Download The Skin and Its Parts

The Skin and Its Parts
Integumentary System
Integumentary System
A complex association of tissues and cells that
play critical roles in maintaining homeostasis.
 The largest organ system
 composed of:
– blood vessels
– connective tissue structures
– glands
– hair
– nails
– nerves
– skin (integument)

The skin’s structure is organized based on
genetic programming during development.
– inborn or inherent features
example nails: the genes for making nails only
turn on in the upper tips of the toes and
fingers
Some flexibility is designed into the
genetics of skin cells.
– envirome or adaptive features
The integumentary system has genes that
allow adaptation to the environment.
examples
calluses: calluses on the feet are produced in
response to walking barefoot on rough surfaces
The callus protects the underlying tissues and
bones from damage
Many peoples’ skin darkens with regular
exposure to the Sun: this prevents sunlight
from damaging sensitive cells underneath the
skin
Skin stretches as the body grows to prevent
exposure of internal organs to protection and
shrinks as in postpartum recovery
Human skin does best under certain
environmental conditions:
temperatures above freezing, but not too
much heat – the body temporarily
compensates for extreme temperatures by
adjusting blood flow and glandular activity
Skin uses sunlight to carry out some
functions, but too much causes damage
Optimum moisture – too much moisture →
infection, too little moisture → weakens
skin’s ability to be a protective barrier
Skin
Skin is a continuous body covering
Includes associated structures and
mucous membranes
– anus, mouth, nose, reproductive tract
mucous membranes – lubricated inner
linings that secrete mucous
The integumentary system is composed of
layered structures formed through
embryonic development
epidermis and dermis layers
Skin is found as 2 different types:
1) thick skin
 palms of hands
 soles of feet
 thicker epidermis
 no hair follicles
2) thin skin
 the rest of the body
Integumentary Development
Integumentary development anatomy
begins 4 – 5 weeks after fertilization from
2 embryological layers
Integumentary Development
ectoderm becomes the outermost layer of
skin
– starts as simple squamous tissue that
becomes stratified as embryo develops
– some areas of the embryo, ectoderm forms
nervous tissue that later becomes integrated
skin
– ectodermal layer doesn’t develop further until
inner layers of skin form
Integumentary Development
mesoderm becomes deeper parts of the
skin
– development begins 6-7 weeks
– at 8-9 weeks group of stem cells,
mesenchyme, begin maturing
Integumentary Development
mesenchyme
 embryonic connective tissue
 star-shaped cells
 gel-like matrix
fibroblasts develop from mesenchyme cells
 secrete collagen fibers that provide
strength
Integumentary Development
As mesenchyme develops, small dents
begin to form in the upper squamous layer
→ body and head hair
Integumentary Development
At 10 weeks, small ridges begin to form between
the outer and inner layers of skin
 large area of contact between layers
 prevents separation of layers when skin is
stretched or rubbed
At 11 weeks, small nails begin to grow at the
tips of fingers and toes
After nail formation, special blood vessels begin
to form in the inner layers of skin.
 initiated by secretions, angiogenic factors, from
newly developing skin → angiogenesis formation
of blood vessels
Integumentary Development
At 20 weeks, glandular structures begin to
form
 inward growths of outermost squamous
layer
 may not be functional until after birth
 will eventually produce oils and sweat
Model
of skin
Integumentary Development
At 25 weeks, melanoblasts differentiate
from mesenchyme
At 27 weeks, melanoblasts mature into
melanocytes
– pigment producing cells
– not usually functional until after birth
Nervous tissue structures that transmit
sensations of pain, temperature, and
touch form at this point of development
Integumentary Development
Many genes are involved in the
development of skin = many errors can
occur during development
These errors lead to a variety of problems
Errors can be due to:
– genetic defects
– environmental factors that affect devlopment
of particular cells
The
complexity of
skin
Comparison of thick and thin skin
epidermis
dermis
pigment – chemical that emits a particular
color when exposed to light