The document provides a comprehensive overview of the skin's structure, including its layers (epidermis and dermis), functions (protection, temperature regulation, sensation), and various components like hair, nails, and glands. It details the processes involved in wound healing, including inflammation, proliferation, and maturation, as well as complications such as infections. Additionally, the document explains the roles of melanin and other factors in skin color and the mechanisms of regulating body temperature.

1. THE
SKIN

2. STRUCTURE OF SKIN
The skin is the largest organ in the body and
has a surface area of about 1.5 to 2m2 in adults
and it include glands, hair and nails .
O There are two main layers i.e. epidermis and dermis.
O Between the skin and underlying structures is the
subcutaneous layers composed of areolar tissue and
adipose tissue.

3. The skin completely covers the body and is continuous
with the membranes lining the body orifices. It
 Protect the underlying structures from injury and from
invasion from microbes.
 Contains sensory (somatic) nerve ending of pain
temperature and touch.
 Involved in regulation of body temperature.

4. EPIDERMIS
The epidermis is most superficial layer of the
skin composed of stratified keratinized squamous
epithelium, which varies in thickness in different
parts of body .
It is thickest on the palms of the hand and soles
of the feet.
There is no nerve ending in the epidermis.
But, in deeper layers bathed in interstitial fluid
from the dermis which provide oxygen an
nutrients and drain away as lymph.

5. 1. There are several layers of epidermis from deepest (germinative
layer) to superficial (stratum corneum) layers.
2. The cells on the surface are flat thin, non-nucleated, dead cells or
squmes in which the cytoplasm has been replaced by fibrous protein
keratin
3. These cells are constantly rubbed off and replaced by cells that
originated in the germinative layer and have undergone gradual
changes as they progressed towards the surface

7. The maintenance of healthy epidermis depends upon three
processes being synchronized
1. desquamation (shedding) of keratinized cells from the
surface.
2. Effective keratinization of the cells approaching the
surface.
3. Continual cell division in the deeper layers with newly
formed cells being pushed to the surface.
Hairs, secretions from the sebaceous glands and ducts of
sweat glands pass through the epidermis to reach the
surface.

8. O The surface of the epidermis is ridged by projections of
cells in the dermis called papillae.
O Pattern on fingertips is unique to every individual.
O The downward projection of the germinative layer between
the papillae are believed to aid nutrition of epidermal cells
and stabilize the two layers preventing damage due to
shearing forces.

10. Skin colour is affected by various factors
1. Melanin
O A dark pigment derived from amino acid tyrosine and
secreted by melanocytes in deep germinative layer is
absorbed by surrounding epithelial cells.
O the amount is genetically determined and varies between
different parts of the body between the people of the
same ethnic origin and ethnic group.
O The melanin protect the skin from harmful effects of
sunlight. Exposure to sunlight promotes synthesis of
melanin.

11. 2. HAEMOGLOBIN
O Normal saturation of hemoglobin and the amount of
blood circulating in the dermis give white skin its pink
colour.
3. Excessive level of bile pigment in blood and carotenes in
the subcutaneous fat give the skin a yellowish colour.

12. DERMIS
O The dermis is tough and elastic.
O Formed from connective tissue and matrix contain
collagen fibers interlaced with elastic fibers.
O Rupture of elastic fibers occur when skin is overstretched
resulting in permanent straie or stretch marks that is
mainly found in obesity and pregnancy.
O Collagen fibers bind with water and give skin its tensile
strength, decline with age.

13. O Fibroblasts, macrophages and masts cells are the main
cells found in the dermis.
O Structures in the dermis are –
1. Blood vessels
2. Lymph vessels
3. Sensory nerve ending
4. Sweat glands
5. Hairs arrector pilli muscles and sebaceous glands

14. Blood and lymph vessels
O Arterioles form a fine network with capillary branches
supplying sweat glands, sebaceous glands, hair follicles
and the dermis .
O Lymph vessels form a network throughout the dermis

15. Sensory nerve ending
O Sensory receptors sensitive to touch, temperature
pressure and pain are widely distributed in the dermis.
O The pacinian corpuscles is sensitive to deep pressure.
O The skin is an important sensory organ through which
individual receive information about their environment.

