Hormonal Mechanisms

What are the 3 types of intercellular messengers? Give an example for each.

Endocrine e.g. TSH (ant pituitary), T3/4. Autocrine/Paracrine e.g. prostaglandins (auto), somatostatin on insulin secretion (para). Neuroendocrine e.g. vasopressin (post pituitary). Neurotransmitter e.g. ACh

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What are the 4 types of hormones?

Peptide: chains of amino acids. Steroid: derived from cholesterol. Hormones derived from tyrosine: thyroid hormones & catecholamines (adrenal medulla). Eicosanoids: prostaglandins

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Compare peptide & steroid/thyroid hormones: solubility? binding to plasma proteins? half life?

Peptides: hydrophilic (soluble), don't need to bind to plasma proteins (free hormone), minutes (vulnerable to protein degradation). Steroids: lipophilic, bind with weak reversible bonds, hours/days (protected from degradation by plasma proteins)

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How are peptide hormones synthesised?

First protein translated is a preprohormone (pre = signal peptide), pre signal cleaved in golgi, prohormone packaged into secretory granules, stored until secretory signal, released by exocytosis -> free hormone

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How are steroid hormones synthesised?

Precursor molecule undergoes catalytic conversion by biosynthetic enzymes -> steroid. Lipophilic nature allows them to cross plasma membrane easily, hormone not stored but released by simple diffusion

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Describe peptide hormone action

Peptides hyrophilic, can't easily cross plasma membrane, use receptor molecules on membrane e.g. G-proteins, tyrosine kinase (insulin). Signal transduction -> response

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Describe steroid hormone action

Steroids lipophilic so can used intracellular receptors which act as hormone-regulated transcription factors -> bind to promoter to switch gene on/off -> increase/decrease gene expression

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Where are hormones metabolised?

Most metabolised by enzymes in liver, kidney and/or blood. Small proportion by target tissue. Excreted in urine and/or faeces

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How is hormone release regulated?

Feedback regulation: simple or involvement of hypothalamic & pituitary tropic hormones (endocrine axis). Neuroendocrine reflexes: input from higher centers, sudden abrupt increase of hormones. Diurnal (day/night) or circadian rhythm (around a day)

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Where in the endocrine axis does a primary defect target?

Peripheral endocrine gland e.g. adrenal cortex

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Where in the endocrine axis does a secondary defect target?

Anterior pituitary (pituitary tropic hormone)

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Hormonal Mechanisms

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