L5: Bone Tissue Pt. 1 Flashcards
is continuously growing, remodeling, and repairing itself. It contributes to homeostasis of the body by providing support and protection, producing blood cells, and storing minerals and triglycerides.
Bone tissue
What type of tissue is bone tissue?
Bone tissue is a complex and dynamic living tissue.
What process does bone tissue continuously engage in?
Bone tissue continuously engages in a process called bone remodeling—the building of new bone tissue and breaking down of old bone tissue.
What was noticed about astronauts when they first returned from space?
It was noticed that they experienced loss of bone mass.
What was learned about the effect of microgravity on bones in space?
It was learned that the microgravity (virtual absence of gravity) of space flight places only minimal strain on bones.
What can result from the minimal strain on bones in space?
This can result in the loss of 1-2% of bone mass per month, especially bones of the pelvis, backbone, and lower limbs.
How do astronauts minimize loss of bone mass?
Astronauts engage in physical exercise using space treadmills, stationary bikes, and devices that simulate weight lifting for two and a half hours a day, six days a week.
How do athletes subject their bones to strain?
Athletes subject their bones to great forces, which place significant strain on the bone tissue.
What is the effect of strain on the bones of accomplished athletes?
Accomplished athletes show an increase in overall bone density.
What is a bone?
A bone is an organ made up of several different tissues working together: bone (osseous) tissue, cartilage, dense connective tissue, epithelium, adipose tissue, blood, and nervous tissue.
What constitutes the skeletal system?
The entire framework of bones and their cartilages.
What is the study of bone structure and the treatment of bone disorders referred to as?
Osteology
What are the 6 basic functions of skeletal system?
Support, protection, assistance in movement, mineral homeostasis (storage and release), blood cell production, and Triglyceride storage.
What does the skeletal system perform?
Several basic functions.
What does the skeleton serve as?
The structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles.
What does the skeleton protect?
The most important internal organs from injury.
What protects the brain?
Cranial cavity bones.
What does the rib cage protect?
The heart and lungs.
What do most skeletal muscles attach to?
Bones.
What happens when skeletal muscles contract?
They pull on bones to produce movement.
What percentage of the weight of the human body does bone tissue make up?
About 18%.
What does bone tissue store?
Several minerals, especially calcium and phosphorus.
What do calcium and phosphorus contribute to?
The strength of bone.
What percentage of the body’s calcium does bone tissue store?
About 99%.
What happens when minerals are needed in the body?
Bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.
What produces red blood cells, white blood cells, and platelets?
A connective tissue called red bone marrow.
What is the process of blood cell production called?
Hemopoiesis (hēm-ō-poy-Ē-sis; hemo- = blood; -poiesis = making).
What does red bone marrow consist of?
Developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers.
Where is red bone marrow present?
In developing bones of the fetus and in some adult bones, such as the hip bones, ribs, sternum (breastbone), vertebrae (backbones), skull, and ends of the bones of the humerus (arm bone) and femur (thigh bone).
What type of bone marrow do newborns have?
All bone marrow is red and is involved in hemopoiesis.
What happens to bone marrow with increasing age?
Much of the bone marrow changes from red to yellow.
What does yellow bone marrow consist mainly of?
Adipose cells.
What do adipose cells store?
Triglycerides.
What are the stored triglycerides?
A potential chemical energy reserve.
How may macroscopic bone structure be analyzed?
By considering the parts of a long bone, such as the humerus (the arm bone).
What is a long bone?
One that has greater length than width.
What does a typical long bone consist of?
The following parts: diaphysis, epiphyses, metaphyses, articular cartilage, periosteum, medullary cavity, and endosteum.
What is the diaphysis?
The long, cylindrical, main portion of the bone.
What is another name for the diaphysis?
The body or shaft.
What are the epiphyses?
The proximal and distal ends of the bone.
What are the metaphyses?
The regions between the diaphysis and the epiphyses.
What does each metaphysis contain in a growing bone?
An epiphyseal (growth) plate.
What is the epiphyseal plate?
