Test 3 Bald man

Two main subdivisions of the human skeleton

Axial skeleton:

• What it is: The center of the body.

• Parts: Head, spine, and chest (skull, backbone, ribs).

Appendicular skeleton:

• What it is: The limbs connected to the body.

• Parts: Arms, legs, shoulders, and hips.

Four primary tissues and structures composing the skeletal system

Bones, joints, cartilages, and ligaments that work collectively to establish an internal framework.

Serves as an internal scaffolding that reinforces body shape and cradles vulnerable soft organs against gravitational forces.

Skeletal function: Support

Encloses delicate vital structures within rigid boundaries, such as the cranial cavity shielding the brain and the thoracic rib cage guarding the heart and lungs.

Skeletal function: Protection

Acts as rigid levers that skeletal muscles pull across joints to generate bodily articulation and locomotion.

Skeletal function: Movement

Reserves critical ionic minerals, predominantly calcium and phosphorus within the matrix, and sequesters energy-dense lipids inside yellow bone marrow.

Skeletal function: Storage

Hematopoiesis

The process of making new blood cells in the red bone marrow..

Compact bone

Dense, homogeneous osseous tissue providing high compressive strength and forming the smooth, hard outer shell of bones.

Spongy (cancellous) bone

Lightweight osseous tissue composed of a lattice of needle-like trabeculae and open spaces typically accommodating marrow.

Long bones

Bones distinctly greater in length than width that feature a defined shaft and two distinct terminal ends, consisting largely of compact bone (e.g., femur, humerus).

Short bones

Roughly cube-shaped bones comprised mainly of spongy bone surrounded by a thin perimeter of compact bone (e.g., carpals and tarsals).

Flat bones

Thin, flattened, and gently curved bones composed of an internal layer of spongy bone sandwiched between two parallel layers of compact bone (e.g., skull bones, ribs, sternum).

Irregular bones

Bones exhibiting complex, asymmetrical geometries that do not conform to long, short, or flat classifications (e.g., vertebrae and pelvic bones).

Diaphysis

The elongated tubular shaft that constitutes the primary longitudinal axis of a long bone, formed of dense compact bone encircling a central marrow cavity.

Epiphyses

The expanded proximal and distal extremities of a long bone, containing an interior mass of spongy bone encapsulated by a compact bone shell.

Periosteum

A double-layered fibrous connective tissue membrane that envelops and nourishes the outer surface of the diaphysis, anchored by collagen fibers.

Articular cartilage

The smooth cartilage cushion at the ends of bones that prevents grinding and absorbs shock during movement

Yellow bone marrow

Adipose-rich tissue residing in the central medullary cavities of adult long bones that functions primarily as an energy store.

Red bone marrow

Vascularized hematopoietic tissue found throughout the skeleton in early childhood, but largely restricted to the spongy bone of axial and proximal limb bones in adults.

Bone projections (processes)

Structural elevations or ridges expanding outward from a bone surface that serve as sites for muscle, tendon, and ligament attachment.

Bone depressions and openings

Indentations, grooves, or channels on bone surfaces that accommodate articulating bones or permit the passage of neurovascular bundles.

Osteocytes

Mature, non-dividing bone cells responsible for monitoring, maintaining, and regulating the extracellular mineralized matrix.

Lacunae

Tiny cavities within the concentric lamellar matrix that house individual osteocytes.

Lamellae

Concentric, calcified collagen rings that surround the central canal in compact bone.

Central (Haversian) canal

A longitudinal core channel coursing through each osteon that conducts blood vessels, lymphatic vessels, and nerves.

Osteon (Haversian system)

The fundamental cylindrical structural unit of compact bone, consisting of concentric lamellae circling a central neurovascular canal.

Canaliculi

Microscopic fluid-filled canals that radiate across lamellae, connecting adjacent lacunae to facilitate transport of nutrients and metabolic waste.

Perforating (Volkmann's) canals

Transverse passageways aligned perpendicular to central canals that route blood vessels from the periosteum deeper into inner bone structures.

Ossification (osteogenesis)

The biological development and mineralization of bone matrix, converting hyaline cartilage models or fibrous membranes into hard osseous tissue.

Epiphyseal plates

Transverse bands of hyaline cartilage located between the diaphysis and epiphyses that facilitate lengthwise longitudinal growth during childhood and adolescence.

Appositional growth

The process by which osteoblasts beneath the periosteum deposit new osseous layers along the outer circumference, expanding bone diameter.

Closed (simple) fracture

A complete or partial break in bone continuity where the fractured fragments do not rupture through the overlying skin.

Open (compound) fracture

A severe bone break in which sharp fragments penetrate the skin, producing an external wound with an increased risk of infection.

Hematoma formation

The initial phase of fracture healing where ruptured local blood vessels form a clotted mass at the injury site, producing swelling and local cellular death.

