Regulation Quiz.text - - 6/8/99

QUESTION 1:  What normally happens to core temperature during exercise?
ANSWER:  During exercise core temperature rises.  How much it rises
depends on the level of exercise. With prolonged strenuous exercise it
may approach 39°C.

QUESTION 2:  How long does it take for core temperature to stabilize
during maintained exercise? ANSWER:  About 30 to 60 minutes at moderate
levels of exercise.  With more strenuous exercise, it may not stabilize
(hopefully you stop exercising because of exhaustion, before you die of
hyperthermia).

QUESTION 3:  What happens to skin blood flow during maintained exercise?
 What causes this and what purpose does it serve? ANSWER:  Initially
skin blood flow drops (due to activation of vasoconstrictor nerves
supplying cutaneous arterioles), but then it rises.  The delayed rise
(due to inhibition of the output from sympathetic vasoconstrictor nerves
& release of bradykinin from activated sweat glands) serves to increase
heat dissipation from the skin.   However, if excessive vasodilatation
begins to threaten maintenance of mean arterial blood pressure,
cutaneous vasoconstriction may again occur (blood pressure regulation
over-rides temperature regulation).

QUESTION 4:  Does the initial cutaneous vasoconstriction at the
beginning of exercise serve any useful purpose? ANSWER:  This is a very
interesting question.  It could be just an incidental effect of a
generalized increase in sympathetic nervous output.  However, it could
be taken as evidence that temperature is regulated at a higher set-point
during exercise (the current view is that set-point doesn't change in
exercise).

QUESTION 5:  From which cutaneous blood vessels is most heat lost and
why? ANSWER:  The veins.  They have a large volume and a low linear
velocity* of blood flow, allowing plenty of time for heat loss to occur.
 They are also close to the surface of the skin, facilitating loss of
heat to environment. * This is different from flow in terms of
volume/time: eg. a narrow river with a high linear velocity of flow can
run into a deep, wide pool with a very low linear velocity of flow.  Yet
the total flow as volume/time may be constant.

QUESTION 6:  Which parts of the nervous system are most important in
automatic  (involuntary) temperature regulation during exercise? ANSWER:
 The hypothalamus (thermoregulatory integrating "centre" and location of
central thermoreceptors), the sympathetic nervous system (controls
cutaneous arterioles and sweat glands) and cutaneous thermoreceptors
(provide additional input to hypothalamus).

QUESTION 7:  At high work rates, particularly under warm conditions, the
skin may become vasoconstricted.  Suggest why. ANSWER:  Temperature
regulatory responses, driven by the combined effects of excessive heat
production and ambient heat gain, may compromise the maintenance of
adequate mean arterial pressure.  The blood pressure regulatory system
then kicks in, causing a degree of vasoconstriction and thereby
increasing total peripheral resistance (TPR).  This helps to increase
mean arterial pressure (proportional to TPR x Cardiac Output).

QUESTION 8:  Suggest why exercise may be more tiring when it is
performed under warm conditions than under cool conditions, at the same
work rate? ANSWER:  Under warm conditions, vasoconstriction may be
initiated by the blood pressure regulatory reflexes, over-riding the
thermoregulatory reflexes (which cause vasodilatation).   Under these
conditions, blood flow to exercising muscle may not be optimal for the
purpose of oxygen supply.   This may lead to use of anaerobic metabolism
and the accumulation of lactic acid.  Lactic acid may contribute to
feelings of fatigue for a number of reasons. For example, the increased
intracellular hydrogen ion competes with calcium, decreasing the
efficiency of muscle contraction.  It may also contribute to sensations
of discomfort by activating nociceptors.

QUESTION 9:  What happens to a rat's weight during and after you
temporarily deprive it of food? What does this suggest regarding
regulation of body weight? ANSWER:  The rat's weight drops during food
deprivation and subsequently rises to a level comparable to its
litter-mates.  This suggests that body weight is regulated to a
predetermined "set-point".

QUESTION 10:  What happens to appetite and basal metabolism when you are
deprived of food? ANSWER:  Appetite is increased (hunger) and the basal
metabolic rate is reduced (all other things being equal).

QUESTION 11:  What happens to a rat when you destroy  the ventromedial
nucleus of its hypothalamus? ANSWER:  It gets very fat, perhaps more
than doubling in weight.  It may also become a "finicky" eater and
unusually aggressive.

QUESTION 12:  What happens to a rat when you destroy  the lateral areas
of its hypothalamus? ANSWER:  It becomes anorexic and may even starve to
death if not forced to eat.

QUESTION 13:  What factors are thought to be important in short-term
regulation of feeding? ANSWER:  Mechanical stimuli such as passage of
food through the mouth and stretch of the stomach (activates sensory
nerves), and entry of chyme into the duodenum (releases
cholecystokinin). Stretch and CCK act on the hypothalamus to decrease
appetite.

QUESTION 14:  What factors are thought to be important in medium-term
regulation of feeding? ANSWER:  Entry of the products of digestion and
associated hormones into the bloodstream (eg. glucose and insulin, which
act on the hypothalamus to decrease appetite).

QUESTION 15:  What factors are thought to be important in long-term
regulation of feeding? ANSWER:  A hormone (leptin) released from adipose
tissue is very important. It acts on the hypothalamus to decrease
appetite and increase basal metabolic rate.

QUESTION 16:  What is the role of neuropeptide Y in control of appetite
and body weight? ANSWER:  It is a neurotransmitter released in the
hypothalamus which has a very potent stimulatory effect on appetite.  It
also acts to decrease basal metabolism.

QUESTION 17:  What is the relationship between leptin and neuropeptide
Y? ANSWER:  Leptin appears to inhibit the release of neuropeptide Y.


QUESTION 18:  What is the Ob gene? ANSWER:  The Ob gene normally
produces leptin.  A mutant form of the gene is responsible for a
recessive obesity disorder in rats (Ob-Ob mutant).

QUESTION 19:  Are morbidly obese humans deficient in leptin? ANSWER: 
This is a active field of research.  To date (1997), studies of obese
human subjects have found only normal or high levels of plasma leptin. 
The obesity problem is therefore hypothesized as due to a deficiency in
the leptin receptor or something further along the chain of
communication.  Or it may have nothing to do with leptin...