#1 of 31
UHS 2024
Permalink
Range of normal total lung capacity in humans is:
A
\( 8\text{-}9 \text{ liters} \)
B
\( 10\text{-}11 \text{ liters} \)
C
\( 5\text{-}6 \text{ liters} \)
D
\( 12\text{-}13 \text{ liters} \)
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Total Lung Capacity (TLC) encompasses every possible measurable volume within the human lung architecture.
Solution:
- TLC is mathematically the sum of Vital Capacity (VC) and Residual Volume (RV).
- In standard human physiology, the normal biological limit for a healthy adult's Total Lung Capacity falls strictly within the range of \( 5 \) to \( 6 \text{ liters} \).
Why other options are incorrect:
- \( 8\text{-}13 \text{ liters} \): These volumes are massive and far exceed the anatomical limits of the human thoracic cage. Such volumes are observed only in much larger mammals.
#2 of 31
SZABMU 2024
Permalink
When the diaphragm muscle lowers and the ribs move outward and forward, the volume of ________ increases, and the pressure on ________ decreases respectively.
A
Abdominal cavity, lungs
D
Lungs, abdominal cavity
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: Inspiration is driven by Boyle's Law: an increase in container volume produces an immediate drop in internal pressure.
Solution:
- When the diaphragm contracts (lowers) and intercostal muscles elevate the ribs, the physical dimensions of the chest cavity expand.
- Because the chest cavity volume increases, the intrapleural pressure plummets.
- This vacuum-like effect pulls on the lungs, causing their internal intrapulmonary pressure to decrease below atmospheric levels, sucking air in.
Why other options are incorrect:
- Abdominal cavity: When the diaphragm lowers, it actually compresses the abdominal cavity, decreasing its volume and increasing abdominal pressure.
- Lungs, Chest cavity (reversed): The structural volume of the chest cavity dictates the pressure applied to the lungs, not vice versa.
#3 of 31
SZABMU 2024
Permalink
Lungs are enclosed in the double membranous sac called:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Vital thoracic and abdominal organs are protected and lubricated by specialized serous membranes.
Solution:
- The lungs are wrapped tightly in a double-layered sac known as the pleura.
- It consists of the visceral pleura (adhered to the lung tissue) and the parietal pleura (lining the chest wall).
- The tiny space between them holds pleural fluid, which eliminates friction during the continuous expansion and recoiling of breathing.
Why other options are incorrect:
- Pericardium: The specific double-membranous sac enclosing the heart.
- Peritoneum: The serous membrane lining the abdominal cavity and its organs.
#4 of 31
SZABMU 2024
Permalink
Which type of the conjugated molecule is absent in respiratory distress syndrome?
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Surfactant is biochemically essential to prevent the collapse of alveoli by interfering with the hydrogen bonding of water.
Solution:
- Pulmonary surfactant is synthesized by Type II alveolar cells.
- Biochemically, it is a highly complex mixture composed predominantly of phospholipids combined with specific proteins—making it a lipoprotein complex.
- In Respiratory Distress Syndrome (common in premature neonates), the severe lack of this specific lipoprotein causes overwhelming alveolar surface tension, leading to lung collapse.
Why other options are incorrect:
- Glycoprotein / Glycolipids: Common components of cell membrane receptors, but not the primary functional surfactant molecule.
- Lipopolysaccharides: Found in the outer membranes of Gram-negative bacteria as endotoxins.
#5 of 31
NUMS 2024
Permalink
Most of the carbon dioxide in blood is transported as by bicarbonate ions. Choose the event not taking place during gaseous exchange at tissue level.
B
Formation of sodium bicarbonate
D
Formation of oxyhaemoglobin
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: Gas exchange events differ completely based on the location: systemic tissues vs. pulmonary capillaries (lungs).
Solution:
- At the tissue level, oxygen is desperately needed for cellular respiration. Therefore, hemoglobin must release its oxygen.
- Because oxygen is being released, oxyhaemoglobin (\( \text{HbO}_2 \)) is breaking down, NOT forming.
- The formation of oxyhemoglobin exclusively happens in the lungs where oxygen is abundant.
Why other options are incorrect:
- Formation of HHb (reduced hemoglobin): Occurs at the tissues as hemoglobin drops oxygen and buffers hydrogen ions.
