Integumentary System Notes

I. General Information

A. Organ system consists of a group of organs working together to perform a specific activity. B. Integumentary System: inte- =whole; gument = body covering = Composed of organs such as skin, hair, and nails.C. Skin (Cutaneous membrane) is the largest organ of the body in surface area and weight. (22 square feet; 10 pounds)D. Functions: Regulate body temperature, protection, detect sensations, excretion, absorption, and synthesis of vitamin D.

II. Structure of the SkinA. Superficial layer – epithelial tissue (epidermis)B. Deep layer – connective tissue makes up the dermisC. Subcutaneous (subQ) layer or (Hypodermis) – Deep to the

dermis but not part of the skin. 1. Also called hypodermis 2. This layer consists of areolar and adipose tissues.3. Anchoring fibers that extend from the dermis attach the skin to the subQ layer.4. The deep layer of the subQ layer is attached to underlying tissue and organs5. The subQ and dermis layers contain nerve endings called lamellated (pacinian) corpuscles, which are sensitive to pressure.

III. EpidermisA. Composed of keratinized stratified squamous

epitheliumB. Contains four types of cells

1. Keratinocytesa). 90% of epidermal cells are keratinocytesb). Arranged in four or five layersc). Produce keratin a tough protein that helps protect skin i. protection from heat, microbes, and

chemicalsd). Produce lamellar granules, which release a water- repellent sealant.

2. Melanocytesa). 8% of the epidermal cells are melanocytesb). Produce the pigment melanin (melano means black)c). Cytoplasmic extensions of the melanocytes extent between the keratinocytes.

d). Melanocytes transfer melanin to the keratinocytese). Melanin – is a yellow-red or brown-black pigment

that gives skin colorf). Melanin absorbs damaging ultraviolet (UV) light g). Melanocytes are more susceptible to UV damage

than keratinocytes

3. Langerhans cellsa). Participate in immune responses against microbes that invade skinb). Langerhans cells, macrophages, and B cells help

other immune cells fight microbes. c). Langerhans cells are damaged by UV light.

4. Merkel cellsa). Contact the flattened process of a sensory neuron called tactile (Merkel) disc.b). Merkel cells and tactile discs detect touch sensations

C. Five Layers of the Epidermis (Notes are from deep to superficial)

1. Stratum basalea). Single row of cuboidal or columnar keratinocytesb). Some stem cells are found in the stratum basale

2. Stratum spinosuma). Superficial to the stratum basaleb). Eight to ten layers many-sided keratinocytes fitted closely togetherc). More superficial layers become flattened as cell

migrate to the surface

3. Stratum granulosum a). Superficial to the stratum spinosumb). Located in the middle of the epidermisc). Three to five layers of keratinocytes that are

undergoing apoptosis.i). Apoptosis – Genetically programmed cell death (nucleus fragments before cell dies)

d). Nuclei and cell organelles degenerate/dissolve e). Keratinocytes contain mostly keratin and lamellar granules (No organelles)f). Lamellar granules release lipids (oils) as a water-repellent sealant.

4. Stratum luciduma). Superficial to the stratum granulosumb). Present only in thick skin: fingertips, palms, and

soles of foot. c). Three to five layers of flattened clear, dead keratinocytesd). Keratinocytes in this layer contain only keratin.

5. Stratum Corneuma). Superficial to the stratum lucidumb). 25 to 30 layers of flattened dead keratinocytesc). These cells are continuously shed and replaced

by migrating keratinocytes from below. d). Multiple layers of cells in the stratum corneum

protect deeper layers from injury.f). Constant friction to this layer will cause a callus.

i. Callus – abnormal thickening of the stratum corneum

D. Keratinization1. Newly formed cells in the stratum basale are pushed to

the surface2. As the cells move from one layer to another, keratin

increases 3. Keratinized cells slough off when they reach the out

layer of the stratum corneum.4. Cells that are sloughed off are replaced by more

keratinocytes from lower layers5. It takes four weeks for a keratinocytes to form and

migrate through the five layers. 6. Dandruff-excessive amount of keratinized cells shed

from the skin of the scalp