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Anatomy > Bone tissue and skeletal system > Flashcards

Bone tissue and skeletal system Flashcards

1
Q

what is the skeletal system

A

an organ system with bones, cartilage, ligaments, and tendons
makes up about 20& of body mass

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2
Q

what are the three well known functions of the skeletal system

A

support - the body (mandible and maxilla support the teeth)
protection - encloses and protects important organs (ex. ribcage and skull)
movement - limbs, breathing

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3
Q

what are the four lesser known functions of the skeletal system

A

electrolyte balance - skeleton stores Ca and P
acid-base balance - buffers blood against major pH changes (hydroxyapetite CaPO4)
blood formation - stem cells in red bone marrow make red blood cells
triglyceride storage - yellow bone marrow is an energy resovoir of adipose tissue

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4
Q

how many bones do we have at birth, explain

A

we are born with 270 bones but as full grown adults we have 206
(around 25 years of age)
some bones fuse together
ex. illium ischium, pubis fuse together
ex. skull bones with sutures
ex. fusion of sacrum and coccyx

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5
Q

what are the cellular and matrix components of osseous tissue

A

osteoblasts, osteoclasts, osteocytes, stem cells
collagen fibers, CaPO4, CaCO3, ground substance

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6
Q

what is an osteogenic cell

A

stem cell which generates osteoblasts
multiply and differentiate
located in endosteum (lines the channels), periosteum
located in places where they need more osteoblasts (need new bone)

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7
Q

what is an osteoblast

A

cell that forms bone matrix
non mitotic
form collagen fibers and ground substance
making glycosaminoglycans, proteoglycans, and glycoproteins

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8
Q

explain how osteoblasts become osteocytes

A

as the osteoblast is laying down the bone matrix around itself, it traps itself in the lacunae, making it an osteocyte
it grows cytoplasmic processes (extensions of the plasma membrane)(basically arms) for when it is trapped in the matrix

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9
Q

what is an osteocyte

A

cell that maintains bone tissue
formerly osteoblasts that are trapped in matrix in small cavities called lacunae
connected by canaliculi
maintains bone tissue by adding and removing tissue
maintains bone/blood concentration of Ca2+ and PO43-
by dissolving bone and putting these ions into blood.

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10
Q

what are canaliculi

A

little tunnels in bone matrix which allows osteocytes to communicate with their appendages

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11
Q

what are osteoclasts

A

cells derived from hematopoietic stem cells (different lineage than osteogenic cells)
multiple hematopoietic stem cells fuse together to form an osteoclast (osteoclast possesses multiple nuclei)
HP stem cells are in red bone marrow (all blood cells are derived from HP stem cells)
osteoclasts possess conspicuous microvillie which increase the surface area so that they can come into contact with the matrix to break it down more easily
they dissolve bone matrix and therefore change the composition of blood (of Ca2+ and PO43-

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12
Q

what are the organic and inorganic components of bone matrix

A

organic
-collagen fibers
-ground substance (glycosaminoglycans, proteoglycans, glycoproteins)

inorganic
-85% hydroxyapatite (CaPO4)
-10% CaCO3
-5% other ions (depend on what you eat/drink/where you live)

we get the inorganic stuff from out diet

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13
Q

describe the process of bone formation

A

occurs through the process of calcification (mineralization)
1. osseous tissue is saturated with CaPO4 and CaCO3 (a supersaturated solution)
2. deposition of collagen (collagen is made by osteoblasts)
3. CaPO4 and CaCO3 crystallize on the collagen fibers

rock candy is made this way

uniport Ca pummps pump Ca out of other body cells so that they dont crystallize and form bone, killing the cells

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14
Q

explain bone is a composite

A

composite of minerals and collagen
minerals provide strength
collagen provides flexibility

reshaping bone is based on activity level
skyscrapers move (they need to be flexible)

too much minerals/not enough collagen = easy breaking bone

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15
Q

what is osteomalacia

A

rickets disease
very flexible bones
presents during growth spurts
caused by lack of minerals in bone
mostly due to dietary deficiency in Ca, P, or vitamin D

can also be genetic (hereditary rickets)
^patient has kidney problems so that they cant hang onto vitamin D and the kidney cleans the blood of vitamin D and it is excreted with urine
very rare in the US

