Bones and skeleton Anatomy exam 2

What are the 6 primary physiological functions of the skeletal system?

1. Support (holds up body and cradles organs).

2. 2) Protection (guards CNS and visceral organs).

3. 3) Attachment point (skeletal muscles attach via tendons to produce movement).

4. 4) Storage (minerals like calcium/phosphate, and fat in yellow marrow).

5. 5) Blood cell formation (hematopoiesis in red bone marrow).

6. 6) Hormone production (secretion of osteocalcin).

What hormone is produced by bone cells, and what are its physiological functions in the body?

Osteocalcin. It helps regulate insulin release, glucose homeostasis, and overall energy expenditure.

What is the perichondrium, and what are its two main functions in cartilage tissue?

a layer of dense external fibrous connective tissue surrounding cartilage. It 1) contains blood vessels that deliver nutrients to avascular cartilage, and 2) resists excessive outward expansion when cartilage is compressed

What is the most abundant type of cartilage, containing fine collagen fibers (provides flexible support)?

hyaline cartilage

what type of cartilage Contains abundant elastic fibers (provides extreme flexibility and recoil)?

elastic cartilage

What type of cartilage contains rows of chondrocytes alternating with thick collagen bands (resists strong compression and tension)?

fibrocartilage

what is appositional growth (in terms of cartilage growth] ? What does it cause to happen with cartilage ?

• Chondroblasts in the perichondrium lay down new matrix on the external surface of pre-existing cartilage (causes cartilage to grow in width/thickness)

What happens with interstitial growth (in terms of cartilage growth)? What does it cause?

• Chondrocytes divide and secrete matrix from within pre-existing cartilage (causes cartilage to grow in length)

What type of growth causes cartilage to grow in length?

interstitial growth

what type of cartilage growth causes cartilage to grow in width/thickness

appositional

The axial skeleton…

Forms the long axis of the body (skull, vertebral column, and thoracic rib cage)

the appendicular skeleton…

Consists of upper/lower limbs (appendages) and the girdles (pectoral and pelvic) that attach limbs to the axial skeleton.

What are the 4 main shape classifications of bones?

• Long bones (longer than wide), Short bones (cube-shaped), Flat bones (thin, flattened, curved), and Irregular bones (complicated shapes).

what is a sesamoid bone ?

• A special type of short bone that forms inside a tendon (e.g., the patella).

Why are bone trabeculae arranged along specific stress lines within spongy bone?

Trabeculae align precisely along lines of mechanical stress to provide maximal structural support and resist force while keeping the skeleton light.

How do the gross structures of short, flat, and irregular bones differ from long bones?

they consist of thin plates of spongy bone covered externally by compact bone, lacking a long shaft, epiphyses, or a central medullary cavity (marrow is distributed between trabeculae throughout).

What are the 4 main anatomical regions/structures shared by all long bones?

1) Diaphysis (tubular bone shaft surrounding a central medullary cavity).

2) Epiphyses (expanded bone ends covered with articular hyaline cartilage).

3) Membranes (periosteum on exterior, endosteum on interior).

4) Vascularization/Innervation (nutrient vessels entering via nutrient foramina).

How do the periosteum and endosteum differ in location and coverage?

• Periosteum: Double-layered membrane covering the entire external bone surface (except at articular cartilage surfaces).

• Endosteum: Delicate connective tissue membrane covering internal bone surfaces (lines medullary cavities, central canals, and covers trabeculae).

what covers the external bone surface

the periosteum

what covers the internal surface of bone?

the endosteum

Where is red bone marrow (hematopoietic tissue) located in infants versus adults?

• Infants: Found in the medullary cavity of long bones and all areas of spongy bone.

• Adults: Restricted primarily to the heads of the femur and humerus, and flat/irregular bones (skull, sternum, ribs, clavicles, scapulae, vertebrae, hips).

What is yellow bone marrow, where is it located in adults, and can it change functions?

Yellow bone marrow consists primarily of fat (adipose) tissue located in the medullary cavity of adult long bones. Under severe anemia or blood loss, it can convert back into red bone marrow to produce blood cells.

How do the organic and inorganic components of bone tissue complement each other to give bone its physical properties?

• Organic components (cells + osteoid/collagen): Provide tensile strength and flexibility, allowing bone to resist stretching and twisting forces.

• Inorganic components (mineral salts / hydroxyapatites): Provide extreme hardness and compression resistance.

What is osteoid, what cell type secretes it, and what are its components?

it is the unmineralized organic bone matrix secreted by osteoblasts. It consists of collagen fibers, proteoglycans, and glycoproteins.

What are osteoprogenitor (osteogenic) cells, where are they located, and what is their function?

Mitotically active stem cells located in the periosteum and endosteum. Upon stimulation, they divide and differentiate into osteoblasts (or remain as stem cells).

How do osteoblasts and osteocytes differ in state of maturity, location, and primary function?

• Osteoblasts: Immature, active bone-forming cells that secrete osteoid matrix.

• Osteocytes: Mature bone cells trapped in lacunae that monitor and maintain the existing bone matrix and act as stress/mechanical sensors.

