EN01 - Endo Intro & GH

What are classical endocrine organs?

Anterior pituitary, adrenals, gonads, thyroid, parathyroid, and endocrine pancreas.

What are non-classical endocrine organs?

CNS (hypothalamus), GI tract, kidneys, heart, liver, and adipose tissue.

What is neural communication?

Cells with long projections release neurotransmitters at synapse with neighboring cells.

What is endocrine communication?

Cells release hormones from glands into interstitial fluid that act on selective receptors in target cells.

What is neuroendocrine communication?

Hormone released from neuron.

What are the three types of hormone action based on location?

Classical endocrine (through bloodstream), paracrine (neighboring cells), and autocrine (same cell).

What defines an exocrine gland?

Secretion into lumen through a duct, mainly along GIT, secretes digestive enzymes.

What defines an endocrine gland?

Secretion out of cell into blood via interstitial fluid, located throughout body, secretes hormones.

What are the types of stimuli regulating endocrine hormone secretion?

Neural (CNS/hypothalamus), hormonal (releasing factors/trophic factors), and non-hormonal (nutrients, ions).

What is a simple feedback loop in endocrine regulation?

Hormone inhibits secretion of its own releasing factor.

What is hierarchical control in endocrine regulation?

Involves more than one gland and feedback occurs at multiple levels.

What are the functions of hormone binding proteins?

Increase solubility, act as a hormone reservoir, and extend hormone half-life.

How do binding proteins affect hormone duration of action?

Bound hormones generally have chronic effects, while free hormones have acute effects.

How can binding protein expression affect hormone action?

Variation of expression of binding proteins can affect hormone actions.

What are peptide/protein hormones?

Hormones secreted in vesicles from specialized cells such as insulin, growth hormone, and ACTH, acting via extracellular receptors.

What are amine hormones?

Hormones derived from amino acids (usually tyrosine), including thyroxine, melatonin, epinephrine, dopamine, and serotonin.

What are eicosanoids?

Hormones derived from fatty acids (arachidonic acid or other PUFA), including prostaglandins, leukotrienes, and endocannabinoids.

What are steroid hormones?

Hormones synthesized from cholesterol such as cortisol, aldosterone, estradiol, and androgens that act via intracellular receptors.

Why is knowing hormone type important?

It helps understand synthesis, duration in body, and types of effects.

What signaling pathways are activated by G protein-coupled receptors?

Activation of cAMP, PLC, PLA2, or inhibition of cAMP.

What signaling pathways are associated with receptor tyrosine kinases?

Activation of cGMP and autophosphorylation or phosphorylation of associated kinases.

What is the mechanism of nuclear hormone receptors?

Transcriptional activation of target genes.

How are peptide hormones processed?

Packaged in ER/Golgi and secreted in granules or vesicles.

What is co-secreted with peptide hormones?

Additional peptide fragments (e.g., insulin and C-peptide).

How are amine hormones synthesized?

From amino acids (tyrosine or tryptophan) depending on enzyme expression.

What enzymes are involved in amine hormone synthesis?

Tyrosine hydroxylase and tryptophan hydroxylase.

Where is PNMT expressed?

Only in the adrenal medulla.

How do amine hormones typically act?

Bind to GPCRs on the surface of target cells.

How are eicosanoids synthesized?

Not stored

synthesized as needed by oxidation of membrane phospholipids.

What stimulates eicosanoid synthesis?

Trauma or cytokines activating phospholipase A2 (PLA2).

What is the precursor to eicosanoids?

Arachidonic acid produced by PLA2.

What enzyme families produce eicosanoids?

Three families including COX.

How are steroid hormones synthesized?

From cholesterol in steroidogenic cells of adrenal cortex and gonads.

What are the sources of cholesterol for steroid synthesis?

Dietary (80%) and de novo (20%).

What determines steroid hormone synthesis pathways?

Specific expression of enzymes in hormone-producing cells.

How do steroid hormones act at the receptor level?

Bind to nuclear receptors that act as DNA-binding transcription factors.

What is the classical effect of steroid hormones?

Transcriptional activation of target genes and translation of new proteins.

What are characteristics of peptide/amine hormone responses?

Use membrane receptors, signal transduction cascades, and act in seconds to minutes.

What are characteristics of steroid hormone responses?

No storage pools, diffuse into cells, act via transcription, and take hours to days.

What structures make up the hypothalamus-pituitary (hypophysis) system?

The hypothalamus and the pituitary gland (anterior and posterior pituitary).

What is the blood supply to the hypothalamus and posterior pituitary?

The hypothalamus and posterior pituitary receive arterial blood.

What happens to hormones released from the posterior pituitary?

Hormones secreted from the posterior pituitary are released into systemic circulation.

What type of blood supply does the anterior pituitary receive?

