Intro Flashcards
ENDOCRINE GLAND
Group of cells which secrete “messenger” molecules directly into bloodstream
HORMONE
Bioactive “messenger” molecule secreted by an endocrine gland into blood
ENDOCRINE hormones act on target cells…
at a distance from source
PARACRINE hormones act on target cells…
nearby
AUTOCRINE hormones have an effect on
its own immediate source
Endocrine effects take place over a
Long time-span: seconds to days
Types of hormone
- Protein/polypeptide/ amino acid derived 2. Steroid hormones3. Miscellaneous
Protein hormone synthesis
AAs in blood -> cellA signal allows DNA to be transcribed to produce relevant mRNATranslation of mRNA to prohormone in RERProhormone –> GolgiIn Golgi, further processed into vesicles with proteolytic enzymes that can cleave prohormone to form active hormone
Which blood vessels are pituitary hormones secreted into?
Pituitary capillary
Example of protein hormone
Adrenocorticotropic hormone (ACTH)
Prohormone of ACTH
POMC
Example of Steroid hormone
Cortisol
Steroid hormone synthesis
LDL in blood–> cell by endocytosisCholesterol split from lipoprotein- esterified and stored in cytoplasmic vacuoles as fatty acid estersEsterase enzyme liberates cholesterol from fatty acid estersSTAR protein (Steroidogenic acute regulatory protein) drives cholesterol into mitochondriaEnzyme pathway in mitochondria generates steroid hormone
Why does cholesterol need to enter the mitochondria?
All enzymes that produces steroid hormone are in the mitochondria
Where are protein hormones stored?
In vesicles within the cell that produced themSecreted when required
Where are steroid hormones stored?
In bloodstream
If a steroid hormone is heavily plasma protein bound, can it still access tissues?
YesThere’s always a small proportion of free hormone that can move in to cells when required (“Active poolâ€)
How are steroid hormones stored in the blood?
Majority are bound to plasma proteins (general or specific)There is a small ‘active pool’ unbound
Bound & Free steroid hormones are in…
Dynamic equilibrium
Most target cells of protein hormones have…
a receptor to recognise relevant hormone
Mechanism of protein hormone e.g. ACTH
n
Why don’t steroid hormones need receptors on their target cells?
They are very lipid solubleFree hormones diffuse across plasma membrane into cell
Location of steroid hormone target
Intracellular
Steroid hormone mechanism
Steroid hormone diffuses into target celland binds to target receptorSteroid receptor complex translocates to nucleus to up/down regulate protein transcription and translation
Why would an endocrine system be described as “acting like a thermostat”?
Most have a closed loop feedback
