The Endocrine System Flashcards
What is the endocrine system?
A system which integrates and controls organs via the secretion of hormones which are carried in the blood to target organs
What system does the endocrine system work with?
Nervous system
What is endocrine communication?
Hormones which travel in the blood to target organs/tissues
Where do hormones act upon?
Receptors.
No receptor = no response
What occurs during Neural Communication?
NT’s are released from presynaptic neurons that travel across the synaptic cleft to post synaptic cleft to influence its activity. NTs released by neuron and acts locally within synaptic cleft
What occurs when the nervous and endocrine systems combine?
Nerves release hormones which eter blood and travel to their target cells. Process is highly specific as only target cells have receptors for the hormone
Define Autocrine
Cells that secrete chemicals that bind to receptors on the same cell
Define Paracrine
Chemicals diffuse in ECF to affect neighbouring cells
What are the features of an endocrine hormones?
Produced by a group of cells, secreted from those cells into the blood, Transported via the blood to distant targets, Exert their effects at very low concentrations, Act by binding to the receptors on target tissues, Have their action terminated (usually by Negative Feedback)
What are peptide/protein hormones comprised of?
Chains of amino acids
What are steroid hormones derived from?
Cholesterol
What are Amine Hormones derived from?
Tryptophan or Tyrosine
Give examples of Peptide Hormones
TRH, FSH, Insulin
What are preprohormones?
Contain one or more copies of the active hormone in their amino acid sequence
How are peptide hormones synthesised?
SYNTHESISED IN ADVANCED
Stored as perprohormone which are eventually cleaved into smaller units in the RER into prohormones. These are packaged into golgi apparatus, alongside proteolytic enzymes, which breakdown prohormone into an active hormone
Where are peptide hormones stored?
In vesicles in endocrine cells until released into plasma
What is C-peptide
The inactive fragment cleaved from insulin prohormone
What feature of peptide hormones makes them dissolvable in plasma?
They are water soluble
Where do peptide hormones bind?
They bind to membrane bound receptors on target cells as they cannot cross cell membrane
What occurs when peptide hormones bind to membrane bound receptors?
Fast biological responses are generated via modulating either the GPCR or Tyrosine Kinase Linked signalling pathways. This results in phosphorylation of existing cellular proteins which modifies their function
Where type of receptors do peptide hormones bind to?
GPCR - activated 2nd messenger systems+/ ion channels which leads to modification of existing proteins
Tyrosine Kinase Linked Receptor - Alters gene expression
When are steroid hormones synthesised?
When they are needed as they are lipophilic and cannot be retained within the lipid membrane
Why are steroid hormones bound to carrier proteins?
As they are poorly soluble in water which stabilises their transport through plasma from enzymatic degradation
Where are steroid hormones produced?
Gonads, Placenta, Kidney, Adrenal Cortex
Describe the action of steroid hormones
Steroid hormones easily cross the plasma membrane and their receptors are located inside the cells and either trigger activation or inhibition of gene function within nucleus.
Which hormone is the only amine hormone not synthesised by tyrosine?
Melatonin which is derived from tryptophan
Describe the physiological activity of lipophilic hormones
Only a small amount of unbound steroid/thyroid hormone in the plasma. Only free hormone can diffuse across capillary walls to target cells
Describe the Law of Mass Action
As free hormone leaves the plasma, more hormone is relased by carriers
How is total plasma hormone concentration calculated?
Free Hormone + Complexed Hormone
How is hormone concentration in blood determined?
It is dependant on rate of secretion and removal.
Where does hormone removal occur?
Kidney or liver via excretion or metabolic transformation
What hormones are respondent to negative feedback control?
Parathyroid Hormone
What hormones respond to neural feedback loops?
Adrenaline
What occurs after prolonged exposure to low hormone concentration in plasma?
An up-regulation, Increased number of hormone receptors on target tissues which increases tissue sensitivity to hormone
What occurs after prolonged exposure to high hormone concentration in plasma?
Down regulation = a decrease in receptor number on target tissues which decreases tissue sensitivity
What is the permissive effect?
The presence of one hormone which enhances the effect of another hormone
