Endocrine Systems Flashcards
The endocrine system regulates ……………. through slow, long-lasting ………………. signalling.
Homeostasis, chemical.
Hormone secreted by …………….. act on target organs via the …………….. system, often requiring activation by the ……………… system.
Glands, circulatory, nervous.
The endocrone system’s glands function in what two mechanisms?
Endocrine and exocrine.
Which mechanism of the endocrine system is internal, secreted into the blood and acts on distant targets?
Endocrine mechanism.
Which mechanism of the endocrine system is external and secreted through the skin or lumen (e.g. into the digestive tract or respiratory tract)?
Exocrine mechanism.
Which area of the brain links the nervous and endocrine systems?
Hypothalamus.
What is the difference between tropic hormones and non-tropic hormones?
Tropic hormones regulates production of another hormone in a gland.
Non-tropic hormones have a direct effect on a target organ.
Hormones can be classified by their structure. What are the three main classes?
Peptides, amines and steroids.
Describe the process whereby peptide hormones are released in the blood.
- Preprohormone precursor translated and packaged into vesicles.
- Hormone packaged into secretory vesicles and stored in the cytosol.
- Vesicles fuse with the plasma membrane and release the hormone into the blood.
Amine hormones are all derived from which amino acid?
Tyrosine.
What are steroid hormones synthesised from?
Lipid cholesterol.
How does the transport of lipid hormones across the plasma membrane differ from that of peptide hormones and amine hormones?
Lipid hormones can diffuse across the plasma membrane, whereas peptide and amine hormones need to be transported in vesicles.
Which type of hormone can be converted into different hormones, either in the blood or at their target organ?
Steroid hormones.
Which hormones are water soluble and which are lipid soluble? How are they transported in the blood?
Water soluble - peptides and some amines, e.g. catecholamines. Either free in the blood or bound to plasma proteins.
Lipid soluble - steroids and some amines, e.g. thyroid hormone. Bound to plasma proteins in blood.
Why do hormones only act on their target organ, when they circulate throughout the body?
The organ has specific receptor cells for the hormone.
The magnitude of a hormone’s response is proportional to…?
…the levels of a hormone.
Name the two types of hormone receptors.
Membrane receptors and internal receptors.
Describe membrane receptors, in terms of which type of receptors they are, which hormones they bind, where in the cell the hormone binds and what response is induced.
Membrane receptors are either GPCR or kinase-linked receptors. They bind peptides, catecholamines, and some (gonadal) steroids. The hormone binds to the receptor outside the plasma membrane. Binding of the hormone induces a response in the cell - either enzyme activation or a change in protein synthesis.
Describe internal receptors, in terms of which type of receptors they are, which hormones they bind, where in the cell the hormone binds and what response is induced.
Internal receptors are nuclear receptors which bind most steroids and thyroid hormone. The free hormone diffuses across the plasma membrane into the cell, where it binds to an internal receptor in the cytosol. The hormone-receptor complex then binds to DNA, inducing an increase or decrease in protein synthesis.
Are hormonal responses slower than neuronal responses?
Hormonal responses are slower and longer-lasting than neuronal responses.
What TWO factors can affect the speed and duration of hormonal responses?
- The nature of the response - i.e. enzyme activation is quicker than translation of a new protein.
- The solubility of a protein, which affects its metabolism.
Do the effects of steroid hormones or peptides / catecholamines last longer?
Steroid hormones - the effects last for hours/days, whereas the effects of peptides/catecholamines last minutes/hours.
Hormones are in miniscule concentration in the blood - it is the ……………… of the hormone action on the cell that causes an effect.
Amplification.
Name the four different mechanisms that can control hormone levels.
- Secretion.
- Activation.
- Binding to plasma proteins.
- Removal from circulation.
What is the most important mechanism for the regulation of hormone secretion, which keeps hormone levels in a narrow range around a set-point?
Negative feedback.
Name the reflex which produces a sudden increase in hormone secretion in response to an external or internal stimulus detected by the nervous system.
Neuroendocrine reflexes.
What is diurnal/circadian rhythm?
A regular change in daily hormone levels (e.g. glucocorticoids).
Give an example of hormones which follow a monthly rhythm.
Female gonadal hormones.
Hormones which control mating and hibernation are examples of those which follow what rhythm?
Annual.
Where are MOST hormones metabolised and therefore inactivated? And where are the rest metabolised?
Most hormones are metabolised in the liver, but some are metabolised in the kidney, blood and cells instead.
Plasma proteins bind hormones in the blood - where are these proteins synthesised and metabolised?
In the liver - this indirectly affects hormone levels.
What happens to MOST inactivated metabolites of hormones?
They are excreted in urine.
True or false? Some hormones are ACTIVATED by metabolism after being released into circulation?
True. An example is thyroid hormone.
How does the solubility of a hormone affect its metabolism?
Water-soluble hormones (e.g. peptides, catecholamines) are easily targeted by enzymes in the blood and tissue for metabolism.
Lipid-soluble hormones (e.g. steroid, thyroid) aer bound to plasma proteins and less easily targeted.
How is the solubility of lipid-soluble hormones increased, so they are more easily metabolised and excreted?
They undergo a series of enzymatic steps to increase their water solubility and reduce their binding to plasma proteins.
