Functional Residual Capacity (FRC) includes which of the following volumes?
- VC + TV
- TV + RV
- ERV + RV
- IRV + ERV
Explanation: FRC is the volume of air that remains in the lungs after a normal expiration, consisting of Expiratory Reserve Volume and Residual Volume.
Which substance in the alveoli prevents them from collapsing by reducing surface tension?
- Mucus
- Carbonic acid
- Plasma protein
- Surfactant
Explanation: Pulmonary surfactant (mainly lecithin) lowers surface tension in the alveoli, preventing collapse (atelectasis) during expiration.
The total thickness of the diffusion membrane in the human lungs is much less than:
- One millimeter
- One centimeter
- Ten millimeters
- Five millimeters
Explanation: The three-layered diffusion membrane is extremely thin (less than 1 mm) to allow for the rapid exchange of gases via simple diffusion.
The 'Vital Capacity' of a healthy adult athlete is generally:
- Exactly 500 mL
- Same as smokers
- Lower than normal
- Higher than normal
Explanation: Regular physical training increases the strength of respiratory muscles and lung elasticity, resulting in a higher Vital Capacity.
Diffusion of gases across the alveolar-capillary membrane is primarily influenced by:
- Active transport
- Ciliary movement
- Blood velocity
- Pressure gradient
Explanation: Gases diffuse across the respiratory membrane from a region of higher partial pressure to lower partial pressure.
What is the primary role of the 'Phrenic nerve' in the respiratory system?
- Vocalizing sound
- Inhibiting bronchioles
- Filtering dust
- Diaphragm contraction
Explanation: The phrenic nerve originates from the cervical spinal cord and provides the primary motor supply to the diaphragm for breathing.
The 'Chloride Shift', which maintains electrical neutrality during $CO_2$ transport, involves the entry of $Cl^-$ into:
- Red cells
- White cells
- Platelets
- Plasma
Explanation: As bicarbonate ions diffuse out of the RBCs into the plasma, chloride ions move into the RBCs to maintain ionic balance (Hamburger phenomenon).
The chemosensitive area near the rhythm center is highly sensitive to which of the following?
- Nitrogen levels
- Oxygen levels
- Glucose concentration
- $CO_2$ and $H^+$
Explanation: The receptors are sensitive to $CO_2$ and hydrogen ions. The role of oxygen in regulating the respiratory rhythm is quite insignificant.
Every 100 mL of oxygenated blood can deliver around how much $O_2$ to the tissues?
Explanation: Under normal physiological conditions, about 5 mL of $O_2$ is delivered to the tissues per 100 mL of blood.
What is the significance of the pCO₂ gradient between the tissues and the blood?
- Drives O₂ in
- Prevents clotting
- Drives CO₂ out
- Regulates temperature
Explanation: Tissues (45 mm Hg) have a higher pCO₂ than deoxygenated blood (40 mm Hg entering capillaries), ensuring CO₂ diffuses into the blood.
In the lungs, $CO_2$ is released from bicarbonate primarily due to:
- Low $pCO_2$
- Low pH
- High temperature
- High $pO_2$
Explanation: In the alveoli, where $pCO_2$ is low, the reaction reverses: bicarbonate and $H^+$ form $H_2CO_3$, which splits into $H_2O$ and $CO_2$ for exhalation.
The enzyme critical for the rapid conversion of $CO_2$ and water into bicarbonate is:
- Lactate dehydrogenase
- Carbonic anhydrase
- Amylase
- Carboxylase
Explanation: Carbonic anhydrase is found in high concentrations in RBCs and facilitates the reversible reaction of $CO_2$ and $H_2O$.
Which factor shifts the Oxygen dissociation curve to the right, favoring $O_2$ release?
- High $H^+$ concentration
- High pH
- Low temperature
- Low $pCO_2$
Explanation: Higher acidity (lower pH), higher $pCO_2$, and higher temperature favor the dissociation of oxygen from hemoglobin (Bohr effect).
The 'Mountain Sickness' experienced at high altitudes is primarily due to:
- Low $pO_2$
- High $pCO_2$
- Low temperature
- Extreme humidity
Explanation: At high altitudes, the atmospheric pressure is low, leading to a decrease in the partial pressure of oxygen, which results in hypoxia.
Which of the following makes up the diffusion membrane in the lungs?
