✨ Nursing Note A&P – Osseous tissue and Bone Structure✨

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Skeletal system

five primary functions

• Support: provide a framework for the attachment of soft tissues and organs

• Storage of Minerals and Lipids: Calcium is the most abundant mineral

  skeleton store energy(lipids) in yellow bone marrow

• Blood Cell Production: red bone marrow > RBC, WBC

• Protection: surround many soft tissues and organs

• Leverage: movements > precise motion, changes in the position

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Bone

Bone Shapes

• Sutural bones / Wormian bones: small, flat, irregularly shaped bones

• Irregular bones: complex shapes. e.g., vertebrae, Skull (Zygomatic, sphenoid, ethmoid, maxilla, palatine, nasal hyoid, mandible, temporal), Pelvic bone, Sarum, Coccyx

• Short bones: boxlike. e.g., Carpal(wrist), tarsal(ankle)

• Flat bones: thin, flattened shape. e.g., Skull (Sphenoid, ethmoid, frontal, parietal, temporal, occipital), Scapula, Sternum, Ribs

• Long bones: Long, slender. e.g., clavicle, Limbs (humers, ulna, radius, femur, tibia, fibula)

  consist of a shaft (diaphysis) with two ends (epiphyses)

• Sesamoid bones: small, flat, like sesame seed. (Figure 6–1f). e.g., patellae (kneecaps)

Bone Markings

Bone Structure

Bone Cells

• Osteocytes(most): mature bone cells, cannot divide

  • Each osteocyte occupies a lacuna

  • FUNCTION:

    • maintain the protein and mineral content of the surrounding matrix

    • take part in the repair of damaged bone

• Osteoblasts: produce new bone matrix (extracellular matrix, ECM), ossification / osteogenesis make and release the proteins and other organic components of the matrix(osteoid)

• Osteogenic cell / osteoprogenitor cell: mesenchymal cells / stem cell > into osteoblasts

  • repair of a fracture

  • found in the inner, cellular layer of the periosteum

• Osteoclasts: add matrix

  • 50 or more nuclei

  • from monocytes and macrophages > body’s defense mechanisms.

  • produce acids and protein-digesting enzymes > dissolve the matrix and release the stored minerals.

  • Osteolysis: erosion process, resorption

    • regulation of calcium and phosphate concentrations in body fluids

    • removing matrix

• Bone Matrix

  • Calcium phosphate (2/3), collagen fibers (1/3)

  • solid and sturdy >> calcium salts around the protein fibers

  • contains bone cells / osteocytes in lacunae

• Compact bone

  • Periosteum: superficial layer > fibrous layer (outer) and cellular layer (inner)

    • FUNCTION:

      • (1) isolates the bone from surrounding tissues

      • (2) provides a route for the blood vessels and nerves

      • (3) takes part in bone growth and repair

        Collagen fibers layer (outer): adjacent joint capsules, attached tendons and ligaments.

  • Osteons / Haversian system: cycle, osteocytes (cell) are arranged in concentric layers around a vascular central canal / Haversian canal

    • FUNCTION: protect, support, and resist stress.

    • Central canals: contains a capillary, a venule (very small vein) > carry blood to and from the osteon 水平的管路，開口在表面

    • Perforating canals / Volkmann’s canals: supply blood to osteons deeper in the bone and to tissues of the medullary cavity. 垂直的管路，在骨頭的中間

    • Lamellae: Surrounding the central canal are rings of bone ECM

    • give compact bone a great deal of strength,

      • Concentric lamellae: encircle the osteon.

      • Circumferential lamellae: encircle outermost

      • Interstitial lamellae: located between osteons

    • Lacunae: between the lamellae are small cavities, spindle-shaped spaces, around blood vessels

      • CONTAIN: osteocytes (mature osteoblasts)

    • Canaliculi (collagen fibers): narrow passageways between the lacunae > exchange of nutrients, wastes, gases (blood vessels)

    • Endosteum: connective tissue membrane (inner layer), incomplete cellular layer

      • CONTAIN: osteoblasts

      • FUNCTION: bone growth, repair, and remodeling

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Spongy bone

• Trabeculae: matrix in spongy bone forms a meshwork of supporting bundles of fibers

  inside of a bone deep to compact bone,

  • FUNCTION: stores marrow

    • red bone marrow: (V) blood vessels, produce blood cells,

    • yellow bone marrow: composed primarily of adipose tissue (energy reserve)

  • no capillaries or venules in matrix

Bones formation and growth

Bone growth until about age 25

• Ossification / osteogenesis: bone formation

  • Endochondral

  • Intramembranous

• Calcification: deposition of calcium salts— takes place during ossification

• Endochondral Ossification

  bones originate hyaline cartilages > gradually replaced by bone

  • e.g., Long bones

    • STEPS

      (1) cartilage enlarges

      Enlarging chondrocytes within calcifying matrix

      Disintegrating chondrocytes of the cartilage model > form cavities

      (2) creating Primary ossification center

      Blood vessels grow around the edges of the cartilage

      perichodrium cell > convert to osteoblasts.

      form Epiphysis, Diaphysis(shaft)

      (3) Blood vessels penetrate the cartilage and invade the central region

      Fibroblasts > migrating with the blood vessels differentiate into osteoblasts,

    > begin producing spongy bone at a primary ossification center.

