The Integumentary System

Chapter 44

The Integumentary System The outer covering of animal

bodies is called the integument. In humans

The skin is the largest organ of the body

It accounts for 12-15% of body weight Occupies an average surface area of

about 1-2 meters

Integumentary Patterns of Animals Porifera (sponges)

Epidermis spicules

Cnidaria Epidermis

Integumentary Patterns of Animals Platyhelminthes

Cuticle Ectoderm

Nematoda Cuticle Ectoderm

Cross-section of Ascaris

Integumentary Patterns of Animals Annelida

cuticle setae

Arthropods exoskeleton made of

chitin undergoes ecdysis

(molting) – exoskeleton is shed periodically

Integumentary Patterns of Animals Mollusks

Shells of calcium

Echinoderms e.g., starfish spiny skin

Integumentary Patterns of Animals Vertebrates

pliable skin structures derived from the epidermal

cells Hair nails

Functions of The Integumentary System Protection from

Abrasion Bacteria, fungi, viruses UV radiation ( melanin pigment) dehydration

Support Temperature regulation

An important part of homeostasis

Functions of The Integumentary System Excretion

Another homeostasic function- maintaining water & salt balance

Secretion of the following: Oil Cerumin ( wax) Sebum ( from sebaceous glands) – softens &

lubricates skin and hair; slows water loss; antibacterial

Fatty acids - antibacterial

Functions of The Integumentary System Movement

In simple animals, contractions of the integument may be the only means of locomotion

In other animals, the integument is closely connected to the muscle layers.

In mammals, the integument is attached to the muscles by a connective tissue layer called the fascia

Functions of The Integumentary System Vitamin D production

Produced on the skin using the energy of UV light from sunlight

a serious deficiency of Vitamin D results in a crippling bone disease called rickets

Functions of The Integumentary System Reproductive

Mammary glands are actually derived from the ectodermal tissue of the integument.

Blood vessels in the skin serve as a blood reservoir for the body .

Functions of The Integumentary System Sensory reception

Sensory receptors in the skin detect external stimuli

Temperature Pressure and touch

Modifications of the Integumentary System Hair Fur Feathers Scales Quills Nails Claws Hooves

Beaks Horns Antlers Cerumin glands

wax Mammary glands

milk Sebaceous glands

Oil and sebum

Types of Tissues All four major types of tissues are

found in the Integumentary System Epithelial Connective Muscular Nervous

Structure of Human Skin

Structure of Human Skin Three Major

Layers A -- Epidermis B -- Dermis C -- Subdermis

(Subcutaneous Layer) – not strictly part of the skin

A

B

C

Epidermis Tissue - Stratified Squamous

Epithelium Epidermal cells called

keratinocytes produce keratin- a tough fibrous protein Keratin layers protect against water

loss & abrasion

Layers of the Epidermis Stratum corneum - outermost; cells are

flattened dead “bags” of keratin Stratum basale (Stratum germinativum)

The lowest or innermost layer generates new cells contains pigments: melanin(from

melanocytes) & carotene - skin color & UV protection

Layers of the Epidermis

Stratum corneum

Stratum basale or germinativum

Middle layers

S. Lucidum

S. Spinosum

S. granulosum

Dermis (“True Skin”) Lies below the

epidermis Cushions against

stretching & mechanical stress

Dense irregular connective tissue

sweat glands sebaceous glands hair follicles blood vessels nerve endings muscle

Glands in the Dermis All are exocrine glands

secrete to a duct or directly to surface Sweat Glands Sebaceous Glands

Sebum is a fatty mixture of oils and fatty acids; These glands are found on the hairy areas of skin

Sense Receptors Free Nerve endings – sense pain, heat

and cold Pacinian bulbs - pressure (found in

subdermis) Ruffini bulbs – deep pressure and

stretch Meissner’s bulbs, Merkel cells – light

touch Hair follicle receptors – light touch

Subdermis subcutaneous tissue ; lies beneath

the dermis technically not considered to be a

part of the skin anchors skin Mostly adipose tissue - stores fat

Insulation cushioning

Hair Composed of hard keratin Shaft – projects from the skin Root – part embedded in the skin Hair follicle – the epidermis folds down into

the dermis, producing a hair follicle. The deep end of the follicle is the hair bulb. The root grows out of the bulb

Hair tissue at the base of the hair bulb –

contains capillaries & free nerve endings which sense temperature & pain

receptors wrap around the bulb – act as very sensitive touch receptors

Sebaceous glands – secrete sebum to soften & waterproof the hair

Hair The arrector pili

muscle Contracts & raises the

hair You see “goose bumps”

under the skin Raising the hair

creates a trapped layer of still air that slows down heat loss & keeps the body warm

Nails A highly keratinized modification of the

epidermis Correspond to the hooves or claws of

other animals The nail matrix is where nail growth

occurs. The skin folds at the edge of the nail are

the cuticle.