Ch. 6 - Bone Tissue Flashcards
First 3 Functions of the skeletal system.
- Provide support by acting as a structural framework and a point of attachment for tendons and ligaments.
- Protect the internal organs (brain, heart, etc.)
- Assist body movements (in conjunction with muscles)
Last 3 functions of the skeletal system,
- Store and release salts of calcium and phosphorus.
- Store triglycerides in adipose cells of yellow marrow
- Participate in blood cell production (hematopoiesis)
two major tissues of skeletal system
bone (osseous tissue) and cartilage.
What is bone?
Bone is a highly vascularized C.T. with a hard, mineralized extracellular matrix. It is found in the body in two different arrangements: compact bone and spongy bone
Compact bone
Function- provides protection and support.
Structure- It forms the external layer of all bones.
Spongy bone
Function- is lightweight and provides tissue support.
Structure- It forms most of the interior of bones.
Cartilage?
is a poorly vascularized C.T. with a matrix composed of collagen, proteoglycans (chondroitin sulfate) and various fibers.
Fiber types
hyaline cartilage
different from fibrocartilage or elastic cartilage.
Articular cartilage?
Structure: thin layer of hyaline cartilage covering the epiphysis of long bones. Found where the bone forms an articulation, or joint (where one bone moves against another bone).
Function: Reduces friction and
Absorbs shock
Periosteum
The periosteum is only found on areas where there is no articular cartilage.
Structure: tough sheath of dense, irregular connective tissue on the outside of the bone.
Periosteum- outer fiber layer
- Provides protection and nourishment
- Attachment point for tendons and ligaments
Periosteum- inner osteogenic layer: osteoblasts
growth and fracture repair.
Medullary Cavity
space within the diaphysis of long bones. contains fatty yellow bone marrow in adults.
Endosteum
Membrane that lines the medullary cavity.
-The endosteum is composed of osteoclasts, osteoblasts, and connective tissue.
Perichondrium
dense irregular connective tissue membrane that surrounds cartilage.
Chondroblasts/chondrocytes are
cells that build/maintain cartilage.
Many major bones are formed from cartilage.
Osteoprogenitor cells:
bone stem cells that differentiate into specialized bone cells
osteoblasts
bone building cells:
- Synthesize and secrete collagen fibers and other organic components
- Initiate calcification
Osteocytes
mature osteoblasts
-maintain tissue
Osteoclasts:
large bone crushing cells:
- White blood cells that migrate from bone marrow to become “fixed ” in bone tissue
- Remodel bones and cause them to release calcium
Tissues of skeletal system- epithelium
(endothelium) form the capillary walls
Tissues of skeletal system- nerves
(the periosteum is especially tender)
Tissues of skeletal system- red marrow
hematopoiesis
Tissues of skeletal system- yellow marrow
fat storage
Chemical constituents of bone
Bone is 15% water, 30% collagen fibers, 55% mineral salts (hydroxyapatite crystals).
Organic constituents of bone
Collagen fibers provide flexibility and tensile strength.
Inorganic hydroxyapatite crystals (mineral salts)
- Calcium Phosphate (Ca3PO4)2
- Calcium Carbonate (CaCO3 – marble)
- Other trace elements: magnesium, fluoride, sulfate
Bone structure- long bone- diaphysis
the shaft/ body of a long bone
Bone structure- long bone- epiphyses
the distal and proximal ends of a long bone, at the joints
Bone structure- long bone- metaphyses
areas where the epiphyses and diaphysis join
Adolescent bone structure
In adolescents, through the end of active growth, the epiphysis of the long bones contains hyaline cartilage and forms an “epiphyseal growth plate”.
-The growth plate is always actively dividing and causing the bone to elongate from each end.
Adult bone structure
In adults, the epiphyseal cartilage is no longer present and elongation of bones has stopped.
The epiphyseal growth plate becomes an “epiphyseal line”,
as growing cartilage is replaced by calcified bone.
The epiphyseal line is visible externally and on X-rays.
Osteons?
AKA: Haversian systems
- structural unit of compact bone
- formed from concentric lamellae –> rings of calcified matrix
Interstitial lamellae
between osteons are left over fragments of older osteons.
Outer circumferential lamellae
encircle the bone beneath the periosteum.
Inner circumferential lamellae
encircle the medullary cavity.
Lacunae
small spaces between the lamellae which house osteocytes.
Canaliculi
small channels filled with extracellular fluid connecting the lacunae.
central canal
contain blood and lymphatic vessels
-found in the center of osteon
Perforating (Volkmann’s) canals
allow transit of vessels to the periosteum and medullary cavity
Spongy bone
Lacks osteons.
Instead, lamellae are arranged in a lattice of thin columns called trabeculae.
Spongy bone details (3)
- Oriented along lines of stress (helps bones resist stresses without breaking).
