Neuroendocrine Quiz.text - - 6/8/99

QUESTION 1:  Explain how regulation occurs by means of 'negative
feedback'. ANSWER:  Regulation by negative feedback occurs when a
stimulus initiates a response which results in the lessening of the
original stimulus;  for example a fall in plasma glucose stimulates
release of various hormones which raise glucose (within the normal
range).

QUESTION 2:  How does 'neuroendocrine' differ from 'endocrine'? ANSWER: 
Neuroendocrine function involves either the release into the bloodstream
of chemical messengers* which have been secreted by neurons  or the
regulation of release of a hormone by stimulation of neurons. *The
chemical messengers are known as hormones simply because they are
released into the bloodstream.

QUESTION 3:  How  does a hormone have very specific effects? ANSWER:  A
hormone has specific effects because it is only able to elicit responses
from target tissues (tissues which bear receptors for the particular
hormone).  The effects of a hormone depend on the nature (functional
capabilities) of the target cells.

QUESTION 4:  How can a single hormone have a number of different
effects? ANSWER:  A particular hormone may have many target tissues and
therefore many different effects ‹ the effect of a hormone depends
entirely on the physiology of the target tissue.

QUESTION 5:  Give two reasons why the adrenal cortex and adrenal medulla
can be regarded as two distinct glands located within the same organ.
ANSWER:  The adrenal cortex and medulla differ respectively in the
following ways:  embryonic origins (embryonic epithelium versus
embryonic neural tissue); secretory products (steroids versus
catecholamines);  and regulation of hormone secretion (by hormones of
anterior pituitary or direct effect of ions versus the sympathetic
nervous system).

QUESTION 6:  Hormone-secreting tumours frequently don't cause problems
associated with the space occupied by the tumour tissue.  What other
problems might a hormone-secreting tumour present? ANSWER:  The
secretion of a hormone by a tumour is unregulated, leading to syndromes
of hypersecretion of the hormone in question.  These can be
life-threatening.  Can you predict the effects of excessive ACTH, ADH,
glucagon, parathyroid hormone?

QUESTION 7:  During pregnancy and the luteal phase of the menstrual
cycle (after ovulation and before menstruation) there is a drop in the
thresholds for thirst and ADH release.  Predict the changes in plasma
volume and concentration. ANSWER:  Plasma volume will expand and
concentration will decrease.

QUESTION 8:  A person who has suffered a head injury in an accident is
subsequently found to be excreting very large volumes of urine, and
complains that he is constantly thirsty.  What is the likely cause of
these signs and symptoms? ANSWER:  Head injury can destroy the
hypothalamic and posterior pituitary functions for the synthesis and
release of ADH (AVP).  Lack of ADH results in diabetes insipidus ‹ the
excretion of large volumes of dilute urine,  > 3 L/ 24 h).

QUESTION 9:  What is the danger to health of lack of ADH? ANSWER:  Lack
of ADH puts the individual at risk of dehydration ‹ and death, in
extreme cases ‹ if he/she is unable to constantly replace the urinary
losses of water.

QUESTION 10:  List five factors which are likely to influence results in
a study of aspects of endocrine function. ANSWER:  Time of day,
circumstances of the study (eg. if the subject is anxious), and
differences between subjects with respect to any of the following: 
state of health, drug use (therapeutic and social), age, habitual level
of activity.

QUESTION 11:  ³If hormone levels are within the normal range, then a
person will not show any signs or symptoms of an endocrine disease². 
True or false?  Why? ANSWER:  This is false because, for example, there
can be defects of: (a) hormone activation from an inactive precursor (b)
function at the receptor level (eg. absent or blocked receptors) or (c)
post-receptor function.

QUESTION 12:  What is circadian rhythm?  What is an example? ANSWER: 
Certain features of physiological function vary with a 24 hour cycle
(around a day).   Sleep, for example.