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Summary Fundamentals of Anatomy & Physiology, Global Edition - PHYSIOLOGY (241PSH01A2)
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- PHYSIOLOGY (241PSH01A2)
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- University Of Johannesburg (UJ)
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CHAPTER 4: INTEGUMENTARY SYSTEMIntro:
● The integumentary system is one of the largest, most accessible organ systems
● Often referred to as integument
● Makes up to 16% of body weight
● Its surface is continually abraded, attacked by microorganisms, irritated by sunlight, and exposed to environmental chemicals
● It is the first line of defense against a hostile environment
● It has two major parts; cutaneous membrane(skin) and accessory systems.
● Has an extensive network of blood vessels branched through the dermis.
● Consist of nerve fiber endings.
● Sensory receptor monitor touch, pressure, temperature, and pain.
● Providing valuable information to the CNS about the state of the body.
● Deep to the dermis is a loose layer of connective tissue called the
subcutaneous layer or the hypodermis
● The hypodermis separates the integument from deep fascia around
other organs, such as bones and muscles.
● The connective tissue of this layer is interwoven with those of the dermis.
FUNCTIONS OF THE INTEGUMENTARY SYSTEM
● Protection of underlying tissues and organs against impact, abrasion, fluid loss, and chemical attack.
● Excretion of salts, water, and organic wastes by glands.
● Maintenance of normal body temperature through either insulation or evaporative cooling, as needed.
● Production of melanin, which protects underlying tissue from ultraviolet (UV) radiation.
● Production of keratin, which protects against abrasion and repels water.
● Synthesis of vitamin D3, a steroid that is converted to calcitriol, a hormone important to normal calcium ion metabolism.
● Storage of lipids in adipocytes in the dermis and in adipose tissue in the subcutaneous layer.
● Detection of touch, pressure, pain, vibration, and temperature stimuli, and the relaying of that information to the nervous
system.
● Coordination of the immune response to pathogens and cancers in the skin.
CUTANEOUS MEMBRANE
1. Epidermis
➔ The epidermis is a stratified squamous epithelium, such epithelium provides physical protection for the dermis.
➔ And prevents water loss, and helps keep microorganisms out of the body.
➔ It is avascular, it relies on the diffusion of nutrients and oxygen from capillaries within the dermis
➔ Epidermal cells with high metabolic demands are found lying closer to the basal membrane, where diffusion
distances are short.
➔ Superficial cells far from the source of nutrients are dead.
Cells of the epidermis
➔ Keratinocytes, dominate the epidermis
➔ Form several layers and contain large amounts of keratin, which is a tough, fibrous protein that is also the basic
structural component of the hair and nails in humans.
➔ Layers of the epidermis:
◆ The two types of skin differ in their number of keratinocytes.
◆ Thick skin contains or has 5 layers, usually the skin of the palms and the sole of the feet.
, ◆ Thin skin contains 4 layers of keratinocytes, usually skin covering most parts of the body.
◆ Note that the term thick or thin skin refers to the epidermis and not the cutaneous membrane as a whole.
Layers of the epidermis
➢ Stratum basale
○ The deepest layer of the epidermis
○ Hemidesmosomes attach the cells of this layer to the basement membrane that separates the epidermis from the
areolar tissue of the dermis.
○ The stratum basale and the underlying dermis interlock, increasing the strength of the bond between the epidermis
and dermis.
○ The stratum basale forms epidermal ridges, which extend into the dermis and are adjacent to dermal projections
called dermal papillae that extend into the epidermis.
○ These ridges and papillae are important because the strength of the attachment is proportional to the surface
area of the basement membrane.
○ Basal cells, or germinative cells, dominate the stratum basale.
○ Basal cells are stem cells that divide to replace the more superficial keratinocytes that are shed at the epithelial
surface.
○ Skin surfaces that lack hair also contain specialized epithelial sensory cells known as tactile (Merkel) cells scattered
among the cells of the stratum basale.
○ Each tactile cell together with a sensory nerve ending is called a tactile disc.
○ The tactile cells are sensitive to touch and, when compressed, release chemicals that stimulate their associated
sensory nerve endings.
○ Melanocytes produce melanin, which provides the skin pigment distributed throughout the stratum basale.
➢ Stratum spinosum
○ Each time a stem cell divides, one of the daughter cells is pushed superficial to the stratum basale into the stratum
spinosum.
○ This stratum consists of 8 to 10 layers of keratinocytes bound together by desmosomes.
○ The name stratum spinosum, which means “spiny layer,” refers to the fact that the cells look like miniature
pincushions in standard histological sections.
○ They look that way because the keratinocytes were processed with chemicals that shrank the cytoplasm but left the
cytoskeletal elements and desmosomes intact.
○ The stratum spinosum also contains cells that participate in the immune response; these cells are called dendritic
cells or Langerhans cells.
○ They stimulate defense against
○ (1) microorganisms that manage to penetrate the superficial layers of the epidermis and (2) superficial skin cancers
➢ Stratum granulosum or “granular layer.”
○ Superficial to the stratum spinosum.
○ It consists of three to five layers of keratinocytes derived from the stratum spinosum.
○ By the time cells are pushed into this layer, most have stopped dividing and have started making large amounts of
keratin.
○ As keratin fibers accumulate, the cells grow thinner and flatter, and their plasma membranes thicken and become
less permeable.
○ The keratinocytes also make a protein called keratohyalin,
○ which forms dense cytoplasmic granules that promote dehydration of the cell as well as aggregation and
cross-linking of the keratin fibers.
○ Gradually the plasma membrane thickens the organelles disintegrate and the cell dies.
➢ Stratum lucidium
○ In the thick skin of the palms and soles.
○ Appears grassy, also known as the clear layer.
○ The cells in the stratum lucidum are flattened, densely packed, largely without organelles, and filled with keratin.
➢ Stratum corneum
○ At the exposed surface of both thick skin and thin skin.
○ It normally contains 15 to 30 layers of keratinized cells
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