Chapter 6 Flashcards
(6) important functions of skeletal system:
- **support **(structural framework) & **point of attachment **for tendons & ligaments
- **protect **internal organs
- assist **body movement **
- **store **& **release **calcium & phosphorus
- blood cell production (hematopoiesis)
- store **triglycerides **in adipose cells of yellow marrow
Bone is **dynamic tissue **… it is always ___
**remodeling **- building up & breaking down
(2) major **bone tissues **
1) bone (osseous tissue)
2) cartilage
Bone
highly vascularized CT with hard mineralized ECM found in 2 different arrangements
(2) different arrangements of bone
1) spongy
2) compact
Compact bone
- functions
- forms?
protection & support
- forms **diaphysis **of long bones & **external layer ** of all bones
Spongy Bone
- functions
- forms?
lightweight
provides tissue support
forms most of epiphysis & internal cavity of long bones
Articular Cartilage
- location
- purpose
thin layer of hyaline cartilage covering epiphysis of long bones
- covers part of epiphysis where bone forms joint
- reduces friction & absorbs shock
Periosteum
membrane covering bone surface not covered by articular cartilage
- attached to bone by Sharpey’s fibers
Periosteum - **purposes (4) **
1) protect bone
2) assist in fracture repair
3) nourish bone tissue
4) attachment point for ligaments/tendones
(2) layers of Periosteum
1) tough **outer **sheath of dense, irregular CT
2) inner **osteogenic **(bone stem cells) layer
How is **periosteum **attached to the bone?
by Sharpey’s Fibers
Medullary Cavity
space within diaphysis of long bones that contains **fatty yellow bone marrow **in adults
Endosteum
membrane that lines medullary cavity
Various cells in **Osseous tissues **
osteogenic cells → osteoblast → osteocyte
osteoclast (WBC)
Osteogenic cells
undergo cell division & develop into osteoblasts
Osteoblasts
bone building cells
Osteocyte
mature bone cells
principal cells of bone tissue
Osteoclasts
derived from monocytes & serve to break down bone tissue
Chemical Constituents of Bone
25% water
25% organic proteins
50% mineral salts (hydroxyapatite crystals).
**Organic constituents **of bone
- functions
**collagen fibers **
- provide flexibility & tensile strength
**Inorganic **constituents of bone
**Hydroxyapatite crystals (mineral salts) **
- Calcium Phosphate (Ca3PO4)2
- Calcium Carbonate (CaCO3 – marble)
- Other trace elements: Mg, F, sulphate
Bone Structure
diaphyses
epiphyses
metaphyses
Diaphysis
shaft or body of a long bone
Epiphyses
forms distal & proximal ends of a long bone
Metaphyses
areas where epiphyses & diaphysis join
Until end of active growth, epiphysis of long bones contains? forms?
hyaline cartilage & forms “epiphyseal growth plate”
In adults, epiphyseal cartilage is?
** no longer present** & elongation of bones has stopped
Compact Bone (cortical bone)
- contains?