16. Sweat glands
O They are widely distributed throughout the skin and are
most numerous in the palm of the hand and soles of the
feet, axilla and groins.
O They are formed from epithelial cells.
O There are two types of sweat glands.
O The first is commonest type open into the skin surface
through tiny pores and sweat produced here is clear,
watery fluid important in regulating body temperature.

17. O The second type open into hair follicles and is found e.g.-
in the axilla.
O Bacterial decomposition of these secretions causes an
unpleasant odour. Best example is cerminous gland of
outer ear which secretes ear wax.
O Most important function of sweat is in the regulation of
body temperature
O Excessive sweating may lead to dehydration and serious
depletion of sodium chloride unless intake of water and
salt is appropriately increased.

18. Hairs
O Formed by down growth of epidermal cells into the
dermis or subcutaneous tissue known as hair follicles.
O At the base of follicle is a cluster of cells called the papilla
or bulb.
O The hair is formed by multiplication of cells of the bulb
and as they push upward away from source of nutrition
the cells die and become keratinsed.

19. O The part of hair above the skin is shaft and the remainder
is root.
O Hair color is depend on melanin.
O White hair is the result of the replacement of melanin by
tiny air bubbles.

20. Arrector Pilli
O These are little bundles of smooth muscle fibers attached
to the hair follicle .
O Contraction makes the hair stand erect and raises skin
around hair causing goose flesh.
O The muscles are stimulated by sympathetic nerve fibers in
response to fear and cold.
O Erect hair trap air which act as insulating layer
O This is an efficient warming mechanism when
accomoblished by shivering i.e. involuntary contraction
of skeletal muscles.

21. Sebaceous gland
O These consist of secretory epithelial cells derived from the
same tissue as their follicle.
O They secrete an oily substance sebum into the hair
follicles and are present in the skin of all parts of the body
except the palms of the hand and soles of the feet.
O Most numerous in the skin of the scalp, face, axilla and
groins.
O Sebum keeps the hair soft and pliable and gives it a shiny
appearance
O It provide some waterproofing and act as a bactericidal
and fungicidal agent, preventing infection.

22. Nails
O They are derived from same cells as epidermis and hair
and consist of hard, keratin plates.
O They protect the tips of the fingers and toes.
O The root of the nail is embedded in the skin and covered
by the cuticle which forms the hemispherical pale area
called the lunula.
O The nail plate is the exposed part that has grown out from
the germinative zone of the epidermis called the nail bed.

24. Functions of skin
Protection –
Skin forms a waterproof layer, provided mainly by
its keratinized epithelium which protect the deeper
and more delicate structure and act as barrier
against-
Invasion by microorganism- The epidermis
contain specialized immune cells called
Langerhans cells type of macrophage
Chemicals
Physical agents e.g.- mild trauma, uv rays
Dehydration

25. Regulation of body temperature
O Body temp. remains fairly constant at about 36.8C .
O Health variation are limited to 0.5 to 0.75C
O Slightly rises in the evening , during exercise and in
women just after ovulation.
O To ensure the constant temperature a negative feedback
mechanism maintain the balance between heat produced
in the body and heat loss in the body

26. Heat production
O When metabolic rate increases temperature rises and
when decreases temperature decreases.
O Some of the energy released during metabolic activity is
in the form heat and the most active organ produce most
heat. The principal organs involved are-
1. Skeletal muscles-
O contraction of skeletal muscles produces a large amount
of heat and more strenuous exercise the greater the heat
produced.
O Shivering also involves skeletal muscle contraction
which increases heat production when there is risk of
falling temperature.

27. 2. The liver-
O Very active metabolically and heat is produced as a
byproduct.
O Metabolic rate and heat production are increases after
eating.
3. The digestive organs-
Produce heat during peristalsis and during the chemical
reactions involved in digestion.

28. Heat loss
O Most heat loss from the body occurs through the skin
O Small amount are expired in air, urine and feaces
O Heat loss through the skin is affected by the difference
between body and environmental temperature, the
amount of body surface exposed and type of cloth worn.

