Unit 2 - Skeletal System

Question 1

What is the difference between axial and appendicular skeletons?

Answer 1

Axial: skull, vertebral column, ribs
Appendicular: appendages

Question 2

What is the function of the skeleton?

Answer 2

Support
Protection
Leverage/movement (attachment site for skeletal muscles)
Blood cell production (‘hematopoiesis’)
Mineral storage (particularly calcium)

Question 3

Bone connective word?

Answer 3

Os/Osteo

Question 4

Bone characteristics?

Answer 4

• Second hardest substance in body (enamel first)
• Living, changing tissue
• Remodels/repairs itself based on stresses

Question 5

How are bones made?

Answer 5

Consist of cells in a matrix:
- Start out as osteoblast -> produce a soft matrix made of collagen fibers in ground substance
- Ossification occurs: osteoblasts harden the matrix by adding minerals (calcium and phosphate)
- Osteoblasts become trapped in small spaces in matrix called lacunae
- Osteoblasts are now considered osteocytes (mature cell)

Question 6

Why is calcium so important in the body?

Answer 6

Required for muscle contraction, blood clotting, milk secretion, and skeleton
Blood calcium is carefully maintained (to allow these functions) by:
- 2 hormones: calcitonin in thyroid (stops calcium from getting too high by placing in bones), and parathyroid (stops calcium from getting too low by removing it from bones)

Question 7

What are the 3 major types of cells in bone?

Answer 7

Osteoblast: cells that form bone (secrete matrix and add minerals to ‘ossify’ it)
Osteocyte: osteoblasts trapped in the ossified matrix
Osteoclasts: cells that eat away at bone, important for remodeling (make it healthy so new bone can be created)

Question 8

What are the 2 types of bone?

Answer 8

Compact bone
Cancellous (spongy) bone

Question 9

What are examples of a long bone?

Answer 9

Humerus
Femur
Tibia
Fibia
Ulna

Question 10

What are characteristics of compact bone?

Answer 10

Dense, strong
Makes up shaft of long bones and outer layer of all bones

Permeated by microscopic tunnels, channels, and interconnecting networks surrounded by a hard matrix (bone is nourished and maintained through these tunnels)

Question 11

What is the Osteon/Haversian System?

Answer 11

The functional and structural unit of compact bone
Contains 1-2 capillaries
Around each central haversian canal are concentric rings of matrix (‘lamellae’)
Small hollow cavities called lacunae that contain osteocytes

Question 12

What are canaliculi?

Answer 12

Part of Haversian System
- Continuous network of communicating cells that join the central canal to the lacunae and adjacent lacunae to each other (nourishment and exchanged, direct the osteocytes through).
- Groups of osteons lie in a parallel arrangement
- Perforating (Volkmanns) canals penetrate the bone and connect the central canals to adjacent osteons

Question 13

What are characteristics of cancellous bone?

Answer 13

Lies adjacent to compact bone and is continuous with it (no clear line, blends together)
Primary feature is trabeculae or spicules = series of branching overlapping plates of matrix

Question 14

What are trabeculae/spicules?

Answer 14

Series of branching, overlapping plates of matrix
- Interconnecting cavelike spaces between plates that store fat and hematopoietic tissue of bone marrow
Reduce the weight of bones so we can move
Arranged to provide support against forces pulling on the bone
Lacunae and blood vessels distributed throughout, provide nourishment to osteocytes

Question 15

What are long bones?

Answer 15

Greater in one dimension than the other (long)
Function as levers, support and sites for muscle attachment
Most bones in the leg

Question 16

What are all the bone shapes?

Answer 16

Long
Short
Flat
Irregular

Question 17

What are the parts of a long bone?

Answer 17

Diaphysis: shaft, mostly compact bone
Epiphysis: enlarged ends, mostly cancellous bone
Epiphyseal plate: area between diaphysis and epiphysis
Periosteum: tough fibrous membrane that covers the outer surface
Endosteum: similar to periosteum, but lines the inner surface of bone
Articular cartilage: smooth layer of hyaline cartilage covering the articular surface of epiphysis

Question 18

What is the function of the Epiphyseal plate?

Answer 18

Area between diaphysis and epiphysis, cartilage in young growing bones (weak area when young), allows bone to increase in length
- Ossifies (turns to bone) when animal reaches full size

Question 19

What is the function of the Periosteum?

Answer 19

tough fibrous membrane that covers the outer surface, except at articular surfaces (where bones are in contact with other bones, covered by cartilage)
- Tightly adhered to outer layer of compact boned, anchored by bundles of collagen fibers embedded in outer lamellae
- Outer layer = fibrous connective tissue, inner layer = osteogenic (new bone-forming cells, provide blood vessel access)
- Important for healing and growth in diameter

Question 20

What is the function of the Endosteum?

Answer 20

Similar to periosteum, but lines the inner surface of bone …….

Question 21

What is the function of articular cartilage?

Answer 21

Smooth layer of hyaline cartilage covering the articular surface of epiphysis
- Reduces friction and wear in joints

Question 22

What are the characteristic of short bones?