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16
Q

what is osteogenesis imperfecta

A

very brittle bones
caused by lack of collagen
typically congenital
there is a defect in the gene which codes for collagen producing stuff

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17
Q

what are the two types of bone tissue

A

compact bone and spongy bone

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18
Q

what is compact bone

A

located in the external surfaces of all bones
dense, calcified tissue (osteons)

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19
Q

what is spongy bone

A

located in heads of long bones and in the middle layer of flat bones
loosely organized tissue
spongy appearance but calcified and hard
is the precursor to compact bone

has lots of empty space
-trabeculae = the web like pattern of bone
-empty spaces = filled with bone marrow

there are no central canals in spongy bone
(it is already vascularized bc the bone marrow is the blood supply)

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20
Q

what is an osteon

A

the basic structural unit of compact bone tissue
composed of one central canal and many concentric lamellae

the radius of an osteon is determined by how far away the last layer can be and still be getting a blood supply
thats why there are multiple osteons squished together (more central canals)

blood is the complete opposite tissue

osteocytes lay down collagen in different layers in opposite directions for each lamellae in order to make the matrix much stronger

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21
Q

what is bone marrow

A

soft, highly vascularized tissue with stem cells

located in:
1. the spaces among trabeculae of spongy bone
2. central canals of compact bone
3. the internal chamber (marrow cavity) of long bones

2 types: red and yellow

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22
Q

what is red bone marrow

A

bone marrow that produces blood and blood cells
has hematopoietic tissues

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23
Q

what is yellow bone marrow

A

fatty adipose tissue made of triglycerides
only in adults
stays yellow unless someone has severe anemia (a bad accident with lots of bleeding) or chronic anemia
acts as an energy resovoir

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24
Q

how does bone marrow change with age?

A

infants have only red bone marrow
children (1-10) the red bone marrow begins to convert to yellow bone marrow at the center of long bones (only a little bit here)
adolescent (10-20) the majority of bone marrow is yellow now
adult (20+) basically all of long bones are yellow bone marrow

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25
Q

what is a bone marrow transplant

A

taking healthy bone marrow (usually from hip) and transplanting it into another person
person who cannot create hematopoietic stem cells
ex. person with leukemia (WBC cancer) needs BM transplant
they need the stem cells so that they can differentiate

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26
Q

what is osteogenesis

A

the development of bone

two types:
intramembranous ossification
endochondrial ossification

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27
Q

generally what is intramembranous ossification

A

bone development that occurs within a membrane (mesenchyme)
develops all flat bones

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28
Q

generally what is endochondrial ossification

A

bone development that occurs within cartilage and then forms bone
develops all long bones
building the cartilage model and replacing it with bone
begins at about the 6th week of fetal development
ends at around 20 years of age

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29
Q

how does osteogenesis begin

A

cleavage of a zygote into the eight cell stage which cleaves into a blastula
gastrulation of the blastula to form the gastrula
gastrula possesses the ectoderm (outside) mesoderm (middle) and endoderm (inside) –> primary germ layers

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30
Q

what are primary germ layers

A

the three layers (ectoderm, mesoderm, and endoderm) of the gastrula from which tissues arise

ectoderm - epidermis and nervous system
endoderm - lining of digestive and respiratory tract
mesoderm - forms into the mesenchyme

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31
Q

what is the mesenchyme

A

a loosely organized tissue that forms connective tissues (including bone tissue)
where all bone development begins
typically very vascularized
possess a lot of different stem cells which dictate what kind of tissue it will become

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32
Q

what is the end product of intramembranous ossification

A

sandwich of spongy bone with compact bone as bread
in detail:

periosteum with fibroblasts
osteogenic stem cells
compact bone
endosteum with osteogenic stem cells
spongy bone
endosteum with osteogenic stem cells
compact bone
osteogenic stem cells
periosteum with fibroblasts

