Respiratory System: Complete Notes

Respiratory System • Gas Exchange • Respiratory Volumes • Breathing Mechanism • Pulmonary Ventilation

CSIR-NET • GATE • DBT • ICMR • MSc Biotechnology

Study Tip: The respiratory system should be studied as a connected physiological process rather than as a collection of isolated facts. Follow this sequence: atmospheric air → respiratory tract → alveoli → gas exchange → blood transport → tissues → cellular respiration The major concepts covered in this lecture are the organization of the respiratory system, gas exchange, respiratory volumes and capacities, and the mechanism of breathing.

1. Introduction to the Respiratory System

The respiratory system is the organ system responsible for the exchange of gases between the organism and its environment. In humans, its principal function is to obtain oxygen from atmospheric air and eliminate carbon dioxide generated during cellular metabolism. Oxygen is essential for aerobic cellular respiration, while carbon dioxide is a major metabolic waste product that must be continuously removed.

Respiration is a broad physiological process and should not be confused only with breathing. Breathing, or pulmonary ventilation, refers to the movement of air into and out of the lungs. Gas exchange refers to the movement of oxygen and carbon dioxide between air and blood and between blood and tissues. Cellular respiration, in contrast, is the biochemical process in which cells use oxygen to generate ATP and produce carbon dioxide and water.

Major stages of respiration

Pulmonary ventilation: Movement of air between the atmosphere and the alveoli.
External respiration: Exchange of oxygen and carbon dioxide between alveolar air and pulmonary capillary blood.
Gas transport: Transport of oxygen and carbon dioxide through the circulation.
Internal respiration: Exchange of gases between systemic blood and tissue cells.
Cellular respiration: Utilization of oxygen by cells for oxidative metabolism and ATP production.

Key Point: The respiratory system does not work independently. It functions closely with the cardiovascular system because blood transports oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs.

2. Functions of the Respiratory System

Although gas exchange is the primary function of the respiratory system, the respiratory organs perform several additional physiological roles. The lungs and respiratory tract participate in acid-base regulation, vocalization, protection from inhaled particles and regulation of certain biologically active substances.

Major functions

Oxygen uptake: Provides oxygen required for aerobic metabolism.
Carbon dioxide elimination: Removes carbon dioxide produced by cellular metabolism.
Acid-base regulation: Regulation of arterial carbon dioxide contributes importantly to maintenance of blood pH.
Protection: Nasal hairs, mucus, cilia, cough and other mechanisms help remove particles and microorganisms.
Speech: Expired air provides airflow through the larynx and contributes to vocalization.
Olfaction: The nasal cavity contains sensory receptors involved in smell.
Heat and water exchange: Respiratory surfaces contribute to loss of heat and water vapour.
Endocrine/metabolic functions: Pulmonary endothelial cells participate in the metabolism of several circulating substances.

Respiration and acid-base balance

Carbon dioxide combines reversibly with water to form carbonic acid, which can dissociate into hydrogen ions and bicarbonate. Therefore, changes in pulmonary ventilation can alter arterial carbon dioxide concentration and consequently influence blood pH.

Exam Point: Increased alveolar ventilation generally decreases arterial CO₂ concentration, whereas decreased alveolar ventilation tends to increase arterial CO₂ concentration.

3. Organs of the Respiratory System

The respiratory tract is organized into conducting and respiratory portions. The conducting portion carries, warms, humidifies and filters air. The respiratory portion contains the structures where gas exchange occurs.

Structure	Major role
Nose and nasal cavity	Entry, filtration, warming and humidification of air
Pharynx	Passageway connecting nasal/oral regions with the larynx
Larynx	Air passage and voice production
Trachea	Conducts air toward the bronchi
Bronchi	Distribute air into the lungs
Bronchioles	Smaller conducting airways that regulate airflow
Alveoli	Primary sites of pulmonary gas exchange
Lungs	Contain the respiratory airways and alveolar gas-exchange surfaces

4. Upper Respiratory Tract

The upper respiratory tract includes structures that receive and condition inspired air before it reaches the lower respiratory system. The nose and nasal cavity are particularly important because inspired air is filtered, warmed and humidified.

Nose and nasal cavity

Nasal hairs help trap relatively large particles.
Mucus traps smaller particles and microorganisms.
The rich blood supply helps warm inspired air.
Moist mucosal surfaces contribute to humidification.
Ciliated epithelial cells help move mucus toward the pharynx.
Olfactory receptors are present in specialized regions of the nasal cavity.

