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Health Sciences 2300A/B Chapter Notes -Blood Vessel, Fissure, Temporal Bone

Health Sciences
Course Code
HS 2300A/B
Graham Fraser

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Chapter 5: The integumentary system 10/09/2014
Composed of organs such as the skin, hair, oil, and sweat glands, nails and sensory receptors
Helps maintain a constant body temperature, protects the body, and provides sensory information about the
surrounding environment,
5.1 Structure of the skin
The skin (cutaneous membrane) covers the external surface of the body and is the largest organ of the
body in weight.
In adults, the skin covers about 2 square meters and weighs 4.5-5 kg (7% of total body weight)
Consists of two main parts
Epidermis: superficial, thinner portion which is composed of epithelial tissue
Dermis: deeper, thicker, connective tissue
Deep to the dermis, but not part of the skin is the subcantaneous or hypodermis which consists of areolar
and adipose tissues.
The skin and subcontaneous layer form the integrument.

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Composed of keratinized stratified squamous epithelium
Contains 4 principle types of cells:
Keratinocytes (90%); produce keratin
Melanocytes (8%); develop from the neural crest of a developing embryo and produce the pigment melanin
Intraepidermal macrophage cells/ Langerhans cells; arise from red bone marrow and migrate to epidermis,
where they constitue a small fraction of the epidermal cell.
Tactile epithelial cells/ merkel cells; least numerous of the epidermal cells. Located in the deepest layer of
the epidermis, where they contact the flattened process of a sensory neuron, called a tactile disc
Several layers of keratinocytes in various stages of development form the epidermis.
Four layers: stratum basale, stratum spinosum, stratum granulosum, and a thin stratum corneum
This is called thin skin
Exposure to friction is greatest, such as in the fingertips has five layers:
Five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and a thick stratum

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Stratum Basale
Deepest layer of the epidermis
Composed of a single row of cuboidal or columnar keratinocytes, some of which are stem cells that
undergo cell division to continually produce new keratinocytes
Stratum Spinosum
Superficial to the stratum basale
Consists of numerous keratinocytes produced by the stem cells in the basal layer, arranged in 8-10 layers
The keratinocytes of this region produce coarser bundles of keratin intermediate filaments than those of the
basal layer
Stratum Granulosum
Middle of the epidermis
Consists of three to five layers of flattened keratinocytes that are undergoing apoptosis (an orderly,
genetically programmed cell death in which the nucleus fragments before the cells die)
Distinctive feature is the presence of darkly staining protein granules; called keratohyalin, involved in
assembling the keratin intermediate filaments into keratin
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