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These questions are to accompany a generalised diagram of a vertical section through the skin of a mammal. This could be, but is not necessarily from, a human being. Click for overlay

1) Why is this called a generalised diagram?
..Everything is cleanly cut to show all components..
How does it differ from an actual section, and how would you make one?
.. An actual section would be more haphazard, with some bits cut at odd angles.
.. It is made from a vertical section (slice) through part of the skin (of a corpse)

What other types of section can you get?)

.. TS - transverse section - same depth...

2) What part of the skin is always dividing? ..Malpighian/germinative layer..

3) What process is happening in the nuclei? ..mitosis..

4) What stops the skin from getting thicker? . .wearing away..

5) What 2 parts are used as insulation?
..subcutaneous fat..

6) How can each effect be increased?
Quick method ..erector muscle contract causing a thicker layer of hair.
Longer term method ..fat layer laid down as winter approaches..

7) Name 2 structures that participate in cooling the body
. .sweat glands..
. .superficial capillaries..

8) Why does the cell shape vary in the outer layer?
..As cells die, they get flatter..

9) Explain why:

- the skin is sometimes red and throbbing after exercise.
.. more superficial blood flow - more excess heat to get rid of - heart rate up - higher blood pressure ..

- the skin, especially of fingers, toes etc, goes white when cold...
.. blood supply reduced - cut off to reduce heat loss ..

- then it goes blue!
..trapped blood becomes deoxygenated - different colour..

10) Why can frost-bite be the ultimate result? Or maybe gangrene?
..cells die of oxygen starvation - ideal conditions for infection by anaerobic bacteria..

11) Skin is not the same all over the body. How different would you expect the following to be:

- back of the hand .. thinner .. - underarm ..more sweat glands..

- sole of foot ..thicker (epidermis) - no hairs.. - scalp ..many more hairs..

12) How would different animals vary?
..most mammals - more hair , non-mammals - no hair/sweat glands..

13) Use the diagram to explain:

- "goosepimples"
..erector muscle contract to mske non-existent/sparse hairs stand on end..

- "creepy feelings" (clue: consider an animal whose "hackles" rise when threatened)
..same effect, especially in neck, back of scalp - in animals serves to look larger and fiercer!..

14) What is the function of the various blood vessels?
- blood carries heat nearer the surface for loss by radiation and convection, and to sweat glands for loss by evaporation
- provides raw materials for growth etc.

15) The UV (ultraviolet) part of sunlight can damage DNA. Where in the cell is DNA to be found?
.. nuclei/chromosomes ..

16) Which layer of cells is likely to be affected by too much exposure to sunlight?

17) What might happen if cells get too much UV light?

18) What substance in skin can prevent the penetration of UV light?
.. melanin..
19) What substance in the upper atmosphere can reduce the penetration of UV light to the earth's surface?.. ozone.. What is thought to be undoing this?
.. CFCs (chlorofluorinated hydrocarbons) e.g. from aerosols, fridges. fire extinguishers..

20) UV light can be useful to the body because fats such as ergosterol can be converted into a vitamin. Which one, and in which layer would it happen?
..vitamin D - produced in the subcutaneous layer..

Use these facts to explain why peoples originating from near the equator are darker skinned, and peoples from further north are lighter skinned.

21) What problems would be suffered by a dark skinned person in Scandinavia, for instance?
..vitamin deficiency - light does not penetrate..

22) What problems would be suffered by a Scandinavian in Africa (or Australians of European origin) , for instance?
..excess sunburning - skin cancer?..

23) What is "suntanning"?
..gradual increase in melanin content of skin..
How does it differ from "sunburn"?
..inflammation of cells near surface..

24) What does suntan lotion do? There are several sorts.
..filters out UV radiation/reduces sunburn/moisturises skin..

25) Sebaceous glands produce an oily secretion. What use might this be to the body?
..keeps hair flexible/conditions skin/acts as waterproofing..

26) Sweat contains salt and water. Where do they come from?
..blood, and ultimately diet..

27) If soaked in water, skin becomes wrinkled. Why?
..cells swell due to osmosis..

28) Does the water penetrate all the way? Explain.
..no - keratin is an impenetrable layer..

29) Why does so-called "indelible" writing on the skin usually disappear in a day or so?
..the outer layer wears away and is sloughed off..

30) Why, on the other hand (sic!), are tattoos permanent?
..pigment is deposited beneath the Malpighian layer..
(What are their health risks?)
..hepatitis, AIDs etc..

31) Why are some nerve endings near to the surface, and some deeper down? To what stimuli do each respond?
..touch - near surface - fine detail .. pain & pressure - deeper down .. gross force ..

32) Why does a hair follicle have a blood supply?
.. needs nutrients for growing cells ..

33) Bacon is really a slice through pig's skin. What part on the diagram is the rind?
.. outer - granular - layer ..

34) Radiation causes burns like severe sunburn, then hairs fall out. Try to explain.
.. damage to dividing cell layer ..

35) From which layer do you expect claws, nails, hooves, etc to be produced?
.. Malpighian layer ..

36) Try to explain the following in relation to the components shown in the diagram:

.. larger than usual pieces of dead skin sloughing off - adhering? ..

corns and callouses
.. thickening of outer layer - compaction of epidermis ..

.. blockage of sebaceous gland ducts - buildup of greasy materials ..

.. patches of cells with different pigment production, esp. promoted by sunlight ..

37) Apart from directly using structures in skin, how may a mammal (or different sorts of mammal) do the following:

- gain heat

.. shivering/bask in the sun ..
- reduce heat loss

.. hibernate in nest ..
- lose heat

.. wallow in water/mud .. - increase heat loss ?

.. panting/dangle out tongue ..
38) What is the meaning of the term homeostasis?
.. keeping constant body conditions ..
What part does the skin play in this?
.. mostly temperature control, but also excretion (sweat) ..
What other organs are involved?
.. kidneys, liver, (lungs) ..

39) Try to list as many functions of skin as possible, and the specific structures that assist in carrying out each one.

40) Are there any other questions you would like to ask (and hopefully also answer!)?

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