contains units osteons (Haversian systems) formed from concentric lamellae (rings of calcified matrix) arranged around **central canal **
- interstitial lamellae
- outer circumferential lamellae
- inner circumferential lamellae
- lacunae
- canaliculi
- **perforating canals **
**Interstitial **lamellae
left over fragments of older osteons between osteons
Outer circumferential lamellae
encircle bone beneath periosteum
- connect to peristeum by **perforating (sharpey’s) fibers **
Inner circumferential lamellae
encircle medullary cavity
Lacunae
small spaces between lamellae which house osteocytes
Canaliculi
small channels filled with extracellular fluid connecting lacunae
Central canal
canal in center of osteons
- blood & lymphatic vessels
Perforating (Volkmann’s) canals
allow transit of vessels in Central Canal to outer cortex of bone
- allows vessels & nerves from periosteum to penetrate compact bone
Spongy bone
lacks osteons → lamellae arranged in lattic of thin columns (trabeculae)
make up interior bone tissue & houses red bone marrow
**lacunae **contain osteocytes (nourish mature bone tissue from blood circulating through trabeculae)
Spongy Bone → Trabeculae
structural unit of spongy bone
-lamellae arranged in lattice of thin columns
- contain **lacunae **→ contain osteocytes that nourish bone tissue from blood circulating through trabeculae
Purpose of spongy bone
reduces overall weight
support/protect red bone marrow → site of hemopoiesis
Blood & Nerve Supply of Bone → periosteal arteries & veins
supply periosteum & compact bone
enter diaphysis through **perforating **(Volkman’s) canals
Blood and Nerve Supply of Bone → **nutrient **artery
near center of **diaphysis **
passes through nutrient foramen
enters medullary cavity & divides proximal & distal branches
Blood & Nerve Supply of Bone
nerves may accompany blood vessels
- periosteum is rich in sensory nerves
Bone formation
**ossification **or **osteogenesis = **process of formaing new bone
ossification or osteogenesis
- occurs in (4) situations
process of formaing new bone
1) formation of bone in embryo
2) growth of bones until adulthood
3) **remodeling **of bone
4) **repair **of fracture
Osteogenesis
- occurs by?
- when does it begin?
occurs by 2 different methods
beginning about 6th week of embryonic development
**Osteogenesis **- (2) methods
1) **Intra-membranous **ossification
2) **Endochondral **ossification
1) **Intra-membranous **ossification
produces spongy bone
- subsequently**, **be remodeled to form compact bone
2) Endochondral ossification
process whereby cartilage is replaced by bone
forms both **compact **& **spongy **bone
Intramembranous Ossification
- forms?
- forms from?
used in forming flat bones of skull, mandible & clavicle
bone forms from mesenchymal cells -without going through cartilage stage
Intra-membranous Ossification
- steps (4)
1) Development of ossification centre
2) Calcification
3) Formation of trabeculae
4) Development of periosteum
Intra-membranous ossification
1) Development of ossification centre
chemical msgs cause mesenchymal cells to cluster (**ossification centre) ** & differentiate into osteogenic cells → osteoblasts - secrete ECM until surrounded
Intramembranous Ossification
2) Calcification
secretion of ECM stops
now osteocytes lie in lacunae & extend cytoplasmic processes into canaliculi that radiate in all directions
within few days: calcium & other mineral salts deposited & ECM calcifies (hardens)
Intramembranous Ossification
3) Formation of trabeculae
As bone ECM forms, develops into trabeculae that fuse to form spongy bone around network of blood vessels
CT asociated with blood vessels differentiates in red bone marrow
Intramembranous Ossification
4) Development of periosteum
In conjunction with formation of trabeculae
mesenchyme condenses into periosteum
eventually, thin layer of compact bone replaces surface spongy bone layers
Much of newly formed bone is remodeled (destroyed and reformed) as bone is transformed into its adult size & shape.
