Endocrine System Flashcards
How does the endocrine system regulate homeostasis ?
By slow, long-lasting chemical signalling
What do hormones secreted from glands act on?
target organs via circulatory system.
What does the endocrine system need to be activated by ?
The nervous system
What are the 2 different mechanisms that glands function through ?
1 - ENDOCRINE
2. EXOCRINE
Where does the endocrine secrete hormones snd what’s its target ?
- Secretion into BLOOD
- Action on distant target
Where does the exocrine mechanisms secrete hormones ?
Secretion through duct to skin or into lumen outside body
Whats the endocrine system scheme function ?
1) sense internal change
2) Integrate sensory information
3) Respond by acting on other body systems.
What do glands release hormone in response to ?
Internal change
What is the hypothalamus ?
Brain area with various physiological functions important for maintaining homeostasis by linking nervous and endocrine systems
What are 3 functions of the hypothalamus ?
1- Integrates sensory input
2- Coordinates appropriate physiological responses
3- Regulates hormone release from pituitary gland and other glands all over body
How are hormones classified ?
According to function and structure
Whats a tropic and non tropic hormone ?
TROPIC HORMONE -
-Regulates production / secretion of another hormone in a gland
NON-TROPIC HORMONE -
- Has a direct effect on target organ
What are 3 structures of hormones ?
PEPTIDE - Most hormones are amino acids
AMINES - Derived from the amino acid tyrosine
STEROIDS - Derived from the lipid cholesterol
How are peptides released into the blood ?
1) Peprohormone precursor is translated and packaged into vesicles
2) PEPROHORMONE - PROHORMONE - HORMONE
3) Hormone packaged into secretory vesicles and stored in cytosol
4) Vesicles fuse with plasma membrane and release hormone into blood
How is the hormone amine released into the blood ?
1- Synthesised from the amino acid tyrosine by specific enzymes
2- Packaged into secretory vesicles and stored until release
3- Vesicles fuse with plasma membrane and release hormone into blood.
What are the 3 different ways that catecholamines are synthesised, stored and released ?
- Dopamine
- Noradrenaline
- Adrenaline
How is steroids synthesised, stored and released ?
1- Synthesised from the lipid cholesterol by specific enzymes
2- diffuse across plasma membrane into blood once synthesised
3- Can be converted into different hormones once in blood or at target
Via what pathways does cholesterol give rise to many hormones ?
Via several enzymatic synthesis pathways.
What does the way a hormone is transported through the circulation depend on ?
Their solubility characteristics
What hormones are water-soluble and where are they located ?
- Peptide, some amines
- FREE in blood or binding to plasma proteins
What hormones are lipid-soluble and where are they located ?
-Steroid, some amines
- Bound to plasma proteins
in what location do hormones circulate in the blood ?
The whole body
Explain how hormones only have specific effects ?
They only act in certain organs
Explain how hormones induce a response within a cell ?
Hormones bind to a specific RECEPTOR on cells in target organs. Hormone binding to its receptor induces a response within cell
What are the two types of hormone receptors ?
Membrane receptors
Internal receptors
What are membrane receptors and what do they bind ?
- GPCR or kinase-linked
- bind peptides, catecholamines, or some steroids
Where do hormones bind on membrane receptors ?
Hormone binds to receptor on outside of plasma membrane
What responses does binding on membrane receptors cause ?
-Enzyme activation
- Change in protein synthesis
What hormones bind to internal receptors ?
Most steroids, thyroid hormone
What internal receptor do hormones bind to ?
Cytosol
How does hormone-receptor complex induce a response and what does it cause ?
By binding to DNA it causes protein synthesis to increase and decrease
How is the speed different in neural responses than hormone ?
Hormone responses are much more slower and prolonged than neural responses
What are the 4 different mechanisms that tightly regulate levels of hormones in circulation ?
- Secretion
- Activation
- Binding to plasma proteins
- Removal from circulation
Whats the most important mechanism for controlling hormone levels ?
Negative feedback keeps hormone levels within a narrow range around a set-point.
How does neuroendrocine reflexes regulate hormone secretion ?
Produce sudden increase in hormone secretion in response to a stimulus detected by nervous system.
Give 2 other ways that the body can regulate hormone secretion ?
- External stimulus
- Internal stimulus
What are the 3 different rhythms of hormones over time ?
- DIURNAL / CIRCADIAN RHYTHM
- Regular change in daily hormone levels - MONTHLY RHYTHM
- female gonadal hormones - ANNUAL RHYTHM
- Mating
- Hibernation
What occurs to most hormones during metabolism in the liver , where are 3 other places this can occur ?
Most hormones are inactivated by metabolism in liver but some are also metabolised in kidney, blood and cells
How can plasma proteins affect hormone levels ?
Plasma proteins that bind to hormones in blood are synthesised in liver and can also be metabolised, which indirectly affects hormone levels.
