The Skeletal System (Ch. 6)

Body's Calcium

Bone stores about 99% Blood Calcium level (9-11mg/100ml of blood) blood calcium levels are controlled by negative feedback loop

Osteons

Consists of concentric lamellae arranged around a central (haversian) canal. (Compact Bone)

Zone of proliferating cartilage

Slightly larger chondrocytes in this zone are arranged like stacks of coins. These chondrocytes undergo interstitial growth as they divide and secrete extracellular matrix. The chondrocytes in this zone divide to replace those that die in the diaphyseal side of the epiphyseal plate.

Periosteal Arteries

Small Arteries accompanied by nerves, enter the diaphysis through many perforating canals and supply the periosteum and outer part of compact bone.

Lacunae

Small spaces between concentric lamellae, which contain the osteocytes.

Periosteum

(Around) - It is a tough connective tissue sheath and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage. It is composed of a outer fibrous layer of dense irregular connective tissue and an inner osteogenic layer that consists of cells. Some cells enable the bone to grow in width but not in length. It also protects the bone, assists in fracture repair, helps nourish bone, and serves as a attachment point for tendons and ligaments. (component of long bones)

Ossification or Osteogenesis

(Bone Making) The process which bone forms.

Osteoclasts

(Break) These are huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell) and are concentrated in the endosteum. On the side of the cell that faces the bone surface, the osteoclasts plasma membrane is deeply folded into a ruffled border. Here the cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying extracellular bone matrix. This breakdown of bone extracellular matrix is termed resorption. It is part of the normal development, maintenance and repair of the bone. (This cell Breaks Down extracellular matrix)

Osteoblasts

(Buds or sprouts) These are bone building cells. These cells secrete extracellular matrix and they initiate calcification. As they surround themselves with extracellular matrix , they become trapped in their Secretion and become osteocytes. These do not undergo cell division. (This cell forms bone extracellular matix)

Development of secondary ossification centers

(Fifth Step of Endochondral Ossification) When branches of the epiphyseal artery enter the epiphyses, Secondary ossification center develop, usually around the time of birth. Bone formation is similar to what occurs in primary ossification center. However, in this center spongy bone remains in the interior of the epiphyses (no medullary cavity is formed). This is also different because it moves outward from the center of the epiphysis toward the outer surface of the bone. Bone tissue replaces most of cartilage.

Development of the cartilage model

(First Step of Endochondral Ossification) Mesenchymal cells develop into chondroblasts, which form the cartilage model.

Development of Ossification Center

(First step of Intramembranous Ossification) Where the bone will develop mesenchymal cells will cluster and differentiate, first into osteogenic cells then into osteoblasts. Site where they cluster is called ossification center. Osteoblasts secrete thee organic extracellular matrix of bone until they are surrounded by it.

Development of the medullary cavity

(Fourth Step of Endochondral Ossification) As the primary ossification center grows toward the ends of the bone, osteoclasts break down some of the newly formed spongy bone trabeculae. Bone breakdown by osteoclasts forms the medullary cavity.

Development of periosteum

(Fourth Step of Intramembranous Ossification) Mesenchyme at the periphery of the bone develops into the periosteum.

Osteogenic Cells

(Producing) Are unspecialized bone stem cells. They are the Only bone cells that undergo cell division: the resulting cells develop into osteoblasts. Osteogenic cells are found on the inner portion of the periosteum, in the endosteum, and in canals within bone that contain blood vessels.

Concentric Lamellae

(Resembling the growth of rings of a tree), they are circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels, lymphatics, and nerves located in the central canal.

Growth of the cartilage model

(Second Step of Endochondral Ossification) Growth occurs by cell division of chondrocytes.

Calcification (Intramembranous Ossification)

(Second Step of Intramembranous Ossification) Extracellular matrix stops and the cells are now called osteocytes. Calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens).

Formation of articular cartilage and the epiphyseal (growth) plate

(Sixth step of Endochondral Ossification) The hyaline cartilage that covers the epiphyses becomes the articular cartilage Prior to adulthood hyaline cartilage remains between the diaphysis and the epiphysis as the epiphyseal (growth) plate.

Development of primary ossification center

(Third Step of Endochondral Ossification) proceeds inward from the external surface of the bone. Stimulates osteogenic cells into osteoblasts. Once the perichondrium starts to form bone it is known as the periosteum. In this region of diaphysis, bone tissue replaces most of the cartilage

Formation of trabeculae

(Third Step of Intramembranous Ossification) Extracellular matrix develops into Trabeculae that fuse to form spongy bone.

Endochondral Ossification

(within Cartilage) Bone forms within hyaline cartilage that develops from mesenchyme. Replacement of cartilage by bone. Most bones are formed in this way.

