Chapter 6: The Skeletal System [A&P I Lecture Exam 2]

“Organs” of the skeletal system:

• Bones

• Cartilages

• Joints

Major cartilaginous structures of the adult body + type:

1. Cartilage in the external ear - elastic

2. Cartilages in the nose - hyaline

3. Articular cartilages, which cover the ends of most bones at movable joints - hyaline

4. Costal cartilages, which connect the ribs to the sternum (breastbone) - hyaline

5. Cartilages in the larynx (voice box), including the epiglottis, a flap that keeps food from entering the larynx and the lungs - elastic

6. Cartilages that hold open the air tubes of the respiratory system - hyaline

7. Cartilage in the discs between the vertebrae - fibrous

8. Cartilage in the pubic symphysis - fibrocartilage

9. Cartilages that form the articular discs within certain movable joints, the meniscus in the knee for example - fibrocartilage

Describe the perichondrium:

A dense layer of connective tissue that protects + functions in growth/repair of the cartilage.

Describe functions of the bony skeleton and bone tissue:

Skeleton function:

• support, protection, movement, mineral storage, blood cell production, energy storage, metabolism

Describe the bone shapes (non-skull):

• short

• sesamoid

• flat

• irregular

• long

• short: cubelike

• sesamoid: develop within a tendon. ie. patella (knee cap)

• flat: ie. scapula

• irregular: ie. vertebra, hip bones

• long: based on proportion, not size. distinct ends upon a long portion.

Classify the following bones based on shape:

• scapula

• clavicle

• ribs

• scapula → flat

• clavicle → long

• ribs → flat

Gross and microscopic structure of compact bone + locations:

• Gross:

  • Dense, outer layer of bone

  • In long bones, compact bone contains medullary cavity (lined by endosteum)

  • Nutrient artery runs along exterior dense irregular connective tissue (periosteum) and enters through “nutrient foramens”

  • “Sharpeys fibers” collagen bundles which attach the periosteum to the bone.

• Microscopic:

  • “1 tree trunk unit” = osteon/Haversian system

  • “tree trunk core” = central canal (Haversian); contains nerve, vein+artery!

  • “tree trunk rings” = lamellae

  • “perimeter tree trunk rings containing multiple tree trunk units” = circumferential lamellae

  • Perforating Volkmann’s canal connects the osteon central canals to spongy bone.

  • Periosteum covers external circumerential lamellae.

  • Dark specks are osteocytes in a lacuna! Canaliculi connect these as tiny junctions.

Gross and microscopic structure of spongy bone + locations:

• Gross:

  • Internal layer of bone “trabecula”

• Microscopic:

  • Receives nutrients from surrounding endosteum’s capillaries.

  • Dark specks are osteocytes.

  • Red bone marrow found in the spaces

Describe detailed anatomy of typical long bone:

• Shaft “diaphysis” + two ends “epiphyses”

• Border between shaft and ends: “metaphysis” (where epiphyseal line exists)

• Articular cartilage covers the epiphyses.

• Periosteum CT covers the diaphysis.

Describe general anatomy of all other bone classes:

• Top and bottom layer of compact bone; covered with periosteum.

• Middle layer of spongy bone (continuous with compact bone); covered with endosteum.

Periosteum and endosteum function+structure+location:

• Periosteum:

  • Covers external bone surface w/ two layers. Superficial layer is dense irregular CT; deep layer is osteogenic (contains osteoclasts/blasts).

  • Attached via Sharpey’s fibers.

  • Located on compact bone where there is NO articular cartilage…

• Endosteum:

  • Thin, osteogenic membrane covering internal bone surfaces.

  • Located - spongy bone trabecula (epiphyses of long bones, medullary cavity, short/irregular/flat bones)

Purpose of bone markings + examples of each kind:

• Bone markings reflect the stresses applied to a particular location:

  • Projections (muscle/ligament attachment sites); ie. illiac crest.

  • Joint formation surfaces; ie. mandibular condyle.

  • Depressions & openings; ie. foramen, fissure.

Types of bones formed from endochondrial vs. intramembranous ossification:

• Intramembranous ossification - formed directly from mesenchyme (embryonic tissue), includes most skull bones + the clavicles.

• Endochondrial ossification - forms within hyaline cartilage to eventually replace, includes all bones from the base of the skull downwards (except the clavicles).

Epiphyseal plate vs. line:

Cartilagenous epiphyseal growth plates close in adulthood and become bone.

This bony structure is then called the epiphyseal line.

Osteoblasts vs. osteoclasts:

• Osteoblasts add bone tissue

  • Become osteocytes once encased by bone matrix.

• Osteoclasts remove bone tissue (at the same rate).

  • Secrete HCl + lymosomal enzymes to release Ca++ ions.

Possible symptoms of osteoblast and osteoclast dysregulation:

• Osteoclasts functioning faster than osteoblasts = osteoporosis/brittle bones

• Osteoblasts inadequately mineralizing = osteomalcia/softened and weak bones