Endocrinology Flashcards
Endocrine
Secretes hormone into a blood vessel
Pancrine
Secretes local hormones
Autocrine
Hormones act on same cell
Neuroendocrine
Neuron axon terminates to bloodstream
Trophic
Stimulates secretion of another hormone
Chemical nature of hormones
- Proteins. polypeptides
- Glycoproteins e.g. LH, FSH
- Derivatives of a.a. tyrosine e.g. adrenaline
- Steroids derived from cholesterol
- Lipid-derived molecules e.g. prostaglandins -> lipohphilic (on demand)
Transport of hormones in blood
- Peptide and proteins float in free form (hydrophilic)
- Steroid and thyroid are transported into blood bound to serum proteins e,g, thyroxine binding proteins (hydrophobic) -> globulins are specific
Only free circulating hormone is ____
Active, remainder acts as a resevoir so hormone levels can be altered by changing levels of binding proteins
How do hormones work?
Most hydrophilic act on c.s. but steroid and thyroid have receptors in the nucleus
Tyrosine phosphorylation as a single transduction event
- Receptors for insulin + DDGF = TK so tyrosine phosphorylation
- GH + prolactin receptors -> single membrane spanning proteins + their mode of signalling is by activation of signal transducers + transcription
Steroid hormones + thyroid hormones are lipid- soluble so ..
- Circulate in the blood bound to globulins
- Unbound hormones enters the blood and bind to a receptors in the nucleus
- Complex binds to DNA
Difference between hydrophilic and hydrophobic hormones
- Hydrophilic -> vesicle -> controlled at level of synthesis and secretion
- Hydrophobic -> freely pass -> direct proportional rate of secretion and synthesis
Hydrophobic hormone structure and example
N-linked/ O-linked + carbohydrate chains
- Catecholamines -> numerous polar hydroxyl groups
- Prostaglandins -> carboxylic acid group
Hydrophilic hormone structure
Often have cyclic carbon structures which may be derivatives of cholesterol , tyrosine or vit A + D
Hypothalamo-pituitary -gonadal axis
GnRH -> LH -> Gonadal steroids -> germ cell maturation
- Gonadal steroids inhibits LH + GnRH
- LH inhibits GnRH
Hypothalamo-pituitary-adrenal axis
CRH- ACTH - Cortiso (+DHEA) -> glucose
Hypothalamo-pituitary-thyroid axis
TRH- TSH - thyroid hormones -> metabolism
Somatorophic axis
GHRH - GH - IGF-1 -> growth
Failure of negative feedback in these systems leads to :
- Defects in synthesis/ secretion of C
- Defects in cellular response to C
- Ectopic production of endocrine stimulus to production of C
Oxytocin
Posterior pituitary hormone
Effects of oxytocin
Stimulates contraction of myometrium -> passage of infant across cervix leads to distension of vaginal walls -> further secretion of oxytocin
+ lobulo-alveolar breast ducts
Control of rate of secretion only
applicable to hydrophilic hormones whereas hepatic metabolism more imp. for clearance of hydrophobic hormones