A layer of hyaline cartilage that allows the diaphysis of the bone to grow in length.
What happens to the epiphyseal plate when a bone ceases to grow in length?
The cartilage is replaced by bone, forming the epiphyseal line.
What is the epiphyseal line?
The bony structure that results when the epiphyseal plate is replaced by bone.
What is the articular cartilage?
A thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone.
What is the function of articular cartilage?
It reduces friction and absorbs shock at freely movable joints.
Why is the repair of damaged articular cartilage limited?
Because articular cartilage lacks a perichondrium and blood vessels.
What is the periosteum?
A tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage.
What are the two layers of the periosteum?
An outer fibrous layer of dense irregular connective tissue and an inner osteogenic layer that consists of osteoprogenitor cells.
What does the periosteum enable bone to do?
Grow in thickness, but not in length.
What are the functions of the periosteum?
Protects the bone, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons.
How is the periosteum attached to the underlying bone?
By perforating fibers or Sharpey’s fibers.
What are perforating fibers (Sharpey’s fibers)?
Thick bundles of collagen that extend from the periosteum into the bone extracellular matrix.
What is the medullary cavity?
A hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels.
What is another name for the medullary cavity?
The marrow cavity.
What is the function of the medullary cavity?
It minimizes the weight of the bone by reducing the dense bony material where it is least needed.
How does the tubular design of long bones benefit them?
It provides maximum strength with minimum weight.
What is the endosteum?
A thin membrane that lines the medullary cavity and the internal spaces of spongy bone.
What does the endosteum contain?
A single layer of osteoprogenitor cells and a small amount of connective tissue.
The ____ of the epiphyses and metaphyses contains either red bone marrow or yellow bone marrow depending on the bone, and the medullary cavity of the diaphysis contains yellow bone marrow in all bones.
spongy bone tissue
is covered by articular cartilage at the articular surfaces of its proximal and distal epiphyses and by periosteum around all other parts of the bone.
long bone
Functions of Bone tissue
- Supports soft tissue and provides attachment for skeletal muscles. 2. Protects internal organs. 3. Assists in movement, along with skeletal muscles. 4. Stores and releases minerals. 5. Contains red bone marrow, which produces blood cells. 6. Contains yellow bone marrow, which stores triglycerides (fats).
What does bone tissue, or osseous tissue, contain?
An abundant extracellular matrix that surrounds widely separated cells.
What is the extracellular matrix composed of?
15% water, 30% collagen fibers, and 55% crystallized mineral salts.
What is the most abundant mineral salt in bone?
Calcium phosphate [Ca₃(PO₄)₂].
What does calcium phosphate combine with to form crystals of hydroxyapatite?
Calcium hydroxide [Ca(OH)₂].
What is the chemical formula of hydroxyapatite?
Ca₁₀(PO₄)₆(OH)₂.
What other mineral salts and ions combine with hydroxyapatite?
Calcium carbonate (CaCO₃), magnesium, fluoride, potassium, and sulfate.
What happens when mineral salts are deposited in the framework formed by collagen fibers of the extracellular matrix?
They crystallize and the tissue hardens.
What is the process of tissue hardening called?
Calcification.
What cells initiate the process of calcification?
Osteoblasts.
What was once thought about calcification?
That it simply occurred when enough mineral salts were present to form crystals.
What is now known about calcification?
The process requires the presence of collagen fibers.
Where do mineral salts first begin to crystallize?
In the microscopic spaces between collagen fibers.
What happens after the microscopic spaces are filled with mineral salts?
Mineral crystals accumulate around the collagen fibers.
What is responsible for the characteristics of bone?
The combination of crystallized salts and collagen fibers.
What does a bone’s hardness depend on?
The crystallized inorganic mineral salts.
What does a bone’s flexibility depend on?
Its collagen fibers.
What provides tensile strength to bone?
Collagen fibers and other organic molecules.
What happens when a bone is soaked in an acidic solution such as vinegar?
Its mineral salts dissolve, causing the bone to become rubbery and flexible.
