Endocrine Flashcards
(102 cards)
What is the endocrine system?
The system that integrates and controls organ function via secretion of chemicals (hormones) from cells, tissues or glands
Hormones carried in blood
Can either have slow or fast responses
What is endocrine communication?
Hormones travel in blood to their target organs/tissues
Tissues detect hormones through the presence of specific receptors for that chemical on/in cells
No receptor = no response
What is neural communication?
Neurotransmitters released from presynaptic neurons travel across synaptic cleft to postsynaptic cell to influence its activity.
A neurotransmitter is the chemical released by the neuron but, in contrast to hormones, acts locally within the synaptic cleft.
The endocrine and nervous systems co-operate intimately to provide further control, particularly for long-term phenomena, e.g. growth.
How does neural communication work with endocrine communication?
Nerves release hormones which enter blood and travel to their target cells e.g. hypothalamic – pituitary axis.
Although all hormones circulate throughout the body in the blood, the response to any one hormone is highly specific because only target cells have receptors for the hormone.
What is autocrine?
Cells secrete chemicals binding to same cell (cytokines)
What is paracrine?
Chemicals diffuse in ECF to affect nearby cells
Eg. Histamine
What is exocrine?
Chemicals released from exocrine glands via ducts to external environment including GI tract (saliva)
What are the features of an endocrine hormone?
Produced by a cell (or group of them)
Secreted into + transported by blood
Exert effects at very low concentrations
Act by binding to receptors on target tissues
Have their action terminated, often via negative feedback loops
What makes up a peptide/protein hormone?
Chains of amino acids
What makes up steroid hormones?
Synthesised from cholesterol
What are amine hormones made up from?
Either tryptophan
Or tyrosine
When are peptide hormones made?
Made ahead of time, then stored until required
How are peptide hormones synthesised?
Initial protein produced by ribosomes is large + inactive - perprohormone
>Preprohormones contain 1+ copies of the active hormone in their amino acid sequence
>Cleaved into smaller units in RER to leave smaller, still inactive proteins called prohormones
>packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone and other fragments.
What can clinically be measured in regards to peptide hormones?
The inactive fragments in plasma
Eg C-peptide in diabetes
How are peptide hormones stored?
Hormones and fragments are stored in vesicles in the endocrine cells until release is triggered
>then all vesicle contents are released into plasma (co-secretion).
What is C-peptide?
Inactive fragment cleaved from the insulin prohormone.
Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (produced in equal amounts).
>Because insulin is metabolised faster, levels of C-peptide are typically about 5x higher than endogenous insulin release.
What is the mechanism of peptide hormones?
Water soluble - easily transported in blood
Difficult to cross cell membrane, need receptors on target cell
Once bound normally create a fast biological responses (seconds to minutes)
What pathways do peptide hormones activate?
Most work via modulating either the G-protein receptors, or tyrosine kinase pathways
How do peptide hormones activate their receptors?
Activates either a GPCR:
>rapid response through second messenger system
Or Activates a Tyrosine Kinase Linked Receptor:
> alter gene expression
> slower, longer lasting activity
What effects does the activation of peptide receptors have on the cell?
Phosphorylate existing proteins in the cell + modify their function
>open/close ion chanels,
>activate/inactivate enzymes
When are steroid hormones made, how are they transported?
Lipid soluble, so need carrier proteins (such as albumin) to carry them
synthesised as needed rather than stored (as would diffuse out of cell otherwise)
Where are steroid hormone receptors found?
Receptors located inside cells (cytoplasmic or nuclear receptors) due to easy crossing of membrane
>Trigger with activation/repression of gene function with nucleus (genomic effect)
What is the mechanisms of action of steroid hormones?
Genes control synthesis of protein so these hormones increase/decreased protein synthesis
Relative slow process - lag time between release + biological effect (hours - days)
Effect persists for a similar amount of time
What are some examples of amine hormones?
Dopamine
Adrenaline
Noradrenaline
Melatonin (only one to not be made from tyrosine)