A&P - Ch. 6 - Bones & Skeletal Tissue - Pt. 2 (2023)

(4 major steps in formation of Skeleton, following the 5 initial steps of Ossification) Step 1

1. Ossification centers are formed when mesenchymal cells cluster and become osteoblast

What are Bisphosphonates?

A drug used to counter-at Osteoporosis by decreasing osteoclast activity and number

Bones increase thickness by ________ growth

Appositional growth

4. Bone Remodeling

Begins during bony callus formation and continues for several months, excess material on diaphysis exterior & w/in medullary cavity is removed

Compression Fracture

bone is crushed; common in porous bones (osteoporotic bones)

What is a direct effect of the Parathyroid hormone?

Calcium is released into blood, raining calcium levels and ceases when homeostatic calcium levels are reached

Leptin

Hormone released by adipose tissue; may play a role in bone density regulation by inhibiting osteoblasts

Intestinal absorption of Ca+ requires what vitamin?

Vitamin D

Rickets

Vitamin D deficiency or insufficient dietary calcium Bowed legs

3. Boney callus formation

W/in one week, new trabeculae appear in fibrocartilaginous callus Callus converts to bony (hard) callus of spongy bone

Wolf's Law

states that bones grow or remodel in response to demands placed on them

What are 2 treatments for Paget's Disease?

Calcitonin & Bisphosphonates

Serotonin

(Hormone) Neurotransmitter regulates mood & sleep, interferes w/ osteoblast activity

Fractures can be classified by what main 3 characteristics?

(Main 3 Classifications) Position of bone ends after fracture, completeness of break, skin penetration

Stress tends to be off center, so bone....

..so bones tend to bend

What percent of 1200-1400 gms of calcium is found in bone?

99%

Bone deposit and bone resorption occurs where?

At surfaces of both periosteum and endosteum

Endochondral Ossification begins where?

At the "Primary Ossification Center"

In step 3 of the ossification process, the Periosteal bud is made up of what?

Blood vessels, nerves, red marrow, osteogenic cells and osteoclasts

Greenstick Fracture

Bone breaks incompletely, much in the way green twigs break, only one side of the shaft breaks, the other side bends

Bone remodeling consists of what two occurrences

Bone deposit Bone resorption

Intramembranous Ossification

Bone develops from fibrous membrane

Compact bone is replaced how often

Every 10 years

At what ages does bone lengthening cease in men and women?

Females - aprx. 18 yrs Males - aprx. 21 yrs

What occurs in the "Fibrocartilaginous callus" stage of fracture repair?

Fibroblasts, cartilage and osteogenic cells begin reconstruction of bone Cartilage matrix of repair tissue formed & Osteoblasts form spongy bone w/in matrix

Hypercalcemia

High levels of calcium cause nonresponsiveness

Endochondral Ossification grows from what type of cartilage?

Hyaline Cartilage

Where is most Serotonin produced?

In the gut

Bones formed by "Intramembranous Ossification" are called what?

Membrane Bones

Mesenchymal cells in the Primary Ossification center specialize into what type of cell

Osteoblasts

What is Calcitonin?

Produced by parafollicular cells of thyroid gland in response to high levels of blood calcium levels

Osteomalacia

Soft weak bone, pain upon bearing weight Bones are poorly mineralized. Osteoid is produced, but calcium salts not adequately deposited

What happens to the Spicules once left behind by chondrocyte deterioration in the Ossification Zone?

Spicules are then eroded by osteoclasts and are covered with new bone by osteoblasts

The spicules of the Ossification Zone are ultimately replaces by what?

Spongy Bone

Spongy bone of which bones are most susceptible to Osteoporosis?

Spongy bone of spinal bone, neck and femur

Mesenchymal cells

Stem cells

Bending compresses on one side of the bone causes what on another side of the bone

Stretches the other side of the bone

What cavity enlarges as spicules are eroded away in the Ossification Zone?

The Medullary Cavity

Under what conditions will the Parathyroid gland release PTH?

When calcium levels in blood is falling too low

Epiphyseal plate closure occurs when?

