2: Endocrine system and receptors Flashcards
The endocrine system consists of ___.
glands
Do endocrine glands have ducts?
No - release hormones into bloodstream
Parietal cells and G cells in the stomach have ___ so they are examples of exocrine cells.
ducts
How do hormones have specific actions i.e why don’t they react with all receptors on all cells?
Hormones have distinct structures
Receptors are specific to each hormone
Receptors are found in different distributions on different cells
The tissues or cells on which a hormone acts are called ___ tissues / cells.
target tissues / cells
What are the three categories of hormone?
Modified amino acids (hormones derived from tyrosine and tyramine)
Steroid hormones (derived from cholesterol)
Peptide hormones (from proteins)
What are some examples of modified amino acid hormones?
Adrenaline
Thyroid hormones
What are some examples of steroid hormones?
Cortisol
Progesterone
Testosterone
What are some examples of peptide hormones?
Insulin
ACTH
ADH
Oxytocin
What types of hormone are derived from:
a) tyrosine and tyramine
b) cholesterol
c) protein?
a) Modified amino acid hormones
b) Steroid hormones
c) Peptide hormones
What type of hormones are:
a) ADH
b) thyroid hormones
c) testosterone?
a) Peptide
b) Modified amino acid
c) Steroid
What is autocrine signalling?
Hormone causes response in the same cell
What is paracrine signalling?
Hormone exits cell and causes response in adjacent cells
What is endocrine signalling?
Hormone exits cell, enters bloodstream and causes response in distant cells
In what types of signalling do hormones:
a) enter the bloodstream and cause a response in distant cells
b) cause a response in the same cell it was made in
c) cause a response in adjacent cells?
a) Endocrine
b) Autocrine
c) Paracrine
Hormones act in (very low / very high) concentrations to cause a response in target cells.
very low concentrations
measured in mmol/L
Specific hormones affect (one / more than one) target cell.
Target cells are regulated by (only one / more than one) hormone.
Specific hormones affect several different cell types
Target cells are regulated by loads of different hormones
Binding of a ligand to a receptor to cause a cellular response (i.e carrying a signal through the cell membrane) is called ___ ___.
signal transduction
Seeing as hormones are present in tiny concentrations, what process often occurs when hormones bind to receptors?
Amplification
to increase the number of responses to a single hormone molecule
Where are hormones deactivated?
Where they bound to the receptor
OR
The liver
Several different hormones can work together to regulate a physiological factor like blood glucose concentration.
What is this process called?
Complementary / cooperative action
What are two processes regulated by complementary action of hormones?
Increase in blood glucose conc. during exercise - adrenaline, cortisol and glucagon working together
Normal growth - growth hormone, insulin, IGF-1 and sex steroids working together
What is antagonistic action of hormones?
Hormones have the opposite effect and work against each other
e.g insulin and glucagon - insulin decreases blood glucose conc., glucagon increases it
Amino acid based proteins like adrenaline are more commonly known as ___ hormones.
amine hormones
Amine hormones are synthesised (within / outwith) cells, stored in ___ and then released in response to activation of a receptor by ligand.
synthesised within cells
stored in vesicles
By what process are vesicles containing amines released from a cell?
Exocytosis
What ion is required for exocytosis of vesicles from cells?
Ca2+
Amines are (hydrophilic / hydrophobic), which means they can flow freely in the blood.
hydrophilic
(remember that thyroid hormones are hydrophobic and therefore lumped in with steroids)
Why are amine hormones always ready to be secreted from cells?
Cells have big reserves of them
Peptide hormones are cleaved off longer ___ proteins before they are stored in vesicles and released by exocytosis.
precursor proteins
Are peptide hormones hydrophilic or hydrophobic?
Hydrophilic
so they freely float in the blood as well
From which precursor molecule are all steroid hormones produced?
Cholesterol
What is the intermediate molecule between cholesterol and all steroid hormones?
