Endocrine Systems

Question 1

The endocrine system regulates ……………. through slow, long-lasting ………………. signalling.

Answer 1

Homeostasis, chemical.

Question 2

Hormone secreted by …………….. act on target organs via the …………….. system, often requiring activation by the ……………… system.

Answer 2

Glands, circulatory, nervous.

Question 3

The endocrone system’s glands function in what two mechanisms?

Answer 3

Endocrine and exocrine.

Question 4

Which mechanism of the endocrine system is internal, secreted into the blood and acts on distant targets?

Answer 4

Endocrine mechanism.

Question 5

Which mechanism of the endocrine system is external and secreted through the skin or lumen (e.g. into the digestive tract or respiratory tract)?

Answer 5

Exocrine mechanism.

Question 6

Which area of the brain links the nervous and endocrine systems?

Answer 6

Hypothalamus.

Question 7

What is the difference between tropic hormones and non-tropic hormones?

Answer 7

Tropic hormones regulates production of another hormone in a gland.

Non-tropic hormones have a direct effect on a target organ.

Question 8

Hormones can be classified by their structure. What are the three main classes?

Answer 8

Peptides, amines and steroids.

Question 9

Describe the process whereby peptide hormones are released in the blood.

Answer 9

1. Preprohormone precursor translated and packaged into vesicles.
2. Hormone packaged into secretory vesicles and stored in the cytosol.
3. Vesicles fuse with the plasma membrane and release the hormone into the blood.

Question 10

Amine hormones are all derived from which amino acid?

Answer 10

Tyrosine.

Question 11

What are steroid hormones synthesised from?

Answer 11

Lipid cholesterol.

Question 12

How does the transport of lipid hormones across the plasma membrane differ from that of peptide hormones and amine hormones?

Answer 12

Lipid hormones can diffuse across the plasma membrane, whereas peptide and amine hormones need to be transported in vesicles.

Question 13

Which type of hormone can be converted into different hormones, either in the blood or at their target organ?

Answer 13

Steroid hormones.

Question 14

Which hormones are water soluble and which are lipid soluble? How are they transported in the blood?

Answer 14

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.

Question 15

Why do hormones only act on their target organ, when they circulate throughout the body?

Answer 15

The organ has specific receptor cells for the hormone.

Question 16

The magnitude of a hormone’s response is proportional to…?

Answer 16

…the levels of a hormone.

Question 17

Name the two types of hormone receptors.

Answer 17

Membrane receptors and internal receptors.

Question 18

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.

Answer 18

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.

Question 19

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.

Answer 19

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.

Question 20

Are hormonal responses slower than neuronal responses?

Answer 20

Hormonal responses are slower and longer-lasting than neuronal responses.

Question 21

What TWO factors can affect the speed and duration of hormonal responses?

Answer 21

1. The nature of the response - i.e. enzyme activation is quicker than translation of a new protein.
2. The solubility of a protein, which affects its metabolism.

Question 22

Do the effects of steroid hormones or peptides / catecholamines last longer?

Answer 22

Steroid hormones - the effects last for hours/days, whereas the effects of peptides/catecholamines last minutes/hours.

Question 23

Hormones are in miniscule concentration in the blood - it is the ……………… of the hormone action on the cell that causes an effect.

Answer 23

Amplification.

Question 24

Name the four different mechanisms that can control hormone levels.

Answer 24

1. Secretion.
2. Activation.
3. Binding to plasma proteins.
4. Removal from circulation.

Question 25

What is the most important mechanism for the regulation of hormone secretion, which keeps hormone levels in a narrow range around a set-point?

Answer 25

Negative feedback.

Question 26

Name the reflex which produces a sudden increase in hormone secretion in response to an external or internal stimulus detected by the nervous system.

Answer 26

Neuroendocrine reflexes.

Question 27

What is diurnal/circadian rhythm?

Answer 27

A regular change in daily hormone levels (e.g. glucocorticoids).

Question 28

Give an example of hormones which follow a monthly rhythm.

Answer 28

Female gonadal hormones.

Question 29

Hormones which control mating and hibernation are examples of those which follow what rhythm?

Answer 29

Annual.

Question 30

Where are MOST hormones metabolised and therefore inactivated? And where are the rest metabolised?

Answer 30

Most hormones are metabolised in the liver, but some are metabolised in the kidney, blood and cells instead.

Question 31

Plasma proteins bind hormones in the blood - where are these proteins synthesised and metabolised?

Answer 31

In the liver - this indirectly affects hormone levels.

Question 32

What happens to MOST inactivated metabolites of hormones?

Answer 32

They are excreted in urine.

Question 33

True or false? Some hormones are ACTIVATED by metabolism after being released into circulation?

Answer 33

True. An example is thyroid hormone.

Question 34

How does the solubility of a hormone affect its metabolism?

Answer 34

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.

Question 35

How is the solubility of lipid-soluble hormones increased, so they are more easily metabolised and excreted?

Answer 35

They undergo a series of enzymatic steps to increase their water solubility and reduce their binding to plasma proteins.

Question 36

True or false? Hormone response is proportional to the number of receptors available for binding.

Answer 36

True.

Question 37

What is receptor downregulation?

