Introduction to Endocrinology 2

Flashcards testing core concepts of endocrine systems, hormone receptor classifications, transport, metabolism, and neuroendocrine regulation based on lecture slides.

How is Tamoxifen classified based on its ligand type and receptor responses in the provided figure?

Tamoxifen is classified as a mixed agonist-mixed antagonist because it acts as an antagonist at the estrogen response element (ERE) and an agonist at AP1.

What is the structural difference between System I and System II regulation of endocrine gland function?

System I involves CNS input, hypothalamic releasing hormones, pituitary tropic hormones, and target gland feedback, whereas System II involves direct inputs onto a free-standing endocrine gland without hypothalamic-pituitary intermediate hormones.

How does plasma protein binding affect hormone availability in proximal versus distal tissue regions as depicted in the diagram?

Unbound (free) hormone is entirely available for immediate uptake by proximal tissue, while bound hormone dissociates gradually to release free hormone as blood flows to more distal tissue regions.

Which specific hypothalamic nuclei belong to the anterior (supraoptic) region in the provided anatomical diagram?

The paraventricular nucleus, medial preoptic nucleus, anterior nucleus, suprachiasmatic nucleus, and supraoptic nucleus.

Which neural tract connects the magnocellular portions of the paraventricular and supraoptic nuclei to the posterior pituitary?

The supraoptico-hypophysial tract.

What are the primary target tissues and physiological effects of the posterior pituitary hormones shown in the diagram?

ADH targets the kidney to promote water retention, and Oxytocin targets the uterus for uterine contractions and the breast for milk letdown.

How do thyroid hormone and retinoic acid receptors differ from the traditional view of nuclear receptor activation?

Unlike traditional receptors that require hormone activation, thyroid hormone and retinoic acid receptors bind to DNA in the absence of ligand and actively repress transcription of nearby genes.

How can two different hormones promote the exact same effect, such as glycogen deposition, in target cells?

Two hormones can promote the same physiological effect by interacting with different receptors; for instance, both glucocorticoids and insulin promote glycogen deposition via distinct receptors.

Why is the plant estrogen genistein considered a partial agonist-partial antagonist?

Genistein blocks the binding of a full estrogen receptor agonist and depresses receptor activity to the level induced by the partial agonist alone.

How does the synthesis of thyroid hormones and steroid hormones differ from standard peptide hormone production?

Thyroid hormones are synthesized by iodination and coupling of tyrosine residues of thyroglobulin, whereas steroid hormones are produced from cholesterol.

Which peptide hormones are exceptions to the general rule that circulating peptide hormones are unbound to plasma proteins?

Growth hormone (GH), IGF-I, IGF-II (bound to IGF-binding proteins), and vasopressin and oxytocin (bound to neurophysins).

Why is measuring the free hormone fraction in circulation clinically superior to measuring total hormone levels?

The free hormone fraction is available for receptor binding, dictates feedback inhibition of hormone release, is cleared from circulation, and correlates best with clinical states of hormone excess and deficiency.

What is the primary degradation pathway for circulating peptide hormones, and which organelle provides the degrading enzymes?

Peptide hormones are primarily degraded by binding to cell surface receptors and nonreceptor binding sites, with lysosomes serving as an important source of degrading enzymes.

What two principal enzymatic routes degrade catecholamines, and which metabolites can be measured to assess catecholamine overproduction?

Catecholamines are degraded by Catechol-O-methyltransferase (COMT) and Monoamine oxidase (MAO). Evaluated metabolites include normetanephrine, metanephrine, and vanillylmandelic acid (VMA).

What are the two major mechanisms governing the relationship between the nervous and endocrine systems?

1. Neurosecretion (neurons secreting hormones directly into general circulation or hypophysial portal vessels). 2. Direct autonomic innervation of endocrine tissues (coupling central nervous system signals to hormone release in tissues like the adrenal medulla, parathyroid gland, and pancreatic islets).

Which hypothalamic releasing hormone is capable of stimulating the release of both TSH and prolactin?

Thyrotropin-releasing hormone (TRH).

Which bioactive amines and neuropeptides specifically influence prolactin release from the anterior pituitary?

Dopamine regulates prolactin release, while VIP, Substance P, and Neurotensin stimulate or affect prolactin release.

How do stress and systemic illness differentially affect anterior pituitary hormone release?

Stress increases the release of ACTH, growth hormone, and prolactin, whereas systemic illness suppresses the hypothalamic-pituitary-thyroid axis and the release of gonadotropins.

Which specific cytokines and peripheral factors act to increase or stimulate CRH and ACTH release?

Interleukin-1 (IL-1), Interleukin-2 (IL-2), epinephrine, Angiotensin II, cholecystokinin, and oxytocin.