The Integumentary System

Chapter 5

The Skin epithelial and connective

tissues working together the largest organ of the

body 1.5 - 2 square meters 4 - 5 kg

variable thickness: 0.5 mm to 4 mm

The Architecture of the Skin2 main parts: Epidermis – keratinized

stratified squamous epithelium

Dermis – areolar & dense irregular connective tissues

Beneath the dermis: Hypodermis (the

subcutaneous layer) – separates skin from muscle; contains areolar and adipose tissues

A Bigger Picture

Skin’s Many Functions

regulation of body temperature protection – a physical barrier & water

conservation sensation – due to sensory nerve endings excretion – sweat immunity – epidermis contains phagocytes synthesis of vitamin D – for calcium absorption

The Epidermis

4 cell types: Keratinocytes

filled with protein keratin; waterproof barrier Melanocytes

produce pigment melanin Langerhans cells

phagocytes (function in immunity); easily damaged by UV light

Merkel cells

detect touch sensations

Epidermal Cell Layers

Stratum basale a single layer; mitosis pushes

the other layers to the top; Merkel cells & melanocytes

Stratum spinosum 8 to 10 layers of closely packed

cells; Langerhans’ cells

Stratum granulosum 3-5 layers of flattened non-

dividing cells; produce large amount of keratin; nuclei & organelles disintegrate

Epidermal Layers Cont. Stratum lucidum

only in thick skin only in thick skin 3-5 layers of clear, flat dead

cells with keratin

Stratum corneum 25-30 layers of flattened,

dead, keratin-filled cells continuously shed and

replaced

It takes 2-4 weeks for each cell to move from the stratum basale to stratum corneum

Epidermal Histology

Stratum Corneum

Stratum Granulosum Stratum Spinosum

Stratum Basale

Skin Pigments

1. Hemoglobin – red, carries oxygen in red blood cells

2. Carotene – yellow/orange, converted to vitamin A, used in the synthesis of vision pigments

3. Melanin – yellow/red or brown/black

Melanin Cont. The number of melanocytes is similar in all races – but the

amount of melanin produced varies The UV ↑ production of melanin; melanin protects the

body against UV radiation by absorbing UV Albinism - inability to produce melanin; genetic

Practice – Be able to complete by Wednesday

Structure Function

A. Epidermis a. Insulation

B. Hair erector muscle b. Water proofing

C. Fat cells c. Protection from sun's rays

D. Sebaceous gland d. Heat retention

E. Dermis e. Heat loss

F. Melanin f. Protection from infection

G. Hair g. Makes hairs stand on end

H. Sweat gland h. Secretes oily substance to coat hairs

I. Blood capillaries in the dermis i. Makes skin tough

J. Keratin k. Constrict or dilate to control heat loss