A&P Final #4

Which skin cancer has the worst prognosis?

Malignant melanoma.

What percentage of body weight is skin?

10 extendash15%.

What are the two main layers of skin?

Epidermis and dermis.

What anchors skin to deeper structures?

Hypodermis.

What are the accessory structures of skin?

Hair, nails, glands.

What are the five main functions of skin?

Protection, sensation, thermoregulation, excretion, vitamin D synthesis.

What is the epidermis composed of?

Keratinized stratified squamous epithelium.

What is the dermis composed of?

Loose connective tissue and dense irregular connective tissue.

What is the hypodermis composed of?

Loose connective tissue and adipose tissue.

What is the main protein produced by keratinocytes?

Keratin.

What structures are included in the skeletal system?

Bones, joints, and associated supporting tissues.

What are bones classified as in the skeletal system?

The main organs of the system.

What tissues compose bones besides osseous tissue?

Dense regular connective tissue, dense irregular collagenous connective tissue, and bone marrow.

How does the skeletal system provide protection?

Bones like the skull, sternum, ribs, and pelvis protect underlying organs.

How does the skeletal system contribute to mineral storage and acid extendashbase homeostasis?

Bones store calcium, phosphorus, and magnesium salts; minerals act as electrolytes, acids, and bases for homeostasis.

What is hematopoiesis?

Blood cell formation in red bone marrow.

What type of marrow is involved in blood cell formation?

Red bone marrow.

What type of marrow is involved in fat storage?

Yellow bone marrow.

What do adipocytes in yellow marrow store?

Triglycerides, which can be broken down into fatty acids for fuel.

How does the skeletal system contribute to movement?

Bones serve as attachment sites for skeletal muscles; muscle contraction pulls on bones to generate movement at joints.

How does the skeletal system provide support?

Skeleton supports body weight and provides structural framework.

What is the primary tissue found in bone?

Osseous tissue.

What is the extracellular matrix of bone composed of?

Inorganic matrix (65%) and organic matrix (35%).

What is the inorganic matrix primarily made of?

Calcium and phosphorus salts forming hydroxyapatite crystals.

What is the function of hydroxyapatite crystals?

Provide hardness and resistance to compression.

What other ions are found in the inorganic matrix?

Bicarbonate, potassium, magnesium, sodium.

What is the organic matrix of bone called?

Osteoid.

What proteins are found in osteoid?

Collagen fibers, proteoglycans, glycosaminoglycans, glycoproteins, bone extendashspecific proteins.

What is the role of collagen fibers in bone?

Resist torsion and tensile forces; align with hydroxyapatite crystals to enhance hardness.

What is the role of glycosaminoglycans and proteoglycans in bone?

Create osmotic gradient, draw water into osteoid, resist compression.

What is the role of glycoproteins in bone?

Bind components of osteoid and inorganic matrix together.

What are the three main types of bone cells?

Osteoblasts, osteocytes, osteoclasts.

What are osteogenic cells?

Flattened precursor cells that differentiate into osteoblasts.

What are osteoblasts?

Bone extendashbuilding cells; perform bone deposition.

What is bone deposition?

Secretion of organic matrix and assistance in formation of inorganic matrix.

What happens when osteoblasts become surrounded by matrix?

They become osteocytes in lacunae.

What are osteocytes?

Mature bone cells that maintain ECM; can recruit osteoblasts under tension.

What are osteoclasts?

Large multinucleated cells derived from bone marrow; perform bone resorption.

How do osteoclasts resorb bone?

Secrete hydrogen ions to dissolve inorganic matrix and enzymes to break down organic matrix.

What happens to substances liberated during bone resorption?

Absorbed into osteoclast cytosol, released into blood, reused or excreted.

What are the two types of bone tissue?

Compact bone and spongy bone.

What is the basic unit of compact bone?

Osteon (Haversian system).

What are lamellae?

Thin layers of bone arranged in concentric rings within osteons.

How do collagen fibers in lamellae resist stress?

Neighboring lamellae have fibers running in opposite directions, resisting twisting/bending.

What is the central canal?

Endosteum extendashlined hole in center of osteon containing blood vessels and nerves.

What are lacunae?

Small cavities between lamellae housing osteocytes.

What are canaliculi?

Small passageways connecting lacunae; allow osteocyte communication and resource sharing.

What are interstitial lamellae?

Remnants of old osteons filling spaces between new ones.

What are circumferential lamellae?

Outer and inner lamellae layers near periosteum and spongy bone; add strength.

What are perforating (Volkmann’s) canals?

