Anatomy and Physiology: Chapter 7 Skeletal System Study Guide

Comprehensive practice questions covering Chapter 7 of the lecture notes on the skeletal system, including histology, gross anatomy, bone growth, and hormonal regulation.

What are the three main components that compose the skeletal system?

Bones, cartilages, and ligaments.

What is the function of ligaments in the skeletal system?

They are collagenous bands that hold bones together at joints.

What is the function of tendons?

They are structurally similar to ligaments but attach muscle to bone.

What is bone marrow and its essential function?

The soft bloody or fatty material enclosed in bones that is essential for blood cell production.

Compare the density and appearance of compact bone and spongy bone.

Compact (dense or cortical) bone is relativamente dense, white, smooth, and solid ($80\%$ of bone mass), while spongy (cancellous or trabecular) bone is porous ($20\%$ of bone mass).

What are the two most common types of cartilage in the skeletal system and where are they found?

Hyaline cartilage (ribs to sternum, growth plates, ends of bones) and fibrocartilage (intervertebral discs, pubic symphysis, knee pads).

Which type of cartilage serves as the model for the formation of most bones?

Hyaline cartilage.

Which organs are protected by the rib cage, cranial bones, and pelvis?

The rib cage protects the heart and lungs; cranial bones protect the brain; the pelvis protects urinary, reproductive organs, and the terminal GI tract.

What is hemopoiesis and where does it occur?

The process of blood cell production, which occurs in red bone marrow connective tissue containing stem cells.

Which two essential minerals are primarily stored in bone matrix?

Calcium and Phosphorus.

What are the functions of phosphate and calcium in the body?

Calcium is essential for muscle contraction, blood clotting, and nerve impulses; phosphate is a component of ATP, nucleotides, and phospholipids.

What are the four classes of bones determined by shape?

Long bones, short bones, flat bones, and irregular bones.

Which bone shape is the most common and found in the limbs?

Long bones.

What are sesamoid bones and what is the largest example?

Small, sesame seed-shaped bones along tendons; the patella (kneecap) is the largest.

Describe the structure of the diaphysis and the medullary cavity in long bones.

The diaphysis is the elongated, cylindrical shaft; the medullary cavity is the hollow space within containing red marrow in children and yellow marrow in adults.

Define epiphysis and its coverings.

A knobby region at the end of a long bone; its joint surface is covered by articular cartilage (hyaline cartilage) to reduce friction and absorb shock.

What are the two layers of the periosteum?

An outer fibrous layer of dense irregular connective tissue and an inner cellular layer containing osteoprogenitor cells, osteoblasts, and osteoclasts.

How do short, flat, and irregular bones differ internally from long bones?

They consist of an external surface of compact bone with a spongy bone interior and have no medullary cavity.

What is the specific name for spongy bone in the flat bones of the skull?

Diploe.

Contrast red bone marrow and yellow bone marrow.

Red marrow produces blood cells and platelets; yellow marrow is fatty marrow that replaces red marrow in adults, primarily in long limb bones.

What are the four types of bone cells and their origins or functions?

Osteoprogenitor cells (stem cells), osteoblasts (bone-forming), osteocytes (mature cells in lacunae), and osteoclasts (bone-dissolving).

Describe the appearance and function of osteoclasts.

Large, multinucleated cells with a ruffled border that secretes hydrochloric acid and enzymes to dissolve bone.

What is osteoid?

The organic component of bone matrix ($\frac{1}{3}$$ by weight) produced by osteoblasts, consisting of collagen, proteoglycans, and glycoproteins.

What is the inorganic portion of bone matrix composed of?

$\frac{2}{3}$ by weight, primarily $85\%$ calcium phosphate, which interacts with calcium hydroxide to form hydroxyapatite crystals.

What happens to bones if there is a loss of protein versus an insufficiency of calcium?

Loss of protein results in brittle bones; insufficient calcium results in soft bones.

What vitamins are required for calcification and what are their specific roles?

Vitamin D enhances calcium absorption from the GI tract; Vitamin C is required for collagen formation.

Explain the process of bone resorption.

Osteoclasts release proteolytic enzymes to digest organic components and hydrochloric acid to dissolve minerals (calcium and phosphate), which then enter the blood.

What is the basic functional and structural unit of mature compact bone?

The osteon, also known as the Haversian system.

What are canaliculi and their purpose?

Tiny interconnecting channels that extend from lacunae to allow nutrients, minerals, gases, and wastes to travel between blood vessels and osteocytes.

What is the function of perforating (Volkmann) canals?

They run perpendicular to central canals to connect multiple central canals, creating vascular and innervation connections between osteons.

What are the bony struts found in spongy bone called?

Trabeculae.

Define interstitial growth and appositional growth in cartilage.

Interstitial growth is an increase in length from within the internal regions; appositional growth is an increase in width along the outside edge.

Differentiate between intramembranous and endochondral ossification.

Intramembranous ossification grows bone within a membrane (mesenchyme) for flat bones; endochondral ossification begins with a hyaline cartilage model for most other bones.

What is the metaphysis and why is it significant?

The transitional zone where cartilage is being replaced by bone; it includes the epiphyseal plate (growth zone).

How does bone grow in length (interstitial growth)?

It occurs at the epiphyseal plate where osteoblasts produce bone on the diaphyseal side and chondrocytes produce cartilage on the epiphyseal side.

How does bone grow in diameter (appositional growth)?

It occurs within the periosteum where layers of external circumferential lamellae are deposited parallel to the surface.

How do osteocytes and osteoblasts respond to mechanical stress?

Stress is detected by osteocytes and communicated to osteoblasts, which increase the synthesis of osteoid and mineral deposition.

What is the role of growth hormone (somatotropin) in bone development?

It stimulates the liver to produce somatomedin; both stimulate cartilage growth in the epiphyseal plate.

How do sex hormones affect long bone growth during puberty?

They accelerate bone growth and cartilage growth in the epiphyseal plate, but eventually bone formation outpaces cartilage growth, causing the plate to close.

Describe the hormonal activation of Vitamin D to calcitriol.

UV light converts precursors in skin to Vitamin $D_3$, the liver converts it to calcidiol, and the kidney (stimulated by PTH) converts it to active calcitriol.

How do PTH and calcitriol interact to increase blood calcium?

They act synergistically to increase osteoclast activity, increase calcium reabsorption in the kidneys (excreting less in urine), and increase absorption in the small intestine.

What is the function of calcitonin?

Secreted by the thyroid in response to high blood calcium, it inhibits osteoclast activity and stimulates the kidneys to increase calcium loss in urine.

What are the four steps of bone repair after a fracture?

1. Fracture hematoma forms; 2. Fibrocartilaginous (soft) callus forms; 3. Hard (bony) callus forms; 4. Bone is remodeled.

Differentiate between osteopenia and osteoporosis.

Osteopenia is a natural reduction in bone mass starting around age $35$-$40$; osteoporosis is a reduction in bone mass significant enough to compromise function.

What bones are included in the axial skeleton?

The skull, vertebral column, sternum, and ribs.

What is the function of Sharpey's (perforating) fibers?

Thick bundles of collagen that anchor muscles, tendons, ligaments, and the periosteum to bone and dissipate mechanical stress.

How does bone contribute to acid-base balance?

By absorbing or releasing alkaline salts like carbonate and phosphate to buffer the blood.

What is the difference between woven bone and lamellar bone?

Woven bone is immature and unorganized; lamellar (secondary) bone is mature bone that replaces woven bone as compact and spongy bone form.