Chapter 7 Flashcards
The skeletal system is composed of…
Bones, cartilage, and ligaments joined tightly together to for a strong, flexible framework for the body.
The forerunner of most bones in embryonic and childhood development is…
Cartilage
What are the tissues that compose the skeleton?
Cartilage covers…
Many joints surfaces in the mature skeleton.
What are the organs that compose the skeleton?
What are the 8 functions of the skeletal system?
Support, protection, movement, electrolyte balance, acid-base balance, blood formation, hormone secretion, and triglyceride storage.
What is the support function of the skeletal system?
Limb bones and vertebrae support the body. Jaw bones support teeth. Some bones support viscera.
What is the protection function of the skeletal system?
Cranial bones protect the brain, vertebrae bones protect the spinal cord, the bones in the thoraces protect the heart, lung etc. The pelvis protects the pelvic cavity organs.
The only organs not protected by bone are the…
Abdominal organs
What is the movement function of the skeletal system?
Limb movements, breathing, and other movements depend on bone
What is the electrolyte balance function of the skeletal system?
Bones are a store house of minerals, especially calcium and phosphorus
What is the acid-base balance function of the skeletal system?
Buffers blood against large pH changes by altering phosphate and carbonate salt levels to maintain an acid-base balance
Phosphate is an…
Intracellular buffer
Carbonate is an…
Extracellular buffer
What is a buffer?
A chemical that resists changes to pH
What is the blood formation function of the skeletal system?
Red bone marrow (red in color) is the chief producer of blood cells
What is the hormone secretion function of the skeletal system?
Bone cells secrete hormones that affect action of insulin and moderate the stress response
What is the triglyceride storage function of the skeletal system?
Most areas of the bone, instead of forming the blood cells, get replaced into fat
Bone that gets replaced into fat is called…
Yellow bone marrow
If there is a need for increased blood cells, the yellow bone marrow can…
Change itself into red bone marrow
What is bone (osseous tissue)?
Connective tissue with the matrix hardened by calcium, phosphate and other minerals
What is mineralization/calcification?
The hardening process of bone
What is the hardest substance in the body?
Tooth enamel
What is the second hardest substance in the body?
Bone
Why are bones classified as organs?
Because they are made up of more than 2 tissues
What is bone made up of?
It is made up of blood, bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue
How are bones classified?
Bones are classified on the bases of their length, meaning how long or tall they are
Distinguish between bone as a tissue and bone as an organ.
What are the general features of a long bone?
They are longer than wider
What are some examples of long bones?
Humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsal, and phalanges
What are the general features of a flat bone?
They are thin curved plates
What are some examples of flat bones?
Parietal bones of skull, sternum, scapula, ribs, and hip bones
Bones that don’t fit the long bone and flat bone categories are either…
Short bones or irregular bones
What are the general features of short bones?
Approx. equal length and width
What are some examples of short bones?
Bones of wrist and ankle
What are the general features of irregular bones?
Elaborate shapes. The bones don’t fit in the other categories. They are neither long, short, or flat.
What are some examples of irregular bones?
Vertebrae and some skull bones.
What are the general features of sesamoid bones?
They look like a sesame seed magnified 1000x.
What is an example of a sesamoid bone?
Patella organ kneecap
What the general feature of sutural bones?
Wherever these cranial bones come together (where those zigzag lines come together), when it gets replaced those are called sutural bones.
Where are sutural bones found?
Found in the sutures, especially in the areas of the cranial bones.
Much of a long bone is composed of an outer shell of dense white osseous tissue called…
Compact, dense or cortical bone.
What does the outer shell of a long bone enclose?
A space called the marrow (medullary) cavity.
What does the marrow (medullary) cavity contain?
Bone marrow
How is compact (dense or cortical) bone packed?
It it tightly/closely packed.
Does compact (dense or cortical) bone have a lot of empty spaces?
No, it doesn’t have a lot of empty spaces
At the ends of the bones, what is the central space occupied by?
Spongy bone
What is spongy bone?
Loosely organize bone tissue.
What does spongy bone look like?
It looks like a sponge. It has lots of empty spaces.