- Formation of sodium bicarbonate & Chloride shift: Occur actively at the tissues as massive amounts of \( \text{CO}_2 \) enter the RBCs, convert to bicarbonate, and exit into plasma in exchange for Chloride.
#6 of 31
SZABMU 2024 Reconduct
Permalink
Which of the following proteins are involved in the expansion and recoiling of alveoli during breathing?
D
Collagens and squamous cells
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: The lung parenchyma must possess both structural integrity to prevent tearing and extreme elasticity to drive passive exhalation.
Solution:
- The connective tissue walls of the alveoli are reinforced with two vital proteins:
- Collagen: Provides tensile strength, preventing the alveoli from over-inflating or tearing.
- Elastin: Acts like molecular rubber bands, allowing the alveoli to stretch easily during inspiration and snap back (recoil) effortlessly during exhalation, pushing air out.
Why other options are incorrect:
- Keratin: A tough, waterproof protein found in hair, nails, and epidermis. It has absolutely no place in the delicate alveoli.
- Squamous cells: These are epithelial cells, not proteins.
#7 of 31
SZABMU 2024 Reconduct
Permalink
The area between the two lungs is called:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: The thoracic cavity is partitioned into distinct zones to isolate organs and prevent the spread of infection.
Solution:
- The specific anatomical region sandwiched securely between the right and left pleural cavities (lungs) is termed the mediastinum.
- This crucial space houses the heart, pericardium, major vessels, esophagus, and trachea.
Why other options are incorrect:
- Ischium / Acetabulum: These are bones/structures of the pelvis (hip joint).
- Hilum: The root of a single lung where bronchi and vessels attach; not the space between the lungs.
#8 of 31
UHS 2023
Permalink
Smooth muscles are found in all mentioned below except:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Form follows function in histology. The thickness of airway walls dictates their capability for gas exchange versus conduction.
Solution:
- The conducting zones (trachea, bronchi, bronchioles) contain layers of smooth muscle that allow the autonomic nervous system to control airway resistance (bronchodilation and bronchoconstriction).
- The alveoli represent the functional gas-exchange zone. They consist strictly of a single microscopic layer of squamous epithelium.
- If alveoli contained bulky smooth muscle tissue, the barrier would be entirely too thick for \( \text{O}_2 \) and \( \text{CO}_2 \) to diffuse. Thus, they lack smooth muscle completely.
Why other options are incorrect:
- Trachea, Bronchi, Bronchioles: All contain smooth muscle within their walls to regulate the diameter of the airway passage.
#9 of 31
ETEA 2023
Permalink
Which of the following statements is not correct about alveoli:
A
Alveoli form the gas exchange surface
B
Alveoli has a dense network of capillaries
C
The wall of each alveolus is \( 0.1 \text{ cm} \) thick
D
Collagen and elastin present in alveoli allow it to expand and recoil easily during breathing
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: The physics of diffusion demand that respiratory surfaces be phenomenally thin. Misunderstanding biological units reveals conceptual errors.
Solution:
- The wall of an alveolus is roughly \( 0.1 \, \mu\text{m} \) (micrometers) thick, not \( 0.1 \text{ cm} \).
- \( 0.1 \text{ cm} \) is equal to \( 1 \text{ mm} \). A barrier \( 1 \text{ mm} \) thick would be an impenetrable fortress to gas diffusion, instantly causing asphyxiation.
- Therefore, the statement claiming a \( 0.1 \text{ cm} \) thickness is mathematically and biologically completely incorrect.
Why other options are incorrect:
- Dense capillary network, Gas exchange surface, Collagen/elastin presence: All of these are highly accurate biological facts regarding alveolar structure and function.
#10 of 31
UHS 2022
Permalink
The respiratory surfaces exhibit following characteristic:
A
It must be thick for low diffusion
C
It should be non-vascularized
D
It should have low ventilation mechanism
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: For a respiratory surface to be efficient, it must maximize the rate of diffusion as described by Fick's Law.
Solution:
- An ideal respiratory surface must have several key traits: large surface area, highly vascularized network, extremely thin walls, and high permeability to gases.
- Permeability allows \( \text{O}_2 \) and \( \text{CO}_2 \) to dissolve and effortlessly cross the cell membranes.
Why other options are incorrect:
- Thick for low diffusion: A thick surface severely impedes diffusion; it must be microscopically thin.
- Non-vascularized: Lack of blood supply means gases cannot be transported away, halting the concentration gradient.
