Physiology Exam 3- HSC 422

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

1. Growth hormone (facilitates growth)

2. Insulin (promotes bone formation)

3. Estrogen/Testosterone (inhibit osteoclasts)

4. Vitamin D (promotes bone mineralization)

Hormones that promote bone resorption

1. Parathyroid Hormone (PTH) (stimulates bone resorption)

2. Cortisol (stimulates resorption)

3. Thyroid hormones (T4) (in excess will stimulate resorption)

4. 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?

1. Actin

2. Myosin

3. Tropomyosin

4. 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