CTO Quiz #2

Question 1

Hyaline Cartilage contains what kind of collagen?

Answer 1

Type II collagen.

Question 2

Where would you expect to find chrondroblasts?

Answer 2

In the perichondrium.

Question 3

What types of growth can cartilage undergo?

Answer 3

Both interstitial and appositional

Question 4

Where do you find chondrocytes?

Answer 4

Chondrocytes (often more than one) are found in lacunae.

Question 5

What gives cartilage its basophilic color?

Answer 5

This is mostly due to sulfated proteoglycans.

Question 6

How do chondrocytes receive their nutrition?

Answer 6

Cartilage is avascular. Nutrition comes by diffusion through the matrix from the extracellular space (including from blood vessels in the perichondrium and from synovial fluid).

Question 7

Where does appositional growth of cartilage take place?

Answer 7

This occurs at the perichodrium.

Question 8

What is the process of interstitial growth?

Answer 8

Chondrocytes replicate, producing isogenous nests. Each daughter cell lays down territorial matrix, pushing them apart. Then the process is repeated.

Question 9

What would you find in the extracellular matrix of hyaline cartilage?

Answer 9

Type II collagen fibers embedded in a ground substance comprised of sulfonated proteoglycans and glycosaminoglycans (GAGs). Some important constituents include: hyaluronic acid, chondroitin sulfate, keratan sulfate, chondroitin sulfate and heparan sulfate.

Question 10

What is the structure of elastic cartilage and where would you find it?

Answer 10

It is basically the same as hyaline cartilage except that it has a large number of elastic fibers in it. It is found in the ear and epiglottis.

Question 11

How does fibrocartilage differ from hyaline cartilage?

Answer 11

It contains a lot of type I cartilage, along with the type II. Therefore, it appears more eosinophilic.

Question 12

Where do you find fibrocartilage?

Answer 12

Fibrocartilage is found in the intervertebral disc, the pubic symphysis and articular discs (including the menisci of the knee).

Question 13

How does fibrocartilage differ from dense, irregular connective tissue ?

Answer 13

Its ground substance is different (like cartilage) and it has chondrocytes in lacunae (including isogenous nests).

Question 14

What kind of fibers are there in bone?

Answer 14

Type I collagen.

Question 15

What are the functions of bone?

Answer 15

Bone functions in support, protection, calcium storage/homeostasis and, when bone is considered as an organ (i.e., including the marrow), in blood cell production.

Question 16

What are the two types of bone and what is the difference between them?

Answer 16

Immature (woven) and mature (lamellar) bone are the two types. The matrix in lamellar bone is laid down in layers that are much stronger, while woven bone has irregular organization of fibers and cells.

Question 17

What are the two types of mature bone?

Answer 17

Cortical (compact; dense) and trabecular (spongy; cancellous).

Question 18

Why do you have spongy bone?

Answer 18

Trabeculae of spongy bone add strength in a particular direction without adding much weight and allowing for a marrow space.

Question 19

What is Wolff’s Law?

Answer 19

Wolff’s law states that bone will remodel to resist forces placed on it.

Question 20

What holds periosteum to the bone?

Answer 20

Sharpey’s fibers hold periosteum to bone (very strong).

Question 21

What is the function of osteoblasts?

Answer 21

They produce the protein content of bone matrix (including fibers), called osteoid. They also secrete alkaline phosptase, which, in the presence of calcium, phosphate and ATP will cause precipitation (mineralization).

Question 22

Where do osteoclasts come from and what is their function?

Answer 22

Osteoclasts arise from the fusion of macrophages that come from circulating monocytes.

Question 23

What do osteoclasts do?

Answer 23

They secrete acid (created by the action of carbonic anhydrase) and acid hydrolases that break down crystals and the protein matrix of bone. Their action is increased by the action of parathyroid hormone and they will release calcium into the blood. Osteoclasts are inhibited by the action of calcitonin.

Question 24

What is an osteon?

