U2 Lecture 3 Flashcards Preview

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Flashcards in U2 Lecture 3 Deck (13)
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1
Q

Why are the bones of infants soft in certain regions?

A
  • Fontanels (skull)
  • Epiphysis of long bones made of cartilage in infant
  • Epiphyseal plates stay as cartilage until adulthood (until end of puberty)
2
Q

What are the “bones” of a fetus (before birth) composed of?

A
  1. Loose connective tissue (mesenchyme)

2. Hyaline cartilage

3
Q

Define ossification

A

the replacement of other connective tissues by bone

  • begins during 2nd month of development
  • continues many years after birth and into adulthood
4
Q

Types of ossification

A
  1. Intramembranous ossification

2. Endochondral ossification

5
Q

Define intramembranous ossification

A

“within membrane”

mesenchyme –> bone

6
Q

Bones formed by intramembranous ossification

A
  • flat bones of the skull ( frontal, parietal)
  • most facial bones (mandible etc)
  • sternum
  • clavicles (medial parts)
  • heterotropic bones (abnormal stresses can stimulate bone formation in places where bone is not normally found… ex: sesamoid bones)
7
Q

Steps of Intramembranous ossification

A
  1. Development of ossification center - Mesenchymal cells differentiate into osteogenic cells, then into osteoblasts; osteoblasts then secrete bone matrix
  2. Calcification - osteoblasts deposit calcium in the matrix; osteoblasts differentiate into osteocytes; extracellular matrix calcifies (hardens)
  3. Formation of trabeculae (spongy bone) - exracellular matrix forms trabeculae which forms around a network of blood vessels to make spongy bone
  4. Development of periosteum - spongy bone remodels to compact bone
8
Q

Calcification vs. Ossification

A

Calcification = the deposition of calcium

Ossification = replacement of other connective tissues by bone

  • Calcification is an essential part of ossification
9
Q

Endochondral ossification

A
  • most of bones in the body are formed by this process

- growth in length at the epiphyseal plate also by endochondral ossification

10
Q

Steps of endochondral ossification

A
  1. Formation of a cartilage model
  2. Cartilage model grows in length and width: model undergoes calcification, blood vessels penetrate model and stimulate differentiation of chondroblasts into osteoblasts, osteoblasts secrete bone matrix, calcification occurs
  3. Primary ossification center forms (spongy bone)
  4. Osteoclasts invade the newly formed bone and carve a marrow cavity: spongy bone is remodeled into compact bone in the diaphysis, epiphyses remain as cartilage (for now), around time of birth blood vessels penetrate the epiphyses
  5. Secondary ossification centers form
  6. Spongy bone replaces most of the cartilage (except the epiphyseal plates & articular cartilage
11
Q

Endochondral ossification types

A

Primary ossification and secondary ossification

12
Q

Define primary ossification

A
  • Marrow cavity formed
  • replaces all cartilage with bone
  • located in diaphysis
  • occurs before birth
13
Q

Define secondary ossification

A
  • no marrow cavity
  • some cartilage is left for epiphyseal plates (growth) and articular cartilage
  • located in epiphyses
  • occurs around the time of birth