True or false? Hormone response is proportional to the number of receptors available for binding.
True.
What is receptor downregulation?
A mechanism of hormone binding regulation. The number of receptors is decreased in response to chronically elevated hormone levels (e.g. insulin).
What is the reason for internalisation of the receptor complex?
The number of receptor cells are reduced and it allows for metabolism of hormones y cells (e.g. insulin).
What is permisiveness?
When a hormone needs another hormone to be present to work. For example, for adrenaline to be effective, thyroid hormone must be present.
What is synergism?
When the combined effect of two hormones is greater than their indiviual effects. For example, the effects of follicle-stimulating hormone and testosterone on sperm.
What is the term for a hormone that reduces levels of receptor available for a second hormone?
Antagonism. An example is progesterone reduces oestrogen receptor levels in the uterus.
What are the two types of endocrine disorders?
Hypersecretion and hyposecretion.
What are the main causes and what is the main treatment of hormone hyposecretion?
The cause can be genetic, dietary, chemical/toxic, autoimmune disease or iatrogenic (gland removal).
The main treatment is with hormone replacement therapy.
What are the main causes and what is the main treatment of hormone hypersecretion?
Hormone hypersecretion can be caused by tumour, abnormal antibody mimicking hormone, or synthetic hormones (e..g. anabolic steroids or growth hormones in livestock).
Hypersecretion can be treated by tumour removal or medicines that reduce hormone synthesis or secretion.
What are endocrine disrupting chemicals?
Man-made chemicals which have a chemical structure to hormones and can therefore disrupt the function of neural and behavioural maturation of animals.
What are:
‘Regular variations in physiology and behaviour which oscillate’?
Biological rhythms.
Name some biological rhythms.
Heart rate, hormone secretion, hibernating, breathing, feeding, sleeping, mating, body temperature, excretion and drinking.
What is the difference between exogenous and endogenous biological rhythms?
Exogenous biological rhythms - generated by and dependent on the EXTERNAL environment.
Endogenous biological rhythms - generated INTERNALLY and self-sustaining.
What is the meaning of the terms diurnal, nocturnal and crepuscular? They are examples of what?
Day, night and twilight. They are examples of circadian rhythms.
Which is the most common biological rhythm in the mammalian endocrine system?
Circadian rhythm.
Give an example of mammalian circadian rhythm.
Glucocorticoid levels, which are involved in energy mobilisation. Levels peak in the morning to prepare for activity.
Which biological rhythm is ‘tidal’, approximately twice daily? In which organisms is it common?
Circalunadian rhythm, common in marine organisms, for example crustaceans, molluscs, fish and insects.
Which biological rhythm controls yearly behaviours? Name some examples.
Circannual rhythm, for example chipmunks, hibernating, geese migrating and stags mating.
What maintains endogenous biological rhythms, INDEPENDENTLY of the external environment? They have been conserved throughout evolution and are involved in all aspects of biological time?
Biological clocks.
What is the function of the biological clock ‘alarm’?
It sets behavioural activity patterns and physiological functions.
What does the biological clock’s ‘clock’ do in the short-term and the long-term?
Short-term - signals certain behaviours or physiological functions.
Long-term - changes in day length signal the changing seasons (e.g. acclimitisation of homeostasis).
True or false? Biological clocks CANNOT be affected by external environments.
False.
What is a ‘zeitgeber’? Give an example.
Zeitgebers are external cues which entrain biological rhythms. Light is the most important circadian rhythm for mammals, setting day length to 24 hours.
What did experiments on rats kept in constant light/darkness prove about mammalian circadian day rhythm?
The circadian rhythm is around 25 hours when allowed to free-run.
The ………… …………… is the ‘master clock’ in mammals. It is part of the ………………… . Neurons here have shown rhythmic activity over a 24-hour period. This rhythmic activity is maintained by ………….. genes.
Suprachiasmatic nucleus, hypothalamus, clock.
Self-activation of clock genes results in the translation of …………. …………, which accumulate in the cytosol of the suprachiasmatic nucleus neurons.
Clock proteins.
Clock proteins are produced in a 24-hour cycle of ……………. and ……………. to ‘keep time’.
How are these clock proteins regulated?
Translation and degradation.
They are regulated by negative feedback.
How do the suprachasmatic nucleus work with the retina to entrain the circadian rhythm to 24 hours?
Light enters the retina, activating photoreceptors. Specific photoreceptors (e.g. melanopsin) activate clock genes in the suprachiasmatic nucleus.
Which hormone, secreted from the pineal gland, ‘keeps time’ by being produced rhythmically throughout the day and the year?
Melatonin.
When in the day are melatonin levels high and when are they low?
Melatonin levels are high at night and low during the day.
Does the pineal gland, which produces melatonin, receive light input from the suprachiasmatic nucleus directly or indirectly?
Indirectly.
Melatonin levels change in the year. Are they higher when the days are longer, or when the days are shorter?
Melatonin levels are higher when the days are shorter and lower when the days are longer.
Some animals, such as birds, fish, reptiles and amphibians have much thinner skulls - how does this affect the pineal gland?
Their pineal gland does not require light input from the retina - photoreceptors in the pineal gland iteself receive light which penetrates the skull directly.