- Single layer epithelium
- Triple layer membrane
- Thick fibrous tissue
- Ciliated columnar cells
Explanation: It consists of the squamous epithelium of alveoli, the endothelium of capillaries, and the basement substance between them.
Which volume cannot be measured directly using a simple spirometer?
- Inspiratory reserve
- Vital capacity
- Residual volume
- Tidal volume
Explanation: Because Residual Volume never leaves the lungs, it cannot be measured by a spirometer and must be calculated using gas dilution techniques.
Trachea is a straight tube extending up to the mid-thoracic cavity, where it divides at the level of:
- 7th thoracic vertebra
- 5th thoracic vertebra
- 3rd cervical vertebra
- 1st lumbar vertebra
Explanation: The trachea divides into right and left primary bronchi at the level of the 5th thoracic vertebra.
Which of the following describes the shape of the diaphragm when it is in a relaxed state?
- Dome-shaped
- Flattened
- Concave
- Circular
Explanation: When the diaphragm relaxes, it returns to its natural dome-shaped position, reducing the volume of the thoracic cavity and helping in expiration.
Difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles is:
- Pneumonia
- Occupational fibrosis
- Asthma
- Emphysema
Explanation: Asthma is a chronic condition where the airways narrow and swell, often triggered by allergens.
The solubility of $CO_2$ is approximately how many times higher than that of $O_2$?
- 20-25 times
- 100 times
- 5 times
- 2 times
Explanation: Because $CO_2$ is much more soluble than $O_2$, the amount of $CO_2$ that can diffuse through the membrane is much higher.
What is the partial pressure of Oxygen ($pO_2$) in the tissues under normal conditions?
- 45 mm Hg
- 104 mm Hg
- 40 mm Hg
- 95 mm Hg
Explanation: Tissues have a lower $pO_2$ (40 mm Hg) compared to oxygenated blood (95 mm Hg), which drives the diffusion of oxygen into the cells.
Inspiration occurs when there is a negative pressure in the lungs with respect to:
- Diaphragmatic pressure
- Atmospheric pressure
- Venous pressure
- Intra-pleural pressure
Explanation: Inspiration is initiated by the contraction of the diaphragm and external intercostal muscles, creating a pressure lower than the atmosphere.
The total volume of air a person can breathe in after a forceful expiration is:
- Total lung capacity
- Inspiratory reserve
- Vital capacity
- Expiratory reserve
Explanation: Vital Capacity (VC) is the maximum volume of air a person can breathe in after a forced expiration (TV + IRV + ERV).
Partial pressure of $CO_2$ ($pCO_2$) in the deoxygenated blood is:
- 40 mm Hg
- 104 mm Hg
- 45 mm Hg
- 95 mm Hg
Explanation: The $pCO_2$ is higher in deoxygenated blood (45 mm Hg) than in the alveoli (40 mm Hg), so $CO_2$ diffuses into the alveoli.
Residual Volume (RV) is defined as the volume of air remaining in the lungs even after:
- Forced inspiration
- Forced expiration
- Normal expiration
- Normal inspiration
Explanation: Residual volume is the air that cannot be expelled from the lungs, even after the most vigorous expiratory effort.
The chemoreceptors in the 'Aortic arch' and 'Carotid artery' primarily detect changes in:
- Oxygen levels
- Nitrogen levels
- Blood pressure
- CO₂ and H⁺
Explanation: Peripheral chemoreceptors are sensitive to CO₂ and hydrogen ion concentrations, sending signals to the rhythm center to adjust breathing.
The enormous surface area for gas exchange in the human lung is provided by the:
- Alveoli
- Large bronchi
- Tracheal wall
- Pleural cavity
Explanation: Millions of tiny, bag-like alveoli provide a surface area of approximately 70-100 square meters for efficient gas diffusion.
Which disorder is characterized by 'fibrosis' or the proliferation of fibrous tissues in the lungs?
- Emphysema
- Bronchitis
- Silicosis
- Asthma
Explanation: Occupational exposure to silica or asbestos dust causes chronic inflammation leading to fibrosis, which seriously damages lung tissue.
The 'Oxygen Dissociation Curve' typically takes which of the following shapes?
- Parabolic
- Sigmoid
- Linear
- Hyperbolic
Explanation: The sigmoid shape reflects the cooperative binding of oxygen to the four subunits of the hemoglobin molecule.
What is the partial pressure of Oxygen ($pO_2$) in the atmospheric air at sea level?
