Module 5 - Bones pt. 1

Question 1

What does the skeletal system include?

Answer 1

1. bones of the skeleton

2. cartilage, ligaments, and other stabilizing connective tissues

Question 2

what are the 6 functions of the skeletal system?

Answer 2

1. support
2. protection of internal organs
3. movement
4. storage of calcium and phosphate
5. production of blood cells (red bone marrow)
6. storage of lipids (yellow bone marrow)

Question 3

What is Osseous Tissue? What is it composed of?

Answer 3

dense, supportive, connective tissue

1. solid extracellular matrix
   - ground substance (intercellular fluid)
   - collagen fibres (1/3 of matrix)
   - calcium and phosphate (2/3 of matrix)
2. specialized bone cells (2% of bone mass)

Question 4

What are the 4 different bone cells?

Answer 4

1. osteogenic cell (develops into osteoblast)
2. osteoblast (forms bone extracellular matrix)
3. osteocyte (maintains bone tissue)
4. osteoclast (functions in reabsorption, the break down of the bone matrix)

Question 5

What are osteoblasts? Where are they found?

Answer 5

• immature bone building cells
• found in single layer on the bone surface
• secrete bone matrix
• before calcium is deposited, the matrix is called osteoid
• when osteoblasts are surrounded by bone, they become osteocytes

Question 6

What are osteocytes? Where are they found? What are their functions?

Answer 6

• mature bone cells
• found in lacunae between layers of bone matrix (enclosed in bone)
• cells connect by cytoplasmic extensions through canaliculi
• do not divide
• functions:
  1. maintain the bone matrix
  2. repair the damaged bone

Question 7

What are osteoclasts?

Answer 7

large cells that line the inside surface of bone

secrete acids and protein digesting enzymes that break down bone matrix and release stored minerals

Question 8

All bone is made of:

Answer 8

1. compact (cortical) bone
2. spongy (trabecular) bone

both contain the same structural units (cells and matrix_ but differ in their organization

Question 9

What is compact bone?

Answer 9

• 75-80% of bone mass
• highly organized
• solid and extremely strong
• forms the outer layer of bones
• basic structural unit is the osteon

Question 10

What are the 6 different parts of the compact bone? What are their functions?

Answer 10

osteon - long cylindrical structure which osteocytes are arranged in concentric lamellae around a central canal

concentric lamellae - rings of hardened matrix form around the central canal

central canal - contains blood vessels (veins and arteries) a lymphatic vessell and a nerve

perforating canals - perpendicular to the central canal, carry blood vessels to the central canals and bone marrow

lacunae - small spaces between lamellae that contain osteocytes

canaliculi - tiny channels that connect lacunae, contains processes of osteocytes (allow communication and exchange of materials between cells)

Question 11

What is spongy bone? what are the features of it?

Answer 11

• 20-25% of bone mass
• no osteons
• the matrix forms trabeculae (=lamellae form a spongy network)
• osteocytes contained in lacunae connected by canaliculi
• no blood vessels
• bone marrow fills the spaces between trabeculae (contains blood vessels)

Question 12

What is the function of spongy bone?

Answer 12

• forms the inner mass of bones
• functions:
  1. reduces weight of bone
  2. supports and protects red bone marrow (blood cell synthesis)
  3. large surface area for bone remodeling

Question 13

What is periosteum? What does it do? What is it composed of?

Answer 13

covers outer surface of bones (except at joints)
outer fibrous layer - contains collagen fibers that connect to bone, tendons and ligaments
inner cellular layer - contains osteoprogenitor cells (stem cells) that divide to produce osteoblasts

Question 14

What is the endosteum?

Answer 14

lines the surface of spongy bone and the central canals of compact bone
contains: 
-osteoprogenitor cells
-osteoblasts
-osteoclasts
surface for bone growth and remodeling

Question 15

what are the 4 classifications of bones?

Answer 15

1. long bones
2. flat bones
3. irregular bones
4. short bones

Question 16

Where are long bones found? Examples?

Answer 16

long and thin

• found in appendicular skeleton
  ex. humerus, femur, phalanges

Question 17

What are flat bones? Examples?

Answer 17

thin bones

• parallel plates of compact bone enclosing spongy bone
  ex. cranial bones, sternum, ribs, scapula

Question 18

What are irregular bones? Examples?

Answer 18

have complex shapes

ex. vertebrae, pelvic bones, facial bones

Question 19

What are short bones? examples?

Answer 19

small, cube shaped

• nearly equal length and width
  ex. ankles (tarsals), wrist bones (carpals)

Question 20

Other 2 bone types are?

