Diabetes & Endocrine Welcome Flashcards
What dictates whether a hormone receptor will be inside or on the surface of the target cell?
Lipophillic hormones will have receptors inside the target cell
Lipophobic hormones will have receptors on the cell surface
Describe the process of neural communication
Neurotransmitters are released from the presynaptic neurons and travel across the synaptic cleft to the postsynaptic cell and influence its activity.
What is a neurotransmitter and how is it different from a hormone?
Neurotransmitters are the chemicals released by the neurons, but they act locally within the synaptic cleft in contrast to endocrine hormones that do not act locally
Describe neuroendocrine communication
Nerves act to release hormones that travel through the blood and act on their target cells
How is the response to a hormone kept specific?
Only the target cell of a hormone will have a receptor for that hormone
How can the same hormone have different effects in different target cells?
A hormone can have different receptor types in different cells, and so different responses can be triggered in different target organs
What is the function of hormones and neurotransmitters?
To bring about a change in the activity of their target cells
What are the main features of an endocrine hormone?
They are transported from the cells that produce them to their distant target cells through the blood
They exert their effects at very low concentrations
They act by binding to receptors on target tissues
They have their action terminated, often by negative feedback systems
What are the three types of endocrine hormone, and how is each made?
Peptide/protein hormones- made of chains of amino acids
Amine hormones- all derived from either tryptophan (melatonin) or tyrosine (all other amine hormones)
Steroid hormones- derived from cholesterol
How are peptide hormones produced and secreted?
Initially produced as preprohormone (large and inactive- contains one or more copies of active hormone)
Preprohormone cleaved into smaller units in endoplasmic reticulum to leave prohormones (small but still inactive)
Prohormones packaged into vesicles in golgi apparatus with proteolytic enzymes that break it down into the active hormone and other fragments.
Vesicles stored in endocrine cells until release is triggered and all contents are released into the plasma
What is C-peptide and why is it useful clinically?
C-peptide is the inactive fragment cleaved from the insulin prohormone. C-peptide in urine can be measured to indicate endogenous insulin production from the pancreas
How do peptide hormones cross cell membranes?
They are water soluble for easy transportation in plasma, but this means they cannot cross cell membranes so have to bind to membrane-bound receptors on the target cell.
Most peptide hormones modulate the GPCR or tyrosine kinase linked signalling pathways, which work by phosphorylating existing proteins in the cell and modifying their function
Describe the differences between the G protein coupled receptor and the tyrosine kinase linked receptor
GPCR activates a 2nd messenger system and/or ion channels leading to modification of existing proteins and yielding a rapid response
TKLR alters gene expression and gives a slower, longer lasting activity
What are some common examples of amine hormones?
Dopamine Norepinephrine Epinephrine Thyroxine Triiodothyronine
How are steroid hormones transported through the blood?
Lipophilic so synthesised as needed as cannot be retained in membranes.
Transport through the blood relies on them being bound to proteins such as albumin