What do osteoclasts secrete when the need for particular minerals arises or during bone formation or breakdown?
Enzymes and acids that break down both the mineral salts and the collagen fibers of the extracellular matrix of bone.
What are the four types of cells present in bone tissue?
Osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts.
What are osteoprogenitor cells?
Unspecialized bone stem cells derived from mesenchyme.
From what tissue are osteoprogenitor cells derived?
Mesenchyme, the tissue from which almost all connective tissues are formed.
What is the only type of bone cell that undergoes cell division?
Osteoprogenitor cells.
Into what do osteoprogenitor cells develop?
Osteoblasts.
Where are osteoprogenitor cells found?
Along the inner osteogenic layer of the periosteum, in the endosteum, and in the canals within bone that contain blood vessels.
What are osteoblasts?
Bone-building cells.
What do osteoblasts synthesize and secrete?
Collagen fibers and other organic components needed to build the extracellular matrix of bone tissue.
What is the process of building the extracellular matrix of bone tissue called?
Bone deposition.
What process do osteoblasts initiate?
Calcification.
What happens to osteoblasts when they become trapped in their secretions?
They become osteocytes.
What does the suffix -blast in the name of a bone cell indicate?
That the cell secretes extracellular matrix.
What are osteocytes?
Mature bone cells.
What is the main function of osteocytes?
To maintain daily metabolism, such as the exchange of nutrients and wastes with the blood.
Do osteocytes undergo cell division?
No.
What does the suffix -cyte in the name of a bone cell indicate?
That the cell maintains and monitors the tissue.
What are osteoclasts?
Huge cells derived from the fusion of as many as 50 monocytes.
Where are osteoclasts concentrated?
In the endosteum.
What is the structure on the side of the osteoclast that faces the bone surface?
A ruffled border.
What do osteoclasts release at the ruffled border?
Powerful lysosomal enzymes and acids.
What do lysosomal enzymes and acids released by osteoclasts digest?
The protein and mineral components of the underlying extracellular bone matrix.
What is the breakdown of the bone extracellular matrix called?
Bone resorption.
What is the function of bone resorption?
It is part of the normal development, maintenance, and repair of bone.
How do osteoclasts help regulate blood calcium levels?
In response to certain hormones.
What disease can be treated with drug therapy targeting osteoclasts?
Osteoporosis.
What mnemonic device helps remember the function of osteoblasts and osteoclasts?
OsteoBlasts Build bone, while osteoClasts Carve out bone.
Is bone completely solid?
No.
What do the small spaces in bone serve as?
Channels for blood vessels that supply bone cells with nutrients and storage areas for red bone marrow.
How are bone regions categorized based on the size and distribution of spaces?
Compact bone or spongy bone.
What percentage of the skeleton is compact bone?
0.8
What percentage of the skeleton is spongy bone?
0.2
undergo cell division and develop into osteoblasts, which secrete bone extracellular matrix
Osteoprogenitor cells
functions in bone deposition, the buildup of bone extracellular matrix
Osteoblast
maintains bone tissue
Osteocyte
functions in bone resorption, the breakdown of bone extracellular matrix
Osteoclast
is organized in concentric bone lamellae around an osteonic canal in compact bone and in irregularly arranged bone lamellae in the bone trabeculae in spongy bone.
bone tissue
What type of bone tissue contains few spaces and is the strongest?
Compact (dense) bone tissue.
Where is compact bone tissue found?
Beneath the periosteum of all bones and makes up the bulk of the diaphyses of long bones.
What does compact bone tissue provide?
Protection and support and resists the strains produced by weight and movement.
What is compact bone tissue composed of?
Repeating structural units called osteons, or haversian systems.
What does each osteon consist of?
Concentric bone lamellae arranged around an osteonic (haversian or central) canal.
What do the concentric bone lamellae resemble?
The growth rings of a tree.
What are concentric bone lamellae?
Circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the osteonic canal.
How do the tubelike units of bone generally form?
A series of parallel cylinders that, in long bones, tend to run parallel to the long axis of the bone.
