Chapter 7 - Bones Flashcards
What are the two most durable components of your body?
Bones and teeth (especially the enamel)
Do we have a dead or living skeleton?
Living
True or false: The skeletal system constantly remodels itself and interacts with other organ systems of the body
True
______ is the study of bone
Osteology
What are the 3 main components of the skeletal system?
Bones, cartilages, and ligaments
Define cartilage, ligaments, and tendons
Cartilage is forerunner of bone formation and coats ends of bones.
Ligaments connect bone to bone
Tendons connect muscle to bone
What are the functions of the skeleton?
Support, protection, movement, electrolyte balance, acid-base balance, and blood formation
How does the skeleton aid in support, protection, and movement?
Support: limb bones and vertebrae support body; jaw bone supports teeth; bones support viscera
Protection: of brain, spinal cord, heart, lungs etc
Movement: of limbs, breathing – action of muscles on bones
How does the skeleton aid in maintaining electrolyte and acid base balances, and how does it aid in blood formation?
Electrolyte balance: calcium & phosphate levels
Acid–base balance: buffers blood against large pH changes by altering phosphate and carbonate salt levels
Blood formation: red bone marrow makes red blood cells
Define bone (osseous tissue)
A connective tissue with its matrix hardened by calcium phosphate and other minerals
Define mineralization/ calcification
The hardening process of bone
What do individual bones consist of?
Individual bones (organs) consist of bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue
Define sesamoid and sutural bones
Sesamoid (type of short bone) and sutural (wormian) bones
Sesamoid bones develop in a tendon (or ligament) in response to a need for more leverage
Sutural bones are the extra bones in the sutures (especially the lambdoid suture) of the skull
Define compact bone
Has a dense outer shell of bone
Define spongy (cancellous) bone
Made up of an internal honeycomb of trabeculae filled with red or yellow bone marrow
The skeleton’s weight is made up of ___% compact bone and _____% spongy bone
75% compact bone; 25% spongy bone
Define diaphysis and epiphyses
Diaphysis—shaft that provides leverage
Epiphyses—enlarged ends of a long bone
Define the epiphyseal line (metaphysis) and marrow cavity (medullary cavity)
Epiphyseal line: separates diaphysis from epiphysis (aka metaphysis)
Marrow cavity: space in the diaphysis of a long bone that contains bone marrow (aka medullary cavity)
Define articular cartilage
A layer of hyaline cartilage that covers joint surface and allows the joint to move more freely
Describe the two layers of the periosteum
Outer fibrous layer made of collagen
Some fibers continuous with tendons
Perforating fibers —penetrate into bone matrix
Inner osteogenic layer of bone-forming cells
Important to bone growth and healing of fractures
Define the periosteum
2 layers covering most of bone
Define the endosteum
A thin layer of reticular connective tissue lining marrow cavity
Contains osteoblasts and osteoclasts
The nutrient foramina is penetrated by what?
Blood vessels
Describe the epiphyseal plate (growth plate)
Area of hyaline cartilage that separates epiphyses and diaphyses of children’s bones
Enables growth in length
When growth is finished turns into Epiphyseal line
List the 8 features of long bone
Epiphyses Diaphysis Compact bone Spongy bone Marrow cavity Articular cartilage Periosteum Endosteum
Describe the anatomy of a flat bone
Bones with a sandwich-like structure: two layers of compact bone with a middle layer of spongy bone (diploë)
Define and describe the diploë of flat bones
Diploë is the spongy middle layer found in flat bones. It absorbs shock and the marrow spaces are lined with endosteum
Define osteogenic cells
Stem cells (cell division) and develop into osteoblasts
Define osteoblasts
Bone-forming cells
Describe how osteoblasts do their job
Osteoblasts secrete collagen (and other carbohydrate-protein complexes) to form a soft fibrous matrix. This matrix hardens with mineral deposition. They make bone by mitosis and differentiation of osteogenic cells
What two organelles are particularly abundant in osteoblasts?
Rough ER and golgi complexes.
What stimulates osteogenic cells to multiply rapidly? What does this do?
Stress stimulates osteogenic cells to multiply rapidly, which increases the number of osteoblasts which reinforce bone
Define and describe osteocytes
Defined as mature bone cells
They’re found in pockets called lacunae, and connected to each other by canaliculi and gap junctions
Some reabsorb bone matrix & others deposit it; regulates bone remodeling
Describe the role of osteocytes when under stress
They act as strain sensors; when stressed, they produce biochemical signals that regulate bone remodeling (shape and density changes that are adaptive)
Define and describe osteoclasts
Defined as bone-dissolving cells found on bone surface
Derived from fusion of multiple white blood cells (WBC’s)
Usually multinucleate
Secrete enzymes and acids for the break down of bone (resorption)
True or false: Dissolving bone is a part of bone remodeling
True
What are the two main parts of the matrix, and what fraction of the matrix do they each make up?
