
  9. Q: What are the different states in which carbon dioxide is transported in the blood?
    • A: Carbon dioxide is transported as carboxyhaemoglobin, dissolved in plasma proteins, and as bicarbonate ions combined with sodium in the plasma.
  10. Q: How does myoglobin differ from haemoglobin in terms of oxygen binding?
    • A: Myoglobin is a muscle pigment with a higher affinity for oxygen compared to haemoglobin. It serves as an intermediate for oxygen transfer to muscle cells and can store some oxygen.
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Wrap up

This comprehensive tutorial goes into the details of the respiratory system, covering the mechanism of breathing, transport of gases, and the vital role played by respiratory pigments in humans.

Mechanism of Breathing: Breathing is a mechanical process involving inspiration (inhalation) and expiration. During inhalation, fresh air rich in oxygen enters the lungs, while during expiration, air with a lower oxygen and higher CO2 concentration is expelled. The diaphragm, ribs, and intercostal muscles contribute to the expansion and contraction of the chest cavity, creating the necessary pressure differentials for air movement.

Transport of Respiratory Gases: Oxygen and carbon dioxide are transported in the blood through capillaries of alveoli. Factors such as diffusion, the rich network of blood vessels, and thin membranes of capillaries and alveoli contribute to this process.

Transportation of Oxygen: Haemoglobin, the respiratory pigment in humans, facilitates the transport of oxygen. Haemoglobin binds with oxygen to form oxyhaemoglobin, which can release oxygen in conditions of low oxygen concentration and pressure. Factors influencing oxygen binding include carbon dioxide levels, temperature, and blood pH.

Transport of Carbon Dioxide: Carbon dioxide, more soluble than oxygen, is transported in various states in the blood. This includes carboxyhaemoglobin, plasma proteins, and bicarbonate ions. Reversible reactions occur in the blood and lungs to facilitate the release of carbon dioxide.

Role of Respiratory Pigments: Haemoglobin, a crucial protein in humans, significantly increases the blood’s oxygen-carrying capacity. Myoglobin, found in muscle fibers, acts as an intermediate for oxygen transfer during aerobic metabolic processes in muscles.

This tutorial provides a comprehensive understanding of the physiological processes involved in breathing, gas exchange, and the pivotal role played by respiratory pigments in ensuring the efficient transport of oxygen and carbon dioxide within the human body.

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