Pharynx

The pharynx is a muscular passage shared by the respiratory and digestive systems. It conducts air toward the larynx and food toward the esophagus.

Larynx

The larynx forms part of the airway between the pharynx and trachea. It contains the vocal folds and therefore plays an important role in sound production. During swallowing, protective mechanisms help prevent food and liquid from entering the lower airway.

5. Lower Respiratory Tract

The lower respiratory tract consists primarily of the trachea, bronchi, bronchioles and respiratory portions of the lungs. The conducting airways progressively branch into smaller tubes, ultimately leading to respiratory bronchioles, alveolar ducts and alveoli.

Trachea

The trachea is a conducting airway connecting the larynx with the main bronchi.
Cartilaginous support helps maintain airway patency.
Ciliated epithelium and mucus contribute to particle clearance.

Bronchi

The trachea divides into right and left main bronchi. These branches enter the lungs and divide repeatedly into smaller bronchi and bronchioles.

Bronchioles

Bronchioles are small airways that contain smooth muscle and lack the cartilage characteristic of larger conducting airways. Changes in bronchiolar smooth-muscle tone can substantially influence airway resistance.

Important: The conducting zone transports air but is not the principal site of respiratory gas exchange. The respiratory zone contains the structures where oxygen and carbon dioxide exchange occurs.

6. Lungs and Pleura

The lungs are paired organs located within the thoracic cavity. The right and left lungs are not identical in structure. The right lung normally has three lobes, whereas the left lung has two major lobes and accommodates the position of the heart.

Pleura

Each lung is surrounded by a pleural membrane. The visceral pleura is closely associated with the lung surface, while the parietal pleura lines the inner surface of the thoracic cavity. A thin film of pleural fluid lies between the pleural layers.

Pleural fluid reduces friction during respiratory movements.
The pleural arrangement helps mechanically couple the lungs to the movements of the thoracic wall.
The pressure relationship within the pleural space is important for maintaining lung expansion.

Elastic properties of lungs

Lung tissue contains elastic components that contribute to its tendency to recoil inward. Surface tension at the air-liquid interface within alveoli also promotes collapse. Pulmonary surfactant reduces surface tension and helps stabilize alveoli.

7. Alveoli and Respiratory Membrane

Alveoli are microscopic air-filled structures located at the terminal portions of the respiratory tree. They provide a very large surface area for gas exchange between alveolar air and pulmonary capillary blood.

Major cells associated with alveoli

Type I alveolar cells: Thin cells specialized primarily for gas exchange.
Type II alveolar cells: Produce pulmonary surfactant and contribute to alveolar epithelial repair.
Alveolar macrophages: Participate in removal of particles and microorganisms reaching the alveolar region.

Respiratory membrane

The respiratory membrane separates alveolar gas from blood in pulmonary capillaries. It is extremely thin, which facilitates rapid diffusion of oxygen and carbon dioxide.

8. Gas Exchange

Gas exchange occurs because oxygen and carbon dioxide move down their respective partial-pressure gradients. Oxygen generally moves from alveolar air into pulmonary capillary blood, while carbon dioxide moves from pulmonary capillary blood into the alveoli.

External respiration

External respiration is the exchange of gases between alveolar air and pulmonary capillary blood.

Oxygen diffuses from alveoli into pulmonary capillary blood.
Carbon dioxide diffuses from pulmonary blood into alveoli.
Gas movement is driven primarily by differences in partial pressure.
The thin respiratory membrane facilitates rapid exchange.

Internal respiration

Internal respiration refers to exchange between systemic capillary blood and tissue cells. Oxygen leaves systemic blood and enters tissues, while carbon dioxide produced by tissues enters the blood.

Process	Oxygen movement	Carbon dioxide movement
External respiration	Alveoli → blood	Blood → alveoli
Internal respiration	Blood → tissues	Tissues → blood

9. Diffusion of Oxygen and Carbon Dioxide

Diffusion is the passive movement of molecules from a region of higher partial pressure toward a region of lower partial pressure. The respiratory system uses diffusion as the fundamental mechanism for pulmonary and tissue gas exchange.

