A&P Chapter 6: Bone Tissue

What is Bone?

bone aka osseous tissue is a hard, dense connective tissue that forms most of the skeleton.

• support structure for the body

• in areas where bones move (ribcage/joints), cartilage provides flexibility and smooth surfaces for movement

• skeletal system is composed of bones and cartilage

What are the five functions of the skeletal system?

1. supports the body

2. facilitates movement

3. protects internal organs

4. produces blood cells

5. stores/releases minerals and fats

[Functions of Skeletal System]

Supports the body

• provides structural support for entire body

• individual bones/groups of bones provide framework for the attachment of soft tissues/organs

[Functions of Skeletal System]

Facilitates Movement (and leverage)

• facilitate movement by serving as points of attachment for your muscles

• many bones function as levers that can change magnitude/direction of forces generated by skeletal muscles

  • bones act as levers and joints serve as fulcrums (pivot point)

• movement produced range from delicate motions to strong changes in position

[Functions of Skeletal System]

Protection (internal organs)

• delicate tissues/organs are surrounded by skeletal elements

  • ribs protect the heart/lungs

  • skull encloses the brain

  • vertebrae shield the spinal cord

  • pelvis cradles urinary/reproductive organs

[Functions of Skeletal System]

Stores/Releases Minerals and Fats

• bone matrix acts as reservoir for minerals (calcium and phosphorus)

• they are incorporated into bone tissue but can be released back into bloodstream to maintain homeostasis

• calcium is most abundant mineral = muscle contractions and controlling flow of ions and nerve impulses

  • humans have 1-2kg of calcium and 98% of it is in bones

• yellow marrow: contains adipose tissue

  • triglycerides stored in adipocytes can serve as source of energy

[Functions of Skeletal System]

Blood Cell Production

• hematopoiesis (aka blood cell production): red blood cells, white blood cells, and platelets are produced in the red bone marrow

  • this fills the internal cavities of bones

Axial skeleton

(the human body has 206 bones)

1. axial skeleton: 80 bones; consists of the bones of the skull, hyoid, sternum, rib cage, vertebral column, sacrum, and coccyx

Appendicular Skeleton

(human body has 206 bones)

• appendicular skeleton: 126 bones; includes bones of the limbs and pectoral/pelvic girdles that attach the limbs to the axial skeleton

Long Bones

• cylindrical in shape (longer rather than wide)

• located in the arm, forearm, thigh, lower leg, palms, soles, fingers, toes

• femur: largest/heaviest bone in body

• ex: humerus, tibia/fibia, radius, ulna, clavicle, phalanges

Short bones

• cube-like in shape

• bones of the wrist (carpals) and bones of the ankles (tarsals)

Flat bones

• thin, often curved

• form the roof of the skull, sternum, ribs, and scapulae

• provide protection from underlying soft tissues + surface for attachment

• they are made of spongy bone (diploe) covered by compact bone

Irregular Bones

• complex shapes with short, flat, notched, or ridged surfaces

• don’t fit into any other category

• ex: spinal vertebrae, bones of pelvis, some skull bones (mandible)

Sesamoid bones

• generally small, flat, and shaped like a sesame seed

• develop inside tendons and most commonly located near joints

• ex: joints of knees, hands, feet

  • sesamoid patellae/kneecaps

• amount can vary

[Anatomy of a Long Bone]

Diaphysis

• long tubular shaft that forms the axis (middle section)

• walls of shaft are made of compact bone

[Anatomy of a Long Bone]

Epiphyses

• ends of the bones composed of spongy bone or trabecular bone

• consists of open network of struts/plates (trabeculae) that resemble latticework

  • red bone marrow fills the space

• proximal epiphyses: ends closest to origin of attachment

• distal epiphyses: ends furthest from origin of attachment

• articular cartilage: covers portions of the epiphysis that articulates with other bones (hyaline cartilage that reduces friction/shock absorber)

[Anatomy of a Long Bone]

Metaphysis

• narrow zone that connects the diaphysis to the epiphyses

• epiphyseal plate: aka growth plate; thin layer of hyaline cartilage that helps growth in length of the bone