What are the small spaces between the concentric bone lamellae called?
Bone lacunae.
What do bone lacunae contain?
Osteocytes.
What are bone canaliculi?
Tiny channels filled with extracellular fluid that radiate in all directions from the bone lacunae.
What is inside the bone canaliculi?
Slender fingerlike processes of osteocytes.
How do neighboring osteocytes communicate?
Via gap junctions.
What is the function of bone canaliculi?
To connect bone lacunae with one another and with the osteonic canals, forming a system of interconnected canals throughout the bone.
What does the canal system in compact bone provide?
Routes for nutrients and oxygen to reach osteocytes and for the removal of wastes.
How are osteons in compact bone tissue aligned?
In the same direction and parallel to the length of the diaphysis.
What does the alignment of osteons help the diaphysis resist?
Bending or fracturing even when considerable force is applied from either end.
Where is compact bone tissue thickest?
In parts of a bone where strains are applied in relatively few directions.
What causes the lines of strain in a bone to change?
Learning to walk, repeated strenuous physical activity such as weight training, fractures, or physical deformity.
Is the organization of osteons static?
No, it changes over time in response to physical demands placed on the skeleton.
What are interstitial bone lamellae?
Bone lamellae located between neighboring osteons.
What do interstitial bone lamellae contain?
Bone lacunae with osteocytes and bone canaliculi.
What are interstitial bone lamellae fragments of?
Older osteons that have been partially destroyed during bone rebuilding or growth.
What structures allow blood vessels and nerves from the periosteum to penetrate compact bone?
Transverse perforating (Volkmann’s) canals.
What do the vessels and nerves of the perforating canals connect with?
Those of the medullary cavity, periosteum, and osteonic canals.
What are circumferential bone lamellae?
Bone lamellae arranged around the entire outer and inner circumference of the diaphysis of a long bone.
When do circumferential bone lamellae develop?
During initial bone formation.
What are the circumferential bone lamellae directly deep to the periosteum called?
External circumferential bone lamellae.
How are external circumferential bone lamellae connected to the periosteum?
By perforating (Sharpey’s) fibers.
What are the circumferential bone lamellae that line the medullary cavity called?
Internal circumferential bone lamellae.
What is a bone scan?
A diagnostic procedure that takes advantage of the fact that bone is living tissue.
What is injected intravenously during a bone scan?
A small amount of a radioactive tracer compound that is readily absorbed by bone.
What is the degree of uptake of the tracer related to?
The amount of blood flow to the bone.
What does a bone scanner (gamma camera) measure?
The radiation emitted from the bones.
How is the information from a bone scan displayed?
It is translated into a photograph that can be read like an x-ray on a monitor.
How is normal bone tissue identified in a bone scan?
By a consistent gray color throughout because of its uniform uptake of the radioactive tracer.
What do darker or lighter areas on a bone scan indicate?
Bone abnormalities.
What are hot spots?
Areas of increased metabolism that absorb more of the radioactive tracer due to increased blood flow.
What may hot spots indicate?
Bone cancer, abnormal healing of fractures, or abnormal bone growth.
What are cold spots?
Areas of decreased metabolism that absorb less of the radioactive tracer due to decreased blood flow.
What may cold spots indicate?
Degenerative bone disease, decalcified bone, fractures, bone infections, Paget’s disease, and rheumatoid arthritis.
How much sooner does a bone scan detect abnormalities compared to standard x-ray procedures?
3 to 6 months sooner.
What is one advantage of a bone scan over standard x-ray procedures?
It exposes the patient to less radiation.
What is a bone scan the standard test for?
Bone density screening.
Why is bone density screening important?
It is extremely important for screening females for osteoporosis.
What is another name for spongy bone tissue?
Cancellous bone tissue.
What does spongy bone tissue not contain?
Osteons.
Where is spongy bone tissue always located?
In the interior of a bone, protected by a covering of compact bone.
What are the thin columns in spongy bone tissue called?
Bone trabeculae.
What is found between the bone trabeculae?
Spaces that are visible to the unaided eye.