Organic portion (1/3) and inorganic portion (2/3)
Describe the organic part of the matrix
Synthesized by osteoblasts
Composed of collagen and carbohydrate–protein complexes
Responsible for the flexibility of bone
Makes up 1/3 of the matrix
Describe the inorganic part of the matrix
85% hydroxyapatite (calcium phosphate) 10% calcium carbonate 5% other minerals (fluoride, sodium, potassium, magnesium) Responsible for the hardness of bone Makes up 2/3 of the matrix
If there is a mineral deficiency, what happens to the bone?
Rickets disease
Describe Rickets disease
A disease caused by mineral deficiency and resulting in soft, deformed bones
If there is a defect in collagen deposition, what happens to the bone?
Osteogenesis imperfecta (brittle bone disease)
Describe osteogenesis imperfecta (brittle bone disease)
Results from a defect in collagen deposition
Histology of compact bone reveals that they have _____
Osteons (haversian systems)
Describe the 3 elements of the haversian system of an osteon
1) Lamellae
Columns of the matrix (mainly collagen) that are weight bearing
Run concentric, circumferential, and interstitially
2) Central (Haversian canal)
Contains blood vessels and nerves
3) Perforating (Volkmann’s) canals
Channels that connect blood and nerves from periosteum to the central (Haversian) canal
Describe lamellae in osteons
Columns of the matrix (mainly collagen) that are weight bearing. The columns run concentric, circumferential, and interstitially
Describe the central (Haversian) canal of the osteon
Contains blood vessels and nerves
Describe the perforating (volkmann’s) canals of osteons
Channels that connect blood and nerves from periosteum to the central (Haversian) canal
Run transverse or diagonal
Where do trabeculae develop in spongy bone?
They develop along the bone’s lines of stress
Something described as a “lattice of bone covered with endosteum” is known as what?
Spongy bone
Describe the structure and function of spongy bone
Structure: It’s a lattice of bone covered with endosteum; made up of trabeculae (thin plates of bone) that develop along the bone’s lines of stress, and the spaces are filled with red bone marrow. Has few osteons and no central canals
Function: Provide strength with minimal weight
Define bone marrow
Soft tissue occupying marrow cavities of long bones and small spaces of spongy bone
What are the two types of bone marrow?
Yellow and red
Describe red bone marrow
- Contains hemopoietic tissue—produces blood cells
- Found in nearly every bone in a child
- In adults, it’s found in the skull, vertebrae, ribs, sternum, part of pelvic girdle, and proximal heads of humerus and femur
Describe yellow bone marrow
- Found in adults
- Stores Triglycerides
- Can transform back to red marrow in the event of chronic anemia
Describe where red bone marrow is found in children and adults
Infants – in nearly every bone
- medullary cavity
- all areas of spongy bone
Adults
- head of the femur and humerus
- diploë (spongy bone) of flat bones
- some irregular bones (such as hip and vertebrae)
Define ossification or osteogenesis
The formation of bone
In the human fetus and infant, bone develops by what two methods?
Intramembranous ossification
Endochondral ossification
When does intramembranous ossification occur?
It produces the flat bones of skull and clavicle in fetuses (and ossifies the fontanels, and thickens long bones throughout life)
During intramembranous ossification, bone develops within what kind of membrane?D
A fibrous connective tissue membrane
Describe the life-cycle of an osteocyte formed by intramembranous ossification
Mesenchymal cells turn into osteoblasts which turn into osteocytes (spongy bone)
Describe intramembranous ossification
Bone develops within a fibrous connective tissue membrane (Mesenchymal cells to osteoblasts to osteocytes (spongy bone))
Forms the flat bones of the skull, clavicles, and ossifies the fontanels.
Most of these bones are remodeled (destroyed and reformed) as we grow to adult size.
Describe endochondral ossification
Bone forms by replacing hyaline cartilage
Forms most the bones of the body below the skull (except the clavicle)
Mesenchyme turn into chondroblasts, which die and are replaced by osteoblasts, which form spongy bone, which forms compact bone
What type of ossification is best described as “bone is formed by replacing hyaline cartilage”?
Endochondral ossification
In endochondral ossification, what do primary and secondary ossification form?
Primary Ossification: forms diaphysis
Secondary ossification: forms epiphysis
When do epiphyseal plates close? What does this mean for growth?
