Physiology

Question 1

What are the stages of intramembranous ossification?

Answer 1

• ossification center appears in fibrous CT membrane
• bone matrix is secreted w/in fibrous membrane
• woven bone and periosteum form
• bone collar of compact bone forms, and red marrow appears

Question 2

Describe the first phase of intramembranous ossification?

Answer 2

• an ossification center appears in fibrous CT membrane: selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an osssification center

Question 3

Describe the 2nd phase of intramembranous ossification?

Answer 3

• bone matrix (osteoid) is secreted w/in fibrous membrane:

osteoblasts begin to secrete osteoid which is mineralized w/in a few days, trapped osteoblasts become osteocytes

Question 4

Describe the 3rd phase of intramembranous ossification?

Answer 4

• woven bone and periosteum form:
  accumulating osteoid is laid down b/t embyronic blood vessels, which form a random network. The result is a network (instead of lamellae) of trabeculae, vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum

Question 5

Describe the 4th stage of intramembranous ossification?

Answer 5

• bone collar of compact bone forms and red marrow appears:
  Trabeculae just deep to the periosteum thicken, forming a woven bone collar that is later replaced w/ mature lamellar bone, spongy bone, consisteing of distinct trabeculae, persists internally and its vascular tissue becomes red marrow.

Question 6

When does endochondral ossification begin? Stages

Answer 6

• begins in 2nd month of development, uses hyalien cartilage “bones” as models for bone construction
• reqrs breakdown of hyaline cartilage prior to ossification

stages of endochondral ossification:

• formation of bone collar
• cavitation of hyaline cartilage
• invasion of internal cavities by periosteal bud, and spongy bone formation
• formation of medullary cavity, appearance of secondary ossification centers in the epiphyses
• ossificaiton of epiphyses, w/ hyaline cartilage remaining only in epiphyseal plates

Question 7

Describe postnatal bone growth?

Answer 7

in long bones:

• cartilage on the side of epiphyseal plate closest to epiphyses is relatively inactive
• cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth
• cells of epiphyseal plate proximal to resting cartilage form 3 fxnlly diff zones: growth, transformation, and osteogenic development

Question 8

What are the fxnl zones in long bone growth?

Answer 8

• growth zone: cartilage cells undergo mitosis, pushing epiphysis away from diaphysis
• transformation zone: older cells enlarge, the matrix becomes calcified, cartilage cells die, and matrix begins to detiorate
• osteogenic zone: new bone formation occurs

Question 9

Remodeling of long bones?

Answer 9

• growth in length: cartilage continually grows and is replaced by bone
• remodeling: bone is resorbed and added by appositional growth
• remodeling units: adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces (this occurs throughout life, especially at stie of fractures)

Question 10

Hormonal regulation of bone growth during youth?

Answer 10

during infancy and childhood, epiphyseal plate activity is stimulated by growth hormone

during puberty: testosterone and estrogens:

• initially promote adolescent growth spurts
• cause masculinization and feminization (hips) of specific parts of the skeleton
• later induce epiphyseal plate closure, ending longitudinal bone growth

Question 11

Where does bone deposition occur? What does this reqr?

Answer 11

• occurs where bone is injured or added strength is needed
• reqrs diet rich in protein, vit C, D, A, calcium, phosphorus, magnesium, and manganess
• alkaline phosphatase is essential for mineralization of bone
• sites of new matrix deposition are revealed by the:
  osteoid seam - unmineralized band of bone matrix
  calcification front - abrupt transition zone b/t the osteoid seam and the older mineralized bone

Question 12

Describe bone resorption?

Answer 12

• accomplished by osteoclasts
• resorptin bays - grooves formed by osteoclasts as they break down bone matrix
• resorption involves osteoclast secretion of:
  lysosomal enzymes that digest organic material, acids that convert Ca salts into soluble forms
• dissolved matrix is transcytosed across the osteoclast’s cell where it is secreted into the interstitial fluid and then into the blood

Question 13

Ca is necessary for what in the body?

