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
What is melanin produced by?
Melanocytes
What is the skin’s response to ultraviolet rays?
- accelerated production of melanin by melanocytes
- leads to tanning effect
- suntan fades as melanin is degraded in older keratinocytes and as the keratinocytes migrate to the surface and exfoliate.
Melatin is less abundant and breaks down more rapidly in what kind of skin?
Light skin
Melanin is good for _____?
Screening radiation
How do Freckles and Moles occur?
Local concentration of melanin
What is Hemoglobin?
- Red pigment of blood
- Gives reddish hue to skin
What is Carotene?
- Yellow pigment from egg yolks and vegetables
- concentrated in stratum corneum and subcutaneous fat
- seen in skin with thickest stratum corneum (heel of foot)
What is Cyanosis?
- Blueness of Skin
- From oxygen deficiency in blood (e.g., drowning, emphysema, and cold weather)
What is Albinism?
- Hereditary lack of pigmentation (in skin, hair and nails.)
- Inability to synthesize melanin.
What is Hematoma?
- bruise, mass of clotted blood
- e.g., from trauma, platelet deficiency, and hemophilia
What is Palor?
- Temporary pale color
- Little cutaneous blood flow
- e.g., from stress, circulatory shock, and cold temp
What is Jaundice?
- Yellowing of skin and whites of eyes.
- e.g., liver diseases and some blood diseases
The Hair, Nails and cutaneous glands are considered _______?
Accessory Organs (Appendages)
Where do the accessory organs originate?
Epidermis of the embryo, but penetrate deeply into the dermis or even the hypodermis of mature skin.
Differences in apparent “hairiness” are due mainly to what?
Hair texture and pigmentation
Soft Keratin make up ____?
Keratinocytes of the epidermis
Hard Keratin make up ____?
Hair and nails
Hair occurs everywhere except where?
lips, nipples, and parts of the genitalia, palms, soles, lateral fingers and toes.
What is the exclusive site of cellular mitosis and hair growth?
Hair Matrix
What are hair receptors?
- nerve fibers which coil around the follicle and respond to hair movements as when an ant crawls on your arm.
What is the cortex?
- Makes up most of the bulk of the hair
- Composed of several layers of elongated keratinized cells
What is the medulla?
- central core of eyebrows and lashes
- composed of loosely arranged cells and air spaces
What is a piloerector Muscle?
- Smooth muscle which contracts in response to stimuli such as cold, fear, and touch, pulling the follicle into a more vertical position and making hair stand upright.
How does hair grow?
Mitosis of cells in the hair matrix
Shades of Blonde to Red hair is caused by ____?
Pheomelanin
What causes gray and white hair?
pigment scarcity and air in medulla.
A typical scalp hair in a young adult grows for how long?
6-8 years at a rate of about 1mm per 3 days (10-18 cm/year)
We typically lose how many scalp hairs per day?
50-100
Name the 5 types of glands of the skin
1) Merocrine Sweat Glands –> Widespread in the skin; produce watery perspiration that serves to cool the body
2) Apocrine Sweat Glands –> occur in the groin, anal region, axilla, areola, and male beard area. Contain more fatty acids than merocrine; scent glands that respond to stress and sexual stimulation
3) Sebaceous glands –> Produce oily secretion called sebum which keeps the skin and hair from beoming dry, brittle, and cracked
4) Ceruminous glands –> Found only in auditory canal, where their secretion combines with sebum and dead epidermal cells to form earwax (Cerumen)
5) mamary glands
What is the function of scalp hair?
- Retain heat
- protects scalp from sunburn and skin cancer
What are Guard Hairs?
Block foreign particles from nostrils, auditory canals, and eyes
What is the function of hair on trunk and limbs?
- Largely an evolutionary remnant
- plays a sensory role
What are the functions of Eyebrows?
- Accentuate facial expressions
- reduce glare of sunlight
- Keep sweat and debris out of eyes
Describe Nails
Clear, hard derivatives of stratum corneum
- Composed of very thin dead cells, densley packed together and filled with parallel fibers of hard keratin
What is sweat made up of?
99% water and K, Na, Ch, Ammonia, Urea and lactic acid.
Ranges from pH range of 4-6
Apocrine and merocrine sweat glands produce sweat by ______?
Exocytosis
The 2 sweat glands are collectively called _____?
Sudoriferous
What is Diaphoresis?
Sweating with visible wetness of the skin
The secretory part of an apocrine gland has a smaller or larger Lumen then the merocrine gland?
Larger
