Skin

The structure of mammalian skin

Epidermis

Dermis

Subcutaneous
layer of fat

Function of the adipose/fat layer:
1. provides a store of energy
2. forms an insulating layer: prevents heat loss

Subcutaneous
layer of fat

Question: Sep, 2011
Give a biological explanation
for each of the following:
Aquatic mammals such as
whales have a thick layer of
blubber. (3)

3 layers in epidermis:

cornified
granular
malpighian

New skin cells are made all the
time at the :
cornified

granular

malpighian

Growth of the epidermis:
cornified
4 The dead cells
become hard and
flat and flake off.

The cells are cut
3 off from the blood granular
supply and so die.

2 This cell enters
the granular
layer.
Cells in this layer
malpighian
1 divide to produce
two cells.

Functions of the cornified layer:
i) reduces water loss
ii) keeps out microbes Cornified layer
dead cells

Function of the malpighian layer:
 cells divide by mitosis to form the granular
layer
Granular layer

Malpighian layer:
produces melanin

Functions of melanin:
1. absorbs ultraviolet
rays
2. gives colour to the
skin

What is present in the dermis?

 sensory nerve endings
 sweat glands
 hair follicles
 capillaries

Let’s f ind out
the f unction of
each.

Where are the sensory nerve
endings located?

Receptors serve as receivers for the body,
keeping it informed of changes in its
environment.

What is present in the dermis?

 sensory nerve endings
 sweat glands
 hair follicles
 capillaries

sweat pore
evaporation
Section
through skin epidermis

The sweat gland dermis
extracts sweat
from the blood
and passes it up
sweat duct
the duct to the
skin surface
where it
evaporates
sweat gland

blood vessel
0.25 mm

Question: SEP, 2010
What is sweat made up of? (3)

 Water
 Salts
 Urea
 A little lactic acid

Sweat cools the body as it
evaporates

The
skin

Evaporative cooling

Hippos bathing

Explain why a person is advised to
take a salt tablet after staying in
the sun for a long time.

To replace salts
lost in sweat.

Question: SEP, 2010
On hot days the volume of urine lost is less
than on cold days. Explain why. (4)
Cold days:
Hot days: No/less sweat
Water lost in sweat

Urine changes colour
The more dilute
the urine is, the
lighter is its
colour.

A hair follicle is a deep pit lined with
granular and malpighian cells

Hair

Hair follicle
Blood vessels

It is not painful
to cut your hair.
Why?
Hair is made of
dead cells.

Human hair:
made of the protein keratin

Hair erector
muscle

Erector
Thicker layer of muscle
Thinner layer of air is trapped. contracted
air is trapped.

Hot day Cold day

Thickness of fur varies according
to season

Sebaceous / Oil gland
produce sebum - waterproof

Capillaries:
 bring food and oxygen to the
skin and remove wastes

 capillary loops near the skin
surface are important in
controlling temperature

Vasodilation

If the
temperature
rises, the blood
vessel dilates
(gets bigger).

This means more heat is lost from the surface of the
skin

Vasoconstriction

If the
temperature
falls, the blood
vessel constricts
(gets shut off).

This means less heat is lost from the surface of the
skin

Give a reason for this observation.
A child looks pale in the face on a cold day but
red after running a race.

Vasoconstriction to Vasodilation to
reduce heat loss. increase heat loss.

Spot 3 ways shown in the diagram
that help cool the body on a hot day.