Where is spongy bone found?
Found in the center of ends and center of shaft of long bones, and the middle of nearly all other bones.
What does spongy bone appear to be?
It appears to be irregular, but it is not.
What is spongy bone covered by?
Durable compact bone.
How much of the skeleton is compact bone by weight?
Three-fourths
How much skeleton is spongy bone by weight?
One-fourth
What would happen if bone was made up of all compact bone?
The bone would be so dense that we wouldn’t be able to walk. It would be too heavy to move.
What does physis mean?
Growth
What is the shaft of a long bone called?
Diaphysis
What is diaphysis?
A long cylindrical tubular shaft that provides leverage.
How much of the diaphysis is made up of compact bone?
The outer third layer
What is on either side of the diaphysis?
Elongated expanded ends called epiphysis.
What does epiphysis provide?
Strengthens the joint and provides added surface area for the attachment of tendons and ligaments.
The joint surface where one bone meets another is covered with…
A layer of hyaline cartilage called articular cartilage.
What does cartilage enable a joint to do?
Move more easily than it would if bone rubbed directly against each other.
Externally, what is a bone covered with?
Periosteum
What is periosteum?
A tough surface membrane.
What is periosteum made up of?
It is made up of 2 layers and perforating fibers.
What are the 2 layers of periosteum?
Outer fibrous layer of collagen and inner osteogenic layer of bone-forming cells.
What do periosteum perforating fibers do?
They penetrate the underlying bone matrix.
What does the periosteum provide?
It provides strong attachment and continuity from muscle to tendon to bone.
Is articular cartilage covered by periosteum?
No
What is periosteum important for?
The growth of bone and healing of fractures.
What is endosteum?
It is a thin layer of reticular connective tissue.
What does endosteum line?
It lines marrow cavities and all internal bone surfaces.
What are the functions of flat bones?
Flat bones protect delicate organs such as the brain and heart, and form brood surfaces for muscle attachment, such as the scapula and hip bones.
Flat bones have a _______ like structure.
Sandwich
What is the sandwich like structure of flat bones?
Inner and outer tables of compact bone enclosing layer of spongy bone in between.
What is the sandwich like structure of flat bones in the cranium called?
Diploe
What is diploe?
It’s the spongy middle layer.
What does the diploe do?
It absorbs shock.
What are the 4 types of bone cells?
Osteogenic cells, osteoblasts, osteocytes, and osteoclasts.
What are osteogenic cells?
Stem cells
Where are osteogenic cells found?
They are found in endosteum and the inner layer of the periosteum.
What do osteogenic cells make up?
They make up the bone structure.
What do osteogenic cells arise from?
They arise from embryonic mesenchyme.
What is the function of osteogenic cells?
They multiply continuously (undergo cell division), make other bone cell types, and give rise to osteoblasts.
What can osteogenic cells transform into?
Osteoblasts
What are the only cells capable of dividing and producing more bone cells?
Osteogenic cells
What are osteoblasts?
Bone-forming cells
Where are osteoblasts found?
They are found in the endosteum and the inner layer of the periosteum.
What type of cells are osteoblasts?
Cuboidal epithelium
What is the function of osteoblasts?
They make ECM for bone. They make ground substance for bone, and make the fibers needed for bone, especially collagen fibers.
What process do osteoblasts perform?
Osteogenesis
What is osteogenesis?
Synthesize soft organic matter of matrix and promote its mineralization.
What does stress on osteoblasts simulate?
It stimulates osteogenic cells to multiply rapidly and increase the number of osteoblasts to reinforce bone
What substance do osteoblasts secrete?
A hormone called osteocalcin.
What is the function of osteocalcin?
It stimulates insulin secretion of the pancreas and increases insulin sensitivity of the adipose (fat cells) and limits its growth.
What can osteoblasts mature into?
Osteocytes
What are osteocytes?
Former osteoblasts that have become trapped the the matrix they deposited. They maintain ECM for bone.
What does it mean that osteocytes maintain ECM for bone?
This means that they make sure that nutrition is received and that waste products are removed.
How do osteocytes maintain ECM for bone?
