Chr. 6 - Skeletal System

Question 1

[6.1] What is a bone?

Answer 1

An organ providing structural framework made of several connective tissues: osseous tissue, cartilage, dense connective tissue, adipose; as well as epithelium and nervous tissue.

Question 2

[6.1] What are the functions of the skeletal system?

Answer 2

Support, protection, assistance in movement, mineral homeostasis, blood cell production, and triglyceride storage.

Question 3

[6.1] How does the skeletal system provide support?

Answer 3

By providing attachment points for tendons and supporting soft tissue with rigid structure.

Question 4

[6.1] How does the skeletal system provide protection?

Answer 4

Creating rigid structures covering vital organs and tissues.

Question 5

[6.1] How does the skeletal system provide assistance in movement?

Answer 5

Provide anchor points for muscles during contractions.

Question 6

[6.1] How does the skeletal system provide mineral homeostasis?

Answer 6

Extracellular matrix of bone contains minerals that are released from or absorbed into the bone to balance out levels throughout the body.

Question 7

[6.1] How does the skeletal system provide blood cell production?

Answer 7

Red bone marrow generates RBCs, WBCs, and platelets through hemopoiesis.

Question 8

[6.1] How does the skeletal system provide triglyceride storage?

Answer 8

Triglycerides are stored in yellow bone marrow, acting as chemical energy reserves.

Question 9

[6.2] What are the typical sections of a long bone?

Answer 9

Diaphysis, epiphyses, metaphyses, articular cartilage, periosteum, medullary cavity, and endosteum

Question 10

[6.2] What is a diaphysis?

Answer 10

The main, central body of a bone.

Question 11

[6.2] What are the metaphyses?

Answer 11

The regions between a bones diaphysis and epiphyses.

Question 12

[6.2] What are the epiphyses?

Answer 12

The proximal and distal ends of the bone.

Question 13

[6.2] What is the articular cartilage of a bone?

Answer 13

A thin layer of hyaline cartilage covering the epiphyses of a bone where it articulates with another.

Question 14

[6.2] What is the periosteum?

Answer 14

Tough connective tissues sheathing the bone where articular cartilage is absent. Consists of an outer fibrous layer and an inner osteogenic layer.

Question 15

[6.2] What is the medullary cavity?

Answer 15

The hollow space within the diaphysis containing red or yellow bone marrow.

Question 16

[6.2] What is the endosteum?

Answer 16

A thin membrane lining the medullary cavity.

Question 17

[6.3] Describe an osteoprogenitor cell.

Answer 17

Unspecialized bone stem cells derived from mesenchyme, develop into osteoblasts.

Question 18

[6.3] Describe an osteoblast.

Answer 18

Cells synthesizing and secreting extracellular matrix and initiating calcification.

Question 19

[6.3] Describe an osteocyte.

Answer 19

Mature bone cells, maintain metabolism and functional activities.

Question 20

[6.3] Describe an osteoclasts.

Answer 20

A large cell composed of many monocytes containing lysosomal enzymes and acids that deconstruct bone matrix to maintain mineral homeostasis.

Question 21

[6.3] What is compact bone tissue?

Answer 21

Bone tissue composed of tightly packed repeating structural units called osteons

Question 22

[6.3] What are osteons? List the components.

Answer 22

Structural units shaped like a tube surrounding blood vessels and nerves. Formed of concentric lamellae, lacunae, canaliculi, and central canals.

Question 23

[6.3] Describe lamellae.

Answer 23

Concentric rings of extracellular matrix formed around central canals.

Question 24

[6.3] Describe lacunae.

Answer 24

Small spaces between lamellae housing osteocytes.

Question 25

[6.3] Describe canaliculi.

Answer 25

Networks of tiny channels allowing the processes of osteocytes to reach other cells for nutrient exchange.

Question 26

[6.3] Define central canals.

Answer 26

Canals located in the center of osteons containing blood vessels and nerves.

Question 27

[6.3] What are interstitial lamellae?

Answer 27

Lamellae located between osteons, also containing osteocytes.

Question 28

[6.3] Describe interosteonic canals.

Answer 28

Blood vessel and nerves that run transverse through osteons.

Question 29

[6.3] What are perforating fibers?

Answer 29

Fibers connecting the periosteum to the osteons of compact bone tissue directly deep to it.

Question 30

[6.3] What is spongy bone tissue?

Answer 30

Bone tissue containing lamellae in columns without central canals, forming a series of connected branches rather than pillars/tubes.

Question 31

[6.3] What is the purpose of spongy bone tissue?

Answer 31

To decrease weight of a bone, and to provide support and protection for the bone marrow found inside.

Question 32

[6.4] What are periosteal arteries?

Answer 32

Small arteries accompanied by nerves entering through interosteonic canals.

Question 33

[6.4] What are the nutrient artery and the nutrient foramen?

