Integumentary System: Skin, Hair, and Nails

• The integumentary system consists of the skin, hair, nails, and associated glands
• It provides a protective barrier against the external environment

Skin Layers

• The epidermis is the outermost layer, composed of keratinized stratified squamous epithelium
• Keratinocytes produce keratin, a fibrous protein that provides protection
• Melanocytes produce melanin, which protects against UV radiation
• The dermis is the layer beneath the epidermis, containing connective tissue, blood vessels, nerve endings, and accessory structures such as hair follicles and glands
• The hypodermis (subcutaneous layer) is located beneath the dermis and contains adipose tissue for insulation and energy storage

Functions of the Integumentary System

• Protection against mechanical damage, UV radiation, and pathogens
• Thermoregulation through sweat glands and blood vessel dilation/constriction
• Sensation via sensory receptors for touch, pressure, temperature, and pain
• Vitamin D synthesis, which is essential for calcium absorption
• Excretion of small amounts of waste products through sweat

Skin Appendages

• Hair consists of a shaft (visible part) and a root (embedded in the dermis)
• Hair follicles produce hair
• Arrector pili muscles cause hair to stand on end (goosebumps) in response to cold or fear
• Nails are made of keratin and protect the tips of fingers and toes
• Sweat glands (sudoriferous glands) produce sweat for cooling
• Sebaceous glands secrete sebum, an oily substance that lubricates the skin and hair

Bone Tissue

• Bone tissue is a type of connective tissue consisting of cells, fibers, and ground substance
• Osteocytes are mature bone cells that maintain the bone matrix
• Osteoblasts are bone-forming cells responsible for bone deposition
• Osteoclasts are bone-resorbing cells that break down bone tissue
• The bone matrix consists of collagen fibers and mineral salts (calcium phosphate) for strength and rigidity

Types of Bone Tissue

• Compact (cortical) bone is dense and forms the outer layer of bones
• Spongy (cancellous) bone contains trabeculae (interconnected rods) and is found in the interior of bones
• Spongy bones reduce the weight of bones and contain red bone marrow for blood cell formation

Bone Structure

• Long bones (e.g., femur) have a diaphysis (shaft) and epiphyses (ends)
• The medullary cavity in the diaphysis contains yellow bone marrow (fat storage)
• The epiphyseal plate (growth plate) is a region of cartilage in growing bones that allows for bone lengthening
• The periosteum is a membrane that covers the outer surface of bones (except at joints)
• The endosteum lines the inner surfaces of bones, including the medullary cavity

Functions of Bone Tissue

• Support and protection for organs and soft tissues
• Movement by providing attachment points for muscles
• Mineral storage (calcium and phosphate)
• Blood cell formation (hematopoiesis) in red bone marrow
• Triglyceride storage in yellow bone marrow

Skeletal System

• The skeletal system consists of bones, cartilage, ligaments, and tendons
• It provides the framework for the body and protects internal organs

Bone Classification

• Long bones: longer than they are wide (e.g., femur, humerus)
• Short bones: cube-shaped (e.g., carpals, tarsals)
• Flat bones: thin and flattened (e.g., skull bones, ribs)
• Irregular bones: complex shapes (e.g., vertebrae, facial bones)
• Sesamoid bones: embedded in tendons (e.g., patella)

Axial Skeleton

• The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and rib cage
• The skull consists of cranial bones (protect the brain) and facial bones (form the face)
• The vertebral column (spine) consists of vertebrae separated by intervertebral discs
• The rib cage includes the ribs and sternum, protecting the thoracic organs

Appendicular Skeleton

• The appendicular skeleton includes the bones of the limbs and their respective girdles (pectoral and pelvic)
• The pectoral girdle (shoulder girdle) connects the upper limbs to the axial skeleton
• The upper limbs include the humerus, radius, ulna, carpals, metacarpals, and phalanges
• The pelvic girdle (hip girdle) connects the lower limbs to the axial skeleton
• The lower limbs include the femur, tibia, fibula, tarsals, metatarsals, and phalanges

Joints (Articulations)

• Joints are points where bones meet
• Fibrous joints are immovable or slightly movable (e.g., sutures in the skull)
• Cartilaginous joints are slightly movable (e.g., intervertebral discs)
• Synovial joints are freely movable and have a joint cavity filled with synovial fluid
• Synovial joints include ball-and-socket joints (e.g., hip), hinge joints (e.g., elbow), and pivot joints (e.g., radioulnar joint)

Bone Development

• Ossification is the process of bone formation
• Intramembranous ossification occurs when bone develops from a fibrous membrane (e.g., skull bones)
• Endochondral ossification occurs when bone develops from hyaline cartilage (most bones)
• Bone remodeling involves bone deposition and resorption and occurs throughout life

Skeletal System Functions

• Support and framework for the body
• Protection of internal organs
• Movement by providing attachment points for muscles
• Mineral storage (calcium and phosphate)
• Blood cell formation (hematopoiesis) in red bone marrow
• Energy storage in yellow bone marrow

Common Bone Markings

• Condyle: Rounded articular projection
• Epicondyle: Raised area on or above a condyle
• Trochanter: Very large, blunt, irregularly shaped process (only on the femur)
• Tuberosity: Large rounded projection; may be roughened
• Process: Any bony prominence
• Foramen: Round or oval opening through a bone
• Fossa: Shallow, basinlike depression in a bone, often serving as an articular surface
• Sinus: Cavity within a bone, filled with air and lined with mucous membrane
• Head: Bony expansion carried on a narrow neck

The integumentary system includes the skin, hair, and nails, providing a protective barrier. The skin consists of the epidermis, dermis, and hypodermis. It protects against damage and pathogens, regulates temperature, provides sensation, and synthesizes Vitamin D.