Skin
The skin is the largest organ of the
body and completely covers the body.
There are two main layers of the skin:
Epidermis and Dermis
Underneath the skin is a layer of
subcutaneous fat.
The Epidermis
A Keratinised stratified squamous
epithelium.
Consists of four layers each
containing different types of cells.
Cells are produced in the germinating
layer and move up through the other layers to the surface.
Cells on the surface contain keratin.
Keratin is a waxy, water repellent,
protein like substance which helps to protect the skin.
Varies in thickness, thickest on soles
of feet and palms of hand and thinnest on lips and eyelids.
No blood vessels or nerve endings.
Deep layers are bathed in tissue fluid
to provide nutrients and oxygen which is drained as lymph.
The dermis
Tough and elastic, made of collagen
and yellow elastic fibres.
Blood vessels - capillaries supply
sweat glands, sebaceous glands hair follicles and the dermis.
Rich blood supply allows rapid
healing.
Lymph vessels.
Sensory nerve endings - sensitive to
touch, change in temperature, pressure
and pain. Nerve impulses that originate in the dermis are sent to the spinal
cord by sensory nerves then to the sensory area of the brain (cerebrum) where
the sensations are perceived.
Sweat glands and their ducts - two
types, smaller eccrine which are all over the body and whose ducts open onto
the skin surface as pores.
Larger apocrine glands are found
mainly in the axillary and perineal area and open into hair follicles. These
glands are not active until puberty and produce an odour.
Hair roots, follicles and muscles -
hair made of keratin, colour dependant on the amount of melanin.
Sebaceous glands - secrete sebum into
the hair follicle.
Sebum is an oily substance that prevent
drying of the hair and skin and
helps to keep the skin soft and pliable.
On the skin it provides water-proofing
and acts as a bactericidal and fungicidal agent preventing the invasion of germs.
Functions of the skin
Protection
Protects deeper organs and acts as a
barrier against invasion of microbes and other harmful agents.
Formation of vitamin D
Ultraviolet light from the sun
converts 7- dehydrocholestrol a fatty
substance contained in the skin into Vitamin D. Vitamin D is used in the formation
and maintenance of bone.
Waterproof
Prevents movement of fluids in and out
of the body
Tactility
Sensation of pain, touch, pressure and
temperature and so protects the body.
Melanin production
Cells called melanocytes produce the
pigment melanin. Amount of pigment is
determined by genetic inheritance and can be stimulated by sunlight.
Regulation of body temperature
Mainly by varying the vasotone of the
blood vessels and the activity of the sweat glands.
These mechanisms either produce or
conserve heat according to the need indicated by the heat regulating centre in
the hypothalamus.
Vasodilation causes extra blood near
the surface which increases heat loss by radiation, conduction and convection.
Vasoconstriction conserves heat.
The body is cooled by loss of the heat
used to evaporate the water in sweat - when conservation of heat is required
there is less sweat.
Quiz
1. Name the two main layers of the
skin. 2. What is found under the skin
3. Describe the role of the following
structures, hair, sebaceous glands, sweat glands, sensory receptors, capillary
bed
4.
What is melanin? 5. What governs the production of sweat?
6.
List five functions of the skin 7. Where is the skin thickest?
8.
Where is the skin thinnest? 9.
What is keratin?
10.
Where is keratin found? 11. What is melanin?
12.
What is the role of the sensory nerve ending?
13.
Mainly what type of blood vessels are found in the skin?