Intramembranous ossification

(within membrane), bone forms directly within mesenchyme, which is arranged in sheetlike layers that resemble membranes. The simpler of the two bone formations Formed this way: flat bone of skull, facial bones, mandible, and medial part of clavicle

Repair of a bone fracture

1. Formation of Fracture hematoma 2. Fibrocartilaginous callus formation 3. Bony Callus formation 4. Bone Remodeling

Role of calcium

1. Helps with blood clotting 2. Nerve transmition 3.Normal heart contraction 4. skeletal muscle contraction etc..

Bone formation Situations

1. Initial formation of bones in an embryo or fetus. 2. The growth of bone during infancy, childhood, adolescence until adult size is reached. 3. The remodeling of bone ( the replacement of old bone by new bone tissue throughout life) 4. The repair of fractures

Growth in length in long Bones

1. Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate 2. Replacement of cartilage on the diaphysial side of the epiphyseal plate with bone by endrochondral ossification.

Factors Affecting Bone Growth and Bone Remodeling

1. Minerals (calcium and phosphorus) 2. Vitamins (Vit.A, Vit.C, Vit. D) 3. Hormones (Insulinlike growth factors IGF, Thyroid Hormone)

Growth in Thickness

1. Ridges in periosteum create groove for the Periosteal blood vessel 2. Periosteal ridges fuze forming, an Endosteum lined tunnel 3. Osteoblasts in Endosteum build new concentric lamellae inward toward center of the tunnel, forming a new osteon. 4. Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels..

Four zones of the Epiphyseal plate

1. Zone of resting cartilage 2. Zone of proliferating cartilage 3. Zone of hypertrophic cartilage 4. Zone of calcified cartilage

Epiphyses

A and E (growing over, singular is Epiphysis) are the proximal and distal parts of the bone. (component of long bones)

Fracture Hematoma

A mass of blood usually forms around the site of the fracture

Fibrocartilaginous (soft) Callus

A mass of repair tissue consisting of collagen fibers and cartilage that bridges the broken ends of the bone.

Spongy Bone Tissue

Also referred to as cancellous bone, does not contain osteons. Spongy bone is always located on the interior of the bone, protected by the compact bone. It is light, which reduces weight of bone, and support and protect red bone marrow.

Circumferential lamellae

Arranged around the entire outer and inner circumference of the shaft of a long bone are lamellae called Circumferential lamellae. The circumferential lamellae directly deep to the periosteum are called outer. The Circumferential lamellae that line the medullary cavity are called the Inner Circumferential lamellae. (Compact bone)

Metaphyses

B and D (between, singular for Metaphysis) are the regions between the Diaphysis and the Epiphyses. In growing bone each Metaphysis contain a epiphyseal (growth) plate, a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length. When the bone ceases to grow in length at the ages 18-21, the cartilage in the epiphyseal plate is replaced by bone; the resulting bony structure is known as epiphyseal line. (component of long bones)

Perforating Canal

Blood vessels, lymphatic vessels, and nerves from the periosteum penetrate the compact bone through transverse perforating canals or volkmann's canals. The vessels and nerves of the perforating canals connect with those of the medullary cavity, periosteum, and central canals. (Compact Bone)

Diaphysis

C (Growing between) is the bone's shaft- the long, cylindrical, main portion of the bone. (component of long bones)

Compact Bone Tissue

Contains few spaces and is the strongest form of bone tissue. It is found beneath the periosteum of all bones and makes up the bulk of the diaphyses of long bones. It provides protection and support and resists the stresses produced by weight and movement. Composed of repeating structural units called Osteons.

Flexibility in the bone

Depends on its collagen fibers

Hardness in the bone

Depends on the Crystallized inorganic mineral salts

Calcification

Deposition of mineral salts (primarily hydroxyapatite) in a framework formed by collagen fibers in which tissue hardens. (Also is called Mineralization). Osteoblasts cause mineral salts to calcify

Bony (hard) Callus

Fibrocartilage is converted to spongey bone and the callus is referred to as ____ this lasts 3-4 months

Medullary Cavity or Marrow Cavity

Is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults. This cavity minimizes the weight of the bone, by reducing dense bony material where it is least needed. (Component of long bones)

Endosteum

Is a thin membrane that lines the medullary cavity. It contains a single layer of bone-forming cells and a small amount of connective tissue. (component of long bone)

Fracture

Is any break in the bone

epiphyseal plate

It is a layer of hyaline cartilage in the metaphysis of a growing bone. The activity of the epiphyseal plate is the only way that the diaphysis can increase in length. The plate stops dividing when become adults aand the bone replaces all the cartilage and it becomes a boney plate called the epiphyseal line.

