Which endocrine gland is not ectodermal in origin?

Which of the following glands is responsible for immunity in humans?

What will happen if the thymus gland is injured in a child?

The thymus gland is a lobular structure located on the $A$ side of the aorta and plays a significant role in the development of the $B$ system.
Choose the correct combination of $A$ and $B$.

If the thymus gland of a newborn child is removed by surgery,which of the following will it fail to produce?

Old people have a weak immune system. What could be the reason?