When the epiphysis and diaphysis fuse

Osteoclasts also phagocytize what other two things?

Demineralized matrix and dead osteocytes

__________ is thickest where bending stresses are greatest

Diaphysis

Postnatal bone growth occurs until what stage in life?

Early adulthood

Describe the effects of Calcitonin

Effects are negligible, but at high pharmacological doses it can lower blood calcium levels temporarily

What is required to be present in the epiphyseal plate in order for Interstitial growth to occur?

Epiphyseal Cartilage

Epiphyseal Fracture

Epiphysis separate from the diaphysis along the epiphyseal plate

Paget's Disease

Excessive and haphazard bone deposit and resorption cause bone to be made fast and poorly High ratio of spongy bone to compact bone

What occurs on bone where heavy, active muscles attach

Large, bony projections

Endochondral Ossification begins when in life?

Late in the second month of development

List 2 other hormones that play a role in bone density nd turnover?

Leptin Serotonin

Bone remodeling and repair occurs until what stage in life?

Lifelong

Where is the "Primary Ossification Center" located?

Located in the center of the shaft

What are another 3 characteristics of fractures that can determine classification?

Location of fracture, external appearance & nature of break

Hypocalcemia

Low levels of calcium causes hyperexcitability

Serotonin may inhibit what after a meal?

May inhibit bone turnover after a meal. So bone calcium is locked in when calcium is flooding into the bloodstream

Remodeling occurs continuously but is regulated by what genetic factors and control loops *** Might take this one out***

Hormone controls Response to mechanical stress

Hypertrophic Zone

- Area with older chondrocytes closer to the diaphysis - Cartilage lacunae enlarge and erode, forming interconnecting spaces

List 2 illnesses related to neuromuscular problems caused by changes in Calcium levels

- Hypocalcemia - Hypercalcemia

Trigger for bone deposit is not confirmed but may include what 4 factors for trigger?

- Mechanical signals -Increased concentration of calcium and phosphate ions for hydroxyapatite formation - Matrix proteins that bind and concentrate calcium - Appropriate amount of enzyme alkaline phosphates for mineralization

List 5 examples of important functions that calcium plays a role in

- Nerve transition - Muscle Contraction - Blood coagulation - Gland & nerve secretions - Cell division

List 3 major bone Diseases

- Osteomalacia & Rickets - Osteoporosis - Paget's Disease

List the 5 steps in the process of Ossification

1. Bone collar forms around diaphysis of cartilage model 2. Central cartilage in diaphysis calcifies, then develops cavities 3. Periosteal bud invades cavities, leading to formation of spongy bone 4. Diaphysis elongated, and medullary cavity forms 5. Epiphysis ossify

List the 4 major steps of Bone Repair

1. Hematoma formation 2. Fibrocartilaginous callus formation 3. Bony callus formation 4. Bone remodeling

List 4 major steps in formation of Skeleton, following the 5 initial steps of Ossification

1. Ossification centers are formed when mesenchymal cells cluster and become osteoblast 2. Osteoid is secreted, then calcified 3. Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae 4. Lamellar bone replaces woven bone, and red marrow appears

(5 Zones of the Epiphyseal Plate) Zone 1

1. Resting (Quiescent) Zone

(Repeat) List the 5 Zones of the Epiphyseal Plate

1. Resting (Quiescent) Zone 2. Proliferation (Growth) Zone 3. Hypertrophic Zone 4. Calcification Zone 5. Ossification (Osteogenic) Zone

List he 5 Zones of the Epiphyseal Plate

1. Resting (Quiescent) Zone 2. Proliferation (Growth) Zone 3. Hypertrophic Zone 4. Calcification Zone 5. Ossification (Osteogenic) Zone

In development, when does the formation of bone begin?

