Breathing and Respiration

  • Oxygen (O2) is used by organisms to break down molecules like glucose and fatty acids to produce energy.
  • Carbon dioxide (CO2), which is harmful, is released during this breakdown process.
  • Therefore, O2 must be supplied to cells, and CO2 must be removed. This exchange of gases (O2 for CO2) is called breathing or respiration.

Types of Respiratory Organs:

  • Different animals have different mechanisms for breathing based on their habitat and body structure.
    • Invertebrates like sponges and flatworms exchange gases through simple diffusion on their body surface.
    • Earthworms use their moist skin, and insects have a network of tubes called tracheal tubes to transport air.
    • Aquatic animals like arthropods and molluscs use gills for gas exchange (known as branchial respiration).
    • Terrestrial animals like amphibians, reptiles, birds, and mammals breathe through lungs (pulmonary respiration).
    • Amphibians, like frogs, can also exchange gases through their moist skin (cutaneous respiration).

Human Respiratory System:

  • The human respiratory system includes the following components:
    1. External Nostrils: Located above the upper lip, they lead to the nasal cavity.
    2. Nasal Chamber: The passage that connects the nostrils to the pharynx.
    3. Pharynx: A shared passage for both food and air, leading to the larynx.
    4. Larynx: A cartilaginous structure that helps in sound production (sound box). The epiglottis prevents food from entering the larynx.
    5. Trachea: A straight tube that divides into the primary bronchi at the 5th thoracic vertebra.
    6. Bronchi: The primary bronchi divide into secondary and tertiary bronchi, which further divide into bronchioles.
    7. Alveoli: Tiny, vascularized air sacs at the end of bronchioles where gas exchange occurs.
  • The lungs are covered by a double-layered pleura with fluid between the layers, reducing friction during breathing.

Respiratory System Function:

  • The conducting part (from nostrils to terminal bronchioles) transports, filters, and humidifies air.
  • The exchange part (alveoli and their ducts) is where the actual gas exchange occurs.

Thoracic Chamber:

  • The lungs are housed in the thoracic cavity which is surrounded by the vertebral column, sternum, ribs, and diaphragm.
  • Changes in the volume of this cavity help in breathing.

Steps of Respiration:

  1. Breathing: Air is drawn into the lungs (inspiration) and CO2-rich air is expelled (expiration).
  2. Gas Diffusion: O2 and CO2 diffuse across the alveolar membrane.
  3. Gas Transport: Blood transports gases (O2 to cells, CO2 away).
  4. Cellular Respiration: Cells use O2 to break down food molecules and release CO2.

Mechanism of Breathing:

  • Inspiration (inhaling) occurs when the diaphragm contracts, increasing the thoracic volume, which decreases the pressure in the lungs, causing air to flow in.
  • Expiration (exhaling) occurs when the diaphragm relaxes, decreasing the thoracic volume, which increases the lung pressure, pushing air out.
  • Muscles Involved: The diaphragm and intercostal muscles between ribs help in breathing.
  • Breathing Rate: A healthy person breathes 12-16 times per minute.
  • Spirometer: A tool used to measure the volume of air involved in breathing movements.

Additional Information:

  • Cellular Respiration: In cells, O2 is used to break down food (like glucose) for energy, releasing CO2 as a byproduct.
  • The pleural membrane (outer and inner layers) in the lungs helps reduce friction during breathing movements.

Respiratory Volumes and Capacities

  • Tidal Volume (TV): The amount of air breathed in or out during normal respiration (about 500 mL). A healthy person breathes 6000-8000 mL of air per minute.
  • Inspiratory Reserve Volume (IRV): The extra air that can be inhaled after a normal breath (2500-3000 mL).
  • Expiratory Reserve Volume (ERV): The extra air that can be exhaled after a normal breath (1000-1100 mL).
  • Residual Volume (RV): The air remaining in the lungs after a forced exhalation (1100-1200 mL).

From these volumes, various capacities can be derived:

  • Inspiratory Capacity (IC): Total air a person can inhale after normal exhalation (TV + IRV).
  • Expiratory Capacity (EC): Total air a person can exhale after normal inhalation (TV + ERV).
  • Functional Residual Capacity (FRC): Air remaining in the lungs after normal exhalation (ERV + RV).
  • Vital Capacity (VC): Maximum air a person can exhale after a forced inhalation (TV + IRV + ERV).
  • Total Lung Capacity (TLC): Total air the lungs can hold after a forced inhalation (VC + RV).