Answer 22

Cuboid shaped
No marrow cavity, just spongy bone
Absorb shock
eg. tarsus, carpus

Question 23

What are characteristic of flat bones?

Answer 23

Thin and flat
Function: to protect vital organs
Act as attachments for large muscle groups
eg. ribs, pelvis, skull

Question 24

What are characteristic of irregular bones?

Answer 24

Misc, any bones that don’t fit into other categories

Sesamoid bones: shaped like sesame seeds
- Embedded in tendons to reduce friction and/or change the course of a tendon
- eg. patella

Question 25

What are common bone features?

Answer 25

Features that help the bone function, help form joints, provide attachments for muscles/ligaments/tendons

Question 26

What are the common features on articular surfaces?

Answer 26

Condyles: large round bulge (mainly femur, humerus, and occipital), located at proximal ends
Head: single spherical portion (the ball of ball and socket joints), united with the shaft by a ‘neck’
Facet: 2 flat (slightly concave and slightly convex) surfaces in contact with each other, allow for rocking/twisting (in carpal/tarsal, vertebrae, radius/ulna)

Processes: general term for bumps
- Processes that articulate (head, condyles, facets) have a smooth surface
- Processes without articulating function have rough irregular surfaces (site of muscle/tendon attachments)
- The larger the process, the more powerful the muscular pull on that bone

Holes and depressed areas: foramen (hole for nerves/blood vessels to pass, exception is the pelvis foramen which exists only to decrease weight), fossa (depression in bone for muscles/tendons to occupy)

Question 27

What are the different processes names?

Answer 27

Trochanter (at femur)
Tubercle (at humerus)
Spine (at spacula)
Just ‘Process’ (eg. spinous process)

Question 28

Where does blood supply to bone come from?

Answer 28

• Through vessels in the periosteum
• Travel through Volkmann’s canals (right angle to long bone) into Haversian canals (parallel to long axis)
• Allow nutrition to osteocytes
• Nutrient foramen: large channel blood vessels and nerves penetrate

Question 29

What is a nutrient foramen?

Answer 29

Large channel in bone that blood vessels and nerves penetrate

Question 30

Where is bone marrow?

Answer 30

Fills the space in the diaphysis of long bone and between spicules in cancellous bones

Question 31

What are the 2 types of bone marrow?

Answer 31

Red
Yellow

Question 32

What is red bone marrow?

Answer 32

Hematopoietic tissue
Majority of marrow in young animals
Small part of older animals (ends of long bones, pelvic, sternum)

Question 33

What is yellow bone marrow?

Answer 33

Mostly adipose tissue
Most common marrow in adults
Doesn’t produce blood cells, but can revert back to red if the body needs more blood cells

Question 34

What are the 2 ways bone forms?

Answer 34

1. Endochondral: grows into and replaces a cartilage network
2. Intramembranous: develops from fibrous tissue membranes

Question 35

What is endochondral bone formation?

Answer 35

Most bones
Start as cartilage -> ossify in center of long bone (primary growth center) -> epiphysis (ends) of bone ossify (secondary growth centers)
…….

Question 36

What is the process of endochondral bone formation?

Answer 36

At birth and during the first 2 months of life, 2 parts of long bone remain cartilage ………
At maturity, cartilage plates completely ossified.
*ununited anconeal process common in large dogs: ossification not complete

Question 37

What is intramembranous bone formation?

Answer 37

Occurs in some skull bones
Fibrous tissue membranes cover the brain of the fetus
As it matures, these membranes are ossified and form cranium

Question 38

What is bone homeostasis?

Answer 38

Bone remodeling
Osteoclasts destroy bones (injured/damage)
Osteoblasts build bone.
Control mineral levels

Question 39

What are the main minerals in bone building?

Answer 39

Calcium and phosphorus
Magnesium
Manganese
Copper

Question 40

What vitamins are important in bone building?

Answer 40

Vitamin D
Vitamin A

Question 41

What hormones are important in bone building?

Answer 41

• PTH (parathyroid hormone): increases calcium in the blood by: stimulating release of Ca from bone, inhibits Ca excretion by kidneys, stimulates absorption of Ca by the intestine
• Calcitriol (vitamin D): increases blood calcium by: inhibits Ca extretion by kidneys, stimulates Ca absorption in intestines
• Calcitonin: decreases blood calcium by: inhibiting release of Ca from bone, stimulate extretion of Ca by kidneys

Question 42

What is growth hormone?

Answer 42

Responsible for overall growth of tissues in body, more in juvenile animals
Stimulates growth of epiphyseal cartilage
Stimulates calcium excretion by kidneys
Stimulates calcium absorption by intestine

Question 43

What does insulin do in bone homeostasis?

Answer 43

Stimulate bone formation

Question 44

What do sex hormones do in bone formation?

Answer 44

Stop longitudional growth by causing the epiphyseal plates to degenerate
Stimulate bone formation
Estrogen helps prevent osteoporosis

Question 45

What do glucocorticoids (steroids: cortisol and alsosterone) do in bone formation?

Answer 45

Suppress calcium absorption
Decrease blood calcium concentration
Weakens bones