    Bone formation > spreads along the shaft toward both ends of the former cartilage model.

    (4) creating a medullary cavity

    Diaphysis > becomes thicker, increases in length and diameter.

  form Metaphysis

  (5) creating secondary ossification centers

  Capillaries and osteoblasts migrate into the epiphysis

  (6) epiphysis filled with spongy bone

  metaphysis> separates the epiphysis from the diaphysis.

  shaft side > osteoblasts continuously invade the cartilage and replace it with bone.

  epiphyseal side > New cartilage is produced

  (7) Bone growth slow, then stop

  At puberty: rate of epiphyseal cartilage production slows, and the rate of osteoblast activity accelerates.

  At Adult: epiphyseal cartilage gets narrower and narrower, until it ultimately disappears. epiphyseal closure: the completion of epiphyseal growth > form epiphyseal line(生長停止線)

  interstitial growth: continue to grow by expansion of the cartilage matrix

  appositional growth:  production of more cartilage at the outer surface

• intramembranous Ossification / dermal ossification

  • begins when osteoblasts differentiate within a mesenchymal or fibrous connective tissue

  • takes place in the deeper layers of the dermis.

  • e.g., dermal bones/flat bones: skull, mandible (lower jaw), clavicles

Bone Blood and Nerve

• Nutrient Artery and Vein

  • Most bones have only one nutrient artery and one nutrient vein

  • Femur > more than one of each

  • Vessels: enter the bone through passageways (nutrient foramina) in the diaphysis

  • large vessels branches: form smaller perforating canals and extend along the length of the shaft into the osteons of the surrounding compact bone

• Metaphyseal Vessels

  • supply blood to the inner (diaphyseal) surface of each epiphyseal cartilage (being replaced by bone)

• Periosteal Vessels

  • provide blood to the superficial osteons of the shaft

  • Periosteum

    • Lymphatics: collect lymph from branches that enter the bone and reach individual osteons by the perforating canals.

    • Sensory nerves: penetrate the compact bone with the nutrient artery to innervate the endosteum, medullary cavity, and epiphyses

Bone remodeling

throughout life

• FUNCTION: bone maintenance > recycling and renewing bone matrix

• INVOLVES: osteocytes, osteoblasts, osteoclasts

  • If removal is faster than replacement > bones weaken

  • If deposition predominates > bones strengthen

Exercise, hormones, nutrition

• exercise effects on Bone

  • exercise > bone is stressed, mineral crystals generate minute electrical fields > Osteoblasts are attracted to these electrical fields >> begin to produce bone

  • inactivity > Degenerative changes in the skeleton

• nutritional and hormonal effects on Bone

  • Minerals

    • (important)calcium and phosphate salts

    • magnesium, fluoride, iron, manganese

  • Calcitriol and cholecalciferol (vitamin D3)

    • expose sunlight > steroid cholecalciferol (vitamin D3) > synthesize calcitriol in the kidneys

    • absorbed from the diet

  • Vitamin C

    • absorbed from the diet

    • required for enzymatic reactions in collagen synthesis, stimulates osteoblast differentiation.

    • vitamin C deficiency: loss of bone mass and strength.

  • Vitamins A, K, B12

    • effects on bone structure

    • Vitamin A: stimulates osteoblast activity

    • Vitamins K and B12: synthesis of proteins in normal bone

  • Growth hormone

    • produced by the pituitary gland

    • stimulates protein synthesis and the rates of cell division and cell growth

  • Thyroxine

    • from the thyroid gland, stimulate bone growth

    • stimulates cell metabolism and increases the rate of osteoblast activity.

  • Sex hormones

    • At puberty

    • estrogens(females) and androgens (males)

    • stimulate osteoblasts to produce bone faster than the rate of epiphyseal cartilage expands

Calcium in bone physiology

(1) the bones (storage)

(2) the digestive tract (absorption)

(3) the kidneys (excretion)

• Low Calcium Ion Level (<8.5 mg/dl)

  • Parathyroid Gland Response: secrete parathyroid hormone (PTH)

    > Bone Response: Osteoclasts release stored calcium ions from bone

    > Intestinal Response: increases intestinal absorption of calcium

    > Kidney Response: Kidneys absorb calcium ions (decrease Calcium loss in urine)

     >> Increase Calcium levels in blood

• High Calcium Ion Level (>11 mg/dl)

  • Parathyroid Gland Response: Parafollicular cells (C cells) secrete calcitonin

    > Bone Response: Osteoclasts inhibited to lock calcium ions in bone matrix

    > Intestinal Response: decreases intestinal absorption of calcium

    > Kidney Response: Kidneys allow calcium loss (Increase Calcium loss in urine)

    >> decrease Calcium levels in blood

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Reference

Martini, F. H., Nath, J. L., & Bartholomew, E. F. (2018). Fundamentals of anatomy & physiology (11th ed.). Pearson.

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