Unit I: Framework Bone Structure Chapter 6

The Human Skeleton AdvantageDisadvantage Weight Structure Number of Bones

Bone Shapes Figure Long Bones long and slender serve as levers to produce movement Humerus Humerous Radius Ulna Metacarpals Phalanges Femur Tibia Fibula Metatarsals

Bone Shapes Figure Flat Bones thin, roughly parallel surfaces provide protection and surface area for the attachment of skeletal muscles. Parietal bone Cranial Ribs Sternum Scapula Pelvis

Bone Shapes Figure Short Bones Carpal bones small and boxy movement in multiple directions Tarsals Carpals

Bone Shapes Figure Sesamoid Bones small, flat, sesame seed shaped develop inside tendons knees, hands, and feet Patella

Bone Shapes Figure Sutural Bones small, flat, irregularly shaped between the flat bones of the skull Sutural bone Sutures

Bone Shapes Figure Irregular Bones complex shapes Vertebra Vertebrae Facial bones

Bone Structure Osseous tissue (bone) is a connective tissue Hardened by calcification/mineralization Ossification Osteogenesis “Bone” can include many other types of tissues Bone is a composite for strength and flexibility Collagen – strong and flexible Minerals – rigid Osteoporosis: Loss of bone mass compromises normal function ↓ osteoblast activity Impacted by other systems: Endocrine, Integumentary, Digestive, Muscle

Diaphysis – shaft Epiphysis – enlarged ends Metaphysis – found between the diaphysis and epiphysis

Bone Structure Compact bone – strength Spongy bone - lightweight Medullary cavity – Red marrow – Yellow marrow –

Bone Structure Nutrient Foramen – allows nutrients and blood vessels passage Articular cartilage – hyaline cartilage covering the joint surface Periosteum – external sheath bone covering Epiphyseal plate/line – zone of growth

Bone Development 1.Intramembranous Ossification 2.Endochondral Ossification

Intramembranous Ossification Produces the flat bones of the skull and the clavicle Connective Tissue Site of future bone Membrane-like layers of connective tissue form at sites of future bones. Some of the connective tissue cells enlarge and differentiate into osteoblasts. Osteoblasts on inside of periosteum form compact bone. Cells of the membrane-like layer of connective tissue that remain outside the developing bone give rise to the periosteum.

Endochondral Ossification Most bones of the skeleton develop this way Bones develop from an existing model made of hyaline cartilage

Bone Remodeling Osteoprogenitor – stem cells divide to produce osteoblasts Osteoblasts – deposit new tissue, produces collagen fibers Osteoclasts – remove matrix Regulated by hormones: Parathyroid, Calcitonin, Calcitriol

Figure 6 Section 2 Composition of Bone Bone Contains … 99% of the body’s calcium 4% of the body’s potassium 35% of the body’s sodium 50% of the body’s magnesium 80% of the body’s carbonate 99% of the body’s phosphate Calcium 39% Potassium 0.2% Sodium 0.7% Magnesium 0.5% Carbonate 9.8% Phosphate 17% 67%Total inorganic components Organic compounds (mostly collagen) 33% Intestines absorb calcium and phosphate ions from the diet. Rate of absorption is hormonally regulated. Normal Ca 2+ levels in plasma Kidneys excrete calcium and phosphate ions in the urine. Rate is hormonally regulated. Bone In the skeleton, osteoblasts and osteoclasts are working simultaneously. Rate is hormonally regulated.

Homeostasis Disturbances can disrupt the functioning of the nervous and muscular systems in particular. –Hypercalcemia –Muscle weakness and sluggish reflexes –Hypocalcemia –Muscle spasms and tremors

Factors That Increase Blood Calcium Levels Secrete parathyroid hormone (PTH). (below 8.5 mg/dL) Low Calcium Ion Levels in Plasma Parathyroid Gland Response Osteoclast Bone stimulates osteoclasts accelerates erosion of bone matrix Enhances the calcium- absorbing effects of calcitriol on the intestines. Increases renal production of calcitriol, which is continuously secreted at low levels. PTH more calcitriol Calcium released Calcium absorbed quicklyCalcium conserved Less calcium lost in urine Ca 2+ levels in plasma increase Bone Response Intestinal Response Kidney Response Figure 6.9 1

Figure Factors That Decrease Blood Calcium Levels Bone Response Intestinal Response Kidney Response High Calcium Ion Levels in Plasma (above 11 mg/dL) Thyroid Gland Response C cells secrete calcitonin. Calcitonin Inhibits osteoclasts osteoblasts continue to deposit calcium within the matrix of bones. Bone less calcitriol Decrease in the rate of calcium ion absorption from the intestinal contents. Inhibitory effect: Suppresses calcium ion reabsorption. Calcium stored Calcium absorbed slowlyCalcium excreted More calcium lost in urine Ca 2+ levels in plasma decrease