The Integumentary System: An Overview
Functions: Protective covering Helps regulate body temperature Retards water loss from deeper tissues Houses sensory receptors Synthesizes biochemicals Excretes small quantities of waste
Consists of Cutaneous membrane Epidermis Dermis Accessory structures- hair, sweat glands, sebaceous glands etc. Subcutaneous layer (hypodermis)
Components Figure 5.1
The Epidermis
Epidermis The epidermis is composed of layers of keratinocytes- cells that produce keratin Figure 5.2
The Epidermis Composed of stratified squamous epithelium Lacks blood vessels Older cells are pushed to the top and harden in a process called keratinization.
Layers of the epidermis: From deep. Stratum basale/ germinativum Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum to superficial
Epidermis Cell Layers Germinative Basal cells (stem) are reproducing Spinosum- spiny layer Granulosum- grainy layer Stops dividing, start producing keratin Lucidum The clear layer found only in thick skin Corneum Exposed to surface and shed every 2 wks.
Skin color depends on Blood supply Interrupted blood supply leads to cyanosis- blue! Carotene Orange-yellow pigment found in orange vegetables Melanin Yellow-brown pigment Protects us from UV radiation Produced by melanocytes
Melanocytes Figure 5.5a, b
Epidermal cells Synthesize vitamin D3 (cholecalciferol) when exposed to UV Aids in absorption of calcium and phosphorusneeded for bone strength
The Dermis
Dermal Organization Located between epidermis and subcutaneous layer Anchors accessory structures- hair follicles, sweat glands, blood vessels etc. Two components: Outer papillary layer Deep reticular layer
Layers of the Dermis Papillary layer Areolar tissue Contains blood vessels, lymphatics, sensory nerves of epidermis Reticular layer Dense irregular connetive tissue Contains network of collagen and elastic fibers to resist tension
Stretch Marks Caused by excessive stretching of the dermis Patterns of collagen and elastic fibers form lines of cleavage
Hypodermis Elastic areolar tissue and adipose tissue Stabilizes skins position against underlying organs and tissues Shock absorber and insulator Few capillaries and no vital organs Subcutaneous injection is useful to administer drugs
Hairs Composed of keratinized dead cells that are produced in hair follicles Project deep into the dermis and often into the hypodermis
Structures Hair papilla Connective tissue containing capillaries and nerves Root Anchors hair into skin Shaft Part we see on the surface Consists of three layers Cuticle- overlapping shingle layer Cortex- underlying layer- pigments Medulla- core of hair
Structures Contd. Sebaceous Glands Discharge oily substance into hair follicles Inhibits growth of bacteria Arrector pili muscle Pulls on follicle, forcing the hair to stand up Cold or emotional states- goosebumps
Hair Color Produced by melanocytes at the hair papilla
Function of Hair Head Protection from UV light Cushion a light blow to head Insulation Nostrils, ears, and eyes Prevent entry of particles Sensory Sensory nerve fiber at base of every hair
Exocrine Glands- Reach Outside Sebaceous glands (Oil glands) Associated with hair Secrete sebum, which lubricates and inhibits bacteria growth Acne- condition when they are clogged Sweat glands (Watery Glands) 2 kinds 1- hormonal- armpits, groin, nipples 2- All over body
Nails Keratinized cells that protects the tips of fingers and toes
Structures Nail Body Covers an area of the epidermis called the nail bed Nail Root Where nail production occurs Not visible on surface Cuticle Portion of stratum corneum
Structure Contd. Lunula Pale crescent area near the root were blood vessels are absent