Factors affecting gas diffusion

Surface area: A larger exchange surface increases potential gas transfer.
Membrane thickness: A thinner respiratory membrane facilitates diffusion.
Partial-pressure gradient: A larger gradient promotes faster diffusion.
Diffusion coefficient: Solubility and molecular properties influence movement through the respiratory membrane.
Ventilation-perfusion relationships: Effective gas exchange requires appropriate matching of airflow and pulmonary blood flow.

Exam Point: Carbon dioxide is much more soluble in biological fluids than oxygen. Therefore, despite its smaller partial-pressure gradient in many situations, CO₂ can diffuse efficiently across the respiratory membrane.

Fick's principle for diffusion

In simplified form, the rate of gas diffusion across a membrane increases with surface area and partial-pressure gradient and decreases as membrane thickness increases.

Diffusion rate ∝ (Surface area × Partial-pressure gradient) / Membrane thickness

10. Oxygen Transport

Once oxygen enters pulmonary capillary blood, it is transported to tissues. Most oxygen is carried bound reversibly to hemoglobin within red blood cells, while a small fraction remains physically dissolved in plasma.

Hemoglobin-bound oxygen

Hemoglobin contains heme groups with iron capable of reversibly binding oxygen. This allows blood to carry much more oxygen than would be possible if oxygen were transported only in dissolved form.

Most blood oxygen is transported bound to hemoglobin.
A small fraction is dissolved in plasma.
Oxygen binding to hemoglobin is reversible.
Hemoglobin affinity for oxygen is influenced by several physiological factors.

Oxygen-hemoglobin dissociation curve

The relationship between oxygen partial pressure and hemoglobin oxygen saturation is commonly represented by the oxygen-hemoglobin dissociation curve. The curve is sigmoidal because oxygen binding to hemoglobin is cooperative.

Factors that shift the oxygen-hemoglobin curve

Increased temperature generally reduces hemoglobin affinity for oxygen.
Increased carbon dioxide can reduce hemoglobin affinity for oxygen.
Increased hydrogen ion concentration can reduce oxygen affinity.
Increased 2,3-BPG in red blood cells promotes oxygen unloading.

Bohr Effect: Increased CO₂ and increased acidity in metabolically active tissues tend to promote oxygen unloading from hemoglobin. This helps match oxygen delivery with tissue metabolic activity.

11. Carbon Dioxide Transport

Carbon dioxide produced by tissues enters the blood and is transported toward the lungs. It is carried in several forms, with bicarbonate being the major form in blood.

Three major forms of CO₂ transport

Form	Description
Dissolved CO₂	A fraction is physically dissolved in plasma.
Bicarbonate	The largest fraction is transported after conversion to bicarbonate ions.
Carbamino compounds	CO₂ can bind reversibly to proteins, particularly hemoglobin.

Role of carbonic anhydrase

Inside red blood cells, carbonic anhydrase rapidly catalyzes the reversible reaction between carbon dioxide and water, facilitating the formation of carbonic acid and subsequently bicarbonate and hydrogen ions.

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

Important: Carbon dioxide transport is closely connected with acid-base physiology. The lungs can alter blood pH by changing the rate at which carbon dioxide is removed from the body.

12. Pulmonary Ventilation

Pulmonary ventilation is the movement of air between the atmosphere and the alveoli. It consists of inspiration, when air enters the lungs, and expiration, when air leaves the lungs.

Basic principle

Air moves because of pressure gradients. When pressure inside the lungs becomes lower than atmospheric pressure, air flows into the lungs. When pressure inside the lungs becomes higher than atmospheric pressure, air flows out.

Core rule:

Air moves from higher pressure toward lower pressure.

During inspiration: Atmospheric pressure > alveolar pressure

During expiration: Alveolar pressure > atmospheric pressure

Muscles involved in breathing

Diaphragm: Major muscle responsible for quiet inspiration.
External intercostal muscles: Assist expansion of the thoracic cage during inspiration.
Accessory inspiratory muscles: Become important during increased ventilatory demand.
Internal intercostal muscles: Can contribute to forced expiration.
Abdominal muscles: Important during active or forced expiration.

13. Mechanism of Breathing

The mechanical process of breathing depends on coordinated changes in thoracic volume, lung volume and pressure. The diaphragm is particularly important because its contraction changes the vertical dimension of the thoracic cavity.

