7.4 Breaking out in a sweat

Question 1

Homeostasis

Answer 1

The maintenance of stable internal
conditions. In a mammal, the concentration of
glucose, ions and carbon dioxide in the blood,
and body temperature are all maintained within a
narrow range of optimum conditions. Each
condition has a norm or set value. The
mechanisms involved in maintaining this set
value rely on negative feedback. This is a
process where a departure from the set value is
detected by receptors. These relay information
to effectors which bring about a return to the
norm value.

Question 2

Norm value

Answer 2

In a mammal, the concentration of
glucose, ions and carbon dioxide in the blood,
and body temperature are all maintained at a
norm value and only vary within a narrow range
of optimum conditions. Homeostasis is the
maintenance of constant internal conditions
around a norm value. The norm value is also
referred to as the set point.

Question 3

Receptor, Receptor cells

Answer 3

Receptor cells that
detect stimuli and send impulses to the central
nervous system. Many receptors are spread
throughout the body, but some types of receptor
cells are grouped together into sense organs.
Rods and cones are the receptor cells in the eye
that detect light.

Question 4

Effectors, Effector cells

Answer 4

A tissue or organ that
responds to a nerve impulse or hormone. An
effector brings about a response or a change. In a
mammal, muscles and glands are examples of
effectors. See also receptor.

Question 5

Negative feedback

Answer 5

Many substances and systems
in living organisms have a set level. This is true
of the concentration of glucose in the blood and
of body temperature. Negative feedback is the
process whereby a departure from this set level
sets in motion changes which return it to the
original level.

Question 6

Positive feedback

Answer 6

Positive feedback is the
sequence of events where a change in a system
sets in motion processes that cause the system to
change even further. For example, water vapour
in the atmosphere is one of the greenhouse
gases which result in global warming. As a
consequence of higher temperatures caused by
global warming, more water will evaporate from
the Earth’s surface. The amount of water vapour
in the atmosphere will increase further. This is
an example of positive feedback.

Question 7

Thermoregulation

Answer 7

Control of core body

temperature.

Question 8

Vasoconstriction

Answer 8

The narrowing of blood vessels
such as arterioles. In cold conditions, the
muscles in the walls of arterioles in the skin
contract, resulting in vasoconstriction. This
reduces the blood supply to the surface
capillaries and helps to conserve body heat.

Question 9

Shunt vessel

Answer 9

A small blood vessel which
connects an arteriole with a venule. Dilation of
the shunt vessel diverts blood from the
capillaries by providing an alternate pathway.
Shunt vessels play an important part in
controlling blood flow through the skin in the
process of temperature regulation.

Question 10

Vasodilation

Answer 10

The widening of blood vessels such
as arterioles. In warm conditions, the muscles in
the walls of arterioles in the skin relax, resulting
in vasodilation. This increases the blood supply
to the surface capillaries so more heat is lost.