Answer 13

in addition to healthy bone growth:

• transmission of nerve impulses
• muscle contraction
• blood coagulation
• secretion by glands and nerve cells
• cell division

Question 14

What are the 2 control loops that regulate bone remodeling?

Answer 14

• hormonal mechanism maintains Ca homeostasis in the blood

- mechanical and gravitational forces acting on the skeleton

Question 15

Hormonal mechanism of bone remodeling?

Answer 15

• rising blood Ca levels trigger the thyroid to release calcitonin
• calcitonin stimulates Ca salt deposit in the bone
• falling blood Ca levels signal the parathyroid glands to release PTH
• PTH signals osteoclasts to degrade bone matrix and release Ca into the blood

Question 16

How do the bones respond to mechanical stress?

Answer 16

• wolff’s law: a bone grows or remodels in response to forces or demands placed upon it
• observations supporting wolff’s law include:
  long bones are thickest midway along shaft (where bending stress is greatest), curved bones are thickest where they are most likely to buckle
• trabeculae form along lines of stress
• large bony projections occur where heavy, active muscles attach (trochanter, tubercle)

Question 17

How are bone fractures classified?

Answer 17

by:

• position of bone ends after the fracture
• completeness of the break
• orientation of bone to long axis
• whether or not the bone ends penetrate the skin

Question 18

What is a nondisplaced fracture? Displaced?

Answer 18

nondisplaced- bone ends retain normal position

displaced: bone ends are out of normal alignment

Question 19

What is a complete fracture? incomplete?

Answer 19

• complete: bone is broken all the way through

- incomplete: bone isn’t broken all the way through

Question 20

What is a linear fracture? Transverse?

Answer 20

• linear: fracture is parallel to long axis of bone

- transverse: fracture is perpendicular to long axis of bone

Question 21

What is a compound and simple fracture?

Answer 21

• compound: (open) bone ends penetrate the skin

- simple: (closed) bone ends don’t penetrate the skin

Question 22

What is a comminuted fracture? Spiral?

Answer 22

• comminuted: bone fragments into 3 or more pieces, common in the elderly
• spiral: ragged break when bone is excessively twisted, common sports injury, if seen in kids: think abuse

Question 23

What is a depressed fracture? Compression?

Answer 23

• depressed: broken bone pressed inward, typically skull fracture
• compression: bone is crushed, common in porous bones (spinal fractures - osteoporosis )

Question 24

What is an epiphyseal fracture? Greenstick?

Answer 24

• epiphyseal: epiphysis separates from diaphysis along epiphyseal line; occurs where cartilage cells are dying
• greenstick: incomplete fracture where one side of bone breaks and the other side bends, common in kids

Question 25

Stages of healing of a bone fracture?

Answer 25

1. hematoma formation 2. fibrocartilaginous callus formation 3. bony callus formation 4. bone remodeling

Question 26

Describe hematoma formation of healing of a bone fracture?

Answer 26

- torn blood vessels hemorrhage - mass of clotted blood (hematoma) forms at fracture site - site becomes swollen, painful and inflammed

Question 27

Describe fibrocartilaginous callus formation of healing of a bone fracture?

Answer 27

- fibrocartilaginous callus forms when: - osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone, fibroblasts secrete collagen fibers that connect broken bone ends, osteoblasts begin forming spongy bone - osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies - after fibrocartilaginous callus forms granulation tissue (soft callus) forms a few days after fracture - capillaries grow into tissue and phagocytic cells begin cleaning debris

Question 28

Describe bony callus formation of healing of a bone fracture?

Answer 28

- new bone trabecular appear in fibrocartilaginous callus - and this converts into a bony hard callus - bone callus begins 3-4 wks after injury, and continues until firm union is formed 2-3 months later

Question 29

Describe bone remodeling of healing bone fracture?