• when the bone stops growing in early adulthood, cartilage is replaced by osseous tissue + epiphyseal plate becomes epiphyseal line

[Anatomy of a Long Bone]

Medullary Cavity

• within shaft of a long bone is cavity where bone marrow is located

• in childhood: medullary cavity is filled with red bone marrow

  • important for hematopoiesis

• as we age: fat accumulates within red marrow transforming it to yellow bone marrow

  • stores fat as important energy source

[Anatomy of a Long Bone]

Membranes - Periosteum

• outermost covering of bone made of dense irregular tissue + collagen fiber

• contains blood vessels, nerves, and lymphatic vessels = nourish compact bone

• tendons/ligaments attach to bones at periosteum

• covers entire outer surface except wehre epiphyses meet other bones

[Anatomy of a Long Bone]

Membranes - Endosteum

• internal membrane of bone made of connective tissue

• where bone growth, repair, and modeling occurs

• lines the canals that pass through bone to supply blood/nerves to the bone

[Bone Markings - Depressions/Openings]

What are depressions?

they are depressions or openings that allow blood vessels and nerves to pass

[Bone Markings - Depressions/Openings]

Fossa

shallow depression or recess in surface of a bone

[Bone Markings - Depressions/Openings]

Fovea

small pit

ex: fovea capitus

[Bone Markings - Depressions/Openings]

Fissure

narrow, slit-like opening or elongated cleft/gap

[Bone Markings - Depressions/Openings]

Foramen

round or oval opening through the bone

[Bone Markings - Depressions/Openings]

Canal or Meatus

large passageway through the bone

[Bone Markings - Depressions/Openings]

Sulcus or Groove

furrow or narrow trough in a bone

[Bone Markings - Depressions/Openings]

Sinus

chamber within a bone filled with air and lined with a mucous membrane

[Bone Markings - Depressions/Openings]

Sulcus

shallow groove

ex: sigmoid sulcus

[Bone Markings - Projections]

What are projections?

they are an area of a bone that projects above the surface and serves as sites for muscle/ligament attachment

[Bone Markings - Projections]

Tuberosity

large, round/rough projection that may cover a broad area

[Bone Markings - Projections]

Crest

narrow ridge of bone; normally prominent

[Bone Markings - Projections]

Trochanter

very large, irregularly shaped projection

[Bone Markings - Projections]

Epicondyle

raised area above a condyle

[Bone Markings - Projections]

Line

narrow ridges of bone, less prominent then a crest

[Bone Markings - Projections]

Tubercle

small, rounded projection

[Bone Markings - Projections]

Spine

sharp, slender, often pointed process

[Bone Markings - Projections]

Protuberance

protruding area such as a chin

[Bone Markings - Projections]

Process

prominent feature that stands out

ex: transverse process

[Bone Markings - Articulations]

What are articulations?

They are projections that form joints

[Bone Markings - Articulations]

Head

expanded proximal end of a bone carried on a nar

[Bone Markings - Articulations]

Facet

smooth, flat articular surface

[Bone Markings - Articulations]

Condyle

smooth, rounded articular surface

[Bone Markings - Articulations]

Ramus

arm-like bar of a bone

[Bone Tissue]

Organic Osteoid

• roughly 1/3 weight of the bone is contributed by collagen fibers

• strong/flexible, but can be bent if compressed

[Bone Tissue]

Inorganic Hydroxyapatites

• mineral salts account for 2/3 weight of bone

• calcium phosphate interacts with calcium hydroxide = hydroxyapatite

• incorporates other salts to form a strong/flexible material

• resistant to shattering

[Bone Cells]

Osteogenic Cells

• mesenchymal cells located within the periosteum and endosteum

• stem cells divide to produce daughter cells that differentiate into osteoblasts + important in formation of osteocytes

[Bone Cells]

Osteoblasts

• immature bone cells located on the surface of bone

• produce new bone matrix in process called osteogenesis/ossification

• make and release proteins in matrix

• before calcium salts are deposited, it’s called the osteoid

• osteocytes develop from osteoblasts that are trapped in a lacuna

• incapable of mitosis

[Bone Cells]

