The Skeletal System
reduction (of fracture)
-Realignment of Broken Ends of Bone into Normal Anatomical Position -Closed: Bone Set Without Surgery -Open: Surgery Needed to Set Bone(s)
Describe the zones in which chondrocytes are organized within the epiphyseal plate.
1. Proliferation zone: Cartilage cells undergo mitosis. 2. Hypertrophic cells: Older cartilage cells enlarge. 3. Calcification zone: Matrix calcifies, cartilage cells die, matrix begins deteriorating, blood vessels invade the cavity. 4. Ossification zone: New bone formed. Calcified spicules invaded by marrow elements from the medullary cavity. Spicules eroded by osteoclasts and covered quickly by osteoblasts with ne bone.
How does aging affect the skeleton? At what age, approximately, do the bones of the body typically achieve their greatest density?
18 for women 20 for men Aging results in a decreased production of collagen fibers, loss of Ca, more porous bones.
hypercalcemia
A condition characterized by an abnormally low concentration of calcium in the blood.
alkaline phosphate
A non-specific marker of metabolic activity in bone tissue, levels are increased with fractures and metabolic bone disease
What factors can affect bone growth , repair and remodeling?
A number of factors influence bone development, growth, and repair. These include nutrition, exposure to sunlight, hormonal secretions, and physical exercise. For example, vitamin D is necessary for proper absorption of calcium in the small intestine.
hypocalcemia
Abnormally high concentrations of calcium circulating in the blood instead of being stored in the bones
How does vitamin D influence bone structure?
Activated vitamin D is a hormone which is essential for adequate calcium absorption. Deficiency of vitamin D causes bones to be poorly mineralized. In children, vitamin D deficiency can result it rickets while in adults it may result in osteomalacia.
Identify normal growth rates by age.
Average Newborn- 20" Growth in First Year- l0" Growth in Second Year- 5" Growth Each Year From Age Two until Puberty- 2 1/2"
What tissues make up the embryonic skeleton before the 6th week of development?
Before the 6th week of development, the embryonic skeleton is constructed entirely from from fibrous membranes and mesenchyme cells.
What is/are the function(s) of bone remodeling?
Bone remodeling is a concurrent process of bone deposit and bone resorption. It serves as a mechanism for bone renewal and healing and is an important mechanism underlying calcium homeostasis.
What is the function of calcitonin? What are the target sites for the action of this hormone
Calcitonin, at abnormally high pharmacological doses, lowers blood calcium levels temporarily. decreases Ca level. It inhibits osteoclasts, enhances mineralization of bone matrix and increases rate of Ca excretion by kidneys.
Describe the location and function of the perforating canals.
Canals of a second type called perforating canals, or Volkmann's canals, lie at right angles to the long axis of the bone and connect the blood and nerve supply of the medullary canal to the central canals.
Describe the general characteristics of cartilage, paying attention to the location of perichondrium, blood vessels & nerves, and chondrocytes as well as the general composition of the extracellular matrix.
Cartilage primary consists of water, which accounts for its resilience. Cartilage, containing no nerves or blood vessels, is surrounded by a layer of dense irregular tissue, the perichondrium. The perichondrium acts like a girdle to resist outward expansion when the cartilage is compressed. The perichondrium contains the blood vessels from which nutrients diffuse through the matrix to reach the cartilage cells internally. Cartilage contains cells called chondrocytes, encased in small cavities (lacunae) within an extracellular matrix containing a jelly like ground substance and fibers.
What is the general function of spongy bone? of compact bone?
Compact bone is the external dense outer layer that looks smooth to the naked eye that is very important for support and structure. Spongy bone is a honeycomb of small needle-like or flat pieces of trabeculae, important for the production of red blood cells.
Compare and contrast the microscopic structure of compact and spongy bone.