What lines the macroscopic spaces between the bone trabeculae?
Endosteum.
What fills the spaces between the bone trabeculae in bones that produce blood cells?
Red bone marrow.
What fills the spaces between the bone trabeculae in other bones?
Yellow bone marrow (adipose tissue).
What do both types of bone marrow contain?
Numerous small blood vessels that provide nourishment to the osteocytes.
What does each bone trabecula consist of?
Bone lamellae, osteocytes that lie in bone lacunae, and bone canaliculi that radiate outward from the bone lacunae.
What types of bones does spongy bone tissue make up most of the interior of?
Short, flat, sesamoid, and irregularly shaped bones.
In long bones, where does spongy bone form the core?
The epiphyses beneath the paper-thin layer of compact bone.
What does spongy bone form in the diaphysis of long bones?
A variable narrow rim bordering the medullary cavity.
Why is spongy bone always covered by a layer of compact bone?
For protection.
How are the bone trabeculae of spongy bone tissue oriented?
Along lines of strain.
What is the purpose of the orientation of the bone trabeculae?
To help bones resist strains and transfer force without breaking.
Where is spongy bone tissue typically located?
Where bones are not heavily strained or where stresses are applied from many directions.
When do the bone trabeculae achieve their final arrangement?
When locomotion is completely learned.
What can alter the arrangement of the bone trabeculae?
A poorly healed fracture or a deformity.
What are the two ways spongy bone tissue is different from compact bone tissue?
First, spongy bone tissue is light, reducing the overall weight of a bone. Second, the bone trabeculae support and protect the red bone marrow.
Why is the lightness of spongy bone tissue important?
It allows the bone to move more readily when pulled by a skeletal muscle.
What does the bone trabeculae of spongy bone tissue support and protect?
The red bone marrow.
Where is the only site where red bone marrow is stored in adults?
Spongy bone in the hip bones, ribs, sternum (breastbone), vertebrae, skull, and the proximal ends of the humerus and femur.
What process occurs in the red bone marrow of spongy bone?
Hemopoiesis (blood cell production).
What is bone richly supplied with?
Blood.
Where are blood vessels especially abundant in bone?
Portions of bone containing red bone marrow.
Where do blood vessels pass into bones from?
The periosteum.
What are small canals that carry small arteries from the periosteum into the bone called?
Perforating canals (Volkmann’s canals).
What are periosteal arteries?
Small arteries accompanied by nerves that enter the diaphysis through numerous perforating canals.
Where do periosteal arteries enter the osteonic canals?
Near the surface.
What do transverse canals transport from one osteonic canal to the next?
Blood vessels.
Where does a large nutrient artery enter the compact bone?
Near the center of the diaphysis at an oblique angle through a hole called the nutrient foramen.
What does the nutrient artery pass through?
A small canal in the compact bone of the diaphysis called the nutrient canal.
Where does the nutrient canal lead?
To the medullary cavity.
What happens to the nutrient artery after entering the medullary cavity?
It divides into proximal and distal branches that course toward each end of the bone.
What do the branches of the nutrient artery supply?
The inner part of compact bone tissue of the diaphysis, spongy bone tissue, and red and yellow bone marrow as far as the epiphyseal plates (or lines).
How many nutrient arteries do most bones, like the tibia, have?
Only one.
What bone has several nutrient arteries entering the diaphysis?
The femur (thigh bone).
What arteries supply the ends of long bones?
The metaphyseal and epiphyseal arteries.
Where do metaphyseal and epiphyseal arteries arise from?
Arteries that supply the associated joint.
Where do metaphyseal and epiphyseal arteries enter the bone?
Through perforating canals.
What do metaphyseal arteries supply?
The red and yellow bone marrow and spongy bone tissue of the metaphyses.
What do epiphyseal arteries supply?
The red and yellow bone marrow and spongy bone of the epiphyses.
Where are veins that carry blood away from long bones evident?
In three places.
What accompanies the nutrient artery and exits through the diaphysis?
One or two nutrient veins.