Fibrocartilage callus formation

The second phase of fracture repair where fibroblasts and chondroblasts reconstruct a temporary cartilage and collagen splint spanning the break.

Bony callus formation

The third stage of fracture healing where migrating osteoblasts and osteoclasts gradually replace the fibrocartilaginous network with spongy bone.

Bone remodeling (fracture repair)

The final reparative phase where mechanical stresses direct osteoblasts and osteoclasts to reshape the bony callus into the original compact and spongy bone configuration.

osteoporosis

a chronic medical condition that silently weakens your bones, making them thin, porous, and highly susceptible to fractures.

Axial skeleton

The division of the skeleton that forms the central longitudinal axis of the human body, encompassing the skull, vertebral column, and bony thorax.

Appendicular skeleton

The division of the skeleton comprising the upper and lower limbs, as well as the shoulder (pectoral) and hip (pelvic) girdles that anchor them to the body trunk.

Primary tissues and structures composing the skeletal system

Bones, cartilage, joints, and ligaments, which operate cooperatively to construct an adaptable internal framework.

Skeletal function: Support

Provides a rigid structural scaffolding that maintains body posture and cradles delicate internal visceral organs against gravity.

Skeletal function: Protection

Encloses vulnerable organs within bony walls, exemplified by the skull shielding the brain and the thoracic rib cage guarding the heart and lungs.

Skeletal function: Movement

Provides rigid levers that skeletal muscles pull across articulations to produce bodily locomotion and mechanical tasks.

Skeletal function: Storage

Maintains homeostatic reserves of ionic minerals, notably calcium and phosphorus, and sequesters energy-dense triglycerides within yellow marrow.

Hematopoiesis

The physiological formation and development of red blood cells, white blood cells, and platelets within red bone marrow tissue.

Compact bone

Dense, hard, and homogeneous osseous tissue providing high compressive resistance, forming the smooth outer layer of bones.

Spongy (cancellous) bone

Lightweight osseous tissue composed of a porous network of needle-like trabeculae and open spaces that accommodate bone marrow.

Long bones

Bones that are noticeably longer than they are wide, characterized by an elongated shaft with two distinct ends, consisting mostly of compact bone (e.g., femur, humerus, tibia).

Short bones

Roughly cube-shaped bones comprised primarily of spongy bone surrounded by a thin protective shell of compact bone (e.g., carpals and tarsals).

Flat bones

Thin, flattened, and gently curved bones structured with an internal layer of spongy bone sandwiched between two parallel layers of compact bone (e.g., sternum, ribs, and cranial bones).

Irregular bones

Oddly shaped bones designed for special protective jobs or complex fittings that don't fit any standard shape category.(e.g., vertebrae and hip bones).

Diaphysis

It's the central shaft of a long bone.

Epiphyses

The expanded proximal and distal terminal ends of a long bone, containing internal spongy bone wrapped in an exterior shell of compact bone.

Medullary cavity

The hollow longitudinal chamber inside the shaft of a long bone that houses marrow tissue.

Periosteum

A double-layered fibrous connective tissue membrane that envelopes and vascularizes the diaphysis, participating in bone growth, repair, and muscular attachment.

Endosteum

A delicate connective tissue membrane lining internal bone cavities, such as trabecular surfaces and the medullary cavity.

Nutrient artery

A principal blood vessel that enters the diaphysis through a dedicated opening to deliver oxygen, nutrients, and circulating cells to osseous tissue.

Articular cartilage

A glass-smooth layer of hyaline cartilage covering epiphyseal joint surfaces that cushions impacts and minimizes frictional resistance.

Epiphyseal plate

A layer of cartilage near the ends of growing bones that lets them grow longer.

Epiphyseal line

A bony horizontal scar visible in adult long bones representing the completely ossified remnant of the cartilage growth plate, signaling that lengthwise growth has stopped.

Yellow bone marrow

Adipose-rich tissue residing within the adult medullary cavity that serves predominantly as an energy storage site.

Red bone marrow

Vascularized hematopoietic tissue situated within trabecular spaces of spongy bone that actively manufactures blood cells.

Bone projections (processes)

Bumps on a bone that act as anchors for muscles and ligaments.

Bone depressions and openings

ips, grooves, and holes in bones that fit neighboring bones or give nerves and blood vessels a safe path through.

Osteon (Haversian system)

The basic building block of hard (compact) bone.

Central (Haversian) canal

A longitudinal microscopic tunnel extending down the center of an osteon that conveys blood vessels, lymphatic vessels, and nerve branches.

Lachman Test

A clinical exam used to test for an ACL (anterior cruciate ligament) tear by pulling the tibia forward relative to the femur while the knee is bent at 20–30 degrees.

Lamellae

Concentric calcified rings of mineralized collagenous matrix that encircle the central canal of an osteon.lined up to give bone its incredible strength against twisting forces.