2 months after birth

(4 major steps in formation of Skeleton, following the 5 initial steps of Ossification) Step 2

2. Osteoid is secreted, then calcified

(5 Zones of the Epiphyseal Plate) Zone 2

2. Proliferation (Growth) Zone

Spongy bone is replaces how often

3 to 4 years

(5 Zones of the Epiphyseal Plate) Zone 3

3. Hypertrophic Zone

(4 major steps in formation of Skeleton, following the 5 initial steps of Ossification) Step 3

3. Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae

(5 Zones of the Epiphyseal Plate) Zone 4

4. Calcification Zone

(4 major steps in formation of Skeleton, following the 5 initial steps of Ossification) Step 4

4. Lamellar bone replaces woven bone, and red marrow appears

Aprx __ to __% of bone mass is recycled each week

5 to 7%

(5 Zones of the Epiphyseal Plate) Zone 5

5. Ossification (Osteogenic) Zone

Osteoporosis

A group of diseases in which bone resorption exceeds deposits Matrix remains normal, but bone mass declines

Excess or deficiencies of any hormones can do what to the skeleton?

Abnormal skeletal growth

Calcification Front

Abrupt transition zone between osteoid seam and older mineralized bone

Bones stop growing during what stage in life ?

Adolescence

Testosterone and estrogens at puberty promote what?

Adolescent growth spurts

What is Denosumab?

An anti-biotic used to counter-act osteoporosis that's shown to reduce fractures in men w/ prostate cancer which then improves bone density in elderly

(5 Zones of the Epiphyseal Plate) Proliferation (Growth) Zone

Area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing

(5 Zones of the Epiphyseal Plate) Resting (Quiescent) Zone

Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive

Osteoid Seam

Band of unmineralized bone matrix that marks area of new matrix

Bone can be hollow because of why?

Because compression and tension cancel each other out in the center of the bone

Endochondral Ossification

Bone forms by replacing hyaline cartilage

Comminuted Fracture

Bone fragments into 3 or more pieces Common in the aged

Depression Fracture

Broken bone portion is pressed inward

Most long bones begin ossifying by when in Embryonic development?

By 8 weeks

What are treatments for Osteoporosis?

Calcium, Vit. D supplements, weight bearing exercise, hormone replacement therapy

Sustained high blood levels of calcium can result in what occurring in the body

Can lead to deposits of calcium salts in blood vessels and formation of kidney stones

2. Fibrouscartilaginous callus formation

Capillaries grow into hematoma; phagocytic cells clear debris; fibroblasts secrete collagen fibers to span break and connect broken ends

Bones that were formed by the ossification of hyaline cartilage are called what type of bone?

Cartilage (Endochondral) Bones

Which characteristic of cartilage enhances its job as the precursor to endochondral bone?

Cartilage can accommodate mitosis

Ossification Zone

Chondrocytes deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction

List and define the 2 types of Reduction treatment

Closed Reduction - Physician manipulates to correct position Open Reduction - Surgical pins or wires secure ends

What type of bone is laid down to reconstruct shaft walls during the 4th step of Fracture repair, "Bone Remodeling"?

Compact Bone

List and define the two categories for "Completeness of break" fracture classification

Complete - Broken all the way through Incomplete - Not broken all the way through

List and define the two categories for "Whether skin is penetrated" fracture classification

Compound (Open) - skin is penetrated Simple (Closed) - Skin is not penetrated

In regards to canaliculi, what may stimulate bone remodeling?

Compression/tension changes fluid flows in canaliculi which may stimulate remodeling

What is the negative feedback loop in regards to Hormonal Control with bone remodeling?

Controls blood Ca+ levels

Intramembranous ossification begins within what tissue formed by mesenchymal cells?

Fibrous connective tissue membranes

How long does the boney callus formation continue for?

For about 2 months

Which hormone is most important in stimulating epiphyseal plate activity in infancy and childhood?

Growth hormone

At what step does the "Secondary Ossification Center" appear in the Ossification process, and where?

In step 4 In the Epiphyses

In the 5th and final step of the ossification process, the ossification of the Epiphyses, Hyaline cartilage only remains in what two areas of the bone?

In the Epiphyseal plate & articular cartilages

Bones thicken in response to what?

Increase stress from muscle activity or added weight

Endochondral bones essentially form all bones inferior to the ______ __ ___ _____, with the exception of which bones?

