Chapter 5 Integumentary System Objectives

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Stratum basale

Deepest layer. Contains basal cells (stem cells that divide to replace shed superficial keratinocytes) and tactile (Merkel) cells in hairless skin which combine with nerve endings to form a touch-sensitive tactile disc. It forms epidermal ridges that lock with dermal papillae for a strong attachment.

Stratum spinosum

Consists of 8–10 layers of keratinocytes bound by desmosomes where some cells are still dividing. Contains dendritic cells to stimulate immune defenses against microorganisms and skin cancers.

Stratum granulosum

Consists of 3–5 layers of flattened keratinocytes that have stopped dividing and are actively making the protein keratin. Cells also produce keratohyalin, which dehydrates the cell and aggregates keratin fibers, causing the nucleus/organelles to disintegrate and the cells to die.

Stratum lucidum

A clear layer found only in thick skin (palms and soles) where cells are flattened, densely packed, filled with keratin, and completely lacking organelles.

Stratum corneum

The dry, exposed surface layer consisting of 15–30 layers of dead, interconnected, keratinized cells that resist microbial growth. It takes 7–10 days for a cell to move from the basale to the corneum, and dead cells stay here for about 2 weeks before shedding.

What is epidermal growth factor and what does it promote?

A peptide growth factor. Promotes the division of basal cells in the stratum basale and stratum spinosum. Accelerates the production of keratin. Stimulates epidermal development and repair after injury. Stimulates the synthesis and secretion of products by epithelial glands

What are the 2 layers of the dermis and what does each of them contain?

Papillary layer (Superficial): Consists of areolar tissue. It contains capillaries, lymphatic vessels, and sensory nerve fibers & Reticular layer (Deeper): Consists of an interwoven meshwork of dense irregular connective tissue. It contains collagen fibers (provide strength, resist bending/twisting) and elastic fibers (allow stretching and recoil)

What are the 2 layers of the dermis?

Papillary Layer and Reticular Layer

What are tension lines and their significance?

The pattern of collagen and elastic fibers arranged in parallel bundles within the dermis; A surgical cut made parallel to tension lines will heal with little scarring, whereas a cut made at right angles will pull open and result in greater scarring

What are the 2 networks of dermal blood supply?

Cutaneous plexus and Subpapillary plexus

Where does the cutaneous plexus supply blood to?

Deeper arterial network lying along the border of the subcutaneous layer. It supplies blood to hair follicles, sweat glands, and other dermal structures

Where does the subpapillary plexus supply blood to?

Superficial arterial network that provides blood to capillary loops tracing the contours of the epidermal-dermal boundary

What are the 2 sensory receptors in the dermis layer?

Meissner corpuscles and Pacinian corpscles

Meissner (tactile) corpuscles

located in the papillary layer; sensitive to light touch

Pacinian (lamellar) corpuscles

located in the reticular layer; sensitive to deep pressure and vibration.

What is the one sensory receptor in the epidermis layer?

Tactile discs

What are tactile discs?

formed by tactile (Merkel) cells in the stratum basale and their underlying sensory nerve endings; sensitive to touch.

What makes up the subcutaneous layer?

Highly elastic layer made mostly of adipose tissue (accounting for 80% of total body fat). Only its most superficial region contains large arteries and veins.

Where is the subcutaneous layer located?

Located deep to the dermis layer (not technically part of the integument, but stabilizes skin position relative to underlying tissues)

What is melanin and how is it produced?

A pigment produced by melanocytes located in the stratum basale. It is packaged into intracellular vesicles called melanosomes and transferred to neighboring keratinocytes.

What is its significance of melanin in our skin color?

In pale skin, melanosome transfer occurs only in the deep basale/spinosum layers, and superficial layers lose color. In dark skin, melanosomes are larger, more numerous, and transfer persists up into the stratum granulosum, making color darker and more persistent.

How does melanin protect us from UV radiation?

Inside keratinocytes, melanosomes concentrate in a "shade" region around the nucleus, acting like a sunshade to block UV radiation from mutating the cell's DNA.

How is vitamin D produced?

Sunlight (UV) hits the stratum spinosum and stratum basale, converting a cholesterol-related steroid into cholecalciferol

What is vitamin D used to produce?

Converts cholecalciferol into an intermediary product, Uses that intermediary product to synthesize the hormone calcitriol

What organs and steps are involved in the production of Vitamin D? Why is this important?

