. What is correct regarding leucocytes ?
(a) These can squeeze out through (can cross) the capillary walls
(b) These are enucleate
(c) Sudden fall in their number indicates cancer
(d) These are produced in thymus
Sol.The great majority of T and B lymphocytes continuously circulate between the blood and lymph. These leave the blood stream, squeezing out between specialized endothelial cuts found in certain small vessels and enter various tissues including all the lymph nodes. After percolating through a tissue, these accumulate in small lymphatic vessels which connect to a series of lymph nodes, from where they ultimately enter the main lymphatic vessel (thoracic duct) which carries them back into the blood.