Muhammad Sohaib Shahid
(Lecturer & Course Co-ordinator BS-MIT)
University Institute of Radiological
Sciences & Medical Imaging Technology
(UIRSMIT)
SKIN/ INTEGUMENTARY SYSTEM
INTRODUCTION
• The integumentary system is the largest organ in
the body and accounts for 8-15% of a person’s
body weight.
• It must be tough to protect us .
Skin Structure
1) Epidermis
• The epidermis is the outer layer of skin. The majority of cells
(95%) are specialised epithelial cells called keratinocytes
which produce a tough protein called keratin.
• There are five distinct sub-layers of cells that represent the
different stages in the keratinisation process.
• New skin cells are produced at the basal membrane (deepest
epidermal layer) pushing the older cells towards the surface.
As the keratinocytes get older and migrate closer to the skin's
surface they change from being square-shaped to flat, they
become engorged with keratin and eventually die, losing all
of their internal structures.
• These overlapping, closely packed layers of keratinized cells
form a permeable barrier and are able to withstand scuffs and
scrapes. It takes 40-60 days for keratinocytes to reach the
surface of the skin where they are sloughed away.
• Other cells in the epidermis include melanocytes and
Langerhans cells.
• Melanocytes are responsible for the surface colour of the skin,
they produce melanin which protects the skin from UV
radiation.
• Langerhans cells are part of the skin's immune response and
engulf foreign material.
• The epidermis does not contain any blood vessels but is
nourished by the capillaries in the dermis below.
2) Dermis
• The dermis is much thicker than the epidermis and
lies immediately underneath it.
• It is a collagen rich connective tissue that contains
fibroblast cells that produce collagen and elastin,
which are responsible for the pliability and strength
of skin. It is connected below to the hypodermis.
• The dermis is made up of two layers, reticular
(deeper) and papillary (superficial).
• The dermis contains the sensory nerve endings, hair
follicles, arrector pili muscles, sweat glands,
sebaceous glands, lymphatics and capillaries.
3) Hypodermis
• The hypodermis is not a skin layer but lies below
the dermis, and is a subcutaneous tissue
which contains fat, blood vessels and sensory
receptors.
Skin Layers
Properties
Functions
Epidermis
Outer layer of skin, composed of 5 zones
of stratified epithelium (keratinocytes);
contains melanocytes and Langerhans
cells.
Responsible for the continual
replenishing of skin, resists
friction, waterproof, prevents
water loss
Stratum corneum
(Horny layer)
15-25 layers of dead, flat, keratinized
Resists friction, waterproof,
squamous epithelial cells, without nuclei. prevents water loss
Normally thin but thick over the soles of
the feet and palms of the hands.
Stratum lucidum
(Clear layer)
Only found in thick skin (palms and
soles of the feet). Transition between the
corneum and lucidum layer.
Resists friction, waterproof,
prevents water loss.
Stratum granulosum
(Granular layer)
3-5 layers of keratinocytes containing
keratin granules.
They form keratin and expel
lipids which stick the cells
together and form a waterproof
barrier.
Stratum spinosum
(Prickly layer)
Usually the thickest layer of keratinocyte Langerhans cells are part of
cells, they are joined together by
the immune response.
desmosomal connections. Also contains
Langerhans cells.
Skin Layers
Properties
Function
Stratum basale
(Basal cells)
A layer of cuboidal-shaped cells, lined up
on a basal membrane. It contains stem
cells, keratinocytes, and melanocytes
(pigment cells).
Keratinocyte cell division
occurs here to replenish skin.
Melanocytes protect the skin
from UV.
Dermis
Deep layer of skin, composed of collagen
and elastin rich connective
tissue. It contains hair follicles, sebaceous
glands, blood vessels and sense receptors.
It is responsible for the
elasticity and mechanical
support of skin. Supplies the
epidermis with nutrients.
Important in thermoregulation.
Papillary
Projections push into the epidermis. Highly Forms finger prints, brings
vascular and innervated.
capillaries closer to the
avascular epidermis.
Reticular
Dense, interlacing connective tissue,
Forms lines of skin tension,
predominantly parallel to the skin's surface. cleavage lines.
Hypodermis
Not part of skin layer. Subcutaneous
connective tissue, rich in fat and vessels.
Protective cushion and
insulator.
Clinical Considerations
• Cleavage lines are the tension lines in skin
which follow the direction of the arrangement of
collagen bundles in the dermis. Incisions along
theses lines heal faster and give minimum
scarring.
• Burns are classified according to how deep the
burn has penetrated, as well as the percentage of
surface area affected. Depth;
• Burns can be classified as partial or full
thickness burns, first, second or third degree
burns.
Degree of Burns
First degree burns
The burn has penetrated the
epidermis only.
Red and painful, only slight
swelling.
Second degree burn
The burn has penetrated the
epidermis and the dermis.
Red and painful, swelling and
blistering.
Third degree burn
The burn has destroyed the
epidermis and dermis and
penetrated the hypodermis.
