At the completion of this unit, learners will be able to: 1. Describe the structure of two layers of skin  Epidermis  Dermis 2. Briefly discuss the structure & function of skin derivatives.  Sweat gland  Sebaceous gland  Hair  Nail 28 3. Discuss the following functions of skin  Protection  Regulation of body temperature  Sensation  Absorption  Excretion

1. 1
The Skin: Anatomy &
Physiology
By
Syed Yousaf Shah

2. 2
Introduction
Largest organ in the body
Varies in thickness at different parts (< 0.5 mm at eyelids to > 5
mm on middle of upper back)

3. Anatomy Of The Skin
Beneath epidermis
Thicker layer
Connective tissue
Dermis
Outermost layer
Epithelial tissue
Epidermis
Skin
3

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Epidermis
Stratified squamous epithelium
No blood vessels
In palms of hand and soles of feet, epidermis is thicker
Composed of five layers:
[1] Stratum corneum
[2] Stratum lucidum
[3] Stratum granulosum
[4] Stratum spinosum
[5] Stratum basale

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[1] Stratum Basale
Single layer of columnar or cuboidal cells
Lower surface of cells attached to dermis
Receives nutrients from blood in the dermal vessels
Mitosis occurs in this layer
Older cells expelled to outer layer
Melanin is produced in this layer

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Stratum Basale

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[2] Stratum Spinosum
Prickle cell layer
Several layers of polyhedral (many-sided) cells
Interlocking spine-like projections help binding of this layer
Active protein synthesis takes place (indicates cell growth and
division)
Obtain nutrients through fine elements
Keratinization begins in this layer
Nuclei-containing cells change into flat cells composed of hard
durable protein)

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Stratum Spinosum
Contain Desmosome

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[3] Stratum Granulosum
Granular + 2 to 4 cells thick
Cells contain keratohyaline in granules
Final stages of keratinization occur
Loss of fluid, nucleus disintegrates
[4] Stratum Lucidum
Transparent layer
Flat + translucent dead cells
Protection against UV
Lucidum appears in palm of hands and soles of feet to protect
against sun burn

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[5] Stratum Corneum (Horny Layer)
Thick layer of dead cells
Soft keratin (keep skin elastic)
Cells below contain fatty substrate  keep skin waterproof +
prevent skin cracking and allowing bacteria inside

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Epidermis

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Dermis
True skin
Highly elastic, tough and flexible tissue
Meshwork of collagenous, reticular and elastic fibres
Collagenous Fibres
Provide support for skin
Reticular Fibres
Thinner, yet still provide support
Elastic Fibres
Skin flexibility

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Cells Of The Dermis
a) Fibroblasts
b) Fat cells
c) Macrophages
Dermis subdivided into two main layers:
{1} Upper papillary layer
{2} Reticular layer

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[1] Upper Papillary Layer
Loose connective tissue
Contain protrusions into epidermis called “PAPILLAE”
Fine capillaries to carry waste away + provide nourishment and
oxygen
Nerve endings for heat, pain, cold, pressure and touch
(Meissner’s corpuscles)
Double row of papillae  better gripping by hands and feet +
distinctive fingerprint patterns

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[2] Reticular Layer
Elastic network of tough collagen fibres interwoven with elastic
fibres
Collagenous fibres arranged in special pattern
Incisions made parallel to these lines during surgery  wound
heals faster
Contains sebaceous and sweat glands, arrector pili muscle and
hair follicle
Pacinian corpuscles are distributed through the dermis and
function as pressure receptors
Stretch marks and pregnancy due to breaks in collagen and
elastic fibres

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Dermo-epidermal Junction

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Dermo-epidermal Junction

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Hypodermis
“Subcutaneous” layer
Thicker than dermis
Thicker in females
Ducts of sweat glands and bases of hair follicles
Area for formation and storage of fat due to:
@ Adipose tissue – containing fat cells
@ Areolar tissue – tissue elasticity

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Hypodermis

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Developmental Anatomy of the Skin
Dermis and epidermis are derived from different embryological
tissues
Epidermis derived from “ECTODERM”
Dermis derived from “MESENCHYME”

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Glands Of The Skin
Two types: Eccrine and Apocrine
Eccrine Glands
Distributed almost all round the body
Secretory portion in hypodermis
Apocrine Glands
Arm pits and dark regions of nipple
Secretes fatty substances
These react to air  YOU STINK
Sweat Glands

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Sebaceous Glands
Located in the dermis
Lubrication and protection
Cluster of cells
Breakdown of inner cells in the cluster  sebum formation
Connected to hair follicles
Sebum  fight bacteria and fungi
Blackheads due to blocked glands

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Hair
Shaft = protrudes from skin
Root = embedded in skin
Follicle surrounds hair
Arrector pili muscle = bundle of smooth muscle
Arrector pili causes:
a) Hair erection
b) Sebum release from the sebaceous glands

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Anatomy Of The Skin

25. 25
Anatomy Of The Skin

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Burns
Seriousness of burns classified according to:
[1] Extent (size of body area involved)
[2] Depth (How many layers of tissue are injured)
First Degree Burn
e.g. Sunburn
Epidermis damaged but not destroyed
Treated by cold water
< 10% of body surface involved

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Second Degree Burn
Epidermis destroyed
Dermis partly destroyed
> 15% of body surface involved (10% for child)
Body capable of regenerating new skin
Third Degree Burn
Epidermis, dermis and underlying issue are involved
Burns to face, eyelids, hands, feet and > 20% of body surfaces
Less painful than second degree burns because nerve endings
are destroyed
Treated by skin graft

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Bedsores
Skin close to bone and under constant pressure
Blood vessels compressed  deprive affected tissues of oxygen
and nutrients
e.g. shoulder blades, hips and elbows
First sign is reddened warm spots
Spots turn purplish (indicate blocked blood flow)
Skin breaks and infection occurs

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Functions Of The Skin
Non-specific immunity (details to follow in later lectures)
[1] Protection
Anatomical barrier against infection
Melanin = screen out excess UV rays
When melanin is darkened by the tan  transferred to outer skin
layers (suntan)  skin less sensitive to sunrays
Dark skin due to wider distribution of melanin beyond stratum
basale into higher levels of epidermis

30. [2] Thermoregulation
Control of heat production
Shivering
Skeletal muscle
Motor neurons
Control of heat loss
Skin vasocontriction and vasodilation
Skin blood vessels
Sympathetic nervous system
Control of heat loss
Sweating
Sweat glands
Sympathetic nervous system
Hypothalamic thermoregulatory integrating centre
Peripheral Thermoreceptors (Skin)
Skin temperature
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[3] Sensory Perception
Millions of nerve endings
Receptor for pain, heat and pressure
Therefore, maintain homeostasis
[4] Excretion
Excretion of lactic acid and sodium chloride
Urea (1 g nitrogenous waste eliminated through skin per hour)

32. [5] Vitamin D Synthesis
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Promotes absorption of calcium and phosphate through intestine
Active vitamin D
Modification by liver and kidney enzymes
Vitamin D3 (Cholecalciferol)
Vitamin D precursor (in skin)

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Commonly Used Terms Describing Skin
Conditions
Intact “Skin is unbroken”
Contusion “Injury in which skin is unbroken”
Excoriation “Removal of an area of the skin”
Abrasion “Spot rubbed bare of mucous membrane or skin,
and thereby damaged”
Cyanosis “Dusky, bluish colour usually seen in the lips and on
the nail beds, caused by lack of oxygen”