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Unformatted text preview: it may be a reflex (an automatic response
to a stimulus involving only 2 or 3 neurons), e.g.
pain withdrawal. 8. 9. Principles of Homeostasis (page 37)
1. Maintaining water and ion balance by:
(a) Water and ions are taken in with food and drink,
helping to replace that lost through urine, faeces,
and sweat. The digestive organs and all of the
digestive hormones (e.g. amylase in the mouth,
pepsin in the stomach, trypsin in the small
intestine) are all involved in breaking down food
and facilitating absorption into the bloodstream.
(b) The kidney is the primary regulator of fluid and
ions. When large quantities of fluid must be
excreted, the kidney produces large amounts
of dilute urine. When water must be conserved,
small amounts of concentrated urine are
produced. ADH (antidiuretic hormone) causes
more water to be reabsorbed from the kidney
(causing a more concentrated urine). ADH
increases when blood water levels are low.
Essential ions (and glucose) are retained by
active reabsorption from the kidney tubules.
Another hormone, aldosterone from the adrenal
glands, increases the absorption of sodium ions.
Note: Water and ions are lost via sweat and
water is lost in breathing. These losses are
compensated for by the homeostatic role of the
kidney. Note that sweating is a mechanism for
thermoregulation. It is not usually an important
way to rid the body of excessive water and salts. 4. Regulating respiratory gases during exercise by:
(a) Increasing breathing rate. This increases both
the rate of oxygen entering the lungs and the rate Receptors (detect stimuli), control and coordination
centre (integration of signals and coordination of
response), effectors (implement an appropriate
response). 2. 3. Negative feedback mechanisms enable maintenance
of a steady state internal environment despite
fluctuations in the external environment (e.g. rising
air temperature). Negative feedback mechanisms
are self-correcting so that physiological systems are
stabilized against excessive change. Body Membranes and Cavities (page 38)
(d) A=parietal pleura
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This document was uploaded on 01/28/2014.
- Winter '13