Introduction to the Endocrine System Flashcards
What does the endocrine system consist of
Ductless endocrine glands occurring at numerous locations in the body
How is communication achieved between glands and other tissues
By secretion of a hormone into the blood stream and transport to a target site
In what 3 ways is specificity of signalling achieved
- Chemically distinct hormones
- Specific receptors for wach hormone
- Distinct distribution of receptors across target cells
Name the 3 endocrines in the brain
Pineal
Hypotahlamus
Pituitary
Name the 2 endocrines in the Neck
Parthyroid
Thyroid
Name the 2 endocrines in the abdomen
Adrenal gland and pancreas
Name the 3 other endocrines depending on the sex of the patient
Testes
Ovaries
Placenta in pregnant females
Name the 6 overall functions of the endocrine system
- Regulation of nutrient metabolism and H2O and electrolyte balance
- Enabling changes to stress
- Promoting growth and development
- Controlling reproduction
- Regulating red blood cell production
- Controlling and integrating the activities of the cardiovascular and digestive systems (co-operation with the autonomic nervous system)
What is cortisol
A chronic stress hormone
What are the 3 main classes of hormones
Glycoproteins and peptides
Steroids
Tyrosine and tryptophan derivatives
What are the most diverse class of hormones
Glycoproteins and peptides
Give two examples of hormones in the proteins and peptide class
Oxytocin and insulin
What are steroid hormones derived from
Cholesterol
Give 2 examples of steroid hormones
Cortisol and testosterone
Give 3 examples of Tyrosine and tryptophan derivatives
Adrenaline (epinephrine)
Thyroid hormones
Melatonin
How are amines synthesised, stored and released
Pre synthesised
Stored in vesicles and released in response to stimuli by Calcium dependent exocytosis
They are hydrophilic and are transported mainly “free” in plasma
How are peptides and proteins synthesised, stored and released
Pre-synthesised usually from a longer precursor, stored in vesicles, released in response to stimuli by Ca2+ dependent exocytosis
How are peptides transported
They are hydrophilic and are mainly “free” in the plasma
How are steroid synthesised and stored?
They are synthesised and secreted on demand
What is the rate limiting step in sterois
Rate of conversion of cholesterol to pregnenolone
How are steroids released and transported
Steroids are hydrophobic and are transported in plasma main young to plasma proteins - only free is biologically active
Describe the solubility of steroids and thyroxine in plasma
Relatively insoluble
What do carrier proteins do
Increase the amount transported in blood and prevent rapid excretion by preventing filtration at the kidney
What are some of the specific carrier proteins
Cortisol-binding globulin (CBG)
Thyroxine-binding globulin (TBG)
Sex steroid-binding globulin (SSBG)
What does CBG do
Binds cortisol in a selective manner (also some aldosterone
What does TBG do
binds thryoxine (T4) selectively (also some triiodothyronine (T3)
What does SSBG do
Binds mainly testosterone and estradiol
What are some of the general carrier proteins
Albumin and Transtyhyretin
What does albumin do
Binds many steroids and thyroxine
What does Transthyretin do
Binds thyroxine and some steroids
Describe the solubility of proteins and peptides in plasma
The are soluble
Why do proteins and peptides not require carrier proteins for transport
Due to their soluble nature in plasma
What do carrier proteins act as
A buffer and reservoir that helps to maintain relatively constant concentrations of free lipophilic hormone in the blood - free and bound hormone are in equilibrium
What type of hormones can cross the capillary wall to activate receptors in target tissues
Free hormones
What are surges in hormone secretion buffered by
Binding to carriers - free concentration does not rise abruptly
A free hormone removed from plasma by elimination is replaced by what
Bound hormone dissociating from carrier protein
What is the primary determinant of plasma concentration
Rate of secretion
Secretion is subect to several controls. What are the 2 main controls
Negative feedback
Neuroendrocrine
Diurnal (circadian) rhythm
What does negative feedback play a role in
Maintains plasma concentration at a set level
Where are the 2 main centres for regulating negative feedback control
Hypothalamus and anterior pituitary
What does the hypothalamus secrete
Corticotropin-releasing hormone
What does the anterior pituitary secrete
Adrenocorticotropic homrone
What does the adrenal cortex secrete
Cortisol
What does neuroendocrine play a roll in
Elicits a sudden burst in secretion to meet a specific stimulus
What is an example of a neuroendocrine control of hormones
Stress
What is the Diurnal rhythm
Secretion rate fluctuates (up and down) as a function of time - entrained to external cues (e.g. night / day)
Elimination occurs by several routes - what are the 2 most important
Generally metabolism by the liver and excretion by the kidney are the most important.
How long does it take for amines e.g. adrenaline to be eliminated
Seconds
How long does it take for proteins and peptides to be eliminated
Minutes
How long does it take for steroids and thyroid hormones to be eliminated
Hours to days
Why doe steroids take much longer to be eliminated
Due to the extensive protein binding
When are the testosterone level highest
In the morning
When should testosterone levels be tested
First thing in the morning
What are the 3 structural and functionally distinct types of hormone receptors
G-protein coupled (GPCR)
Receptor kinases
Nuclear receptors
How are G protein coupled receptors activated
By amines and some proteins/peptides
Major signalling pathways involve coupling to what GPCRs
Gs, Gi or Gq
How are receptor kinases activated
by some proteins/ peptides
What are nuclear receptors subdivided into
Class 1, class 2 and a hybrid class
What are the cell surface receptors
GPCR and Receptor kinases
What are the intracellular receptors
Nuclear receptors
What is a class 1 nuclear receptor
Activated by any steroid hormones - in the absence of activating ligand these are mainly located in the cytoplasm bound to inhibitory heart shock proteins (HSP) - they move to the nucleus when activated
What are the class 2 nuclear receptors
Activated mostly by lipids - constitutively present in the nucleus
What are the hybrid class of nuclear receptors
Activated by thyroid hormone (T3) and other substances - similar in function to class 1
