Hormones

How does negative feedback for hormones work?

• as the concentration of a circulating hormone decreases, the secretion of the corresponding hormone increases

• inversely, as the concentration of a circulating hormone increases, secretion of the corresponding hormone (like a pituitary hormone) decreases

The half-life for many hormones varies. What is half-life?

the time required for the concentration of a hormone in the bloodstream to reduce to half its original value

What happens to hormones when they are no longer needed?

• they are metabolized into components that can be used for other purposes

• or they are excreted

hypothalamic hormones are regulated by:

pituitary hormones or signals from target organs

List 7 hormones that are secreted from the hypothalamus

• RELEASING AND INHIBITING HORMONES

• corticotropin-releasing hormone (CRH)

• thyrotropin-releasing hormone (TRH)

• gonadotropin-releasing hormone (GnRH)

• growth hormone-releasing hormone (GHRH)

• growth hormone-inhibiting hormone (GHIH)

• prolactin-releasing hormone (PRH)

• prolactin-inhibiting hormone (PIH)

antidiuretic hormone (ADH)

• secreted by the posterior pituitary gland

• helps regulate water balance

• stimulated by increased plasma osmolality

• targets the collecting ducts in the nephrons

• increased hydration = low ADH = increased water excretion

• decreased hydration = high ADH = decreased water excretion

oxytocin

• secreted by the posterior pituitary gland

• stimulates uterine contractions and lactation

How is growth hormone released and how is it regulated?

• hypothalamus releases growth hormone-releasing hormone

• posterior pituitary gland releases growth hormone into the bloodstream

• the hypothalamus can inhibit the release of growth hormone by releasing growth hormone-inhibiting hormone

functions of growth hormone

• promote growth of bone and body tissues

• stimulate protein synthesis

• affect fat and carb metabolism

In what instances is growth hormone increased and decreased?

• increased

  • in children

  • in patients with gigantism or acromegaly (abnormal enlargement of extremities in adults)

• decreased

  • dwarfism

adrenocorticotropic hormone (ACTH)

• regulates the activity of the adrenal cortex of the adrenal glands

• stimulates steroid hormone synthesis, like cortisol

How does adrenocorticotropic hormone affect the body’s metabolism?

• by producing cortisol

  • cortisol increases plasma glucose, increases cell permeability to glucose, and increases fatty acid metabolism (gluconeogenesis)

What is the cascade of effects that occurs when there is low cortisol in circulation? (3 steps)

• the hypothalamus releases corticotropin-releasing hormone (CRH)

• CRH stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH)

• ACTH stimulates the adrenal cortex to release cortisol

Causes of increased ACTH

• stress

• Addison’s Disease (Primary Adrenal Insufficiency)

  • autoimmune or due to adrenal damage

  • no cortisol is produced, but excess ACTH is released

  • may cause adrenal hyperplasia (cells of the adrenal cortex increase in response to ACTH)

Causes of decreased ACTH

• hypopituitarism

• adrenal carcinoma