Osteocytes

• mature bone cells that maintain protein/mineral content of surrounding matrix

• secrete enzymes that dissolve the adjacent matrix + release minerals into circulation

• rebuild matrix = deposition of mineral crystals

• repair damaged bones

• communication + receive nutrients via canaliculi channels

• incapable of mitosis

[Bone Cells]

Osteoclasts

• bone digesting cells that remove/recycle bone matrix

• have 50+ nuclei

• originate from white blood cells, not osteogenic cells

• osteolysis: acids/enzymes are secreted by osteoclasts and release stored minerals; important in bone remodeling

[Compact Bone]

Osteon

basic structural/functional unit if bone

• consists of bone cells organized around a central canal and separated by concentric lamellae

[Compact Bone]

Central Canal/Haversian Canal

• runs parallel to the axis of bone

• located in the middle of each osteon

• possesses an artery and vein, lymph vessel, and nerve

[Compact Bone]

Perforating Canals

passageways that extend perpendicular to the axis of bone

connect the central canals of adjacent osteons

[Compact Bone]

Lamellae

nested, concentric rings of matrix surrounding the central canal

• circumferential lamellae: found at the OUTER/INNER LININGS of the bone, where they are covered by periosteum and endosteum. produced during growth/maintenance

• interstitial lamellae: OUTSIDE OSTEON. fill in spaces between adjacent osteons of compact bone. remnants of osteons

[Compact Bone]

Lacunae

• they hold the osteocytes

• each one only contains one osteocyte

[Compact Bone]

Canaliculi

narrow crevices

• this is what the osteocytes extend into

• they penetrate the lamellae and connect the lacunae to central canal

Spongy Bone

• contains osteocytes housed in lacunae, but they’re not arranged in concentric circles

• lacunae and osteocytes are found in lattice-like network of matrix called trabeculae

• the trabeculae provide strength to the bone

• the space between the network provide balance to the dense/heavy compact bone = lighter and easier to move

• some spaces contain red marrow

[Blood/Nerve Supply]

Nutrient Foramen

• nutrient foramen is a tunnel that penetrates the diaphysis and provides access for blood vessels into the shaft of the bone

  • in order for bones to grow/be maintained, they require extensive blood supply

• nutrient artery: transports oxygenated, nutrient-rich blood to the bone

• nutrient vein: transports deoxygenated, waste0laden blood from the bone

[Blood/Nerve Supply]

Metaphyseal Artery/Metaphyseal Vein

• metaphyseal arteries deliver oxygenated blood and nutrients to support bone growth

• metaphyseal veins remove deoxygenated blood and metabolic waste from the bone

• they go from the metaphysis to the epiphysis

[Blood/Nerve Supply]

Nerves

• nerves follow same paths into the bone

• they concentrate in the more metabolically active regions of the bone

• they sense pain and regulate blood supplies in bone growth

[Bone Formation/Development]

Cartilage Template

• bone is a replacement tissue = uses model tissue (cartilage) to lay down mineral matrix

• during fetal development, framework is laid down that determines where bones will form

  • flexible, semi-solid matrix produced by chondroblasts

• cartilage is avascular = no blood vessels

• functions are carried on by diffusion through the matrix

  • damaged cartilage doesn’t repair itself as easily as tissues

[Bone Formation/Development]

Intramembranous Ossification

• formation of bones without a cartilage model

• typical in flat bones, mandible, clavicles, and patella

• begins around 8 weeks after fertilization

• compact bone and spongy bone develops directly from sheets of connective tissue

[Bone Formation/Development]

Steps of Intramembranous Ossification

1. mesenchymal cells gather together and differentiate into specialized cells. some become osteogenic cells —> osteoblasts (appear in cluster called ossification center)

2. osteoblasts secrete osteoid (uncalcified matrix), which calcifies (hardens) in a few days with mineral salts = entraps osteoblasts inside. osteoblasts now become osteocytes.

