Chapter 5: The Integument System Flashcards
What is the integument system and what is it composed of?
Covers entire outer surface of body
Includes skin, hair, nails, various glands, & sensory receptors
Functions of Skin - 5
Is the largest organ of the body by surface area and weight
Has several functions:
1. Protects the body against:
- dehydration (keratin layer)
- impact & friction injuries
- mold & bacterial invasion
- UV light damage (melanin
production)
2. Acts as a receptor organ for sensory input 3. Regulates body temp (capillary network & sweat glands) 4. Secretes some wastes urea, salts, & water 5. Synthesizes vitamin D from cholesterol molecules under action of sunlight
Skin Layers
Composed of 2 layers:
• Outer, thinner layer called the epidermis
> Blood vessles directly in the dermis but not in the epidermis
> No direct blood supply to the epidermis
• Inner, thicker layer called the dermis
•Subcutaneous layer
> Also called hypodermis
> Located underneath the dermis
Epidermis
- Characteristics
- List four major types of cell
- List five cell layers
Characteristics: • Composed of keratinized stratified squamous epithelium • Contains four major types of cells 1) Keratinocytes 2) Melanocytes 3) Langerhans cells 4) Merkel cells • Contains five cell layers 1) Stratum basale 2) Stratum spinosum 3) Stratum granulosum 4) Stratum lucidum 5) Stratum corneum
Keratinized = thick layer of dead cells on the top Stratified = more than one layer Squamous = flat type of cell
Keratinocytes - Epidermal cell types
- (90%)
- Produce keratin (fibrous protein)
- Protect skin & underlying tissues from heat, microbes, & chemicals
- Surface cells die & only contain keratin
Melanocytes - Epidermal cell types
- (8%)
- Spider-shaped epithelial cells
- Secrete & transfer the pigment melanin to keratinocytes
- Found near basal surface & their cell projections extend between keratinocytes
- Melanocytes – shield the skin cells from UV light. Increase in sun make more of these which gives you a tan. The tan fades as the cells regenerate/flake off
Langerhans cells - Epidermal cell types
- (or intraepidermal cells)
- Arise from red bone marrow & migrate to epidermis
- Involved in immune responses
Merkel cells - Epidermal cell types
- (or Tactile cells)
- Least numerous
- Contact sensory neurons & function in touch sensations
- Located deep in epidermis
Stratum basale - Epidermal cell layers
- (or stratum germinativum)
- Deepest layer, attached to dermis by wavy border
- Single row of cuboidal/columnar keratinocytes
- Cells divide by mitosis
- Contains melanocytes & Merkel cells
Stratum spinosum - Epidermal cell layers
- 8 to 10 layers of irregular-shaped keratinocytes
- Cells contain many keratin filaments
- Contains Langerhans cells & projections of melanocytes
- The cells are attached to one another very strongly
Stratum granulosum - Epidermal cell layers
- 3 to 5 layers of flattened keratinocytes; nucleus & organelles disintegrate
- Cells contain keratohyalin (protein) & lamellated granules
- Lamellated granules release a lipid-rich, water repellent secretion
- Transition layer between living cells below & dead cells above
- Starting to die bc epidermis is avascular so it’s getting farther from blood supply
Stratum lucidum - Epidermal cell layers
- Present only in thick skin (fingertips, palms, & soles)
- Consists of 3-5 layers of clear, flat, dead keratinocytes
- Missing in thin skin like eyelinds
Stratum corneum - Epidermal cell layers
- 25 to 30 layers of flat, dead keratinocytes containing keratin
- Lamellar secretion (lipids) between the cells waterproofs this layer
Dermis
-2 regoins/layers
• Connective tissue with fibroblasts, adipocytes, macrophages, mast cells, & embedded with fibers
• Contains blood vessels, hair follicles, glands, & nerves
•Layers/Regions
1) Papillary region
2) Reticular region
Papillary region - Dermis Layer
- Upper 1/5 of dermis
- Has dermal papillae at junction with epidermis
- These papillae contain capillaries, free nerve endings and Meissner’s corpuscles
- fingertips are caused by the wavy boarders and they’re for giving texture to help with grip
Meissner’s corpuscles
nerves that sence light touch, found in dermis
Reticular region - Dermis Layer
- Lower portion of dermis
- Collagen fibers give skin strength & resiliency, & bind water to keep skin hydrated
- Elastic fibers provide stretch-recoil properties
- Stretch marks can appear if the skin is stretched too much
- Contains Pacinian corpuscles
Pacinian corpuscles