Cold 1
Hot
2

3

5 functions of the skin:
1. Protection –
 barrier to microbes
 reduces water loss
 absorbs UV rays


2. Sensation
sensory cells make the body
aware of the changes around it
through pain, touch, heat cold
and pressure

3. Formation of vitamin D
by the action of sunlight on the skin

4. Temperature regulation
helps to keep a constant body temperature

5. Excretion
removes urea in sweat

Question: Sep, 2011
Give a biological explanation for each of the
following:
African elephants flap their large ears
frequently in hot weather. (4)

Balance in heat gain and heat loss

HEAT GAIN HEAT LOSS

Ways to GAIN heat
1) INTERNAL CHANGES

2) EXTERNAL CHANGES

Ways to GAIN heat
1) INTERNAL CHANGES
i) reactions release heat
ii) muscular contractions release heat

IRATION
RESP

Ways to GAIN heat
2) EXTERNAL CHANGES
i)body absorbs heat if temperature is more
than 37°C

ii) hot foods and drinks add heat

Ways to LOSE heat
a)conduction, convection, radiation
b) evaporation of sweat
c) cold air inhaled
d) cold drinks and food

Find the SA:Vol of the cube
Area of 1 side = length x width
= 1 x 1 = 1 cm2

Area of 6 sides = 1 x 6 = 6 cm2

Volume = length x width x height
= 1 x 1 x 1 = 1 cm3

Surface area to volume ratio = 6:1

Find the SA:Vol of the cube
Area of 1 side = 2 x 2 = 4 cm2

Area of 6 sides = 4 x 6 = 24 cm2

Volume = 2 x 2 x 2 = 8 cm3

Surface area to volume ratio = 3:1

What happens to the SA:Vol ratio
as the cube increases?

2 cubes were immersed in a dye for the
same amount of time. They were
removed and cut in half. Explain the
result.

Rate of diffusion is the same in all cubes
BUT distance to centre is different

A LARGE organism has
 a small surface area to volume ratio which
means:
1. little heat is lost
2. cannot take in oxygen from the body surface
by diffusion

Curling up when cold
 reduces surface area for heat loss

A large organism needs a:
 Circulatory system
 Breathing system

Why does an amoeba lack a circulatory
system?
Being small, it has a large surface area to
volume ratio. Materials reach all parts of
the cell quickly.

A SMALL organism has
 a large surface area to volume ratio which
means:

1. a lot of heat is lost
2. can take in oxygen from the body surface by
diffusion

Which animal has the
higher metabolic rate?

Arctic animals
 Are large
 Have small ears
 Thick fur

Two species of Lepus adapted to live at
different temperatures. Explain how.

A baby and an adult, both naked,
are placed in a room at a low
temperature. Which one loses heat
faster and dies first? Why?

Small body- Large body-
large SA: Vol ratio small SA: Vol ratio

Rule is:
LARGE animals in cold climates
SMALL animals in hot climates

Large body- Small body-
little heat loss large heat losses

 fish, reptiles, amphibians and invertebrates
 absorb heat from their surroundings - this is
called basking
 are poikilotherms

Marine iguana
basking

 birds and mammals
 produce heat inside their bodies
 are homeotherms

Endotherms insulate
their body by:
Feathers

Fur

Blubber

Question: MAY, 2011
Give a biological explanation for each of the following
situations:
a)A volunteer student sat in a sauna (a chamber with
a temperature reaching 80°C for an hour. Sweat
production increased rapidly. (3)

Increase in external environmental
temperature will result in an increase in the
internal body temperature.
Body produces sweat to regulate the internal
temperature.
Evaporation of sweat cools down the body
temperature.

Question: MAY, 2011
Give a biological explanation for each of the following
situations:
b) A young child falls in a frozen lake in winter. The
child starts shivering vigorously after being pulled out
of the lake. (4)

Muscles contract and relax quickly – this
produces heat.
The heat generated in the muscles warms the
blood as it flows through them.
The blood distributes this heat all over the
body.

Question: MAY, 2011
List THREE ways by which the parents of a child
who fell in a frozen lake in winter can prevent
further heat loss. (3)

 Provision of dry clothes/moving
child next to a warm environment
such as a heater/removing cold
clothes and covering child with a
blanket/
 Help child to take a warm bath
 Provide a warm drink or fluid such
as soup.

Question: SEP, 2010
Give a biological explanation for each of the
following statements:
In cold weather we tend to shiver and eat
more. (3)

Shiver: to produce heat
Eat more: higher rate of respiration = more
heat

Skin

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