Compact bone: Central canal w/ arter, vein, and nerve fibers, surrounded by layers of lamellae with collagen fibers running in different connections, contains osteocytes in lacunae Spongy bone: honeycomb of small needle like or flat pieces called trabeculae filled with red or yellow bone marrow
metaphysis
Contains the growth portion of the bone and are located where the diaphysis and epiphysis converge. Depending on the bone's age it can contain the Epiphyseal plate or epiphyseal line.
avasuclar
Describes any tissue that does not have a direct blood supply
Describe the general structure of a long bone.
Diaphysis-tubular diaphysis forms axis of the bone, constructed of thick collar of compact bone that surrounds a medullary cavity Epiphyses- bone ends, outer shell is compact bone and interior contains spongy bone, thin layer of articular cartilage covers the joint surface of each epiphysis Epiphyseal line- divides diaphysis and epiphysis Membranes: periosteum covers external surface everywhere except joints-made of dense irregular connective tissue, inner osteogenic layer made of osteogenic cells Nutrient foramen: provides nerve fibers and blood vessels to periosteum Sharpey's fibers: tufts of collagen fibers extend from fibrous layers into bone matrix-secure periosteum to underlying bone Endosteum: delicate connective tissue membrane covers internal bone surfaces
What happens to bones during prolonged period of inactivity? Why do athletes have stronger bones than sedentary people?
During prolonged periods of inactivity, bones weaken. Reduced mechanical stress, leads to reduced osteoblast activity, which has a net loss of bone mass. Increased mechanical stress stimulates osteoblasts and results in increased bone production.
periosteal bud
Elements (blood vessels, lymphatics, nerve fibres, red marrow elements, osteoblasts, and osteoclasts) which invade the cavities during endochondral ossification
Describe the process of endochondral ossification.
Except for clavicles, essentially all bones below the base of the skull form by endochondral ossification. Beginning late in the second month of development, this process uses hyaline cartilage bones formed earlier as models or patterns for bone construction. The formation of a long bone begins in the center of the hyaline cartilage shaft called the primary ossification center. Blood vessels infiltrate the perichondrium covering the hyaline cartilage causing underlying mesenchymal cells to specialize to osteoblasts. The four steps are as follows: 1) A bone collar forms around the diaphysis of the hyaline cartilage model. 2) Cartilage in the center of the diaphysis calcifies and then develops cavities. 3) In month 3, the periosteal bud (collection of elements containing nutrient artery and vein, nerve fibers red marrow elements, osteogenic cells, and osteoclasts) invades the internal cavities and spongy bone forms. 4) The diaphysis elongates and the medullary cavity forms. 5) The epiphyses ossify. Bone trabeculae appear, just as they did earlier in the primary ossification center.
Describe the best practices for measuring growth in children 2 and under, of age versus best practices for children 3 years of age and older.
For children younger than 2 years, two people are needed to measure body length. Place the child supine on a length board, as shown. Direct measurement of the infant using a tape measure or drawing on the paper on an examination table is inaccurate. For children 3 years of age and older,measure height, using a height board (sometimes called a stadiometer) mounted at a right angle between a level floor and against a straight, vertical surface such as a wall or pillar.
Name and describe the process by which long bones grow in thickness/diameter.
Growing bones widen as they lengthen. As with cartilages, bones increase in thickness or, in the case of long bones, diameter, by appositional growth. Osteoblasts beneath the periosteum secrete bone matrix on the external bone surface as osteoclasts on the endosteal surface of the diaphysis remove bone.
Compare and contrast the three types of skeletal cartilage. Thinking about where each type of cartilage is located in the body, describe how the structure of each type supports its function.
HYALINE: looks like frosted glass, provides support with flexibility and resilience, most abundant, spherical chondrocytes with only fine collagen fibers, types include: articular (cover ends of movable joints), costal (connect ribs to sternum), respiratory, and nasal ELASTIC: resemble hyaline cartilages but contain more stretchy elastic fibers, better able to stand up to bending, found only in external ear and epiglottis FIBROCARTILAGE: highly compressible w/ great tensile strength, roughly parallel rows of chondrocytes alternating with think collagen fibers, occur in sites subject to pressure and stretch (ex. knee, vertebrae)
In what part of bone does blood cell production occur?
