Body Fluids and Circulation Test - 62

Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart. The P- wave represents the electrical excitation or depolarization of the atria. The QRS complex represents the depolarization of the ventricles which initiates the ventricular contraction.
The contraction starts shortly after Q and marks the beginning of the systole.
The T- wave represents the return of the ventricles from excited to a normal state or repolarization. The end of the T-wave marks the end of systole.
So, the correct option is 'It shows complete blockage and there is no synchrony between atrial and ventricular activities'.

Mature erythrocytes are the only cells which lack a nucleus. They are enucleated. Mature erythrocytes do not have cellular organelles like mitochondria, Golgi apparatus, ribosomes and endoplasmic reticulum in order to accommodate maximum space for haemoglobin. They also do not possess DNA and hence cannot synthesize RNA.

There is no correlation between cell size and body size. A larger body size is due to the presence of more cells and not due to cells of bigger size. So, the size of the RBCs in an elephant and a mouse will remain the same. But, their number may vary.

Willem Einthoven (21 May 1860 – 29 September 1927) was a Dutch doctor and physiologist. He invented the first practical electrocardiogram (ECG or EKG) in 1903 and received the Nobel Prize in Medicine in 1924 for it ("for the discovery of the mechanism of the electrocardiogram"). Before Einthoven's time, it was known that the beating of the heart produced electrical currents, but the instruments of the time could not accurately measure this phenomenon without placing electrodes directly on the heart. Beginning in 1901, Einthoven completed a series of prototypes of a string galvanometer. This device used a very thin filament of conductive wire passing between very strong magnets. When a current passed through the filament, the magnetic field created by the current would cause the string to move. A light shining on the string would cast a shadow on a moving roll of photographic paper, thus forming a continuous curve showing the movement of the string. This device increased the sensitivity of the standard galvanometer so that the electrical activity of the heart could be measured despite the insulation of flesh and bones.

 Jan Swammerdam was a Dutch biologist and microscopist. He was the first to observe and describe RBCs in 1658.

Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium.

The number of RBCs per cubic millimetre of blood is likely to be higher in people living at high altitudes. This is in response to the air being less dense at high altitudes.  Thus, more RBCs (haemoglobin) are needed to absorb the required amount of $$O_{2}$$ from the air.

Immunocomplexes also called antigen-antibody complexes are harmful and long deposition of then inside the cell can lead to various autoimmune disorders and primarily removed from the cell by phagocytosis in which eosinophils and monocytes (destruction of antibody)  have an important role to play.