Endocrine System Flashcards
What are hormones?
Chemical messengers that are secreted from one cell, travel through the bloodstream and affect another cell in another part of the body.
What does endocrine communication enable?
Enables homeostasis and cellular activities to be coordinated throughout the body
What is the general process of endocrine communication?
Stimulus –> Hormone release from endocrine cell and into the blood –> hormone binds to a specific receptor in a distant cell –> distant cell responds to stimulus
What are hormones made of?
- Amino acids (proteins)
- Cholesterol (lipid)
How do amino acids travel through the blood?
Amino acids are water soluble so they travel in blood unbound because they are soluble
How does cholesterol travel through the blood?
Cholesterol is fat soluble so travel in blood bound to carrier proteins because they are insoluble
How do hormones have specific effects?
Hormones only bind to receptors specifically designed to receive it
What happens to the hormone once it has served its purpose?
It is removed, broken down and recycled or excreted in sweat and urine
How can you detect hormones in sweat?
Non-invasive, skin patches
How can you determine pregnancy through urine?
By detecting Human Chorionic Gonadotrophin (hCG) in the urine
What is the chemical classification of water soluble hormones?
Proteins, peptides and some amines (catecholamines eg. adrenaline)
What is the chemical classification of lipid soluble hormones?
Steroids and some amines (thyroid hormones)
Where are the receptors for water soluble hormones located?
Plasma membrane receptors. Can’t cross through the lipid based membrane
Where are the receptors for lipid soluble hormones located?
Intracellular receptors (in cytosol or nucleus). Once they become unbound to the carrier protein they can go right through the cell.
How do water soluble hormones work in the cell to produce an effect?
Activation of 2nd messengers to amplify hormone response
How do lipid soluble hormones work in the cell to produce an effect?
Alternation of gene transcription (to make new proteins)
How long does it take for water soluble hormones to initiate a response?
Fast - the effects last milliseconds to seconds)
How long does it take for lipid soluble hormones to initiate a response?
Slow - the effects last hours to days
What is an example of a water soluble hormone?
Example: Adrenaline (fast, short-acting response to stress)
- Anti diuretic hormone
- Oxytocin
- Insulin
What is an example of a fat soluble hormone?
Example: Cortisol (slow, long-lasting response to stress)
- Estrogen
- Progesterone
- Testosterone
What is the connection between the hypothalamus and the posterior pituitary gland?
Axon connection
Where are the posterior pituitary hormones made?
In the hypothalamus then travel down axons and stored in axon terminals
Action potentials cause hormone release from posterior pituitary
What is the connection between the hypothalamus and the anterior pituitary?
Blood vessel connection. (two hormones)
One hypothalamus hormone and one anterior pituitary hormone
What is anterior pituitary hormone secretion influenced by?
Releasing/inhibiting hormones made in the hypothalamus travel through the bloodstream to release or inhibit release of anterior pituitary hormones.
What are the 5 hormones released from the anterior pituitary?
ACTH
FSH
LH
TSH
Growth hormone
What are the 2 hormones released from the posterior pituitary?
ADH
Oxytocin
What are the 2 hormones released from the adrenal medulla?
Adrenaline
Noradrenaline
What are the five neuroendocrine axes?
- The “stress axis”
- The “thyroid hormone axis”
- The “reproductive axis”
- The “growth hormone axis”
- Th “prolactin hormone axis”
What is the stress axis?
Corticotropin-releasing hormone (CRH) is released from the hypothalamus and travels through the blood vessel connection to the anterior pituitary gland. There it binds to its receptor and stimulates the release of a 2nd hormone, Adrenal Corticotropin Hormone (ACTH). That leaves the anterior pituitary and binds to its receptor on the adrenal gland which leads to the production of the 3rd hormone, cortisol
What are the target cells and effects of cortisol?
- Skeletal muscle; Effect – increased protein breakdown and decreased glucose uptake/use
- Adipose (fat); Effect – increased fat breakdown and decreased glucose uptake/use
- Liver; Effect – increased glucose synthesis/creation
What is the thyroid hormone axis?
