Chapter 6: Osseous Tissue and Bone Structure Flashcards

• Skeletal system includes:
– bones of the skeleton
– cartilages, ligaments, and connective tissues

1. Support
2. Storage of minerals (calcium)
3. Storage of lipids (yellow marrow)
4. Blood cell production (red marrow)
5. Protection
6. Leverage (force of motion)

• Bone are identified by:
– shape
– internal tissues
– bone markings

1. Long bones
2. Flat bones
3. Sutural bones
4. Irregular bones
5. Short bones
6. Sesamoid bones

• Are long and thin
• Are found in arms, legs, hands, feet, fingers, and toes

• Diaphysis:
– the shaft
- A heavy wall of compact bone, or dense bone
- A central space called marrow cavity

• Epiphysis:
– wide part at each end
– articulation with other bones
• Mostly spongy (cancellous)bone
• Covered with compact bone (cortex)

• Metaphysis:
– where diaphysis and epiphysis meet

• Are thin with parallel surfaces
• Are found in the skull, sternum, ribs,and scapula

• Resembles a sandwich of spongy bone
• Between 2 layers of compact bone

• Are small,irregular bones
• Are found between the flat bones of the skull

• Have complex shapes
• Examples:
– spinal vertebrae
– pelvic bones

• Are small and thick
• Examples:
– ankle
– wrist bones

• Are small and flat
• Develop inside
tendons near joints of knees, hands, and feet

• Depressions or grooves:
‐ along bone surface
– Projections:
– where tendons and ligaments attach
– at articulations with other bones

• Tunnels:
– where blood and nerves enter bone

• Dense, supportive connective tissue
• Contains specialized cells
• Produces solid matrix of calcium salt deposits
• Around collagen fibers

• Dense matrix, containing:
– deposits of calcium salts
– bone cells within lacunae organized around blood vessels

• Canaliculi:
– form pathways for blood vessels
– exchange nutrients and wastes

• Periosteum:
– covers outer surfaces of bones
– consist of outer fibrous and inner cellular layers

• 2/3 of bone matrix is calcium phosphate, Ca3(PO4)2:
– reacts with calcium hydroxide, Ca(OH)2 to form – crystals of hydroxyapatite, Ca10(PO4)6(OH)2
– which incorporates other calcium salts and ions

• 1/3 of bone matrix is protein fibers (collagen)

• Make up only 2% of bone mass:

- Osteocytes
- Osteoblasts
– osteoprogenitor cells
– osteoclasts

• Mature bone cells that maintain the bone matrix
• Live in lacunae
• Are between layers (lamellae) of matrix
• Connect by cytoplasmic extensions through canaliculi in lamellae
• Do not divide

Functions
• To maintain protein and mineral content of
matrix
• To help repair damaged bone

• Immature bone cells that secrete matrix compounds
(osteogenesis)

• Matrix produced by osteoblasts, but not yet
calcified to form bone
• Osteoblasts surrounded by bone become
osteocytes

• Mesenchymal stem cells that divide to produce
osteoblasts
• Are located in inner,cellular layer of periosteum
(endosteum)
• Assist in fracture repair

• Secrete acids and proteindigesting enzymes
• Giant, mutlinucleate cells
• Dissolve bone matrix and release stored minerals
(osteolysis)
• Are derived from stem cells that produce macrophages

• Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance:
– more breakdown than building, bones become weak
– exercise causes osteocytes to build bone

• The basic unit of mature compact bone
• Osteocytes are arranged in concentric lamellae
• Around a central canal containing blood vessels

• Perpendicular to the central canal
• Carry blood vessels into bone and marrow

• Lamellae wrapped around the long bone
• Binds osteons together

• Does not have osteons
• The matrix forms an open network of trabeculae
• Trabeculae have no blood vessels

• The space between trabeculae is filled with red bone marrow:
– which has blood vessels
– forms red blood cells
– and supplies nutrients to osteocytes

• In some bones, spongy bone holds yellow bone marrow:
– is yellow because it stores fat

• The femur transfers weight from hip joint to knee joint:
– causing tension on the lateral side of the shaft
– and compression on the medial side

• Compact bone is covered with membrane:
– periosteum on the outside
– endosteum on the inside

• Covers all bones:
– except parts enclosed in joint capsules

• It is made up of:
– an outer, fibrous layer
– and an inner,cellular layer

Functions of Periosteum
1. Isolate bone from surrounding tissues
2. Provide a route for circulatory and nervous
supply
3. Participate in bone growth and repair

• Collagen fibers of the periosteum:
– connect with collagen fibers in bone
– and with fibers of joint capsules,attached tendons,and ligaments

• An incomplete cellular layer:
– lines the marrow cavity
– covers trabeculae of spongy bone
– lines central canals