- Support and protect red bone marrow
- Hematopoiesis (blood cell production) occurs in spongy bone.
Spongy bone - trabecula contains…
lacunae.
As in compact bone, lacunae contain osteocytes that nourish the mature bone tissue from the blood circulating through the trabeculae.
Benefit of spongy bone
lessens the overall bone weight.
Long bones are primaritly made of…
spongy bone.
Details of the blood in bone (3)
- bone is richly supplied with blood.
- Nutrient artery enters nutrient foramen in diaphysis
- Periosteal arteries and veins supply the periosteum and compact bone.
Details of nerves in bones (2)
- nerves often accompany blood vessels.
2. The periosteum is rich in sensory nerves sensitive to tearing or tension (think hitting your shin)
Ossification?
AKA (osteogenesis): the process of forming new bone.
Bone formation occurs in four situations:
- Formation of bone in an embryo/fetus.
- Growth of bones until adulthood
- Remodeling of bone
- Repair of fractures
Ossification by two different methods involve and lead to what?
- Both involve replacement of pre-existing C.T. with bone.
- Both lead to spongy and compact bone.
Intramembranous ossification:
Mesenchyme replaced by spongy bone.
- Some bone subsequently remodeled to form compact bone.
- think flat bones.
Endochondral ossification:
method used in the formation of most bones, especially long bones.
It involves replacement of cartilage by bone.
There are one primary and two secondary centers of growth.
Intramembranous ossification (4 details):
- Simple(r)
- Forms the flat bones of the skull, mandible, and clavicle.
- Bone forms from mesenchymal cells that develop within a membrane
- No cartilage stage (mesenchyme is the tissue from which almost all other C.T. develop.)
4.Many ossification centers.
Intramembranous ossification STEPS
- development of ossification center: osteoblasts secrete organic extracellular matrix.
- calcification: calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens)
- formation of trabeculae: extracellular matrix develops into trabeculae that fuse to form spongy bone.
- Development of the periosteum: mesenchyme at the periphery of the bone develops into periosteum.
Endochondral ossification STEPS
- development of cartilage model: mesenchymal cells develop into chondroblasts, which form the cartilage model.
- growth of cartilage model: growth occurs by cell division of chondrocytes.
- development of primary ossification center: in this region of the diaphysis. bone tissue replaced most of the cartilage.
- development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity.
- development of secondary ossification centers: these occur in the epiphyses of the bone.
- formation of articular cartilage and epiphyseal plate: both structures consists of hyaline cartilage.
Growth along the epiphyseal plate- THE ZONE OF RESTING CARTILAGE
Zone of resting cells- they are cartilage; they are dead
Growth along the epiphyseal plate- THE ZONE OF PROLIFERATING CARTILAGE-
Proliferation - they are dividing; they are lengthening the bone.
Growth along the epiphyseal plate- THE ZONE OF HYPERTROPHYING CARTILAGE
Hypertrophy- they are getting bigger;
Growth along the epiphyseal plate- THE ZONE OF CALCIFYING CARTILAGE
Calcification is occurring from the middle towards each end of the bone. Osteoblasts are taken over by the chondroblast then it calcifies and becomes bone.
What can bone do once the epiphyseal plate is closed?
Bones thicken and capable of repair after the epiphyseal growth plates have closed.
How do bones thicken?
Bones thicken due to appositional growth:
Cooperative action of osteoblasts and osteoclasts.
Remodeling of bone?
- Removes injured bone
- Accommodates lifestyle changes
-A balance must exist between the actions of osteoclasts and osteoblasts.
Acromegaly
Too much new tissue formed: bones become abnormally thick and heavy
Osteoporosis
Excessive loss of calcium: weakens bones, as occurs in osteoporosis.
Rickets or osteomalacia
bones becoming soft.
minerals essential for normal bone metabolism
Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling.
Vitamins essential for normal bone metabolism- Vitamin A
stimulates activity of osteoblasts.
Vitamins essential for normal bone metabolism- Vitamin C
needed for synthesis of collagen.
Vitamins essential for normal bone metabolism- Vitamin D
essential to healthy bones because it promotes the absorption of calcium from foods in the gastrointestinal tract into the blood.
Vitamins essential for normal bone metabolism- Vitamin K and B12
needed for synthesis of bone proteins.
Hormones essential for normal bone metabolism- hGH
Human growth hormones (hGH; somatotropin) - released from the anterior pituitary gland.
-one of the body’s many anabolic hormones.
- Secretion stimulates bone growth, muscle growth, loss of fat, and increased glucose output in the liver.
- Use of growth hormone has increased in popularity due to the numerous benefits associated with its use; side effects also result
Hormones essential for normal bone metabolism- IGF
- IGFs stimulate osteoblasts
- Promotes mitosis at the epiphyseal growth plate.