14. Inspiration

Inspiration is the process by which air enters the lungs. During quiet breathing, inspiration is primarily an active process because contraction of respiratory muscles is required.

Sequence of quiet inspiration

The diaphragm contracts.
The diaphragm moves downward and becomes flatter.
External intercostal muscles contract.
The thoracic cavity expands.
Lung volume increases.
Alveolar pressure decreases below atmospheric pressure.
Air flows into the lungs.

Remember: Inspiration requires an increase in thoracic and lung volume, which decreases alveolar pressure and causes air to enter.

Forced inspiration

During exercise or respiratory distress, additional muscles can assist inspiration. These include muscles of the neck and upper thorax that elevate the ribs and increase thoracic volume.

15. Expiration

Expiration is the movement of air out of the lungs. During quiet breathing, expiration is generally passive. It occurs largely because inspiratory muscles relax and elastic recoil of the lungs and thoracic structures causes lung volume to decrease.

Sequence of quiet expiration

The diaphragm relaxes.
The diaphragm moves upward.
External intercostal muscles relax.
Thoracic and lung volume decrease.
Alveolar pressure rises above atmospheric pressure.
Air flows out of the lungs.

Forced expiration

Forced expiration is an active process. Internal intercostal muscles and abdominal muscles can contract to reduce thoracic volume and increase the pressure driving air out of the lungs.

Feature	Inspiration	Expiration
Quiet breathing	Active	Mostly passive
Diaphragm	Contracts and moves downward	Relaxes and moves upward
Thoracic volume	Increases	Decreases
Alveolar pressure	Falls below atmospheric pressure	Rises above atmospheric pressure
Air movement	Into lungs	Out of lungs

16. Respiratory Volumes

Respiratory volumes describe the amount of air moved or present in the lungs under specific conditions. These measurements are important in respiratory physiology and are commonly tested in competitive examinations.

1. Tidal Volume (TV)

Tidal volume is the volume of air inspired or expired during a normal quiet breath. In a healthy adult at rest, it is commonly approximated as about 500 mL, although actual values vary with body size and physiological conditions.

Represents normal quiet breath volume.
Approximately 500 mL in a typical adult at rest.
Not all of this air reaches gas-exchange surfaces.

2. Inspiratory Reserve Volume (IRV)

Inspiratory reserve volume is the additional volume of air that can be forcibly inspired after a normal tidal inspiration.

3. Expiratory Reserve Volume (ERV)

Expiratory reserve volume is the additional volume of air that can be forcibly expired after a normal tidal expiration.

4. Residual Volume (RV)

Residual volume is the volume of air remaining in the lungs after a maximal forced expiration. It cannot be voluntarily expelled completely.

Important Exam Point: Residual volume helps prevent complete collapse of the lungs and cannot be measured directly by simple spirometry.

Volume	Meaning	Approximate adult value*
Tidal Volume (TV)	Air moved during quiet breathing	500 mL
Inspiratory Reserve Volume (IRV)	Extra air inspired after normal inspiration	~3000 mL
Expiratory Reserve Volume (ERV)	Extra air expired after normal expiration	~1100 mL
Residual Volume (RV)	Air remaining after maximal expiration	~1200 mL

*Approximate textbook values; actual values vary according to age, sex, body size, posture and physiological condition.

17. Respiratory Capacities

Respiratory capacities are combinations of two or more respiratory volumes.

Inspiratory Capacity (IC)

IC = TV + IRV

Inspiratory capacity is the maximum amount of air that can be inspired after a normal expiration.

Expiratory Capacity (EC)

EC = TV + ERV

Expiratory capacity is the maximum amount of air that can be expired after a normal inspiration.

Functional Residual Capacity (FRC)

FRC = ERV + RV

Functional residual capacity is the volume of air remaining in the lungs at the end of a normal passive expiration.

Vital Capacity (VC)

VC = IRV + TV + ERV

Vital capacity is the maximum volume of air that can be expired after a maximal inspiration.

Total Lung Capacity (TLC)

TLC = IRV + TV + ERV + RV

Total lung capacity represents the total volume of air contained in the lungs after a maximal inspiration.

