Introduction Flashcards
Define the endocrine system
A system that controls organ function via the secretion of hormones that are carried in the blood to a distal target organ from the site of hormone synthesis
What is paracrine signalling?
Acts on cells nearby to the site of hormone synthesis
What is autocrine signalling?
Acts on the same cell that synthesises it
What is exocrine signalling?
Usually secreted through ducts onto a surface
How does tissue detect hormones in circulation?
Presence of hormone specific receptors extra/intracellularly
What effect will hormones have on tissue without any receptors?
No effect
What is neuroendocrine signalling?
- The co operativity of the endocrine and nervous system
- The direct release of a hormone packaged in a neurotransmitter vesicle into the bloodstream
Give an example of different responses to the same hormone on two different areas in the body
Insulin
- Skeletal muscle/adipose tissue = increased glucose uptake
- Liver = increased glycogenesis and decreased gluconeogenesis
What are the 6 typical features of an endocrine hormone?
- Produced by cells
- Secreted into the blood
- Transported to different targets
- Exert effects at very low conc.
- Act by binding to receptors on the targets
- Have their action controlled (usually by negative feedback loops)
What are the 3 types of hormone?
Peptide
Steroid
Amine
What makes up peptide hormones and how can their structure vary?
Chains of amino acids
Can be very long or short
When are peptide hormones made and how are they stored?
Made before they’re required
Stored in vesicles
What is the preprohormone?
The initial protein
Very large
Inactive
Can contain one or more copies of the active hormone
What happens to the preprohormone?
It is cleaved into smaller units in the RER into prohormones (still inactive)
What happens to the prohormone?
Packaged into vesicles in the golgi
Proteolytic enzymes are packed with it that cleave it to activate it
When a response occurs, what happens to the vesicles containing the hormone?
ALL vesicle contents, including the inactive fragments, are released
How do peptide hormones illicit a response?
Water soluble
Bind to G protein coupled receptors or tyrosine kinase receptors
These phosphorylate proteins and modify their function
What are steroid hormones made from?
Cholesterol
When are steroid hormones synthesised?
When they are required
They can’t be stored due to their lipophilic nature
How are steroid hormones transported in the blood?
Bound to carrier proteins (usually albumin)
These complex bound molecules are not active
What steroids do the gonads produce?
Sex steroids
What steroids are produced by the placenta?
hCG (human chorionic gonadotrophin)
Sex steroids
What steroid is produced by the kidneys?
Vitamin D3
What steroids are produced by the adrenal glands?
Corticosteroids
How do steroids carry out their effect on the target cell?
Can readily cross cell membrane
Receptors usually cytoplasmic/nuclear and play a role in gene expression and therefore protein synthesis
How fast is the steroid response?
Fairly slow
What happens to the complex bound hormone as more free hormone leaves the bloodstream?
It too leaves its carrier and leaves the bloodstream
What are amine hormones made from?
Tryptophan (only melatonin)
Tyrosine
What two subdivisions of amine hormones can be produced from tyrosine?
Catecholamines
Thyroid hormones
What do catecholamines have a similar effect to
Peptide hormones
What do thyroid hormones have a similar effect to?
Steroid hormones
What does hormone concentration in the blood depend on?
Secretion levels
Removal
How are most hormones removed from the blood?
By the kidneys (excretion)
Metabolic transformation
Which hormones are easily excreted and therefore have a short halflife?
Catecholamines
Peptides
Which hormones are not readily excreted and therefore have a longer halflife?
Steroids
Thyroid hormones
How are most hormonal pathways controlled?
Through negative feedback loops
What systemic effect does prolonged exposure to high hormone levels have?
Reduction in the number of receptors
What systemic effect does prolonged exposure to low hormone levels have?
Increase in the number of receptors
Describe permissive effects?
Prolonged exposure to one hormone effects the response to a different hormone