Hemaptopoiesis, blood cell formation, occurs in the red marrow cavities of certain bones.
Which bones are sites of red blood cells production in children? In adults?
In children (infants), the site of red cell production is the medullary cavity of the diaphysis and all areas of spongy bone. In most adults, blood cell production occurs only in the heads of the femur and humerus.
Compare and contrast intramembranous and endchondral ossification.
In endochondral ossification, a bone develops by replacing hyaline cartilage. the resealing bone is called a cartilage, or endochondral bone. In intramembranous ossification, a bone develops from fibrous membrane and the bone is called a membrane bone.
Describe the process of intramembranous ossification.
In intramembranous ossification, a bone develops from fibrous membrane and the bone is called a membrane bone. Intramembranous ossification forms the cranial bones of the skull and the clavicles. Most bones formed by this process are flat bones. At abut week 8 of development, ossification begins within fibrous connective tissue membranes formed by mesenchymal cells. This process involves four major steps: 1) Ossification centers appear in the fibrous connective tissue membrane. 2) Osteoid is secreted within the fibrous membrane and calcifies. 3) Woven bone and periosteum form. 4) Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears.
Name, describe, and give an example of each of the four categories of bone, classified by shape.
LONG BONES: considerably longer than they are wide, shaft plus two often expanded ends,parts include diaphysis (shaft), epiphyses (ends), membranes, and nutrient foramen ex. limb bones SHORT BONES: roughly cube shaped, sesamoid bones are special type formed in a tendon, ex. wrist and ankle bones FLAT BONES: thin, flattened, usually a bit curved, ex. sternum IRREGULAR BONES: complicated shapes that fit none of preceding classes
What is the significance of the epiphyseal plate closure?
Longitudinal bone growth ends when the bone of the epiphysis and diaphysis fuses, called epiphyseal plate closure. This process happens at about 18 years of age in females and 21 years of age in males.
How do long bones grow in length?
Longitudinal bone growth mimics many of the events of endochondral ossification and depends on the presence of epiphyseal cartilage.
Identify and describe the four types of cells that form and maintain bone tissue.
OSTEOGENIC CELLS: (aka osteoprogenitor cells)-mitotically active stem cells found in the membranous periosteum and endosteum, flat/squamous cells in growing bones, when stimulated differentiate into osteoblasts or bone lining cells OSTEOBLASTS: bone forming cells that secrete the bone matrix. They are actively mitotic. Secrete unmineralized bone matrix including collagen and osteoid. They play a role in matrix calcification. Active=cube shaped, inactive=flattened, become osteocytes when surrounded by the matrix OSTEOCYTES: Mature bone cells that occupy lacunae that conform to their shape. They monitor and maintain the bone matrix. Act as stress or strain "sensors" and respond to mechanical stimuli-communicate to osteoblasts and osteoclasts. BONE LINING CELLS: flat cells found on bone surfaces, help maintain matrix, periosteal (outer lining) or endosteal (inner lining OSTEOCLASTS: giant multinucleate cells located at sites of bone reabsorption, rest in reabsorption bay and exhibit ruffled border
What are the anatomical landmarks for correctly measuring head circumference in children up to 3 years old?
Occipital and supraorbital ridges
In which zone of the epiphyseal plate does ossification occur? Which zone exhibits a high rate of chondrocyte cell division?
Ossification occurs in the ossification zone. A high rate of chondrocyte cell division occurs in the proliferation zone.
What cells secrete osteoid?
Osteoblasts secrete osteoid.
Describe the cellular structure of osteoclasts. What is the function of these cells?
Osteoclasts are giant multinucleate cells located at sites of bone resorption. When actively resorbing bone, the osteoclasts rest in a shallow depression called a resorption bay and exhibit a distinctive ruffled border that directly contacts the bone. The deep plasma membrane inholdings of the ruffled border tremendously increase the surface area for the enzymatically degrading the bones and seal off that area from the surrounding matrix. Osteoclasts accomplish bone resorption.