Capacity	Formula
Inspiratory Capacity	IC = TV + IRV
Expiratory Capacity	EC = TV + ERV
Functional Residual Capacity	FRC = ERV + RV
Vital Capacity	VC = IRV + TV + ERV
Total Lung Capacity	TLC = IRV + TV + ERV + RV

Memory Trick:

IC = TV + IRV
EC = TV + ERV
FRC = ERV + RV
VC = IRV + TV + ERV
TLC = VC + RV

18. Dead Space

Dead space refers to portions of the respiratory system in which air is present but effective gas exchange does not occur. Understanding dead space is important because not every millilitre of inspired air contributes equally to alveolar ventilation.

Anatomical dead space

Anatomical dead space is the volume of air contained within the conducting airways, such as the trachea and bronchi, where significant gas exchange does not normally occur.

Alveolar dead space

Alveolar dead space refers to alveoli that are ventilated but receive insufficient or no blood flow for effective gas exchange.

Physiological dead space

Physiological dead space is the total volume of air that does not participate effectively in gas exchange. In healthy individuals at rest, it is usually close to anatomical dead space.

Important Formula:

Alveolar Ventilation = (Tidal Volume − Dead Space) × Respiratory Rate

Therefore, effective gas exchange depends more closely on alveolar ventilation than on total minute ventilation alone.

19. Neural Regulation of Breathing

Breathing is controlled automatically by neural networks located mainly within the brainstem, while voluntary control can temporarily modify breathing. The respiratory control system continuously integrates information about carbon dioxide, oxygen, pH and mechanical conditions of the lungs.

Medullary respiratory centers

Neuronal networks in the medulla are essential for generating the basic rhythmic pattern of breathing.

Pontine influence

Pontine respiratory regions influence the timing and pattern of respiratory activity and interact with medullary networks.

Chemoreceptors

Central chemoreceptors: Respond primarily to changes related to CO₂ and hydrogen ion concentration in the brain extracellular environment.
Peripheral chemoreceptors: Located mainly in carotid and aortic bodies and respond to changes in arterial oxygen, carbon dioxide and pH.

Role of carbon dioxide

Under normal conditions, arterial carbon dioxide is a particularly important chemical stimulus influencing ventilation. An increase in arterial CO₂ tends to increase ventilatory drive.

Exam Point: Severe decreases in arterial oxygen can strongly stimulate ventilation through peripheral chemoreceptors, especially when arterial oxygen falls substantially.

20. Pulmonary Surfactant

Pulmonary surfactant is a surface-active material produced mainly by type II alveolar cells. It reduces surface tension at the air-liquid interface of alveoli.

Functions of surfactant

Reduces alveolar surface tension.
Helps prevent alveolar collapse, particularly at low lung volumes.
Increases lung compliance.
Reduces the work required for breathing.
Contributes to stabilization of alveoli of different sizes.

Laplace relationship

For a simplified spherical structure, the pressure required to prevent collapse is related to surface tension and radius.

P = 2T / r

Here P represents pressure, T represents surface tension and r represents radius. By reducing surface tension, surfactant decreases the tendency of alveoli to collapse.

Key Point: Surfactant is especially important in premature infants because insufficient surfactant can contribute to respiratory distress caused by increased alveolar surface tension and reduced lung compliance.

21. Ventilation, Perfusion and Efficient Gas Exchange

Effective pulmonary gas exchange requires both ventilation and blood flow. Ventilation refers to delivery of air to alveoli, while perfusion refers to delivery of blood to pulmonary capillaries.

Ventilation-perfusion relationship

The ventilation-perfusion relationship, commonly represented as the V/Q ratio, describes the relationship between alveolar ventilation and pulmonary blood flow. An idealized whole-lung V/Q ratio is often approximated as around 0.8 because pulmonary blood flow is somewhat greater than alveolar ventilation.

Low V/Q: Ventilation is relatively low compared with perfusion.
High V/Q: Ventilation is relatively high compared with perfusion.
Shunt-like condition: Blood receives little or no oxygen because ventilation is inadequate relative to perfusion.
Dead-space-like condition: Ventilation occurs without adequate perfusion.

Competitive Exam Point: Efficient gas exchange requires appropriate matching between ventilation and perfusion. Disturbances in V/Q matching can impair oxygenation even when the lungs are receiving adequate total ventilation.

22. Important Respiratory Physiology Terms

Ventilation

Movement of air into and out of the lungs.

Perfusion

Blood flow through pulmonary capillaries.

Diffusion

Passive movement of gases down partial-pressure gradients.

Alveoli

Principal microscopic sites of pulmonary gas exchange.

