Flashcards in The Endocrine System Deck (29):
Describe endocrine hormones?
Secreted by endocrine glands into the blood stream where they affect other organs
Describe paracrine hormones?
Secreted and acts on neighbouring cell via diffusion (i.e. neurotransmitters)
Descibe autocrine signalling?
The cell secretes something that it has receptors for so it will act on itself
How can the hormone be secreted into the blood but not affect everything?
Must it must bind with specific receptors on the cell surface or inside the cell in order to have its effect
Can one endocrine gland only secrete one type of hormone? Give an example
No as for example the pancreas secretes insulin and glucagon
How many different hormones can a single cell secrete - what is the exception?
One cell secretes one hormone except for nerve cells
Can one type of hormone only be secreted by one endocrine gland? Give an example
No for example somatostatin is secreted by the pancreas and the hypothalamus
How are peptide hormones synthesised?
From amino acids in cells
How are steroid hormones synthesised?
From precursors in the cell
What are the two factors that affect the concentration of hormones in the blood?
1. Rate of Secretion
2. Rate of Inactivation/Excretion
How are hormones usually removed from the blood?
By the kidneys and the liver
What does the rate of removal depend on?
Whether they are long or short acting
How are peptide hormones bound to receptors normally inactivated?
By endocytosis where the cell turns the hormone inward to be metabolised
What are steroid and thyroid hormones bound to?
Proteins (the plasma)
Why do steroid and thyroid hormones have a longer circulation time?
Because of their protein binding proteins means they are released slowly
Where are receptors for peptide and catecholamine hormones?
On the cell surface (GPCRs)
Where are the receptors for steroid and thyroid hormones?
In the cell (nuclear receptors)
What is down regulation?
When a high concentration of the hormone is around for a long time and the total number of receptors for that hormone decreases
What is an example of downregulation?
High levels of insulin being around leads to down regulation of receptors for it which leads to type 2 diabetes
What is upregulation?
Occurs when cells are left for a long period of time without the hormone or low concentrations of it so more receptors are snthesised
What is long loop feedback?
Where hormones have negative feedback on the anterior pituitary (directly) and the hypothalamus (indirectly) to inhibit their production
What is short loop feedback?
The anterior pituitary hormones negatively feedback to the hypothalamus
What is ultrashort loop feefback?
Where the hypothalamic hormones feedback on themselves by attaching to hypothalamic receptors to inhibit their release
When would short loop feedback be seen?
Only in cases where the target organ isnt there anymore
What is an example of long loop feedback not working?
Large concentration of gonadotrophins in post menopausal woman with no feedback
Give an example of thyroid hormones participating in long loop feedback?
The thyroid hormones (T3, T4) act directly on the anterior pituatary and indirectly on the hyporthalamus to inhibit their production
Give an of example of TSH in short loop feedback?
The thyroid stimulating hormone (thyrotrophin) is released from the anterior pituitary and acts on the hypothalamus to inhibit its release
Give an example of TRH in ultra short loop feedback?
The hypothalamus releases thryotrophin release hormone which acts on the receptors on the hypothalamus to inibit its release