The anterior pituitary only receives portal blood.

What do hypothalamic neurons secrete to regulate the anterior pituitary?

Releasing factors.

How do hypothalamic releasing factors reach the anterior pituitary?

They travel through the hypothalamic-pituitary portal system.

What is the function of hypothalamic releasing factors?

They regulate the secretion of tropic hormones from anterior pituitary trophic cells.

What hypothalamic hormone stimulates GH release?

Growth hormone-releasing hormone (GHRH).

What anterior pituitary cell type responds to GHRH?

Somatotrophs.

What hormone is released from somatotrophs?

Growth hormone (GH), also called somatotropin.

What is the main effect of GH from the anterior pituitary?

Stimulates IGF-1 production by multiple tissues, especially the liver.

What hypothalamic hormone stimulates TSH release?

Thyrotropin-releasing hormone (TRH).

What anterior pituitary cell type responds to TRH?

Thyrotrophs.

What hormone is released from thyrotrophs?

Thyroid-stimulating hormone (TSH), also called thyrotropin.

What is the target of TSH?

Thyroid follicular cells.

What is the effect of TSH?

Stimulates thyroid hormone production.

What hypothalamic hormone stimulates ACTH release?

Corticotropin-releasing hormone (CRH).

What anterior pituitary cell type responds to CRH?

Corticotrophs.

What hormone is released from corticotrophs?

Adrenocorticotropic hormone (ACTH).

What is the target of ACTH?

Adrenal cortex.

What is the effect of ACTH?

Stimulates glucocorticoid production.

What hypothalamic hormone stimulates LH and FSH release?

Gonadotropin-releasing hormone (GnRH).

What anterior pituitary cell type responds to GnRH?

Gonadotrophs.

What hormone stimulates Leydig cells to produce testosterone?

Luteinizing hormone (LH).

What hormone stimulates ovarian follicular cells and spermatogenesis?

Follicle-stimulating hormone (FSH).

What is the effect of FSH in females?

Stimulates ovarian follicular cells to produce estrogen and progestin.

What is the effect of FSH in males?

Stimulates spermatogenesis in Sertoli cells.

Which hormone inhibits prolactin secretion?

Dopamine.

What anterior pituitary cell secretes prolactin?

Lactotrophs.

What is the function of prolactin (PRL)?

Stimulates mammary glands to initiate and maintain milk production.

What hormones are synthesized in the hypothalamus but released from the posterior pituitary?

Arginine vasopressin (AVP/ADH) and oxytocin (OT).

What is the function of ADH (AVP)?

Increases water permeability in the collecting duct.

What is the function of oxytocin?

Stimulates contraction of smooth muscle in the uterus.

What is long-loop feedback in endocrine systems?

Hormone secreted from endocrine gland inhibits both hypothalamus and pituitary.

What is short-loop feedback?

Hormone secreted from pituitary inhibits hypothalamus.

What is ultra-short feedback?

Hormone secreted at pituitary inhibits its own secretion at the pituitary.

What is a common cause of endocrine disorders?

Tumors in endocrine tissue often lead to hypersecretion of hormone.

What defines a primary endocrine disorder?

Tumor in the endocrine gland.

What defines a secondary endocrine disorder?

Tumor in the pituitary.

What defines a tertiary endocrine disorder?

Tumor in the hypothalamus.

What are key patient findings suggestive of GH excess in the patient case?

Jaw pain, frequent headaches, wedding ring no longer fits, and frontal bossing.

What type of hormone is growth hormone (GH)?

Peptide hormone.

How many isoforms of GH exist?

Two isoforms.

What characterizes the major GH isoform?

22 kD, 191 amino acids (larger)

What is the minor GH isoform?

20 kD with fewer acute metabolic actions.

Where is GH secreted from?

Somatotrophs of the anterior pituitary.

What hormones are homologous to GH?

Placental GH (pvGH), chorionic somatomammotropins (hCSs), and prolactin (hPRL).

What is the homology percentage of placental GH to GH?

93%.

What is the homology percentage of chorionic somatomammotropins to GH?

84%.

What is the homology percentage of prolactin to GH?

16%.

What hypothalamic hormone is the major stimulator of GH?

GHRH.

What is the effect of GHRH on cAMP?

Increases cAMP.

What type of secretion does GHRH stimulate?

Ca²⁺-dependent secretion.

What hypothalamic hormone inhibits GH?

Somatostatin.

What is the effect of somatostatin on cAMP?

Decreases cAMP.

What is ghrelin?

A hormone secreted from the stomach when empty.

When are ghrelin levels highest?

Before meals.

What are the effects of ghrelin?

Stimulates GH secretion and appetite.

How is GH secreted?

In pulses.

How frequently does GH secretion vary?

By the minute.