Chapter 5 Flashcards
What are the 2 principal layers which compose the skin?
1) Epidermis –> Superficial Epithelium
2) Dermis –> Deeper connective tissue
What is the looser connective tissue layer between the skin and muscle?
Hypodermis (Not part of the skin but customarily studied in conjunction with it.
List the functions of the Skin?
1) Protection
2) Resistance to trauma & infection
3) Water retention
4) Vitamin D synthesis
5) Sensation
6) Thermoregulation
7) Nonverbal Communication
What is the protein in Epidermal cells?
Keratin
What is the protective acidic film which helps keep bacteria and fungi populations in check?
Acid Mantle
How much Water do we lose per day through the skin even in the absence of sweating?
400ml
What 2 organs complete the Vitamin D synthesis process?
Kidneys and Liver
What is Vitamin D necessary for?
Bone development and maintenance
The skin account for ___% of the body weight?
15
The skin is classified either as thin or thick based on what?
The thickness of the epidermis
THICK skin covers what?
palms, soles, and corresponding surfaces of the fingers and toes (areas subject to the greatest mechanical stress)
- Here the epidermis is about 0.5mm thick, owing to a thick surface layer of dead cells (stratum corneum)
- Has sweat glands but no hair follicles or sebaceous glands
What does THIN skin cover?
It has 0.1 thick epidermis, with a thin stratum corneum.
- Possesses hair follicles, sebaceous glands, and sweat glands.
The skin is classified either as thin or thick based on what?
The thickness of the epidermis
What are most of the cells of the epidermis?
Keratinocytes
The basal layer of the epidermis contains what cells?
1) Melanocytes (pigment producing)
2) Tactile cells (specialized for touch)
3) Stem cells (divide and replace other epidermal cells that die)
4) Dendritic Cells (Found higher in the epidermis, the skin has these which detect foreign matter and mircorbes that invade the skin and alert the immune system to ward off the infection)
Describe the Epidermis
- Keratinized Stratified Squamous Epithelium
- Surface consists of dead cells packed with keratin
How long does a keratinocyte usually live?
30-40 days from it’s birth in the statum basale to its exfoliation from the stratum corneum.
Name the layers of the epidermis from deepest to surface
1) Stratum Basale –> deep single layer of stem cells, keratinocytes, melanocytes, and tactile cells. Stem cells divide and maintain their own population while producing new keratinocytes. All dead keratinocytes that exfoliate are replaced by mitosis in this layer.
2) Stratum Spinosum –> The thickest layer of epidermis, consisting of many layers of keratinocytes and dentritic cells. As keratinocytes are pushed upward by dividing cells below, they cease dividing and synthesize keratin. Keratin accumulation causes the cells to flatten and assume a squamous shape.
3) Statum granulosum –> Consists of 3 to 5 layers of flat keratinocytes with coarse, dark-staining granules. These cells aggregate their keratin filaments into thick, tough bundles and produce a water barrier that enables the skin to resist water loss from the body. the cells die here as the water barrier cuts them off from nutrients from below.
4) Statum lucidum –> Present only in the thick skin of the palms and soles. It is a thin, clear layer of dead cells with no nuculei or other visible internal structure.
5) Stratum Corneum –> Consists of up to 30 layers of dead, keratin-packed keratinocytes that give the skin much of its toughness.
What does “Exfoliate” mean?
Flake off
What are the 2 zones of the Dermis?
1) Papillary layer –> Thin zone of areolar tissue in and near the dermal papillae. Allows leukocytes to move around easily and attack bacteria.
2) Reticular layer –> constitues about 4/5 of the dermis. Consists of dense irregular connective tissue composed mainly of thick bundles of collagen but also containing elastic fibers, fibroblasts, and small clusters of adipocytes. Sweat glands, nail roots and half follicles are embedded in this layer.
What fibers does the Dermis consist of?
Collagen (mainly), reticular, elastic and fibrous
What is the dermal papillae?
- Boundary between the epidermis and dermis
- Interlock with the epidermis like corrugated cardboard, an arrangement that resists slippage of the epidermis across the dermis and gives the skin more resistance to stress.
What is melanin produced by?
Melanocytes (but they transfer it to the keratinocytes , where it accumulates)
Describe the Hypodermis
- Exhibits looser connective tissue and more adipose tissue (subcutaneous fat).
- Binds the skin to the muscles or other underlying tissue
- Pads body
- Serves as an energy reservoir
- Provides thermal insulation
- Differs in thickness distribution between sexes.
What is the most significant factor in skin color?
Melanin