Introduction to the Endocrine System Hormones, Receptors and Signalling Flashcards
What kinds of glands are in the endocrine system?
Ductless
How do glands communicate with each other over a distance?
Secretion of hormone into the blood stream and bulk transport to a target site
What is an example of an integrated functional system?
Hypothalamus releases CRF that stimulates the anterior pituatru to release ACTH that causes the adrenal cortex to synthesise and release cortisol
How is specificity of signalling achieved?
Chemically distinct hormones
Specific receptors for each hormone
Distinct distribution of receptors across target cells
What are the major endocrine organs?
Pineal gland Hypothalamus Pituatry gland Thyroid gland Parathyroid gland Thymus Adrenal glands Pancreas Ovary Testis
What are the 4 chemical natures of hormones?
Modified Amino acids
Steroids
Peptides
Proteins
What are some examples of modified amino acids?
Adrenaline
Thyroid hormone
What are some examples of steroids?
Cortisol
Progesterone
Testosterone
What are some examples of peptides?
Anrenocorticotrophic hormone (ACTH)
Anti-diuretic hormone (ADH)
Oxytocin
What is an example of a protein?
Insulin
What are all steroid hormones derived from?
Cholesterol
What is autocrine signalling?
Cell produces signalling molecule that is released into to ECF, these molecules act on the cell itself
(Self-signalling)
What is Paracrine signalling?
Cell signals to its close neighbors
What is endocrine signalling?
The signalling molecule enters the circulation and signals via molecules transported by the blood to target distant cells
What levels of hormones can affect organ function?
Can be very low concentrations
utilises signals which act at an extremely low concentration
If the signal is very scarce, what must be increased?
Receptor Affinity
Hormone Potency
What are some examples of where insulin can act?
Skeletal Muscle
Adipose tissue
Hepatocytes
How is a biological response brought about?
Hormone binds to its cognate receptor which is expressed in a tissue selective manner
What triggers a biological response?
Activated receptor engaging in a preferred signal transduction cascade that differs between individual receptors but typically causes amplification of the original signal
Is the speed of onset and duration of a hormone variable?
Yes very
seconds to days
How is hormone action terminated?
Enzyme mediated metaboloic inactivation in the liver or site of action
What is a complementary action of a group of hormones?
Regulates many complex physiological functions on both short and long term scales
What is an example of a complementary action of a group of hormones?
Adrenaline, cortisol and glucagon contribute to the response of the body to short term intense exercise enhancing physical performance and preventing potential hypoglycaemia
How does an antagonistic action occur?
The balance of opposing influences
What 2 hormones have opposing actions that regulates plasma glucose levels?
Insulin
Glucagon
How are amines made, stores and released?
Pre-synthesised
Stored in vesicles
Released in response to stimuli by Ca2+ dependent exocytosis
Are amines hydrophilic or hydrophobic?
Hydrophillic
How are peptides and proteins made, stores and released?
Presynthesised from longer precursors
Stored invesicles
Released in response to stimuli by Ca2+ dependent exocytosis
Are peptides hydrophillic or hydrophobic?
Hydrophyllic
How are steroids made, stores and released?
Synthesised and secreted upon demand
Stimuli increase:
-Cellular uptake and availlibility of cholesterol
-Rate of conversion of choolesterol to pregnenolone
When is cortisol released?
Immediately after it is formed
No prestorage or packaging
What must occur for a cell to produce a steroid hormone?
The cell must initiate synthesis and release the steroid immediately
Are steroids hydrophobic or hydrophyllic?
Hydrophobic
How are steroids transported in blood?
Bound to specific transport proteins
What is the fraction of steroid that is unbound able to do?
Biologically active
Can cross the wall
What are 3 steroids that must be carried by circulating carrier proteins?
Steroids
Thyroxine
Triiodothyronine
What are some functions of carrier proteins?
Increase amount transported in blood
Provide a reservoir of hormone
Extends half life of the hormone in the circulation
What are 3 important plasma carried proteins?
Cortisol-binding globulin (CBG)
Thyroxine-binding globulin (TBG)
Sex steroid-binding globuling (SSBG)
What are 2 general carrier proteins?
Albumin
Transthyretin
What do carrier proteins act as?
A buffer and reservoir that helps to maintain relatively constant concentrations of free lipophilic hormone in the blood - equillibrium between free and bound hormone
What hormones can cross the capillary wall?
Only free hormone
What are surges in hormone secretion buffered by?
Binding to carriers - free concentration does not rise abruptly
How is free hormone removed from plasma?
By elimination
What is the free hormone that is removed by plasma replaced with?
Bound hormone dissociating from carrier proteins
What is the primary determinant of plasma concentration?
Rate of secretion
Describe the pathway in which cortisol is released?
Hypothalamus Secretes corticotrophin releasing factor (CRF) Anterior pituitary Secretes ACTH Adrenal cortex Secretes cortisol
What is diurnal circadian rhythm?
Secretion rate fluctuates (up and down) as a function of time entrained by external cues
What important routes can elimination occur by?
Metabolism locally
Metabolism by the liver
Excretion by the kidney
What is plasma concentration of a hormone equal to?
Rate of secretion - rate of elimination
What are 3 types of Hormone receptors?
G coupled protein receptors
Receptor kinases
Nuclear receptors
How are GPCR activated and where are they found?
Activater by amines and some proteins and peptides
Found on the cell surface
What are receptor kinases activated by and where are they found?
Proteins and petides
Found on the cell surface
Where are nuclear receptors found?
INtracellularly
- In cytoplasm (class 1)
- In nucleus
What are the 3 classes of nuclear receptors?
Class 1 - activated by many steroid hormones, in the absense of activating ligand these are mainly located in the cytoplasm bound to heat shock proteins
Class 2 - activated mostly by lipids, present in the nucleus
Hybrid class - Activated by thyroid hormone and other substances
What is constitutive activity?
Always active without any signals
What kind of receptor is the insulin receptor?
Receptor kinases
What subunits are present in the insulin receptors?
Alpha and Beta subunits
What does the binding of insulin to the receptor cause?
Autophosphorylation of intracellular tyrosine residues
Recruitment of multiple adapter proteins (IRS1) that are also tyrosine phosphorylated
- binding of Insulin receptor substrate proteins which become phosphorylated
-AKT/Protein Kinase B
-Metabolic effects
