Ex 7: Itergumentary System

• composed of thick keratinized stratified squamous epithelial cells, outermost protective shield of the body that consists of 4 cell types 
• & 4 or 5 layers.

a tough leathery layer composed of fibrous connective tissue that makes up a bulk of the skin.

vascularized nutrients reach the epidermis by diffusing through the tissue fluid. 

regulation of body temp, hot(arterioles-dilate); cold (arterioles-constrict)

(subcutaneous tissue) consist mostly adipose.

• 1. Keratinocytes — produces keratin* fibrils, which arises from stratum basale layer.
• *(a fibrous protein that gives the epidermis its protective properties)

2. Melanocytes — provide protection for the keratinocyte nucleus by forming a pigment shield (melanin granules) that protects the nucleus from the damaging effects of ultraviolet (UV) radiation in sunlight.

— freckles due to a concentration of melanin in one spot.

3. Langerhans’ cell (also ⇒ epidermal dendritic cells) — phagocytic (macrophage) cells play a role in immunity that arise from bone marrow.

4. Merkel cells — form touch receptors ⇒ Merkel discs associated with sensory nerve ending at the epidermal-dermal junction

4/5 LAYERS OF THE EPIDERMIS – all 5 layers are present in thick skin (palms, finger tips & soles

Stratum corneum (horny layer) – accounts for up to 3⁄4 of epidermal thickness (20 – 30 cell layers thick)

Stratum lucidum (clear layer) – very thin translucent band with flattened, dead keratinocytes with indistinct boundaries, not present in regions of thin skin

• Stratum granulosum (granular layer) – the cells contains an abundance of granules.
• – cells flatten, nuclei & organelles disintegrate due to inadequate nourishment.

Stratum spinosum* (spiny or prickly layer) – appear spiky and contain a weblike system of intermediate filaments made of prekeratin protein.

Stratum basale* (basal layer) – constantly undergo mitotic cell division. (single cell layer) also known for its alternate name -- stratum germinativum

*only layer to receive adequate nourishment is spinosum & basale layers.

• Major Layers of dermis – a strong, flexible connective tissue layer.
• 1). Papillary layer – thin, superficial, heavily invested w/blood vessels contain free nerve
• endings (pain receptors) & Meissner’s corpuscles (touch receptors).
• – fingerlike projections on its superior surface

• 2). Reticular layer – deepest layer, accounts for about 80% of dermis
• – typical dense irregular connective tissue.

• Bedsores (decubitus ulcers)
• Jaundice Addison’s disease
• Blackheads
• Acne

ACCESSORY ORGANS OF THE SKIN: all of the epidermis, but reside in dermis.

A. Cutaneous glands (2 categories)

• Sweat (sudoriferous) glands :
• – distributed over the entire skin surface, except nipples & parts
• of external genitalia.

– body’s heat regulation controlled by nervous system.

• Sebaceous glands – found nearly all over the skin, except on palms & soles of feet.
• – secrete oily substances & fragmented cells ⇒ sebum.
• – active during puberty especially when ♂ hormones (androgens) is produced.

• B. Hairs (or pili) – enclosed in hair follicles that are found over the entire body surface, except
• for thick-skinned areas:

• – palms of the hands & soles of feet,
• – parts of external genitalia,
• – the nipples & the lips
• – structure consists of medulla, a central region (cortex), cuticle.

• C. Nails – hornlike or scalelike modification of the epidermis that forms a clear protective
• covering, consist of several named parts:

• – Body – visible attached portion.
• – Free edge – portion of the nail that grows out away from the body.
• – Root – embedded in skin & adheres to an epithelial nail bed.
• – Nail folds – borders of the nail overlap by skin folds.
• – Eponychium or cuticle – thick proximal nail fold projects onto nail.
• – Lunula – proximal region of nail that appears white crescent.
• – transparent & nearly colorless, but appears pink.