Second half of Chapter 7 Flashcards
Compact bone
Histology of compact bone reveals osteons (haversian systems)
Compact bone:Concentric lamellae and
Perforating (Volkmann) canals
Concentric lamellae surround a central (haversian) canal running longitudinally
Perforating (Volkmann) canals—transverse or diagonal passages
Compact bone:Circumferential lamellae and Interstitial lamellae
Circumferential lamellae fill outer region of dense bone
Interstitial lamellae fill irregular regions between osteons
Spongy bone consists of:
Lattice of bone covered with endosteum Slivers of bone called spicules Thin plates of bone called trabeculae Spaces filled with red bone marrow.Few osteons and no central canals All osteocytes close to bone marrow
Provides strength with minimal weight
Trabeculae develop along bone’s lines of stress
Bone marrow
Bone marrow—soft tissue occupying marrow cavities of long bones and small spaces of spongy bone
Red marrow (myeloid tissue)
Red marrow (myeloid tissue)
Contains hemopoietic tissue—produces blood cells
In nearly every bone in a child
In adults, found in skull, vertebrae, ribs, sternum, part of pelvic girdle, and proximal heads of humerus and femur
Yellow marrow
Yellow marrow found in adults
Fatty marrow that does not produce blood
Can transform back to red marrow in the event of chronic anemia
Ossification or osteogenesis
Ossification or osteogenesis—the formation of bone
In the human fetus and infant, bone develops by two methods
Intramembranous ossification
Endochondral ossification
Intramembranous Ossification
Produces flat bones of skull and clavicle in fetus
Thickens long bones throughout life.Note the periosteum and osteoblasts
osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue.
Endochondral Ossification,
During infancy and childhood, the epiphyses fill with spongy bone
Cartilage limited to the articular cartilage covering each joint surface, and to the epiphyseal plate.By late teens to early 20s, all remaining cartilage in the epiphyseal plate is generally consumed
Bone Growth and Remodeling:Ossification
Ossification continues throughout life with the growth and remodeling of bones
Bones grow in two directions
Length
Width
Bone Elongation:Epiphyseal plate
Epiphyseal plate—cartilage transitions to bone
Functions as growth zone where bone elongates
Has typical hyaline cartilage in the middle with transition zones on each side where cartilage is replaced by bone.
Bone Elongation: Metaphysis
Metaphysis is zone of transition facing the marrow cavity
interstitial growth
interstitial growth—growth from within
Bone elongation is a result of cartilage growth within the epiphyseal plate
epiphyseal line
Epiphyses close when cartilage is gone—epiphyseal line of spongy bone marks site of former epiphyseal plate
Achondroplastic dwarfism
Long bones stop growing in childhood
Normal torso, short limbs
Failure of cartilage growth in metaphysis
Spontaneous mutation produces mutant dominant allele
Pituitary dwarfism
Lack of growth hormone
Normal proportions with short stature
Bone remodeling
(absorption and deposition) occurs throughout life—10% of skeleton per year
Repairs microfractures, releases minerals into blood, reshapes bones in response to use and disuse
Wolff’s law of bone
Wolff’s law of bone: architecture of bone determined by mechanical stresses placed on it
Remodeling is a collaborative and precise action of osteoblasts and osteoclasts
Bony processes grow larger in response to mechanical stress
Physiology of Osseous Tissue
A mature bone remains a metabolically active organ
Involved in its own maintenance of growth and remodeling
Exerts a profound influence over the rest of the body by exchanging minerals with tissue fluid
Disturbance of calcium homeostasis in skeleton disrupts function of other organ systems
Especially nervous and muscular
Mineral Deposition and Resorption
Mineral deposition (mineralization)—process in which calcium, phosphate, and other ions are taken from blood and deposited in bone
Mineral Deposition and Resorption:
Osteoblasts
Osteoblasts produce collagen fibers that spiral the length of the osteon
Mineral Deposition and Resorption:solubility product
Hydroxyapatite crystals form at solubility product—critical level of calcium times phosphate concentration
Mineral Deposition and Resorption: seed crystals
First few crystals act as seed crystals that attract more calcium and phosphate from solution
Mineral Deposition and Resorption: Abnormal calcification (ectopic ossification)—
Abnormal calcification (ectopic ossification)—formation of a calculus (calcified mass) in an otherwise soft organ such as a lung, brain, eye, muscle, tendon, or artery (arteriosclerosis)
Mineral Resorption
Mineral resorption—process of dissolving bone and releasing minerals into blood.Performed by osteoclasts at ruffled border
Mineral Deposition and Resorption: Hydrogen pumps
Hydrogen pumps in membranes secrete hydrogen into space between osteoclast and bone surface
Mineral Deposition and Resorption:Chloride ions,Hydrochloric acid,Acid phosphatase
Chloride ions follow by electrical attraction
Hydrochloric acid (pH 4) dissolves bone minerals
Acid phosphatase enzyme digests collagen
Calcium Homeostasis
Calcium and phosphate are used for much more than bone structure
Phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers
Calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis
Minerals are deposited in the skeleton and withdrawn when they are needed for other purposes
Calcium Homeostasis:Hypocalcemia
Hypocalcemia—deficient calcium in blood
Changes membrane potentials and causes overly excitable nervous system and tetany (muscle spasms)
Laryngospasm can cause suffocation
Caused by vitamin D deficiency, diarrhea, thyroid tumors, underactive parathyroid glands
Pregnancy and lactation increase risk of hypocalcemia
Calcium Homeostasis:Hypercalcemia
Hypercalcemia—excessive calcium levels
Makes ion channels less responsive and thus nerve and muscle are less excitable
Can cause emotional disturbance, muscle weakness, sluggish reflexes, cardiac arrest
Hypercalcemia rarely occurs
Calcium Homeostasis
Calcium homeostasis depends on a balance between dietary intake, urinary and fecal losses, and exchanges between osseous tissue
Calcitrio
Calcitriol—most active form of vitamin D
Produced by actions of skin, liver, and kidneys .Liver adds hydroxyl group converting that to calcidiol
Kidney adds hydroxyl group converting that to calcitriol
Calcitriol,
Calcitriol is a hormone that raises blood calcium level
Mainly, it increases calcium absorption by small intestine
It also increases calcium resorption from the skeleton.It weakly promotes kidney reabsorption of calcium ions, so less lost in urine.
Calcitriol, continued
Calcitriol is also necessary for bone deposition—helping provide adequate calcium and phosphate
Calcitonin
Calcitonin—secreted by C cells (clear cells) of thyroid gland when blood calcium levels rise too high
Lowers blood calcium concentration in two ways:
Inhibits osteoclasts thereby reducing bone resorption
Stimulates osteoblasts to deposit calcium into bone.May inhibit bone loss in pregnant and lactating women
Parathyroid hormone (PTH)
Parathyroid hormone (PTH)—secreted by parathyroid glands on posterior surface of thyroid
PTH released when calcium levels low in blood
PTH raises calcium blood level by four mechanisms
Increaes osteoclast population and bone resorption.
Phosphate Homeostasis
Phosphate levels are not regulated as tightly as calcium levels. It is
Other Factors Affecting Bone
At least 20 or more hormones, vitamins, and growth factors affect osseous tissue
Bone growth especially rapid in puberty and adolescence
Anabolic steroids
Anabolic steroids cause growth to stop
Epiphyseal plate “closes” prematurely
Results in abnormally short adult stature
Orthopedics
Osteoporosis—the most common bone disease
Severe loss of bone density
Bones lose mass and become brittle due to loss of organic matrix and minerals