Pregnenolone
Are steroid hormones stored in vesicles?
No
Secreted as soon as they are synthesised from cholesterol > pregnenolone
Steroids are (hydrophilic / hydrophobic).
How are they transported in the blood?
hydrophobic
transported by carrier proteins
The receptors responsible for activating steroid synthesis are found (within / on the membrane) of cells.
within
Amine and peptide synthesis receptors are found on the cell membrane
Steroid hormones are ___ when bound to carrier proteins and ___ when freely floating around.
(active / inactive)
inactive when bound
active when free
Which proteins are hydrophobic and require carrier proteins to transport them in the bloodstream?
Steroid hormones
Thyroid hormones (like thyroxine and triiodothyronine) - the other amine proteins are all hydrophilic and flow freely
___ proteins increase the amount of hydrophobic protein which can be transported in the blood.
Carrier proteins
Carrier proteins also extend the ___ ___ of hormones i.e their duration of action.
half-life
Which classes of hormone are
a) soluble
b) insouble in the blood?
a) Amines, peptides
b) Steroids and thyroid hormones (which are amines)
Name three specific carrier proteins for steroids and thyroid hormones.
Cortisol-binding globulin (CBG)
Thyroxine-binding globulin (TBG)
Sex steroid-binding globulin (SSBG)
Name two general carrier proteins for steroids and thyroid hormones.
Albumin
Transthyretin
Carrier proteins act as a reservoir for hormones.
What does this mean?
There is both bound and free hormone in the blood (existing in equilibrium with each other)
When free hormone diffuses out of the bloodstream into cells, bound hormone is freed to replace it, keeping blood hormone concentration the same
Carrier proteins act as a buffer for hormones.
What does this mean?
If a lot of hormone is suddenly secreted, free carrier proteins are available to bind them (“mopping up the excess”)
So free blood hormone concentration doesn’t suddenly rise
The secretion of many hormones is controlled by what feedback mechanism?
Negative feedback
e.g the presence of cortisol inhibits its own secretion by inhibiting glands all the way up the chain
Negative feedback loops can be short or long.
What does this mean?
Short - negative feedback to a gland “one up the chain” - see diagram
Long - negative feedback to glands “at the top of the chain”
The rate of ___ of a hormone is the primary determinant of its plasma concentration.
rate of secretion
Apart from negative feedback via the endocrine system, what other body system influences levels of hormone secretion by endocrine glands?
Nervous system
e.g stress increases secretion of hormones by the hypothalamus, leading to cortisol secretion
The secretion of some hormones changes througout the day.
What is this called?
Diurnal variation
A hormone whose secretion is affected by diurnal variation is cortisol.
When is the secretion of cortisol at its highest and lowest?
So what is likely responsible for the diurnal variation?
Highest during the day (late morning)
Lowest at night
So sunlight is the likely factor
Where is most hormone
a) metabolised
b) excreted?
Liver
Kidneys
The plasma concentration of hormone depends on the rates of ___ and ___.
secretion
elimination
The plasma concentration of hormone is equal to the rate of ___ - the rate of ___.
Rate of secretion - rate of elimination
Different hormones have (the same / different) rates of secretion and elimination.
different rates
In which two places are hormone receptors found?
On the cell membrane
Within the cell (either in the cytoplasm or nucleus)
What specific types of hormone receptor are found on the cell membrane?
G-protein coupled receptors
Receptors associated with tyrosine kinase
Ligands for cell surface hormone receptors are (hydrophilic / hydrophobic).
hydrophilic
Ligands for intracellular hormone receptors are (hydrophilic / hydrophobic).
hydrophobic
remember they’re associated with steroids which are fatty and hydrophobic
revise g protein signalling
receptor tyrosine kinases
when insulin binds, beta subunits autophosphorylate each other (why they’re called tyrosine kinases)
THEN tyrosine phosphorylation of a protein which produces the cellular effect
revise nuclear receptors (resp - asthma)