Endochondral Ossification
- steps (6)
1) Development of Cartilage model
2) Growth of Cartilage Model
3) Development of primary ossification centre
4) Development of medullary cavity
5) Development of secondary ossification centre
6) Formation of articular cartilage & epiphyseal (growth) plate
Endochondral Ossification
1) Development of Cartilage model
chemical msgs cause mesenchymal cells to crowd into general shape of bone
→ develop into chondroblasts - secrete cartilage ECM → produce cartilage model (hyaline)
- perichondrium develops around
Endochondral Ossification
2) Growth of Cartilage Model (4)
once chondroblasts buried in cartilage ECM → chondrocytes
- interstitial/appositional growth
as model grows, chondrocytes in mid-region hypertrophy (increase in size) & surrounding cartilage ECM calcifies
- chondrocytes die & spaces left behind merge into small cavities (lacunae)
2a) Interstitial (endogenous) growth
grows in length by continual cell division of chondrocytes & further secretions of cartilage ECM
2b) Appositional (exogenous) growth
growth in thickness due to deposition of ECM on cartilage model surface by new chondroblasts developed from perichondrium
Endochondral Ossification
3) Development of primary ossification centre (4)
primary ossification proceeds inward from external bone surface
- nutrient artery penetrates perichondrium & calcifying cartilage model through nutrient foramen → stimulates osteogenic cells in perichondrium to differentiate into osteoblasts
- (once perichondrium starts to form bone - known as periosteum)*
- near middle of model, periosteal capillaries grow into calcified cartilage & induce growth of primary ossification center (region where bone tissue will replace most of cartilage)
osteoblasts deposit bone ECM over remnants of calcified cartilage → forms trabeculae
- eventually, most of diaphysis wall replaced by compact bone
Endochondral Ossification
4) Development of medullary cavity
as primary ossification centre grows towards ends of bone, osteoclasts break down trabeculae leaving medullary cavity in shaft
eventually, most of diaphysis wall replaced by compact bone
Endochondral Ossification
5) Development of secondary ossification centre
when branches of epiphyseal artery enter epiphyses → secondary ossification centres develop (around time of birth)
bone formation similar to primary oss. centres but:
spongy bone remains in interior of epiphysis (no medullary cavity formed) & secondary ossification proceeds outwards from centre of epiphysis to outer bone surface
Endochondral Ossification
6) Formation of articular cartilage & epiphyseal (growth) plate
hyaline cartilage that covers epiphyses become articular cartilage
before adulthood, hyaline cartilage remains b/w diaphysis & epiphysis as epiphyseal (growth) plate (region responsible for lengthwise growth of long bones)
During infancy, childhood, and adolescence, bones throughout the body grow in thickness by?
and long bones lengthen by?
appositional growth
interstitial growth - addition of bone material on the diaphyseal side of epiphyseal plate
Growth in Length
- (2) major events
1) Interstitial growth of cartilage on epiphyseal side of epiphyseal plate
2) Replacement of cartilage with bone on diaphyseal side of epiphyseal plate
Growth in Length
- epiphyseal (growth) plate has (4) zones
1) Zone of Resting Cartilage
2) Zone of Proliferating Cartilage
3) Zone of Hypertrophic Cartilage
4) Zone of Calcified Cartilage
Epiphyseal (growth) plate
1) Zone of Resting Cartilage
nearest epiphysis
- consists of small, scattered chondrocytes
- do not function in bone growth
- anchor epiphyseal plate to epiphysis of bone
Epiphyseal (growth) plate
2) Zone of Proliferating Cartilage
slightly larger chondrocytes arranged like stacks of coins
- undergo interstitial growth as they divide & secrete ECM
→ divide to replace those that die at diaphyseal side of plate
Epiphyseal (growth) plate
3) Zone of Hypertrophic Cartilage
consists of large, maturing chondrocytes arranged in columns
Epiphyseal (growth) plate
4) Zone of Calcified Cartilage
final zone → only few cells thick
- mostly dead chondrocytes b/c ECM around them is calcified
- osteoclasts dissolve calcified cartilage
- osteoblasts & capillaries from diaphysis invade area
- osteoblasts lay down bone ECM (replacing calcified cartilage by endochondral ossification)
- becomes new diaphysis firmly cemented to rest of diaphysis of bone
Ossification contributing to bone length usually completed by?
18-21 years old
Even after epiphyseal growth plates have closed, bones still continue to? are capable of?
thicken & are capable of repair
Only way diaphysis can increase in length?