Answer 33

A large artery entering the diaphysis; the hole through which the nutrient artery passes.

Question 34

[6.4] What are the metaphyseal arteries and the epiphyseal arteries?

Answer 34

Arteries that enter a bone at a location respective of their names.

Question 35

[6.5] What is ossification?

Answer 35

The process of bone formation.

Question 36

[6.5] What are the situations where bone formation occurs?

Answer 36

1. Initial formation in embryo/fetus.
2. Growth during infancy to adolescence.
3. Remodeling of bone.
4. Repair of bone.

Question 37

[6.5] What are the types of bone formation in embryonic/fetal development?

Answer 37

Intramembranous ossification and endochondral ossification.

Question 38

[6.5] Describe the process of intramembranous ossifcation.

Answer 38

1. Cells of mesenchyme cluster and differentiate into osteoblasts, forming the ossification center.
2. Osteoblasts secrete extracellular matrix until enveloped, at which point they mature into osteocytes.
3. Extracellular matrix forms trabeculae and red bone marrow forms from red bone marrow.
4. Mesenchyme concurrently condenses at the periphery of the bone, developing the periosteum and developing a layer of compact bone overlaying the spongy bone tissue.

Question 39

[6.5] Describe steps 1, 2, and 3 of the process of endochondral ossification.

Answer 39

1. Mesenchyme clusters in the shape of the bone and differentiates into chondroblasts, developing a cartilage model of the bone covered in a perichondrium.
2. Chondroblasts deep in extracellular matrix mature into chondrocytes and divide, growing the cartilage model through interstitial growth. The periosteum carries out appositional growth.
3. A nutrient artery penetrates the periosteum and calcifies the cartilage model while stimulating osteoprogenitor cells. The primary ossification center forms, a region where bone first forms and extending its development inward

Question 40

[6.5] Describe steps 4, 5, and 6 of the process endochondral ossification.

Answer 40

4. Osteoclasts break down bone within the center of the spongy bone tissue forming, creating the medullary cavity.
5. Branches of epiphyseal arteries penetrate the epiphyses and calcify the cartilage around them. This forms the secondary ossification center. where spongy bone tissue develops without a medullary cavity. Bone formation proceeds outwards.
6. Cartilage covering the epiphyses develops into articular cartilage.

Question 41

[6.5] What is interstitial growth of a bone during endochondral ossification?

Answer 41

Lengthwise cartilage growth by secretion of extracellular matrix and cell division of chondrocytes.

Question 42

[6.5] What is appositional growth of a bone during endochondral ossification?

Answer 42

Widthwise growth of a bone by secretion of extracellular matrix from chondroblasts in the perichondrium.

Question 43

[6.5] How does bone grow in length during infancy to adolesence?

Answer 43

1. Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate.
2. Replacement of cartilage on the diaphyseal side of the epiphyseal plate.

Question 44

[6.5] Describe each of the zones of the epiphyseal plate.

Answer 44

1. Zone of resting cartilage - Layer nearest epiphysis consisting of sparse chondrocytes.
2. Zone of proliferating cartilage - Layer above resting cartilage, involves chondrocytes undergoing interstitial growth.
3. Zone of hypertrophic cartilage - Layer above proliferating cartilage, consists of large, matured chondrocytes in columns.
4. Zone of calcified cartilage - Layer above hypertrophic cartilage, consists of dead chondrocytes in calcified extracellular matrix. Osteoclasts clear away calcified cartilage, and osteoblasts replace it during endochondral ossification.

Question 45

[6.5] What is the epiphyseal line?

Answer 45

A bony structure formed when all cartilage has been replaced by bone at the end of adolescent growth.

Question 46

[6.5] How does bone grow in width during infancy to adolesence?

Answer 46

1. Periosteal cells differentiate into osteoblasts, secreting extracellular matrix and maturing into osteocytes.
2. Bone ridges form around blood vessels, eventually enclosing them in the central canal.
3. This process continues as the periosteum is pushed further away from the medullary cavity.

Question 47

[6.5] What is the process of bone remodelling?

Answer 47

Ongoing replacement of old bone tissue by new bone tissue.

Question 48

[6.5] What is bone resorption?

Answer 48

The removal of minerals and collagen fibers from bone by osteoclasts.

Question 49

[6.5] What is bone deposition?

Answer 49

Addition of minerals and collagen fibers to bone by osteoblasts.

Question 50

[6.5] Which factors affect bone growth/remodeling?

Answer 50

1. Mineral availability.
2. Vitamin availability.
3. Hormones.

Question 51

[6.7] What is parathyroid hormone?

Answer 51

A hormone produced by the parathyroid, functions to increase blood calcium.

Question 52

[6.7] What is calcitriol?

Answer 52

The active form of vitamin D that promotes absorption of calcium from ingested substances.

Question 53

[6.7] What is calcitonin?

Answer 53

A hormone promoting bone deposition by inhibiting osteoclasts.