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What is articular cartilage composed of?
water (70%), chondrocytes, Type-2 collagen, and an extracellular matrix of glycoproteins (like aggrecan)
How much articular cartilage declines each year?
decreases in thickness by 0.25 mm per year
Does articular cartilage appear on x-rays?
Cartilage of the long bones does not appear on X-rays
What are BMUs?
Basic Multicellular Unit
What are BMUs comprised of?
osteoclasts and osteoblasts
What is BMU job?
needed for bone remodeling
Wolfe's Law
"Bones are remodeled to fit their mechanical functions."
Law of Bone Transformation
"Bone is deposited where it is needed and is removed from where it is not needed."
What effect does menopause have on bone decline in women?
-a decline in estrogen in older women -inhibits the activity of osteoclasts -decline in bone density
What are loading regimes in bones?
test a bone's strength: -tension -compression -shear -torsion
When bone is strong and when is it weak?
-Bone is strongest in compression
Bone is weakest in torsion or shear
Bone is intermediately strong in tension
What is stress?
Force/Area (equivalent to pressure)
What is strain?
the percentage of length change that occurs under stress (applied force)
What is Yield Strength?
the amount of stress a material can absorb before it deforms
How many BMUs are working per year?
-In healthy adults, 3-4 million -1 million operating at any moment in time.
Are there more osteoclasts or osteoblasts?
Osteoblasts greatly outnumber osteoclasts
For every 10 or so osteoclasts, there are several hundred osteoblasts
What are the types of fracture healing?
-Direct (primary bone healing) -Indirect (secondary bone healing
Direct (primary bone healing)
Occurs without callus formation
Indirect (secondary bone healing)
Occurs with a primary callus precursor
Has 4 stages of healing: *Impaction stage *Inflammation stg *Reparative stage *Remodeling stage
Impaction stage
The initial damage is done. Pain lasts about a week
Inflammation stage
fracture ecchymosis. This stage lasts about 2 weeks.
Reparative stage
-The primary callus will form around the fracture -New tissue is deposited and connected with cartilaginous tissue -This stage can last for months.
Remodeling stage
The callus will harden and begin being reshaped by BMUs. This stage can last for years.
fracture ecchymosis
Internal bleeding causes a painful blood bruise
What is a fracture callus?
a set of new, soft tissue that surrounds a fracture
When do we see fracture callus?
-during the reparative stage -starts soft becomes hard (bony callus formation)
What is collagen?
the most common form of protein found in connective tissues in mammals
How many types of collagen are there?
29
What is collagen made of?
amino acids and fibroblasts
what % of proteins in the body are collagen?
25-30%
What are the different types of cartilage?
Hyaline (articular)
Yellow elastic (non-articular)
Fibrocartilage (articular)
when does fracture ecchymosis form?
the inflammatory stage
what causes fracture ecchymosis?
lysosomes have emptied their acidic contents to the surrounding tissue causing swelling and pain
Hormones that help bone growth OR inhibit bone loss
Growth hormone (facilitates growth)
Insulin (promotes bone formation)
Estrogen/Testosterone (inhibit osteoclasts)
Vitamin D (promotes bone mineralization)
Hormones that promote bone resorption
Parathyroid Hormone (PTH) (stimulates bone resorption)
Cortisol (stimulates resorption)
Thyroid hormones (T4) (in excess will stimulate resorption)
Anti-inflammatory hormones (stimulate resorption)
What is Aggrecan?
One of those "all of the above" questions
-a building block of cartilage -It is composed of chondroitin and keratin sulfate
What are GAGs, proteoglycans, and Mucopolysaccharides?
"All the above" question
These are all similar compounds that are found in cartilage
What are Type 1 and Type 2 collagen?
Type 1 collagen is found in the skin, tendons, vascular ligature, organs, and bone
Type 2 collagen is found can be found in all kinds of cartilage
Both these collagen types are made of matrices that include aggrecan, GAGs, proteoglycans, and mucopolysaccharides.
What is Elastin?
It is a protein found in connective tissues
Helps the skin restore its shape
Important in the skin, bladder, lungs, ligaments, vertebral discs, and the Aorta
What is the Parathyroid gland?
set of four endocrine glands situated above or within the thyroid gland
Where is Parathyroid gland located?
the neck behind the thyroid
What is the parathyroid gland job?
constantly monitoring the Calcium levels in the blood
The parathyroid gland is comprised of what?
"Chief cells" (monitor Ca levels) and "Oxyphil cells" (whose function is not actually known)
When and where is PTH released?
from the parathyroid gland when Calcium levels in the blood drops
What does PTH do?
promote Vitamin D which helps the bones and intestines absorb Calcium as well as help the kidneys (renal system) hold onto its Calcium
Hypocalcemia
too little Calcium
Hypercalcemia
too much Calcium
What role(s) does Vitamin D play?