Canals connecting central canals of osteons; carry blood vessels at right angles.

What is spongy bone composed of?

Trabeculae (struts/ribs of bone) covered with endosteum.

Do trabeculae contain osteons?

No, but they have concentric lamellae with osteocytes in lacunae.

How do trabeculae receive blood supply?

From vessels in bone marrow, not central canals.

What is osteopetrosis (“marble bone disease”)?

Defective osteoclasts fail to degrade bone; bone mass increases but becomes brittle.

What are the two main forms of osteopetrosis?

Infantile (severe, inherited, fatal if untreated) and adult (milder, symptomatic).

What are symptoms of infantile osteopetrosis?

Skull openings fail to enlarge, nerve trapping (blindness, deafness), decreased blood cell production.

What are symptoms of adult osteopetrosis?

Bone pain, recurrent fractures, nerve trapping, joint pain.

How is infantile osteopetrosis treated?

Drugs to stimulate osteoclasts and red marrow.

How is adult osteopetrosis treated?

Symptom management only.

What is ossification (osteogenesis)?

The process of bone formation.

When does ossification begin?

During the embryonic period.

When is ossification mostly complete?

By about age 7.

What is primary (woven) bone?

Immature bone with irregular collagen bundles, osteocytes, and sparse inorganic matrix.

What is secondary (lamellar) bone?

Mature bone with more inorganic matrix and increased strength.

What are the two mechanisms of ossification?

Intramembranous ossification and endochondral ossification.

What bones are formed by intramembranous ossification?

Many flat bones, including skull bones and clavicles.

What is the starting material for intramembranous ossification?

Mesenchymal membrane of embryonic connective tissue.

What is the primary ossification center?

Site where mesenchymal cells differentiate into osteoblasts.

What do osteoblasts secrete during intramembranous ossification?

Organic matrix, which calcifies with calcium salts.

What happens to osteoblasts trapped in lacunae?

They become osteocytes.

How is early spongy bone formed?

Osteoblasts lay down trabeculae that merge into larger structures.

What forms the periosteum during intramembranous ossification?

Differentiated mesenchymal cells.

What happens to spongy bone deep to periosteum?

It becomes heavily calcified and rearranged into immature compact bone.

What are fontanels?

Soft spots in newborn skulls where ossification is incomplete.

What bones are formed by endochondral ossification?

All bones below the head except clavicles.

What is the starting material for endochondral ossification?

Hyaline cartilage model.

When does endochondral ossification begin?

In the fetal stage.

When is ossification complete for most bones?

By age 7.

What is the primary ossification center?

Site in diaphysis where bone first replaces cartilage.

What are secondary ossification centers?

Sites in epiphyses where bone formation occurs later.

What is the first step of endochondral ossification?

Chondroblasts in perichondrium differentiate into osteoblasts, forming periosteum.

What is the bone collar?

Early bone formed around external surface of cartilage model.

What happens to internal cartilage during ossification?

It calcifies, chondrocytes die, leaving cavities.

What role do osteoclasts play in endochondral ossification?

They etch openings in bone collar for blood vessels and bone cells to enter.

What replaces calcified cartilage in primary ossification center?

Early spongy bone.

What develops as cavities enlarge and combine?

Medullary cavity.

What happens in secondary ossification centers?

Epiphyses ossify by similar pattern.

Where does cartilage remain after ossification?

Epiphyseal plates and articular cartilage.

What happens to epiphyseal plates in adulthood?

They are replaced by bone, leaving epiphyseal lines.

What is osteoporosis?

Most common bone disease in the U.S.; bones become weak and brittle due to inadequate inorganic matrix.

What are risk factors for osteoporosis?

Calcium/vitamin D deficiency, female gender, age, lack of exercise, low estrogen, genetics, other diseases.

How is osteoporosis diagnosed?

Bone density measurement.

How can osteoporosis be prevented?

Balanced diet, supplements, weight extendashbearing exercise, estrogen replacement if appropriate.

How is osteoporosis treated?

Drugs that inhibit osteoclasts or stimulate osteoblasts.

How do long bones lengthen?

By longitudinal growth at the epiphyseal plate.

Which cells divide during longitudinal growth?

Chondrocytes (not osteocytes or osteoblasts).

Where does bone growth take place?

At the epiphysis closest to the diaphysis.

What tissue composes the epiphyseal plate?

Hyaline cartilage.

What are the five zones of the epiphyseal plate?

Reserve cartilage, proliferation, hypertrophy/maturation, calcification, ossification.

What happens in the zone of reserve cartilage?

Cells are inactive but can be recruited for division.