Introduction to the endocrine system Flashcards
Define endocrine system
A system that controls organ function through the secretion of chemicals from cells, tissues or glands which are then carried in the blood to the target organs where they influence the activity of the organ
How do tissues detect hormones
The presence of specific receptors for the hormones on or in the cell
How does neural communication work
Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity
How does endocrine communication work
Hormones travel in the blood to their target hormones
What is neuroendocrine
Endocrine and nervous system combine
Nerves release hormones which enter the blood and travel to target cells e.g hypothalamus and posterior pituitary axis
How can one hormone produce a different effect in different cells
Because each cell can have a different receptor for the hormone which leads to a different downstream pathway
How do exocrine glands deliver their secretions
Through ducts to the external environment including the GI tract e.g bile and saliva
What are autocrine secretions
cells secrete chemicals that bind to receptors on the same cell
What are paracrine secretions
Chemicals diffuse in the extracellular fluid to affect neighbouring cells
What are peptide hormone composed of
chains of amino acids
What are amino hormones derived from
one of two amino acids - tryptophan or tyrosine
What are steroid hormones derived from
cholesterol
What is one of the only amine hormones that comes from tryptophan
melatonin
Describe the sequence of how peptide hormones get synthesised and then stored and released
They are synthesised by ribosomes as preprohormone until they are needed when the preprohormone is cleaved in the endoplasmic reticulum into prohormone and packaged into vesicles by the golgi apparatus with proteolytic enzymes until it is needed
What do the proteolytic enzymes which are packaged with prohormone do
Break the prohormone into the active hormone
What is C-peptide and why is it measured instead of insulin directly
Inactive fragment cleaved from insulin prohormone - it is measured instead of insulin directly due to insulin b eing metabolised 5x as fast
What is the mechanism of action of peptide hormones
they are water soluble so dissolve in the plasma and travel easily but cannot cross cell membranes so they have to bind to receptors on the target cell
What are the two receptors that peptide hormones usually bind to
GPCR
tyrosine kinase linked
What is a GPCR
G protein coupled receptor
activates 2nd messenger system or ion channels which leads to modification of existing proteins
What is the difference between tyrosine kinase linked receptors and G protein coupled receptors
GPCR have a rapid response while tyrosine kinase linked receptors are slower and longer lasting which is why they are associated with growth
How are steroid hormones different to the other hormones in terms of production and storage
They are synthesised directly as needed and not stored like the other hormones
Why can steroid hormones not be stored
They are highly lipophilic so can therefore not be retained within a lipid membrane
How are steroid hormones transported in the blood considering they are poorly water soluble
They are transported bound to carrier proteins such as albumin - this protects them from enzymatic degredation
Are steroid hormones quick or slow acting
Slow onset of action but action persists longer then peptide and amine hormones
Where in the body are steroid hormones produced
Gonads
Placenta
Kidney
Adrenal cortex
What steroid hormones are produced by the gonads
Sex steroids e.g testosterone and estrogen
What steroid hormones are produced by the placenta
hCG, sex steroids
What steroid hormones are produced by the kidney
Vitamin D3
What steroid hormones are produced by the adrenal cortex
corticosteroids
Why are steroid hormone receptors located within cells
Because steroid hormones are very lipophilic so can cross in and out of the cell membrane
What is the effect of steroid hormones when they bind to their receptors
Their receptors change the gene expression at the nucleus so they either increase or decrease protein synthesis
What do steroid hormones have to be to diffuse into target cells
unbound to plasma protein carriers
What is the free hormone: protein bound hormone ratio in favour of
Protein bound is much in favour but free hormone is the physiologically important fraction