Thryotopin releasing hormone (TRH) is released from the hypothalamus and travels through the blood vessel connection to the anterior pituitary gland. There it binds to its receptor and stimulates the release of a 2nd hormone, Thyroid Stimulating Hormone (TSH). That leaves the anterior pituitary and binds to its receptor on the thyroid gland which leads to the production of a number of hormones, one of which is the thyroid hormone
What is the reproductive axis?
There is one releasing hormone coming from the hypothalamus, gonadotrophin releasing hormone (GnRH) which stimulates two anterior pituitary hormones, known as gonadotropins and these are Luteinising hormone (LH) and follicle stimulating hormone (FSH). These hormones act together at the gonads (ovaries/testes) to produce the gonadal steroid hormones; estrogen, progesterone and testosterone
What is the growth hormone axis?
There are two hypothalamic hormones, Growth hormone releasing hormone (GHRH) and Growth hormone inhibiting hormone (GHIH). These both have different effects on the anterior pituitary hormone, growth hormone (GH). GH released from the anterior pituitary gland then acts on a variety of cell types including the liver and one of the main hormones that it stimulates comes from the liver and its known as Insulin like growth factor (IGF-1)
Which two hormones promote growth in tissues?
GH and IGF-1
What gets broken down in liver to mobilise fuel (glucose) into the blood?
Glycogen
Which fuel is mobilised from the breakdown of fat?
Free fatty acids
What is the prolactin axis?
This axis is different because the hypothalamic hormone, Dopamine (DA) is constantly inhibiting the anterior pituitary hormone, prolactin (PRL). If dopamine is signalling to the anterior pituitary gland you have no prolactin release. If dopamine is inhibited, prolactin will be produced and acts throughout your body. Acts predominately in the breasts to promote milk production
What does GHRH stimulate?
Stimulates the release of GH which targets muscle, liver and fat
Stimulate the release of IGF-1 from the liver which targets nearly all cells in the body
When is the growth hormone stimulated?
- After you’ve eaten
- After exercise
- Sleep (increases GH the most)
What effects does the GH axis have on growth?
- GH stimulates protein synthesis in muscle
- IGF-1 (from liver) stimulates the growth of bones, muscles and other tissues
What effects does the GH axis have on metabolism?
- GH actions in the liver to increase blood glucose
- GH increases the breakdown of adipose tissue to free fatty acids
How is the growth hormone axis regulated?
- Both IGF-1 and GH inhibit the hormones that control their release
- GHIH or somatostatin, is stimulated by IGF-1 to inhibit downstream GH release
Both and negative and positive feedback loop for GH
What does TRH stimuate?
Stimulates TSH which stimulates TH which targets nearly all cells in the body
What are the functions of the thyroid hormone?
- increases metabolic rate
- increases growth & development
- regulates heart rate
- regulates body temperature
- regulates muscle contraction
How is the TH axis regulated?
- Negative feed back loop: TH inhibits both TRH and TSH release
- Removal of stimulus: stop exercising
What is hypothyroidism?
Decreased cellular metabolism
- weight gain
- constipation
- slow heart beat
- puffy face
- goiter
What is hyperthyroidism?
Increased cellular metabolism
- weight loss
- diarrhoea
- rapid heart beat
- bulging eyes
- goiter
What does CRH stimulate?
Stimulates production of ACTH which binds to receptors in the adrenal gland and stimulates the release of cortisol which targets skeletal muscle, adipose tissue and the liver.
What is cortisol?
- cortisol is important to survival during stress
- it is a glucocorticoid which means it has the ability to generate glucose in the liver from other body substrates
- it allows you to survive stress and fasting by mobilising fuels
What effect does cortisol have on muscle?
Protein is broken down for fuel. less glucose uptake
What effect does cortisol have on the liver?
More glucose is produced from fuels
What effect does cortisol have on adipose tissue?
Fat is broken down for fuel, less glucose uptake
When is cortisol beneficial?
In the fight or flight response to acute stress
When is cortisol not beneficial?
In chronic, unmanaged stress. Can lead you towards diabetes due to the constant breakdown of glucose
How is the stress axis regulated?