• Contains osteoblasts,osteoprogenitor cells, and osteoclasts

• Is active in bone growth and repair

• Human bones grow until about age 25

• Osteogenesis:
– bone formation

• Ossification:
– the process of replacing other tissues
with bone

• The process of depositing calcium salts
• Occurs during bone ossification and in other
tissues

• The 2 main forms of ossification are:
– intramembranous ossification
– endochondral ossification

• Also called dermal ossification:
– because it occurs in the dermis
– produces dermal bones such as mandible and
clavicle

• There are 3 main steps in intramembranous
ossification

• Mesenchymal cells aggregate:
– differentiate into osteoblasts
– begin ossification at the ossification center
– develop projections called spicules

• Blood vessels grow
into the area:
– to supply the osteoblasts

• Spicules connect:
– trapping blood vessels inside bone

• Spongy bonedevelops and is remodeled into:
– osteons of compact bone
– periosteum
– or marrow cavities

• Ossifies bones that originate as hyaline
cartilage

• Most bones originate as hyaline cartilage

• Growth and ossification of long bones occurs in 6 steps

• Appositional growth:
– compact bone thickens and strengthens long bone with layers of circumferential lamellae

• Chondrocytes in the center of hyaline cartilage:
– enlarge
– form struts and calcify
– die, leaving cavities in cartilage

• Blood vessels grow around the edges of the cartilage

• Cells in the perichondrium change to osteoblasts:
– producing a layer of superficial bone around the shaft which will continue to
grow and become compact bone (appositional growth)

• Blood vessels enter the cartilage:
– bringing fibroblasts that become osteoblasts
– spongy bone develops at the primary ossification center

Step 4
• Remodeling creates a marrow cavity:
– bone replaces cartilage at the metaphyses

• Capillaries and osteoblasts
enter the epiphyses:
– creating secondary ossification centers

• Epiphyses fill with spongy bone:
– cartilage within the joint cavity is articulation cartilage
– cartilage at the metaphysis is epiphyseal
cartilage

• As long as the epiphyseal cartilage continues to grow at its epiphyseal surface, the bone will continue to increase in length.

• Epiphyseal plate or cartilage growth plate
- cartilage cells are produced by mitosis on epiphyseal side of plate
- cartilage cells are destroyed and replaced by bone on diaphyseal side of plate

• Between ages 18 to 25, epiphyseal plates close.
- cartilage cells stop dividing and bone replaces the cartilage (epiphyseal line)

• Growth in length stops at age 25

• Zone of resting cartilage
- anchors growth plate to bone

• Zone of proliferating cartilage
- rapid cell division (stacked coins)

• Zone of hypertrophic cartilage
- cells enlarged & remain in columns

• Zone of calcified cartilage
- thin zone, cells mostly dead since matrix calcified
- osteoclasts removing matrix
- osteoblasts & capillaries move in to create bone over calcified cartilage

• Only by appositional growth at the bone’s surface

• Periosteal cells differentiate into osteoblasts and form bony ridges and then a tunnel around periosteal blood vessel.

• Concentric lamellae fill in the tunnel to form an osteon.

• When long bone stops growing, after puberty:
– epiphyseal cartilage disappears
– is visible on X‐rays as an epiphyseal line

• As long bone matures:
– osteoclasts enlarge marrow cavity
– osteons form around blood vessels in compact
bone

• 3 major sets of blood vessels develop

1) Nutrient artery and vein:
– a single pair of large blood vessels
– enter the diaphysis through the nutrient foramen
– femur has more than 1 pair

2) Metaphyseal vessels:
– supply the epiphyseal cartilage
– where bone growth occurs

3) Periosteal vessels provide:
– blood to superficial osteons
– secondary ossification centers

• The periosteum also contains:
– networks of lymphatic vessels
– sensory nerves

• The adult skeleton:
– maintains itself
– replaces mineral reserves

• Remodeling:
– recycles and renews bone matrix
– involves osteocytes, osteoblasts, and osteoclasts

• Bone continually remodels, recycles, and replaces
• Turnover rate varies
• If deposition is greater than removal, bones get stronger
• If removal is faster than replacement, bones get weaker

• Mineral recycling allows bones to adapt to stress
• Heavily stressed bones become thicker and stronger

• Bone degenerates quickly
• Up to 1/3 of bone mass can be lost in a few weeks of inactivity

• What you don’t use, you lose
• Stresses applied to bones during physical activity are essential to maintain bone strength and mass

• Normal bone growth and maintenance
requires nutritional and hormonal factors

• A dietary source of calcium and phosphate salts:
– plus small amounts of magnesium, fluoride, iron,
and manganese

• Vitamin C is required for collagen synthesis,
and stimulates osteoblast differentiation