Osteocytes talk to other osteocytes. However, they cannot move from one place to another so put out their extensions that look like little canals called canaliculi.
Who do osteocytes give their waste to?
Blood vessels
What is lacunae?
Tiny cavities where osteocytes reside. Little lakes.
What are canaliculi?
Little channels that connect lacunae.
What do canaliculi also act like? What is the function?
Strain sensors. They produce biochemical signals that regulate bone remodeling when we exercise.
What happens when an osteocyte says that the matrix isn’t being maintained?
The osteocytes will send messages to the osteoclasts. They will come and destroy the bone. They eat the area where the matrix isn’t being maintained then osteoblasts will deposit the matrix.
Some osteocytes _____ bone matrix while others ______ it.
Reabsorb, deposit
How do osteocytes act as strain sensors?
When stressed they produce biochemical signals that regulate bone remodeling.
What is bone remodeling?
Adjustments in bone shape and density to adapt to stress.
Osteoblasts and osteocytes are also what type of important cell?
Endocrine cell
What do osteoblasts and osteocytes secrete?
They secrete a hormone called osteocalcin.
What is osteocalcin a part of?
It’s a part of the body acute stress response. “Flight or fight”
What does osteocalcin do?
It stimulate pancreatic secretion of insulin, increases insulin sensitivity of fat cells, acts on skeletal muscles to promote energy available, influences brain development and function, and male fertility.
What are osteoclasts?
They are bone-dissolving cells.
Where are osteoclasts found?
On the bone surface.
Osteoclasts are referred as what kind of cells?
Big cells
How big are osteoclasts?
140 micrometers in diameter
How many nucleuses do osteoclasts have?
They are multinucleated. Usually 3-4 nuclei, but up to 50.
Why are osteoclasts big and multinucleated?
Because they are made from several stem cells fused together.
What do osteoclasts look like?
They look like old-fashioned pacman with a ruffled border, and this border faces the bone.
What action do osteoclasts perform?
Osteolysis
What is osteolysis?
Bone resolution or bone dissolving. The breakdown of bone.
Osteolysis is opposite of what action?
Osteogenesis
Do osteoclasts rise from osteogenic cells?
No
Where do osteoclasts rise from?
They rise from the same bone marrow stem cells that give rise to blood cells.
Where do osteoclasts often reside?
Often reside in pits call resorption bays that they etch into the bone surface.
What combination is bone remodeling a result from?
It’s a combination of osteogenesis by osteoblasts and osteolysis by osteoclasts.
The combination of the cells and the ECM is called…
An osteoid
What is an osteoid?
The organic part of the bone.
What is an osteon?
The structural and functional unit of a compact bone.
What is another name for osteon?
Haversian system
What is an osteon made up of?
A central (Haversian) canal through which blood vessels enter and leave the bone.
Lamella means…
Little plate
What is lamella?
The ground substance laid out in forms of tubes. Laid down in the bone in the form of concentric rings, placed one behind the other.
What is in the center of the lamella?
A central canal through which blood vessels enter and leave the bone.
What is lamella laid out by?
Osteoblasts
What is ground substance in the bone (especially compact bone) made up of?
It is made up of concentric rings or lamella. So, compact bone is called is also called lamellar bone.
In addition to ground substance, bone ECM is going to be made up of what?
Collagen fibers
For each lamella, what direction do the collagen fibers go?
They go in opposite directions.
What is the advantage of the collagen fibers in lamella going in opposite directions?
If bone is undergoing a twisting force, instead of the bone breaking apart, these collagen fibers are sacrificed. These collagen fibers resist the twist. Also called twister resisters.
The organic matter in bone ECM is synthesized by what?
Osteoblasts
Organic matter makes up how much of the bone?
35%
What is the organic matter of the bone?
Cells, ECM, and collagen fibers
Inorganic matter makes up how much of the bone?
65%
What is the inorganic matter of the bone?
85% hydroxyapatite
10% calcium carbonate
Many inorganic ions
What is hydroxyapatite?
It is a crystalized calcium phosphate salt.
What is the appearance of hydroxyapatite and what does it do?