- Low ventilation: High ventilation is strictly required to bring in fresh air and maintain steep partial pressure gradients.
#11 of 31
NUMS 2022
Permalink
The following part is common in both digestive system and respiratory system of human beings:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: The anatomical pathways for food and air briefly intersect in the throat before diverging.
Solution:
- The pharynx is a muscular tube located at the back of the mouth and nasal cavity.
- It acts as a dual-purpose thoroughfare: it funnels inhaled air toward the larynx (respiratory) and ingested food/liquids toward the esophagus (digestive).
- The epiglottis ensures that food correctly bypasses the airway during swallowing.
Why other options are incorrect:
- Trachea & Larynx: Strictly belong to the respiratory tract.
- Esophagus: Strictly belongs to the digestive tract.
#12 of 31
SZABMU 2022
Permalink
The area between the two lungs is called:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: The thoracic cavity is partitioned into specific anatomical compartments housing vital organs.
Solution:
- The central compartment of the thoracic cavity, situated safely between the two pleural cavities (which house the lungs), is called the mediastinum.
- It acts as a protective housing for the heart, great vessels (aorta, vena cava), esophagus, and trachea.
Why other options are incorrect:
- Periosteum: A dense fibrous membrane covering the surfaces of bones.
- Infundibulum: A funnel-shaped cavity or structure, often referring to a part of the brain (pituitary stalk) or fallopian tube.
- Hilum: The specific depression on a single lung where bronchi and blood vessels enter and exit, not the entire area between the lungs.
#13 of 31
ETEA 2022
Permalink
Which of the following part of human respiratory system forms the gas exchange surface?
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: The respiratory system is divided into a conducting zone (bringing air in) and a respiratory zone (where actual gas exchange happens).
Solution:
- The alveoli are clustered, highly vascularized microscopic sacs that form the terminal ends of the respiratory tree.
- Their exceedingly thin squamous epithelium allows for the rapid diffusion of oxygen into the blood and carbon dioxide out of the blood.
Why other options are incorrect:
- Trachea, Larynx, Bronchi: These are thick-walled, cartilaginous tubes belonging to the conducting zone. Gas cannot diffuse through their thick structural layers.
#14 of 31
ETEA 2022
Permalink
The percentage of carbon dioxide carried as carboxyhaemoglobin is:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: Carbon dioxide is managed by the cardiovascular system through three distinct transport mechanisms to maintain acid-base balance.
Solution:
- \( \text{CO}_2 \) is distributed in the blood as follows:
- 1. As bicarbonate ions (\( \text{HCO}_3^- \)): Approximately \( 70\% \) is converted via carbonic anhydrase.
- 2. Bound to hemoglobin (carbaminohemoglobin): Approximately \( 23\% \) (often called carboxyhaemoglobin in older local syllabus).
- 3. Dissolved in plasma: Approximately \( 7\% \) remains as a dissolved gas in the blood fluid.
Why other options are incorrect:
- \( 70\% \): Represents the bicarbonate ion fraction.
- \( 7\% \): Represents the dissolved plasma fraction.
#15 of 31
ETEA 2022
Permalink
The average adult human has a lung capacity of approximately:
D
\( 12 \text{ liters} \)
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Total Lung Capacity (TLC) is the maximum volume of air the lungs can hold after a maximal forced inspiration.
Solution:
- TLC is calculated as the sum of Vital Capacity (VC) and Residual Volume (RV).
- In a healthy, average-sized adult, this total volume ranges between \( 5 \) to \( 6 \text{ liters} \) (\( 5000 \text{ - } 6000 \text{ mL} \)).
Why other options are incorrect:
- \( 2 \text{ liters} \): Far too low for total capacity; closer to isolated volumes like Functional Residual Capacity.
- \( 9 \text{ liters} \) / \( 12 \text{ liters} \): Massively exceed biological human limits; these volumes are seen in large mammals like horses.
#16 of 31
DUHS 2022
Permalink
The tidal Volume of lungs at rest or during normal breath is:
D
\( 0.5 \text{ liters} \)
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: Respiratory volumes vary greatly depending on exertion. Tidal volume represents baseline, resting respiration.
Solution:
- Tidal Volume (TV) is the amount of air inhaled or exhaled during a single, normal, relaxed breath without any extra effort.
