Anatomy of the skin

1. ANATOMY OF THE SKIN
PREPARED BY:
USHA RANI KANDULA,
ASSISTANT PROFESSOR,
DEPARTMENT OF ADULT HEALTH NURSING,
ARSI UNIVERSITY,ASELLA,ETHIOPIA,
SOUTH EAST AFRICA.

3. INTRODUCTION
•The skin completely covers the body and is
continuous with the membranes lining the
body orifices.

4. •It Protects the underlying structures from injury
and from invasion by microbes.

5. •It Contains sensory (somatic) nerve endings of
pain, temperature and touch.

6. •It is involved in the regulation of body
temperature.

7. Structure of the skin
•The skin has a surface area of about 1.5 to 2 m
in adults and it contains glands, hair and nails.

9. •There are two main layers:
•• Epidermis
•• Dermis.
•Between the skin and underlying structures
there is a layer of subcutaneous fat.

10. EPIDERMIS
•The epidermis is the most superficial layer of
the skin and is composed of stratified
keratinized squamous epithelium which varies
in thickness in different parts of the body.

11. •It is thickest on the palms of the hands and
soles of the feet.

12. •There are no blood vessels or nerve
endings in the epidermis,
•but its deeper layers are bathed in
interstitial fluid from the dermis, which
provides oxygen and nutrients, and is
drained away as lymph.

13. •There are several layers (strata) of cells in the
epidermis which extend from the deepest
germinative layer to the surface stratum
corneum (a thick horny layer).

17. •The cells on the surface are flat, thin, non-
nucleated, dead cells, or squames, in which the
cytoplasm has been replaced by the fibrous
protein keratin.

18. •These cells are constantly being rubbed off and
replaced by cells which originated in the
germinative layer and have undergone gradual
change as they progressed towards the surface.

20. •Complete replacement of the epidermis
takes about 40 days.
•The maintenance of healthy epidermis
depends upon three processes being
synchronised:

21. Desquamation
•desquamation (shedding) of the
keratinised cells from the surface.
•Effective keratinisation of the cells
approaching the surface.

23. •Continual cell division in the deeper layers
with newly formed cells being pushed to the
surface.

24. •Hairs, secretions from sebaceous glands and
ducts of sweat glands pass through the
epidermis to reach the surface.

26. •The surface of the epidermis is ridged by
projections of cells in the dermis called the
papillae.

28. •The pattern of ridges is different in every
individual and the impression made by them is
the 'fingerprint'.

29. •The downward projections of the
germinative layer between the papillae are
believed to aid nutrition of epidermal cells
and stabilise the two layers, preventing
damage due to shearing forces.

30. •Blisters develop when acute trauma causes
separation of the dermis and epidermis and
serous fluid collects between the two layers.

31. •The colour of the skin is affected by three main
factors.

32. •Melanin, a dark pigment derived from the
amino acid tyrosine and secreted by
melanocytes in the deep germinative layer,
is absorbed by surrounding epithelial cells.

34. •The amount is genetically determined
and varies between different parts of the
body, between members of the same
race and between races.

35. •The number of melanocytes is fairly constant so
the differences in colour depend on the amount
of melanin secreted.

36. •It protects the skin from the harmful effects of
sunlight.
•Exposure to sunlight promotes synthesis of
increased amounts of melanin.

37. •The level of oxygenation of haemoglobin and
the amount of blood circulating in the dermis
give the skin its pink colour.

38. •Bile pigments in blood and carotenes in
subcutaneous fat give the skin a yellowish
colour.

39. DERMIS

40. DERMIS
•The dermis is tough and elastic. It is formed
from connective tissue and the matrix contains
collagen fibres interlaced with elastic fibres.

42. •Rupture of elastic fibres occurs when the skin is
overstretched, resulting in permanent striae, or
stretch marks, that may be found in pregnancy
and obesity.

43. •Collagen fibres bind water and give the skin its
tensile strength, but as this ability declines with
age, wrinkles develop.

44. •Fibroblasts, macrophages and mast cells are the
main cells found in the dermis.

45. •Underlying its deepest layer there is areolar
tissue and varying amounts of adipose tissue
(fat).

47. THE STRUCTURES IN THE DERMIS
ARE:
• Blood vessels
• Lymph vessels
• Sensory (somatic) nerve endings
• Sweat glands and their ducts
• Hairs, arrector pili muscles and sebaceous
glands.

49. BLOOD VESSELS.
•Arterioles form a fine network with capillary
branches supplying sweat glands, sebaceous
glands, hair follicles and the dermis.