Looks like needle shaped crystals. The needles give the bone exceptional strength and the capacity to last forever.
What makes bones last forever?
Hydroxyapatite
What direction are the hydroxyapatite needles oriented?
In the same direction as the collagen fibers.
Inorganic salts make up how much of the bone?
65%
What are the inorganic salts in the bone?
Calcium phosphate, calcium hydroxide, calcium carbonate, fluoride, sodium, potassium, and magnesium.
What is the ceramic of the bone and what is the polymer of bone?
Hydroxyapatite and other minerals are the ceramic of the bone. Collagen is the polymer of the bone.
What do collagen and minerals of the bone form?
They form a composite material that provides flexibility and strength.
Which portion allows the bone to support body weight without sagging? Ceramic portion or polymer portion?
The ceramic portion.
Which portion gives the bones flexibility? Ceramic portion or polymer portion?
The polymer portion
What do sacrificial bonds do? Where are they located?
They break under stress and dissipate shock under load. They are located in collagen molecules.
When do the sacrificial bonds reform?
When the collagen is relieved of stress.
When bones are deficient in calcium salts, the bones become…
Soft and bend easily.
Without protein, a bone is excessively…
Brittle
What are central canals connected by?
Perforating canals
What are perforating canals?
Transverse or diagonal passages
What are central and perforating canals lined with?
Endosteum
What are circumferential lamellae? Where are they located?
They fill the outer region of dense bone. They go around the entire circumference of the bone.
What are interstitial lamella? Where are they located?
They are broken lamellas. They fill irregular regions between osteons.
What are osteons separated from their neighbors by?
A cement line
What is the function of a cement line?
Block microfractures of the bone from spreading and minimizes the chance of them causing a large-scale fracture.
What are spongy bones made up of?
Spicules and trabeculae
What are spicules?
Lattice of bone slivers.
What are trabeculae?
Irregular bars or beams
What is the appearance of spongy bone?
Sponge-like appearance
What are the spaces of spongy bone filled with?
Red bone marrow
What is the function of spongy bone?
Provides strength wile adding minimal weight.
Where do trabeculae develop in spongy bone?
Along the bone’s lines of stress. They are laid where the bone experiences lots of stress and pulling force.
Are there any well-defined osteons in spongy bone?
No
Does spongy bone have central canals?
No
What is bone marrow?
Soft tissue occupying marrow cavities of long bones, small spaces of spongy bone, and the larger central canals.
What are the 2 types of bone marrow?
Red bone marrow and yellow bone marrow.
Red bone marrow is also called…
Myeloid tissue
What does red bone marrow contain?
Multiple tissues including hematopoietic tissue.
What is hematopoietic tissue?
Tissue that produces blood cells.
Where is red bone marrow found in children?
In every bone
Where is red bone marrow found in adults?
Found in skull, vertebrae, ribs, sternum, part of pelvic girdle, and proximal heads of femur and humerus.
What is the longest and thickest bone in the body?
Femur
What is the most easily accessible location for donating red bone marrow in adults?
The hip bone
Is yellow bone marrow found in children or adults?
Adults
What is yellow bone marrow?
Fatty marrow that does not produce blood.
What can yellow bone marrow transform into in an event of severe/chronic anemia?
Red bone marrow
How much blood does the skeleton receive?
Half a liter of blood per minute
What is nutrient foramina?
Minute holes in bone surface that allows blood vessels to penetrate.
Why is nutrient foramina important for bones?
Bones need nutrition and they need their waste products to be removed. For this to be done you need blood vessels to be able to come in. Blood vessels can’t just come into bone because bone is hard. So a space needs to be made.
What do the dendrites of osteocytes maintain?
A two-way flow of nutrients and waste between the central canal and the outermost cells of the osteon.
What is ossification/osteogenesis?
The formation of bone
From conception up to 8-10 weeks of intrauterine life, what is the skeleton made up of?
Clavicle and above are made up of fibrous membrane. Skeleton below the clavicle are made up of hyaline cartilage model.
After 8 weeks of intrauterine life, fibrous membrane is replaced into what? What is this process called? What type of bones are they?
Bone, intramembranous ossification, dermal bones.