1.5 – 4 mm thick
8% of body mass in adults (liver is
less than 3%)
1.5 – 2 m2
Skin is normally under tension
10% of keratinocytes are stem cells
Turnover is 52 – 75 days
Keratinocytes secrete a variety of
lipids, mostly in the upper layers
Dehydrocholesterol is a lipid based
molecule found in the epidermis which is converted into a form of vitamin D
Dendritic cells
Melanin is a free radical scavenger
Langerhans cells
Lymphocytes
There are normally 4 layers to the
epidermis with 5 layers on areas exposed to friction
Single layer of mitotic cuboidal to
columnar cells
Germinative layer
8 – 10 layers of cells which fit
closely together
In hairless skin this layer contains
some Merkel`s discs
3 – 5 layers of flattened cells
Contain a dark substance called
keratohyalin, the first step towards keratin formation
Cell nuclei are in various stages of
degeneration
By the top of this layer all cells are
dead
Stratum lucidum (clear)
Mostly on thick skin of palms and
soles, absent from thin skin
Several layers of clear flat dead
cells
Contains eleidin which is later
converted to keratin
25 – 30 rows of flat dead keratin
filled cells
Forms an effective barrier
Is constantly being rubbed off and
replaced
Basement membrane zone
Fibroblasts, produce the fibres and
ground substance
Collagen
Elastic fibres
Proteoglycan ground substance
Messner`s receptors – under epidermis
– touch
Merkel cell receptors – in epidermis
and around hair follicles – light touch
Pacinian corpuscles – pressure, often
in hypodermis
Heat and cold thermoreceptors
Nociceptors pain
Sweat
glands
Eccrine –
thermoregulation, common on soles and palms
Apocrine –
function from puberty, viscous secretions, bacterial action, pheromones
Deep
cutaneous vascular plexus at base of dermis
Shunt
vessels
Connective tissues
Genetics determines ageing
Flattening of epidermal – dermal
junction so 50% less keratinocytes
Reduced volumes of epidermal lipids
produced – dry skin
Photoaging
Reduced numbers of fibroblasts
Reduced dermal vascularity – delayed
healing
Reduced melanocyte populations
Reduced numbers of peripheral
receptors
Changes in hair distribution
Wrinkles begin with contraction of
underlying muscles
Lesson Plan - Introductory anatomy and
physiology of the skin
Course Dip HE/RN
Module NUR105 Physiology
Lecturer John Campbell
Date Tuesday 26th January 99
Time 11.00 - 13.00
Venue Room 19, Fuse Hill St. Campus
Aim
Appreciate the basic structure of the
skin and relate this to function
Objectives
At the end of the session the student
will be able to;-
Describe the structure of the skin as
composed of two layers.
Describe the structure of the
epidermis and how a cell migrates from the lower to the upper layers
Describe the structure and function of
the following components of the skin,
hair and hair follicle
Sebaceous gland Sweat gland Sensory
receptor Capillary bed
State how the skin functions as a
protective barrier State how the
skin aids in homeothermy
Proposed lesson structure
11.00
Introduce subject area and outline the
session objectives to students
Aids - Acetate and OHP
11.05 - 12.05
Build up a diagram of the skin using
white board identifying the following structures
Epidermis Dermis Adipose
layer Hair follicle and erector
muscle
Sebaceous gland Sweat gland Four
types of sensory receptor
The principle functions of the
identified structures will be given
Aids - White board and pens,
photograph and pre prepared diagrams of the skin, large plastic model of a skin
cross section
12.05 - 12.50
Discuss the role of the skin in
relation to temperature regulation
Identify the nature of the circulation
through the dermis and how this can be regulated to give theromregulation
Describe the function of sweat and why
sweating cools the body
Aids - White board and pens
12.50 - 12.55
Give out further information in
handout form and explain the nature of the work sheet based homework
12.55 - 13.00
Review objective given at the start of
the session to check achievement
How session fits in to the module and
previous sessions
The physiology module, (NUR 105) is a
double longitudinal module running throughout the Common Foundation Programme
of the Dip HE/RN. It is assessed with a stand alone three hour written
examination. This session follows previous work on the nature of cells, tissues
and body systems so brings together concepts such as the relationship between
the skin and the circulatory and peripheral nervous systems. The session is the
first of a series of three on the protection of the body against infection so
is immediately followed by a discussion of the concept of innate (ie. non -
specific) immunity. Innate immunity in turn leads onto an exploration of
specific (acquired) immunity.
Reason for choosing the mode of
delivery
I feel if the students build up their
own diagram they learn an appreciation of the structures concerned. By relating
these structures to function as the lesson proceeds a feel for the whole system
is systematically built up. The overall style is necessarily on the didactic
side of a continuum as much of the material is low level cognitive. A
`conversation`, relaxed style is encouraged to allow opportunity for the
students to interact with presented material.