Close in late teens to early 20s, which is when bone can no longer grow in length
During infancy and childhood, in endochondral ossification the epiphyses fill with _______ bone
spongy
Describe the role of cartilage in endochondral ossification
Cartilage is limited to the articular cartilage covering each joint surface, and to the epiphyseal plate
Describe the role of the epiphyseal plate in bone growth
Serves as a growth zone for bone elongation, covered with cartilage
True or false: bones grow in two directions, which are length and width
True
True or false: Ossification continues throughout life with the growth and remodeling of bones
True
Describe how bones grow in length
Occurs at Epiphyseal plates
Cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis
Cartilage cells die and are replaced by bone.
When growth is finished, there’s no more cartilage at the plate, which then becomes an epiphyseal line, and bone can no longer grow in length
Describe achondroplastic dwarfism
Long bones stop growing in childhood
Normal torso, short limbs
Failure of cartilage growth in metaphysis
Spontaneous mutation produces mutant dominant allele
Describe pituitary dwarfism
Lack of growth hormone
Normal proportions with short stature
Describe how bones become wider/thicker
Happens through appositional growth: continual growth in diameter and thickness throughout the lifespan through intramembranous ossification.
Osteoblasts of inner periosteum deposit osteoid tissue
Lay down matrix in layers parallel to surface
Forms circumferential lamellae
Osteoclasts of endosteum enlarge marrow cavity
Define appositional growth and where it happens
The growth of bone horizontally; happens on the surface of bone
About ___% of an adult’s skeleton is remodeled each year
10%
What are the two main types of cells involved in bone remodelling?
Osteoblasts: Bone deposition
Osteoclasts: Bone resorption
Describe Wolff’s Law of Bone
Bone grows or remodels in response to the demands placed on it
Exercise: promotes bone growth
Lack of exercise (bedridden): atrophies bones
Define mineral deposition/ mineralization
The process in which calcium, phosphate, and other ions are taken from blood and deposited in bone
Describe the process of mineral deposition/ mineralization
Osteoblasts produce collagen fibers
Fibers become encrusted with minerals
First few crystals act as seed crystals that attract more calcium and phosphate
Abnormal calcification (ectopic ossification)
Formation of a calculus (calcified mass) in lung, brain, eye, muscle, tendon, or artery (arteriosclerosis)
Define mineral reabsorption
The process of dissolving bone and releasing minerals into blood
Describe the process of mineral reabsorption
Performed by osteoclasts
Pump hydrogen to extracellular fluid (chloride follows). Hydrochloric acid (pH 4) dissolves bone minerals
Produce an enzyme which digests collagen in an acidic environment
Describe the role of osteoclasts and osteoblasts in braces
Braces reposition teeth, which move because osteoclasts dissolve bone ahead of the tooth; osteoblasts deposit bone behind the tooth
Describe the role of the bone matrix in homeostasis
Minerals are deposited in the skeleton and withdrawn from the skeleton when they are needed for other purposes
Phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers
Calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis
What is phosphate a component of?
DNA, RNA, ATP, phospholipids, and pH buffers
What is calcium needed for in the body?
Neuron communication, muscle contraction, blood clotting, and exocytosis
True or false: Calcium and phosphate are used for much more than bone structure
True
Define homeostasis
The ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions
Describe negative feedback
It allows for a dynamic equilibrium within a limited range around a set point.
The body senses a change and “negates” or reverses it.
The fundamental mechanism to keep body in homeostasis.
Loss of homeostatic control causes what?
Illness or death
Why are feedback loops called feedback loops?
Because feedback mechanisms alter the original changes that triggered them, they are called feedback loops.
Describe the role of homeostasis in body temperature
If too warm, vessels dilate in the skin and sweating begins (heat-losing mechanism).
If too cold, vessels in the skin constrict and shivering begins (heat-gaining mechanism).
What are the 3 main components of feedback loops?
Receptor, integration (control) center, and effector.
Define a receptor in feedback loops
Structure that senses change in the body (chemical, temperature, pain, pressure, volume, etc.)
Define an integration (control) center in a feedback loop
The control center that processes the sensory information, “makes a decision,” and directs the response (e.g., cardiac center of the brain)
Define an effector in a feedback loop
The cell or organ that carries out the final corrective action to restore homeostasis (e.g., the heart)
Define and describe positive feedback loops
It’s a self-amplifying cycle that leads to greater change in the same direction; the feedback loop is repeated (change produces more change).
It’s a normal way of producing rapid changes
(ex: childbirth, blood clotting, protein digestion, and generation of nerve signals)
However, they can sometimes be dangerous
(ex: the vicious cycle of runaway fever)
Calcium homeostasis depends on a balance between what two things?
Intake (diet) and loss (urinary and fecal eliminations)
How is calcium homeostasis maintained?