50. • The epidermis has no blood supply.

51. •It obtains nutrients and oxygen from interstitial
fluid derived from blood vessels in the papillae
of the dermis.

52. LYMPH VESSELS.
•These form a network throughout the dermis.

53. SENSORY NERVE ENDINGS.
•Sensory receptors (specialized nerve endings)
which are sensitive to touch, change in
temperature, pressure and pain are widely
distributed in the dermis.

54. •Incoming stimuli activate different types of
sensory receptors.

55. •The skin is an important sensory organ through
which individuals receive information about
their environment.

56. •Nerve impulses, generated in the sensory
receptors in the dermis, are conveyed to the
spinal cord by sensory (somatic cutaneous)
nerves, then to the sensory area of the
cerebrum where the sensations are
perceived.

57. SWEAT GLANDS
•Sweat glands are found widely distributed
throughout the skin and are most numerous in
the palms of the hands, soles of the feet, axillae
and groins.

59. •They are composed of epithelial cells.
•The bodies of the glands lie coiled in the
subcutaneous tissue.

60. •Some ducts open onto the skin surface at tiny
depressions, or pores, and others open into
hair follicles.

61. •Glands opening into hair follicles do not
become active until puberty.

62. •In the axilla they secrete an odourless milky
fluid which, if decomposed by surface
microbes, causes an unpleasant odour.

63. •The functions of this secretion are not known.

64. •Sweat glands are stimulated by sympathetic
nerves in response to raised body temperature
and fear.

65. •The most important function of sweat secreted
by glands opening on to the skin surface is in
the regulation of body temperature.

66. •Evaporation of sweat from body surfaces takes
heat from the body and the amount of sweat
produced is governed by the temperature-
regulating centre in the hypothalamus.

67. •Excessive sweating may lead to dehydration
and serious depletion of body sodium chloride
unless intake of water and salt is appropriately
increased.

68. •After 7 to 10 days' exposure to high
environmental temperatures the amount of salt
lost is substantially reduced but water loss
remains high.

69. HAIRS
•These are formed by a down-growth of
epidermal cells into the dermis or
subcutaneous tissue, called hair follicles.

71. •At the base of the follicle is a cluster of cells
called the bulb.

72. •The hair is formed by multiplication of cells of
the bulb and as they are pushed upwards, away
from their source of nutrition, the cells die and
become keratinised.

73. •The colour of the hair is genetically determined
and depends on the amount of melanin
present.

74. •White hair is the result of the replacement of
melanin by tiny air bubbles.

75. THE ARRECTOR PILI.
•These are little bundles of smooth muscle fibres
attached to the hair follicles.

77. •Contraction makes the hair stand erect and
raises the skin around the hair, causing 'goose
flesh'.

79. •The muscles are stimulated by sympathetic
nerve fibres in response to fear and cold.

80. •Erect hairs trap air, which acts as an insulating
layer.

81. •This is an efficient warming mechanism
especially when accompanied by shivering,
•i.e. involuntary contraction of the skeletal
muscles.

82. THE SEBACEOUS GLANDS.
•These consist of secretory epithelial cells
derived from the same tissue as the hair
follicles.

84. •They secrete an oily substance, sebum, into the
hair follicles and are therefore present in the
skin of all parts of the body except the palms of
the hands and the soles of the feet.

85. •They are most numerous in the skin of the
scalp, face, axillae and groins.

86. •In regions of transition from one type of
superficial epithelium to another, such as lips,
eyelids, nipple, labia minora and glans penis,
there are sebaceous glands that are
independent of hair follicles, secreting sebum
directly on to the surface.

87. •Sebum keeps the hair soft and pliable and gives
it a shiny appearance.

88. •On the skin it provides some waterproofing and
acts as a bactericidal and fungicidal agent,
preventing the successful invasion of microbes.

89. NAILS
•The nails in human beings are equivalent to the
claws, horns and hoofs of animals.

92. •They are derived from the same cells as
epidermis and hair and consist of a hard, horny
keratin plate.

93. •They protect the tips of the fingers and toes.

94. •The root of the nail is embedded in the skin, is
covered by the cuticle and forms the
hemispherical pale area called the lunula.

95. •The nail plate of the nail is the exposed part
that has grown out from the germinative zone
of the epidermis called the nail bed.

96. •Finger nails grow more quickly than toe nails
and growth is quicker when the environmental
temperature is high.

97. THANKING YOU