Introduction to Endocrinology Flashcards
What is the endocrine system?
The system that integrates and controls organ function via hormones from tissues or glands which are then carried in the blood to target organs distal from the site of the hormone synthesis where they influence the activity of the target organ
What are paracrine chemicals?
Act locally at the site of synthesis
What are autocrine chemicals?
Act on or in the same cell that synthesised them e.g. cytokines
What are exocrine chemicals?
Released from exocrine glands via ductus to the external environment and the GI tract e.g. saliva, sweat, bile
How do the basics of the endocrine communication operate?
Hormones travel in the blood to their target organs and/or tissues
Tissues detect the hormones via specific receptors for that chemical on or in the cells, if there are no receptors present there is no response
What is the link between the neural and endocrine systems?
The neuroendocrine systems are the combination of the neural and endocrine systems, where nerves release hormones and they travel in the blood to the target organs
Describe the specificity of tissues to organs
Generally tissues are highly specific, despite the perfusion of many hormones throughout the circulation
Give some examples of endocrine functions both in physiological systems and as distinct glandular systems
Physiological - reproductive, renal, GI
Glands - thyroid, adrenal, pituitary
Describe the secretion of endocrine hormones
Secretion is by a cell or group of cells and is directly into the blood, where the hormones are directed to the distant targets
Describe the concentration of endocrine hormone required to exert their effect
Very low concentrations required to have effect
What is often the termination stage that ceases the function of endocrine hormones?
Action of a negative feedback loop
What are the three classifications of endocrine hormone?
Peptide or Protein - most common
Steroid
Amine
From what are all steroid hormones derived?
Cholesterol
From what are all amine hormones derived?
One of two amino acids, either tyrosine or tryptophan
Give some examples of peptide hormones
TRH
FSH
Insulin
At what point are peptide hormones synthesised?
In advance of need and stored in vesicles until required
Describe the stages of the synthesis of peptide hormones
The initial protein produced by the ribosome contains at least one copy of the active hormone and is called the preprohormone
These are then cleaved into smaller units in the RER and are called prohormones
These prohormones are then packaged in vesicles in the golgi apparatus with proteolytic hormones which breakdown the prohormone into the active hormone and other fragments
The hormones are stored in these vesicles until required
Are peptide hormones water soluble?
Yes
Can peptide hormones cross cell membranes? Why?
No, because they are water soluble
What do peptide hormones do as they are unable to cross cell membranes?
Bind to membrane bound receptors on the target cell
Are the responses caused by peptide hormones usually fast or slow?
Usually fast - seconds to minutes
What are the two different pathways that peptide hormones may modulate once attached to a cell receptor?
GPCR pathway
Tyrosine Kinase Linked pathway
Are peptide hormones hydrophilic or hydrophobic?
Hydrophilic
What is the result and response speed if a peptide hormone modulates a GPCR pathway?
There is activation of a 2nd messenger system and modification of the existing protein
Rapid response
What is the result and response speed if a peptide hormone binds to and modulates a tyrosine kinase linked pathway?
Gene expression is altered
Slower, longer lasting activity
At what stage are steroid hormones synthesised?
Directly as needed rather than in advance
Are steroid hormones lipophilic or lipophobic?
Highly lipophilic (lipid soluble)
What happens once steroid hormones have been synthesised?
They diffuse across the membrane into the ISF and the blood
Are steroid hormones easily soluble in water?
No, they are transported with carrier proteins like albumin, stabilising their transport and protecting them from enzymatic degradation, massively increasing their half life - 60-90 minutes versus 2 mins for adrenaline
Where are steroid hormones produced?
The gonads, placenta, kidney, adrenal cortex
Can steroid hormones cross the cell membrane?
Yes, easily, both in and out
Where in/on the cell are receptors for steroid hormones?
Within the cell as the hormones can easily pass in and out of the cell
What is the term for the effect that steroid hormones have on a cell? What is the result of this?
Genomic effect - this has a knock-on effect in altering the proteins
What is the usual timescale for the effect of steroid hormones?
Relatively slow between release and biological effect - hours to days
What is the only amine hormone not derived from tyrosine? What is its role?
Melatonin - regulating circadian rhythm
Is the bound steroid hormone or the unbound free hormone in the physiologically relevant?
The free hormone - the vastly smaller portion
Which two quantities make up the total plasma hormone content?
Free hormone + complexed hormone
What are the functions of hormone carrier proteins?
Transport hormones in the plasma by increasing solubility
Protecting hormones from degradation
Increasing hormone half life
How does the removal of hormone from the blood take place? Where?
By excretion or metabolic transformation and mainly occurs in the liver and kidneys
Do steroid and thyroid hormones take more or less time than peptide and catecholamine hormones to be excreted/metabolised? Why?
Steroid and thyroid hormones take considerably more time - hours to days, because they are bound to carrier proteins
What is an important principle in monitoring/testing hormone levels?
Single/instantaneous values may be misleading and so 24 hour monitoring is required to provide a clinically useful picture
What is endocrine up-regulation?
An increase in the number of hormone receptors on target tissues in response to prolonged exposure to low levels of plasma hormone
What is endocrine down-regulation?
A decrease in the number of hormone receptors on target tissues in response to prolonged to high levels of plasma hormone
