SKIN and TEMPERATURE CONTROL

This topic is another aspect of homeostasis.
What is the normal human body temperature and range of variation?
> 37 ± > 1 °C (< units?)

Hypothermia can result if this temperature falls to > 35 °C .

Name the parts labelled A to H in the diagram.

A > sweat gland

B > outer layer- epidermis

C > (sweat) pore

D > superficial capillaries

E > sebaceous gland

F > hair shaft

G > root of hair

H > (subcutaneous) fat layer
(not really oil)

Give 2 reasons why the skin shown in this diagram must come from a mammal.

> only mammals have sweat glands
> only mammals have hairs
NOT " because they are warm-blooded"
Why does layer H get thicker in wild animals in autumn?
(2 possible answers)
> increase insulation to keep in heat
> fat is a fuel used in respirationNOT "to trap air"/"to keep them warm"
What process must be going on in the lower part of layer B?
> cell division/mitosis
Why does structure A have a blood supply?
> to provide water and salts (and heat!) for sweat
Why does structure G have a blood supply?
> it needs raw materials (amino acids make protein) for growth,also oxygen, "food" etc.
Your body can get too hot if you are in a hot place, or if you are exercising, because the release of heat accompanies the production of other energy, e.g. muscular movement. So heat may be seen as a form of waste, and can be said to be excreted.

Your body can "get too cold" if you are exposed to cold weather conditions, or if you are inadequately clothed - but it is preferable to say you are losing heat in these conditions.
This means that, in order to keep the same temperature, your body must able to do the following things:
- get rid of excess heat, or:
- conserve heat, or:
- (wastefully?) release more heat energy from food due to increased respiration
n.b. Even though the skin often feels hot or cold, the internal temperature of the body remains remarkably constant.
State 2 ways your skin may help you to get rid of excess heat:
Briefly explain the principle behind the methods.
>sweating >evaporates and cools by providing latent heat of vaporisation

> superficial blood vessels expand (vasodilation) > blood flows near the skin's surface and heat is radiated away

State 2 ways in which your skin may help you conserve heat:

>superficial blood vessels contract (vasoconstriction), so less heat is lost

>insulation - due to fat layer

State one way in which your body may also release more heat, i.e. get warmer:

>shivering - wasteful muscle movement

State one extra way in which furry animals can quickly increase the way their bodies conserve their heat:
> hair erector muscles contract - bringing hairs on end, so a thicker layer of air is trapped

Explain, in 2 stages, why the skin, especially of fingers and toes, goes (1) from pink to white when cold, then (2) blue!

(1)>blood supply cut off - no pinkness (2)>oxygen used up, leaving deoxygenated blood (duller in colour?)

Why do we need to go to the toilet more in cold weather?

> we sweat less - but must still excrete excess water!

Why is it that manual workers, e.g. gold miners, who work in very hot conditions are provided with salt tablets?
> to replace salt lost in sweat

What is melanin? What is its function?

>brown pigment > protects skin from harmful UV rays

Experiment to show some of the functions of mammalian skin

In this experiment, you will measure the cooling of hot water in test-tubes, representing warm "bodies". Various coverings have been placed around the tubes, to represent some of the features of skin .

CARE - HOT WATER CAN SCALD!
Read through these instructions first, and get organised, so the experiment gets off to a good start.
After this, gathering of results should be straightforward!
Work in groups of 4-6: 4 managing one tube each, and the rest attending to general data collection.

Procedure

1) Take room temperature with each of the 4 thermometers, and record each value in the table overleaf - in the section marked before insertion (calibration check). Why is this necessary?
> to check thermometers are giving comparable readings
2) Using plastic measuring cylinders, measure 40 ml of hot water into each of the 4 tubes, and carefully insert the thermometer. Leave it in for the duration of the experiment.
Tube 4 only: Pour 10 ml of hot water over the paper towel on the outside of the tube.
Why hot - not cold - water?
> for a fair comparison - all start with the same temperature (and sweat initially carries heat from blood below)
3) Place the tubes at an angle into a plastic beaker or other rack (or just hold them at the top).
4) At 3 minute intervals, take the temperature of the water in each tube (leaving the thermometer bulb in the liquid), and record it in the table.

Tube number	1	2	3	4
All covered tubes have 1 sheet of paper towel wrapped around them
Description of experimental treatment	uncovered tube	loosely wrapped (sellotape)	tightly wrapped (elastic bands)	wet & tight (elastic bands)
Time after start /min	Thermometer readings °C
0 (before insertion)
3
6
etc

5) Plot the results from 3 minutes onwards as a graph. Join the points as appropriate, and include a key to identify the 4 curves.
6) Answer the following questions.

What do you think are represented by the various treatments applied to the tubes?

tube 1 > nude body - control

tube 2 >thick insulation layer - hairs on end

tube 3 >thin insulation layer - hairs flat/erector muscles relaxed

tube 4 >sweating/ mammal drying out after leaving water, etc

What do you conclude by comparing tube 2 with tube 1?
>insulation reduces (rate of) heat loss

What do you conclude by comparing tube 3 with tube 2?
>thick insulation retains heat longer/better than thin

What is the best tube to compare with tube 4?
>either 1 or 3

What does this comparison tell you in the context of the human body, and homeostasis?
>sweating cools the body, and more insulation slows down the heat loss