- Enhances the synthesis of bone proteins needed to build bone matrix.
Hormones essential for normal bone metabolism- estrogen
inhibits osteoclast; menopause there is no estrogen.
osteoclast would be more active then. The bone tend to be weaker after menopause.
Promote widening of the pelvis in the female skeleton.
Responsible for closing the epiphyseal plates at the end of puberty.
Hormones essential for normal bone metabolism- thyroid hormone and insulin
promote bone growth by stimulating osteoblasts and protein synthesis.
Calcium Homeostasis hormones?
Parathyroid hormone (PTH) and calcitonin are critical for balancing the levels of calcium and phosphorus between blood and bone.
Why is calcium homeostasis important?
Maintaining blood calcium levels is more “important” than bone mineralization because normal heart function depends on a normal ionized serum calcium level (between 8.5-10.2 mg/dl)
Why is calcium important?
- Nerves
- Muscles
- Clotting factors
- Enzyme functioning
Day to day control of calcium regulation mainly involves:
PTH
PTH stimulates osteoclast activity and vitamin D production in kidneys, which raises serum calcium level.
Day to day control of calcium regulation mainly involves: Vitamin D
Vitamin D is needed for absorption of the Ca2+ and PO4– ions from the small intestine, and reabsorption of those same ions in the kidneys.
Day to day control of calcium regulation mainly involves: Calcitonin
Calcitonin, and to a lesser extent hGH and the sex hormones, stimulate osteoblastic activity and lower serum calcium level.
What is a fracture?
any break in a bone.
Fracture- stress
Stress - microscopic fissures resulting from repeated strenuous activity like running
Open fracture
AKA compound.
damage to the bone and through the skin.
Closed fracture
AKA simple
bone broken but does not break skin.
Comminuted fracture
bone is crushed; more than two pieces of the bone; many fragments.
Greenstick Fracture
Partial break; not a complete break in the bone; does not penetrate through the bone.
-Common in children.
Impacted fracture
pieces of fractured bone forcefully driven into each other.
Pott Fracture
fracture to the distal end of the fibula and tibial articulation.
Colles fracture
fracture to the distal end of the radius
Fracture repair - 1. reactive phase (1)
Formation of a fracture hematoma begins 6-8 hours after injury when broken blood vessels leak blood into the surrounding tissue and blood clotting occurs.
Phagocytic cells (neutrophils and macrophages) and osteoclasts begin to remove damaged tissue.
- Bone; vasodilation; increase blood to that area. Fracture hematoma. Clot starts. Helps to hold the two ends of the bones together.
Fracture repair - 2. reparative phase #1
Fibrocartilaginous (soft) callus formation takes about 3 weeks and involves collagen fibers (from fibroblasts) and fibrocartilage (from chondroblasts) producing repair tissue between the broken bones.
- Fibroblast (takes place of the hematoma)- fibroblast produce collagen fiber inthe ECS. helps to hold the bones together, now it is stronger CT putting the bones together. Fibrocartilaginous.
Fracture repair - 3. reparative phase #2
Bony callus formation lasts about 3-4 months and occurs when osteogenic cells differentiate into osteoblasts that replace the fibrocartilage with spongy bone.
- Osteoblast - replaces the fibroblast - starts to release bone matrix and calcification occurs. Now the two bones are held together by normal bone matrix, but there will be rough edges.
Fracture repair - bone remodeling phase
replaces spongy bone with compact bone. Osteoclasts resorb any bone fragments. The fracture line disappears, but evidence of the break remains.
- The newly repair part is stronger.
The most important thing is to hold the bone together during this time until there is a callus formation between them.
Bone and mechanical stress
Under mechanical stress, bone tissue becomes stronger through deposition of mineral salts and production of collagen fibers by osteoblasts.
what happens to unstressed bones?
Unstressed bones, on the other hand, become weaker.
-Astronauts in space suffer rapid loss of bone density.
What is considered mechanical stress?
The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity (weight-bearing activities).
Why is there a decrease in bone mass with aging?
A decrease in bone mass occurs as the level of sex hormones diminishes during middle age (especially in women after menopause).
Bone resorption by osteoclasts outpaces bone deposition by osteoblasts.
Since female bones are generally smaller and less massive than males to begin with, old age has a greater adverse effect in females.
Principal effect of aging on bone tissue #1
Loss of bone mass
-The loss of calcium from bones is one of the symptoms in osteoporosis.
Principal effect of aging on bone tissue #2
Brittleness
- Collagen fibers give bone its tensile strength, and protein synthesis decreases with age.
- The loss of tensile strength causes the bones to become very brittle and susceptible to fracture.
What is osteoporosis?`
Osteoporosis is a condition where bone resorption outpaces bone deposition.
Often due to depletion of calcium from the body or inadequate intake
at least partially due to aging.
