Respiration and Gas Transport

CO combines with haemoglobin to form carboxyhaemoglobin.

Sickle cell disease (sickle cell anemia) causes red blood cells to assume a sickle shape due to abnormal hemoglobin S. These misshapen, rigid cells have reduced oxygen-carrying capacity and block blood vessels, causing tissue hypoxia. Hemophilia impairs clotting, thrombocytopenia reduces platelet count, and 'blood transfusion' is a procedure, not a disease.

Mammalian erythrocytes are non-nucleated cells in their mature form. They have nuclei during early phases of erythropoiesis, but extrude them during development as they mature in order to provide more space for haemoglobin. The colour of erythrocytes is due to the heme group of haemoglobin.

Hemoglobin has the highest affinity for carbon monoxide (CO), binding it approximately 200-250 times more strongly than oxygen. This is why CO poisoning is so dangerous - it displaces oxygen from hemoglobin and prevents oxygen transport to tissues.

CO₂ is the cellular waste that needs to be excreted out by the cell. It accumulates in high concentrations inside the cell. In the cell’s external environment, the concentration of CO₂ is low as compared to that inside the cell. As soon as there is a difference of concentration of CO₂ inside and outside a cell, CO₂ moves out of the cell, from a region of high concentration to a region of low concentration outside the cell by the process of diffusion. Thus, this is the correct answer.  

The Hamburger phenomenon (or Hamburger shift) refers to the chloride shift in red blood cells during CO2 transport. When CO2 enters blood, bicarbonate ions move out and chloride ions move in to maintain electrical neutrality, facilitating CO2 transport from tissues to lungs.

Ketamine is unique among anesthetic agents in that it increases cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow. This occurs because ketamine is a dissociative anesthetic that maintains or even stimulates cerebral activity, unlike most other anesthetics which depress cerebral metabolism. Propofol significantly decreases CMRO2 and is used for neuroprotection. Atracurium is a neuromuscular blocker with minimal direct cerebral effects. Fentanyl is an opioid that also decreases CMRO2.

The binding of oxygen to one haemoglobin sub-unit induces conformational changes that are relayed to the other sub-units.

Oxygen binding curve for myoglobin is hyperbolic, which reflects non-cooperative binding.

Insects have a tracheal system, a network of tubes that delivers oxygen directly to body cells without using blood as the transport medium. Spiders and scorpions use different respiratory systems (book lungs/gills).

At high altitudes, lower oxygen pressure stimulates increased erythropoietin production, causing polycythemia - elevated RBC and hemoglobin concentration. This gives skin a rosy appearance. Option A is incorrect because hemoglobin affinity actually decreases (right shift of oxygen dissociation curve) to facilitate oxygen release to tissues. Option C is not the primary physiological adaptation.

Haemoglobin (Hb) is a transport protein that carries oxygen in the blood. It is necessary because oxygen is not very soluble in water - most part of the blood is water. Each Hb is capable of binding a total of 4 oxygen molecules (one molecule per subunit).

Approximately 98.5% of oxygen in blood is bound to hemoglobin, with only about 1.5% dissolved in plasma. This high hemoglobin binding capacity makes red blood cells efficient oxygen transporters.

Each haemoglobin molecule contains four iron-containing heme groups, and each heme can bind one oxygen molecule. Therefore, one haemoglobin molecule carries four oxygen molecules.