Endocrine Control Review Flashcards
What is endocrinology?
Study of homeostatic mechanisms controlled by hormones
What is a hormone?
Blood-borne chemical mediator released from endocrine glands > act on distant target cells
What must a target cell have to respond to a hormone?
Receptor for that hormone
Compare the nervous and endocrine systems in terms of anatomical arrangement
Nervous system: wired system
Endocrine system: wireless system
Compare the nervous and endocrine systems in terms of the type of chemical messenger
Nervous system: neurotransmitters released into synaptic cleft
Endocrine system: hormones released into blood
Compare the nervous and endocrine systems in terms of the distance of action of chemical messenger
Nervous system: very short distance
Endocrine system: long distance
Compare the nervous and endocrine systems in terms of the means of specificity of action on target cells
Nervous system: dependent on close anatomical relationship
Endocrine: dependent on specificity of target cell binding
Compare the nervous and endocrine systems in terms of speed of response
Nervous system: rapid
Endocrine system: slow
Compare the nervous and endocrine systems in terms of duration of action
Nervous system: brief
Endocrine system: long
Do endocrine glands only produce one hormone?
No, may produce multiple
Are hormones produced by only one endocrine gland?
No, may be produced by multiple
Can hormones have more than one target and function?
Yes
Can a single cell/organ be influenced by more than one hormone?
Yes
can the same chemical messenger be both a hormone and neurotransmitter?
Yes
What are autocrine signals?
Act on same cell that secreted them
What are autocrine signals for?
Self-regulation
What are paracrine signals?
Secreted by one cell and diffuse to adjacent cells
What are paracrine signals for?
Response propagation
What kinds of permeability/solubility do hormones have?
Lipophilic = hydrophobic Hydrophilic = lipophobic
What is a neurohormone?
Neurocrine secreted into bloodstream
What are the major groups of neurohormone systems?
Hypothalamus > anterior pituitary
Hypothalamus > posterior pituitary
Catecholamines made by modified adrenal medulla neurons
What is a trophic hormone?
Controls secretion of another hormone
What is the mechanism of action of peptide hormones and catecholamines?
Bind to surface receptors
Generate intracellular 2nd messenger signal
Hydrophilic = lipophobic
What is the mechanism of action of steroid hormones?
Alter gene expression and production of new proteins
Takes time
Lipophilic = hydrophobic
What hormone group do thyroid hormones behave like?
Steroids
What influences plasma hormone concentration?
Rate of secretion by endocrine gland = major factor
Rate of metabolic activation - for few
Extent of binding to plasma proteins - for lipophilic
Rate of metabolic inactivation and excretion
How are hormones generally removed?
Liver > kidney > urine
How are steroid hormones removed?
Conjugation > urine (and bile)
How are amines removed?
Specific circulating degrading enzymes
How are large peptides removed?
Receptor-mediated endocytosis
How are smaller peptides removed?
Kidneys
What is the long loop of negative feedback control?
Hormone acts on hypothalamus and pituitary to decrease secretion of trophic hormone
What is the short loop of negative feedback control?
Anterior pituitary acts on hypothalamus to decrease secretion of trophic hormone
Which is more common in negative feedback control: long loop, or short loop?
Long loop
What regulates hormone secretion?
Neuroendocrine reflexes Feedback Diurnal and circadian rhythms - Pineal gland - Suprachiasmatic nucleus Down-regulation of receptors - Endocytosis - Target cell desensitisation Antagonism Synergy Permissive
What is permissive in regulation of hormone secretion?
First hormone can’t exert effects without presence of second hormone
What can cause decreased hormone activity?
Hyposecretion
Increased removal from blood
Abnormal tissue response
What can cause increased hormone activity?
Hypersecretion
Decreased plasma protein binding
Decreased removal from blood
What can cause hyposecretion?
Primary = gland abnormal Secondary = abnormal trophic hormone
What can cause hypersecretion?
Primary = gland abnormal Secondary = excessive stimulation
What can cause an abnormal tissue response, leading to decreased hormone secretion?
Lack of receptors
Lack of enzyme for cell response
What can cause decreased removal from the blood, leading to increased hormone secretion?
Damaged liver and kidneys
- Decreased inactivation
- Decreased excretion