3. osteoid (bone matrix) secreted makes trabecular matrix. the osteoblasts on the surface of spongy bone become the periosteum (protective layer of compact bone outside)

4. at birth, skull and clavicles are not fully ossified + sutures aren’t closed = deforms during passage through birth canal. last bones to ossify are flat bones of the face (reach adult size at end of growth spurt)

[Bone Formation/Development]

Endochondral Ossification

• formation of bones using hyaline cartilage model

• bone develops by replacing hyaline cartilage

• around 6 weeks after fertilization, some mesenchymal cells differentiate into chondrocytes that form cartilaginous skeletal precursor

• after, perichondrium appears

[Bone Formation/Development]

Steps of Endochondral Ossification

• cavitation of hyaline shaft

  • chondrocytes calcify; impermeable matrix causes chondrocytes to die from lack of nutrients = deteriorates; blood vessels grow around edges of cartilage = medullary cavity

• invasion of internal cavities

  • blood vessels invade spaces = enlarges and brings osteoblasts (this area is called the primary ossification center); the periosteal bud (fibroblasts, lymph vessels, nerve fibers, red marrow) migrate; osteoblasts secrete osteoid = spongy bone

• formation of medullary cavity

  • primary ossification center enlarges; osteoclasts break down spongy bone + opens up medullary cavity; osseous tissue of outer shaft becomes thicker = compact bone

• formation of epiphyses

  • secondary ossification center appears, cartilage calcifies/deteriorates = cavities for periosteal bud to enter; epiphyses are filled with spongy bone; cartilage remains

[Bone Formation/Development]

Longitudinal Growth: How Bones Grow in Length

1. Reserve Zone —> ANCHOR

• Cells: Small, inactive chondrocytes.

• Action: Anchors the growth plate to the epiphysis bone.

2. Proliferative Zone —> MULTIPLY & STACK

• Cells: Chondrocytes doing mitosis.

• Action: Divide rapidly and stack into tall columns to make new cells.

3. Hypertrophic Zone —> GROW & DIE

• Cells: Older, larger chondrocytes.

• Action: Cells swell up (hypertrophy), die, and the matrix breaks down.

4. Calcified Matrix Zone —> CALCIFY & INVADE

• Cells: Mostly dead cells.

• Action: Matrix hardens (calcifies); capillaries and osteoblasts invade from the shaft.

5. Ossification Zone —> BONE FORMATION

• Cells: Osteoblasts.

• Action: Osteoblasts turn leftover cartilage fragments (spicules) into spongy bone.

6. Early Twenties —> STOP

• Action: Mitosis stops, cartilage turns entirely to bone, leaves an epiphyseal line.

[Bone Growth/Development]

Appositional Growth: How Bones Grow in Diameter

1. osteoprogenitor cells beneath the periosteum differentiate into osteoblasts + form new osteons on external bone surface

2. as bone is being added on the outside, osteoclasts remove/recycling lamellae in the inner surface = medullary cavity gradually enlarges as the bone increases in diameter

3. this process is called modeling

[Bone Growth/Development]

Bone Modeling

the process in which matrix is resorbed on one surface of a bone and deposited on another

• takes place during bone growth

• in adult life, bone undergoes remodeling: resorption of old/damaged bone takes place on same surface where osteoblasts lay new bone (injury, exercise, etc. leads to this)

[Fractures: Bone Repair]

What is a Fracture

a fracture is a broken bone

• will heal regardless of if it’s reset to its original anatomical position

• if it isn’t reset correctly, healing process will keep bone in deformed position

[Fractures: Bone Repair]

How to Classify a Fracture

type of reduction

• when a broken bone is manipulated and set into natural position without surgery, it’s called a closed reduction

• when it requires surgery to expose and reset: open reduction

bone location relative to skin

• simple (closed): fracture where the skin remains intact

• compound (open): fracture where at least one end of the broken bone tears through the skin = risk of infection

orientation of the break

• transverse: break occurs perpendicular (90 degrees) to the axis of the bone

• oblique: occurs at an angle that isn’t 90 degrees

• spiral: bone segments are pulled apart as result of twisting motion

position of bone ends after the fracture

• non-displaced: bone ends retain their position

• displaced: bone end is out of normal alignment

[Fractures: Bone Repair]