33
Q

explain the process of intramembranous ossification

A
  1. the mesenchyme condenses
    mesenchyme possesses fibroblasts and osteogenic stem cells
    blood vessels form into the mesenchyme which feed it
  2. the blood vessels form the framework
    the osteogenic cells begin to surround the blood vessels
  3. the osteogenic cells lay down bone
    the osteogenic cells do mitosis and differentiate into osteoblasts which lay down bone (trabiculae) along blood vessels
    the remaining mesenchyme becomes bone marrow
    this is spongy bone
  4. blood vessels migrate away from mesenchyme
    the osteogenic cells move with the blood vessels, building osteons (compact bone) as they go
    this happens from both sides of the mesenchyme, forming the compact bone bread
    fibroblasts travel through the blood vessels and build the periosteum after the layer of osteogenic stem cells on both sides
34
Q

explain the process of endochondrial ossification

A
  1. the hyaline cartilage model is formed
    a long bone possesses lacunae with chondrocytes (just hyaline cartilage)
  2. blood vessels bring osteogenic stem cells
    form the bony collar (layer of bone outside of cartilage)(basically ice cream coated with hardened chocolate layer)
    there needs to be room inside of the cartilage for the blood vessels and osteogenic cells to get in
  3. chondrocytes in lacunae undergo hypertrophy
    they grow super duper big and break down the matrix, weakening the cartilage model
    blood vessels are then able to get into the model
    osteogenic stem cells follow and build spongy bone in the same process as IM ossification
    (forming trabiculae and then osteons)
    this first happens in the middle (forming primary cavity) and then happens at both ends (forming secondary cavities)
35
Q

what is the end product of endochondrial ossification

A

secondary marrow cavity surrounded by compact bone
hyaline cartilate (epiphyseal plate)
primary marrow cavity surrounded by compact bone
hyaline cartilage (epiphyseal plate)
secondary marrow cavity surrounded by compact bone

36
Q

what are the different kinds of growth and remodeling of bone

A

happens after bones have developed
2 types:
interstitial growth (growing longer)
appositional growth (growing wider)

37
Q

where does interstitial growth happen

A

happens at epiphyseal plate
under x rays, you can see the epiphyseal plate in children but in adults it is all gone (you can still see the epiphyseal line)
there are two ends of the epiphyseal plate: metaphysis
this is where the bone growth happens: mitosis of the catilage which lengthens and ossifies to create more bone

38
Q

what are the zones of metaphysis/process of interstitial growth

A
  1. zone of reserve cartilage
    just regular hyaline cartilage that isnt in the metaphysis
  2. zone of cell proliferation - chondrocytes multiplying and lining up in rows of small, flattened lacunae
  3. zone of cell hypertrophy - cessation of mitosis, enlargement of chondrocytes, and thinning of lacunae walls
  4. zone of calcification - temporary calcification of cartilage matrix between columns of lacunae
    so that the growing cartilage does not collapse bc its not strong enough to hold your body up
  5. zone of bone deposition - breakdown of lacunae walls, leaving open channels, death of chondrocytes, bone deposition by osteoblasts, forming trabeculae of spongy bone
    blood vessels with osteogenic cells go in and do all of that stuff to form osteons
39
Q

explain the two types of dwarfism

A

pituitary dwarfism - everything is proportional but everything is just smaller
all bones stop growing
due to a growth hormone deficiency in the pituitary gland which normally will cause interstitial growth

achondroplastic dwarfism - possess a proportional torso of average size but appendages arent proportional
long bones stop growing during childhood
no problem with development of flat bones
hyaline cartialge in long bones cant do interstitial growth

40
Q

what is appositional growth

A

growing in girth from superficial surface
deposition of new osseous tissue at the bone surface by osteogenic cells that are in the periosteum
they become osteoblasts and build bone appositionally (in diameter)
this is what creates the circumferential (outer) lamellae which surrounds ALL of the osteons in the middle

41
Q

what is the relationship between interstitial and appositional growth

A

IS and APP growth can happen at the same time
APP growth can always happen without IS growth

42
Q

what are the multiple different categories of bone fractures

A

stress fracture - due to abnormal stress (falls, impact, etc.)
pathological fracture - bone is weakened due to disease (cancer, osteoporosis, etc.) and breaks as a result

closed - doesnt break through skin
compound - breaks through skin

in position - no reducing required
out of position/displaced - requires the bone to be reduced
incompletely broken/greenstick - bone hasnt broken all the way through but is bent
comminuted - bone broken in 3+ pieces, usually also displaced

43
Q

why might a bone fracture need to be reduced (what is that)

A

reducing a bone is putting it back in its place so that it wont be deformed when it heals
out of position bones need reducing

44
Q

how long does it taken uncomplicated stress fractures to heal?