• Vitamin A stimulates osteoblast activity

• Vitamins K and B12 help synthesize bone proteins

• The hormone calcitriol:
– is made in the kidneys
– helps absorb calcium and phosphorus from digestive tract
– synthesis requires vitamin D3 (cholecalciferol)

• Growth hormone and thyroxine stimulate
bone growth
• Estrogens and androgens stimulate osteoblasts
• Calcitonin and parathyroid hormone regulate
calcium and phosphate levels

• Bones store calcium and other minerals
• Calcium is the most abundant mineral in the
body

• Calcium ions are vital to:
– membranes
– neurons
– muscle cells, especially heart cells

• Calcium ions in body fluids:
– must be closely regulated

• Homeostasis is maintained:
– by calcitonin and parathyroid hormone
– which control storage, absorption, and excretion

KEY CONCEPTS
• Calcium and phosphate ions in blood are lost in urine
• Ions must be replaced to maintain homeostasis
• If not obtained from diet, ions are removed
from the skeleton, weakening bones
• Exercise and nutrition keep bones strong

• Bones:
– where calcium is stored

• Digestive tract:
– where calcium is absorbed

• Kidneys:
– where calcium is excreted

• Low calcium ion levels in the blood cause the parathyroid glands in neck to secrete Parathyroid Hormone (PTH)

• Increases calcium ion levels by:
– stimulating osteoclasts to release stored calcium ions from the bone
– increasing intestinal absorption of calcium
- kidneys retain calcium ions

– decreases calcium loss in urine
- calcium is absorbed quickly in intestines

• High calcium ion levels in blood cause Calcitonin to be secreted by C cells (parafollicular cells) in thyroid

• Decreases blood calcium ion levels by:
– inhibiting osteoclast activity
- rate of intestinal absorption decreases
- Kidneys allow calcium loss

– increasing calcium excretion at kidneys and increased calcium loss in urine
- Calcium is absorbed slowly in intestines
- Calcium is stored in bone matrix

• Fractures:
– cracks or breaks in bones
– caused by physical stress

• Fractures are repaired in 4 steps

• Bleeding:
– produces a clot (fracture hematoma)
– establishes a fibrous network

• Bone cells in the area die

• Cells of the endosteum and periosteum:
– Divide and migrate into fracture zone

• Calluses stabilize the break:
– external callus of cartilage and bone surrounds break
– internal callus develops in marrow cavity

• Osteoblasts:
– replace central cartilage of external callus
– with spongy bone

• Osteoblasts and osteocytes remodel the fracture for up to a year:
– reducing bone calluses

- occurs at the ankle and affects both bones of the leg

- shatter the affected area into a multitude of bony fragments.

- break a bone shaft across its long axis

- twisting stresses that spread along the length of the bone

- produce new and abnormal bone arrangements, non-displaced fractures retain the normal alignment of the bones or fragments

- break in the distal portion of the radius (usually from reaching to cushion a fall)

- one side of the shaft is broken, and the other side is bent.

- where bone matrix is undergoing calcification and chondrocytes are dying. A clean transverse fracture along this line can generally heal well. Unless carefully treated, fractures between the epiphysis and the epiphyseal cartilage can permanently stop growth at this site.

- occur in the vertebrae subjected to extreme streses

• Bones become thinner and weaker with age
• Osteopenia begins between ages 30 and 40
• Women lose 8% of bone mass per decade, men 3%

• The epiphyses, vertebrae, and jaws are most
affected:
– resulting in fragile limbs
– reduction in height
– tooth loss

• Severe bone loss
• Affects normal function
• Over age 45, occurs in:
– 29% of women
– 18% of men

• Estrogens and androgens help maintain bone mass
• Bone loss in women accelerates after menopause

• Cancerous tissues release osteoclastactivating
factor:
– that stimulates osteoclasts
– and produces severe osteoporosis

The 5 primary functions of the skeletal system are: - support,
- storage of minerals and lipids,
- blood cell production,
- protection,
- and leverage.

The 6 broad categories for classifying bones according to shape are:
- flat
- irregular
- long
- sesamoid
- short
- sutrural

A bone marking, (surface feature) is an area on the surface of a bone structured for a specific function, such as:
- joint formation,
- muscle attachment,
- or the passage of nerves and blood vessels.

Mature bones cells are known as OSTEOCYTES, bone-building cells are called OSTEOBLASTS, and OSTEOCLASTS are bone-resorbing cells.

IF the ration of collagen to hydroxyapatite in a bone increased, the bone would become less strong (as well as more flexible.)

because osteoclasts break down or demineralize bone, the bone would have a reduced mineral content (less mass), as a result, it would be weaker.

