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

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.