Answer 29

- excess material on bone shaft exterior and in the medullary canal is removed - compact bone is laid down to reconstruct shaft walls

Question 30

What is osteomalacia? Signs?

Answer 30

- aka rickets - bones are inadequately mineralized causing softened, weakened deformed bones - main sx is pain when wt is put on affected bone - caused by insufficient Ca in the diet, or by vitamin D deficiency - signs of rickets: soft spot on baby's head slow to close, bony necklace (ribs), curved bones, big lumpy jts, bowed legs

Question 31

What is osteoporosis?

Answer 31

- group of diseases in which bone resorption outpaces bone deposit - spongy bone of spine is most vulnerable - occurs most often in postmenopausal women - bones become so fragile that sneezing or stepping off curb can cause fractures

Question 32

Tx of osteoporosis?

Answer 32

- Ca and Vit D supplements - increased wt bearing exercise - hormone (estrogen) replacement therapy (HRT) slows bone loss - natural progesterone cream prompts new bone growth - statins increase bone mineral density

Question 33

What is Paget's disease?

Answer 33

- characterized by excessive bone formation and breakdown - pagetic bone w/ an excessively high ratio of woven to compact bone is formed - usually localized in spine, pelvis, femur and skull - unknown cause (possibly viral) - pagetic bone, along w/ reduced mineralization, causes spotty weakening of bone - osteoclast activity wanes, but osteoblast activity continues to work - may develop arthritis and deafness - tx: bisphosphonates (fosamax), didronate, calcitonin

Question 34

Development of bones (from fetus - old age)?

Answer 34

- mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form embryonic skeleton - the embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined by sonograms - at birth most long bones are well ossified (except for epiphyses) - by 25: nearly all bones are completely ossified - old age: bone resorption predominates - a single gene that codes for Vit D docking determines both tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life

Question 35

Fxn of tendons and ligmanents?

Answer 35

- ligaments: connect bone to bone, provide stability and limit motion in a jt - tendons: connect muscle to bone, allows for motion at a jt - comprised of parallel collagen fibers

Question 36

Tenditis and tendon ruptures tx?

Answer 36

- overuse injuries: usually respond to rest | - if acute: may need surgery

Question 37

Tx of strains, sprains, and tears?

Answer 37

- partial injuries will heal if protected | - complete injuries often need surgical repair

Question 38

What is bursitis? diff types?

Answer 38

- inflammation from overuse - deep: greater trochanteric and rotator cuff - superficial: olecranon and pre-patellar

Question 39

Comparison of skeletal, cardiac and smooth muscle cells?

Answer 39

- skeletal: elongated cell, mult peripheral nuclei, visible striations, voluntary - cardiac: branching cell, single central nucleus, visible striations, involuntary - smooth: spindle-shaped cell, single central nucleus, lack visible striations, involuntary

Question 40

Main fxns of skeletal muscle?

Answer 40

1. movement of bones or fluids 2. maintaining posture and body position 3. stabilizing jts 4. heat generation (shivering)

Question 41

Make up of skeletal muscle?

Answer 41

- each muscle is served by one artery, nerve, and one or more veins CT sheaths of skeletal muscle: - epimysium: dense regulat CT surrounding entire muscle - perimysium: fibrous CT surrounding fascicles (groups of muscle fibers) - endomysium: fine areolar CT surrounding each muscle fiber

Question 42

What is the microscopic anatomy of a skeletal muscle fiber?

Answer 42

- cylindrical cell 10-100 - multiple peripheral nuclei - many mitochondria - glycosomes - contain myofibrils, sarcoplasmic reticulum and T tubules

Question 43

What are myofibrils? components?

Answer 43

- densely packed, rodlike elements - 80% of cell volume - exhibit striations: dark A bands and light I bands

Question 44

What is a sarcomere?

Answer 44

- smallest contractile unit (fxnl unit) of a muscle fiber - region of myofibril b/t 2 successive Z discs - composed of thick and thin myofilaments made of contractile proteins - optimal sarcomere operating length is (80-120% of resting length)

Question 45

What are the components of a sarcomere?

