Bone physiology
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Bone Physiology. Bones are Classified by shape and structure. limbs. Carpals tarsals. vertebrae. Skull bones Ribs Sternum scapula. Epiphysis Epiphyseal Line Diaphysis Periosteum Articulating Cartilage. Anatomy of Long Bone. Compact Bone. Canaliculi Haversian Canal Lamellae Osteon.

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Bones are classified by shape and structure
Bones are Classified by shape and structure





Skull bones




Epiphysis epiphyseal line diaphysis periosteum articulating cartilage
EpiphysisEpiphyseal LineDiaphysisPeriosteumArticulating Cartilage

Anatomy of Long Bone

Compact bone
Compact Bone

  • Canaliculi

  • Haversian Canal

  • Lamellae

  • Osteon

Spongy bone located along the epiphyses of long bones site of erythrocyte rbc formation
Spongy Bone Located along the epiphyses of long bonesSite of Erythrocyte (RBC) formation

Collagen fibers are not arranged in concentric rings. But the lamellae form rods called trabeculae. No Osteons or Haverian Systems are present.

Cells in bones
Cells in Bones

Osteocyte – mature bone cells; recycle Ca and PO4

Osteoclasts– dissolve bone by secreting enzymes and acids. Release Ca to be returned to blood stream

Osteoblasts– cells that produce new bone cells referred to as osteogenesis

Osteoclasts remove matrix, osteoblasts adds matris.

When an osteoblast’s lacunae is calcified the cell becomes and osteocyte.

Endochondrial ossification
Endochondrial Ossification

  • Bone tissue in a fetus begins as hyaline cartilage

  • Inside is cartilage, cartilage becomes ossified.

  • In 6 weeks cartilage is replaced tobone except at growth plates.

Bone physiology

  • Two growth plates plates.

    • Composed of hyaline cartilage

    • Longitudinal growth is completed when epiphyseal lines become completely ossified.

Bone physiology

Bone physiology

Resting Zone division

Mitosis Zone



Ossification Zone

Bone physiology

Growth along Epiphyseal Line division

Mitosis Zone

  • Resting Zone

Bone physiology

Maturation/Hypertrophy Zone division

  • Ossification Zone

Longitudinal growth
Longitudinal Growth division

  • Controlled by 3 hormones

    • Growth Hormone

      • Baby to prepuberty

    • Sex Hormones (estrogen/testosterone)

      • Causes growth spurt at puberty

      • Shapes your skeleton to your sex

    • Thyroid Hormones (PTH & Calcitonin)

      • PTH = parathyroid hormone

      • Controls whether bone growth occurs

      • Affects Appositional Growth – bone growth in diameter

Bone homeostasis bone remodeling
Bone Homeostasis divisionBone Remodeling

  • Osteons are formed by osteoblasts

  • In healthy adults:

    • Bone deposit = bone resorption

    • Osteoblasts = Osteoclasts

  • Bone Remodeling refers to the regular mineral turnover that occurs in bone.

  • In adults, 18 % of proteins and minerals turns over yearly. Not uniform. I.e. Head of femur is remodeled more. Why?

Bone remodeling controlled by negative feedback loop
Bone Remodeling divisionControlled by Negative Feedback Loop

  • Bone Deposit

    • Occurs where bone is injured or added bone strength is required

    • Deposits Ca+2 into bone

  • Bone Resorption

    • Osteoclasts break down bone

    • Calcium is taken from bone and placed into blood stream

    • Lysosomes assist in the process

    • Ca and PO4 are released; eventually releasing the blood stream

Bone remodeling is controlled by 2 hormones by a negative feedback loop
Bone Remodeling is controlled by 2 hormones by a Negative Feedback Loop

  • Blood Calcium is the original stimulus

  • Normal Blood Ca is 9-11 mg CA/100 ml of blood

  • When blood Ca decreases (< 9 mg) Parathyroid Hormone (PTH) is released into bloodstream.

  • Bone resorption occurs causing Ca to leave bone and goto the blood stream

  • Osteoclasts are working

High levels of blood ca 11mg
High levels of blood Ca (>11mg) Feedback Loop

  • When blood Ca levels are high, Calcitonin is released.

  • Causes bone deposit to occur

  • Ca from the blood is stored into bone.

  • (Osteoblasts and Osteocytes are working.)

  • 99% of all Ca is found in bone.

Bone physiology

PTH Feedback Loop


Bone physiology

Bone physiology

Factors that help with Bone Deposit Feedback Loop

  • Vitamin D – aids in the absorption of Calcium into the bone. Part of vitamin D is converted to the hormone calcitriol which allows Ca to pass through the S.I.(What food is Vitamin D fortified?)

    i.e. rickets results from Vitamin D deficiency

  • Vitamin C – helps osteoblasts function

    i.e scurvy – caused from a reduction in osteoblast activity

  • Calcium tablets -

  • Diet -

2 nd response to regulating bone remodeling
2 Feedback Loopnd Response to Regulating Bone Remodeling

  • Wolff’s Law

    • Bone grows or remodels in response to the forces or stresses placed on it.

    • Appositional growth – growth in diameter is controlled by the amount of mechanical stress and gravity placed on the bone

    • Heavy usage leads to heavy bones; nonuse leads to atrophy (bone loss)

Controlling bone remodeling
Controlling Bone Remodeling Feedback Loop

  • Hormones PTH and Calcitonin determines whether and when bone remodeling occurs.

  • Mechanical Stess determines where remodeling occurs. High stress areas grow appositionally.

Bone physiology

  • Body’s Needs for Calcium Feedback Loop

    • Transmit nerve impulses

    • Muscle contractions

    • Blood coagulation

    • Cell division

      If blood Ca levels are low for an extended time, bones continually lose Ca.

      Once bone density loss begins, women lose 8% of their bone mass every decade, men lose 3% every decade

Osteoporesis Feedback Loop

  • Osteoporesis

  • Normal Bone

Risk Factors

Sex (females more affected than males; especially after menopasue)

Insufficient exercise or too much exercise

Poor diet (low in Ca and protein


Race: Black > bone density

Bone fracture and repair
Bone Fracture and Repair Feedback Loop

  • Simple Fractures take 8-12 weeks to heal

  • Healing time increases age due to poor circulation

Phases of bone repair
Phases of Bone Repair Feedback Loop

Hematoma formation

  • A mass of clotted blood appears

  • Blood vessels

    hemorrhage, causing

    internal bleeding

  • Blood pools and clots around fx area; which closes off injured blood vessels

Bone physiology

Fibrocartilage Callus Formation Feedback Loop

  • Macrophages invade and clean area

  • Fibroblasts help form chondroblasts and collagen fibers

  • Helps to form cartilage splint that will connect ends of broken bones

Bone physiology

Bony Callus Feedback Loop

  • Osteoblasts replace the cartilage with spongy bone

  • Bone cells replace cartilage from the outside fx toward the inside

  • Cells are not organized in the bony callus

Continues 4 months to a year removes excess material a layer of compact bone is produced

Bone Remodeling Feedback Loop

Continues 4 months to a yearRemoves excess material; a layer of compact bone is produced