2. Exchange of Gases

  • Alveoli: Primary sites where oxygen (O₂) and carbon dioxide (CO₂) are exchanged.
  • Partial Pressure: The pressure exerted by each gas in a mixture. O₂ and CO₂ diffuse according to their partial pressures.

Factors affecting gas exchange:

  • Oxygen Diffusion: From alveoli to blood and from blood to tissues, driven by concentration gradients.
  • Carbon Dioxide Diffusion: Diffuses in the opposite direction—from tissues to blood, then from blood to alveoli.

Diffusion Membrane: The thin barrier (alveolar epithelium, capillary endothelium, and basement membrane) allows gases to diffuse efficiently.

Key points:

  • Solubility: CO₂ is 20-25 times more soluble than O₂, facilitating its faster diffusion.

3. Transport of Gases

  • Oxygen Transport:
    • 97% of O₂ is carried by hemoglobin (Hb) in red blood cells (RBCs).
    • Hemoglobin binds to O₂ to form oxyhemoglobin (HbO₂), depending on the partial pressure of O₂.
    • In tissues, low O₂ pressure and high CO₂ pressure cause HbO₂ to release O₂.
  • Carbon Dioxide Transport:
    • 70% of CO₂ is transported as bicarbonate ions (HCO₃⁻).
    • 20-25% is carried by hemoglobin as carbaminohemoglobin (HbCO₂).
    • CO₂ is released in the alveoli where the CO₂ pressure is low, and O₂ pressure is high.

Role of Carbonic Anhydrase: This enzyme catalyzes the conversion of CO₂ to bicarbonate and vice versa, aiding in CO₂ transport.

4. Regulation of Respiration

  • Respiratory Rhythm: Controlled by the respiratory rhythm center in the medulla of the brain. The pneumotaxic center in the pons modifies this rhythm.
  • Chemoreceptors: Sensitive to CO₂ and H⁺ concentrations, they regulate respiration. High CO₂ or H⁺ levels stimulate the brain to increase breathing rate to expel excess CO₂.

5. Disorders of the Respiratory System

  • Asthma: Difficulty in breathing due to inflammation of bronchi and bronchioles, leading to wheezing.
  • Emphysema: A chronic condition where alveolar walls are damaged, reducing the respiratory surface area, often caused by smoking.

Summary:

Breathing involves the intake of air (inhalation) and the release of CO₂ (exhalation). Gases are exchanged in the alveoli through diffusion, depending on partial pressures and solubility. O₂ is transported by hemoglobin, while CO₂ is carried as bicarbonate or bound to hemoglobin. The respiratory system is regulated by the brain, adjusting the breathing rate based on blood CO₂ levels. Various disorders like asthma and emphysema affect the respiratory system.

Competitive Exam Tips:

  • Partial Pressure Gradients: Understand how gases diffuse based on differences in partial pressures between tissues, blood, and alveoli.
  • Oxygen Dissociation Curve: The sigmoid curve indicates the relationship between O₂ binding to hemoglobin and the partial pressure of O₂.
  • Carbon Dioxide Transport: CO₂ is mostly carried as bicarbonate. Know the role of carbonic anhydrase in converting CO₂ to bicarbonate.
  • Spirometry: Familiarize with the terms tidal volume, inspiratory and expiratory reserve volumes, and how they help in diagnosing respiratory conditions.

These concepts can help in solving questions on respiratory physiology in competitive exams.

These all are the notes of chapter 14. And important questions are below HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊

1. What is Breathing and Respiration?

Answer:
Breathing is the process of taking in oxygen (O₂) and releasing carbon dioxide (CO₂) from the body. Respiration is how our body uses oxygen to break down food like glucose to produce energy. Oxygen is needed by cells for energy, and CO₂ is produced as a waste product, which must be removed from the body.

2. What are the Different Types of Respiratory Organs?

Answer:
Different animals have different respiratory organs based on where they live and their body structure:

  • Invertebrates (like sponges and flatworms) exchange gases through their body surface.
  • Earthworms use their moist skin for gas exchange.
  • Insects have a network of tubes called tracheal tubes.
  • Aquatic animals (like fish) use gills for gas exchange.
  • Terrestrial animals (like humans) breathe through lungs. Some animals, like frogs, also use their skin for breathing.