- In a healthy adult, this volume is precisely \( 500 \text{ mL} \), which translates to \( 0.5 \text{ liters} \).
Why other options are incorrect:
- \( 3 \), \( 4 \), and \( 6 \text{ liters} \): These are massive volumes representing forced vital capacities or total lung capacities, not a relaxed, resting breath.
#17 of 31
NTS 2019
Permalink
In the passageways of the respiratory system, mucus secreting cells are called:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: The respiratory epithelium utilizes specialized glandular cells to maintain moisture and trap debris.
Solution:
- The epithelial lining of the respiratory tract contains modified columnar cells shaped like a wine goblet.
- These goblet cells synthesize and secrete mucus directly onto the surface of the respiratory passageways.
Why other options are incorrect:
- Tracheal cells: A non-specific term; the trachea contains multiple cell types (ciliated, basal, goblet).
- Surfactant cells: Also known as Type II pneumocytes, these are found exclusively in the alveoli to reduce surface tension, not in the general passageways to secrete mucus.
- Pleural cells: Form the mesothelial lining of the pleural cavity.
#18 of 31
MDCAT 2019
Permalink
During inspiration, the space inside the chest cavity is increased due to:
A
The contraction of the muscles of the diaphragm
B
The relaxation of the muscle of the diaphragm
C
Relaxation of the external intercostal muscle
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Boyle's Law states that pressure is inversely proportional to volume. Inspiration requires a volume increase to drop internal pressure below atmospheric pressure.
Solution:
- During active inspiration, the nervous system signals the skeletal muscles of the respiratory pump.
- The diaphragm contracts, causing its dome shape to flatten and move downward.
- Simultaneously, the external intercostal muscles contract, lifting the rib cage. These combined muscle contractions dramatically increase the volume of the chest cavity.
Why other options are incorrect:
- Relaxation of diaphragm / intercostals: This occurs during expiration, reducing chest cavity volume.
- Increased pressure: Volume must increase to decrease pressure for inspiration to occur.
#19 of 31
MDCAT 2018
Permalink
During breathing air from pharynx enters to:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: The pathway of airflow must be understood sequentially from the external environment to the site of gas exchange.
Solution:
- When air is inhaled, it travels through the nasal cavity \( \rightarrow \) pharynx \( \rightarrow \) larynx \( \rightarrow \) trachea.
- From the trachea, it bifurcates into the left and right bronchi, which further subdivide.
- Because the larynx is not listed in the options, the trachea is the immediate next major respiratory structure the air enters after the pharynx.
Why other options are incorrect:
- Alveoli, Bronchi, Bronchioles: These structures are located much deeper in the respiratory tract and receive air only after it has passed through the trachea.
#20 of 31
MDCAT 2018
Permalink
The low levels of surfactant produced by alveolar epithelium causes:
C
Respiratory distress syndrome
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Surfactant is a lipoprotein complex that decreases surface tension inside alveoli, preventing them from collapsing during exhalation.
Solution:
- If Type II pneumocytes fail to produce adequate surfactant (commonly seen in premature infants), the surface tension inside the alveoli becomes too high.
- This leads to alveolar collapse and severe breathing difficulty, a condition medically termed as Respiratory Distress Syndrome (RDS).
Why other options are incorrect:
- Emphysema: Destruction of alveolar walls, not a lack of surfactant.
- Bronchitis / Asthma: Inflammatory diseases of the airways (bronchi/bronchioles), not directly caused by alveolar surfactant deficiency.
#21 of 31
MDCAT 2018
Permalink
Which of the following statement is correct about the respiratory pigments?
A
Myoglobin has more affinity for oxygen as compared to haemoglobin
B
Albumin, globulin and globular proteins are present in respiratory pigments
C
Myoglobin and haemoglobin has higher affinity for nitrogen
D
Cyanide and haemoglobin has low affinity for oxygen
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Different respiratory pigments are adapted for transport versus storage of oxygen.
Solution:
- Hemoglobin (in blood) is designed to transport oxygen; it binds it in the lungs and easily drops it off in tissues.
- Myoglobin (in muscle tissue) acts as an oxygen reservoir. It must be able to steal oxygen away from hemoglobin.
- Therefore, myoglobin has a significantly higher binding affinity for oxygen than hemoglobin, holding onto its \( \text{O}_2 \) tightly until the muscle experiences extreme hypoxia.
