What are some examples of organs and tissues where mitosis occurs regularly? what are some of the tissues where mitosis is practically absent? why the discrepancy?

There are many organs in our body. Some examples for organs are heart, brain, lungs, kidneys, stomach, liver, pancreas,  oesophagus , intestine, sense organs like eyes, ears, skin, tongue, nose.  

There are four main types of tissue: muscle, epithelial, connective and nervous. Each is made of specialized cells that are grouped together according to structure and function. Muscle is found throughout the body and even includes organs such as the heart. Our outer layer of skin is epithelial tissue

.Actually the greatest mitosis occurs in the epithelium. Epithelium can include the lining of your GI or even the skin. For example, the skin is the largest organ in the human body and almost all of it is exposed to the environment, which makes it more susceptible to rubs, aberrations, and wounds. The skin has to replenish this by making more skin cells at a higher rate.  

The slowest mitosis occurs in the nervous system. Nerve cells almost never multiply which is why it is difficult to heal once you have an injury involving the Nervous system.

Generally, in vertebrates, mitosis is more frequent in tissues that require frequent renewal due to their function, such as epithelial tissues and bone marrow.  In some adult tissues, mitosis is almost absent, such as in the nervous tissue and striated muscle tissue (skeletal and cardiac).