Untitled Notes

Exam Material
- Current focus on Chapter 3, including Protein Synthesis, Translation, and Replication.
- Second exam covers material primarily from Chapter 3.
- Potential questions regarding the Cell Cycle: G1, S phase, G2, and Mitosis.
- Upcoming exam material will focus on Chapters 5 and 6 after completion of Chapter 6.

Compact vs. Spongy Bone
- Compact bone includes units called osteons.
- Osteocytes are embedded within the bone tissue of compact bone.
- Spongy bone has a more disorganized appearance but follows a specific architecture called trabeculae.
Bone Cells
- Osteocytes
- Mature bone cells located within the matrix of the compact bone.
- Functions include maintaining bone tissue and sensing mechanical stress.
- Osteoblasts
- Immature bone cells derived from osteogenic stem cells (also referred to as osteoprogenitor stem cells).
- Responsible for creating bone matrix (osteoid) and contributing to the mineralization process.
- Osteoclasts
- Multi-nucleated cells that are derived from monocyte lineage (white blood cells).
- Responsible for bone resorption; they secrete acids that dissolve bone tissue for calcium mobilization into the bloodstream.

Cell differentiation is a key biological concept applicable to various types of cells.
In bone tissue:
- Osteogenic stem cells undergo mitosis to become osteoblasts.
- Osteoblasts function to lay down the ^osteoid^ and can become osteocytes upon maturation.
- Osteocytes become more specialized and contribute to the maintenance of bone stability and integrity.
Pathway:
- Osteogenic Stem Cell → Osteoblast → Osteocyte

Bone Matrix
- Consists of osteoid (organic matrix) and hydroxyapatite (inorganic component composed of calcium and phosphorous).
- Osteoid is secreted first, followed by the addition of minerals to form mature bone tissue.
Location of Osteoblasts/Osteocytes
- Osteoblasts located on the surface of the bone (e.g., periosteum).
- Osteocytes found within lacunae of compact bone.

Endochondral Ossification (How long bones develop)
- Cartilage is formed and then gradually replaced by bone through a process involving calcification.
- Primary ossification center forms in the diaphysis, and secondary ossification centers form in the epiphyses.
Intramembranous Ossification (How flat bones develop)
- Fibrous connective tissue is transformed directly into bone without a cartilage stage.

Longitudinal Growth: Occurs at the epiphyseal plate, where cartilage is replaced with bone in a process that allows bones to elongate during childhood into adolescence.
Appositional Growth: Responsible for increasing girth and changing bone structure in response to mechanical stress.
Key zones within the epiphyseal plate:
- Resting Zone: Stem cells for chondrocytes.
- Proliferative Zone: Chondrocytes undergo mitosis here, gradually moving towards the diaphysis.
- Hypertrophic Zone: Older chondrocytes expand, preparing for calcification.
- Calcification Zone: Calcium is deposited, leading to the death of chondrocytes.
- Ossification Zone: New bone formation occurs as osteoblasts fill in the region where cartilage once was.

Growth Hormone: Promotes general growth and regulates the activity of chondrocytes in the epiphyseal plates.
Testosterone and Estrogen: Signal the cessation of chondrocyte growth during adolescence; essential for maintaining bone strength.
Parathyroid Hormone (PTH): Regulates blood calcium levels; increases osteoclast activity in response to low blood calcium levels.

Continuous process involving the replacement of old bone with new bone by osteoblasts and osteoclasts.
Factors impacting bone remodeling include stress and hormonal levels, leading to a balance between the creation and resorption of bone.
The takeaway from bone remodeling is that it occurs throughout life as bones adapt to changes in stress, physical activity levels, and overall health.

For examination coverage on Tuesday, material only covers through Slide 51.
Focus on growth, bone types, cell differentiation, and hormonal regulation highlighted in lectures leading up to the exam.