Anatomy Unit 4 Part 3

what do bones begin as?

cartilage

when does cartilage form?

third week of fetal development

when happens around the sixth week of fetal development?

ossification begins

when do bones stop growing?

at age 25

what is osteogenesis?

bone formation

what is ossification?

the process of replacing other tissues with bone

what is endochondral ossification?

when bone replaces existing hyaline cartilage

what is intramembranous ossification?

when bone develops directly from the stem cells of connective tissue

briefly describe the 6 steps of endochondral ossification

1. matrix thins, struts begin to calcify

2. osteoblasts begin producing a thin layer of bone around the shaft of the cartilage

3. bone develops begins at the primary ossification center

4. bones enlarge

5. capillaries and osteoblasts migrate into the secondary ossification center

6. epiphysis fills with spongy bone

   • growth plate begins to grow

how do bones lengthen in interstitial growth?

• as long as epiphyseal cartilage continues to grow on the epiphyseal surface, bone continues to grow in length

• osteoblasts in the shaft continuously invade cartilage and replaces it with bone

• new cartilage is added in the epiphyseal

what does bone growth look like in the youth?

• osteoblasts invade at the same rate as the epiphyseal cartilage expands

• bones continue growing

what does bone growth look like in puberty?

• rising levels of sex, growth, and thyroid hormones stimulate bone growth

  • bone-making osteoblasts produce faster than chondrocytes produce new epiphyseal cartilage

• epiphyseal cartilage gradually decreases until it disappears

what does bone growth look like in adults?

• epiphyseal closure

  • remnants of the end of epiphyseal growth creates the epiphyseal line

where does intramembranous ossification occur? what does it produce? give some examples

• occurs in the deeper layers of the dermis

• produces:

  • dermal bones (i.e. mandible, clavicle, cranial skull bones)

briefly describe the 3 steps of intramembranous ossification

1. stem cells differentiate into osteoblasts

   • developing bone grows outwards in small struts

2. spicules (bony spikes) fuse together

3. spongy bone in the intramembranous bone remodels around blood vessels to produce osteons of compact bone

what are the 3 blood supplies of mature bone?

• nutrient artery and vein

• metaphyseal vessels

• periosteal vessels

describe the nutrient artery and vein: where is it located?

single pair of large blood vessels

• enters the diaphysis through the nutrient foramen

what do the metaphyseal vessels supply blood to?

epiphyseal cartilage

what do periosteal vessels supply blood to?

superficial osteons

briefly describe 3 functions of the adult skeleton

• maintains itself

• replaces mineral reserves

• recycles and renews bone matrix

involves osteocytes, osteoblasts, and osteoclasts

how does the turnover rate vary?

• if deposition (osteoblasts) is greater than removal (osteoclasts), bones get stronger

• if removal (osteoclasts) is faster than replacement (osteoblasts), bones get weaker

why is exercise important?

what are the effects of exercise? what about the lack of exercise?

bones adapt and change shape based on the stresses put on them

exercise allows osteoblasts and osteoclasts to break down “damaged” bone & replace it with healthy bone

• exercise:

  • more stress leads to thicker bones

  • bumps and ridges at muscle attachment become more prominent

• lack of exercise:

  • causes bones to become weak and brittle

  • after a few weeks, bones can lose up to a 1/3 of their mass

  • concerns astronauts and bedridden patients

how does the skeleton act as a calcium reserve? what parts of the body require calcium ions?

• bones store calcium and other minerals

• calcium ions are vital to:

  • membranes

  • neurons

  • muscles cells

    • especially heart cells

what is a bone fracture?

when the bone is cracked or splintered due to physical injury

what components are required to repair a fracture?

• blood

• periosteum and endosteum cells

• osteoblasts

• osteocytes

briefly describe the 4 steps of bone fracture repair

1. bleeding & clotting create a fibrous network

2. calluses stabilize the bone break

3. osteoblasts replace callusus with spongy bone

4. osteoblasts and osteocytes remodel

describe the 2 categories of fractures

• open v. closed

  • open: projects through the skin (higher risk of infection)

  • closed: does not break the skin

• displaced v. nondisplaced

  • displaced: obvious deformity

  • nondisplaced: bone is still inline

describe the 5 types of fractures

• transverse: shaft breaks along the long axis

• greenstick: one side frayed, the other twisted but not fractured (seen in children)

• comminuted: one or more bones displaced or shattered

• spiral: twisting force

• epiphyseal: fracture where bone growth is still happening; can impact future growth

what is osteopenia? when does it occur?

when bones become thinner and weaker with age

• (inadequate ossification) osteoblast activity declines while osteoclasts remain the same

• begins between ages 30 and 40

why do we lose bone mass?

what percent do women lose bone mass per decade? what about men?

we produce less sex hormones as we age

• women lose 8% bone mass/decade

  • menopause greatly impacts bone loss

• men lose 3% bone mass/decade

what bones are most affected during aging bone loss?

• epiphyses

• vertebrae

• jaws

what are the effects of aging bone loss?

• fragile limbs

• height reduction

• tooth loss

what is osteoporosis? what does it affect? when does it occur? include what percentage men/women are affected

severe bone loss

• affects normal function

• occurs over the age of 45

  • 29% of women

  • 18% of men

what are the causes of osteoporosis?

• malnutrition

• low estrogen

• lack of calcium/vitamin D

• smoking

• excessive drinking

• lack of exercise

what does MCL mean? what is its function?

medial collateral ligament

• function: prevents side-to-side knee movement

what does ACL mean? what are its functions?

anterior cruciate ligament

• functions:

  • prevents excessive front-to-back sliding of the knee

  • prevents the tibia from sliding in front of the femur

what are the causes of ACL/MCL tears?

• rapid direction change

• sudden stopping

• incorrectly landed jump

what are the symptoms of ACL/MCL tears?

• “pop” noise

• pain

• swelling

• loss in range of motion

• tenderness

• discomfort walking

what are the 2 types of treatments for ACL/MCL tears? describe them and their pros/cons

• nonsurgical:

  • allows use during recovery; increases the chance of reinjury

    • brace

    • physical therapy

• surgical:

  • high success rate, long-term treatment; longer and more painful recovery

    • ligament reconstruction

what can the ACL/MCL both do?

stretch and “loosen” knee