L13 - Endocrine System Flashcards
What is endocrinology?
study of the homeostatic mechanisms that are controlled by hormones
What is a hormone?
blood-borne chemical mediator released from endocrine glands that act on distant target cells
What does endocrine refer to?
hormones which pass directly through to the blood stream e.g. insulin
What does exocrine refer to?
hormones which pass through ducts e.g. digestive enzymes
What are general principles of the endocrine system?
- endocrine glands may produce multiple hormones (pituitary) and hormones may be produced by multiple endocrine glands (sex steroids)
- hormones may have more than one target/function
- rate of secretion of some hormones varies in a cyclic pattern
What does autocrine refer to?
self-regulating hormones which affect the cell that produced it
What does paracrine refer to?
hormones which affect cells in the near vicinity (histamine)
What affects the movement of hormones?
their permeability/solubility
hormones can be lipophilic or hydrophilic
What is a neurohormone?
a neurocrine secreted into the bloodstream
What are three major groups of neurohormones?
those from the anterior and posterior pituitary gland and catecholamines (made by modified adrenal medulla neurons)
What are tropic hormones?
a hormone that controls the secretion of another hormone
often have names that end in tropin e.g. thyrotropin (TSH)
What are the characteristics of lipophilic hormones?
act intracellularly as able to permeate target cell membrane
What are the characteristics of hydrophilic hormones?
dissolvable in water/solution and target receptors on cell membrane
What are the characteristics of nontropic hormones?
exert and effect directly on target cell/organ
How are steroid hormones shuttled around the body?
via carrier proteins
How do steroid hormones result in a response?
activate genes for transcription and translation; may have nongenomic actions
From which molecules are steroid hormones produced?
cholesterol
What are the characteristics of catecholamines?
made in advance (hydrophilic), dissolved in plasma, short half life, receptor located on PM, activation of second messenger systems (NA, A)
What are the characteristics of thyroid hormones?
made in advance (lipophilic), bound to carrier proteins, long half life, receptor located on nucleus, activation of genes for transcription/translation (thyroxine)
From which molecules are amines produced?
tyrosine
What is the mechanism of action of peptides and catecholamines?
bind to surface receptors -> generate an intracellular signal or “second messenger” (hydrophobic)
What is the mechanism of action of steroids?
altering gene expression and production of new proteins (lipophilic) e.g. thyroid hormones
What are some of the influences on plasma/hormones concentration?
- the hormone’s rate of secretion by the endocrine gland (major factor)
- rate of metabolic activation (for a few)
- extent of binding to plasma proteins (for lipophilic)
- rate of metabolic inactivation/excretion (for all)
How are steroid hormones removed from the body?
liver first makes it inactive then conjugation increases solubility in water
How are amines removed from the body?
by specific circulating degrading enzymes
How are large peptides removed from the body?
receptor-mediated endocytosis
smaller peptides = kidneys
What are the different types of negative feedback control?
long loop and short loop negative feedback control
How is hormone function regulated?
down-regulation e.g. target cell desensitisation
antagonism e.g. insulin and glucagon which act together but in opposite directions (fine-tuning)
synergism: multiple stimuli and effect is more than additive
permissive: first hormone cannot exert effect without presence of second e.g. cortisol and adrenaline
What hormones does the anterior pituitary gland produce?
ACTH (adrenocorticotropin)
PRL, FSH, LH (reproduction)
TSH (thyroid)
GH (growth hormone)
What hormones does the posterior pituitary gland produce?
Vasopressin (ADH) and Oxytocin
What is decreased hormone activity caused by (hyposecretion)?
increased removal from blood and abnormal tissue response e.g. lack of receptors and lack of enzyme for cell response
treatment = hormone administration
What is increased hormone activity caused by (hypersecretion)?
decreased removal from blood and decreased plasma protein binding
treatment = tumour removal, inhibiting drugs
What is primary hypo/hypersecretion caused by?
abnormal gland
What is secondary hypo/hypersecretion caused by?
normal gland; excessive stimulation
