Endocrinology Quiz: Hormones and Pancreas Functions

Endocrinology

• The study of hormone secretion, hormone action, and feedback control
• Involves the endocrine system which secretes hormones directly into the bloodstream
• Endocrine system is evaluated by measuring hormone concentrations
• Exocrine glands secrete other substances through a duct

Pancreas

• Has both exocrine and endocrine functions
• Exocrine enzymes include proteases, lipases, and amylase
• Endocrine hormones include insulin (beta cells) and glucagon (alpha cells)
• Islets of Langerhans are regions of the pancreas containing endocrine cells

Hormones

• Derived from the Greek term “to set in motion”
• Dynamic in nature and elicit cellular responses by regulating physiological processes through feedback mechanisms
• Cholesterol is a precursor for many steroid hormones like estrogen, testosterone, and progesterone.

Mechanisms of Hormone Release

• Humoral: In response to changing levels of ions or nutrients in the blood (e.g. insulin)
• Neural: Stimulation by nerves (e.g. oxytocin, ADH - hypothalamus)
• Hormonal: Stimulation received from other hormones (e.g. hypothalamic-pituitary axis)

Neuroendocrine system & Neurohormones

• Mechanism by which the hypothalamus maintains homeostasis by regulating reproduction, metabolism, eating behavior, drinking behavior, energy utilization, osmolarity and blood pressure.
• Hypothalamus regulates pituitary functions
• Hypothalamus secretes releasing hormones and inhibiting hormones into the anterior pituitary gland
• Secretory activity of endocrine glands (pituitary, thyroid, adrenal and gonads) is controlled by the nervous system
• Neurohormones are produced by specialized neurosecretory cells of the nervous system (e.g. oxytocin and vasopressin - neurohypophysial hormones)

Neurotransmitters vs Neurohormones

• Neurotransmitters act locally, within synapses, and often have a rapid, short-lived effect.
• Neurohormones are secreted into the bloodstream and have a more widespread and lasting effect.

Master Regulator - Pituitary gland

• Anterior pituitary - responsible for the synthesis and secretion of many hormones
• Posterior pituitary - stores and releases hormones produced by the hypothalamus

Hypothalamic-pituitary axis

• HPT (Hypothalamic-Pituitary-Thyroid) axis
• HPG (Hypothalamic-Pituitary-Gonad) axis
• HPA (Hypothalamic-Pituitary-Adrenal) axis

Hypothalamus role

• Controls many fundamental physiological activities like body temperature, hunger, thirst, sleep and some ANS functions
• The interface between the endocrine and the nervous systems – it receives nerve fibres from nearly all areas of the brain
• Synthesizes and releases neurohormones directly into the circulation via the posterior pituitary
• Synthesizes and releases hypophysiotropic hormones (releasing hormones) into the hypophyseal portal blood system to regulate hormone release from the anterior pituitary
• Sends neural signals to regulate the release of sympathetic nervous system hormones from the adrenal medulla

Hypothalamic Releasing and Inhibiting hormones

• Releasing hormones:
  • CRH (Corticotropn releasing Hormone) - stimulates the release of ACTH
  • TRH (Thyrotropin-Releasing Hormone) - stimulates the release of TSH
  • GnRH (Gonadotropin-Releasing Hormone) - stimulates the release of FSH & LH
  • GHRH(Growth Hormone Releasing Hormone) - stimulates the release of GH
• Inhibiting hormones:
  • MIH (melanotropin-inhibiting hormone) - inhibits the secretion of MSH.
  • Dopamine - inhibits the secretion of PRL
  • SRIF (Somatostatin Release Inhibiting Factor) - inhibits the secretion of STH