Overview and hormonal mechanisms Flashcards
What is a hormone
Secreted directly into blood stream from ductless endocrine gland
What is the Thyroid -stimulating hormone (TSH) and where is it released from
Released from ant. pituitary gland and acts on thyroid gland. It regulates the production and secretion of thyroid hormones T3 and T4
What are autocrine messengers and an example of this
Travels by itself into the interstitial fluid which means it is able to act on the same cell that made that hormone
-Prostaglandins
What are paracrine messengers and example
Substance secreted by one cell and travels short distance to a cell nearby such as a neighbouring cell and acts on that
Somatostatin
What are neuroendocrine hormones and when are they secreted?
Examples
Nerve cell secretes a hormone which travels some distance within circulation. Hormone is stored in axon terminal until it is ready for secretion
Oxytocin and ADH (both from posterior pituitary gland)
What are neurotransmitters
Secreted when there’s an action potential in that neurone and goes to an adjacent neurone e.g. Acetylcholine
What are peptide hormones
Chains of amino acids
Where are peptide hormones excreted from
HYpothalamus
Anterior and posterior pituitary gland
Pancreas
GIT
Where are steroid hormones derived from
Cholesterol
What are some examples of steroid hormones
Cortisol
Aldosterone
Sex hormones
What are examples of hormones derived from tyrosine
Thyroid hormones and catecholamines
What are examples of Eicosanoid hormones
Prostaglandins
How are peptide hormones synthesised and secreted
Same way a normal protein is
- Gene for peptide hormone is transcribed into mRNA
- mRNA is translocated into cytoplasm and translation occurs
- Translation takes place on ribosome
- Ribosome is attached to ER and forms RER
- Preprohormone is formed at first. It is hydrophobic and needs further processing and packaging
- Post translational modification takes place (e.g. protein folding, disulphide bridge forming and glycosylation)
- By the time prehormone gets to Golgi, prohormone is formed
- IN Golgi, there is additional processing, cleaving and packaging in secretory granules
- Hormone is now in its mature state
Hormone is stored until stimulus comes
How are steroid hormones formed and excreted from cell
Biosynthetic enzymes convert cholesterol into steroid hormone. Cholesterol complex Is lipid soluble so is able to pass through the cell and are not stored in cells
What do steroid hormones need in order to be transported in circulation
Be bound by plasma proteins
Why are steroid hormones not stored
Because they are lipid soluble and so diffuse out of cells
If you need an increase in steroid hormone, what needs to happen? and why
There needs to be an increase in synthesis of hormones because it is not stored
If you need an increase in peptide hormone, what needs to happen? and why
Secretion is regulated by release of pre made peptide hormones because they are stored in cells
How does the half life of peptide hormones compare to steroid hormones and why
Peptide- MInutes
Steroid- Hours- days
Because peptide hormones exist as free hormones so they are susceptible to protease whereas steroid hormones are bound to plasma proteins by weak, reversible bonds
How are steroid hormones able to bind to receptors even though they are bound to plasma proteins
Theres a small proportion of them which are free and so are able to bind
Why are peptide hormones not readily available to cross the lipid bilayer and why?
-How do they overcome this
They are hydrophilic
Plasma membrane receptors mediate their effects (G protein coupled receptors and tyrosine kinase kinked receptor)
Which membrane receptors mediate the effects of peptide hormones and how do they do this
G protein coupled receptors
Tyrosine kinase linked receptor
-Mediate signal transduction which bring about a physiological response (altered activity of enzymes or ion channels or altered expression of specific proteins)
Why are steroid hormones able to pass through the lipid bilayer and what are their effects mediated by
Because they are lipophilic
-Intracellular receptors
What do the intracellular receptors act as inside the cell
Hormone-regulated transcription factors. They increase or decrease transcription so therefore have an effect on the associated functions of that protein
How are hormones metabolised
BY enzymes in liver, kidney and/or blood
Small proportion by target tissues
Excreted in urine and/or faeces
What happens when peripheral levels get too high
Inhibit anterior pituitary hormone and decrease hypothalamus from releasing hormones which affect the anterior pituitary
When the peripheral hormone levels get too high how does the long feedback loop get affected
The long feedback loop loop is less used
What can be a cause of excess hormones (hyper secretion)
Tumour or immunological factor
What can be a cause of lack of hormones (hyposecretion)
Genetic
Immunological attack Destruction by disease
Surgical removal
what can be the cause of decreased target cell responsiveness
At level of receptor or downstream enzyme
What is a primary defect
problem with gland that makes that hormone
What is a secondary defect
Problem with something else higher up in the system
How to investigate endocrine disorders
Signs and symptoms
Endocrine investigations (hormone levels)
-Single point (base-line)
-Dynamic or provocative test to check the integrity of feedback control
-Imaging
When are stimulation tests used and how to do them
If suspect hypo secretion (failure to stimulate conforms hormone insufficiency)
-Increase a particular hormone
When are suppression tests used and how to do them
If suspect hyper secretion (failure to suppress indicates autonomous secretion i.e. tumour)
-Give a hormone that suppresses the secretion of that hormone
How to treat a hormone deficiency
Hormone replacement
How to treat a hormone excess
Drugs to block production
How to treat patient if there is decreased cell responsiveness
Drugs to enhance cellular response to hormone
What is a primary cause of hormone disorders
Endocrine gland secreting hormone
What is a secondary cause of hormone disorders
control by pituitary tropic hormone