After 8 weeks of intrauterine life, hyaline cartilage is replaced into what? What is this process called? What type of bones are they?
Bone, endochondral ossification, chondral bones.
What is the line of separation between the fibrous membrane and the hyaline cartilage in the fetal skeleton?
The clavicle
What are the 2 methods that bone develops?
Intramembranous ossification and endochondral ossification
What bones are produced by intramembranous ossification?
The flat bones of the skull, most of the clavicle, and part of the mandible.
What is intramembranous ossification also important for?
Lifelong thickening and remodeling of long bones.
In intramembranous ossification where the bones are called membranous bones, you must remember the 4 letters: O.C.T.P. What do these letters stand for?
Ossification, calcification, trabecular, and periosteum.
What does fontanel mean?
Little fountains
What bones are produces by endochondral ossification?
Most bones of the body: bones of limbs, vertebrae, ribs, sternum, scapula, and pelvic girdle.
When does endochondral ossification begin and end?
It starts around the 6th week of intrauterine life and continues into a person’s 20’s.
What kind of cells does periosteum have?
Bone-forming and bone-destroying cells.
What does epiphyseal plate serve as?
Growth plate
What does the epiphyseal plate consist of?
Hyaline cartilage in the middle, with transitional zone on each side where cartilage is being replaced by bone.
What is metaphysis?
Transitional zone on each side of the epiphyseal plate, where cartilage is replaced by bone.
What is interstitial growth?
Cartilage growth from within.
When is cartilage of epiphyseal plate depleted?
By late teens, early twenties.
How does a child grow in height?
Chondrocyte multiplication in zone 2 and hypertrophy in zone 3 push zone of reserve cartilage towards ends of bone, and bone elongates.
The site of original epiphyseal plate becomes what?
The epiphyseal line
What type of bone is the epiphyseal line?
Spongy bone
Bone elongation in the lower limbs causes…
A person to grow in height.
Bone elongation in the upper limbs causes…
The bones to grow proportionally.
What does it mean when all of the epiphyses have closed in the lower limbs?
The person cannot grow any taller.
What is appositional growth? What does it aid in?
Deposition of new tissue at the bone surface. This aids in bone widening and thickening.
Bone widening and thickening (appositional growth) occurs by what process?
Intramembranous ossification at the bone surface
Throughout life, bones continually _______.
Remodel
How much of the skeleton is replaced every year through bone remodeling?
10%
What is the function of bone remodeling?
Repairs microfractures, releases minerals into blood, reshapes bones in response to use and disuse.
What is Wolf’s law of bone?
The architecture of bone is determined by the mechanical stress placed on it.
What cells are function in bone remodeling?
Osteoblasts and osteoclasts
There needs to be a balance between bone deposition and bone destruction. So, there must be a balance between what 2 things?
Osteoblasts and osteoclasts
A mature bone remains a what?
Metabolically active organ
The bone is a store house for what?
Calcium
What is mineral deposition (mineralization)?
The crystallization process in which calcium, phosphate, and other ions are taken from blood and deposited in bone.
What is the solubility product formed by hydroxyapatite crystals?
Critics level of calcium times phosphate concentrations.
What do osteoblasts produce during mineralization?
Osteoblasts produce collagen fibers that spiral in length of the osteon; fibers become encrusted with minerals.
What is abnormal calcification (ectopic ossification)?
Abnormal calcification of tissues, such as a lung, brain, eye, muscles, tendon, or artery (arteriosclerosis).
What is a calculus?
A calcified mass in an otherwise soft organ.
What is mineral resorption?
Process of dissolving bone; releases minerals into blood.
What cells perform mineral resorption?
Osteoclasts
Where is mineral resorption performed at by osteoclasts?
At the ruffled border.
What is the process of mineral resorption?
- Hydrogen pumps in membranes (at the ruffled border) secrete hydrogen into space between osteoclasts and bone surface.
- Chloride ions follow by electrical attraction.
- Hydrochloric acid (pH 4) dissolves bone minerals.
- Acid-tolerant protease enzyme digests collagen.
What is calcium needed for?
