Skeletal System

Question 1

What are the major organs of the skeletal system?

Answer 1

Bones, cartilage, ligaments

Question 2

What are the functions of the skeletal system?

Answer 2

• Provide support and protection for other tissues
• Store calcium and other minerals
• Blood cell production

Question 3

Describe the composition of bone

Answer 3

Bone Matrix
-Consists of extracellular protein fibres, ground substance (fluid), and inorganic compounds (e.g. calcium)
Bone Cells
-Osteocytes
-Osteoblasts
-Osteoclasts
-Osteogenic

Question 4

What is an osteocyte?

Answer 4

Mature bone cell that maintains bone matrix

Question 5

What is an osteoblast?

Answer 5

Immature bone cell that produces new bone matrix in a process called ‘ossification’

Question 6

What is an osteoclast?

Answer 6

Absorb and remove bone matrix

Question 7

What is osteogenic?

Answer 7

Stem cells that ultimately become osteoblasts

Question 8

Describe an osteon

Answer 8

• Mature compact bone

- Consists of venule, canaliculi, central canal, capillary, lacunae and lamellae

Question 9

What is a venule?

Answer 9

• Transport blood to heart

- Small blood vessel

Question 10

What is the canaliculi?

Answer 10

Narrow passageway that permits transport of nutrients/wastes

Question 11

Describe the central canal?

Answer 11

Contains blood vessels that carry blood to and from osteon

Question 12

What is a capillary?

Answer 12

Small blood vessel that transport blood to osteon

Question 13

What is the lacunae?

Answer 13

Mature bone cell that maintains bone matrix

Question 14

What is the lamellae?

Answer 14

Layers of bone matrix and collagen that add strength and resiliency

Question 15

What is the structure of spongy bone?

Answer 15

• Bone marrow

- Trabeculae

Question 16

Describe bone marrow

Answer 16

• Within epiphyses of long bones & large bones
• Red bone marrow (blood cell production) is present between trabeculae
• Yellow bone marrow (adipose tissue-energy reserve) present at other sites

Question 17

Describe the trabeculae

Answer 17

• Meshwork of supporting bundles of fibres in the matrix of spongy bone
• Nutrients reach osteocytes by diffusion along canaliculi

Question 18

Describe periosteum

Answer 18

• Membrane that covers superficial layer of compact bone
• Isolates bone from surrounding tissues
• Involved in bone growth & repair

Question 19

Describe endosteum

Answer 19

-Thin layer of osteogenic cells,
osteoblasts, and osteoclasts
-Covers trabeculae of spongy bone and lines the medullary cavity
-Bone growth, repair, and
remodelling

Question 20

Describe endochondral ossification

Answer 20

• Chondrocytes in hyaline cartilage calcify and die
• Cells of perichondrium turn into osteoblasts
• Formation of periosteum
• Osteoblasts form compact and spongy bone
• Osteoclasts remodel bone
• Some cartilage remains exposed to joint cavity as articular cartilage

Question 21

Describe intramembranous ossification

Answer 21

• Occurs in clavicles, mandible, and flat bones of skull

- Begins when osteoblasts differentiate within mesenchymal or fibrous connective tissue

Question 22

Can you briefly describe the effect of exercise on bone growth and maintenance?

Answer 22

Increased physical activity
Increased applied force (stress) to bones
Increased bone production by osteoblasts

Decreased physical activity & weightless environment
Decreased applied force (stress) to bone
Bone loss

Question 23

Describe what occurs when blood calcium ion levels increase

Answer 23

-Low calcium ion level in blood
-Parathyroid gland secretes parathyroid hormone
Bone response: osteoclasts stimulated to release stored calcium ions from bone- calcium released
-Kidney response: kidneys absorb calcium ions, more calcitriol- calcium conserved, decreased calcium loss in urine
-Intestinal response: intestinal absorption of calcium increases- calcium absorbed

Question 24

Describe what occurs when blood calcium ion levels decrease

Answer 24

• High calcium ion level in blood
• Thyroid gland secretes calcitonin
• Bone response: osteoclast activity decreases, osteoblast activity unaffected- calcium release slowed
• Kidney response: kidneys excrete less calcium ions, less calcitriol- calcium excreted, increased calcium loss in urine
• Intestinal response: intestinal absorption of calcium decreases- calcium absorbed slowly

Question 25

What type of cell is present in the matrix of cartilage?

Answer 25

Matrix: firm gel containing proteoglycans
Cells: chondrocytes located in lacunae (small chambers within the matrix)

Question 26

What type of cartilage covers the bony surfaces in many joints?

Answer 26

Hyaline cartilage

-Covers opposing bone surfaces in many joints (articular cartilage)

Question 27

What is the most abundant type of fibre in ligaments and how are the fibres arranged?

Answer 27

• Consisting of primarily collagen fibres that are aligned parallel to direction of force applied to tissue
• Collagen fibres: bundle fibrous protein subunits wound together, strong and flexible

Question 28

What type of cells are responsible for producing and maintaining collagen?

Answer 28

Fibroblasts: secrete protein subunits that interact in the matrix to form collagen
Fibrocytes: maintain collagen fibres

Question 29

How does Vitamin D contribute to calcium homeostasis?

Answer 29

• Body uses vitamin D to make calcitriol
• Calcitriol is a hormone released by kidneys
• Calcitriol promotes calcium absorption by digestive tract