Anatomy Chapter 7 Review

Skeletal System

Composed of bones, cartilages, and ligaments

Cartilage

• Forerunner of most bones

• Covers many joint surfaces of mature bone

Ligaments

Hold bones together at joints

Tendons

Attach muscle to bone

Functions of the Skeleton

1. Support

2. Protection

3. Movement

4. Electrolyte balance

5. Acid-base balance

6. Blood formation

7. Hormone Selection

Movement

Limb movements, breathing, and other movements

Electrolyte Balance

Calcium and phosphate levels

Acid-base balance

Buffers blood against large pH changes

Blood Formation

Red bone marrow

Bone (osseous tissue)

Connective tissue with the matrix hardened by calcium phosphate and other minerals

Mineralization or calcification

Hardening process of bone

Individual bones (organs)

Consist of bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue

Flat bones

Thin, curved plates; protect soft organs

Long bones

Longer than wide; levers; crucial for movement

Short bones

Equal in length & width; glide across one another

Irregular Bones

Elaborate shapes that do not fit into other categories

Compact bone

Dense outer shell of bone

Spongy bone

loosely organized bone tissue

Marrow (medullary) cavity

Location of bone marrow

Diaphysis

the shaft of long bone

Epiphysis

located at each end of long bone

Articular cartilage

hyaline cartilage covers joint surface

Nutrient foramina

holes in bone allows blood vessels to penetrate

Periosteum

external sheath covering most of bone

Outer fibrous layer of collagen

Some fibers continuous with tendons

Inner layer of bone-forming cells

Important to bone growth and healing of fractures

Endosteum

thin layer of connective tissue lining marrow cavity

Epiphysial plate (growth plate)

• hyaline cartilage of children’s bones

• Enables growth in length

Epiphysial line

in adults, a bony scar that marks where growth plate used to be

Flat bone

• Sandwich-like construction

• Two layers of compact bone enclosing a middle layer of spongy bone (inner and outer tables)

• Both surfaces covered with periosteum

Bone

Connective tissue that consists of cells, fibers, and ground substance

Four principles types of bone cells

1. Osteogenic cells

2. Osteoblasts

3. Osteocytes

4. Osteoclasts

Osteogenic cells

• stem cells

• Arise from embryonic mesenchyme

• Multiply and give rise to most other bone cell types

• In endosteum & inner layer of perisoteum

Osteoblasts

• Produce new bone called "osteoid" which is made of bone
  collagen and other protein

• Control calcium and mineral deposition

• Stress stimulated to reinforce bone

Osteocytes

Osteoblasts that are trapped in the matrix they deposited

Lacunae

tiny cavities where osteocytes reside

Canaliculi

little channels that connect lacunae

Osteoclasts

Dissolving bone (osteolysis) is part of bone remodeling

Organic matter (1/3)

Collagen, carbohydrate-protein complexes

Inorganic matter (2/3)

• 85% hydroxyapatite - crystallized calcium phosphate salt

• 10% calcium carbonate – Prevent/treat a calcium deficiency.

• Other minerals (fluoride, sodium, potassium, magnesium)

Ceramic

allows bone to support body weight without sagging

Polymer (protein)

gives some flexibility

Central (haversian) canal

• Aligned parallel to the long axis of the bone.
• Contains the bone's blood vessels and nerve fibers

Concentric lamellae

• Layers of compact matrix that surround a central canal

• Circumferential lamellae fill outer region of dense bone

Perforating canals

transverse or diagonal passages

Spicules

Silvers of bone

Trabeculae

Thin plates or beams of bone

Red bone marrow

Fill spaces

Hematopoietic tissue

produces blood cells

Red marrow

• Child – in nearly every bone

• Adults, found in skull, vertebrae, ribs, sternum, part of
  pelvic girdle, and proximal heads of humerus and femur

Yellow marrow

• Adults

• Fatty marrow that does not produce blood

Ossification or osteogenesis

The formation of bone

Intramembranous ossification

Flat bones of skull, clavicle, and part of the mandible in fetus

Endochondral ossification

Are long bones

Length and Width

Bones grow in two directions

Epiphysial plate

• Hyaline cartilage that is replaced by bone
• Functions as growth zone where bone elongates

Appositional growth

• Growth on bone surface •

• Continual growth in diameter and thickness

• Intramembranous ossification

• Forms circumferential lamellae

Bone remodeling (absorption and deposition)

• occurs throughout life—10% of skeleton per year

• Repairs microfractures, releases minerals into blood,
  reshapes bones in response to use and disuse

Wolff’s law of bone

architecture of bone determined by mechanical stresses placed on it

Mineral deposition (mineralization)

process in which calcium, phosphate, and other ions are taken from blood
and deposited in bone

Mineral resorption

process of dissolving bone and releasing minerals into blood

Calcium Homeostasis

depends on a balance between dietary intake, urinary and fecal losses, and exchanges between
osseous tissue

Hypocalcemia

• deficient calcium in blood

• Changes membrane potentials and causes overly excitable
  nervous system that results in muscles tremors, spasms and
  tetany (inability to relax)

• Caused by vitamin D deficiency, diarrhea, thyroid tumors,
  underactive parathyroid glands

• Pregnancy and lactation increase risk of hypocalcemia

Hypercalcemia

• excessive calcium levels

• Makes ion channels less responsive and thus nerve and
  muscle are less excitable

• Can cause emotional disturbance, muscle weakness, sluggish
  reflexes, cardiac arrest

• Rarely occurs

1. Calcitrol

2. Calcitonin

3. Parathyroid hormone

Calcium homeostasis is regulated by three hormones

Calcitriol

Hormone that raises blood calcium level
Most active form of vitamin D
Produced by skin, liver, and kidneys
• Mainly, it increases calcium absorption by small intestine
• It also increases calcium resorption from the skeleton
• It weakly promotes kidney reabsorption of calcium ions, so
less lost in urine

Calcitonin

Secreted by C thyroid gland when blood calcium levels rise
too high
Lowers blood calcium concentration in two ways:
1. Inhibits osteoclasts thereby reducing bone resorption
2. Stimulates osteoblasts to deposit calcium into bone
Important in children, weak effect in adults
• Osteoclasts more active in children due to faster
remodeling
May inhibit bone loss in pregnant and lactating women

Parathyroid Hormone

• Secreted by parathyroid glands on surface of thyroid
• Released when calcium levels low in blood
PTH raises calcium blood level by four mechanisms, but
essentially promotes bone resorption and inhibits bone depsition

Orthopedics

branch of medicine dealing with prevention and correction of injuries and disorders of bones, joints, and muscles

Fracture

break caused by acute trauma to a bone

Stress fracture

break caused by chronic trauma to a bone, often referred to as a hairline fracture

Pathological fracture

break in a bone weakened by disease (such as bone cancer or osteoporosis)

Cast

normally used to stabilize and immobilize healing bone

Closed reduction

procedure in which bone fragments are manipulated into their normal positions without surgery

Open reduction internal fixation (ORIF)

involved surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments

Osteoporosis

the most common bone disease

severe loss of bone density

Kyphosis

deformity of spine due to vertebral bone loss

Treatments for Osteoporosis

• Estrogen replacement therapy (ERT) slows bone
resorption, but increases risk of breast cancer, stroke, and
heart disease
• Drugs Fosamax, Actonel destroy osteoclasts
• PTH slows bone loss if given as daily injection
• Forteo (PTH derivative) increases density by 10% in 1 year
• May promote bone cancer so use is limited to 2 years
• Best treatment is prevention: exercise and a good bone-
building diet between ages 25 and 40