What accompanies their respective arteries and exits through the epiphyses and metaphyses?
Numerous epiphyseal veins and metaphyseal veins.
What accompanies their respective arteries and exits through the periosteum?
Many small periosteal veins.
What accompanies the blood vessels that supply bones?
Nerves.
What part of the bone is rich in sensory nerves?
The periosteum.
What sensations do some sensory nerves in the periosteum carry?
Pain sensations.
What explains the severe pain resulting from a fracture or a bone tumor?
Nerves in the periosteum being especially sensitive to tearing or tension.
Why is there some pain associated with a bone marrow needle biopsy?
Because the needle penetrates the periosteum.
What happens once the needle passes through the periosteum during a bone marrow biopsy?
There is little pain.
What is a bone marrow needle biopsy used to examine?
Conditions such as leukemias, metastatic neoplasms, lymphoma, Hodgkin’s disease, and aplastic anemia.
What is the process by which bone forms called?
Ossification or osteogenesis.
In how many principal situations does bone formation occur?
Four.
What is the first principal situation in which bone formation occurs?
The initial formation of bones in an embryo and fetus.
What is the second principal situation in which bone formation occurs?
The growth of bones during infancy, childhood, and adolescence until their adult sizes are reached.
What is the third principal situation in which bone formation occurs?
The remodeling of bone (replacement of old bone by new bone tissue throughout life).
What is the fourth principal situation in which bone formation occurs?
The repair of fractures (breaks in bones) throughout life.
What is the initial composition of the embryonic “skeleton”?
Mesenchyme.
During which week of embryonic development do cartilage formation and ossification occur?
The sixth week.
How many patterns of bone formation are there?
Two.
What do both patterns of bone formation involve?
The replacement of a preexisting connective tissue with bone.
Do the two patterns of bone formation lead to differences in the structure of mature bones?
No.
What is the first type of ossification called?
Intramembranous ossification.
Where does intramembranous ossification occur?
Directly within mesenchyme.
How is mesenchyme arranged in intramembranous ossification?
In sheetlike layers that resemble membranes.
What is the second type of ossification called?
Endochondral ossification.
Where does endochondral ossification occur?
Within hyaline cartilage that develops from mesenchyme.
Which method of bone formation is the simpler of the two?
Intramembranous ossification.
What bones are formed through intramembranous ossification?
The flat bones of the skull, most of the facial bones, mandible (lower jawbone), and the medial part of the clavicle (collar bone).
What helps the fetal skull pass through the birth canal and later hardens through intramembranous ossification?
The “soft spots.”
What is the first step of intramembranous ossification?
Development of the ossification center.
What causes mesenchyme cells to cluster together at the site where bone will develop?
Specific chemical messages.
Into what do mesenchyme cells first differentiate?
Osteoprogenitor cells.
Into what do osteoprogenitor cells further differentiate?
Osteoblasts.
What is the site of a mesenchymal cell cluster called?
Ossification center.
What do osteoblasts secrete until they are surrounded by it?
The organic extracellular matrix of bone.
What is the second step of intramembranous ossification?
Calcification.
What happens when the secretion of extracellular matrix stops?
The cells become osteocytes and lie in bone lacunae.
Where do osteocytes extend their narrow cytoplasmic processes?
Into bone canaliculi that radiate in all directions.
What happens within a few days of osteocytes forming?
Calcium and other mineral salts are deposited, and the extracellular matrix hardens or calcifies.
What is the third step of intramembranous ossification?
Formation of bone trabeculae.
What happens as the bone extracellular matrix forms?
It develops into bone trabeculae that fuse to form spongy bone.
What do connective tissues associated with blood vessels in bone trabeculae differentiate into?
Red bone marrow.
What is the final step of intramembranous ossification?
Development of the periosteum.
What happens to mesenchyme at the periphery of the bone?
It condenses and develops into the periosteum.
What replaces the surface layers of the spongy bone?
A thin layer of compact bone.
What remains in the center of the bone after periosteum development?
Spongy bone.
What happens to much of the newly formed bone?