A

8-12 weeks

45
Q

explain the process of healing bone fractures

A
  1. formation of a hematoma
    broken blood vessels form a blood mass that possesses fibroblasts, macrophages (clears broken bone fragments), and osteoclasts (smooths bone over the rough breakage)
    osteogenic cells become abundant (in periosteum and endosteum) within 48 hours (undergo massive mitosis to help build bone back
    blood clot forms into granulation tissue
  2. formation of soft callus
    osteogenic cells differentiate into chondroblasts which build cartilage
    produces a soft callus of fibrocartilage model (NOT HYALINE)
    this is similar to endochondrial ossification and interstitial growth
  3. conversion to a hard callus
    osteogenic cells produce osteoblasts which produce the hard callus
    hard callus is a bony collar which outlines joint where the bone is broken (not in model, but around it)
    acts as a temporary joint that solidifies and supports regrowth of new bone
    you wear a cast for 4-6 weeks so that you can form this
    similar to building a bone collar in endochondrial ossification
  4. remodeling
    hard callus persists for 3-4 months then forms into bone –> exactly like IS growth
    the osteoblasts deposit spongy bone and superficially it becomes compact bone
    the remnant of the hard callus can be seen after healing on an x ray (appears as a little bump over the place where the break happened)
46
Q

how is bone a metabolically active organ

A

bone is constantly exchanging between self maintenance, growth and remodeling
and exchange of calcium and phosphorous with the body
by way of blood vessels

47
Q

what is mineral deposition and resorption

A

how bone tissue exchanges minerals with the body

mineral deposition builds bone
minerals are extracted from blood plasma and deposited into bone tissue
(lower amount of Ca and P in the blood)
bone forms this way (calcification/mineralization)

mineral resorption breaks down bone
minerals are extracted from bone tissue and released into blood plasma
(higher amount of Ca and P in the blood)

48
Q

why doesnt mineral deposition happen in all tissues

A

most cells have uniport Ca pumps using ATP pump calcium out of cells

49
Q

what is ecctopic ossification

A

osseous tissue in places other than bone
can be anywhere
forms a calculus - a calcified mass in a soft organ

ex. arteriosclerosis
plaque buildup in endothelium of blood vessels
can cause a heart attack

ex. kidney stones are calculi

50
Q

how does mineral resorption occur

A

osteoclasts possess ruffled borders (foldings of plasma membrane) which increase surface area for resorption
they possess hydrogen pumps which secrete H+ into the matrix of bone
Cl- is electrically attracted to H
forms HCl (pH=4) which dissolves bone minerals
(bone experiment in lab –> acid pulls out minerals making bone flimsy)

secretes acid phosphatase which digests collagen
breaks down collagen and minerals have no where to crystallize and they can then go into the blood stream

51
Q

what is the balance between bone cells

A

there is balance between osteocytes and osteoblasts which do mineral deposition and osteoclasts which do resorption
^^ creates the balance of continual turnover of bone

about 10% of skeletal tissue is remodeled per year
^ releasing minerals into blood
repairing micro-fractures
reshaping bones due to use

52
Q

what are some examples of bone remodeling because of use

A

leg muscles that attach to tibial tuberosity
increased muscle movement increases the size of the tibial tuberosity in order to support the muscles

the hip muscles that are involved in walking are attached to the greater trochanter of the femur
infants dont have a greater trochanter since they dont walk but it forms once they start learning how to walk

braces

53
Q

what are characteristics of bone remodeling

A

releasing minerals into blood (osteoclasts breaking down bone)
repairing micro fractures (dont even know that it has happened
reshaping of bones due to use - change in use of muscles changes shape of bones

54
Q

explain how braces work

A

teeth are embedded in the spongy bone of the mandible - they dont actually touch bone, they are connected by the periodontal ligament
braces are needed when the alignement is off and they are trying to move the teeth
they attach a wire to teeth and pull it to one side or another
very slow process

there is a compression side and a tension side.
the compression side is where the orthodontic force is pulling the teeth to - causes more osteoclasts to be expressed and therefore more bone to be broken down on that side
the tension side is where the orthodontic force is pulling the teeth away from - causes more osteoblasts to be expressed and therefore more bone to be produced on that side.

