BNG-338 Mechanobiology
Exam 1
BNG -338 Mechanobiology
Exam 1
October 15, 2013
Name: SOLUTION
This exam is closed book, closed notes. There are 5 section/questions, please write your name
on each page.
Grade:
#1 _______/ 10
#2 _______/ 10
#3 _______/ 30
#4 _______/ 25
#5 _______/ 25
Final Grade __________/ 100
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
1. Complete the crossword puzzle using the clues. Each answer is worth 1 pt. Total 10 pts
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
2. Identify and describe the processes indicated by the white arrows and the black *. 10 pts
The white arrows indicate interstitial
growth. Interstitial growth is the
formation of cartilage within the
cartilage mass. This is done through the
process of chondrocyte division within
the lacunae. The cells initially reside in
the same lacunae, but as they secret
matrix, they move apart and reside in
different lacunae. 5 points
The black asterisks indicate apposition
growth. Apposition growth is the
formation of cartilage on the surface of
existing cartilage. Cells initially have
the appearance of fibroblasts and
produce type I collagen. When cartilage growth is initiated, the cells undergo a change and
become chondroblasts and secrete type II collagen. 5 points
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
3. Analyze the following images.
(a) Label the types of bone indicated in the femur. 2 pts
Cancellous/Spongy/Trabecular Bone
Compact/Cortical Bone
(b) What are the types of tissues indicated by the histological slides A and B? Where can they
can they be found and why are they found there? 4 pts
A
B
A is Hyaline Cartilage. Hyaline cartilage is 60-70% water which is bound to proteoglycans
which are hydrophylic. This gives hyaline cartilage rigidity allowing it to absorb high loads.
With this in mind, it is on the bone surface of joints as well as the ribs.
B is Elastic Cartilage. Elastic cartilage is similar in composition to hyaline cartilage, but it also
contain elastic fibers and interconnecting sheets of elastic material. The elastin allows it to
expand and contract and be flexible. With this in mind, it is found in the walls of the external
auditory canal, external ear, eustachian tubes, epiglottis, and larynx.
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
(c) Define and describe the process depicted in this image. 5 pts
This is Intramembranous ossification. It
begins with mesenchymal cells migrating and
aggregating in the mesenchyme. The area
becomes more vascularized and the cells
become larger and rounder and differentiate
into osteoblasts. The osteoblasts start to
secret osteoid, collagen, and proteoglycans.
The matrix eventually become mineralized.
(d) Identify and describe the common feature among these animals. 4 pts
These animals all have tetrapod limbs. The
tetrapod limb consists of a single long bone
(humerus or femur), followed by two smaller
bones (radius/ulna or tibia/fibula) followed by
an array of smaller bones of the hand or foot.
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
(e) Name the cells indicated below. Describe the characteristics and functions of B, C, and D.
15 pts
A: Osteoprogenitor Cell
B: Osteoblast
C: Osteocyte
D: Osteoclast
4 points
Osteoblasts differentiate from mesenchymal stem cells. They are cuboidal in shape and secrete
osteoid. They have an extensive endoplasmic reticulum. 3 points
Osteocytes reside in lacunae and are surrounded by extracellular fluid. They have cellular
processes that they extend into the canaliculi and meet processes from other osteocytes. They
can pass ions from one cell to the other. They are believed to be sensors of mechanical load in
bone. They are derived from osteoblasts that get embedded within the matrix. 4 points
Osteoclasts are giant multinucleated cells that for from hematopoietic stem cells. They are ~100
um in diameter and have a ruffled edge. They attach to the surface of bone, forming a tight seal.
They secrete acid that dissolves bone and expels the debris into the blood steam. 4 points
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
4. (a) What is this an image of and where can it be found? 5 pts
(b) Describe what is happening in A, B, C, and D. 20 pts
A
B
C
D
This is an image of a growth plate. It can be found at the ends of the bones that form by
endochondral ossification. These include long bones and bones in the hands and feet. 5
points
A: Zone of reserved cartilage: exhibits no cellular proliferation or matrix production 5
points
B: Zone of proliferation: cartilage cells under go division and are organized into distinct
columns, cells are larger than cells in reserve zone and are actively producing matrix 5
points
C: Zone of hypertrophy: cells are greatly enlarged, matrix is compressed into linear bands b/
t columns of hypertrophied cells 5 points
D: Zone of calcified cartilage: enlarge cells begin to degenerate and matrix becomes
calcified 5 points
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BNG-338 Mechanobiology
Exam 1
Name: SOLUTION
5. You are working in Dr. Ulna’s lab and you have been asked
to design an experiment to “grow” a long bone in the lab. To
do this, you would need to describe what the tissue would
need to do to develop into a long bone. This description
will help you design your experimental parameters. You can
use pictures and words to describe the stages/steps. 25 pts
In order to develop into a long bone, it must undergo the process of endochondral
ossification. This process involves several steps as outlined below.
•
•
•
•
•
First, we would need to have mesenchymal cells proliferate and differentiate into
chondrocytes. This could perhaps be on a scaffold or in a mold so that we can get the
hyaline cartilage to forms the general shape of bone. This bone shape grows by
interstitial and appositional growth
Second, we would need to have the appearance of a cuff. This is happens when the
perichondral cells stop differentiating into chondrocyte and instead become osteoblasts,
no longer perichondirum, now periosteum
The periosteal bone collar causes compression of chondrocytes become hypertropic and
begin to synthesize alkaline phosphatase and cartilage starts to calcify
The calcificatoin inhibits diffusion and cells die in the cartilage matrix, bone vessels
grow in from bone collar
The periosteal cells migrate with blood vessels and become osteoprogenitor cells
• when these cells come in contact with the broken down and partially removed matrix,
they become osteoblasts and begin to lay down osteoid
All of this would require an extensive system with addition of various media as well as
introducing cells that could develop the blood vessels.
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