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Chapter 5

BIO210Y5 Chapter Notes - Chapter 5: Stratum Corneum, Subcutaneous Tissue, Arrector Pili Muscle

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Sanja Hinic- Frlog

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Chapter 5: The Integumentary System
Section 1: Functional Anatomy of the Skin
Module 5.1: The Integumentary system consists of the skin and various accessory structures
Integumentary system: most accessible and the least appreciated system
This system makes up 16% of the total body weight
Integumentary system is the place where you and the outside world meet
it is the body's first line of defence against a harsh environment
the Integumentary system has two major components: the cutaneous membrane and the accessory structures (including hair, nails, and
exocrine glands)
The Integumentary system:
- protects the inner tissues and organs from impact, abrasion, fluid loss, and chemical attacks
- excretes salts, water, and organic wastes using the Integumentary glands
- maintains a normal body temperature by insulation or evaporation cooling
- produces melanin, which protects the inner tissues from UV radiation
- produces keratin, which protects against abrasions and serves as a water repellent
- synthesizes vitamin D3, a steroid that is converted to calcitriol (hormone important to normal calcium metabolism)
- stores lipids in adipocytes in the dermis and in adipose tissue in the hypodermis
- senses touch, pressure, pain, and temperature stimuli, and relays that info to the CNS
Module 5.2: The epidermis is composed of strata that have various functions
The epidermis is dominated by Keratinocytes
Keratinocytes: the body's most abundant epithelial cells
They form layers (strata)
They are continuously produced by stem cells division in the deepest layer
The deeper layer of the epidermis forms Epidermal ridges, which extends into the dermis and are adjacent to a dermal projection called
Dermal Papillae
The ridges and papillae increase surface area for attachment
Thin skin (covers the body surface) contains 4 strata
Thick skin (found on palms of the hand and soles of the feet) have 5 strata
The epidermis lacks blood vessels. They rely on the diffusion of nutrients and oxygen from capillaries within the dermis
Layers of the Epidermis:
1. Stratum Corneum:
- located at the exposed surface of both thick skin and thin skin
- contains 15 to 30 layers of keratinized cells
- Keratinization: the formation of protective, superficial layers of cells with keratin
- the dead cells in each layer of stratum corneum stay tightly interconnected by desmosomes
- stratum corneum is water resistant, but not water proof
- water from the interstitial fluids penetrates through the surface and evaporates into the air
- a person loses 500mL of water every day in this way. It is called Insensible Perspiration, because we are unable to see or feel the water
- Sensible perspiration: when we are able to see and feel water loss (ex. sweat)
2. Stratum Lucidum (clear layer)
- in the thick skin of palms and soles, the stratum lucidum separates the stratum corneum from deeper layers
- cells in this layer are flattened, densely packed, mostly without organelles, and filled with keratin and Keratohyalin
3. Stratum Granulosum (grainy layer):
- has 3-5 layers of keratinocytes
- by the time the cells reach this layer, most of them have stopped dividing and instead have started making large amounts of keratin and
- as these protein fibers develop, the cells grow thinner, and their membranes thicken and become less permeable
4. Stratum Spinosum (spiny layer):
- has 8-10 layers of keratinocytes that are held together by desmosomes
- Stratum Spinosum also contains Dendritic (Langerhans) cells
- Dendritic (Langerhans) Cells: participates in immune responses by stimulating a defense against
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(1) microorganism that penetrate the superficial layer of the epidermis
(2) superficial skin cancer
5. Stratum Basal:
- the Hemidesmosomes attach the cell of this layer to the basement membrane that separates the epidermis from the areolar tissue
- Basal Cells: stem cells whose divisions replace the superficial keratinocytes that are lost by shedding
- Merkel cells involved with touch sensations are scattered among the basal cells
- Tactile disc: Merkel cell along with a sensory nerve terminal
Module 5.3: Factors influencing skin color include epidermal pigmentation and derma circulation
Skin color is influenced by 3 things: pigments in the skin, the degree of dermal circulation, and the thickness and degree of keratinization in
the epidermis
primary pigments involved in skin color is Carotene and Melanin
People have different skin pigmentation because of different levels of melanin synthesis
Deficiency or absence of melanin production leads to a disorder called Albinism
People with albinism have a normal distribution of melanocytes, but the cells are incapable of producing melanin
Melanin: a brown, yellow-brown, or black pigment that is produced by Melanocytes
Melanocytes are located in the stratum basale. They manufacture melanin from the amino acid tyrosine, and package it in a intracellular
vesicle called Melanosomes
Melanosomes travel within the processes of melanocytes and they are transferred intact to keratinocytes
The transfer of pigmentation colors the keratinocytes temporarily, until the melanosomes are destroyed because of lysosomes
For pale skinned people, this transfer happens in the stratum basale and stratum spinosum
For dark skinned people, the melanosomes are larger and the transfer can occur in the stratum granulosum as well
Carotene: orange-yellow pigment that accumulates in the epidermal cells.
It is most apparent in the stratum corneum cells of light skinned people, but it also accumulates in fatty tissues in the deep dermis and
Blood supply also affects skin color because blood contains red blood cells filled with red pigments called Hemoglobin
When hemoglobin is bound to oxygen, it is a bright red. This gives capillaries in the dermis its reddish tint, which is apparent in light skinned
When these vessels are dilated, the red tones are more pronounced
When blood supply is reduced, the skin becomes pale. The oxygen levels in the tissues drop. Under these conditions, hemoglobin releases
oxygen and turns a dark red
This is why the skin appears blue from the outside. This condition is called Cyanosis
Skin cancer is the most common type of cancer
Most common type of skin cancer is Basal Cell Carcinoma. It originates in the Stratum Basale because of a mutation caused by overexposure
to UV radiation
The melanin in keratinocytes provides some protection against UV rays because the melanosomes are concentrated around the nucleus.
They act like shades for the enclosed DNA
Malignant Melanoma is extremely dangerous. In this condition, many cancerous melanocytes grow rapidly and metastasize (spread) through
the lymphatic system
Module 5.4: The dermis supports the epidermis, and the hypodermis connects the dermis to the rest of the body
dermis lies between the epidermis and the hypodermis
Collagen fibers are very strong and they resist stretching, but they are easily bent and twisted
Elastic fibers allow stretching and then they come back to their original length
Aging, hormone changes, and UV rays permanently reduce the amount of elastic in the dermis. This causes wrinkles and sagging skin
Papillary Layer: consists of a highly vascularized areolar tissue. It also contains capillaries, lymphatic vessels, and sensory neurons that supply
the surface of the skin
Reticular Layer: made of dense irregular connective tissues that contain both collagen and elastic fibers
collagen fibers extend superficially beyond the reticular layer and blend into the papillary layer
Collagen fibers also extend into the hypodermis
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