Describe the difference between the endocrine and exocrine systems
Endocrine - hormones secreted into Extra-cellular fluid
Exocrine - secretes hormones into duct system which then empties hormones into various parts of body
Name the main endocrine glands in the body
Name the four main chemical groupings of hormones
Modified Amino Acids
What substance is the precursor for steroid hormones?
Adrenaline, T3 and T4 are examples of what type of hormone?
Modified amino acids
Give examples of steroid hormones
Adrenocorticotrophic hormone (ACTH) and anti-diuretic hormone are members of what group of hormones?
Give one example of a protein hormone
Describe the difference between Autocrine, Paracrine and Endocrine
Autocrine - cell that releases the signal also receives the signal
Paracrine - cell that sends the signal is adjacent to the cell which recieves the signal
Endocrine - cell sends signal into bloodstream and signal is recieved at an organ distal to the original cell site
It is possible for hormones to act in more than one manner (e.g. both paracrine and endocrine). TRUE/FALSE?
e.g. somatostatin = paracrine in pancreas
BUT endocrine in brain
Hormones act at very high concentrations. TRUE/FALSE?
Act at very low concentrations
=> act with very high potency
What occurs when a hormone binds to its target receptor?
- biological response is triggered
- signal transduction cascade
- causes amplification of the original signal
How is hormone action terminated?
- enzyme-mediated metabolic inactivation in the liver
- or terminated at sites of action
Give an example of hormones which work together in a complementary manner
Adrenaline, cortisol, glucagon
Prevent hypoglycaemia and hypokalaemia in short term intense exercise
What hormones work in an antagonistic manner?
INSULIN and GLUCAGON
- lowers plasma glucose levels
- increases plasma glucose levels
=> opposite effects
How are amine hormones released from cells?
- stored in vesicles
- released by Ca2+ dependent exocytosis
Are amine hormones hydrophilic or hydrophobic? Can they be transported freely in plasma?
Amines are hydrophilic
=> transported mainly free in plasma
Are peptide hormones hydrophilic or hydrophobic? Can they be transported freely in blood plasma?
=> transported mainly free in plasma
How are peptide hormones released from cells?
- pre-synthesised usually longer precursors
- stored in vesicles
- released by Ca2+-dependent exocytosis
How are steroid hormones synthesised and released from cells?
- synthesised and secreted upon demand
How do stimuli increase the production/secretion of steroid hormones?
(i) cellular uptake and availability of cholesterol
(ii) rate of conversion of cholesterol to pregnenolone (rate limiting step)
Are steroid hydrophilic or hydrophobic?
=> transported in plasma mainly bound (~90%) to plasma proteins
only ‘free’ steroid hormone is biologically active
What are the main functions of carrier proteins?
- increase amount transported in blood
- provide a reservoir of hormone
- extend half-life of the hormone in the circulation
Give examples of specific carrier proteins
cortisol-binding globulin (CBG) – binds cortisol in a selective manner (also some aldosterone)
thyroxine-binding globulin (TBG) – binds thyroxine (T4) selectively [also some triiodothyronine (T3)]
sex steroid-binding globulin (SSBG) – binds mainly testosterone and oestradiol
Give an example of a general carrier protein
albumin – binds many steroids and thyroxine
Why do peptide and protein hormones not last as long?
They do not have carrier proteins to prolong their half life
How do carrier proteins prevent surges in hormone?
bind free hormone to buffer surge in concentration
If hormone is eliminated from the plasma, what is the role of carrier proteins?
To dissociate from hormone and create more “free” to enter plasma and maintain concentration
What elements of the HPA axis can cortisol negatively feedback on?
What external factor can have a positive effect on the HPA pathway, causing it to be stimulated more?
Stress at level of hypothalamus
elicits sudden burst in secretion
How are hormones usually eliminated
metabolism locally, by the liver
excretion by the kidney
How is the plasma concentration of a hormone defined?
plasma conc. = rate of secretion – rate of elimination
Roughly how long are the half lives of each hormone group?
amines t½ = seconds
proteins and peptides t½ = minutes
steroids and thyroid hormones - t½ = hours to days
What types of receptors do hormones usually bind to?
G-protein coupled (GPCR)
Nuclear receptors (Class 1, Class 2 and Hybrid class)
What hormone receptors are found on the cell surface?
How are the classes of Nuclear Receptor different?
- activated mainly by steroids
- located in the cytoplasm
- bound to inhibitory heat shock proteins (HSP)
- move to the nucleus when activated
- activated mostly by lipids
- present in the nucleus
- activated by thyroid hormone (T3) etc
- similar in function to class 1
What type of hormone activates GPCRs?
activated by amines and some proteins/peptides
What types of hormone activate receptor kinases?
activated by some proteins/peptides
What effect does Gs have on the formation of adenylyl cyclase?
Causes it to convert more ATP to cAMP
What effect does Gi have on adenylyl cyclase?
Negative effect on production of cAMP from ATP
What hormones signal via GPCR Gs?
Corticotrophin Releasing Factor (CRF)
What hormone signals via GPCR Gi?
for sleep => causing cellular effects to lessen
What hormones signal via GPCR Gq?
Gonadotrophin releasing hormone
Thyrotropin releasing hormone
Describe the mechanism of receptor kinases
Target Hormone Binds Autophosphorylation of tyrosine residues Recruitment of phosphorylated adapter proteins Stimulate Protein kinase B Metabolic effects
Describe the basis of Class 1 nuclear receptor signalling
- lipophilic molecules diffuse across plasma membrane
- combine with intracellular receptor
- HSP dissociate
- receptor steroid complex moves to nucleus
- dimer forms and binds to DNA hormone response elements
- transcription either ‘switched-on’ or ‘switched off’
=> alters mRNA levels/rate of synthesis of proteins