3. What is the Structure of the Human Respiratory System?

Answer:
The human respiratory system includes:

  • Nostrils: Where air enters the body.
  • Nasal cavity: The passage that connects the nostrils to the throat.
  • Pharynx: A common passage for both food and air.
  • Larynx: Known as the voice box, it helps in sound production.
  • Trachea: A tube that carries air to the lungs.
  • Bronchi: The trachea divides into two main bronchi that lead to the lungs.
  • Bronchioles: Smaller branches of bronchi inside the lungs.
  • Alveoli: Tiny air sacs where oxygen and carbon dioxide are exchanged.

4. What is the Function of the Respiratory System?

Answer:
The respiratory system helps in:

  1. Breathing: Taking in oxygen (inhaling) and removing carbon dioxide (exhaling).
  2. Gas exchange: Oxygen and carbon dioxide are exchanged in the alveoli (tiny air sacs in the lungs).
  3. Transport of gases: Blood carries oxygen from the lungs to the body and carbon dioxide from the body back to the lungs.
  4. Cellular respiration: Cells use oxygen to break down food molecules for energy and produce carbon dioxide.

5. What is the Mechanism of Breathing?

Answer:

  • Inspiration (Inhaling): The diaphragm contracts, increasing the space in the chest cavity, causing air to flow into the lungs.
  • Expiration (Exhaling): The diaphragm relaxes, reducing chest space, and air is pushed out of the lungs.

6. What is the Role of the Diaphragm and Intercostal Muscles in Breathing?

Answer:
The diaphragm is a large muscle beneath the lungs that helps control breathing by moving up and down. The intercostal muscles are between the ribs and also help in expanding and contracting the chest cavity during breathing.

7. What are the Different Respiratory Volumes?

Answer:
There are several types of air volumes involved in breathing:

  • Tidal Volume (TV): The amount of air we breathe in and out with each normal breath (about 500 mL).
  • Inspiratory Reserve Volume (IRV): Extra air that can be inhaled after normal breathing (about 2500-3000 mL).
  • Expiratory Reserve Volume (ERV): Extra air that can be exhaled after normal breathing (about 1000-1100 mL).
  • Residual Volume (RV): The air that remains in the lungs after forced exhalation (about 1100-1200 mL).

8. How does Gas Exchange Occur in the Lungs?

Answer:
Gas exchange happens in the alveoli. Oxygen moves from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli. This is driven by differences in the partial pressures of the gases. Oxygen diffuses into the blood where its concentration is lower, and carbon dioxide diffuses out into the lungs where its concentration is lower.

9. How is Oxygen Transported in the Blood?

Answer:
About 97% of oxygen is carried by red blood cells (RBCs) in a molecule called hemoglobin. Hemoglobin binds with oxygen to form oxyhemoglobin. When blood reaches tissues with low oxygen, the oxygen is released from hemoglobin and delivered to the cells.

10. How is Carbon Dioxide Transported in the Blood?

Answer:
About 70% of carbon dioxide is transported in the blood as bicarbonate ions (HCO₃⁻). Another 20-25% binds to hemoglobin to form carbaminohemoglobin. The remaining CO₂ is dissolved in plasma. In the lungs, the CO₂ is released from the blood and exhaled.

11. What Regulates Breathing?

Answer:
Breathing is controlled by the medulla and pons in the brain. The medulla sets the basic rhythm of breathing, while the pons modifies this rhythm. Chemoreceptors in the body sense levels of CO₂ and hydrogen ions (H⁺). If CO₂ levels rise, these receptors signal the brain to increase the breathing rate to remove excess CO₂.

12. What are Some Common Respiratory Disorders?

Answer:

  • Asthma: Inflammation of the bronchi and bronchioles, causing difficulty in breathing and wheezing.
  • Emphysema: A condition where the alveolar walls are damaged, reducing the surface area for gas exchange. It is often caused by smoking.

Additional Knowledge:

  • Pleural Membrane: The lungs are surrounded by a pleural membrane that has two layers (outer and inner) with fluid between them. This fluid helps reduce friction during breathing, allowing smooth expansion and contraction of the lungs.
  • Carbonic Anhydrase: An enzyme that helps convert carbon dioxide into bicarbonate ions in the blood, aiding in the transport of CO₂ from tissues to the lungs.