Inferior to the base of the skull, with the exception of the clavicles

Long bones grow (longer) lengthwise by _____________ (longitudinal) growth of the epiphyseal plate

Interstitial growth

Serotonin is secreted where after a meal?

Into the blood stream

What does the thyroid hormone do for the growth hormone?

Modulates activity of growth hormone, ensuring proper proportions

Intramembranous ossification forms which bones?

Most bones of the skull (Frontal, parietal, occipital, temporal and clavicle bones)

Endochondral bones form how much of the human skeleton?

Most of the skeletaon

New cells formed in the "Proliferation (Growth) Zone" move and do what?

Move upward, pushing epiphysis away from diaphysis, causing lengthening

At what stage in life do chondroblasts divide less often?

Near the end of Adolescence

Define Bone Deposit

New bone matrix is deposited by Osteoblasts

How does growth in long bones occur? (Hint: Proliferation Zone of Epiphyseal Line, Cartilage)

New cells formed in the Proliferation Zone which is located on the diaphysis side of the epiphyseal plate and rapidly divide. They move upward, pushing epiphysis away from diaphysis, causing lengthening

List and define the two categories for "Position of bone ends after fracture" classification

Nondisplaced - bone ends retain normal position Displaced - Bone ends are out of normal alignment

Bone with occurs by what cell doing what where?

Osteoblasts beneath periosteum secrete bone matrix on external bone

How does bone widening occur? List cells involved, where they are and what they are doing.

Osteoblasts beneath periosteum secrete bone matrix on external bone to grow width while Osteoclasts remove bone on endosteal surface

Bone Resorption is the function of which bone cell type?

Osteoclasts

Parathyroid hormone stimulates which bone cell?

Osteoclasts (to resorb bone)

Osteoclast activation involves ______ _____ and _______ _ ____ ______

PTH (Parathyroid Hormone) Immune T Cell Proteins

Remodeling units

Packets of adjacent osteoblasts and osteoclasts coordinated remodeling process

Calcitonin is produced by what gland?

Parafollicular cells of thyroid gland

List 2 important hormones involved in bone remodeling

Parathyroid Hormone (PTH) & Calcitonin

Blood vessels of the Primary Ossification Center infiltrate the ______________, converting it into _________.

Perichondrium Periosteum

The outer layer of woven bone in step 3 becomes the what?

Periosteum

Parathyroid Hormone (PHT)

Produced by parathyroid glands in response to low blood calcium levels

Mechanical stress causes remodeling by producing what and when?

Producing electrical signals when bone is deformed

Spiral Fracture

Ragged break occurs when excessive twisting forces are applied to a bone Common in sport fractures

Calcification Zone

Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate

Ossification (Osteogenesis)

The process of bone tissue formation

Reduction

The realignment of broken bone ends, fracture treatment and repair

How do Osteoclasts break down (digest) bone matrix for resorption

They secrete lysosomal enzymes & protons (H+) that digest matrix and convert calcium salts to soluble forms

Curved bones are thickest where?

Where most likely to buckle

Define Hematoma

Torn blood vessels hemorrhage forming a mass of clotted blood

1. Hematoma formation

Torn blood vessels hemorrhage, forming mass of clotted blood Site is swollen, painful and inflamed

Fractures in youth typically result from What? In old age they result from what?

Trauma Weakened old bones

True/False Bones of fetus and bedridden people are featureless because of lack of stress on bones

True

True/False During Endochondral Ossification, the prior Hyaline cartilage required to be broken down prior to ossification.

True

True/False Fractures are breaks

True

True/False Some facial bones continue to grow slowly throughout life

True

Trabeculae form what along lines of stress?

Trusses

Trusses

a framework, typically consisting of rafters, posts, and struts, supporting a roof, bridge, or other structure.

Up to about week _#_, fibrous membranes and hyaline cartilage of fetal skeleton are replaced with bone tissue

week 8

Hormone controls determine ________ & ________ remodeling occurs in response to changing ________ _____ _____, but mechanical stress determine ________ it occurs

whether & when blood calcium levels Where