How are most inactive metabolites excreted ?
In urine
How can liver or kidney disease alter hormone levels ?
Liver or kidney disease can alter hormone levels due to effects on hormone / plasma protein metabolism and hormone excretion.
How does being soluble in water affect hormones ?
Water soluble hormones are easily targeted by enzymes in blood and tissue for metabolism
How does hormones being soluble in lipids affect metabolism ?
Lipid-soluble hormones are bound to plasma proteins and less easily targeted for metabolism or excreted.
How can lipid soluble hormones increase their water solubility and reduce binding to plasma proteins ?
Undergo a series of enzymatic steps to increase their water solubility and reduce binding to plasma proteins
What is hormone response proportional to ?
The number of receptors it binds to
What is receptor down regulation ?
A decrease in receptor number in response to chronic elevation of hormone levels
What does internalisation of hormone receptor complex reduce ?
Reduces receptor levels and can also allow for metabolism of hormone by cells.
How do endocrine disorders come about ?
Mainly due to abnormal hormone secretion but can also result from abnormal responsiveness to hormone with normal hormone levels
What is hyposecretion ?
Is a decrease in secretion of a hormone by a gland or of a topic hormone
How are endocrine disorders treated ?
Mainly treated with hormone replacement
What is the endocrine disorder hypersecretion ?
Is an increase in secretion of a hormone by a gland ( primary ) or of a tropic hormone ( secondary )
What is hypersecretion caused by ?
Caused by tumour, abnormal antibody mimicking hormone, synthetic hormone
What is hyper secretion treated by ?
Treated by removing tumour or medicines that reduce hormone synthesis or secretion.
How can chemicals disrupt the endocrine system ?
-Chemicals made by humans such as pesticide released as sewage or industrial waste into water sources.
–Chemical structures are similar to hormones and can disrupt endocrine control of neural and behavioural maturation of animals
-Many can mimic or block effects of gonadal hormones and so can alter sexual development and differential of brain in animals
What are some regular variation I’m physiology and behaviour that oscillate ?
- Heart rate
- Breathing
- Body temp
- Hormone secretion
- Excretion
What is an endogenous rhythm and an example ?
- generated internally
- Self- sustaining
e.g Body temp
What is an exogenous rhythm and an example ?
-Generated by external environment
- depends on external environment
- Barnacle cirri
What does it mean if the biological rhythms are circadian ?
Means many biological rhythms are around a day
What does diurnal, nocturnal and crepuscular ?
DIURNAL - day
NOCTURNAL - night
CREPUSULAR - Dawn and dusk
Give examples of behavioural patterns of activity that are subject to natural selection for diurnal, nocturnal and crepuscular animals ?
- Diurnal predators with goof eyesight
- Nocturnal prey animals avoiding predators
- crepuscular animals have high food availability
What are glucorticoids ?
Hormones involved in energy mobilisation.
When is glucorticoids at peak level and how does it differ for cortisol ( most mammals ) and corticosterone ( rodents ) ?
Peak level is when waking up to prepare for activity
CORTISOL - Peak levels in morning
CORTICOSTERONE
- Peak levels in evening
What is a tidal rhythm and what marine organisms have this ?
its a 2 day circulation and
-crustaceans
- Mollusks
-fish
-Insects
What is circannual rhythms and 3 examples ?
Occurs annually around a year
- MATING
- HIBERNATION
- MIGRATION
What does a biological clock do ?
Maintains endogenous rhythms independently of external environment
What is ZEITGEBER ?
External cues which entrain biological rhythms
What do experiments in mammals living in constant light or dark show the endogenous circadian rhythm is ?
25 hours
What is the suprachiasmatic nucleus ?
Is the master clock in mammals
What is the rhythm of neuronal activity maintained by ?
Clock genes
What does self-activation of clock genes result in ?
In translation of clock proteins which accumulate in cytosol of suprachiasmatic nucleus neutrons
What does high clock proteins levels act on ?
on nucleus to signal an end to further translation
What does the suprachiasmatic nucleus synchronise the circadian rhythm with ?
- RETINA
- PINEAL GLAND
Explain how the retina can activate clock genes ?
1- Light entrains the circadian rhythm to 24 hours
2- light activates photoreceptors in retina
3- certain photoreceptors activate clock genes in neurone of suprachiasmatic nucleus
What does the pineal gland do when receives light indirectly from suprachiasmatic nucleus and at what levels in night and day is it involved in circadian rhythm ?
controls rhythmic production and secretion of melatonin hormone
involbed in circadian rhythm
NIGHT - High levels
DAY - LOW LEVELS
How does melatonin levels alter as changing day lengths change over a year ?
- Increase as days shorten
- Decrease as days lengthen
What does an animal contain if light is able to penetrate skull and directly activate pineal gland ?
Contains light-sensitive cells that do not depend on retinal input.