29. Mechanism of heat loss-
O Evaporation – Body heat turns sweat into vapor. The
body is cooled as the heat converts the water in sweats to
water vapours.
O Convection – Heat loss by air or water moving across
the skin surface. When exposed to cold air, cover
exposed skin and take shelter from the wind. The thicker
the insulating clothing layer, the better it prevents
convection.
O Conduction –clothes and other objects Direct contact
with an object take up the heat
O Radiation – exposed parts of body radiate heat away
from the body.

31. Control of body temperature
O The temp. regulating Centre is in hypothalamus is
sensitive to temp of circulating blood. This center
respond to decreasing temp by sending nerve impulses to
• Arterioles in the dermis which constrict decreasing blood
flow to the skin.
• Skeletal muscles stimulating shivering.
o When body temp rises heat loss is increased by dilatation
of arterioles increasing blood flow to skin stimulation of
sweat glands causing sweating until it falls to normal

32. Activity of sweat glands-
O When the body temp is increased b 0.25 to 0.5 C the
sweat glands secrete sweats onto the surface of skin.
O Evaporation of sweat cools the body.
O Loss of heat from the body by evaporation of water
through the skin and expired air still occurs when there is
low temp. this is known as insensible loss of water

33. Regulation of blood flow through the capillaries-
O Amount of heat loss from the skin depend on blood flow
through dermal capillaries.
O As the temp. rises the arterioles dilates and more blood
enter in the capillaries network in the skin.
O The skin is warm and pink in color.
O If the environmental temp. is low the or if heat production
is deceased the arterioles constricts, this reduce the blood
flow and conserve the heat. The skin feels paler and cool.

34. Fever
O This is often result of infection caused by release of
chemicals (pyrogens) from inflammatory cells and
invading bacteria.
O Pyrogens act on the hypothalamus which release
prostaglandins that reset the hypothalamic thermostat to a
higher temp.
O The body responds by heat promoting mechanism i.e.
shivering and vasoconstriction.
O When thermostat is reached to normal heat –loss
mechanism is activated , profuse sweating and
vasodilation accompanied by warm skin until the body
temp. falls to the normal level.

35. Hypothermia
O This means when temp falls below normal level i.e. below
32C, compensatory mechanism to restore body temp.
usually fails
O E.g. shivering is replaced by muscle rigidity and cramps.
O Vasoconstriction fails and blood pressure, pulse and
respiration rates falls.
O Mental confusion and disorientation occurs
O Death occurs usually when the temp. falls below 25C

36. Formation of vitamin D
O 7-dehydrocholestrol is a lipid –based substance in the
skin and ultraviolet rays in the sunlight convert it to
vitamin D.
O This circulates in the blood and is used with calcium and
phosphate in the formation and maintaince of bone

37. Absorption
Substance that can be absorbed includes-
 Some drugs in transdermal patches e.g.- hormones
replacement therapy during menopause
 Some toxic chemicals e.g.- mercury

38. Excretion
Minor excretory organ for some substances like-
 Sodium chloride in sweat
 Urea, when kidney function is impaired
 Aromatic substances- garlic and other spices.

39. WOUND
HEALING

40. Conditions required for wound healing
1. Systemic factors-
These includes good nutritional status and general health.
Infection, impaired immunity poor blood supply and
systemic conditions like DM and cancer reduce the rate of
wound healing.
2. Local factors-
Good blood supply to provide oxygen and nutrients and
remove waste products and freedom from contamination by
e.g. microbes, foreign bodies or toxic chemicals.

41. Primary wound healing
Stages of wound healing-
1. Inflammation-
O the cut surfaces become inflamed and blood clots and cell
debris fill the gap between them in few hours.
O Phagocytes includes macrophages and fibroblasts migrate
into the blood clot:-
O Phagocytes begins to remove the clot and cell debris
stimulating fibroblasts activity.
O Fibroblasts secret collagen fibers which begins to bind the
surfaces together.

