UNIT 2: Integumentary System

Tissues!

Tissue: Groups of cells that are similar in structure & perform a common or related function tissu = woven 4 primary types that interweave to form the “fabric of the body”: Epithelial (covering) Connective (support) Muscle (movement) Nervous (control) *You have completed a handout which gives more info. on these 4 tissue types.*

Skin: Integumentary System

Functions of the Skin Thermoregulation Protection (non-specific immunity) Retards (slows) water loss Excretes wastes Holds sensory receptors (pain, touch,..) Synthesis of biochemicals (ex:Vitamin D)

The skin is the largest organ in the body Cool facts: Skin surface can be as large as 17-20 ft Anywhere from 1/50 in. to 1/8 in. thick Together with its accessory organs, it constitutes the Integumentary System

epidermis is subdivided into several layers. • Skin is divided into 2 distinct layers: EPIDERMIS and DERMIS separated by a BASEMENT MEMBRANE (anchors epidermis to dermis) epidermis is subdivided into several layers.

There is also a distinct 3rd layer beneath the dermis called the subcutaneous layer (hypodermis) Binds skin to underlying tissues

Before we get to the epidermal layers… the cells of the Epidermis: Keratinocytes-produce keratin (fibrous protein that helps give epidermis its protective properties most common type arise in deepest layer of epidermis through mitosis & are pushed to the surface Are dead by the time they reach the surface animation

Melanocytes-produce melanin to protect nucleus against UV Transfer melanin to nearby epidermal cells (keratinocytes)

 Skin Color • all people have about the same concentration of melanocytes; • where we differ is in the amount and distribution of melanin • environmental (sun exposure) and physiological factors, as well as GENES, influence skin color

Three pigments contribute to skin color: Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors Freckles and pigmented moles – result from local accumulations of melanin Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet Hemoglobin – reddish pigment responsible for the pinkish hue of the skin (located within red blood cells; binds oxygen)

Epidermal Cells continued: Langerhans cells- help activate our immune system arise in bone marrow & migrate to the epidermis

NOW WE CAN LEARN ABOUT the layers of the epidermis! The epidermis is avascular. What does that mean? The epidermis is the most superficial layer of the skin and provides the first barrier of protection from the invasion of foreign substances into the body (such as?…)

The epidermis is subdivided into five layers or strata from the bottom they are: Stratum basale (germanitivum) (basal layer) Stratum spinosum (prickly layer) Stratum granulosum (granular layer) Stratum lucidum (clear layer) Stratum corneum (horny layer)

1. stratum germinativum (Stratum basale) provides the germinal cells (germinate: to start growing) necessary for the regeneration of the layers of the epidermis. These germinal cells are separated from the dermis by a thin layer of basement membrane. Germinal cells undergo mitotic division & then a progressive maturation called keratinization as they migrate to the surface.

Stratum germanitivum=Stratum basale

2. stratum spinosum (prickly layer) Several cell layers thick When skin is prepared for histological studies, these cells shrink until they have a spiny appearance Cells with melanin granules and Langerhans’ cells are abundant in this layer

3. stratum granulosum (granular layer) 3-5 cell layers Keratinocyte appearance changes accumulate keratin granules that contain glycolipids which help to form a waterproof barrier that functions to prevent fluid loss from the body.

4. stratum lucidum (clear layer) Appears as a thin translucent band May be absent in some areas of the skin Consists of a few rows of clear, flattened, dead keratinocytes with indistinct boundaries normally only well seen in thick epidermis and represents a transition from the stratum granulosum to the stratum corneum.

5. Stratum Corneum (tough like an animal’s horn: horny layer) outer most layer of cells 20-30 cell layers thick; 3/4 of epidermal thickness The dead and dying cells are filled with mature keratin (protection against abrasion & water loss!) These cells are pushed to the surface by newly forming cells of the stratum germinativum and the dead cells gradually break apart and are lost. (You’ve seen dandruff right?)

The Epidermis varies in thickness throughout the body depending mainly on frictional forces and is thickest on the palms of the hands and soles of the feet.

 DERMIS: • strong, flexible connective tissue layer -contains fibroblast cells which secrete collagen, elastin, & ground substance (support & elasticity) • nerve fibers are scattered throughout the dermis -some carry impulses to muscles and glands of the skin -some are associated with sensory receptors and carry impulses to the brain and spinal cord • contains hair follicles, sebaceous glands, and sweat glands • macrophage immune cells present

Oil gland Sweat gland

 SUBCUTANEOUS LAYER or HYPODERMIS: • lies beneath the dermis; consists of loose connective and adipose tissues • adipose tissue helps conserve body heat • subcutaneous layer contains blood vessels that supply the skin and adipose tissue

Short video clip on skin