Why other options are incorrect:
- Affinity for nitrogen: Neither pigment actively binds or transports nitrogen gas.
- Albumin/Globulin: These are standard plasma transport/immune proteins, not oxygen-carrying respiratory pigments.
#22 of 31
MDCAT 2017
Permalink
Site of gaseous exchange in humans is:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Gaseous exchange requires a thin, moist, and highly vascularized surface to allow efficient diffusion of respiratory gases.
Solution:
- The alveoli are microscopic, balloon-like air sacs at the terminal ends of the respiratory tree.
- They consist of a single layer of squamous epithelial cells surrounded by a dense network of pulmonary capillaries.
- This creates an optimal, extremely thin barrier for the rapid diffusion of \( \text{O}_2 \) and \( \text{CO}_2 \).
Why other options are incorrect:
- Trachea, Bronchus, Nose: These form the conducting zone of the respiratory system. Their thick walls and structural cartilage prevent any meaningful gas exchange. They only filter, warm, and humidify the air.
#23 of 31
MDCAT 2017
Permalink
Respiratory tubules are termed as bronchioles when they attain the diameter of or lesser.
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: The respiratory tree is classified based on structural changes, particularly the presence or absence of cartilage and overall diameter.
Solution:
- As the bronchi branch repeatedly, their diameter decreases and the cartilaginous rings are gradually replaced by irregular plates.
- Once a tubule reaches a diameter of \( 1 \text{ mm} \) or less, it loses its cartilage entirely.
- At this specific structural threshold, the passage is officially termed a bronchiole.
Why other options are incorrect:
- \( 1.2 \text{ cm} \), \( 1 \text{ cm} \), \( 1.2 \text{ mm} \): These measurements are either too large (representing bronchi or the trachea) or slightly above the strict anatomical threshold for defining a bronchiole.
#24 of 31
MDCAT 2017
Permalink
Label the prominent dome-shaped muscular boundary located at the base of the lungs separating the thoracic and abdominal cavities:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: The mechanism of breathing relies heavily on muscular boundaries that alter the volume of the thoracic cavity.
Solution:
- In standard anatomical diagrams of the human respiratory system, the prominent dome-shaped structure at the very base of the lungs is the diaphragm.
- It is a thin sheet of skeletal muscle that completely separates the thoracic (chest) cavity from the abdominal cavity.
Why other options are incorrect:
- Pleura: The double membrane enclosing the lungs, not a muscular boundary at the base.
- Inter-coastal muscle: Muscles located between the ribs.
- Chest cavity: The entire space, not a specific muscular structure.
#25 of 31
MDCAT 2017
Permalink
Low partial pressure of oxygen in tissues favors ____ of oxyhaemoglobin.
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: The behavior of hemoglobin changes dynamically based on the partial pressures of gases in its surrounding environment (Oxygen-Hemoglobin Dissociation Curve).
Solution:
- In the lungs, where the partial pressure of oxygen (\( \text{pO}_2 \)) is very high, hemoglobin's affinity for oxygen peaks, favoring the formation of oxyhemoglobin.
- Conversely, at the tissue level, cellular respiration heavily consumes oxygen, resulting in a very low \( \text{pO}_2 \).
- This low \( \text{pO}_2 \) triggers hemoglobin to lose its affinity and release its bound oxygen. This process is called dissociation.
Why other options are incorrect:
- Formation / Stability: These are favored in high \( \text{pO}_2 \) environments (the lungs), ensuring oxygen gets securely loaded onto the RBCs.
#26 of 31
MDCAT 2017
Permalink
Gaseous exchange in animals takes place with the help of process called as:
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: The movement of gases across biological membranes is solely governed by kinetic energy and concentration gradients.
Solution:
- Gaseous exchange does not require ATP or carrier proteins.
- Oxygen and carbon dioxide are small, uncharged molecules that pass freely through the phospholipid bilayers of alveoli and capillaries.
- They move exclusively via simple diffusion, traveling strictly from areas of higher partial pressure to areas of lower partial pressure.
Why other options are incorrect:
- Active transport: Requires ATP and pushes molecules against gradients; gases never utilize this.
- Cyclosis: Cytoplasmic streaming inside cells.
- Phagocytosis: Cellular eating (engulfing large particles).
#27 of 31
MDCAT 2017
Permalink
Which of the following is a respiratory disorder related to malnutrition?