activity of epiphyseal plate
Order of Zones in Epiphyseal plate from epiphysis to diaphysis
Zone of:
Resting cartilage
Proliferating cartilage
Hypertrophic cartilage
Calcified cartilage
Growth in Thickness/Width by appositional growth
periosteal cells differentiate into osteblasts → secrete ECM
- become surrounded → osteocytes
- forms grooves around periosteal blood vessel → becomes tunnel
- periosteum becomes endosteum that lines tunnel
- osteoblasts in endosteum deposit bone ECM forming new concentric lamellae
→ proceeds inward, filling in tunnel
- as osteon forms, osteoblasts under periosteum deposit new circumferential lamellae (further increasing thickness of bone)
- osteoclasts of endosteum destroy bone lining forming medullary cavity
Human Growth Hormone (HGH)
- functions (secretion)
one of body’s many anabolic hormones
Secretion of HGH stimulates:
- bone growth
- muscle growth
- loss of fat
- increase glucose output by liver
*
Bone remodeling
- involves? (2)
ongoing replacement of old bone tissue by new bone tissue
involves: bone resorption & bone deposition
Bone Remodeling
a) Bone resorption
b) Bone deposition
a) removal of minerals & collagen fibers from bone by osteoclasts
(results in destruction of bone ECM)
b) addition of minerals & collagen fibers to bone by osteoblasts
(results in formation of bone ECM)
At any given time, __% of total bone mass in body is being remodeled
5%
renewal rate for compact bone tissue is about ___% per year
4%
renewal rate for spongy bone tissue is about __% a year
20%
Benefits of Remodeling
(3)
1) since strength of bone is related to degree to which it is stressed, if newly formed bone is subjected to heavy loads, it will grow thicker and therefore be stronger than old bone.
2) shape of a bone can be altered for proper support based on the stress patterns experienced during remodeling process
3) new bone is more resistant to fracture than old bone
Bone Growth and Remodeling
- balance must exist between..
actions of osteoclasts & osteoblasts
Imbalance between actions of osteoclasts & osteoblasts can result in? (4)
1) acromegaly
2) osteoporosis
3) rickets
4) osteomalacia
1) acromegaly
bone becomes abnormally thick & heavy b/c too much new tissue is formed
2) osteoporosis
excessive loss of calcium weakens bones - osteoclast activity
3) rickets
4) osteomalacia
excessive loss of calcium causes bones to be too flexible/soft
Factors Affecting Bone Growth and Bone Remodeling
- normal bone metabolism depends on (3)?
adequate dietary intake of:
1) Minerals
2) Vitamins
sufficient levels of:
3) Hormones
Factors Affecting Bone Growth and Bone Remodeling:
1) Minerals
large amounts of Ca, P
smaller amounts of Mg, F & Mn
- required for bone growth & remodeling
Factors Affecting Bone Growth and Bone Remodeling
2) Vitamins (5)
Vitamin A
Vitamin C
Vitamin D
Vitamin K
Vitamin B12
Vitamin A
stimulates activity of osteoblasts
Vitamin C
needed for synthesis of collagen
Vitamin D
promotes absorption of calcium from foods in GI tract into blood
Vitamins K & B12
needed for synthesis of bone proteins
3) Hormones (6)
1) HGH
2) insulinlike growth factors (IGFs)
3) estrogen
4) testosterone
5) Parathyroid hormone (PTH)
6) Calcitonin
3) Hormones - most important to bone growth in childhood?
Human Growth Hormone (HGH - produced by pituitary gland
Growth Factors (IGFs) - produced by liver
3) Hormones
- HGH & IGFs both… (3)
stimulate osteoblasts
promote cell division at epiphyseal plate
enhance protein synthesis
3) Hormones - Thyroid hormones (a) & Insulin (b)
promote bone growth
by stimulating osteoblast activity (a) & increasing synthesis of proteins (b)
3) Hormones - Sex Hormones (4)
At puberty - secretion of estrogen & testosterone
Responsible for:
- increased osteoblast activity
- synthesis of bone ECM
- sudden “growth spurt” that occurs during teen years
- closing down epiphyseal plates
Estrogen promotes widening of pelvis in females
During adulthood, sex hormones contribute to? by?
bone remodeling by slowing resorption of old bone & promoting deposition of new bone
- Estrogen slows resorption by promoting apoptosis (programmed death) of osteoclasts
3) Hormones - PTH & calcitonin
critical for balancing levels of Ca & P between blood & bone
Why does maintaining a normal serum Ca2+ level take precedence over mineralizing bone?
too high Ca2+ → cardiac arrest
too low Ca2+ → respiratory arrest (stop breathing)
Ca2+ exchange is regulated by hormones, the most important of which is?
