Integumentary System

Functions Covers and protects the body What does the skin protect us from? Pathogens Injury Ultra-violet radiation

Functions How does it regulate temperature? 2. Regulate body temperature How does it regulate temperature? Sweating Dilate/constrict of blood vessels Goose bumps

Functions 3. Excretes Waste What wastes are excreted? Urea as sweat subcutaneous

Functions 4. Reduces water loss Keeps the body from drying out!

Functions 5. Houses sensory receptors Chemo Mechano Chemo Photo

Four basic types of integumentary tissue Epithelium – epidermis Connective tissue - dermis Muscle tissue Nervous tissue

There are 2 main layers of skin I. Epidermis II. Dermis

Epidermis Keratinized stratified squamous epithelium Four types of cells Keratinocytes – deepest, produce keratin (tough fibrous protein) Melanocytes - make dark skin pigment melanin Merkel cells – associated with sensory nerve endings Langerhans cells – macrophage-like dendritic cells Layers (from deep to superficial) Stratum basale or germinativum – single row of cells attached to dermis; youngest cells Stratum spinosum – spinyness is artifactual; tonofilaments (bundles of protein) resist tension Stratum granulosum – layers of flattened keratinocytes producing keratin (hair and nails made of it also) Stratum lucidum (only on palms and soles) Stratum corneum – horny layer (cells dead, many layers thick) (see figure on next slide)

Epidermis Outer (surface) layers of skin Two Parts: Dead keratinocytes Lamellar granules Keratinocyte Langerhans cell Melanocyte Merkel cell Tactile disc Sensory neuron Stratum corneum lucidum granulosum spinosum basale Dermis Outer (surface) layers of skin 10-30 cells thick Two Parts: Inner part composed of living cells Outer part is of dead cells

Epidermis Inner layers Lowest layer of cells reproduce and push older cells toward the surface. As cells near the surface, they flatten and their organelle disintegrate

Epidermis Inner layers These cells also begin producing Keratin a tough, fibrous protein. This replaces cytoplasm.

Epidermis – Outer layers The Keratin producing cells die as they move toward the surface. Outer dead layer waterproofs and protects inner layers It is shed continually and is completely replaced in 2 - 4 weeks

Epidermis What do we find in the epidermis? Melanocytes What are melanocytes? Cells that produce melanin. What is melanin? A dark brown pigment What does melanin do? Gives skin it’s color Protects sensitive dermis from U-V radiation

Skin color Three skin pigments Melanin: the most important Carotene: from carrots and yellow vegies Hemoglobin: the pink of light skin Melanin in granules passes from melanocytes (same number in all races) to keratinocytes in stratum basale Digested by lysosomes Variations in color Protection from UV light vs vitamin D?

Epidermis NO! Melanocytes Do some people have more melanocytes than other people? NO!

Epidermis Skin pigmentation is due to the type and amount of melanin produced Eumelanin produces darker pigments Phaeomelanin produces lighter pigments and freckles These often occur together in varying amounts

Dermis Deeper layers of skin 10-20 times thicker than epidermis. Top layer arranged In ridges.

Dermis Ridges help the epidermis bind to the dermis. The uneven ridges create fingerprints

Accessory Organs of the Dermis 1. Hair follicles – tube-like depression where the hair develops

Hair and hair follicles: complex Derived from epidermis and dermis Everywhere but palms, soles, nipples, parts of genitalia *“arrector pili” is smooth muscle * Hair bulb: epithelial cells surrounding papilla Hair papilla is connective tissue________________

Make up of hair – hard keratin Three concentric layers Functions of hair Warmth – less in man than other mammals Sense light touch of the skin Protection - scalp Parts Root imbedded in skin Shaft projecting above skin surface Make up of hair – hard keratin Three concentric layers Medulla (core) Cortex (surrounds medulla) Cuticle (single layers, overlapping)

Hair growth: averages 2 mm/week Types of hair Vellus: fine, short hairs Intermediate hairs Terminal: longer, courser hair Hair growth: averages 2 mm/week Active: growing Resting phase then shed Hair loss Thinning – age related Male pattern baldness Hair color Amount of melanin for black or brown; distinct form of melanin for red White: decreased melanin and air bubbles in the medulla Genetically determined though influenced by hormones and environment

Accessory Organs of the Dermis 2. Sebaceous glands – secret oily sebum to soften and waterproof skin

Sebaceous (oil) glands Entire body except palms and soles Produce sebum by holocrine secretion Oils and lubricates

Accessory Organs of the Dermis 3. Nails – protective covers of ends of fingers and toes.

Nails Of hard keratin Corresponds to hooves and claws Grows from nail matrix

Accessory Organs of the Dermis 4. Sweat glands: secrete waste regulate heat produces ear wax produces milk during lactation

Sweat glands Entire skin surface except nipples and part of external genitalia Prevent overheating 500 cc to 12 l/day! (is mostly water) Humans most efficient (only mammals have) Produced in response to stress as well as heat

Types of sweat glands Eccrine or merocrine Apocrine Most numerous True sweat: 99% water, some salts, traces of waste Open through pores Apocrine Axillary, anal and genital areas only Ducts open into hair follices The organic molecules in it decompose with time - odor Modified apocrine glands Ceruminous – secrete earwax Mammary – secrete milk

Types of sweat glands Eccrine or merocrine Apocrine Most numerous True sweat: 99% water, some salts, traces of waste Open through pores Apocrine Axillary, anal and genital areas only Ducts open into hair follices The organic molecules in it decompose with time - odor Modified apocrine glands Ceruminous – secrete earwax Mammary – secrete milk

Accessory Organs of the Dermis 5. Blood vessels – to nourish skin cells

Accessory Organs of the Dermis 6. Nerves – to send and receive messages Subcutaneous

Accessory Organs of the Dermis 7. Erector pilli muscle -smooth muscle -causes “goosebumps” hair to stand erect subcutaneous

Subcutaneous layer – connective tissue Anchors dermis to the body Contains fat cells to protect and cushion Subcutaneous layer

Some disorders of the integumentary system Burns Threat to life Catastrophic loss of body fluids Dehydration and fatal circulatory shock Infection Types First degree – epidermis: redness (e.g. sunburn) Second degree – epidermis and upper dermis: blister Third degree - full thickness Infections Skin cancer

Disorders of the integumentary system Burns Threat to life Catastrophic loss of body fluids Dehydration and fatal circulatory shock Infection Types First degree – epidermis: redness (e.g. sunburn) Second degree – epidermis and upper dermis: blister Third degree - full thickness Infections Skin cancer

Interesting Tidbits Your body is composed of approximately 100 Trillion cells About 16% of your body weight is skin The skin is completely renewed every 27 days You will make almost 1000 new skins in a lifetime If all the layers of your skin were laid out on the ground, it would cover about 20 m2 or 2 parking spaces

Interesting Tidbits A fingernail or toenail takes about 6 months to grow from base to tip Fingernails grow faster than toenails An average human scalp has 100,000 hairs We lose between 40 and 100 hairs per day Blondes have more hair than brunettes

Interesting Tidbits Fingerprints provide traction for grasping objects Even identical twins have different fingerprints Every square inch of dermis contains twenty feet of blood vessels Skin on our hands and feet is thicker. When we bathe, skin takes on water and swells slightly. In the thicker areas, increased surface area creates crowding. The skin must wrinkle to accommodate the changes

Interesting Tidbits Friction of the epidermis causes cell division to increase. This outward thickening is called a callous. Sometimes growth is inward, creating a corn. Humans shed about 600,000 particles of skin per hour – about 1.5 pounds per year. At age 70, you will have lost about 105 lbs of skin.