Earlier in this lesson we have considered the basic principles of the endocrine system. As we consider the different systems of the human body later this semester and throughout second semester we will see how important a role the endocrine system plays in controlling them. In this respect our study of the endocrine will be ongoing and integrated into the study of the other body systems. However it might be useful at this juncture to reflect on some of the fundamental principles of endocrine control by looking at a body function almost entirely regulated by hormones.
In absolute terms the maximum size that a person can attain is determined by their genes and is consequently predetermined at birth. To what extent this size is attained depends upon a whole range of variables including the availability of amino acids for for protein synthesis, calcium for bone growth and energy for all cellular processes.
Not surprisingly the regulation of growth is a very complex process but it is one that is almost entirely controlled by the endocrine system. For this reason it is a useful system to illustrate some of the ways in which the endocrine system functions.
In humans growth is a progressive process from birth to adulthood but as shown in the graph opposite, growth is characterised by periods of accelerated growth during infancy and again at puberty.
Growth involves two distinct but integrated mechanisms:
- Longitudinal Growth - the lengthening of somatic tissues such as bone, muscle and tendons.
- RRadial Growth - the increase in diameter of these somatic tissues as well as other organs.
Growth also involves two specific cellular processes:
- Hyperplasia - the increase in the number of cells.
- Hypertrophy - an increase in the size of cells.
A large number of hormones work cooperatively to regulate growth during different stages of human development. However in this lesson we will focus on growth hormone.