- Negative feedback loop: both cortisol and adrenocorticotrophin hormone (ACTH) inhibit the hormones that control their release
- remove the stress stimulus
What are the 4 hormones involved in the integrated stress response?
- cortisol (glucocorticoid)
- anti-diuretic hormone (ADH)
- Adrenaline (epinephrine)
- Noradrenaline (norepinephrine)
What are the 3 systems involved in the integrated stress response?
- Indirect control through releasing hormones (CRH-ACTH-cortisol)
- Direct release of hormone in posterior pituitary (ADH)
- Direct control by nervous system (adrenaline/noradrenaline)
What is anti-diuretic hormone (ADH)?
- Stops water loss by inhibiting urine production.
- ADH is also known as vasopressin because it also restricts blood vessels to increase blood pressure
- its release is stimulated by stress and dehydration or excess body fluid loss
- it combats dehydration by maintaining fluid volume
- It’s important in stress to maintain blood flow in vital organ systems
Where is ADH released from?
ADH neurons in the hypothalamus send their axons into the posterior pituitary gland which is released from nerve terminals and enters the blood stream to reach distant target cells.
What does ADH target?
Kidneys
- stimulates kidney cells to reabsorb water back into the blood which increases blood volume and pressure
Blood Vessels
- vasoconstriction which increases blood pressure
What are the catecholamines?
- Adrenaline and Noradrenaline are catecholamine hormones released from the adrenal medulla
- Catecholamine release is stimulated by neurons of the sympathetic nervous system
- Secreted with stress and during exercise
What does adrenaline/noradrenaline target?
Cardiovascular
- Heart: increased HR and strength of heart contraction
- Blood Vessels: dilation and constriction of vessels to direct blood flow
- Lungs: airway dilation
Metabolic
- Muscle: glycogen breakdown for fuel
- Adipose tissue: fat is broken down for fuel
- Liver: more glucose is produced from fuels, glycogen breakdown for fuel
What is the adrenaline rush?
- Increased intake of O2 & delivery of oxygenated blood to cells
- Increased fuel released into the blood to be available to cells
What does the adrenal cortex release?
cortisol
What does the adrenal medulla release?
adrenaline/noradrenaline
What is the cortisol response to stress?
Long term stress response
- starts slow
- lasts hours to days
- lipid soluble hormone (travels bound to carrier proteins)
What is the adrenaline/noradrenaline response to stress?
Short term stress response
- starts fast
- lasts seconds to minutes
- water-soluble hormones
What does adrenaline bind to?
- Both alpha and beta catecholamine receptors.
- receptors can drive different effects: adrenaline causes vasoconstriction (alpha) or vasodilation (beta)
- Drugs that block or enhance these receptors are banned in competitive sports
What are agonists to the catecholamine receptors?
Sympathomimetics - chemicals that stimulate or increase function of adrenergic receptors
What does pseudoephedrine hydrochloride do?
Acts on a-adrenergic receptors
- vasoconstriction at nasal sinus tissue
- decreased blood flow = decreased swelling
Acts on b-adrenergic receptors
- dilates airways to make it easier to breathe
Banned in sports
What are agonists to the catecholamine receptors?
Chemicals that block or inhibit the function of adrenergic receptors
What does propanolol do?
Treats abnormal heart rhythm or high blood pressure (medicine)
Blocks b-adrenergic receptors
- slows HR and lowers BP
- reduces muscle tremors & anxiety
- increased ability to focus
Athletes in certain sports eg. archery may use this to calm nerves and improve performance
Banned in sports
When is insulin secreted?
High blood glucose stimulates insulin secretion from pancreatic islet beta cells. This triggers the uptake of glucose to restore blood glucose levels.
When is glucagon secreted?
Low blood glucose stimulates glucagon secretion from pancreatic islet alpha cells. This triggers the release of glucose to restore blood glucose levels.
What is glycogenolysis?
The breakdown of glucose
What is gluconeogenesis?
Making new glucose from other substances
What is ketone synthesis?
Another fuel source for the brain
What is type 1 diabetes caused by?
A loss of beta cells in the pancreas leading to a deficiency in insulin.
What is type 2 diabetes caused by?
Due to insulin resistance or reduced insulin sensitivity.