Surfactant

Surface-active material that reduces alveolar surface tension.

Tidal Volume

Volume of air inspired or expired during quiet breathing.

Residual Volume

Air remaining in lungs after maximal forced expiration.

Vital Capacity

Maximum volume expired after maximal inspiration.

23. Quick Revision Notes

⭐ Must-Remember Points

The major function of the respiratory system is exchange of oxygen and carbon dioxide.
Pulmonary ventilation means movement of air into and out of the lungs.
External respiration occurs between alveoli and pulmonary blood.
Internal respiration occurs between systemic blood and tissues.
Alveoli provide a large surface area for gas exchange.
Type I alveolar cells are specialized for gas exchange.
Type II alveolar cells produce pulmonary surfactant.
Alveolar macrophages help remove particles and microorganisms.
Oxygen moves from alveolar air into pulmonary capillary blood.
Carbon dioxide moves from pulmonary blood into alveolar air.
Gas exchange occurs primarily by diffusion down partial-pressure gradients.
Most oxygen is transported bound to hemoglobin.
Most carbon dioxide is transported in the form of bicarbonate.
Carbonic anhydrase accelerates the conversion between CO₂ and bicarbonate-related forms.
The diaphragm is the major muscle of quiet inspiration.
Quiet inspiration is an active process.
Quiet expiration is primarily passive because of elastic recoil.
During inspiration, thoracic volume increases and alveolar pressure decreases.
During expiration, thoracic volume decreases and alveolar pressure increases.
Tidal volume is approximately 500 mL in a typical resting adult.
Inspiratory reserve volume is the additional volume that can be inspired after a normal inspiration.
Expiratory reserve volume is the additional volume that can be expired after a normal expiration.
Residual volume remains in the lungs after maximal forced expiration.
Residual volume cannot be measured directly by simple spirometry.
IC = TV + IRV.
EC = TV + ERV.
FRC = ERV + RV.
VC = IRV + TV + ERV.
TLC = IRV + TV + ERV + RV.
Anatomical dead space consists mainly of conducting airways.
Alveolar dead space refers to ventilated alveoli that receive inadequate perfusion.
Physiological dead space includes anatomical and alveolar dead space.
Pulmonary surfactant reduces surface tension.
Surfactant increases lung compliance and reduces the tendency of alveoli to collapse.
Carbon dioxide is an important regulator of ventilation.
Central and peripheral chemoreceptors contribute to regulation of breathing.
Ventilation-perfusion matching is essential for efficient pulmonary gas exchange.
The V/Q ratio for the whole lung is approximately 0.8 under typical resting conditions.

25. Final Exam-Oriented Summary

The respiratory system maintains continuous exchange of gases between the atmosphere, blood and tissues. Air reaches the alveoli through the conducting airways, and oxygen and carbon dioxide are exchanged across the thin respiratory membrane by diffusion. Oxygen is transported primarily by hemoglobin, whereas carbon dioxide is transported mainly as bicarbonate.

Primary function: Oxygen uptake and carbon dioxide elimination.
Gas-exchange site: Alveoli.
Main inspiratory muscle: Diaphragm.
Quiet expiration: Mostly passive.
Oxygen transport: Mainly bound to hemoglobin.
CO₂ transport: Mainly as bicarbonate.
Surfactant: Produced mainly by type II alveolar cells.
Tidal volume: Approximately 500 mL in a typical resting adult.
Residual volume: Air remaining after maximal forced expiration.
Vital capacity: IRV + TV + ERV.
Total lung capacity: VC + RV.
FRC: ERV + RV.
Inspiration: Thoracic volume increases and alveolar pressure falls.
Expiration: Thoracic volume decreases and alveolar pressure rises.
Carbonic anhydrase: Facilitates rapid CO₂/bicarbonate interconversion.
Dead space: Ventilated air that does not effectively participate in gas exchange.
V/Q matching: Important for efficient pulmonary gas exchange.
Chemoreceptors: Detect chemical changes that influence respiratory drive.

For CSIR-NET, GATE Biotechnology, DBT-BET, ICMR-JRF and MSc Biotechnology examinations, special attention should be given to the relationships between pressure, volume and airflow; respiratory volumes and capacities; oxygen and carbon dioxide transport; surfactant function; diffusion; and regulation of breathing.

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Sunday, 23 August 2026