- further down in skin, specialized for deep pressure touch sensations
- found in dermis
Skin Colour
- Many pigments contribute to skin colour but the most important one is melanin
- Melanocytes produce melanin
- The number of melanocytes are about the same in all people but the amount of melanin produced differs
- Exposure to UV light increases melanin production
- Melanin absorbs UV radiation
- Neutralizes free radicals (electrically chanrged atoms that have unpaired electron in outer shell)
- A mole is a benign localized overgrowth of melanocytes
Hair & Hair Follicles
Hair (pili) is present on most skin surfaces
Hair shaft protrudes from the skin while the root is embedded in the skin
Eyebrow, eyelash, & nose hairs protect structures from foreign objects
Hairs provide touch sensations in certain areas
Hair Shaft & Root Structure
• Consists of 3 concentric rings of dead keratinized cells:
> medulla → core of large cells
> cortex → several layers of flattened cells
> cuticle → single layer of cells that overlap onevanother from below
• Hair pigment is made by melanocytes at the base of the
• hair follicle & is transferred to cortex & medulla cells
Hair Follicle Structure
• The follicle is a tube-like in-pocketing of epidermis that extends into the dermis
• Base of follicle is expanded as hair bulb
• Hair papilla protrudes into hair bulb:
> contains capillaries
> contains layer of cells (matrix)
> matrix cells divide mitotically as hair grows
> cells move upwards & become dead keratinized cells
Hair Growth - 3 stages
Each hair follicle goes thru a growth cycle which includes:
i) Growth stage → cells of matrix divide
ii) Regression stage → matrix cells stop
dividing
iii) Resting stage → nothing happens
After resting stage, old hair root falls out of follicle and a new hair begins to grow
Arrector pili muscle
- This is smooth muscle which attaches to the hair follicle & raises the hair, creates a bump in skin and creates goosebumps
- Sensory nerve endings around hair bulb
Sweat (sudoriferous) glands types
1) Merocrine (eccrine) sweat glands
2) Apocrine sweat glands
Merocrine (eccrine) sweat glands
- simple coiled tubular glands emptying into a pore (eg. palms, soles, forehead)
- functional from birth
- sweat is composed of water, ions, urea, uric acid, ammonia, amino acids, glucose, & lactic acid (pH 4-6)
- helps to regulate body temperature & has a small role in eliminating wastes
Apocrine sweat glands
- Are larger & empty into hair follicles
- Found in skin of axilla & groin
- Begin to function at puberty
- Secretion also contains lipids & proteins
Ceruminous glands are modified apocrine glands found in skin lining the external ear canal
> Secrete sticky earwax (cerumen)
> Helps prevent foreign substances from entering ear
Ceruminous glands
are modified apocrine glands found in skin lining the external ear canal
> Secrete sticky earwax (cerumen)
> Helps prevent foreign substances from entering ear
Sebaceous glands
- Simple branched alveolar glands connected to hair follicles
- Produce & secrete an oily substance called sebum
- Sebum softens & lubricates hair & skin
- Also prevents dehydration of hair and skin
- Also inhibits growth of certain bacteria on skin
Nails
- Are hard, keratinized epidermal cells
- Deeper layers of epidermis form nail bed under nail
- Proximal portion of nail bed is nail matrix, responsible for nail growth
- Matrix layer actively divides and pushes out of the nail bed, grows ~1mm a week
- Nails function to protect distal phalanx & aid in grasping
Nail structures -3
- Free edge extends over digit
- Nail body is visible portion
- Nail root embedded in a fold of skin
Body Temperature Regulation
- Body temperature is 37 ± 0.5 oC
- At normal body temp., conditions are optimal for enzymatic activity
- Body core (organs in skull, thoracic & abdominal cavities) temp. is relatively constant
- Shell (skin) temp. can fluctuate
Vitamin D Synthesis
- Vitamin D is actually a group of closely related compounds
- Synthesis of vitamin D begins in the skin with the formation of a precursor molecule, cholecalciferol
- Required to increase calcium absorption from food
Vitamin D Synthesis
1) Sunlight (uv radation) – >
2) Cholesterol in dermal blood converted to vitamin D precursor – >
3) precursor molecule transported on blood to liver and kidney – >
4) coverted to calcitrol (active vitamin D) – >
5) Vitamine D stimulates absorption of cacium ions from ingested foods in the intestine – >
6) increases blood Ca2+ levels