It is remodeled (destroyed and reformed) into its adult size and shape.
involves the formation of bone within mesenchyme arranged in sheetlike layers that resemble membranes
Intramembranous ossification
bone gradually replaces a cartilage model.
endochondral ossification
What is the replacement of cartilage by bone called?
Endochondral ossification.
In which type of bone is endochondral ossification best observed?
A long bone.
What is the first step of endochondral ossification?
Development of the cartilage model.
What causes mesenchyme cells to crowd together in the shape of the future bone?
Specific chemical messages.
Into what do mesenchyme cells develop at the site where the bone will form?
Chondroblasts.
What do chondroblasts secrete?
Cartilage extracellular matrix.
What does the secretion of cartilage extracellular matrix produce?
A cartilage model consisting of hyaline cartilage.
What is the covering that develops around the cartilage model?
Perichondrium.
What is the second step of endochondral ossification?
Growth of the cartilage model.
What are chondroblasts called once they become deeply buried in the cartilage extracellular matrix?
Chondrocytes.
How does the cartilage model grow in length?
By continual cell division of chondrocytes and further secretion of cartilage extracellular matrix.
What is the type of cartilaginous growth that results in an increase in length?
Interstitial (endogenous) growth.
What is the growth of cartilage in thickness mainly due to?
The deposition of extracellular matrix material on the cartilage surface by new chondroblasts from the perichondrium.
What is the process of cartilage growing at the outer surface called?
Appositional (exogenous) growth.
What happens to chondrocytes in the midregion of the cartilage model as it continues to grow?
They hypertrophy (increase in size).
What happens to the surrounding cartilage extracellular matrix as chondrocytes hypertrophy?
It begins to calcify.
Why do some chondrocytes in the calcifying cartilage die?
Because nutrients can no longer diffuse quickly enough through the extracellular matrix.
What is left behind in the extracellular matrix as chondrocytes die?
Empty spaces.
What is the third step of endochondral ossification?
Development of the primary ossification center.
In which direction does primary ossification proceed?
Inward from the external surface of the bone.
What penetrates the perichondrium and the calcifying cartilage model?
A nutrient artery.
Through what structure does the nutrient artery penetrate the cartilage model?
A nutrient foramen.
What does the penetration of the nutrient artery stimulate?
Osteoprogenitor cells in the perichondrium to differentiate into osteoblasts.
What does the perichondrium become once it starts forming bone?
Periosteum.
What grows into the disintegrating calcified cartilage near the middle of the model?
Periosteal capillaries.
What do periosteal capillaries induce?
Growth of a primary ossification center.
What is a primary ossification center?
A region where bone tissue will replace most of the cartilage.
What do osteoblasts begin to deposit over the remnants of calcified cartilage?
Bone extracellular matrix.
What is formed as osteoblasts deposit bone extracellular matrix?
Spongy bone trabeculae.
In which direction does primary ossification spread?
From the central location toward both ends of the cartilage model.
What is the fourth step of endochondral ossification?
Development of the medullary cavity.
What do osteoclasts break down as the primary ossification center grows?
Some of the newly formed spongy bone trabeculae.
What is the cavity left behind in the diaphysis called?
Medullary cavity.
What eventually replaces most of the wall of the diaphysis?
Compact bone.
What is the fifth step of endochondral ossification?
Development of the secondary ossification centers.
What causes secondary ossification centers to develop?
Branches of the epiphyseal artery entering the epiphyses.
When do secondary ossification centers usually develop?
Around the time of birth or after.
How is bone formation in secondary ossification centers similar to primary ossification centers?
Bone tissue replaces most of the cartilage.
How is bone formation in secondary ossification centers different from primary ossification centers?
Spongy bone remains in the interior of the epiphyses, and no medullary cavities are formed.
In which direction does secondary ossification proceed?
Outward from the center of the epiphysis toward the outer surface of the bone.
What is the sixth step of endochondral ossification?
Formation of articular cartilage and the epiphyseal (growth) plate.
What does the hyaline cartilage covering the epiphyses become?
