Investigations of Endocrine System Flashcards
What are hormones secreted by?
endocrine glands
A hormone can only influence cells that have…?
specific target receptors for that particular hormone
Peptide hormones:
- examples?
- where are they generally released from?
- PTH, ACTH, TSH
- Generally released from anterior pituitary lobe
Steroid hormones:
- examples?
- where are they generally released from?
- precursor?
- Testosterone, Oestradiol, Cortisol
- Released from gonads and adrenal glands
- precursor is generally cholesterol
What are the 2 types of tyrosine-based hormones?
Thyroxine (T4) and Triiodothyronine (T3)
What are the 3 ways in which a steroid hormone can interact with a cell?
- The classical model
- Receptor-mediated endocytosis
- Signalling through cell-surface receptors
Describe the ‘classical model’ method in which a steroid hormone can interact with a cell?
- The steroid hormone dissociates from its plasma carrier protein and diffuses across the cell membrane.
- After gaining entry to the cell, the free hormone binds to an intracellular receptor and alters gene transcription.
Describe how a steroid hormone can interact with a cell via receptor-mediated endocytosis
- The steroid hormone, bound to its plasma carrier protein, is brought into the cell via a cell-surface receptor.
- The complex is broken down inside the lysosome, and free steroid hormone diffuses into the cell, where it subsequently exerts its action at the genomic level or undergoes metabolism
Describe how a steroid hormone can interact with a cell via signalling through cell surface receptors
- The free steroid hormone alters intracellular signalling by binding to cell-surface receptors.
- The steroid hormone could exert these effects directly or could alter signalling by blocking the actions of peptide hormones.
What is TBG? Where is it produced
Thyroxine-binding globulin; a globulin protein that reversibly binds thyroid hormones in circulation. Produced in liver.
How does TBG affect thyroid function tests?
- Only the ‘free’, unbound forms of thyroid hormones are physiologically active
- TBG binds thyroid hormones; if the level of TBG changes (e.g. due to conditions), this results in a change in the level of the free hormones.
- Therefore, measurement of total hormone levels can be misleading
Causes of abnormal plasma TBG concs:
Describe TSH and T4 levels in:
- 2ary hypothyroidism
- 1ary hypothyroidism
- 1ary hyperthyroidism
- low TSH and low T4
- high TSH and low T4
- low TSH and high T4
What does high TSH and high T4 levels indicate?
pituitary gland overproduction or failure of feedback
TSH front line testing
Why isnt free T4 tested in front line testing?
- Cost
- 2ary hypothyroidism is very rare
N.B. 2ary hypothyroidism can have a normal TSH with a low fT4.
What is non-thyroidal illness?
- Also known as Euthyroid sick syndrome
- Patients suffering from non-thyroidal illness may show abnormalities within their thyroid function tests, despite being euthyroid.
- TSH levels may be suppressed (<0.1 mU/L) in acute phases of illness
How often should we repeat TFTs in healthy people?
Every 3 years
How often should we repeat TFTs for those with hyperthyroid problems
How often should we repeat TFTs for those with hypothyroid problems
Which type of biochemical test is used for TFTs?
Immunoassays