55
Q

what is osteoporosis

A

severe loss of bone density over time
one of the most common bone diseases
occurs to a point where the bones are so brittle that they can have pathological fractures

56
Q

who is affected by osteoporosis

A

mostly develops in the 40s and shows symptoms in the 60-70s
there is no way to prevent it – everybody gets it as you age

post menopausal women are at higher risk

57
Q

why are post menopausal women more affected by osteoporosis

A

menopause is the stopping of the reproductive cycle
when this happens, estrogen levels decrease
normally, ovulation causes the release of estrogen and estrogen inhibits osteoclasts from breaking down bone
without this there is no proper regulation of osteoclasts

58
Q

explain how osteoporosis can cause problems in the body

A

about 30-50% of bone tissue is lost by about 70 years old
affects mostly spongy bone
can cause spine problems – spine compression – kyphosis – very convex (hunchback) spine
can happen to everyone

59
Q

what are treatments of osteoporosis

A

injections of Denosumab (active ingredient of things like Prolia, Xgeva, etc.)
this behaves just like estrogen (competitively inhibits RANKL receptor) without the hormonal effects of actual estrogen.

60
Q

what is the importance of PO43-?

A

DNA, RNA, ATP, phospholipids, acid base homeostasis, etc.

61
Q

what is the importance of Ca2+

A

communication, exocytosis, muscle contraction, blood clotting

communication between neurons – the release of a neurotransmitter through exocytosis is triggered by Ca

Ca has to bind to a protein (troponin) so that actin and myosin can bind leading to muscle contraction

maintaining the resting membrane potential
^^outside of the cell is positive and inside of the cell is negatively charged
all cells need this to function, especially muscle and nervous cells

62
Q

what is RANKL

A

receptor activator of nuclear factor Kappa beta-ligand
is a chemical ligand that is released when they want to stimulate the development of osteoclasts

63
Q

explain how osteoblasts/cytes causes differentiation of osteoclasts

A

osteoblasts/cytes do two things: make and deposit collagen, and make and release RANKL (receptor activator of nuclear factor Kappa Beta-ligand)
when RANKL is released into the ECM, they travel to the transmembrane protein RANKL receptor on a hematopoietic stem cell
this causes the stem cell to differentiate into osteoclasts

64
Q

explain how estrogen inhibits osteoclast production

A

estrogen acts as a competetive inhibitor on the RANKL receptor. It binds to this receptor on a hematopoietic stem cell so that RANKL cannot bind
therefore, there is no differentiation of the stem cell into osteoclasts

estrogen prevents osteoclast overproduction
(with a lack of estrogen (like in postmenopausal women) osteoclasts are produced too much)

65
Q

how are blood calcium levels regulated – what are the extremes

A

by hormones
hypercalcemia and hypocalcemia

66
Q

what is hypercalcemia

A

rare disease
too much blood Ca2+ levels

makes it hard to send messages
less excitability of nervous and muscle tissue
sluggish reflexes, depression, coma

there are so many Ca ions on the outside of the cell blocking the negative glycolipids that the positive charge on the outside is so large compared to the negative inside charge

67
Q

what is hypocalcemia

A

too little blood Ca2+
has a wide variety of causes
- vitamin D deficiency
- diarrhea (short term hypocalcemia)
- thyroid tumors and underactive parathyroids
- pregnancy and lactation

can lead to physiological problems

excess excitability of nervous and muscle tissue
tremors, spasms, cardiac failure
too easy to send messages

there are not enough Ca2+ ions on the outside of the cell so that the charge is a smaller positive than what it should be

since the difference in charge is so little, it is much easier to send messages (its almost spontaneous)