View Answer & Propolis Autopsy
Correct Key: Option C
Diagnostic Explanation
Concept: Nutritional status profoundly impacts immune competence, making the body susceptible to opportunistic respiratory infections.
Solution:
- Tuberculosis (TB) is a contagious bacterial infection caused by Mycobacterium tuberculosis.
- Historically and clinically, TB is strongly associated with poverty, overcrowding, and strictly malnutrition. A malnourished body lacks the immune strength (like macrophages) to contain the mycobacterium, allowing the infection to ravage the lung tissue.
Why other options are incorrect:
- Emphysema / Cancer: Strongly correlated with smoking and environmental toxins, not directly caused by malnutrition.
- Asthma: An allergic/inflammatory hypersensitivity disorder, often genetic or environmental.
#28 of 31
MDCAT 2017
Permalink
Breakdown of thin wall of alveoli occurs in:
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: Chronic respiratory diseases present with distinct structural damages to the lung architecture.
Solution:
- Emphysema is a form of Chronic Obstructive Pulmonary Disease (COPD) predominantly caused by long-term smoking.
- Toxins cause chronic inflammation, triggering enzymes that actively digest the elastin and collagen in the alveolar walls.
- This breakdown of thin alveolar walls merges many small alveoli into fewer, larger, floppy air sacs, drastically reducing the surface area available for gas exchange.
Why other options are incorrect:
- Asthma: Involves constriction and inflammation of the bronchioles, not the physical destruction of alveoli.
- T.B: Causes necrotic tubercles and granulomas.
- Cancer: Characterized by uncontrolled cellular proliferation and tumor masses.
#29 of 31
MDCAT 2016
Permalink
Breathing consists of:
View Answer & Propolis Autopsy
Correct Key: Option A
Diagnostic Explanation
Concept: Breathing (pulmonary ventilation) is a cyclic, mechanical process driven by pressure gradients.
Solution:
- Breathing strictly consists of two distinct phases:
- 1. Inspiration (Inhalation): Active intake of air as thoracic volume increases and pressure decreases.
- 2. Expiration (Exhalation): Passive (or forced) expulsion of air as thoracic volume decreases and pressure increases.
Why other options are incorrect:
- Breathing is fundamentally a binary cycle of air moving in and air moving out. There are no tertiary or quaternary mechanical phases in standard pulmonary ventilation.
#30 of 31
MDCAT 2016
Permalink
Carboxyhemoglobin (\( 10 \text{-} 20\% \)) is formed when \( \text{CO}_2 \) combines with:
A
Haem portion of haemoglobin
B
Amino group of haemoglobin
C
Iron part of haemoglobin
View Answer & Propolis Autopsy
Correct Key: Option B
Diagnostic Explanation
Concept: Hemoglobin acts as a dual-transport molecule. While oxygen binds to the heme iron, carbon dioxide binds to a completely different site to prevent competition.
Solution:
- About \( 20\text{-}23\% \) of carbon dioxide is transported in the blood bound directly to hemoglobin.
- It binds to the terminal amino groups of the globin polypeptide chains, forming carbaminohemoglobin.
- Note: Some older regional curricula erroneously refer to this as "carboxyhemoglobin", though modern medicine strictly reserves that term for Carbon Monoxide (\( \text{CO} \)) binding. Regardless of terminology, \( \text{CO}_2 \) targets the amino group.
Why other options are incorrect:
- Haem / Iron part: These are the specific binding sites for Oxygen (\( \text{O}_2 \)) and Carbon Monoxide (\( \text{CO} \)), not Carbon Dioxide.
#31 of 31
KMDC 2014
Permalink
Mucus secreting goblet cells are present in:
View Answer & Propolis Autopsy
Correct Key: Option D
Diagnostic Explanation
Concept: The human respiratory tract is lined with ciliated epithelium interspersed with specialized secretory cells to protect the delicate alveolar surfaces.
Solution:
- Goblet cells are unicellular glands that secrete mucus.
- In the respiratory system, they are abundantly present in the lining of the trachea and bronchi.
- The secreted mucus traps incoming dust, microbes, and foreign particles, which are then swept upward by cilia.
Why other options are incorrect:
- Larynx, Glottis, Epiglottis: These structures are primarily cartilaginous and are involved in sound production and preventing food from entering the airway. While they have mucosal linings, the trachea is the classical primary site known for its rich distribution of goblet cells for air filtration.
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