- 104 mm Hg
- 95 mm Hg
- 40 mm Hg
- 159 mm Hg
Explanation: The atmospheric $pO_2$ is higher than in the alveoli (104 mm Hg), allowing oxygen to move into the lungs.
Every 100 mL of deoxygenated blood delivers approximately how much $CO_2$ to the alveoli?
Explanation: While 100 mL of oxygenated blood delivers 5 mL of $O_2$, 100 mL of deoxygenated blood delivers about 4 mL of $CO_2$ for excretion.
Which part of the respiratory system is known as the 'conducting part'?
- Respiratory membrane
- External nostrils-Bronchioles
- Alveoli
- Alveolar ducts
Explanation: The conducting part transports atmospheric air to the alveoli, clears it from foreign particles, and humidifies it.
Which of the following is supported by 'incomplete' cartilaginous rings?
- Alveolar ducts
- Terminal bronchioles
- Trachea
- Alveoli
Explanation: The trachea and primary/secondary bronchi are supported by C-shaped cartilaginous rings to prevent collapse during pressure changes.
The partial pressure of $CO_2$ ($pCO_2$) in the oxygenated blood is approximately:
- 159 mm Hg
- 40 mm Hg
- 45 mm Hg
- 95 mm Hg
Explanation: Oxygenated blood carries $CO_2$ at a partial pressure of 40 mm Hg, which increases to 45 mm Hg after picking up $CO_2$ from the tissues.
The Pneumotaxic center, which can reduce the duration of inspiration, is located in the:
- Spinal cord
- Midbrain
- Thalamus
- Pons
Explanation: Neural signals from the pneumotaxic center in the pons can limit the inspiration phase, thereby altering the respiratory rate.
Inspiratory Capacity (IC) refers to the total volume of air a person can inspire after a:
- Forced expiration
- Forced inspiration
- Normal inspiration
- Normal expiration
Explanation: Inspiratory Capacity is the sum of Tidal Volume and Inspiratory Reserve Volume (TV + IRV).
A chronic disorder in which alveolar walls are damaged, reducing the respiratory surface, is:
- Asthma
- Bronchitis
- Silicosis
- Emphysema
Explanation: Emphysema is primarily caused by cigarette smoking and leads to permanent damage to the alveoli.
The 'vocal cords' responsible for sound production are located within the:
- Larynx
- Nasopharynx
- Bronchi
- Pharynx
Explanation: The larynx contains two folds of tissue called vocal cords that vibrate to produce sound when air is expelled from the lungs.
The percentage of $CO_2$ transported bound to hemoglobin as carbamino-hemoglobin is:
- 97 percent
- 70 percent
- 7 percent
- 20-25 percent
Explanation: About 20-25% of $CO_2$ is carried by hemoglobin; this binding is related to the partial pressure of $CO_2$.
Which of the following shifts the oxygen-hemoglobin dissociation curve to the 'Left'?
- High $pCO_2$
- High $H^+$
- Low temperature
- Low pH
Explanation: A left shift (higher affinity) occurs with low temperature, low $pCO_2$, and high pH, conditions typically found in the lungs.
Expiratory Capacity (EC) is mathematically defined as the sum of:
- VC + RV
- TV + ERV
- ERV + RV
- TV + IRV
Explanation: Expiratory Capacity is the total volume of air a person can expire after a normal inspiration (Tidal Volume + Expiratory Reserve Volume).
Which of the following volumes is the amount of air inspired or expired during a normal breath?
- Inspiratory capacity
- Tidal volume
- Residual volume
- Vital capacity
Explanation: Tidal Volume (TV) is approximately 500 mL in a healthy man and represents the volume of air moved during quiet breathing.
The Total Lung Capacity (TLC) is the sum of all pulmonary volumes, which equals:
- IC + EC
- IRV + ERV
- TV + IRV
- VC + RV
Explanation: Total Lung Capacity is the total volume of air accommodated in the lungs at the end of a forced inspiration (RV + ERV + TV + IRV or VC + RV).
Each molecule of hemoglobin can carry a maximum of how many molecules of $O_2$?
Explanation: Hemoglobin is a tetramer with four iron-containing heme groups, each of which can bind one molecule of oxygen.
What is the primary cause of Occupational Respiratory Disorders like Silicosis?
- Genetic mutation
- Viral infection
- Inhalation of dust
- Long-term smoking
Explanation: In industries like stone-breaking or grinding, excessive dust leads to lung inflammation and fibrosis (proliferation of fibrous tissues).