Bone structure, for the nervous system to be able to send signals, muscle contraction, blood clotting, and exocytosis (glandular secretions).
How much skeletal calcium is exchanged with blood each year?
18%
What is the normal calcium concentration in blood plasma?
9.2-10.4 mg/dl
How much g of calcium is in the adult body? How much is in the bones?
1,100 g of calcium, 99% in bones
What is hypocalcemia?
Calcium deficiency; when the blood calcium goes below 9.2 mg/dl
What happens in hypocalcemia?
There’s a change in meme rate potential which causes excessive excitability of the nervous system and tetany (muscle spasms).
What gland aids in reversing hypocalcemia?
Parathyroid gland
What does the parathyroid gland do to reverse hypocalcemia?
It releases a hormone called parathyroid hormone. This hormone stimulates the osteoclasts to destroy the bone to release calcium into the blood.
What organ does the parathyroid hormone increase calcium resorption by?
Kidneys
What organ does the parathyroid hormone increase calcium absorption by?
Intestines
Pregnancy and lactation increase risk of what?
Hypocalcemia
What is hypercalcemia?
Calcium excess; when the blood calcium goes above 10.4 mg/dl
What happens in hypercalcemia?
It makes ion channels less responsive which causes nerve and muscle cells to be less excitable than normal.
What can hypercalcemia cause?
Emotional disturbance, muscle weakness, sluggish reflexes, and cardiac arrest.
Which is more common, hypocalcemia or hypercalcemia?
Hypocalcemia
What does calcium homeostasis depend on?
A balance between dietary intake, urinary and fecal losses, and exchanges between osseous tissue.
What 3 hormones is calcium homeostasis regulated by?
Calcitriol, calcitonin, and parathyroid hormone.
What is calcitriol?
It’s a hormone. Its the most active form of vitamin D produced by actions of the skin, liver, and kidneys.
What is the main function of calcitriol?
To increase the blood calcium.
What 3 ways does calcitriol act to raise blood calcium?
- Increases calcium absorption by small intestine.
- Increases calcium resorption from skeleton.
- It weakly promotes kidney reabsorption of calcium ions so less lost in urine.
What is calcitriol also necessary for?
Bone deposition by helping provide adequate calcium and phosphate.
What does inadequate calcitriol result in for children and adults?
It results in abnormal softness of bones. Called rickets in children and osteomalacia in adults.
What is rickets?
Abnormal softness of bones before bones have fused.
What is osteomalacia?
Softness of bones after bones have fused.
What is calcitonin?
It is a hormone that C-cells in the thyroid gland make and release to help regulate calcium levels in blood.
What 2 ways does calcitonin lowers blood concentration?
Osteoclast inhibition and osteoclasts stimulation.
What is osteoclast inhibition?
Inhibits osteoblasts thereby reducing bone resorption.
What is osteoclast stimulation?
Stimulates osteoclasts to deposit calcium into bone.
The average adult has how many g of phosphorus? How much of it is in the bones?
500 to 800 g of phosphorus, with 85 to 90% of it in bones.
What is the normal plasma phosphate concentration?
3.5 to 4.0 mg/dl
What raises phosphate levels? By doing what?
Calcitriol, by promoting its absorption by the small intestine.
What lowers the blood phosphate levels? By doing what?
P T H (parathyroid hormone), by promoting its urinary excretion.
Bone growth is especially rapid in…
Puberty and adolescence.
Why do girls grow faster than boys and reach their full height earlier?
Estrogen has a stronger effect than testosterone on bone growth.
How many bones does the body have at birth?
270
How many bones does the typical adult have?
206
How many bones in the axial skeleton and how many n=bone in the appendicular skeleton of an adult?
80 bones in the axial skeleton, 126 bones in the appendicular skeleton.
What is the difference between the male pelvic girdle and the woman pelvic girdle?
The male pelvic is heavier and thicker. The women pelvic is wider and shallower.
What are sesamoid bones?
Bones that form within the tendons (e.g., patella).
What are wormian bones?
Extra bones that develop in skull suture lines.
Why does the number of bones decrease from birth to adulthood?
Because of fusion of some bones.
