Bone Notes

Review of Hair, Sweat, Nails, and Skin

Regions of Hair and Hair Color

• Hair has three main regions: the shaft, root, and bulb.

• Hair color is determined by the type and amount of melanin produced by melanocytes in the hair follicle.

Parts of a Hair Follicle

• Components include the dermal papilla, hair matrix, and surrounding connective tissue.

• The dermal papilla contains blood vessels and sensory nerves that nourish and stimulate hair growth.

• The hair matrix consists of rapidly dividing cells that produce hair.

Relationship Between Arrector Pili Muscles and Hair Follicles

• Arrector pili muscles are small muscles attached to hair follicles, located in the dermis layer of the skin.

• They contract in response to cold or fear, causing hair to stand up (goosebumps).

Types of Glands

• Sebaceous Glands: Secretes sebum to lubricate skin and hair, prevents water loss; located in the dermis layer and associated with hair follicles.

• Eccrine Sweat Glands: Produce a watery sweat for temperature regulation; found primarily on palms, soles, and forehead.

• Apocrine Sweat Glands: Located in axillary and genital areas, release a thicker sweat rich in fatty acids; activated during emotional stress or hormonal changes.

• Modified Apocrine Glands: Such as mammary glands, produce milk; located in the breast tissue.

Structure of Nails

• Nails consist of a hard keratinized plate, nail bed, and cuticle (eponychium).

• Serve protective functions and provide support for the fingertips, located at the tips of fingers and toes.

Heat Regulation Mechanisms

• Heat production involves metabolic processes; heat retention maintains body temperature, while heat loss occurs through radiation, conduction, and sweating.

• Extreme heat can cause heat exhaustion or heat stroke, while extreme cold can result in hypothermia.

Skin Cancers

• Basal Cell Carcinoma: Most common, arises from basal layer cells, slow-growing; typically found on sun-exposed areas like the face and neck.

• Squamous Cell Carcinoma: Second most common, can metastasize if untreated; often appears on sun-exposed skin as well.

• Melanoma: Most dangerous, arises from melanocytes, rapidly metastasizes; can occur anywhere on the body but often starts in existing moles.

Burns

• Serious burns can lead to fluid loss, infection, and hypothermia, making them life-threatening.

• Burn Degree Classification:

  • First-Degree: Affect only the epidermis, causing redness and pain; typically heal without scarring.

  • Second-Degree: Affect the epidermis and part of the dermis, causing blisters and swelling; can lead to scarring.

  • Third-Degree: Affect all layers of skin and may extend to underlying tissues, often painless due to nerve damage; require medical intervention.

Functions of Bones

• Support: Provides structural support for the body and its organs; essential for maintaining upright posture.

• Protection: Protects vital organs like the brain and lungs; forms protective encasements for these organs.

• Movement: Serves as levers for muscle action, facilitating movement; bones attach to muscles and joints to enable mobility.

• Mineral Storage: Stores minerals like calcium and phosphorus; serves as a reservoir for growth factors that aid in bone healing.

• Blood Cell Formation (Hematopoiesis): Occurs in red bone marrow, primarily in the flat bones like the pelvis and ribs.

• Triglyceride Storage: Yellow bone marrow stores fat for energy, mainly found in the long bones of the body.

Bone Structures

• Bone as an Organ: Composed of various tissue types: bone connective tissue, nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells.

• Compact and Spongy Bone:

  • Compact Bone: Dense outer layer appearing smooth and solid; forms the outer layer of all bones and provides strength.

  • Spongy Bone: Contains trabeculae, filled with red and yellow bone marrow; located mainly at the ends of long bones and inside flat bones.

Structure of Long Bones

• Diaphysis: Long tubular shaft made of compact bone surrounding medullary cavity with yellow bone marrow; provides leverage for movement.

• Epiphyses: Ends of long bones, containing spongy bone filled with red marrow; important for joint formation.

• Metaphysis: Region between diaphysis and epiphysis where the epiphyseal line is found, indicating past growth; involved in bone growth during development.

Periosteum and Endosteum

• Periosteum:

  • Covers the outer surface of bone; contains nerve fibers and blood vessels, anchoring tendons and ligaments.

  • Has an outer fibrous layer made of dense irregular connective tissue.

• Endosteum:

  • Lines the internal surfaces of bone, covering the trabeculae of spongy bone and the canals of compact bone.

  • Contains osteogenic cells that can differentiate into bone cells to aid in repair and growth.

Bone Cells

• Osteogenic Cells:

  • Stem cells found in periosteum and endosteum; differentiate into osteoblasts or bone-lining cells.

• Osteoblasts:

  • Bone-forming cells that secrete osteoid (matrix composed of collagen and calcium-binding proteins), which will ultimately become mineralized bone.

• Osteocytes:

  • Mature bone cells located in lacunae, acting as stress sensors maintaining bone matrix; communicate with other bone cells to regulate bone homeostasis.

• Osteoclasts:

  • Large, multinucleate cells that resorb bone, derived from the same stem cells as macrophages; important for bone remodeling.

• Bone-Lining Cells:

  • Flat cells on bone surfaces assisting osteocytes, distinguishing between periosteal (external) and endosteal (internal) cells.

Post-Lecture Objectives

• List and describe functions of bones, gross anatomy of long bones, and the role of different bone cell types in maintenance and remodeling of bone.