Lacunae

Tiny microscopic pockets inside bone tissue where mature bone cells live.

Canaliculi

Hair-like microscopic channels radiating outward from lacunae to link osteocytes together and connect them to central nutrient pathways.

Osteocytes

Mature, non-dividing bone cells residing within lacunae that supervise, maintain, and chemically regulate the extracellular osseous matrix.

Osteoblasts

Bone-forming cells that synthesize and deposit unmineralized organic matrix components to generate new bone tissue.

Osteoclasts

Large multinucleated cells that secrete acids and hydrolytic enzymes to degrade and reabsorb mineralized bone tissue.

Tissue diversity within bone organs

The integration of osseous tissue, cartilage, dense fibrous connective tissue, adipose tissue, nervous tissue, and vascular blood within an individual bone.

Collagen versus calcium salts in bone matrix

Collagen stops the bone from twisting/snapping, while calcium stops it from being crushed. Together, they make bones both strong and flexible.

Two primary triggers of bone remodeling

Systemic calcium ion concentrations in blood plasma and mechanical stresses applied to the skeleton by gravity and muscular pull.

Role of Vitamin D in bone health

Stimulates the active intestinal absorption of dietary calcium into the bloodstream, making it available for skeletal mineralization.

Parathyroid hormone (PTH)

A endocrine hormone released during hypocalcemia that stimulates osteoclast activity to resorb bone and restore normal plasma calcium concentrations.

Calcitonin

A thyroid hormone released during hypercalcemia that curbs osteoclastic resorption and facilitates calcium deposition into bone matrix.

Post-menopausal estrogen decline and bone density

A drop in circulating estrogen diminishes restraint on osteoclasts, causing bone resorption to outpace bone deposition and dramatically elevating osteoporosis risk.

Ossification (osteogenesis)

The body's blood cell factory inside your bones manufactures red and white blood cells.

Embryonic and fetal bone formation

Osteoblasts initially construct a bony exterior collar over hyaline cartilage models in embryos, after which internal cartilage is broken down in fetuses to yield the medullary cavity.

Appositional growth

The mechanism whereby osteoblasts beneath the periosteum deposit new matrix layers along the outer circumference while endosteal osteoclasts widen the cavity, expanding bone diameter.

Hormonal control of bone growth

Growth hormone promotes longitudinal chondrocyte division during childhood, followed by surges of estrogen and testosterone during puberty that drive growth spurts and prompt plate ossification.

Closed (simple) fracture

A bone break where the fractured osseous fragments do not pierce or break through the overlying skin.

Open (compound) fracture

A severe bone break where bone fragments rupture through the skin, establishing an external opening with a substantial vulnerability to deep infection.

Greenstick fracture

An incomplete fracture where one cortex of the bone bends while the opposing cortex cracks, commonly encountered in pediatric patients due to elevated organic matrix flexibility.

Spiral fracture

A jagged helical break generated when excessive twisting or rotational torque is exerted across a bone.

Hematoma formation (fracture repair)

The initial phase of fracture healing wherein ruptured blood vessels form a localized, clotted blood mass accompanied by inflammatory swelling and local tissue necrosis.

Fibrocartilage callus formation

The second phase of fracture repair wherein invading capillaries, fibroblasts, and chondroblasts produce a temporary fibrocartilaginous network that splints the broken ends.

Bony callus formation

The third phase of fracture repair wherein migrating osteoblasts gradually replace the fibrocartilaginous framework with spongy trabecular bone.

Bone remodeling (fracture repair)

The final reparative phase where mechanical loads guide osteoblasts and osteoclasts in reshaping the bony callus, reproducing the original cortical and cancellous bone architecture.

Vascularity and healing: Bone versus Cartilage

Bone heals substantially faster because it possesses a rich vascular supply carrying reparative cells and oxygen, whereas cartilage is avascular and depends on slow fluid diffusion.

Articulation

The functional junction where two or more bones meet, permitting variable degrees of mechanical movement while preserving structural support.

Fibrous joints

Joints joined directly by dense connective tissue lacking a joint cavity, typically allowing no movement (e.g., cranial sutures).

Cartilaginous joints

Articulations connected by cartilage without a cavity, providing slight flexibility and restricted movement (e.g., pubic symphysis and intervertebral joints).

Synovial joints

Freely movable joints characterized by an articular capsule enclosing a fluid-filled joint cavity (e.g., knee, shoulder, elbow, and hip).

Hinge joint

A uniaxial synovial joint allowing back-and-forth movement in a single anatomical plane, exemplified by the elbow and knee.

Ball-and-socket joint

A multiaxial synovial joint featuring a rounded spherical head articulating in a rounded socket, offering broad multiaxial mobility and rotation (e.g., shoulder and hip).