Skin (absorbs UV and converts into cholecalciferol), liver (converts cholecalciferol into an intermediary product), and kidneys (uses that intermediary product to synthesize the hormone calcitriol).

What pigment can give us orange skin?

Carotene (accumulates in the stratum corneum, deep dermis, and subcutaneous fatty tissues)

What pigment can give us red/pink skin?

Hemoglobin from dermal circulation (capillaries dilate and red tones show through, especially in fair skin).

Hair follicle

An epidermal organ extending deep into the dermis/hypodermis that produces a nonliving hair

Root hair plexus

A network of sensory nerves surrounding the base of each follicle that allows you to detect hair movement.

Arrector pili muscle

A bundle of smooth muscle cells that contracts when stimulated, pulling on the follicle to make the hair stand straight up (goosebumps)

Hair root

Anchors the hair into the skin

Hair shaft

The upper portion extending out to the exposed surface

Hair bulb

the massive base of the hair that surrounds the papilla (a core of connective tissue loaded with capillaries and nerves)

Papilla

The hair matrix right above it contains basal cells that divide to build the hair.

Sebaceous Glands (Oil glands)

Produce sebum into hair follicles; inhibits bacterial growth, lubricates/protects the hair shaft, and conditions the surrounding skin

Sudoriferous Glands (Sweat glands)

Produces sweat (99% water + NaCl, ph 4-6.8); thermoregulatioin (cools skin surface), excretes water/electrolytes, minimizes microbial growth via the antibiotic peptide dermicidin

What are the 4 phases of injury repair for the skin?

Inflammation, migration, proliferation, and scarring

Inflammation Phase

Bleeding occurs instantly; mast cells trigger an immediate inflammatory response.

Migration Phase

(After several hours) A scab forms. Stratum basale cells move along the wound edges. Phagocytic cells (macrophages) clear debris. Clotting partially isolates the region, and granulation tissue forms

Proliferation Phase

(About 1 week later) The scab is undermined as epidermal cells migrate over a meshwork of collagen fibers produced by rapid fibroblast proliferation. Phagocytic activity finishes, and the fibrin clot dissolves.

Scarring Phase

(After several weeks) The scab sheds and the epidermis is fully replaced. Fibroblasts in the dermis keep creating scar tissue to elevate the indentation. Note: Excessive scar production can form a thick, raised keloid.

Dermatitis

Inflammation of the papillary dermis caused by infection, irritation, chemicals, or radiation (e.g., psoriasis or seborrheic dermatitis)

Albinism

Normal distribution of melanocytes, but a genetic deficiency prevents any melanin production

Vitiligo

An autoimmune condition (1% of population) where antibodies attack and completely destroy melanocytes, leaving distinct white patches

Rickets

Abnormal bone development and bending in children due to severe lack of Vitamin D3

Basal Cell Carcinoma

Most common skin cancer; originates in the stratum basale and rarely metastasizes.

Melanoma

Extremely dangerous; cancerous melanocytes grow rapidly and easily metastasize via the lymphatic system and blood vessels.

Cyanosis

Skin turns blue/bluish-purple (best seen in lips/nails) because of a severe drop in blood oxygen levels, making hemoglobin look dark red.

Jaundice

Skin and eyes turn yellow because the liver cannot properly secrete bile, causing yellowish pigments to build up in body fluids

MSH (Melanocyte-Stimulating Hormone)

Secreted in massive amounts by certain pituitary gland tumors, overstimulating melanocytes to create a deep bronze skin color.

Addison’s Disease

The pituitary gland oversecretes adrenocorticotropic hormone (ACTH), which mimics MSH and causes a similar dramatic darkening/bronzing of the skin.

1st Degree Burn

Only the surface of the epidermis is damaged (e.g., typical sunburn). Causes redness (erythema) and pain

2nd Degree Burn

Entire epidermis and part of the dermis are damaged. Causes blistering, intense pain, and swelling (takes 1–2 weeks to heal)

3rd Degree Burn

Destroys epidermis, dermis, and extends into the subcutaneous layer. Swells up, but is less painful because sensory nerves are completely destroyed. Cannot heal on its own.

What is a skin graft and what degree of burn needs them?

Transplanting sections of healthy, intact skin (often meshed to cover wide zones) over a damaged area; Mandatory for 3rd-degree burns because the tissue cannot regenerate on its own

Without our skin, what 3 things can we lose that can become life-threatening?

Fluid and electrolyte balance, Thermoregulation (body temperature control), Protection from infection (leading to sepsis, which is the leading cause of death in burn victims)