Parathyroid Hormone (PTH)
PTH
- effect on Ca2+ level
increases blood Ca2+ level
operates via negative feedback system
Negative Feedback System of PTH
stimulus causes decrease in blood Ca2+ level
PT gland cells (receptors) detect change → increase production of cAMP (input)
detected by gene for PTH within nucleus of PT gland cell (control center)
increased PTH synthesis (output) →released into blood
stimulates osteoclasts (effectors) → bone resorption
release of Ca2+ from bone into blood
How else does PTH increase Ca2+ level?
PTH acts on kidneys (effectors) to decrease Ca2+ loss in urine
PTH stimulates formation of calcitroil (active form of vitamin D) → promotes absorption of calcium from food in GI tract into blood
What Hormone works to decrease blood Ca2+ level?
How?
Calcitonin (CT)
increase in blood Ca2+ level → parafollicular cells in thyroid gland secrete CT → inhibits osteoclast activity, increase blood Ca2+ uptake by bone & Ca2+ deposition into bone
What hormones stimulate osteoclast activity & lower serum calcium level?
Calcitonin
HGH & sex hormones (to lesser exent)
Calcium Homeostasis
high blood Ca2+ level → thyroid gland parafollicular cells release more CT → CT inhibits osteoclasts → decreases Ca2+ level → stimulates parathyroid chief cells to release more PTH
(1) → PTH promotes release of Ca2+ from bone ECM into blood & slows loss of Ca2+ in urine
(2) → PTH stimulates release of calcitriol from kidneys → stimulates increased absorption of Ca2+ from food
→ increases Ca2+ level
Fractures
- different criteria for naming (3)
1) anatomical appearance
2) disease/mechanism which produced fracture
3) common pattern of injury
Fractures named by anatomical appearance (10)
- Partial
- Complete
- Closed (simple)
- Open (compound)
- “Green stick”
- Impacted
- Comminuted
- Spiral
- Transverse
- Displaced
1) Partial
incomplete break of bone
2) complete
fracture all the way through bone
3) closed (simple)
broken bone does NOT puncture skin
4) open (compound)
broken ends of bone puncture skin
5) Greenstick
partial fracture in which one side of bone is broken & other side bends
- similar to breaking green twig
- occurs only in children (bones not fully ossified & contain more organic than inorganic material)
6) Impacted
one end of fracture bone forcefully driven into interior of other
- distal part shoved up into proximal part
7) Comminuted
bone is splintered/crushed/broken into pieces at site of impact
8) spiral
occurs when rotating force applied along axis
9) Transverse fracture
broken straight across
10) displaced fracture
both ends of broken bone seperated
Fractures classified by disease/mechanism which produced fracture
(3)
1) Pathological
2) Compression
3) Stress
1) Pathological
caused by disease that led to weakness of bone structure
-chronic disease like osteoporosis or cancer weakens bone
2) Compression
produced by extreme forces such as in trauma
3) Stress
produced by repeated strenuous activites such as running
- series of microscopic fissures in bone that form without any evidence of injury to other tissues
Fractures described by common pattern of injury (2)
1) Colles’
2) Pott’s
1) Colles’ fracture
- usually occurs by?
