Functions Layers Throughout Life Integumentary System Functions Layers Throughout Life

Integumentary System Cutaneous membrane (skin) – our largest organ Accounts for 7% of body weight Divided into two distinct layers Epidermis Dermis Accessory structures Subcutaneous layer (hypodermis)

Functions Of The Integument Cushions and insulates deeper organs Protects body from abrasion, trauma, chemicals, pathogens, temperature extremes and UV rays Excretion and secretion Contains sensory receptors associated with nerve endings Synthesis and storage of nutrients (vitamin D3)

Integumentary Structures Components of the Integumentary System Figure 5-1

Skin Structures

The Epidermis- Four Main Cell Types Melanocytes - found in basal layer, manufacture and secrete pigment Merkel cells - basal layer, attached to sensory nerve endings Keratinocytes – Arise from deepest layer of epidermis to stratum spinosum Produce keratin – a tough fibrous protein Produce antibodies and enzymes Keratinocytes are dead at skin's surface Langerhans cells - stratum spinosum, part of immune system macrophage-like

The Epidermis Stratified squamous epithelium Several distinct cell layers Thick skin—five layers on palms and soles Thin skin—four layers on rest of body

Layers of The Epidermis Stratum corneum Most superficial layer Dead, flattened (squamous) cells Abundant keratin - Keratinized (cornified) tough, water-resistant protein Protects skin against abrasion and penetration Stratum lucidum (clear layer) Occurs only in thick skin – palms and soles Composed of a few rows of flat, dead keratinocytes

Layers of The Epidermis Stratum granulosum (grainy layer) Consists of keratinocytes Tonofilaments Keratohyaline granules – help form keratin Lamellated granules – contain a waterproofing glycolipid Stratum spinosum (spiny layer) “Spiny” appearance caused by artifacts of histological preparation Contains thick bundles of intermediate filaments (tonofilaments) Resist tension Contain protein prekeratin Contains star-shaped Langerhans cells

Layers of the Epidermis Stratum basale Deepest layer of epidermis Attached to underlying dermis Stem cells actively divide Merkel cells – associated with sensory nerve ending Melanocytes – secrete the pigment melanin

Epidermal Cells and Layers of the Epidermis Figure 5.3

Sources of Skin Color Melanocytes Carotene Hemoglobin - blood pigment Make melanin from tyrosine Melanin provides UV protection Gives reddish-brown to brown-black color Carotene Contributes orange-yellow color Provided from diet (carrots and tomatoes) Hemoglobin - blood pigment Caucasian skin contains little melanin Allows crimson color of blood to show through

Dermis Second major layer of the skin Provides mechanical strength, flexibility, and protection for underlying tissues Highly vascular and contains a variety of sensory receptors that provide information about the external environment Two layers Papillary layer – includes dermal papillae Reticular layer - deeper layer – 80% of thickness of dermis Flexure lines - creases on palms

Layers of the Dermis Papillary layer Reticular layer Underlies epidermis Named for dermal papillae Aerolar connective tissue Supports, nourishes epidermis Provides sensory nerves, lymphatics, and capillaries Reticular layer Tough, dense, fibrous layer Dense irregular connective tissue Collagen fibers - limit stretch Elastic fibers - provide flexibility Blends into papillary layer (above) Blends into subcutaneous layer (below)

Dermal Components Epidermal accessory organs Cells of connective tissues proper Communication with other organ systems Cardiovascular Lymphatic Nervous Sensation Control of blood flow and secretion

Subcutaneous Layer - Hypodermis Composed of loose connective tissue - areolar and adipose Stabilizes skin position Loosely attached to dermis Loosely attached to muscle Contains many fat cells Provides thermal insulation Cushions underlying organs Safely receives hypodermic needles

The Skin Throughout Life Epidermis Develops from embryonic ectoderm Dermis and hypodermis Develop from mesoderm Melanocytes Develop from neural crest cells

The Skin Throughout Life Fetal skin Well formed after the fourth month At 5-6 months The fetus is covered with lanugo (downy hairs) Fetal sebaceous glands produce vernix caseosa

The Skin Throughout Life Middle to old age Skin thins and becomes less elastic Shows harmful effects of environmental damage Skin inflammations become more common