68
Q

what is calcium homeostasis and what does it involve

A

maintaining the balance of the membrane potential
involves dietary intake, urinary/fecal loss, exchanges with bone
in a healthy person
-if you ingest too much Ca, you will excrete it or store it in bone
-if you dont ingest enoguh Ca, you will take it from bone and put it in blood

69
Q

what are the three hormones that regulate Ca homeostasis

A

calcitriol (vit d)
parathyroid hormone
calcitonin

70
Q

what are endocrine glands

A

glands that are highly vascularized an secrete hormones into the blood stream so that they can have their physiological effect

71
Q

what kind of gland is the thyroid

A

endocrine

72
Q

what is resorption

A

the reverse of sorbtion (the binding of two things)
pulling Calcium off of collagen and putting it in blood

73
Q

what is absorption

A

taking something outside of the body and taking in anything with the digestive tract (tubes not cells)
once it is in the cells, it is absorbed

74
Q

what is reabsorption

A

reabsorbing something that was in the body but is about to be excreted as waste

75
Q

what is calcitriol and what (and how) does it do for Ca levels

A

calcitriol is the active form of vitamine D (produced in the skin, liver, and kidneys)
behaves like a hormone but is not derived from an endocrine gland (^)

calcitriol raises blood Ca levels

-increases Ca absorption by the small intestine
-increases Ca reabsorption in the kidneys (not excreting it out)
-increases Ca resorption from the skeleton

76
Q

how does calcitriol cause increased Ca2+ resorption

A

increases the production of osteoclasts indirectly

calcitriol is a steroid hormone (it can pass through the PM (lipid soluble))

calcitriol goes into an osteocyte/blast and activates kinases which activate enzymes which activates RANKL production
RANKL then goes on to activate the RANKL receptor on hematopoietic stem cells, causing their differentiation into osteoclasts (secreting H+ and acid phosphatase)

this is why we need vitamin D
found in supplements
its also put in milk bc a lot of people used to drink milk (now its put into orange juice)

77
Q

what is parathyroid hormone and what (how) does it do to blood calcium levels

A

parathyroid hormone is secreted by the parathyroid gland which sits posterior to the thyroid gland and lateral to the pharynx (and trachea/esophagus)
increases calcium levels in 4 ways:

  1. increases osteoclasts for more bone resorption in the same way as calcitriol
    - it is not steroid based so it cannot pass through the plasma membrane
    -PTH binds to a PTH receptor (transmembrane protein) on the PM of an osteocyte/blast
    -when it binds, it stimulates the release of a G protein which travels to adenylate cyclase which converts ATP into cAMP
    -cAMP goes on to activate kinases which activates enzymes which increases RANKL production (just like calcitriol does)
  2. promotes Ca2+ reabsorbtion in kidneys
    -less Ca is lost into the urine (increases blood Ca levels)
  3. promotes the final step of calcitriol synthesis
    - the hydroxylating of calcidiol in the kidneys
    - enhances the amount and effect of calcitriol
  4. inhibits collagen synthesis by osteoblasts
    - inhibiting bone deposition
    - conservation of calcium
78
Q

what is calcitonin and what (and how) does it do for blood Ca levels

A

hormone secreted by the thyroid gland (anterior to the trachea)
lower Ca2+ levels in 2 mechanisms:

  1. osteoclast inhibition
    -less Ca resorption from skeleton
    -stops osteoclasts in two ways:
    — in HP stem cells, there are calcitonin receptors that, when calcitonin binds, release a G protein which turns off adenylate cyclase (no ATP is converted into cAMP and no mitosis and differentiation)
    — in osteoclasts, there are calcitonin receptors that, when calcitonin binds, the G protein is relesed and activates adenylate cyclase to convert ATP to cAMP, activating kinases which activates enzymes which shuts down the H+ pumps and shuts down the release of acid phosphatase
  2. osteoclast stimulation
    -more deposition of Ca into the skeleton
    - calcitonin tells osteoblasts to make more collagen through a more complicated secondary messenger system
79
Q

calcitonin and parathyroid work _________

A

antagonistically to balance blood Ca levels so that it is just right for the membrane potential

Anatomy (11 decks)

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