How do osteoclasts break down bone matrix?
Osteoclasts move along a bone surface, digging depressions or grooves as they break down the bone matrix. The ruffled border of the osteoclast clings tightly to the bone, sealing off the area of bone destruction and secreting protons and lysosomal enzymes that digest the organic matrix. The resulting acidic brew in the resorption bay converts the calcium salts into soluble forms that pass easily into solution. Osteoclasts may also phagocytize the demineralized matrix and dead osteocytes, passing them at the opposite side.
Which of the above materials (#10 and #11) are primarily responsible for the tensile strength of the bone? for the compression strength of the bone? Which of these materials makes the bone hard and heavy?
Osteoid is responsible is responsible for the bones tensile strength that allows it to resist stretch and twisting. Bone resilience for the compression strength of the bone comes from sacrificial bonds in or between collagen molecules. Hydroxyapatites, or mineral salts are responsible for making the bone hard and heavy.
Name the organic portion of bone matrix.
Osteoid is the organic part of the bone matrix. Osteoid, which makes up approximately 1/3 of the matrix, includes ground substance (composed of proteoglycans and glycoproteins), and collagen fibers, both of which are secreted by osteoblasts.
What is the most important hormone regulating blood calcium levels and calcium storage in adults?
Parathyroid hormone (PTH) is the most important hormone regulating calcium levels and calcium storage in adults.
Identify the primary hormones that regulate bone growth and development. What is the general function of each of the hormones identified?
Paratyroid Hormone (PTH)-produced by the parathyroid glands, increased PTH levels stimulates osteoclasts to reabsorb bone, releasing calcium into the blood. Calcitonin-appears to be a hormone in search of function because effects on calcium homeostasis are negligible. When administered at pharmacological doses, it lowers blood calcium temporarily. Leptin- released by adipose tissue, plays a role in regulating bone density Serotonin- neurotransmitter that regulates mood and sleep, also produced in the gut
What is the function of Sharpeys fibers?
Perforating Sharpey's fibers-tufts of collagen fibers that extend from its fibrous layer into the bone matrix-secure the periosteum to the underlying bone.
Describe the structure and function(s) of the periosteum
Periosteum is a glistening, white, double layered membrane that covers the external surface of the bone except the joint surfaces. The outer fibrous layer of the periosteum is dense irregular connective tissue. The inner osteogenic layer, next to the bone surface, consists primarily of primitive stem cells called osteogenic cells that give rise to all bone cells except bone destroying cells. The periosteum also provides anchoring points for tendons and ligaments.
What are the differences between red and yellow marrow?
Red marrow, also known as hematopoietic tissue, is found within the trabecular cavities of spongy bone of long bones and in the the diploe of flat bones. The red marrow is much more active in hematopoiesis. Yellow marrow is fat. Yellow marrow in the medullary cavity can revert to red marrow if a person becomes very anemic.
rickets
Rickets is a disorder caused by a lack of vitamin D, calcium, or phosphate. It leads to softening and weakening of the bones.
What is the impact on the skeleton of rising levels of sex hormones at puberty?
Rising levels of sex hormones at puberty initially promote the growth spurt of a typical adolescent, as well as masculinization or feminization of specific parts of the skeleton. Later the hormones induce epiphyseal closure, ending longitudinal bone growth.
Describe the location and function of central canals.
Running through the core of each osteon is a central canal, or Haversian canal containing small blood vessels and nerve fibers that serve the osteon's cells.
Describe the medullary cavity (i.e. where is it located? what structures are found there?)
Th medullary cavity is a "middle" marrow cavity found at the center of the diaphysis. In adults, the medullary cavity contains fat (yellow arrow) and is called the yellow marrow cavity.
What bones make up the appendicular skeleton? How many bones are included in the appendicular skeleton?
