Protein Synthesis, Tissues, and Skeletal Biology

A comprehensive vocabulary review of protein synthesis, basic histology, long bone anatomy, bone cells, ossification mechanisms, calcium homeostasis, and skeletal pathology.

Triplet

A sequence of $3$ complementary bases in DNA that codes for an amino acid.

Messenger RNA (mRNA)

A single-stranded RNA molecule transcribed in the nucleus that carries coded genetic information to the cytoplasm in $3$-base groupings called codons.

Transfer RNA (tRNA)

A cloverleaf-shaped RNA molecule located in the cytoplasm that translates nucleotide sequences by delivering a specific amino acid to the ribosome.

Ribosomal RNA (rRNA)

A primary component of a ribosome that directs translation and decodes the mRNA strand.

Codon

A $3$-nucleotide sequence on an mRNA strand that codes for a specific amino acid or stop signal.

Transcription Factor

A gene-activating molecule that binds DNA at the promoter to establish the starting site for RNA polymerase.

RNA Polymerase

The enzyme that unwinds a region of DNA and synthesizes a complementary strand of RNA nucleotides.

Transcription

The process in the cell nucleus where DNA is used as a template by RNA polymerase to synthesize an mRNA strand.

Translation

The cytoplasmic process where a ribosome reads mRNA codons, pairs them with tRNA anticodons, and links amino acids to assemble a functional polypeptide.

Histology

The scientific study of the normal microscopic structure of biological tissues.

Extracellular Matrix (ECM)

The non-living material surrounding tissue cells, composed of ground substance and protein fibers (collagen, elastic, and reticular).

Ground Substance

The fluid, gel-like, or solid component of the extracellular matrix in which cells and connective fibers are suspended.

Epithelial Tissue

A cellular, innervated, and avascular primary tissue with high regenerative capacity that covers external surfaces, lines internal cavities, and forms glands.

Connective Tissue

The most abundant and varied primary tissue that provides binding, support, protection, and transportation, varying from avascular to highly vascularized.

Fibroblast

An active connective tissue cell that secretes and forms the components of the extracellular matrix.

Suffix '-blast'

A suffix indicating an immature, developing cell that secretes extracellular matrix substances.

Suffix '-cyte'

A suffix indicating a mature, non-dividing cell that maintains and repairs the extracellular matrix.

Mast Cell

A migrating connective tissue cell involved in the immune response that releases histamine.

Macrophage

A wandering white blood cell in connective tissue that acts as an immune defender by engulfing cellular debris and pathogens.

Hematopoiesis

The process of blood cell formation (red blood cells, white blood cells, and platelets) occurring within red bone marrow.

Chondroblast

An immature cartilage cell that secretes the extracellular matrix of cartilage tissue.

Epiphyseal Plate

A band of hyaline cartilage located at the metaphysis of growing long bones where interstitial elongation takes place.

Epiphyseal Line

The bony remnant that replaces the epiphyseal plate once longitudinal bone growth ceases.

Diaphysis

The elongated shaft of a long bone containing the medullary cavity, which houses yellow marrow in adults.

Periosteum

A tough, vascularized connective tissue sheath covering the outer surface of bone that provides blood supply and serves as an anchor for tendons and ligaments.

Endosteum

The membranous connective layer that lines the internal surfaces and cavities of a bone.

Articular Cartilage

A smooth, avascular layer of hyaline cartilage capping the ends of long bones at synovial joints to reduce friction and absorb shock.

Hydroxyapatite

The inorganic mineral salt complex (calcium and phosphorus) that deposits into bone matrix to provide hardness and rigidity.

Calcification

The process in which mineral salts (hydroxyapatite) deposit and crystallize around collagen fibers, hardening the extracellular matrix of bone.

Osteoblast

A bone-forming cell that secretes extracellular matrix, deposits new bone tissue, and initiates calcification.

Osteocyte

A mature bone cell trapped within calcified matrix that no longer divides or secretes matrix, but maintains the bone tissue.

Osteoclast

A large multinucleated cell derived from fused monocytes that secretes enzymes and acids to dissolve the organic matrix and minerals of bone.

Bone Resorption

The breakdown and degradation of bone matrix by osteoclasts, which releases stored calcium back into the blood.

Intramembranous Ossification

The bone formation process where osseous tissue develops directly within sheets of embryonic connective tissue, forming cranial bones and clavicles.

Endochondral Ossification

The process of bone development where a preexisting hyaline cartilage model is gradually replaced by bone tissue.

Appositional Growth

Growth in bone thickness occurring as osteoblasts in the periosteum deposit new matrix while osteoclasts in the endosteum erode internal bone.

Bone Remodeling

The ongoing replacement of old bone tissue with new bone tissue via balanced resorption and deposition, replacing approximately $10\%$ of the skeleton each year.

Calcitonin

A hormone secreted by the thyroid gland in response to high blood $Ca^{2+}$ levels that stimulates osteoblasts to deposit calcium into bone.

Parathyroid Hormone (PTH)

A hormone released by the parathyroid glands during low blood $Ca^{2+}$ conditions that stimulates osteoclast activity and activates renal calcitriol synthesis.

Calcitriol

The active hormonal form of Vitamin D produced by the kidneys that increases the absorption of calcium across the digestive tract.

Rickets

A pediatric bone disease caused by Vitamin D deficiency that causes impaired calcium absorption, soft bones, and bowed legs.

Scurvy

A disorder caused by Vitamin C deficiency that disrupts collagen matrix synthesis, resulting in brittle bones and loose teeth.

Osteoporosis

A degenerative skeletal condition characterized by porous, fragile bones that occurs when bone resorption exceeds bone deposition.