Answer 24

Osteons are blood vessel/osteocyte units. They are comprised of lamellar bone organized around a Haversian canal.

Question 25

How are lacunae organized in an osteon? How are osteocytes nourished?

Answer 25

Osteocytes within the lacunae are organized circumferentially around a central blood vessel. Each osteocyte is connected to at least one closer to the blood vessel, with the innermost being directly associated with the blood vessel.

Question 26

What is the difference between circumferential lamellae and lamellae of the osteon?

Answer 26

Circumferential lamellae are layers of bone beneath the periosteum and adjacent to the endosteum that border the inner and outer aspect of the compact part of a long bone shaft.

Question 27

Where would you expect to find osteons?

Answer 27

You find osteons in mature compact bone. This would make up the majority of the compact part of the bone, with some circumferential lamellae bordering the inner and outer surface of the bone. Rarely, you might find an osteon in a very large trabecular of spongy bone, but this is uncommon.

Question 28

What is intramembranous ossification? Where might you find intramembranous ossification in an adult?

Answer 28

This is the process of forming bone from a connective tissue precursor. In the embryo, this precursor is a condensation of primitive mesenchyme. In adults, this continues in the periosteum and, therefore, a large percentage of every bone in the body is formed from intramembranous ossification. Also, fractures heal by intramembranous ossification of a fibrous “scar” called callous.

Question 29

Where do osteoblasts come from during intramembranous ossification?

Answer 29

Osteoblasts differentiate from primitive mesenchymal cells.

Question 30

What would you find within canaliculi in the bone?

Answer 30

The processes of osteocytes would be in the canaliculi. They contact the cytoplasmic processes of adjacent osteocytes and have gap junctions whereby they pass nutrients back and forth.

Question 31

What are the steps in intramembranous ossification?

Answer 31

Osteoblasts develop from mesenchymal osteoprogenitor cells. Cancellous bone (immature) is laid down. This bone undergoes compaction into cortical bone (immature) and remodeling then occurs with maturation of the bone.

Question 32

What bones originally develop by intramembranous ossification?

Answer 32

Much of the skull (except the bones at the base), the shaft of the clavicle and much of the scapula and pelvis originate in an intramembranous ossification process.

Question 33

What is endochondral ossification?

Answer 33

This is the process whereby a cartilage model is replaced by bone. Most bones begin as cartilage models.

Question 34

What are the steps in endochrondral ossification?

Answer 34

A cartilage “model” forms from mesencymal tissue. This model gwows appositionally and interstitially. A bone collar forms at the middle of the shaft, cutting this area off from nourishment and resulting in dystrophic calcification f the cartilage model. Blood vessels invade through the bone collar. These bring other cells into the model. Osteoclasts break down the calcified cartilage, forming a marrow cavity. Osteoblasts lay down bone on calcified cartilage “spicules”. Secondary ossification centers forms at the epiphyses.

Question 35

How does a bone increase in length?

Answer 35

The bone can only increase in length at the cartilage growth plate zones (epiphyseal plates). The growth in length of the bone is due to interstitial growth of cartilage (bone can not grow interstitially). There are zones of cartilage cells in the epiphyses. These include: a resting zone; a zone of proliferation; a zone of hypertrophy; a zone of calcification; and a zone of resorption. Osteoblasts will lay bone down on spicules of calcified cartilage and osteoclasts will break down calcified cartilage and the early bone in order to allow for production of mature bone.

Question 36

About how often is your entire skeleton turned over?

Answer 36

About every three years your entire skeleton is replaced.

Question 37

What is the appearance of skeletal muscle?

Answer 37

Skeletal muscle consists of long, unbranched cells with multiple, peripherally located nuclei and a cytoplasm dominated by protein filaments that are organized in order to give a striated appearance.

Question 38

What are the connective tissue layers of skeletal muscle?

Answer 38

The epimysium surrounds the entire muscle. Perimysium surrounds fascicles (which are comprised of a bundle of muscle fibers). Endomysium is delicate connective tissue that surrounds each individual muscle fiber. The blood vessels and nerves in the muscle run within the connective tissue.

