Intro to Endocrine Flashcards
Define the endocrine system?
A system that integrates & controls organ function via secretion of chemicals carried in the blood to target organs where they influence the organ activity.
What makes endocrine hormones different to paracrine, exocrine and autocrine?
Endocrine are carried in the blood to distant target cells whereas:
- Autocrine act on the cell that syntehsised them e.g. cytokines
- Paracrine act on neighbouring cells through the ECF e.g. Histamine
- Exocrine reach the external environment through ducts e.g. sweat/bile/saliva
What are the three major types of hormones?
Peptide hormones derived from amino acids
Steroid hormones derived from cholesterol
Amine hormones derived from 2 specific amino acids (tryptophan & Tyrosine)
How are peptide hormones produced?
1) As preprohormones
2) Cleaved into prohormones in RER
3) Stored in vesicles with enzymes that cleave them down to active hormones and peptide fragment in the Golgi
4) Released into blood when needed along with inactive fragments
Why is it relevant that peptide hormones are released into blood along with inactive fragments of prohormones?
The fragments can be measured to assess hormone levels
E.g. C-peptide levels tell us about the levels of endogenous insulin production
How do peptide hormones travel/work?
- Water soluble so dissolves in blood
- Act on membrane bound receptors
- Have rapid effects (S or mins)
What are the main differences between water and lipid soluble hormones?
Water soluble - Peptide hormones & Catecholamine hormones
Lipid Soluble - Steroid hormones & Thyroid hormones
Water soluble: #Dissolve in blood #Act on membrane bound receptors #Short half life
Lipid Soluble: #Bound to Carrier proteins #Act on cytoplasmic/nuclear receptors #Long half life (hours/days)
How are steroid hormones produced?
They’re synthesised directly when needed (since they’re lipophilic they can’t be stored inside cells)
How are steroid hormones transported?
In carrier proteins e.g. Albumin
How do steroid hormones work?
They move into cells and act on internal receptors
Activate/inhibit gene function which raises/lowers protein synthesis
This is a slow process compared to peptide hormones taking hours/days and persisting for a similar time after production stops
What are the types of amine hormone?
3 main types:
1) Catecholamines which are water soluble
2) Thyroid hormones which are lipid soluble
3) Melatonin, the only one derived from tryptophan
(1&2 derived from tyrosine)
What are the types of protein carriers for lipid soluble hormones?
Specific e.g. CCS-binding globulin
Non-specific E.g. Albumin
If lipid soluble hormones are carried by proteins how do they cross the cell membrane to have action?
There’s a constant ratio of free hormone:Complexed hormone.
The law of mass action dictates that as free hormone is taken up by cells more is released from carrier proteins.
This equilibrium ensures the prolonged activity of the hormone
Why don’t hormones go round the blood continuously causing effects?
They are metabolised and excreted, mainly by the liver/kidneys.
Protein complexed hormones are protected from this hence their long half-lives.
What mechanisms exists to control the level of hormone secretion?
1) Most endocrine pathways are have a trigger (E.g. low Calcium) and are then inhibited by the correction of this trigger in a -ve feedback loop
2) Some respond to neural feedback loops (Fight/flight -> Generalised symp. activation -> Adrenaline release from adrenal medulla)
3) Some (e.g. insulin) have multiple methods of control