The appendicular skeleton is structured from 126 bones and is composed of the upper and lower limbs, the pectoral girdle, and the pelvic girdle.
What bones make up the axial skeleton? How many bones are included in the axial skeleton?
The axial skeleton is structures from 80 bones segregated into three major regions; skull, vertebral column, and the thoracic cage.
epiphyseal line
The cartilage present at the junction of the diaphysis and epiphyses; a remnant of the epiphyseal plate.
What complementary processes are involved in bone remodeling?
The complementary processes involved in bone processing are bone depositing and bone resorption.
What type of bone makes up the diaphysis?
The diaphysis is constructed of a relatively thick collar of compact bone. It is surrounded by a double layered membrane called the periosteum made of of an outer fibrous layer (dense irregular connective tissue) and inner osteogenic layer.
What is the function of the epiphyseal plate?
The epiphyseal plate cartilage next to the diaphysis organizes into a pattern that allows fast, efficient growth.
What type of bone makes up the epiphyses?
The epiphyses are made of an outer shell of compact bone and an interior of spongy bone. A thin layer of articular cartilage covers the joint surface of each epiphysis.
What is the function of the epiphyses? of the articular cartilage?
The epiphyses, the rounded ends, are layered with cartilage, which makes it easier for the bones of the joint to move with each other. The articular cartilage covers the joint surface of each epiphysis, cushioning the opposing bone ends during movement and absorbing stress.
Identify factors that can cause variations in growth.
The factors that cause variations in growth are genetics, the environment, and race- not recessive more SES.
Identify and describe the two mechanisms of cartilage growth.
The first method of growth is APPOSITIONAL growth, when cartilage-forming cells int he surrounding perichondrium secrete new matrix against the external face of the existing carriage tissue. The second method of growth is INTERSTITIAL growth, when lacunae bound chondrocytes divide and secrete new matrix, expanding the cartilage from within.
What are the four basic components of the skeletal system?
The four basic components of the skeletal system are bones, cartilages, joints, and ligaments.
Identify the functions of the skeletal system.
The functions of the skeletal system are: 1) Support-framework that supports body and cradles soft organs 2) Protection 3) Anchorage- skeletal muscles use bones as levers to move the body and its parts 4) Mineral and growth factor storage-reservoir for minerals (esp. calcium and phosphate) and store growth factors 5) Blood cell formation-hemapoiesis 6) Triglyceride (fat) storage 7) Hormone production-osteocalcin (helps regulate insulin secretion, glucose homeostasis, and energy expenditure)
What is the importance of growth assessment in children?
The importance of growth assessment in children is that is is an important indicator. Short stature can be a physical symptom and growth failure can be the first sign of a serious disorder.
Where is the metaphysis? What is the functional significance of this part of the bone?
The metaphysis is the wide portion of a long bone between the epiphysis and the narrow diaphysis. It contains the growth plate, the part of the bone that grows during childhood and as it grows, it ossifies near the diaphysis and the epiphyses.
What is the function of the nutrient foramen?
The nutrient foramen richly supplies the periosteum with nerve fibers and and blood vessels, passing through the shaft to enter the marrow cavity via the nutrient foramen.
What materials make up the organic and the inorganic parts of the bone matrix?
The organic parts of the bone matrix is called osteoid. It is made up of ground substance (made of proteoglycans and glycoproteins) and collagen fibers. The inorganic parts of the bone matrix are hydroxyapatite or mineral salt, largely calcium phosphates, in and around collagen fibers in the extracellular matrix.
Where are the primary centers of ossification typically located? the secondary centers of ossification?
The primary centers of ossification are typically located in the center of the hyaline cartilage shaft. Secondary centers of ossification appear in one or both epiphyses and the epiphyses gain bony tissue.
What are the primary minerals stored by the bone?
The primary minerals stored by the bone are calcium and phosphate.
Identify and describe the physiologic steps involved in the repair of bone fractures.