Type of Fractures

• comminuted: bone fragments into many pieces

• compression/impacted: bone is crushed from upward/downward forces

• depressed: broken bone is pressed inward (skull)

• spiral: raged break as a result of excessive twisting of bone

• greenstick: bone breaks incompletely (young patients)

• colle’s: distal part of radius breaks

• pott’s: malleolus of tibia/fibula break

[Fractures: Bone Repair]

Bone Repair

hematoma formation

• blood vessels in bone tear = hemorrhage

• hematoma (large blood clot) forms. disruption of blood flow to bone = death of bone cells around fracture

fibrocartilage callus formation

• capillaries grow into hematoma and phagocytic cells invade area

• fibroblasts/osteoblasts migrate to fraction and secrete cartilage matrix

• chondrocytes from endosteum create internal callus by secreting matrix between two ends of broken bone, while chondrocytes from periosteum form external callus of hyaline cartilage/bone = stabilizes the fracture

bony callus formation

• osteoclasts resorb the dead bone; osteogenic cells become very active

• cartilage is replaced by trabecular bone

• internal/external calli unite, compact bone replaces spongy bone = complete healing

this process takes several weeks + slight swelling may remain after

[Exercise, Nutrition, and Hormones]

Exercise and Bone Tissue

1. lack of mechanical stress causes bones to lose mineral salts/collagen fibers = weakens

2. mechanical stress stimulates growth/strengthening of mineral salts/collagen fibers

3. people who exercise regularly have greate bone density

   1. any type of exercise stimulates strengthening, but resistance training is the best

   2. resistant training slows down eventual bone loss due to aging (prevents osteoporosis)

[Exercise, Nutrition, and Hormones]

Nutrition and Bone Tissue

• calcium: critical component of bone, must be obtained by diet because the body can’t make it.

  • can’t be absorbed in the intestine without vitamin D, so that’s also critical to bone

• vitamin K: supports bone mineralization

• magnesium: only small amount in body but 60% of it is in the skeleton

• fluoride: helps stabilize and strengthen bone mineral

• omega-3 fatty acids: reduce inflammation in the body (can interfere with function of osteoblasts = new osseous tissue)

[Exercise, Nutrition, and Hormones]

Hormones and Bone Tissue

hormones are involved in controlling bone growth, maintaining bone once formed, and remodeling it

• growth hormone: triggers chondrocyte proliferation = increasing length of bones. increases calcium retention = enhanced mineralization, osteoblastic activity = greater bone density

• thyroxine: promotes osteoblastic activity and synthesis of bone matrix

• estrogen/testosterone: promote osteoblastic activity + production of bone matrix. responsible for growth spurt.

• calcitriol: active form of vitamin D, stimulates calcium absorption

Calcium Homeostasis

Why Calcium Matters

• Most abundant mineral in the body.

• 6 Functions to memorize: Bones, teeth, heartbeat strength, blood clotting, muscle contraction, and nerve signals.

The Two Conditions

• Hypocalcemia (Too Low): Brittle bones, poor clotting, skipped heartbeats, muscle/nerve failure.

• Hypercalcemia (Too High): Underactive nervous system —> Lethargy, slow reflexes, constipation, confusion, coma.

How the Body Fixes It

1. If Blood Calcium is Too LOW —> PTH raises it

• How it senses it: Receptors on the Parathyroid Gland notice calcium isn't binding to them.

• Bones: Activates osteoclasts to erode bone and release calcium into blood.

• Intestines: Triggers kidneys to make Calcitriol (Vitamin D), which absorbs calcium from food.

• Kidneys: Calcitriol tells kidneys to reabsorb calcium back into the blood.

2. If Blood Calcium is Too HIGH —> Calcitonin lowers it

• Where it comes from: C cells of the Thyroid Gland.

• Bones: Stops osteoclasts (bone eaters) but lets osteoblasts (bone builders) keep working to store calcium.

• Intestines: Absorbs less calcium from food.

• Kidneys: Prevents kidneys from keeping calcium so you pee it out.

