Organization of the Endocrine System Flashcards
Four categories of the endocrine system
Peripheral Substrate-Regulated Systems
Hormone Negative Feedback-Regulated Systems
Hormone Positive Feedback-Regulated Systems
Hypothalamic-Pituitary Neuroendocrine Reflex Systems
What is the Peripheral Substrate-Regulated System
Monitoring of substrate is done by the endocrine gland that secretes the hormone
Regulation of hormone secretion occurs independent of the central nervous system
Examples: regulation of plasma glucose concentrations by insulin and glucagon; plasma calcium concentrations by parathyroid hormone (PTH), calcitonin and vitamin D; and plasma sodium and potassium concentrations by aldosterone
What is the Hormone Negative Feedback-Regulated System
Neurosecretory neurons located in the hypothalamus secrete releasing neuropeptides into the hypophysial portal blood that stimulate the secretion of trophic hormones from the anterior pituitary which stimulate the secretion of hormones from peripheral endocrine glands.
Peripheral hormones feedback to inhibit the secretion of hypothalamic stimulatory neuropeptides and decrease the responsiveness of anterior pituitary to these neuropeptides.
Hormone secretion oscillates around a mean, but can be overridden by higher central nervous system centers to cause rhythmic or phasic secretion.
Examples: secretion of cortisol from the adrenal cortex; thyroxine from the thyroid gland; estrogen and progesterone from the ovary; testosterone from the testes
What is the Hormone Positive Feedback-Regulated System
No peripheral gland involvement as the peripherally active hormone is secreted from the anterior or posterior pituitary gland
Anterior pituitary hormone secretion is controlled by both stimulatory and inhibitory hypothalamic neurohormones; inhibition is dominant
What is the Hypothalamic-Pituitary Neuroendocrine Reflex System
Posterior pituitary hormones are released from hypothalamic magnocellular neurons directly into peripheral circulation in response to direct neural stimulation
Examples: anterior pituitary secretion of prolactin and growth hormone; posterior pituitary secretion of oxytocin and vasopressin (aka antidiuretic hormone)
