Respiratory system MCQ Quiz in বাংলা - Objective Question with Answer for Respiratory system - বিনামূল্যে ডাউনলোড করুন [PDF]

Concept:

• The oxygen dissociation curve is a graph that shows the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen (SO2).
• It is an important tool in understanding how hemoglobin binds and releases oxygen in response to changes in oxygen tension.
• The curve is sigmoidal in shape, indicating the cooperative binding of oxygen by hemoglobin.
• At low partial pressures of oxygen, such as those found in the tissues, the curve is relatively flat, indicating that hemoglobin releases oxygen less readily.
• At higher partial pressures of oxygen, such as those found in the lungs, the curve becomes steeper, indicating that hemoglobin binds oxygen more readily.
• This allows for efficient oxygen uptake in the lungs and delivery to the tissues where it is needed.
• The sigmoidal shape of the curve arises from the cooperative binding of oxygen by hemoglobin.
• Hemoglobin is a tetrameric protein, composed of four subunits, each containing a heme group that can bind oxygen.
• When one heme group binds oxygen, it changes the conformation of the hemoglobin molecule, making it easier for the remaining heme groups to bind oxygen. This cooperative binding results in the sigmoidal shape of the oxygen dissociation curve.
• The oxygen dissociation curve can also be affected by factors such as pH, temperature, and the presence of certain molecules such as carbon dioxide and 2,3-bisphosphoglycerate (2,3-BPG).
• For example, an increase in acidity (decrease in pH) or an increase in temperature shifts the curve to the right, indicating that hemoglobin releases oxygen more readily.
• This is known as the Bohr effect, and it allows for increased oxygen delivery to metabolically active tissues.

Explanation:

• The oxygen dissociation curve is a graph that shows the relationship between the partial pressure of oxygen and the saturation of hemoglobin with oxygen.
• When oxygen binds to hemoglobin, it causes a conformational change in the protein, making it easier for additional oxygen molecules to bind.
• This is called cooperative binding, and it is responsible for the sigmoidal shape of the oxygen dissociation curve. In the absence of oxygen, hemoglobin adopts a T-state or tense state, which has a lower affinity for oxygen.
• However, when oxygen binds to one of the heme groups, it triggers a conformational change in the hemoglobin molecule, which increases the affinity of the remaining heme groups for oxygen.
• This conformational change involves a shift from the T-state to the R-state or relaxed state, which is more favorable for oxygen binding.
• Therefore, the interactions between globin subunits are altered when O2 binds with deoxyhemoglobin.
• The quaternary structure of hemoglobin and the T-configuration are important determinants of its affinity for O2.

Concept:

• Humans are highly aerobic organisms consuming oxygen per metabolic demand.
•  In aerobic respiration, oxygen and pyruvate produce adenosine triphosphate (ATP), producing energy for the whole body.
•  To maintain homeostasis, there needs to be a gradient of pressure within the tissues that pushes oxygen by diffusion from the membranes into the tissues.
•  Many factors influence the amount of dissolved oxygen present within the cells and tissues one of them is  higher altitude

​Graph 1: Partial Oxygen pressure v/s haemoglobin saturation​

• At higher altitudes, the air becomes thinner and the amount of breathable oxygen decreases.
• The lower barometric pressures of high altitudes lead to a lower partial pressure of oxygen in the alveoli, or air sacs in the lungs, which in turn decreases the amount of oxygen absorbed from the alveoli by red blood cells for transport to the body’s tissues.
• The resulting insufficiency of oxygen in the arterial blood supply causes the characteristic symptoms of altitude sickness.
• Also elevated erythropoietin (EPO) production in hypoxia is a key factor in the achievement of enhanced hematological variables.
• The level of the EPO increase and acceleration of erythropoiesis depend on the duration of exposure and degree of hypoxia.

The correct answer is Option 1 i.e. A,B and C

Concept:

• Due to the fluid link between the parietal and visceral pleura and the parietal pleura's attachment to the body wall and diaphragm, there is intrapleural pressure within the pleural cavity.
• Similar to intra-alveolar pressure, intrapleural pressure varies throughout the various breathing phases.
• The intrapleural pressure, however, is always lower than or opposite the intra-alveolar pressure due to particular features of the lungs (and therefore also to atmospheric pressure).
• Intrapleural pressure changes during inspiration and expiration but remains constant at about -4 mm Hg throughout the breathing cycle.
• The negative intrapleural pressure is created by opposing forces within the thorax.
• The elasticity of the lungs themselves is one of these forces; elastic tissue pulls the lungs inward and away from the thoracic wall.
• The majority-water alveolar fluid's surface tension also causes the lung tissue to draw inward.
• The pleural fluid and thoracic wall exert opposing forces to balance this internal lung tension.
• Lungs are pulled outward by surface tension within the pleural cavity.
• The development of negative intrapleural pressure would be hampered by too much or too little pleural fluid, so the lymphatic system and mesothelial cells must carefully monitor and drain the level.
•  The size of the lungs is determined by transpulmonary pressure, which is the difference between intrapleural and intra-alveolar pressures. A bigger lung is associated with higher transpulmonary pressure.

