54 - Endocrine Control Review Flashcards
Six general principles of hormones
• Endocrine glands may produce multiple hormones (pituitary)
• Hormones may be produced by multiple endocrine glands (sex
steroids)
• Hormones may have more than one target and function (sex steroids,
GH)
• Rate of secretion of some hormones varies over time in a cyclic pattern
(sex steroids)
• Single cell/ organ may be influenced by more than one hormone
(pancreas, reproductive)
• Same chemical messenger may be hormone or neurotransmitter (NE)
Neurohormones
Neurocrine that is released into the bloodstream.
Three major groups of neurohormones
1) Hypothalamus→ Anterior Pituitary. 2) Hypothalamus→ Posterior Pituitary. 3) Catecholamines (made by modified adrenal medulla neurons).
Neurotransmitters
A neurocrine molecule secreted to a target cell
Tropic hormones
1
2
1) A hormone that controls the secretion of another hormone (trophic usually stimulates growth & development)
2) Often (not always) have names that end with -tropin
Eg. Thyrotropin (TSH), Corticotropin, ACTH, etc.
Simple endocrine reflex
Stimulus leads to endocrine gland releasing endocrine into blood, which affects target.
Where are catecholamine receptors located on cells?
Cell surface
Synthesis and storage of peptide hormones
Made in advance, stored in secretory vesicles
How are peptide hormones released from cells?
Exocytosis
Transport of peptide hormones in blood
Dissolved in plasma
Location of peptide hormone receptors
Cell surface
General target response of peptide hormones
Modification of existing proteins, induction of new protein synthesis
Examples of peptide hormones
Insulin, parathyroid hormone
Synthesis of steroid hormones
Synthesised on demand form precursors (cholesterol)
Release of steroid hormones from parent cell
Simple diffusion
Transport of steroids in blood
Bound to carrier proteins
Half life of steroid hormones
Long
Amine hormones
Catecholamines and thyroid hormones
Synthesis and release of amine hormones
Both made in advance.
Catecholamines stored in secretory vesicles.
Thyroid hormone prohormones stored in secretory vesicles.
Precursor to amine hormones
Tyrosine
Half life of amine hormones
Catecholamines are short.
Thyroid hormones are long.
Location of amine hormone receptors
Catecholamines in cell membrane.
Thyroid hormones in nucleus.
Which other hormones do thyroid hormones behave like?
Like steroids
Things influencing plasma hormone concentration 1 2 3 4
1) Rate of hormone secretion by the endocrine gland (major factor, for all hormones)
2) Rate of metabolic activation of hormone (for a few hormones)
3) Extent of binding to plasma proteins (for lipophilic hormones)
4) Rate of metabolic inactivation and excretion (for all hormones)
Removal of steroid hormones
Conjugation and excretion in urine and bile
Removal of amine hormones
Specific circulating degrading enzymes
Removal of large peptide hormones
Receptor mediated endocytosis and recycling
Removal of most small hormones
Kidneys
Two broad negative feedback systems
Long-loops (back up system)
Short-loops
What triggers LH surge in menstruation?
High oestrogen levels (if oestrogen levels don’t rise enough, don’t get LH surge)
Regulation of hormone secretion 1 2 3 4
1) Down‐regulation
2) Antagonism
3) Synergism
4) Permissive
Down-regulation in hormone secretion
– Endocytosis
– Target cell desenitisation
Antagonism in regulating hormone secretion
– Act together but act in opposite directions (insulin & glucagon)
– Allows fine tuning
Synergism in regulating hormone secretion
– Multiple stimuli and effect is more than additive (glucagon,
cortisol & adrenaline regulating blood glucose; reproductive)
Permissive hormone regulation
– First hormone cannot exert effects without presence of second hormone (cortisol & adrenaline)
Primary endocrine disorders
Secreting gland of hormone is abnormal
Disorders of decreased hormone activity 1 2 3 4
– Hyposecretion
• Primary (gland abnormal)
• Secondary (normal gland; abnormal tropic hormone)
– Increased removal from blood
– Abnormal tissue response
• Lack of receptors
• Lack of enzyme for cell response
– Treatment: hormone administration
Disorders of increased hormone activity 1 2 3 4
– Hypersecretion
• Primary (gland abnormal)
• Secondary (normal gland; excessive stimulation)
– Decreased plasma protein binding
– Decreased removal from blood
• Decreased inactivation
• Decreased excretion
– Treatment: Tumor removal, inhibiting drugs
