endocrine system Flashcards
What is the endocrine system?
What is it secondary to?
How long can it take to respond?
The endocrine system is a system of loads of hormone producing glands that are scattered around the body, which use hormones as chemical messengers
The endocrine (hormone) system is the second integrative control System of the body – slower than the nervous system
Hormones of the endocrine system can have a lag of seconds, weeks or months before they work
* The endocrine system is responsible for:
What are the 5 things the endocrine system is responsible for?
1) Cellular metabolism
2) Growth and development
3) Sexual development
4) Homeostasis e.g Ca++
5) Behaviour e.g mood/sleep
What are endocrine glands?
Why do they have a rich blood supply?
Where are the typical target tissues of endocrine glands located?
How do hormones act on target tissues?
What concentrations are hormones released in?
How can hormones elicit such a big response?
What other hormone systems is the endocrine system in line with?
What is an example
- Endocrine glands are ductless glands with a rich blood supply, that secrete hormones into the bloodstream
- Having a rich blood supply ensures rapid movement of hormones into the blood and around the body
- Endocrine glands typically act on tissues distant from the source
- Hormones are able to act on target tissues, as these tissues have specific receptors that re complementary to the hormone
- Hormones are released in very small concentrations, but can elicit a huge response, because target tissue receptors have every high affinity for their hormones
- The endocrine system is also alongside other local hormonal systems, such as the paracrine and autocrine systems e.g. testosterone produced in testes and acting on testes is paracrine
What do exocrine glands may or may not have?
How do exocrine and endocrine glands differ?
What are 3 examples where exocrine glands are used?
A
* Exocrine glands may or may not have ducts, where whatever substance is secreted travels up the ducts (typically have ducts)
* Exo refer to the fact that secretions come out of the gland onto an external epithelial layer, rather than internally into the blood stream or extracellular fluids, like endocrine glands
* 3 places where exocrine glands are used:
1) Tongue – saliva
2) Skin – sebum/sweat
3) GI tract – digestive enzymes
What are the 3 different classes of hormones?
- proteins
- steroids
- amino acids
PEPTIDE HORMONES
How are they usually transported?
What is their half life like?
How do they act as chemical messengers for cells?
What does this initiate?
How are they degraded?
When might they be used?
Peptide hormones are readily transported in the blood, as they ae usually water soluble
They have a short half life of a few minutes, as they are not attached to transport proteins
Peptide hormones bind to plasma membrane receptors on plasma membrane cells
This initiates a cascade response in the cell, which can initiate cell changes, such as in gene expression or phosphorylation of proteins
Peptide hormones are degraded via proteolysis
Peptide hormones can allow generation of short term elicited response in an immediate crisis
What are steroids synthesised from?
What are they soluble in?
What do they need to be transported and why?
How does this affect their half-life?
How do steroid hormones get into cells?
How do steroids target cells?
When is the steroid hormone biologically active?
Steroids are synthesised from cholesterol
They are lipid soluble
Steroids require specific transporter proteins to move through the blood, due tot being lipophilic
This increases their half life
Hormones can readily diffuse into and out of the cell through the plasma membrane
Steroids can then bind to intracellular receptors/transcription factors and modify gene expression e,g hormone can bind to a receptor, and the complex becomes a transcription factor
Only the free hormone is biologically active
What are amino acid derivative hormones derived from?
What are the 2 types?
What are the example of each type?
How are they similar?
What 2 ways do they differ?
Amino acid derivative hormones are derived from tyrosine
There are 2 types of amino acid derivative hormones:
1) Catecholamines – neurotransmitters
* Adrenaline
* Noradrenaline
* Dopamine
2) Thyroid hormones
* Throxine (T4)
* Tri-iodothyronine (T3)
Although catecholamines and thyroid hormones have a common pre-cursor, they behave very different.