Compact bone consists of osteons (Haversian systems) with little space between them. Compact bone lies over spongy bone and makes up most of the diaphysis. It functions to protect, support, and resist stress. Spongy bone consists of trabeculae with numerous red marrow-filled spaces. Spongy bone makes up most of the structure of short, flat, and irregular bones and is also found at the epiphyses of long bones. Spongy bone functions in storing marrow and providing some support.

The presence of lamellae that are not arranged in osteons is indicative of spongy bone, which is located in an epiphysis.

During intramembranous ossification, fibrous connective tissue is replaced by bone.

In endochondral ossification, cells of the inner layer of the pericondrium differentiate into osteoblasts, and a cartilage model is gradually replaced by bone.

Long bones of the body, such as the femur, have an epiphyseal cartilage, a plate of cartilage that separates the epiphysis from the diaphysis so long as the bone is still growing lengthwise. An x-ray would indicate whether the epiphyseal cartilage is still present. If it is, growth is still occurring; if it is not, the bone has reached its adult length.

Bone remodeling refers to the process whereby old bone is continuously being destroyed by osteoclasts while new bone is being constructed by osteoblasts.

The biochemistry of some heavy-metal ions, such as strontium, cobalt, uranium, and plutonium, is very similar to that of calcium. Osteoblasts cannot differentiate these abnormal heavy-metal ions from normal calcium ions, so the heavy metal ions become incorporated into the bone matrix. Over time, these dangerous ions can be released into circulation during normal bone remodeling.

The larger arm muscles of the weight lifter would apply more mechanical stress to the bones of the upper limbs. in response to that stress, the bones would grow thicker.

Growth continues throughout childhood. At puberty, a growth spurt occurs and is followed by the closure of the epiphyseal cartilages. The later puberty begins, the taller the child will be when the growth spurt begins, so the taller the individual will be when growth is completed.

increased levels of growth hormone prior to puberty will result in excessive bone growth, making the individual taller.

Parathyroid hormone (PTH) influences osteoclast activity to cause a release of stored calcium ions from the bone. Under the influence of calcitonin, osteoclast activity is inhibited, while osteoblasts continue to lock calcium ions in the bone matrix. Therefore, PTH serves to increase blood calcium levels by causing its release from bone, and calcitonin decreases blood calcium levels by causing calcium to remain in bone.

The bones of children who have rickets are poorly mineralized and as a resulte are quite flexible. under the weight of the bondy, the leg bones bend. The instability makes walking difficult and can lead to other problems of the legs and feet.

Parathyroid hormone (PTH) stimulates osteoclasts to release calcium ions from bone and enhances calcitriol's effect on the intestinal absorption of calcium. Increase PTH secretion would result in an increase in the level of calcium ions in the blood.

Calcitonin lowers blood calcium levels by inhibiting osteoclast activity and increasing the rate of calcium excretion by the kidneys.

Immediately following a fracture, extensive bleeding occurs at the site of injury. after several hours, a large blood clot called a fracture hematoma develops. Next, an internal callus forms as a network of spongy bone unties the inner edges, and an external callus of cartilage and bone stabilizes the outer edges. The cartilaginous external callus is eventually replaced by one, and the struts of spongy bone now unite the broken ends. With time, the swelling that initially marks the location of the fracture is remodeled, and little evidence that a break occurred remains.

An external callus forms early in the healing process, when cells from the endosteum and periosteum migrate to the area of the fracture. These cells form an enlarged collar (external Callus) that encircles the bone in the area of the fracture.

Osteopenia is inadequate ossification and is common to the aging process. It results as a consequence of decreasing osteoblast activity accompanied with normal osteoclast activity.

In women, the sex hormones known as estrogens play an important role in moving calcium into bones. after menopause, the level of these hormones decreases dramatically; as a result, older women have difficulty replacing the calcium in bones that is being lost due to normal aging. In men, the level of sex hormones (androgens) does not decrease until much later in life.

contraction

long bones

short bones

diaphysis

osteocytes

It is made primarily of cells.

osteoclasts

Osteoclasts are responsible for removing and recycling bone.

trabeculae

Red bone marrow

Red bone marrow is responsible for blood cell formation.

periosteum

intramembranous ossification

endochondral ossification

appositional growth

Appositional growth allows a bone to increase in diameter.

remodeling

The bone will become thicker.

Bones become thicker and stronger in response to stress.

Vitamin C

calcitonin and parathyroid hormone

open or compound

An open or compound fraction occurs when the broken bone projects through the skin.

remodeling to return the bone to its normal shape

Remodeling is the last step of fracture repair.

osteoporosis

Osteoporosis is a reduction in bone mass that is sufficiently large to compromise the normal function of bone. It results in weakening of the bones, making them likely to break.