BIOD27H3 Lecture : Textbook notes-Chapter 23-The Hypothalamic-Pituitary Control System
11 Aug 2010
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Chapter 23
The Hypothalamic-Pituitary control system
-Several hormones are controlled by hypothalamic and anterior pituitary trophic hormones
Feedback patterns
-the negative feedback signal for simple endocrine pathways is the systemic response to the
hormone
Hormone receptors
-hormone receptors may be on the cell surface or inside the cell
Cellular responses
-in general hormone target cells respond by altering existing proteins or by making new
proteins
-the historical distinctions between the actions of peptide and steroid hormones are no longer
valid (some steroid hormones have receptors on the cell surface)
Magnitude of target cells response
-the amount of active hormone available to the cell and the number/activity of target cell
receptors determine the magnitude of target cell response
Endocrine Pathologies
-endocrine pathologies result from
x excess hormone secretion
x inadequate hormone secretion
x abnormal target cell response
x failure of target cell response
ADRENAL GLUCOCORTICOIDS
x Adrenal medulla occupies over a quarter of the inner mass while adrenal cortex occupies
three quarters of the gland and secretes steroid hormones
The Adrenal Cortex Secretes Steroid Hormones
-The three major types of steroid hormones secreted are
x Mineralocorticoids (e.g. aldosterone, which effects sodium and potassium)
x Glucocorticoids (e.g. cortisol)
x Sex Hormones
-All steroid hormones begin with cholesterol, which is modified by multiple enzymes to end up as
aldosterone, glucocorticoids or sex steroids (androgens or estrogens/progesterone)
-The pathways are the same in the adrenal cortex, gonads, and placenta; what differs is the
enzyme distribution
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-Because of structural similarities, steroid hormones can have crossover effects in which one
steroid hormone binds to a receptor of a related molecule; can lead to endocrine disorders
Cortisol Secretion Is Controlled by ACTH
-The control pathway for cortisol secretion is known as the hypothalamic-pituitary-adrenal
pathway (HPA pathway), which begins with
Hypothalamus secretes Corticotropin-Releasing Hormone (CRH) into the Hypothalamus
Hypophyseal Portal System (HHPS)
Anterior Pituitary is stimulated by CRH and secretes Adrenocorticotropic Hormone (ACTH)
ACTH stimulates the Adrenal Cortex to promote synthesis and release of cortisol, which acts as
a negative feedback signal to inhibit CRH and ACTH release
-Cortisol secretion normally peaks in the morning and diminishes during the night and increases
with stress
-once it diffuses it binds to carrier protein, transcortin, until it reaches the target cell to diffuse
into
Cortisol Is Essential For Life
-Cortisol is essential for life in that an animal will die if exposed to any significant environment
stress; also exerts a protective effect by
x Promoting glucogenesis
x Breakdown of skeletal muscle proteins
x Enhance lipolysis
x Suppressing the immune system
x Causing negative calcium balance through loss of calcium from the bones and kidneys
x Influencing brain function through mood changes
Cortisol Is a Useful Therapeutic Drug
-Cortisol suppresses the immune system by preventing cytokine release and antibody
production against inflammatory response; useful in treating various allergies and rejection of
transplanted organs
-exogenous administration of glucocorticoid has a negative feedback effect on the anterior
pituitary and may shut down ACTH production, causing atrophy
Cortisol Pathologies Result From Too Much or Too Little Hormone
-Hypercortisolism is excess cortisol in the body arising from hormone secreting tumors or
exogenous administration of the hormone; causing µZ]vP[Çv}u
-hypercortisolism mimics diabetes in increasing blood glucose, excess cortisol deposits, mania
and depression and increased appetite
-The three common causes of hypercortisolism are
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