Endocrine system Flashcards
(22 cards)
What does the endocrine system consist of?
Ductless endocrine glands that secrete hormones.
What specialised glands are part of the endocrine system?
Thyroid gland, adrenal glands, etc.
Which tissues contain endocrine cells?
Hypothalamus, adipose tissue, gastrointestinal tract.
What are the types of hormones derived from cholesterol?
- Steroids, which are hydrophobic.
- Produced by gonads and adrenal cortex; derived by cholesterol.
Classification of hormones
Peptides, Amines, Steriods
What are peptide hormones
- Cleaved from larger polypeptides during posttranslational modification.
- Small peptides: TRH (GluHisPro), vasopressin.
- Proteins: Insulin, Growth hormone.
- Glycoproteins: long polypeptides bound to one or more carbohydrate groups (FSH & LH).
Property of peptide hormones
- Water-soluble.
- Travel in bloodstream without carriers.
- Rapid but short-lived effect.
How does peptide hormones work?
Charged hormone (first messenger) → bind to extracellular receptor → activates second messenger → signalling cascade through amplification.
Example: GPCR
What are hormones?
A signalling molecule secreted by glands into bloodstream to distant target tissue → bind to receptor → regulate gene expression/cellular functions.
Property of steroid hormones
- Lipid-soluble.
- Travel in bloodstream with carriers.
- Bound hormones are inactive.
- Slower but long-lived effect.
How does steroid hormones work?
Non-polar hormone → bind to intracellular/intranuclear receptors → receptor conformational change (eg. Receptor dimerization) → hormone receptor complex bind directly to DNA → alter gene transcription.
What are amine hormones?
- Derived from modified amino acids (tyrosine).
- Share traits from both peptide & steroid hormones.
- Catecholamines (epinephrine & norepinephrine) → GPCR. Adrenaline rush
- Thyroid hormones (thyroxine) → Intracellular receptors. Metabolic rate.
How are the action of hydrophilic hormones mediated?
By membrane receptors.
- G-protein linked: Activate second messenger pathway.
- Ion-channel linked: Mostly for neuropeptide hormones.
- Enzyme-linked: Most are protein kinases (Insulin receptor → Receptor tyrosine kinase).
How are the action of hydrophobic hormones mediated?
By nuclear receptors.
Elaboration: Direct hormones
Secreted & act directly on target (non-endocrine) tissue.
Example: Insulin
Elaboration: Tropic hormones
Stimulate secretion of other hormones to travel to target (endocrine) tissue.
Example: GnRH & LH
How is endocrine function regulated?
- Hormone secretion
- Tissue and sensitivity
- Hormone binding to plasma proteins, metabolism and activation in organs (liver and kidney).
Elaboration: Hormone secretion
- Respond to changes in internal & external environment.
- Negative and positive feedback; feed forward.
- Neuroendocrine reflexes (eg. Secretion of oxytocin in response to uterine stretching.)
- Circadian rhythms (cortisol secretion)
Elaborate: Tissue and sensitivity
- Tissue receptors.
- Transcription cofactors (co-repressors and co-activators).
Endocrine disorders: Hyposecretion
- Resulted from heredity, dietary deficiency, immunologic factors.
- Causes can be primary/secondary (deficiency of another hormone).
- Can be treated by Hormone Replacement Therapy.
Endocrine disorders: Hypersecretion
- Due to tumours of endocrine glands, autoimmune disease.
- Causes can be primary/secondary.
Endocrine disorders: Lack of tissue response
- Endocrine dysfunction can arise from the unresponsiveness of target cells (eg. Testicular feminisation syndrome, type II diabetes).
