Endocrine Flashcards
Nonspecific binding protein
located in the cytoplasm and used by T3 as a stepping stone to enter the nucleus where T3 can bind to ligand-binding domain at the receptor
What is the difference between steroids and thyroid binding
- Thyroid hormone receptors are located in the nucleus and bind to DNA even in the absence of thyroid hormone ligands, corepressors are recruited if its absent
- one half side of thyroid hormone response elements binds to T3 another to vitamin A derivatives
Where do coactivators and corepressors bind?
- Not the DNA, buy the receptor pockets different from the ligand binding domain for the hormone
- binding of the steroid ligand to a nuclear receptor binding domain recruits coactivators and changes its shape
What hormones make use of homodimers? Which ones use Heterodimers?
- Homodimers: Steroids
- Heterodimers: T3 and retinoic acid
Origin, Location and Binding of Corticosteroids
- Adrenal Cortex
- Cytoplasm
- move towards the nucleus post binding, then bind to hormone receptor elements in the regulatory region of target genes
Mechanisms of Steroid Hormone Action
- Stimulation of gene transcription; ~ 30 min
- Nongenomic action occurs when a steroid binds to a receptor on the plasma membrane activating second-messenger system
- Distribution of receptors within the cell varies by tissue and hormone
Prehormone
Molecules like thyroxine; secreted by endocrine glands , but inactive until converted to an active hormone in the Target Cell
Activation of lipophylic hormones
Receptor has to bind to the hormone ligands before being allowed to bind to a specific DNA region; hormone response element
Nonpolar (Lipophilic) mechanisms of Action
- Pass easily through the plasma membrane and bind to the receptors within the nucleus or cytoplasm
- Delivered to target cells via carrier proteins in blood
- two domains: Hormone and DNA binding one on the receptors
Polar ( hydrophilic) mechanisms of action
- bind to receptors on the plasma membrane
- use second-messenger system
- carried by blood
Steroid hormone that is active in some tissue, but converted to another one in other tissues in order to activate`
Testosterone to DHT
Prohormone
- Precursor of hormones consisting of peptide hormones synthesized together; minimal hormonal effects on its own
- cut and splices within a gland to make a hormone
Catecholamine
- water soluble
- epinephrine and norepinephrine
Two types of hormones
- polypeptide and glycoproteins
- would be broken down and digested into inactive form
Example: insulin
2 endocrine glands that secrete steroids and what types
- Adrenal cortex (coritcosteroids: cortisol and aldesterone)
- Gonads:: Sex steroids
What glands release Amines?
Adrenal medulla, thyroid and pineal glands
How many amino acids to polypeptide and protein hormones have? Examples
`100+ EACH, GH and insulin
What is a glycoprotein and an example of one
protein and a carbohydrate : FSH
Neurotransmitters
- diffuse across a narrow synaptic cleft to cell outer membrane
- Most hormones can also function as neurotransmitters if present in a different organ
- Require proteins that combine with a regulatory molecule; the change will provoke a specific set of change; there is a mechanism to turn off the action of the regulator
Synergistic hormonal interaction
2 hormones work together to produce a particular effect that’s
- Additive: epinephrine and norepinephrine raise HR; together the increase is greater
- Complementary: E + cortisol + prolactin + oxytoccin each promote lactation, but have different functions
Permissive Hormonal Interaction
- Enhances the responsiveness of a target organ to the second hormone or increase its activity:
Presence of Estradiol within the uterus, induces the formation of progesterone receptor proteins
Antagonistic hormonal interaction
- high concentration of a hormone inhibits the secretion of another
During pregnancy estrogen inhibits production of prolactin
Insulin and glucagon have opposite effects: promotes fat formation/breakdown
Hormone concentration and tissue response
- depends primarily on the rate of secretion by endocrine glands or administration
- hormones do not accumulate in the blood, organs like liver use enzyme to convert them to more water soluble compounds then excrete them
- subsequent administration expresses greater response
Desensitization and downregulation
- Prolonged exposure to high concentrations of polypeptide hormone desensitizes the target cells
- down-regulation of receptor decreases their number partially causing desensitization
- administration in spurts prevents receptor downregulation
4 hormones that promote fat catabolism
- epinephrine
- cortisol
- thyroxine
- GH
3 levels of implementing hormonal effects
- autocrine ( controls changes within the same cell)
- paracrine ( nearby cells)
- endocrine (bloodstream to Target Cell)