Nutrient Artery and Nutrient Foramen

Near the center of the diaphysis, a large _____ passes through a hole in the compact bone called the _______. On entering the Medulla cavity the Artery divides into proximal and distal branches that course toward each end of the bone. These branches supply both the inner part of compact bone tissue of the diaphysis and the spongy bone tissue and red bone marrow as far as the epiphyseal line (or plate).

Perforating Fibers

Outer Circumferential lamellae are connected to the periosteum by perforating fibers. (Compact Bone)

Tensile Strength

Resistance to be stretched or torn apart. (Collagen fibers and other organic molecules provide this strength)

Trabeculae

Spongy Bone consists of lamellae that are arranged in a irregular pattern of these thin columns. Between them are spaces that are filled with red bone marrow in bones that produce blood cells, and yellow bone marrow (adipose tissue) in other bones. They consist of concentric lamellae, osteocytes that lie in lacunae, and canaliculi that radiate outward from the lacunae.

Stress Fracture

This is a series of microscopic fissures in bone that forms without any evidence of injury to other tissues

Bone deposition

The addition of minerals and collagen fibers to bone by osteoblasts

First six weeks of embryonic development

The embryonic "skeleton" initially composed of mesenchyme in the general shape of bones, is the site where cartilage formation and ossification occur during this time period.

Zone of calcified cartilage

The final zone of the epiphyseal plate is only a few cells thick and consists of mostly chondrocytes that are dead because the extracellular matrix around them has calcified. Osteoclasts dissolve the calcified cartilage, and osteoblasts and capillaries from the diaphysis invade area. The osteoblasts lay down bone extracellular matrix, replacing the calcified cartilage by the process of endochondral ossification. (Remember that endochondral ossification is replacement of cartilage with bone). As a result the zone of calcified cartilage becomes "new diaphysis" that is firmly cemented to the rest of the diaphysis of the bone.

Bone remodeling

The ongoing replacement of old bone tissue by new bone tissue.

Bone resorption

The removal of minerals and collagen fibers from bone by osteoclasts

Osteocytes

These are Mature bone cells. They are the main cells in bone tissue and maintain it daily metabolism, such as the exchange between nutrients and wastes between blood. These do not undergo cell division. (This cells is in charge of maintaining the tissue)

Canaliculi

These are Radiating in all directions from lacunae, which are filled with extracellular fluid. Inside them are slender fingerlike processes of the osteocytes. They connect lacunae with one another and with the central canals, forming an intricate, miniature system of interconnected canals throughout the bone. This system provides many routes for nutrients and oxygen to reach the osteocytes and for the removal of wastes.

Epiphyseal Arteries

These enter the Epiphyses of the long bone and supply the red bone marrow and the bone tissue of the Epiphyses.

Metaphyseal Arteries

These enter the metaphyses of the long bone and together with the nutrient artery, supply the red bone marrow and the bone tissue of the metaphyses.

compound (open) fracture

the broken ends of the bone protrude through the skin

Articular Cartilage

This is a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. Articular cartilage reduces friction and absorbs shock at freely movable joints. Because Articular Cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited. (component of long bone)

Interstitial lamellae

This is in the area between neighboring Osteons. These also have lacunae with osteocytes and canaliculi. They are fragments of older Osteons that have been partially destroyed during bone rebuilding or regrowth. (Compact Bone)

Zone of hypertrophic cartilage

This layer consists of large maturing chondrocytes arranged in columns.

Zone of resting cartilage

This layer is nearest the epiphysis and consists of a small, scattered chondrocytes. The term "resting" is used because the cells do not function in bone growth. Rather they anchor the epiphyseal plate to the epiphysis of the bone.

1. Nutrient Veins 2. Epiphyseal Veins and Metaphyseal Veins 3. Periosteal Veins

Veins that Carry blood away from long bones are evident in three places : 1. One or two _________ accompany the nutrient artery and exit the diaphysis; 2. numerous ________ and _______ accompany their respective arteries and exit through the epiphyses; and 3. many small ________ accompany their respective arteries and exit through the perioteum.

Pott fracture

any kind of fracture in the distal end of the fibula, with serious injury of the distal tibial articulation

Greenstick fracture

bone bends and breaks

Calcitonin ( from thyroid gland)

decreases blood calcium levels by inhibiting osteoclasts activity

Parathyroid Hormone

elevates blood calcium level: -Activation Osteoclasts (effector) -stimulate kidneys (effector)to activate calcitroil (Vit. D) and increase reabsorption of Ca+2 from the small intestine

Colles fracture

fracture in the distal end of the radius

Comminuted fracture

the bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments

Impacted Fracture

one end of the fractured bone is forcefully driven into the interior of the other