Biology Reference
In-Depth Information
equally spaced in time). For example, data may be collected every 10
minutes or every hour, because equally spaced data points are perceived
as best for capturing the dynamic nature of the secretion processes. This
procedure, however, may be too restrictive at times, and it is also
common for data points to be taken at times not separated by intervals of
equal length. In describing mathematical methods, we shall be careful to
separate those requiring time series data from those that do not. The
latter class of methods is certainly more general.
Throughout the chapter, we use two sets of actual hormone
concentration data sets, one for luteinizing hormone (LH) and one for
growth hormone (GH, also called somatotropin). These are then
examined using several analytical approaches. Software and
documentation for many of these algorithms can be downloaded from
Dr. Michael Johnson's site at the University of Virginia (see Internet
Resources at the end of this chapter).
I. INTRODUCTION
The endocrine system consists of endocrine glands and the hormones
they secrete. Hormones reach their target cells by traveling through the
bloodstream. Figure 9-2 shows the location of the major endocrine
glands of the human body.
The pituitary gland, often called the ''master gland,'' is located at the
base of the brain. It receives signals from the hypothalamus, a
neurosecretory region of the brain. Figure 9-3 shows the positional
relationship of the pituitary and hypothalamus. The hypothalamus
enables communication between the nervous system and the endocrine
system by producing releasing hormones and inhibiting hormones
that act on the anterior pituitary. It also produces two hypothalamic
hormones that are stored in, and released from, the posterior pituitary.
Acting under this hypothalamic control, the anterior pituitary in
turn produces hormones that themselves stimulate other endocrine
glands.
The term hormone was originally applied to chemical substances secreted
by endocrine glands and transported in the bloodstream to regulate the
activity of distant target organs. This is the classical endocrine action.
However, there are many other cell-signaling substances not produced
by endocrine glands that have similar effects. Examples include the
insulin-like growth factor type I (IGF-I) secreted by the liver; the
histamines released by mast cells in response to injury, infection, or
allergy; and the releasing hormones secreted by the hypothalamus.
These other forms of chemical communication are called autocrine,
paracrine, and neuroendocrine regulation, and are now generally
grouped under the heading of endocrine signaling. Autocrine action
occurs when a cell both secretes and has receptors for a regulatory