42. 2. Proliferation –
O Epithelial cells proliferate across the wound through the
clot.
O The epidermis meets and grows upwards until full
thickness is restored.
O The clot above the new tissue become the scab and
separate after 3 to 10 days.
O Granulation tissue consisting of new capillaries buds,
phagocytes and fibroblasts develops invading the clot and
restoring the blood supply to the wound.
O Fibroblasts continue to secret collagen fibers as the clot
and any bacteria are removed by phagocytes.

43. 3. MATURATION-
O The granulation tissue is replaced by fibrous scar tissue.
O Rearrangement of collagen fibers occurs and the strength
of wound increases
O In the time scar becomes less vascular appearing after a
few months as a fine line

45. Secondary wound healing
This method of healing follows destruction of a
large amount of tissue or when edges of a wound
cannot be brought into apposition e.g.- pressure
ulcers

46. 1. INFLAMMATION-
This develops on the surface of healthy tissue and
separation of necrotic tissue begins, mainly action of
phagocytes in the inflammatory exudate.
2. Proliferation –
O This begins as granulation tissue, consisting of capillary
buds, phagocytes and fibroblasts and develops at the base
of the cavity.
O It grows towards the surface, stimulated by macrophages

47. O Phagocytes in the plentiful blood supply tend to prevent
infection of wound by ingesting bacteria
O Some fibroblasts in the wound develops a limited ability
to contract reducing the size of wound and healing time
O When granulation tissue reached the level of dermis
epithelial cells at the edges proliferate and grow towards
the center

48. 3. Maturation-
O This occurs by fibrosis in which scar tissue replaced by
granulation tissue usually over several months until the
full thickness of the skin is restored
O Scar tissue is shiny and does not contain sweat glands
hair follicle or sebaceous gland.

51. Fibrosis (scar formation)
O Fibrosis tissue is formed during healing by secondary
intention e.g.- chronic inflammation, persistent
ischemia, suppuration or large scale trauma.
O The process begins with granulation tissue then over
time the new capillaries and inflammatory material are
removed leaving the collagen fibers secreted by
fibroblasts.
O Fibrosis tissue may have long lasting damaging effect

52. Adhesion-
These consist of fibrosis tissue which causes adjacent
structures to stick together and may limit movement e.g.-
between the layers of pleura, preventing inflammation of
lungs or between loops of bowel interfering with
peristalsis,

53. Fibrosis of infarcts-
O Blockage of a vessel by a thrombus or an embolus cause
an infarction.
O Fibrosis of one large infract or of numerous small infacts
may follow leading to varying degree of organ
dysfunction, e.g.- in heart, brain, kidney and liver

54. Tissue shrinkage-
This occurs as fibrosis tissue ages. The effect depend
upon the site and extend of the fibrosis e.g.-
O Small tubes such as blood vessels, air passage, ureters,
the urethra, and ducts of glands may become narrow
and lose their elasticity,
O Contractures may extend to joints e.g.- in a limb or digit
there may be limitation of movements or following
burns of the neck the head may pulled to one side.

55. Complications of wound healing
O Infections- arise from microbial contamination by
bacteria and result in pus (suppuration).
O Pus consist of dead phagocytes, dead cells, cell debris,
fibrin and inflammatory exudate and living and dead
microbes.
O Most common pyogenic pathogens are staphylococcus
aureus and streptococcus aureus.
O Small amount of pus forms boil and large form abscesses.

56. O Superficial abscess tend to rupture and discharge pus
through the skin. Healing is complete if tissue damage is
not extensive.
O Deep abscesses may have a Varity of outcomes-
1. Early rupture with complete discharge of pus onto
surface , followed by healing
2. Rupture and limited discharge followed by
development of chronic abscess with an infected open
channel or sinus.

57. 3. Rupture and discharge into adjacent organ or cavity
with infected open channel on both sided or fistula.
4. Removal of pus by phagocytes followed by healing
5. Formation of adhesion between adjacent structures or
membranes e.g.- pleura or peritoneum
6. Shrinkage or fibrous tissue which cause narrowing of
tubes or lumen e.g.- esophagus.