- 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)
hypodermis/ superficial fascia-
(subcutaneous tissue) consist mostly adipose.
name and describe the function of the 4 distinct cell types
- 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
name the layers of the epidermis and describe the characteristics of each.
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.
name the layers of the dermis and describe the characteristics of each.
- 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.
describe the various skin conditions:
- Bedsores (decubitus ulcers)
- Jaundice Addison’s disease
describe the distribution and function of the skin derivatives – cutaneous gland, nail, and hair.
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.