Thymus Gland

Structure: 

The thymus is the main lymphoid organ. It is divided into three parts called the subcapsular cortical, the cortical and medullary regions which is located in each lobule and then divided into many other lobules. It is located behind the upper area of the sternum, the cortex tends to be the a higher cellular area whereas the medulla is lower cellular area. In reference to how the cortex is considered a higher cellular area vs the medulla which is a lower cellular area, it get categorized that due to the density level of "T-cells" which stands for Thymocytes  

Function: 

The thymus is important due to it's production of the T-cells mentioned above which help fight against cancer and other infectious diseases, it's also very important for the immune system which needs to be protected in order for successful immune functioning to occur. When a thymus isn't functioning how it's suppose to due to various reasons, it's seen in most cases where someone has an autoimmune disorders like ulcerative colitis and myasthenia gravis.

References/URLS:

https://www.histology.leeds.ac.uk/lymphoid/thymus.php

https://www.kenhub.com/en/library/anatomy/histology-of-the-thymus

https://www.histology.leeds.ac.uk/lymphoid/assets/Thymus_85_2-5x_.gif