The Skeleton's Big Picture

• The skeleton is the primary manager of calcium homeostasis.

• It also balances other ions, not just calcium.

[Bone Disorders]

Pituitary Growth Failure (dwarfism)

• results from inadequate production of growth hormone

• leads to reduced epiphyseal cartilage = abnormally short bones

• rate in US because children can be treated with synthetic growth hormone

[Bone Disorders]

Achondroplasia

• results from abnormal hyaline cartilage development

• individuals have short, stocky limbs but the torso/head are normal size

[Bone Disorders]

Marfan Syndrome

• very tall with long, slender limbs

• due to excessive cartilage formation at epiphyseal plates

• can cause life-threatening cardiovascular problems

[Bone Disorders]

Gigantism

• results from overproduction of growth hormone before puberty

• puberty can be delayed

• most common cause is pituitary tumor which can be treated with surgery, radiation, or drugs

[Bone Disorders]

Acromegaly

• results from too much growth hormone after epiphyseal plates close

• bones don’t grow longer but instead thicker

• bones of face, hands, jaw

[Bone Disorders]

Fibrodysplasia Ossificans Progressiva (FOP)

• rare gene mutation that causes deposition of bone around skeletal muscles and soft tissues

• no effective treatment

• painful/debilitating

• patients rarely live into the 40’s

[Bone Disorders]

Paget’s Disease

• overactive osteoclasts cause pores and weakening of long bones = bending/bowling

• osteoblasts try to compensate for overactive osteoclasts

• weak/brittle, prone to fractures

[Bone Disorders]

Osteoporosis

• decrease in bone mass when bone resorption exceeds formation

• common with aging

• women lost bone mass more quickly than men starting at 50

  • 50 is also start of menopause (ovaries reduce production of estrogen = less osteoblastic activity for production of bone matrix)

[Bone Disorders]

Osteogenesis Imperfecta (OI)

• AKA brittle bone disease

• genetic disease where bones don’t form properly = fragile/break easily

• present from birth and stays throughout life

• impacts body’s production of collagen

[Quiz]

Which are functions of skeletal system (4 answers)

1. Support , protection and movement

2. Thermoregulation

3. Vitamin D production

4. Mineral homeostasis

5. Blood cell production

6. Triglyceride storage

7. Communication

1. Support , protection and movement

2. Mineral homeostasis

3. Blood cell production

4. Triglyceride storage

[Quiz]

Match bones to shapes

1. long bones: ulna, tibia, radius, metacarpals

2. short bones: carpals/tarsals

3. flat bones; sternum, scapula, and cranium

4. irregular bones: vertebrae

5. seasmoid bones: patella

[Quiz]

Calcium plays critical roles in: (5 answers)

1. smooth muscle contraction

2. cardiac muscle contraction

3. blood clotting

4. endocrine function

5. bone remodeling

6. skeletal muscle contraction

1. smooth muscle contraction

2. cardiac muscle contraction

3. blood clotting

4. bone remodeling

5. skeletal muscle contraction

[Quiz]

What are extracellular fluid filled extensions of lacunae called?

canaliculi

[Quiz]

How are osteons in compact bone tissue aligned and how does the osteon arrangement affect bone strength?

Parallel to the length of the diaphysis; the shaft resists bending even when stresses are applied in certain directions.

[Quiz]

Match bone disorders to description

1. dislocation: Occurs when a bone slips out of place, tearing the ligaments that attach the bone at the joint

2. torn cartilage: Can result from a sharp blow to a joint or a severe twisting of a joint

3. bursitis: Painful inflammation of bursa, a fluid-filled sac that helps reduce friction in joints.

4. bunions: Painful swellings of the bursae in the first joints of big toes.

5. arthritis: Inflammation of a joint, resulting from an injury, natural wear and tear, or autoimmune disease.

[Quiz]

The cells active in fracture repair during the production of the hard (spongy bone) callus are called______

Osteoblasts

Images

Images

Images

1. osteons

2. central canal

3. concentric lamellae

4. canaliculi

5. lacuna

6. osteocytes

7. interstitial lamellae

8. multiple osteons