What is the origin, structure, and cellular function of osteoclasts?

Giant, multinucleated bone-resorbing cells derived from hematopoietic stem cells. They secrete lysosomal enzymes (collagenase) and metabolic acids to break down bone matrix for remodeling and blood calcium homeostasis.

What is an osteon (Haversian system), and how does the structural arrangement of collagen fibers in adjacent lamellae resist twisting forces?

An osteon is the structural unit of compact bone, consisting of concentric rings of bone matrix (lamellae) surrounding a central canal. Collagen fibers run in a single direction within one lamella, but run in alternating/opposite directions in adjacent lamellae to resist torsional (twisting) stress.

How do central (Haversian) canals and perforating (Volkmann's) canals differ in orientation and contents?

• Central canal: Runs vertically through the center of an individual osteon, housing blood vessels and nerve fibers.

• Perforating canal: Runs at right angles (horizontally) to the central canal, connecting blood vessels/nerves from the periosteum to central canals and the medullary cavity.

How do canaliculi and gap junctions allow osteocytes inside lacunae to receive nutrients despite an impermeable mineralized matrix?

they are tiny hair-like canals connecting lacunae to each other and to the central canal. Osteocyte cytoplasmic extensions meet inside canaliculi and connect via gap junctions, allowing nutrients and wastes to diffuse cell-to-cell from central canal blood vessels.

in compact bone, Circumferential lamellae…

Extend around the entire outer and inner circumference of the diaphysis (deep to periosteum/endosteum) to resist twisting of the whole bone.

in compact bone, Interstitial lamellae..

are Incomplete lamellae filling the triangular gaps between neighboring, active osteons (remnants of remodeled osteons)

What tissue serves as the initial embryonic model for endochondral ossification, and which skeletal bones form via this process?

hyaline cartilage serves as the blueprint model. Endochondral ossification forms essentially all bones below the base of the skull (except the clavicles).

What two key events occur during Steps 1 and 2 of endochondral ossification in the primary ossification center (POC)?

1. Osteoblasts secrete osteoid against the hyaline cartilage diaphysis to form a protective bone collar

2. Cartilage in the center of the diaphysis calcifies and cavitates (cartilage cells die due to blocked nutrient diffusion).

What is the periosteal bud (Step 3 of endochondral ossification), and what structural components does it deliver to the internal cavity?

An invading collection of structures that enters the cavitated diaphysis. It delivers a nutrient artery and vein, nerve fibers, red marrow elements, osteoprogenitor cells, and osteoclasts to begin forming initial spongy bone.

How does diaphysis development in the primary ossification center (POC) differ from epiphysis development in secondary ossification centers (SOC)?

In the POC (diaphysis), spongy bone formed initially is broken down by osteoclasts to create a hollow medullary cavity. In SOCs (epiphyses), spongy bone is retained internally (no medullary cavity forms).

At the end of endochondral ossification, where does hyaline cartilage permanently remain on a long bone?

1) Articular cartilage (on epiphyseal joint surfaces),

2) Epiphyseal plates (junction between diaphysis and epiphysis, enabling post-natal growth in length).

: How does growth in length (interstitial growth) occur at the epiphyseal plate?

New cartilage is continuously produced via mitosis on the epiphyseal side of the plate, pushing the epiphysis away from the diaphysis. Older cartilage on the diaphyseal side calcifies, dies, is broken down by osteoclasts, and is replaced by new bone tissue laid down by osteoblasts.

What causes a long bone to cease growing in length at the end of adolescence?

High levels of sex hormones (estrogen and testosterone) cause cartilage production in the epiphyseal plate to slow down and stop. The remaining cartilage is completely calcified and replaced by bone, fusing the diaphysis and epiphysis into an epiphyseal line.

How does growth in width/thickness (appositional growth) occur in long bones throughout life?

Osteoblasts beneath the periosteum secrete new bone matrix onto the external bone surface, while osteoclasts beneath the endosteum break down bone on the internal medullary surface (osteoblast activity slightly exceeds osteoclast activity, widening the bone without making it excessively heavy).

How does Parathyroid Hormone (PTH) regulate blood calcium levels when plasma Ca2+ drops below normal?

1. Declining blood Ca2+ triggers the parathyroid glands to release PTH.

2. PTH stimulates osteoclast number and activity to resorb bone matrix

3. stored calcium released into the blood until homeostatic levels are restored.

What is Wolff’s Law, and how do bones adapt physically to mechanical stress or gravity?

Bone remodels in response to stress. Increased stress strengthens bone by aligning trabeculae along stress lines and thickening compact bone.

What are the 4 sequential stages of bone fracture repair in correct order?

1) Hematoma formation (clotted blood mass forms; swelling and inflammation occur).

2) Fibrocartilaginous (soft) callus formation (capillaries, fibroblasts, chondroblasts, and osteoblasts invade to form a soft collagen/cartilage bridge).

3) Bony (hard) callus formation (trabeculae of spongy bone replace soft callus).

4) Bone remodeling (excess material removed, compact bone reconstructed according to mechanical stress lines).