Hormones Flashcards
What is the overall function of hormones?
To bring about changes in the activity of the target cell or organ
What are endocrine hormones produced by?
A cell or group of cells
Name 5 properties of endocrine hormones
- Secreted form cells into the blood
- Travel through the blood to distant organs
- Are able to exert effects at very low concentrations
- Act by binding onto specific receptors
- Have their action terminated by negative feedback
What are the 3 classes of endocrine hormones
Peptide - composed of chins of amino acids
Steroid - derived from cholesterol
Amine of which there are 2 types catecholamines and thyroid hormones - derived from tryptophan or tyrosine
Where are peptide hormones initially produced and in what form?
In the ribosome as a preprohormone
Where are preprohormones cleaved?
Cleaved in the rough endoplasmic reticulum into the prohormone
What is the fate of the pro hormone?
It is packaged into vesicles in the golgi apparatus and when triggered is degraded by proteolytic enzymes into the active hormone which enters the ECF and then the blood
What else is produced when the pro hormone is cleaved?
Inactive peptide fragment which can have an active function for example in insulin cleavage C-peptide is produced and can be measured in diabetes
Why would we measure C-peptide instead of insulin directly in diabetes?
It will give a value of how much insulin is being produced by the patient themselves rather than the combined value with the injected insulin.
Are peptide hormones water soluble?
Yes, they are hydrophilic
Can they passively diffuse across the cell membrane?
No, because they are lipophobic they must bind to a surface receptor
Name two mechanisms by which peptide hormones can bing abut the phosphorylation of proteins within the cell.
Either via a G-protein coupled receptor e.g. cAMPor by activating tyrosine kinase
Do peptide hormones have a short or long half-life and why?
Short because they are water soluble so they dissolve easily in the plasma
When are peptide hormones synthesised?
They are made in advance and stored in secretory vesicles
Give 2 examples of peptide hormones
Insulin and parathyroid hormone
What are steroid hormones and where are they derived from?
They are lipid hormones derived form cholesterol
Where are they synthesised?
In the adrenal cortex, gonads and placenta
When are they synthesised and why?
Directly as needed because they are highly lipophilic so cannot be maintained within lipid membranes, they immediately diffuse into the blood
How are they transported through the blood?
Bound to carrier proteins, which increases their half-life significantly by protecting them form degradation
where are they produced?
Smooth endoplasmic reticulum
Where are steroid receptors located?
On the inside of the cell and are either cytoplasmic or nuclear receptors
How do steroid bring about a response?
Activation or depression of gene function by altering transcription of protein
Are steroids fast in bringing about their response?
No, they take a long time but persist over a long time for example growth
Where are amine hormones derived from?
The amino acid tyrosine with the exception of melatonin which is produced by tryptophan