By calcium exchange between osseous tissue and blood, which is mediated by three hormones
Calcium homeostasis is regulated by what three hormones?
Calcitriol (vitamin D), calcitonin, and parathyroid hormone
Describe the role of calcitriol (vitamin D) in calcium homeostasis
It raises blood calcium levels; mainly, it increases calcium absorption by small intestine, and it also increases calcium resorption from the skeleton.
It weakly promotes kidney reabsorption of calcium ions, so less is lost in urine
Produced by actions of skin, liver, and kidneys
What is calcitriol (vitamin d) needed for in the body? What does a calcitriol deficiency result in?
Calcitriol is necessary for bone deposition; lack of calcitriol results in abnormal softness of bones.
In children, a deficiency results in rickets. In adults, a deficiency results in osteomalacia
Describe the role of calcitonin in calcium homeostasis
Produced by the thyroid gland
Its release is triggered by high blood calcium, and it lowers blood calcium concentration in 2 ways: Inhibits osteoclasts and stimulates osteoblasts
Important in children, weak effect in adults (except may inhibit bone loss in pregnant and lactating women)
What increases blood calcium? What decreases blood calcium?
Calcitriol (vitamin D) and parathyroid hormone increase blood calcium; calcitonin decreases blood calcium
Describe the role of parathyroid hormone in calcium homeostasis
PTH increases blood calcium 4 ways:
1) Stimulates osteoclast population and bone resorption
2) Promotes calcium reabsorption by kidneys
3) Promotes calcitriol synthesis
4) Inhibits osteoblasts, inhibiting bone deposition
Produced by parathyroid glands
Release triggered by low blood calcium
Describe the causes and effects of hypocalcemia
Effects: causes overly excitable nervous system and tetany (muscle spasms) (laryngospasm)
Some cases are caused by vitamin D deficiency or underactive parathyroid glands
Pregnancy and lactation increase risk of hypocalcemia
Define hypocalcemia and hypercalcemia
Hypocalcemia: low blood calcium.
Hypercalcemia: high blood calcium.
Describe the causes and effects of hypercalcemia
Makes nerve and muscles less excitable
Can cause emotional disturbance, muscle weakness, sluggish reflexes, cardiac arrest
Hypercalcemia rarely occurs
Describe bone development from infancy to early adulthood
Infancy and childhood: epiphyseal plate activity is stimulated by Human Growth Hormone (hGH)
Puberty: (testosterone and estrogens) promotes adolescent growth spurts and differentiates the male/female skeleton; bone growth ends (18 - 21 years)
At least __ or more hormones, vitamins, and growth factors affect osseous tissue
At least 20 or more hormones, vitamins, and growth factors affect osseous tissue
Why do girls grow faster than boys and reach full height earlier?
Estrogen has stronger effect than testosterone on bone growth
Describe the effects of anabolic steroids on growth
Causes bone growth to stop and the epiphyseal plate to “close” prematurely
Results in abnormally short adult stature
Define a stress fracture
A break caused by abnormal trauma to a bone
Define a pathological fracture
A break in bone that’s been weakened by disease (cancer or osteoporosis)
Fractures are classified by their structural characteristics; what are they?
Displaced vs nondisplaced
Open vs closed
Define closed reduction
A procedure to treat fractures in which bone fragments are manipulated into their normal positions without surgery
Define open reduction
A procedure to treat fractures that involves surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments
Define a cast
Normally used to stabilize and immobilize healing bone
Describe osteoporosis
The most common bone disease
Affects spongy bone the most since it is the most metabolically active
Subject to pathological fractures of hip, wrist, and vertebral column
Kyphosis (widow’s hump)—deformity of spine due to vertebral bone loss
Complications of loss of mobility are pneumonia and thrombosis
The most common bone disease is __________
osteoporosis
What is kyphosis and why does it happen?
It’s a deformity of the spine due to vertebral bone loss
What demographics are most likely to get osteoporosis?
- Estrogen maintains bone density in both sexes; inhibits resorption by osteoclasts
- Postmenopausal white women at greatest risk; this is because white women begin to lose bone mass as early as age 35 and By 70, average loss is 30% of bone mass
- Osteoporosis also seen in young female athletes with low body fat causing them to stop ovulating and decrease estrogen secretion
- Risk factors: race, age, gender, smoking, diabetes mellitus, diets poor which are poor in: calcium, protein, vitamins C and
What are the treatments for osteoporosis?
- Estrogen replacement therapy (ERT) (slows bone resorption, but increases risk of breast cancer, stroke, and heart disease)
- Certain medications destroy osteoclasts
- Best treatment is prevention: exercise and a good bone-building diet between ages 25 and 40
