Lenbury, Pacheenburawana, 1991

Model Structure

Biological systems often display periodicity and oscillatory behaviour. Several studies have described the fluctuations in plasma corticosteroid levels in humans. Through these investigations it has become clear that although many hormones cycle smoothly through circadian rhythms, on a shorter timescale their levels can experience much sharper changes; especially during the latter half of sleep. These secretory bursts during the early morning sleep period are a biological reality rather than a sampling artifact.

The corticotropin-releasing hormone (CRH) is synthesised in the hypothalamus and is carried to the anterior pituitary gland where it stimulates cells to produce adrenocorticotrophic hormone (ACTH). In turn, ACTH stimulates the synthesis and secretion of cortisol (F). Cortisol exerts a negative feedback effect on the ACTH secretion in the pituitary and also suppresses CRH synthesis in the hypothalamus. In addition, there is also a negative feedback effect of ACTH on the secretion of CRH. Therefore the entire process can be thought of as a self-regulating system, as summarised in the figure below).

The current CellML file describes a mathematical model of this self-regulating system, published by Lenbury et al. (1991). The complete original paper reference is cited below:

Modelling fluctuation phenomena in the plasma cortisol secretion system in normal man., Yongwimon Lenbury and Pariwatana Pacheenburawana, 1991, BioSystems , 26, 117-125. (A PDF version of the article is available to journal subscribers on the BioSystems website.) PubMed ID: 1668715

Schematic diagram of the self-regulatory system for corticol secretion. CRH represents corticotropin-releasing hormone, ACTH is adrenocorticotropic hormone, and F represents cortisol. The red lines represent positive feedback pathways, while the blue lines represent negative feedback loops.