Catecholamines have the shortest half-life of all hormones (can be a few seconds e.g adrenaline released instantly, but degraded very quickly)
Thyroid hormones have the longest half-life of all hormones, and can stay around for a few days
Catecholamines (like peptide hormones) bind to plasma membrane receptors, which triggers secondary messenger signal responses in the cell
Thyroid hormones (like steroids) diffuse across the plasma membrane, and bind to receptors inside the cell.
How do all hormones act?
What can make response vary?
What changes will all of them bring about?
What 3 hormones use plasma membrane receptors?
What 2 hormones use intracellular receptors?
All hormones act by binding to receptors on target cells
Cellular response can vary depending on the numbers of receptors present.
All hormones bring about changes in gene expression
* Hormones that use plasma membrane receptors:
1) Peptides
2) Glycoproteins (peptide hormones)
3) Catecholamines
- Proteins that use intracellular receptors:
1) Steroids
2) Thyroid hormones
what are the 3 different rhythms hormones can be secreted at
1) Episodic
* In response to physiological demand e.g insulin
2) Diurnal
* Predictable pattern over 24 hours e.g cortisol
* May also respond to episodic stimuli
3) Constant
* Fairly constant blood concentrations for normal physiological function e.g thyroxine, which is involved in BMR
what are the 3 stimuli for endocrine glands?
1- humeral = circulating molecules in blood
2- neuronal = stress response - sympathetic ns
3- hormonal = in response to hormones produced by other endocrine glands
where is the pineal gland
centre of brain between the 2 hemispheres, it is for the circadian sleep cycle
What does the hypothalamus link?
What is the role of the hypothalamus and pituitary gland?
What do they provide?
What does the hypothalamus release?
What does the pituitary then release?
How is the hypothalamus connected with the pituitary gland?
The hypothalamus links the nervous system and the endocrine system together via the pituitary gland
The hypothalamus, along with the pituitary gland, coordinate the endocrine system, and orchestrate the activity of other endocrine glands
They provide signal amplification through cascades and fine control
The hypothalamus releases and inhibits hormones that have an effect on its target cells: the pituitary gland cells
This stimulates the pituitary gland to release hormones which stimulates/controls many other endocrine glands.
The hypothalamus is connected to the pituitary gland by a stock that receives the neuronal and hormonal and stimuli from the hypothalamus
what 3 things is the hypothalamus responsible for?
- circadian rhythms
- reproduction
- growth
What does the hypothalamus respond to?
Describe 4 stages of the endocrine axis using the thyroid as an example.
How is this system regulated?
The hypothalamus responds to neuronal and hormonal stimuli from circulating hormones
The endocrine axes (thyroid example):
1) Hypothalamus releases hormone through the stock that targets the pituitary gland cells e.g TRH (Thyrotropin releasing hormone)
2) TRH stimulates the target cells of the anterior lobe of the pituitary gland to produce and release TSH (throxine-stimulating hormone)
3) The TSH travels towards the thyroid through systemic circulation and stimulates the thyroid cells to produce Thyroxine
4) Thyroxine then goes into systemic circulation towards the target cells
- This system is regulated by a negative feedback control, where products can inhibit hormones produced earlier in the chain, stimulate glands to produce inhibitory hormones, or inhibit glands from producing hormones
What does the hypothalamus do with the 2 lobes of the pituitary gland?
What are the 2 types of hormones the hypothalamus releases?
The hypothalamus uses hormones to stimulate the production and secretion of hormones in the anterior pituitary lobe
The hypothalamus synthesises hormones (oxytocin and anti-diuretic hormone) which are stored in the posterior lobe of the pituitary gland
The hypothalamus releases:
1) Releasing hormones
* E.g growth hormone releasing hormone (GHRH) which stimulates the anterior pituitary to release Growth hormone
2) Inhibitor hormones
* E.g growth hormone inhibiting hormone (GHIH)
when do growth hormone levels peak
adolescence - the Growth hormone targets the epiphyseal growth plate
what causes Gigantism
- hyper secretion of GH in pre-pubescent children
- may be caused by an interior pituitary tumour
