The Hypothalamic Pituitary Axis and Adrenal Gland Physiology

The Hypothalamic Pituitary Axis

Release of hypothalamic signals is regulated by afferent signals from other brain regions, from visceral afferents, and by circulating levels of substrates and hormones

Posterior Pituitary

is where hypothalamic neurons end & release substrate

Releasing Hormone/Factors

the cells that get released from hypothetical neurons into the blood supply

• target the anterior pituitary

• short lived

• CRH, TRH, GHRH, GnRH

Anterior Pituitary

• individual cells communicating with other cells within the anterior

• chemical signals

• GH - 50%

Posterior Hormones

ADH, Oxytocin

Trophic Hormones

• not biologically active

• will target additional end structure

• ACTH = adrenal gland

• TSH = thyroid gland

• LH, FSH = Testes . Ovaries

Hormones

growth hormone, prolactin

Neurons

synthesizing trophic neurohormones release them into capillaries of the portal system

Portal Veins

carry the trophic neurohormones directly to the anterior pituitary, where they act on the endocrine cells

Endocrine Cells

release their peptide hormones into the second set of capillaries for distribution to the rest of the body

In complex endocrine pathways

• the hormones of the pathway serve as negative feedback signals

• short loop negative feedback occurs with prolactin, growth hormone, and ACTH

Control Pathway for Cortisol Secretion

• cortisol is a steroid hormone secreted by the adrenal cortex

• ACTH , CRH

Adrenal cortex

receives stimulation from the hypothalamic-pituitary axis via the release of CRH and ACTH

Adrenal medulla

receives stimulation from preganglionic sympathetic neurons that activate chromaffin cells (modified postganglionic sympathetic organ)

Circadian Rhythm

dictates cortisol release

• highest in the morning

• chronic & acute stressors produce cortisol release

pro hormone

pituitary stimulation by CRH results in the formation of a ____ that needs to be post-translationally processed

post-translation products

release of ACTH into the blood is concomitant with the release of ___

Cortisol

• liver - gluconeogensis

  • make new glucose

• muscle - protein catabolism

  • breakdown of muscle to release amino acids for energy

• adipose tissue - lipolysis

  • break down of triglycerides into units that can be used for energy

Primary Hypersecretion due to Problem with Adrenal Cortex

• conditions happens because the end target gland is producing to much cortisol

• tumor in the adrenal tissue

Secondary Hypersecretion Due to Pituitary Problem

• pituitary gland is hyper secreting ACTH and as a result hyper secreting of cortisol

• tumors in pituitary and secrete ACTH

• skin color change

Tertiary Hypersecretion due to hypothalamic problem

• when the issue starts in the hypothalamus

• hyper secreting tumors that produce CRH

Increased Cortisol Release: Hypercortisolism

• Excess gluconeogenesis mimics conditions of hyperglycemia (e.g. diabetes)

• Excess muscle tissue breakdown and lipolysis result in muscle wasting

• Fat deposition in trunk and face

• Mood changes, including depression and difficulty with memory

Decreased Cortisol Release: Hypocortisolism

• Primary hypocortisolism resulting from autoimmune destruction of the adrenal cortex

• Lack of hormone feedback results in increased ACTH

• Presents with hypoglycemia, hypotension, and hyperpigmentation