Answer 45

- thick filaments: run the entire length of an A band - thin filaments: run length of I band and partway into A band - z disc: coin shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another - H zone: lighter midregion where filaments don't overlap - M line: line of protein mymesin that hold adjacent thick filaments together - the fundamental until which allow contraction of muscle to take place - z discs are pulled toward each other

Question 46

Structure of thick and thin filament?

Answer 46

- think filament: myosin tails, myosin heads - thin filament: G actin bears active sites for myosin head attachment during contraction, tropomyosin and troponin: regulatory proteins bound to actin

Question 47

What is the sarcoplasmic reticulum?

Answer 47

- network of smooth endoplasmic reticulum - pairs of terminal cisternae form perpendicular cross channels - fxns in regulation of intracellular Ca levels

Question 48

What are the T tubules?

Answer 48

- continuous w/ sarcolemma - penetrate the cell's interior at each A band-I band jxn - paired terminal cisternae to form triads that encircle each sarcomere

Question 49

SLiding filament model of contraction?

Answer 49

- in relaxed state, thin and thick filaments overlap only slightly - during contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments towards the M line - as H zones shorten and disappear, sarcomeres shorten, and whole muscle shortens

Question 50

What are the requirements for skeletal muscle contraction?

Answer 50

1. activation: neural stimulation at neuromuscular jxn | 2. excitation-contraction coupling: generation and propagation of an action potential along sarcolemma

Question 51

Where is the neuromuscular jxn?

Answer 51

- situated midway along length of muscle fiber - synaptic cleft - synaptic vesicles of axon terminal contain the neurotransmitter ACh - junctional folds of sarcolemma contain ACh receptors

Question 52

What happens at the neuromuscular junction?

Answer 52

- skeletal muscles are stimulated by somatic motor neurons - axons of motor neurons travel from CNS via nerves to skeletal muscles - each axon forms several branches as it enters a muscle - each axon ending forms a neuromuscular junction w/ a single muscle fiber - nerve impulse arrives at axon terminal - ACh released (binds w/ receptors) - generation of AP

Question 53

Summary of events of an action potential?

Answer 53

1. AP arrives at axon terminal of motor neuron 2. voltage gated Ca channels open and Ca enters the axon terminal 3. Ca entry causes some synaptic vesicles to release their contents (ACh) by exocytosis 4. ACh diffuses across the synaptic cleft and binds to receptors in the sarcolemma 5. ACh binding opens ion channels that allow simultaneous passage of Na into the muscle fiber and K out of muscle fiber 6. ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase

Question 54

Where does Myasthenia gravis interupt the pathway of muscle contraction?

Answer 54

- doesn't allow ACh to bind to AChR so ion channel isn't opened so muscle fibers don't depolarize and there is no muscle contraction

Question 55

Where do neuromuscular blocekers interupt the pathway of muscle contraction?

Answer 55

- also doesn't allow ACh to bind to AChR so ion channel isn't opened

Question 56

Where does botulinum toxin interupt muscle contraction pathway?

Answer 56

- prevents Ca influx (no release of ACh)

Question 57

Where does MS interupt muscle contraction pathway?

Answer 57

- in beginning: no action potential at nerve terminal

Question 58

What is summation and tetanus?

Answer 58

- summation: rapid sequence of stimuli: muscle twitches fuse into each other, each subsequent one being stronger than its precedent (due to Ca++_ - tetanus: very rapid sequence of stimuli: no relaxation

Question 59

Components of muscle fiber?

Answer 59

- sarcolemma: muscle cell membrane - sarcoplasma: muscle cells cytoplasm - motor end plate: contact surface w/ axon terminal - T tubule: cell membrane extension into sarcoplasm (to reach myofibrils) - cisternae: areas of ER dedicated to Ca++ storage - myofibrils: organized into sarcomeres