13.1 Flashcards
endocrine system
- system of organs, cells, and tissues that secrete hormones
- connects using “blood highways”
the endocrine system complements the
nervous system
What essential functions does the endocrine system regulate?
- Smooth and cardiac muscle activity
- Metabolism
- Growth
- Reproduction
- Circadian rhythms
What are endocrine glands?
Ductless glands that secrete hormones into interstitial fluid, which then diffuse into the bloodstream.
what are hormones?
chemical messengers that are carried by the blood to distant target cells
hormones are secreted by cell into
interstitial fluid
hormones diffuse into the
bloodstream
Name some examples of endocrine glands.
- Pituitary
- Thyroid
- Parathyroid
- Adrenal
- Pineal glands
what is the role of hormone receptors?
- hormones affect only specific target cells
- hormones influence their target cells by binding to specific protein receptors leading to target cells producing a cellular response
receptor expression levels can change
upregulated or downregulated
What is the typical concentration range for circulating hormones?
Picomolar to nanomolar range.
What happens during down-regulation of receptors?
Excess hormones decrease receptor numbers, making cells less sensitive.
What happens during up-regulation of receptors?
hormone deficiency increases receptor numbers, making cells more sensitive
chemical classes of hormones
lipid soluble and water soluble
lipid soluble hormones include
steroid hormones and thyroid hormones
steroid hormones
derived from cholesterol, contain 4 interconnected hydrocarbon rings
List examples of steroid hormones.
- Aldosterone
- Cortisol
- Dehydroepiandrosterone
- Testosterone
- Estrogens
- Progesterone
- Calcitriol
(All Cute Dinosaurs Take Epic Pictures Constantly)
thyroid hormones
synthesized by attaching iodine to the amino acid tyrosine
T3 and T4 are lipid soluble thyroid hormones because they contain
two hydrocarbon rings
water soluble hormones include
amine hormones and peptide/protein hormones
What characterizes water-soluble hormones?
they act on receptors at the cell surface and are the most abundant type of hormones in the body
amine hormones are synthesized by
modifying certain amino acids
two categories of amine hormones
catecholamines and melatonin
catecholamine =
epinephrine, norepinephrine, and dopamine
catecholamines are derived from
amino acid tyrosine
melatonin is derived from
amino acid tryptophan
peptide/protein hormones
- amino acid polymers
- most hormones belong to this category
most water-soluble hormones circulate through
the watery blood plasma in free form
most lipid soluble hormones are not bound to
transport proteins because they are not soluble in blood (they are carried in blood via transport proteins)
What is the free fraction of lipid-soluble hormones?
A small percentage (0.1%-10%) of lipid-soluble hormone molecules that are unbound and ready to diffuse out of capillaries.
What is a general mechanism of hormone action?
Hormones bind to specific receptors in or on target cells, activating a signaling pathway.
Where are plasma membrane receptors located?
On the surface of target cells.
plasma membrane receptors are used by
water soluble hormones since they cannot cross the hydrophobic plasma membrane
intracellular membrane receptors are used by
lipid soluble hormones, which pass through call membrane and bind receptors in the cytosol or nucleus
G protein coupled receptors examples
- ADH (uses Gs, producing cAMP)
- oxytocin (uses Gq, producing IP3/DAG and releasing Ca2+)
- growth hormone inhibiting hormone (uses Gi)
receptor tyrosine kinase examples
insulin and IGFs bind to receptor tyrosine kinases
receptor guanylyl cyclases examples
ANP bind to receptor guanylyl cyclases
Janus Kinase (JAK) coupled receptor examples
growth hormones, prolactin, erythropoietin bind to JAK
a single hormone can act upon multiple target cels and a single target cell can respond to multiple different hormones, but
each receptor type is specific to a particular hormone
permissive effect
required for another hormone to elicit a greater response in its target cell
examples of permissive effect
- epinephrine and thyroid hormone control of lipolysis
- TH increases # of beta-adrenergic receptors for EN
synergistic effect
if the effect of the hormones acting together is greater than the sum of their individual effects
examples of synergistic effect
glucagon and epinephrine control of blood glucose levels
antagonistic effect
if the hormones effects have opposing actions
examples of antagonistic effects
insulin and glucagon modulation of glycogen metabolism