Painless, the colour can be white,
tan, brown black or red. Surface
area;;
Surface Area:
• In adults the Wallace's 'Rule of Nines' is used to
work out an approximate percentage of total skin
surface area that has been affected by the burn. Each
area is approximately divided into multiples of 9. In
infants and children (under 15) the body proportions
are different and so this rule is not the same
Body Area
Surface Area
Head
Upper limb (single)
Trunk (front or back)
Genitals
Lower Limb (single)
9%
9%
18%
1%
18%
Accessory Skin Structures
Skin Appendage
Structure
Function
Hair
Hairs originate in the dermis
Sensory role, retains heat of
and are shafts of modified
the head and protects it from
keratinized epithelium which
UV, advertises sexual maturity
grow from the roots of hair
and disperses scents.
follicles.
Arrector pili muscles
Smooth muscle cells which
extend from the hair follicle to Cause the hair to stand on end
the papillary layer of the
- "Goose Bumps".
dermis.
Sweat glands
There are two types;
merocrine and apocrine. They Produce a watery substance to
consist of coiled tubes
cool the body, excretion of
embedded in the dermis or
wastes, excretion of body
hypodermis and open out onto
scents.
the skin surface.
Skin Appendage
Structure
Function
Nails
The nail plate is composed
Allows the tips of our
of dead hard keratinized
fingers to be soft and
cells which lie on top of a
sensory. They serve as
nail bed and which grow
tools to aid in the
from the nail matrix under
manipulation of objects.
the skin.
Sebaceous glands
Produce sebum, an oily
Flask shaped glands,
secretion which prevents
located in the dermis and
the hair and skin
open into the hair follicles.
becoming dry.
Skin Functions
Skin Function
•Protects our bodies from trauma.
•Wound healing.
•Acts as a barrier to bacteria and viruses.
•Produces vitamin D, essential for growth and bone maintenance.
•Prevents us absorbing and losing excess water.
•Secretes waste products.
•Regulates our body temperature (thermoreceptors, sweat, vasodilation).
•Sense what is happening in our external environment (touch, pressure, heat).
•Pigments as well as hair on our heads protect us from the sun.
•Secretes sebum.
•Advertises sexual maturity.
•Disperses scents.
Temperature Control
(Thermoregulation)
• It is very important to keep the core body temperature at
a constant 37 degrees otherwise the bodies cells can not
function properly. Sweat glands are present in the skin of
the entire body, but are more frequent in the palms, soles,
armpit, groin and forehead. Sweat is similar to blood
plasma and consists of water, salts, and waste products
such as urea. Sweat is forced to the skin surface where it
immediately evaporates; this approximates to about 500600 ml a day. When the body needs to lose more heat,
such as when partaking in strenuous exercise, sweat is
produced at higher rates.
• The blood supply to the skin also plays an important
role in thermoregulation. The capillaries to the skin in
someone who is cold constrict, decreasing the blood
flow and conserving heat. If a person is hot then the
capillaries in the skin dilate, increasing the blood
flow to the skin and allowing the loss of heat.
Clinical Considerations
Temperature control in the elderly
• Older people have fewer sweat glands, blood vessels
and subcutaneous fat and because of this
thermoregulation can become a serious problem.
They
become
increasingly
susceptible
to
hyperthermia in cold weather and heat stroke in hot
weather.
Sensation
• The skin has a variety of sensory receptors embedded
in it. Touch receptors are found in the dermis and
receptors for pain, heat, pressure and vibration are
found in the dermis and hypodermis. Hair follicles
have receptors that can detect the slight movement of
a hair.
Vitamin D production
• Sun exposure (UV) triggers the skin to produce
vitamin D. Vitamin D is a hormone and is important
in maintaining calcium blood levels.
Superficial Fascia
• The subcutaneous tissue (the so called superficial
fascia) is the second layer of the body beneath the
skin .
• It is the combination of loose connective tissue and
adipose tissue.
• Its character varies in different regions of the body.
• The fatty tissue is most abundant in the buttocks and
absent in the eyelids, pinna of the ear , penis and
scrotum.
• In some regions like scalp, face, scrotum it is
characterized by the presence of muscle fibers forming
the subcutaneous muscles of the region.
• The subcutaneous layer is a sort of fibrous membrane
attached firmly to the dermis of the skin and also to the
deeper structures like deep fascia, periosteum and the
perichondrium.
• In it nerves, blood vessels and lymphatics pass to the
skin. The layer is also termed as Hypodermis . Its main
functions are :
1) Padding
2) Storage of fuel in the form of fat, to be used in the time
of starvation.
Deep Fascia
• Deep fascia is the third layer, covering the body in
the same manner as the skin and the superficial
fascia.
• It is the real fascia.
• This fascia is a sheet like connective tissue structure
and is continuous everywhere in the body.
• It forms fascial compartments in the body to isolate
other structures like muscles , nerves and blood
vessels.
• The nature of the fascia depends upon the nature of
the function to be performed.
• The deep fascia named according to the area of the
body it covers or the functions it performs i.e. Pectoral
Fascia, Extensor or Flexor retinacula.
Clinical Consideration:
• A general understanding of the fascia of the whole
body will make the clinician to know about where and
how certain fluids like pus, blood accumulates and
will permit the surgeon to Find and Follow the
cleavage planes for the easy separation of the anatomic
structures.
• Since lymphatics are carried on the fascia, therefore its
knowledge will aid in knowing the extent of resection
in case of malignancy of any organ.