What are the reasons for not increase in height

There could a number of reasons why an individual has stagnation on growth or sometimes there's a no growth in height at all.
Factors could be:
1. Genetics
2. Physiopathology
3. Environmental

Heredity has a part to play in every individual growth and overall progress. Genes almost are an encrypted database that shapes, form and structure who we are, even in intelliegence, attitudes, personality traits and drives, mostly.
Physiopathology could be that the hypothalamus is damaged since it is responsible for the growth factor of the organism.
Environment can be the surroundings of the organsm. 

Dis the answer hopefully

Small intestine because that is the organ which absorbs nutrients