The Skin and Its Parts Integumentary System

A complex association of tissues and cells that play critical roles in maintaining homeostasis. A complex association of tissues and cells that play critical roles in maintaining homeostasis. The largest organ system The largest organ system composed of: 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 embryonic connective tissue star-shaped cells star-shaped cells gel-like matrix gel-like matrix fibroblasts develop from mesenchyme cells secrete collagen fibers that provide strength 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 large area of contact between layers prevents separation of layers when skin is stretched or rubbed 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 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 inward growths of outermost squamous layer may not be functional until after birth may not be functional until after birth will eventually produce oils and sweat 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 pigment –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