-maintain normal blood Calcium and phosphorus levels. -maintain healthy immune functions and fights excessive inflammation -inhibits PTH secretion
Where does Vitamin D come from and where does it activate?
Vitamin D is derived from cholesterol (it's a hormone)
Its active from plants (Ergocalciferols), UV rays, and plant sterols
How can one get D2 from?
-eating bread, milk, and other grains
where does D3 come from and where are you get it from?
-comes from animals (Cholecalciferols)
One can get D3 from animal oils, fish, and egg yolks
What is a Motor Unit?
a functional unit consisting of A-alpha motor neuron and all muscle cells (myocytes)
What is a Neuromuscular Junction?
the junction where the motor neuron and the muscle fibers meet.
The NMJ serves to transmit and amplify what?
the nerve impulse to the muscle
The neurotransmitter released by what?
the A-alpha motor neuron onto each myocyte in the motor unit is Acetylcholine (ACh)
All muscle cells of a motor neuron will contract in sync when ____ is released
ACh
If there is a signal, an _______________ is guaranteed
an action potential (AP)
If you activate the neuron, of the muscle, ________ will occur and will contract
depolarization
______ of the motor unit will have varying diameters depending on how many myocytes they have "recruited"
Axons
why are small axons easier to stimulate?
because they have lower thresholds
why are large axons harder to stimulate?
because they have higher thresholds
What is Calcitonin?
a man-made hormone that can be found in supplement form
what is calcitonin used for:
It is used to stabilize Calcium levels when they are too high (Hypercalcemia)
Where can Vitamin D be stored when it is inactive? when can it release?
in the skin and can be released by Keratinocytes
Hypercalcemia
too much Calcium in the blood
Hypocalcemia
too little Calcium in the blood
What is a Sarcomere?
It is a repeating, structural unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band
A Sarcomere is how many microns in length?
2-3
The Sarcomere defines what?
the functional contractile unit of the myocyte
striated muscle
The visible striations (light and dark regions) give the myocyte its name
"A" bands (A = anisotropic)
The dark bands created by the myofilaments in the myofibril
"I" bands (I = isotropic)
The light bands created by the myofilaments in the myofibril
In the middle of each dark "A" band is a lighter _____
"H" zone
In the middle of each light "I" band there is a strong ____
(dark) "Z" line
The "M" line binds the thick myosin filaments together in the middle of the _______
sarcomere
What happens to the muscle zones during contraction?
"A" bands do not change
"I" bands slide toward the center -> <-
"H" zones become smaller or will disappear in the central region of the "A" bands
The space between the "Z" lines (Sarcomeres) will shorten
where is actin filament found?
in the "I" bands -These bands are thinner and lighter
what is actin made up of?
the regulatory proteins: G-actin, F-actin, and Troponin complex
what will actin act upon?
myosin
where is myosin filament found?
in the "A" bands -These bands are thick and darker -about 250 myosin molecules entwined along their length
Each myosin is surrounded by
6 actin filaments
Actin filaments outnumber myosin by
a factor of 5-10x as much
What are the contractile proteins that comprise the myofilaments?
Actin
Myosin
Tropomyosin
Troponin
How does muscle contraction occur?
The myosin globular head will bond to an actin
A high-energy phosphate breaks the bond
After, energy is stored in the myosin head
Calcium enables the binding sites
Tropomyosin hides the binding sites once more
what is stored in the muscle when the muscle is at rest
calcium
When the skeletal muscle is depolarized, ______ rushes to the contractile proteins
Calcium
Calcium has a strong affinity for ________
troponin
what happens after Calcium binds to troponin
the troponin undergoes a conformational change
what does troponin undergoing a conformational change allow?
allows troponin to pull tropomyosin away from the myosin attachment sites on the actin strands
actin and myosin can chemically interact because?
the binding sites are uncovered
Magnesium catalyzes what enzyme?
Myosin-ATPase -which provides energy for the actomyosin contraction
________ is necessary to initiate the contraction
Calcium
What role does Calcium play in depolarization?
-Calcium ions regulate whether or not contraction can occur -Thus, what is needed is a way to link muscle excitation (the depolarization of the action potential) to Ca++ release from the sarcoplasmic reticulum
Depolarization
the loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior
Where is Calcium stored?
in the lateral sacs and move through the T-tubules
The resting potential of skeletal muscles
80-90 millivolts
Calcium will return to the lateral sacs via the?
SR (active transport)
What are the components of the skeletal muscle fiber?
-The Sarcoplasmic Reticulum (SR) -The Transverse Tubules (T-tubules)
The Sarcoplasmic Reticulum (SR) surrounds what?
the myofibrils
where is the Transverse Tubules (T-tubules) located
adjacent to the terminal cisterns
Note 
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