Answer 37

A mechanism of hormone binding regulation. The number of receptors is decreased in response to chronically elevated hormone levels (e.g. insulin).

Question 38

What is the reason for internalisation of the receptor complex?

Answer 38

The number of receptor cells are reduced and it allows for metabolism of hormones y cells (e.g. insulin).

Question 39

What is permisiveness?

Answer 39

When a hormone needs another hormone to be present to work. For example, for adrenaline to be effective, thyroid hormone must be present.

Question 40

What is synergism?

Answer 40

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.

Question 41

What is the term for a hormone that reduces levels of receptor available for a second hormone?

Answer 41

Antagonism. An example is progesterone reduces oestrogen receptor levels in the uterus.

Question 42

What are the two types of endocrine disorders?

Answer 42

Hypersecretion and hyposecretion.

Question 43

What are the main causes and what is the main treatment of hormone hyposecretion?

Answer 43

The cause can be genetic, dietary, chemical/toxic, autoimmune disease or iatrogenic (gland removal). The main treatment is with hormone replacement therapy.

Question 44

What are the main causes and what is the main treatment of hormone hypersecretion?

Answer 44

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.

Question 45

What are endocrine disrupting chemicals?

Answer 45

Man-made chemicals which have a chemical structure to hormones and can therefore disrupt the function of neural and behavioural maturation of animals.

Question 46

What are: 'Regular variations in physiology and behaviour which oscillate'?

Answer 46

Biological rhythms.

Question 47

Name some biological rhythms.

Answer 47

Heart rate, hormone secretion, hibernating, breathing, feeding, sleeping, mating, body temperature, excretion and drinking.

Question 48

What is the difference between exogenous and endogenous biological rhythms?

Answer 48

Exogenous biological rhythms - generated by and dependent on the EXTERNAL environment. Endogenous biological rhythms - generated INTERNALLY and self-sustaining.

Question 49

What is the meaning of the terms diurnal, nocturnal and crepuscular? They are examples of what?

Answer 49

Day, night and twilight. They are examples of circadian rhythms.

Question 50

Which is the most common biological rhythm in the mammalian endocrine system?

Answer 50

Circadian rhythm.

Question 51

Give an example of mammalian circadian rhythm.

Answer 51

Glucocorticoid levels, which are involved in energy mobilisation. Levels peak in the morning to prepare for activity.

Question 52

Which biological rhythm is 'tidal', approximately twice daily? In which organisms is it common?

Answer 52

Circalunadian rhythm, common in marine organisms, for example crustaceans, molluscs, fish and insects.

Question 53

Which biological rhythm controls yearly behaviours? Name some examples.

Answer 53

Circannual rhythm, for example chipmunks, hibernating, geese migrating and stags mating.

Question 54

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?

Answer 54

Biological clocks.

Question 55

What is the function of the biological clock 'alarm'?

Answer 55

It sets behavioural activity patterns and physiological functions.

Question 56

What does the biological clock's 'clock' do in the short-term and the long-term?

Answer 56

Short-term - signals certain behaviours or physiological functions. Long-term - changes in day length signal the changing seasons (e.g. acclimitisation of homeostasis).

Question 57

True or false? Biological clocks CANNOT be affected by external environments.

Answer 57

False.

Question 58

What is a 'zeitgeber'? Give an example.

Answer 58

Zeitgebers are external cues which entrain biological rhythms. Light is the most important circadian rhythm for mammals, setting day length to 24 hours.

Question 59

What did experiments on rats kept in constant light/darkness prove about mammalian circadian day rhythm?

Answer 59

The circadian rhythm is around 25 hours when allowed to free-run.

Question 60

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.

Answer 60

Suprachiasmatic nucleus, hypothalamus, clock.

Question 61

Self-activation of clock genes results in the translation of ............. ............, which accumulate in the cytosol of the suprachiasmatic nucleus neurons.

Answer 61

Clock proteins.

Question 62

Clock proteins are produced in a 24-hour cycle of ................ and ................ to 'keep time'. How are these clock proteins regulated?

Answer 62

Translation and degradation. They are regulated by negative feedback.

Question 63

How do the suprachasmatic nucleus work with the retina to entrain the circadian rhythm to 24 hours?

Answer 63

Light enters the retina, activating photoreceptors. Specific photoreceptors (e.g. melanopsin) activate clock genes in the suprachiasmatic nucleus.

Question 64

Which hormone, secreted from the pineal gland, 'keeps time' by being produced rhythmically throughout the day and the year?

Answer 64

Melatonin.

Question 65

When in the day are melatonin levels high and when are they low?

Answer 65

Melatonin levels are high at night and low during the day.

Question 66

Does the pineal gland, which produces melatonin, receive light input from the suprachiasmatic nucleus directly or indirectly?

Answer 66

Indirectly.

Question 67

Melatonin levels change in the year. Are they higher when the days are longer, or when the days are shorter?

Answer 67

Melatonin levels are higher when the days are shorter and lower when the days are longer.

Question 68

Some animals, such as birds, fish, reptiles and amphibians have much thinner skulls - how does this affect the pineal gland?

Answer 68

Their pineal gland does not require light input from the retina - photoreceptors in the pineal gland iteself receive light which penetrates the skull directly.