Integumentary System

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The integumentary system is the external covering of the chordate body, comprising the skin, its pigments, and various exocrine glands that produce sweat, tears, sebum and other oils, mucous, waxes, scents, and milk. It also includes all derived structures such as hair, feathers, scales, teeth, baleen, nails, claws, horns, beaks, and hooves. The word integument is derived from the Latin word integumentum, which means a covering The skin is the largest organ in the body; 12 -15% of the body weight, with a surface area of 1 -2 meters. Its thickness varies from 0.3-4.0 mm depending on the localization on the body. Skin is continuous with, but structurally distinct from mucous membranes that line the mouth, anus, urethra, and vagina

FUNCTIONSSkin is extremely impor tant to normal physiologic function secondar y to the roles that it plays in maintaining homeostasis The integumentar y system ser ves multiple functions in promoting homeostasis of the body: 1. Restricts the movement of fluids leaving and entering the body 2. Cushions and protects vital organs 3. Protects the body against abrupt changes in the weather and helps to regulate temperature 4. Helps excrete waste materials through per spiration 5. Houses sensor y receptors, which inform the brain of external stimuli 6. Provide a front line of defense against foreign invaders 7. Provides for gaseous exchange (respiration) 8. Provides coloration and protection from the sun with skin pigments 9. Generates vitamin D through exposure to UVR 10. Stores water, fat, and vitamin D

Types of animals according to regulation of body temperature Homoiothermus animals warm-blooded or those with a regulated body temperature because of their heat -conserving body Ex: birds, mammals Poikilothermus cold-blooded animals whose body temperature closely follows that of the environment Ex: fishes

INVERTEBRATE INTEGUMENT1. Protozoa with delicate cell membrane. Ex. Amoeba 2. Coelenterata epidermis is made up of single layer of cells 3. Platyheminthes and nemathelminthes the epidermis contains a resistant cuticle 4. Arthropods and mollusks epidermis secretes a protective external skeleton called chitin in insects and shrimps (arthropods) or shells in snails and bivalves

VERTEBRATE INTEGUMENTA. The Epidermis The epidermis is a keratinized stratified squamous epithelium. The main function of the epidermis is to protect the body from harmful influences from the environment and against fluid loss. It is the outermost layer of the skin that varies in thickness (in people) from 0.07-0.12 mm. The palms of the hands average about 0.8 mm and the soles of the feet have a thickness of about 1 .4 mm. Its microscopic appearance is that of a keratinized stratified squamous epithelium Contains four main cell types: 1. Keratinocytes 2. Melanocytes 3. Merkel cells 4. Langerhans cells

There are four principal cells that compose the epidermis. These cells are as follows: 1. Keratinocytes comprise approximately 90% of all epidermal cells. These cells produce a protein mixture known as keratin which helps waterproof and protect the skin 2. Melanocytes comprise approximately 8% of all epidermal cells. These cells produce a group of pigments known as melanin which are responsible for skin, hair, and eye color 3. Langerhans cells these cells arise from the bone marrow and migrate to the epidermis. These cells play an important role in the immune response 4. These cells are located in the deepest regions of the epidermis and are associated with sensory neurons and are thought to function in the sensation of touch

LAYERS OF THE EPIDERMIS1. Stratum basale - Deepest layer of epidermis - Attached to underlying dermis - Cells actively divide - Contains:Merkel cells associated with sensory nerve endings Melanocytes secrete the pigment melanin

LAYERS OF THE EPIDERMIS2. Stratum spinosum (spiny layer) - spiny appearance caused by artifacts of histological preparation - Contains thick bundles of intermediate filaments (tonofilaments) - Contains star-shaped langerhans cells

LAYERS OF THE EPIDERMIS3. Stratum Granulosum - Consists of keratinocytes and tonofilaments - Tonofilaments contain keratohyaline granules help form keratin lamellated granules contain a waterproofing glycolipid

LAYERS OF THE EPIDERMIS4. Stratum Lucidum (clear layer) - Occurs only in thick skin - Composed of a few rows of flat, dead keratinocytes

LAYERS OF THE EPIDERMIS5. Stratum Corneum (horny layer) - Thick layer of dead keratinocytes and thickened plasma membranes - Protects skin against abrasion and penetration

DERMIS- Second major layer of the skin - Strong, flexible connective tissue - Richly supplied with blood vessels and nerves - Has two layers: 1. Papillary layer includes dermal papillae 2. Reticular layer deeper layer 80% of thickness of dermis

HYPODERMIS Deep to the skin also called superficial fascia Contains areolar and adipose connective tissues Anchors skin to underlying structures Helps insulate the body

SKIN COLOR Three pigments contribute to skin color 1. Melanin most important pigment made from tyrosine 2. Carotene yellowish pigment from carrots and tomatoes 3. Hemoglobin caucasian skin contains little melanin - allows crimson color of blood

APPENDAGES OF THE SKIN Hair Flexible strand of dead, keratinized cells Hard keratin tough and durableChief parts of a hair 1. Root imbedded in the skin 2. Shaft projects above skins surface Hair three concentric layers keratinized cells 1. Medulla central core 2. Cortex surrounds medulla 3. Cuticle outermost layer

APPENDAGES OF THE SKIN Hair follicles extend from epidermis into dermis 1. Hair bulb deep, expanded end of the hair follicle 2. Root plexus knot of sensory nerves around hair bulb Types and growth of Hair 1. Vellus hairs body hairs of women and children 2. Terminal hairs hair of scalp; axillary and pubic area 3. Hair thinning and baldness due to aging; male pattern baldness

SEBACEOUS GLANDS Occur over entire body, except palms and soles Secrete sebum an oily substance; simple alveolar glands; holocrine secretion (entire cell breaks up to form secretion) Most are associated with a hair follicle Function of sebum collects dirt, softens and lubricates hair and skin

SWEAT GLANDS Sweat glands (sudoriferous glands) widely distributed on the body Sweat is a blood filtrate 99% water with some salts Contains traces of metabolic wastes Two types of sweat glands 1. Eccrine gland most numerous produce true sweat 2. Apocrine gland confined to axillary, anal and genital areas; produce a special kind of sweat

NAILS Nails scale-like modification of epidermis Made of hard keratin Parts of the nail 1. Free edge 2. Body 3. Root 4. Nail folds 5. Eponychium - cuticle

BURNSClassified severity First degree burn only epidermis is damaged Second degree burn upper part of dermis is also damaged; blisters appear; skin heals with little scarring Third degree burn consume thickness of skin; burned area appears white, red or blackened