Explanation:

Statement A:- CORRECT

• The outward rebound of the chest wall counteracts the lung's propensity to fold inward at the conclusion of exhalation, creating a negative (subatmospheric) intrapleural pressure.

Statement B:- CORRECT

• The diaphragm and the inspiratory intercostal muscles actively contract during inspiration, which causes the thorax to expand. The intrapleural pressure increases in subatmospheric or negative terms from its normal resting value of -4 mmHg.

Statement C:- CORRECT

• Intrapleural pressure decreases during inspiration, which results in a reduction in intrathoracic airway pressure and airflow from the glottis into the lung's gas exchange zone.
• The pleural fluid's adhesive force causes the lungs to flex and expand in response to the thoracic cavity's expansion. A pressure that is lower than atmospheric pressure results from this increase in volume and a drop in intra-alveolar pressure.

Statement D:- INCORRECT

• The external intercostal muscles and diaphragm relax during expiration, reducing the size of the thoracic cavity. The transpulmonary pressure drops, the intrapleural pressure becomes less negative, and the lungs passively contract.

Statement E:- INCORRECT

• Intrapleural pressure decreases during inspiration, which results in a reduction in intrathoracic airway pressure
• The diaphragm is forced upward during active expiration, and as a result, the pleural pressure that results may rise. Positive pleural pressure has the potential to momentarily compress the bronchi and restrict airflow.

Therefore, the correct answer is A, B, and C

The correct answer is Option 2 i.e. B and C

Concept:

• The spleen is the largest secondary lymphoid organ that plays a crucial role in the RBCs life cycle. 
• In the spleen, senescence RBCs are engulfed by the macrophages.
• Hemoglobin is the most prominent protein present in RBCs. 
• Hemoglobin is a heterotetramer consisting of two α-chains and two β- chains. 
• Each chain is bound to a heme group. 
• Each heme group contains one iron molecule that can bind to one oxygen molecule, so each hemoglobin molecule can bind and transport 4 molecules of oxygen. 
• Heme and globin synthesis need to be balanced.
• Heme-regulated kinase (HKI) plays an important role in creating this balance, this in turn is regulated by intracellular heme concentration.
• HKI have four binding sites for heme, out of which two are constantly occupied, but when the concentration of heme increases, then two heme groups bind to the remaining two sites rendering HKI inactive. 
• This causes an increase in the synthesis of globin protein so that more hemoglobin is produced. 
• When the concentration of heme is low, then two sites are vacant and HKI autophosphorylates and becomes active.
• Activated HKI in turn phosphorylates eIF2α, then inhibit globin chain synthesis. 
• The hemoglobin is degraded to form globin protein and heme.
• Globin protein is recycled as amino acids while heme is broken down further.

Explanation:

• Heme oxygenase (HO) is a rate-limiting enzyme involved in the breaking down heme tetrapyrrole ring.
• In the presence of NADPH and three oxygen molecules, heme oxygenase catalyses the oxidative cleavage of heme molecule to produce biliverdin, one molecule of carbon monoxide and ferrous iron (Fe²⁺).
• In the next reaction, biliverdin is converted to bilirubin by the cytosolic enzyme biliverdin reductase (BVR). 
• So, statements 'B' and 'C' are correct.

Hence, the correct answer is Option 2. 

The correct answer is Option 2 i.e.Curve A

Key Points

​Haemoglobin Oxygen dissociation curve

• The hemoglobin's oxygen saturation is correlated with a range of oxygen pressures using the oxygen-hemoglobin dissociation curve.
• The oxygen transport to tissues may be impacted by factors that change the curve; these effects are especially notable at low oxygen partial pressures:
• Left shift: Under conditions that cause the curve to shift to the left (dashed red line), hemoglobin becomes more oxygen-affine and, at a given arterial oxygen pressure, distributes less oxygen to the tissues. The ability to transport oxygen from the maternal to the fetal circulation is made possible by the left-shifted Hb F curve.
• Right shift: Under conditions that cause the curve to shift to the right (dashed blue line), hemoglobin has a lower oxygen affinity and can carry more oxygen to the tissues at a given arterial oxygen pressure.

Explanation:

• Due to an increase in pH and a decrease in H+ ions, affinity will increase, and when the affinity increases the curve shifts to left.

Hence, the correct answer is Option 2.