Fracture of distal end of lateral forearm bone (radius) in which distal fragment is displaced posteriorly
- commonly caused by falling onto hard surface with outstretched hand
2) Pott’s fracture
Fracture of distal end of lateral leg bone (fibula), with serious injury of distal tibial articulation
Fracture & Repair
- steps (4)
1) Formation of fracture hematoma
2) Fibrocartilaginous callus formation
3) Bony callus formation
4) Bone remodeling
Fracture repair:
1) Formation of fracture hematoma
blood vessels crossing fracture line broken - in peristeoum & osteons
leaking blood forms mass (usually clotted) around site of fracture → fracture hematoma
- usually forms 6-8 hours after injury
lack of blood circulation →nearby bone cells die → swelling & inflammation
→ produces additional cellular debris →removed by phagocytes & osteoclasts
Fracture Repair
2) Fibrocartilaginous callus formation
fibroblasts from periosteum invade fracture side → produce collagen fibers
cells from periosteum develop into chondroblasts → produce fibrocartilage
- lead to development of fibrocartilaginous (soft) callus (mass of repair tissue consisting of collagen & cartilage that bridges broken ends of bone)
- takes about 3 weeks (can take up to 6 months)
Fracture Repair
3) Bony callus formation
- In areas closer to well‐vascularized healthy bone tissue:* osteogenic cells develop into osteoblasts → produce spongy bone trabeculae
trabeculae joins living & dead portions of original bone fragments
fibrocartilage converted to spongy bone →callus referred to as a bony (hard) callus
- lasts about 3 to 4 months.
Fracture Repair
4) Remodeling
dead portions of original broken bone fragments resorbed by osteoclasts
compact bone replaces spongy bone around fracture periphery
- fracture line disappears but thicken area on surface remains as evidence
Bone Tissue & Mechnical stress
bone tissue has limited ability to alter strength in response to changes in mechanical stress
- when stressed, can become stronger through increased mineral salt deposition & production of collagen fibers by osteoblasts
Main mechanical stresses on bone (2)
pull of skeletal muscles
pull of gravity
Unstressed bones
become weaker
- can have dramatic bone loss (up to 1% per week)
Aging & Bone Tissue
decrease in bone mass occurs as level of sex hormones diminishes during middle age
As the level of sex hormones diminishes during middle age… what happens?
- especially for who?
bone resorption (by osteoclasts) outpaces bone deposition (by osteoblasts)
- especially for womejn after menopause
Why does loss of bone mass in old age typically have a greater adverse effect in females?
women’s bones generally smaller & less massive to begin with
- contributes to higher incidence of osteoporosis in females
(2) principal effects of aging on bone tissue
1) Loss of bone mass
2) Brittleness
Effects of Aging:
1) Loss of bone mass
- results from?
Demineralization - loss of calcium & other minerals from bone ECM
- usually begins after age 30 in females
- accelerates greatly around age 45 (as estrogen levels decrease)
- continues until as much as 30% of calcium in bones is lost by age 70
Once bone loss begins in females, about ___% of bone mass is lost every 10 years
8%
For men:
Calcium loss typically does not begin until ___ , and about __% of bone mass is lost every 10 years
after age 60
3%
Effects of Aging
2) Brittleness
- results from?
decreased rate of protein synthesis
- organic part of bone ECM (mainly collagen fibers) gives bone its tensile strength
- loss of tensile strength causes bone to become brittle & susceptible to fracture
- collagen fiber synthesis slows partly due to diminished HGH production*
Osteoporosis
- often due to? (2)
condition where bone resorption outpaces bone deposition
- often due to depletion of calcium from body OR inadequate intake
Estrogen & Osteoporosis
- both sexes
Estrogen maintains density in both sexes (inhibits resorption)
Men: testes & adrenal glands produce estrogen
Women: rapid loss after menopause if:
- body fat too low
OR
- with disuse during immobilization
Osteoporosis
- Treatment
Estrogen Replacement Therapy (ERT)
- slows bone resorption but increases risk of breast cancer, stroke & heart disease
Best Treatment = prevention - exercise & calcium intake (1000-1300 mg/day) between ages 9 and 71+
- milk = ~300 mg/250 ml
- Vitamin D - ~600 IU per day*
40** IU/100 ml milk **by law
Bone difference in late adulthood of:
1) retired athlete
2) control
1) 2 hypotheses
- # 1 → larger circumference but thinner (FALSE)
- # 2 → larger circumference & thicker (TRUE)
2) smaller circumference & thinner