The repair of bone fracture involves four major stages. 1) A hematoma forms-mass of clotted blood forms at fracture site depriving bone cells of nutrition and tissues at the site become swollen, painful and inflamed. 2) Fibrocartilaginous callus forms. The cartilage cells farthest from the capillaries secrete and externally bulging cartilaginous matrix that later calcifies and splints the bone. 3) Bony callus forms-New bone trabeculae appear in the fibrocartilaginous callus and gradually convert it to a bony callus. 4) Bone remodeling occurs.
Describe the microscopic structure of the compact bone, paying attention to the location of the lamellae, lacunae, osteocytes, and canaliculi.
The structural unit of compact bone is either called the osteon or the Haversian system. An osteon is a group of hollow tubes of bone matrix, each placed outside the next like growth rings of a tree trunk. Each matrix tube is called a lamella. Spider shaped osteocytes occupy lacunae at the junctions of lamellae. Hairlike canals called canaliculi connect the lacunae to each other and the central canal. The canaliculi tie all the osteocytes in a mature osteon together, allowing them to communicate and permitting nutrients and wastes to be relayed.
How do the trabeculae of spongy bone respond to changes in the patterns of stress to which bone is exposed?
The trabeculae is spongy bone align precisely along lines of stress and help the bone resist stress as much as possible.
Describe the general structure of short, flat, and irregular bones.
They all consist of thin plates of spongy bone covered by compact bone. The compact bone is covered outside and inside by connective tissue membranes, respectively the periosteum and endosteum. They contain bone marrow but no well-defined marrow cavity. ("stiffened sandwich")
How does vitamin C influence bone structure?
Vitamin C is required for collagen synthesis.
What is the function of the parathyroid hormone? What are the target sites for the action of this hormone? What effect does parathyroid hormone have on its target sites?
When blood levels decline pTH is released. The increased PTH levels stimulates osteoclasts to resorb bone, releasing calcium into blood. As blood concentrations of calcium rise, the stimulus for PTH release ends. The decline of PTH reverses its effects and causes Ca levels to fall. The target site of the PTH is the kidney (decreases rate of Ca is excreted by kidneys- stays in blood). It stimulates conversion of vitamin D to active form (increases absorption rate).
Identify and describe the location of the hyaline cartilage structures that remain when secondary ossification is complete.
When secondary ossification is complete, hyaline cartilage remains only at two places, on the epiphyseal surfaces at the articular cartilages, and at the junction of the diaphysis and epiphysis, where it forms the epiphyseal plates.
lacuna
a small space, cavity, or depression; lacunae in bone or cartilage are occupied by cells
hemopoiesis
blood cell formation; hemopoiesis
endosteum
connective tissue membrane covering internal bone surfaces
osteoporosis
decreased density and strength of bone resulting form a gradual decrease in rate of bone formation
osteomalacia
disorder in which bones are inadequately mineralized; soft bones
periosteum
double layered connective tissue that covers and nourishes the bone
diaphysis
elongated shaft of a long bone
appositional growth
growth accomplished by the new layers onto those previously formed
interstitial lamella
incomplete lamellae that lie between intact osteons, filling the gaps between forming osteons, or representing the remnants of an osteon that has been cut through by bone remodeling
diploe
internal layer of spongy bone in flat bones
circumferential lamella
located deep to periosteum and superficial to endosteum and extend around entire circumference of the diaphysis and resist twisting of long bone
periosteal bone collar
osteoblasts of the newly converted periosteum secrete osteoid against the hyaline cartilage diaphysis encasing it in a cuff or collar of bone
ossification (osteogenesis)
osteogenesis; the process of bone formation
bone remodeling
process involving bone formation and destruction in response to hormonal and mechanical factors
osteon
system of interconnecting canals in the microscopic structure of adult compact bone; unit of bone; also cal Haversian system
epiphysis
the end of a long bone; attached to the shaft
bone resorption
the removal of osseous tissue; part of the continuous bone remodeling process
osteoid
unmineralized bone matrix