The thoracic chamber is an anatomically air-tight box formed dorsally by the:
- Diaphragm
- Vertebral column
- Sternum
- Ribs
Explanation: The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs, and on the lower side by the diaphragm.
The 'Dead Space' refers to the volume of air that stays in the conducting part and is approximately:
- 500 mL
- 1100 mL
- 50 mL
- 150 mL
Explanation: Out of the 500 mL of Tidal Volume, about 150 mL does not participate in gas exchange as it remains in the conducting passages.
The Respiratory Rhythm Center, primarily responsible for regulating breathing, is in the:
- Cerebellum
- Hypothalamus
- Cerebrum
- Medulla oblongata
Explanation: The medulla contains the primary rhythm center, while the pons contains the pneumotaxic center which moderates its function.
Which specific structure prevents the entry of food into the larynx during swallowing?
- Thyroid cartilage
- Epiglottis
- Pharynx
- Glottis
Explanation: The epiglottis is a thin elastic cartilaginous flap that covers the glottis during swallowing to prevent food from entering the windpipe.
The 'Bohr Effect' describes the influence of which factor on the affinity of hemoglobin for oxygen?
- Carbon dioxide
- Blood pressure
- Glucose levels
- Nitrogen concentration
Explanation: The Bohr effect explains how increased $pCO_2$ or decreased pH reduces hemoglobin's affinity for oxygen, promoting its release to tissues.
Approximately what percentage of Oxygen is transported by Red Blood Cells (RBCs)?
- 3 percent
- 20-25 percent
- 70 percent
- 97 percent
Explanation: Most oxygen is carried as oxyhemoglobin in RBCs; the remaining 3% is dissolved in the plasma.
The transport of $CO_2$ bound to the 'amino group' of hemoglobin forms:
- Carbamino-hemoglobin
- Methemoglobin
- Oxyhemoglobin
- Carboxyhemoglobin
Explanation: $CO_2$ does not bind to the iron (heme) like oxygen; instead, it binds to the globin part of the hemoglobin molecule.
The double-layered membrane that reduces friction on the lung surface is the:
- Pleura
- Meninges
- Pericardium
- Peritoneum
Explanation: Lungs are covered by a double-layered pleura with pleural fluid between them, which reduces friction on the lung surface during breathing.
Approximately what percentage of $CO_2$ is transported in a dissolved state through the plasma?
- 25 percent
- 70 percent
- 7 percent
- 97 percent
Explanation: About 7% of $CO_2$ is carried in dissolved form in the plasma, 20-25% as carbamino-hemoglobin, and 70% as bicarbonate ions.
The 'Haldane Effect' refers to the increased ability of blood to carry $CO_2$ when:
- Oxygen levels low
- $O_2$ levels high
- Temperature is low
- pH is high
Explanation: Deoxygenation of the blood increases its ability to carry carbon dioxide, which facilitates $CO_2$ pickup at tissues.
Which of the following anatomical structures is also known as the 'Sound Box'?
- Pharynx
- Trachea
- Larynx
- Nasopharynx
Explanation: The larynx is a cartilaginous box which helps in sound production and is hence called the sound box.
Which of the following anatomical structures serves as a common passage for both food and air?
- Pharynx
- Esophagus
- Larynx
- Trachea
Explanation: The pharynx is the crossroads of the respiratory and digestive tracts, leading into the larynx for air and the esophagus for food.
Carbon Monoxide ($CO$) is extremely dangerous because its affinity for hemoglobin is:
- Lower than Nitrogen
- Same as Oxygen
- 200 times higher
- Very low
Explanation: CO binds almost irreversibly to hemoglobin, forming carboxyhemoglobin, which prevents the transport of oxygen to vital organs.
Which form of transport handles the majority (70%) of Carbon Dioxide in the blood?
- Bicarbonate ions
- Carbamino-hemoglobin
- Carbonic acid
- Dissolved gas
Explanation: Most $CO_2$ reacts with water inside RBCs to form bicarbonate ($HCO_3^-$), which is then transported in the plasma.
Which of the following structures lack cartilaginous rings for support?
- Trachea
- Terminal bronchioles
- Primary bronchi
- Initial bronchioles
Explanation: Trachea, bronchi, and initial bronchioles are supported by incomplete cartilaginous rings, but terminal bronchioles are not.