Answer 20

1. sutural bones

2. sesamoid bones

Question 21

what are sutural bones?

Answer 21

small, irregular bones

found between the flat bones of the skull

Question 22

what are sesamoid bones?

Answer 22

small and flat
develop inside tendons near joints of knees, and feet.
ex. patella

Question 23

What does the strucutre of long bones consist of?

Answer 23

1. diaphysis
2. epiphysis
3. metaphysis
4. articular cartilage
5. medullary cavity
6. periosteum
7. endosteum

Question 24

What does each part do? What are they?

Answer 24

1. diaphysis -the shaft, formed by compact bone, central space = medullary cavity (bone marrow)
2. epiphysis - distal and proximal ends of long bones, mostly spongy bone covered by a thin layer of compact bone (articular cartilage covers sufaces where bones meet in order to reduce friction)
3. metaphysis - where diaphysis and epiphysis meet, contains the epiphyseal plate, line

Question 25

What are the 4 situations that bone is formed?

Answer 25

1. the initial formation of bones in the embryo and fetus 2. the growth (length and width) of bones in infancy, childhood and adolescence 3. the remodeling of bone (replacement of old bone with new bone throughout life) 4. repair of fractures

Question 26

What is ossification?

Answer 26

the process of replacing other tissues with bone ossification follows two patterns: 1. intramembranous ossification - a connective tissue sheet is replaced by bone - responsible for the development of some flat bones (soft spots of the skull) 2. endochondral ossification - involves the replacement of a hyaline cartilage "model" by bone - responsible for the formation of most bones hyaline cartilage that remains forms: 1. the epiphyseal plate (allows for bone growth in length until adulthood) 2. articular cartilage (lines joint surfaces)

Question 27

What happens with bones grow in length?

Answer 27

- cartilage on the diaphysis side of the epiphyseal plate is replaced by bone - chondrocytes on the epiphysis side divide to produce more cartilage - the width of the epiphyseal plate does not change - the epiphyseal plate cells stop dividing between 18 and 25 years of age, when it is replaced by bone (called the epiphyseal line)

Question 28

What is bone remodeling? what happens?

Answer 28

bone remodelling is the process in which existing bone is broken down and replaced by new bone bone is a dynamic tissue -osteoclasts are constantly breaking down bone (=bone resorption) -osteoblasts are constantly adding new bone (=bone deposition) - the shape of bones is not necessarily changed

Question 29

What is the function of bone remodeling?

Answer 29

1. part of the normal process is bone maintenance --> the entire skeleton is gradually repalced over a period of years 2. provides access to skeletal mineral stores (calcium and phosphate) 1/5 of the skeleton is replaced each year

Question 30

bone turnover must be kept in balance because

Answer 30

- bone deposition exceeds removal = bone spurs | - bone resorption exceeds desposition = osteoporosis

Question 31

requirements for bone growth and remodeling

Answer 31

1. hormones (growth hormone, thyroid hormone, insulin, estrogen, androgens, calcitonin, parathyroid hormone) 2. vitamins (A, C and D) 3. adequate mineral supply (calcium and phosphate) 4. exercise

Question 32

Bone and exercise:

Answer 32

stresses applied to bones during physical activity (weight bearing exercise) are essential to maintain bone strength -stimulates bone formation and inhibits osteoclast activity without bone stress, resorption outpaces formation and bone weakens - bone degenerates quickluy - up to 1/3 of bone mass can be lost in a few weeks of inactivity

Question 33

role of bone in calcium balance

Answer 33

bones store calcium and other minerals (potassium, sodium, magnesium, carbonate, phosphate)

Question 34

calcium ions are vital for

Answer 34

1. nerve function 2. muscle contraction (heart contraction, diaphragm contaction with breathing) 3. enzyme function 4. blood clotting calcium levels in body fluids must be closely regulated

Question 35

blood calcium levels are regulated by

Answer 35

1. parathyroid hormone 2. calcitonin 3. vitamin D control calcium storage in bone, absorption by digestive tract and excretion by kidneys

Question 36

What is parathyroid hormone? Function?

Answer 36

produced by parathyroid glands in neck increases blood calcium levels by: 1. stimulating osteoclast activity 2. increasing intestinal absorption of calcium (via vitamin D synthesis) 3. decreases calcium excretion by kidneys Vitamin D - PTH stimulates the formation of the active form of vitamin D (calcitrol) that is needed to absorb calcium in the intestines

Question 37

what is calcitonin? function?

Answer 37

secreted by C cells (parafollicular cells) in the thyroid gland - decreases blood calcium levels by: 1. inhibiting osteoclast activity 2. increasing calcium excretion by the kidneys