Question 39

What are the functional units of a myofibril and what defines the limits of these units?

Answer 39

Myofibrils are made up of repeating units called sarcomeres. The sarcomeres extend from one Z disc to the next.

Question 40

What is the A band? The I band? The H zone?

Answer 40

The I band is the part of the sarcomere dominated by actin filaments. The A band is the region in which Myosin II molecules give the sarcomere the darker color. The H zone is the somewhat lighter region in the center of the sarcomere where there is myosin, but no actin. The M line is at the center of the sarcomere (the center of the H zone).

Question 41

Which parts of the sarcomere would get shorter during muscle contraction? Which would not?

Answer 41

The I band and the H zone would get shorter; the A band would not.

Question 42

What is the sequence of events in excitation-contraction coupling?

Answer 42

Depolarization of the skeletal muscle fiber membrane is produced by the action of acetylcholine at the neuromuscular junction. This depolarization is distributed over the muscle fiber membrane and deep into the skeletal muscle fiber along the T-tubules. Depolarization of the sarcolemma opens a calcium channel that allows a small amount of calcium to enter the muscle fiber through voltage-gated calcium channels. This calcium, in turn, opens calcium-gated calcium channels in the sarcoplasmic reticulum, with rapid increase in calcium inside the muscle cell. The calcium binds to troponin-C, which causes a conformational change that pulls tropomyosin away from the myosin binding site on the actin filament. Myosin binds to this binding site and undergoes conformational change that flexes the head on the myosin filament. In this process, the myosin filament detaches from the ADP molecule that has been bound to the myosin in the neck region. The net result of this process is that there is movement of the actin along the myosin. It takes multiple iterations of this process to produce visible shortening of the muscle.

Question 43

How does the myosin reset after engaging and moving actin?

Answer 43

ATP must bind to the myosin head in order for it to release the actin and reset. In this process of resetting, it hydrolyzes the ATP to ADP.

Question 44

How many muscle fibers are contacted by one nerve fiber?

Answer 44

The muscle fibers contacted by a single nerve fiber are called a motor unit. The size of the motor unit depends on the muscle. Muscles that produce very fine movements may have 5-20 muscle fibers in the motor unit. Muscles built for power may have hundreds.

Question 45

How many nerve fibers contact a single muscle fiber.

Answer 45

Only one nerve fiber contacts a muscle fiber no matter how long it might be!

Question 46

How are skeletal muscle fibers different from cardiac muscle fibers?

Answer 46

Skeletal muscle fibers are unbranched (cardiac are branched); skeletal muscle fibers are multinucleated (cardiac are individual cells with single nuclei, connected at intercalated discs); skeletal muscle fibers have triads of a T tubule and two cisternae of endoplasmic reticulum (cardiac have dyads, with one of each); skeletal muscle triads are at the A-I junctions (cardiac dyads are at the Z discs); skeletal muscle fibers only normally contract when the nerve acts on it (cardiac have rhythmic contraction). Also there are fewer mitochondria in skeletal muscle than in cardiac muscle.

Question 47

What are intercalated discs?

Answer 47

Intercalated discs are connections between the ends of cardiac muscle fibers and consist of many desmosomes, facia adherens and gap junctions (that allows direct communication along the chain of muscle fibers.

Question 48

What is the appearance of smooth muscle cells?

Answer 48

These are fusiform (spindle shape), with a single, central nucleus and no striations. There may be gap junctions that allow coordinated actions between adjacent cells. Inside the smooth muscle cell there are intermediate filaments, with actin anchored to membrane at dense plaques. Myosin I attaches to actin and pulls on it, allowing contraction.

Question 49

What is the process of excitation-contraction coupling in a smooth muscle cell?

Answer 49

Calcium enters the smooth muscle cell following depolarization of the membrane. Calcium binds to calcium-calmodulin that, in turn, binds to myosin light chain kinase (mlck). This phosphorylates myosin light chains, allowing it to bind to actin.