Articular cartilage.
What remains between the diaphysis and epiphysis prior to adulthood?
Epiphyseal plate.
What is the function of the epiphyseal plate?
It is responsible for the lengthwise growth of long bones.
How do bones grow in thickness during infancy, childhood, and adolescence?
By appositional growth.
How do long bones lengthen during infancy, childhood, and adolescence?
By the addition of bone material on the diaphyseal side of the epiphyseal plate by interstitial growth.
What are the two major events involved in the growth in length of long bones?
(1) Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate and (2) replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification.
What is the epiphyseal plate also known as?
Epiphyseal cartilage.
What is the epiphyseal plate composed of?
A layer of hyaline cartilage in the metaphysis of a growing bone.
How many zones does the epiphyseal plate consist of?
Four zones.
What is the first zone of the epiphyseal plate?
Zone of resting cartilage.
Where is the zone of resting cartilage located?
Nearest the epiphysis.
What does the zone of resting cartilage consist of?
Small, scattered chondrocytes.
Why is it called the “resting” zone?
Because the cells do not function in bone growth in length.
What is the function of the zone of resting cartilage?
To anchor the epiphyseal plate to the epiphysis of the bone.
What is the second zone of the epiphyseal plate?
Zone of proliferating cartilage.
How are chondrocytes arranged in the zone of proliferating cartilage?
Like stacks of coins.
What process occurs in the zone of proliferating cartilage?
Chondrocytes undergo interstitial growth as they divide and secrete extracellular matrix.
What happens to chondrocytes in the zone of proliferating cartilage?
They divide to replace those that die at the diaphyseal side of the epiphyseal plate.
What is the third zone of the epiphyseal plate?
Zone of hypertrophic cartilage.
What does the zone of hypertrophic cartilage consist of?
Large, maturing chondrocytes arranged in columns.
What is the fourth zone of the epiphyseal plate?
Zone of calcified cartilage.
How thick is the zone of calcified cartilage?
Only a few cells thick.
What does the zone of calcified cartilage mostly consist of?
Chondrocytes that are dead because the extracellular matrix around them has calcified.
What do osteoclasts do in the zone of calcified cartilage?
Dissolve the calcified cartilage.
What do osteoblasts and capillaries do in the zone of calcified cartilage?
Invade the area and lay down bone extracellular matrix.
What process replaces calcified cartilage with bone?
Endochondral ossification.
What does the zone of calcified cartilage become after endochondral ossification?
The “new diaphysis” that is firmly cemented to the rest of the diaphysis.
What is the only way that the diaphysis can increase in length?
The activity of the epiphyseal plate.
How do chondrocytes contribute to bone growth?
They proliferate on the epiphyseal side of the plate and replace older ones that are destroyed by calcification.
What happens to the cartilage on the diaphyseal side of the plate?
It is replaced by bone.
Why does the thickness of the epiphyseal plate remain relatively constant?
Because new chondrocytes replace older ones at the same rate that bone replaces cartilage.
What happens if a bone fracture damages the epiphyseal plate?
The fractured bone may be shorter than normal once adult stature is reached.
Why does damage to the epiphyseal plate cause shorter bone growth?
Because damage to avascular cartilage accelerates closure of the epiphyseal plate, inhibiting lengthwise growth.
When does the epiphyseal plate close in females?
At about age 18.
When does the epiphyseal plate close in males?
At about age 21.
What happens when the epiphyseal plate closes?
The epiphyseal cartilage cells stop dividing and bone replaces all remaining cartilage.
What structure remains after the epiphyseal plate closes?
The epiphyseal line.
What does the appearance of the epiphyseal line indicate?
That bone growth in length has stopped completely.
Why is the closure of the epiphyseal plate useful?
It helps determine bone age, predict adult height, and establish age at death from skeletal remains.
What does an open epiphyseal plate indicate?
A younger person.
What does a partially closed or completely closed epiphyseal plate indicate?
An older person.
How does the timing of epiphyseal plate closure differ between males and females?
It takes place 1–2 years earlier in females.
