Chapter 6

Which minerals are stored in bones?

calcium and phosphorus

Which ossification method would form a femur? Which would form most skull bones?

(a) endochondrial ossification (b) intramembraneous ossification

Which cells turn into osteoblasts? Into osteocytes?

(a) osteogenic cells; (b) osteoblasts

Which type of bone is small and located in tendons?

(a) sesamoid bone

Which type of bone has a boxy shape? Which has an elongated shape?

(a) short bone; (b) long bone

What is bone remodeling? What roles do osteoblasts and osteoclasts play in the process?

(a) the ongoing replacement of old osseous tissue by new osseous tissue (b) osteoblasts produce new extracellular matrix and osteoclasts breakdown old extracellular matrix

How are bones classified according to their shape? What are some examples of bones of each class in the body? IRREGULAR BONES

- complex shapes (short + flat...etc.) Example: vertebrae, hip bones, certain facial bones, and the calcaneus (heel bone)

What are the histological features of cartilage, including the cell types present in each tissue and the components of the matrix?

- connective tissue w/ few cells, lots of extracellular space (matrix) Cell Types: Chondrocytes ("Adult cartilage cells") - lacuna: space filled w/ extracellular fluid ("lake") Extracellular Matrix: 1. Ground Substances - made up of amino acids w/ glucose (aka proteins) - glucosamine and chondroitin sulfate are the material in the extracellular matrix 2. collagen and elastic fibers (tissue specific)

What are the histological features of bone tissue including the cell types present in each tissue and the components of the matrix?

- connective tissue w/ few cells, lots of extracellular space (matrix) - combination of crystallized salts and collagen fibers is responsible for the characteristics of bone Cell Types: 1. Osteogenic cells - bone "stem cells" - develops into an osteoblast 2. Osteoblasts - produce new matrix, bone deposition - forms bone matrix (forming new bone) - synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of osseous tissue, and they initiate calcification 3. Osteocytes - maintenance of matrix - mature bone cells, are the most numerous cells in osseous tissue and maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood - lacuna = little lakes filled w/ osteocytes - canaliculi = little canals filled w/ extracellular fluid (can pass material from one cell to another 4. Osteoclasts - breakdown matrix, bone resorption - huge cells derived from multiple cells (monocytes) - secrete acids + enzymes to breakdown bone [resorption] - help regulate blood calcium levels Extracellular Matrix: 1. Ground Substance - calcium phosphate (hydroxyapatite) = forms crystal around collagen fibers and allows strength "concrete" 2. Collagen Fibers - embedded in bone tissue matrix - allows flexibility "wire" - produced by osteoblasts

What are some factors that affect bone growth?

- dietary and hormonal factors influence bone growth and remodeling - growth and sex hormones - vitamins A, C, K, and B12, D - Minerals such as calcium, phosphorus, magnesium, fluoride and manganese

How are bones classified according to their shape? What are some examples of bones of each class in the body? FLAT BONES

- generally thin - considerable protection - provide extensive surfaces for muscle attachment Examples: cranial bones, the sternum and ribs, and the scapulae

How are bones classified according to their shape? What are some examples of bones of each class in the body? LONG BONES

- longer than they are wide - consist of a shaft and two extremities (ends) - slightly curved for strength Examples: femur, tibia and fibula, humerus, ulna and radius, and phalanges.

How are bones classified according to their shape? What are some examples of bones of each class in the body? SHORT BONES

- more square (cube-shaped) - equal in length and width Examples: most carpal (wrist) bones and most tarsal (ankle) bones.

What is bone remodeling?

- replacement of old osseous tissue by new osseous tissue - a major stimulus is exercise, b/c it adds stress to bones which allows them to grow - refers to knocking down old stuff (bone tissue), and adding new stuff (bone tissue) Bone Resorption "knocking down old stuff" (by osteoclasts) Bone Deposition "adding new stuff" ( by osteoblasts)

How are bones classified according to their shape? What are some examples of bones of each class in the body? SESAMOID BONES

- shaped like a sesame seed - develop in tendons where there is friction, tension, and physical stress - protect tendons from excessive wear and tear, and they often change the direction of pull of a tendon Examples: Palms and soles, patellae

What are the two major types of bone tissue? COMPACT BONE

1. Compact Bone - contains few spaces - the strongest form of osseous tissue - found beneath the periosteum and makes up the bulk of the diaphyses (shaft) of long bones - provides protection and support and resists the stresses produced by weight and movement - matrix is made of osteons Osteons "rings in a tree [concentric lamellae]" - run lengthwise to give support (in the middle of them are blood vessels)

What are some important factors that affect the rate of bone growth and bone remodeling?

1. Hormones that increase blood calcium levels (important for adults) Parathyroid Hormone (PTH): - produced by endocrine glands that are carried by blood - raises blood calcium level to normal by (1) increasing osteoclast activity to release calcium from bone, (2) stimulating the kidneys to decrease calcium loss in the urine, and (3) activating vitamin D - NET EFFECT = increases blood calcium level and decreases blood phosphate level 2. Hormones that decrease blood calcium levels (stimulates bone growth -- important for children) Calcitonin: - produced by cells in the thyroid gland (regulates amount of calcium in blood) - When blood calcium rises above normal, the thyroid gland secretes calcitonin - inhibits the activity of osteoclasts and accelerates blood calcium uptake into bones - NET EFFECT = calcitonin promotes bone formation and DECREASES BLOOD CALCIUM LEVEL

How does intramembranous ossification differ from endochondral ossification? What are some examples of bones that ossify by each process?

1. Intramembranous Ossification (mesenchyme -> bone) - involves the formation of a bone within mesenchyme arranged in sheetlike layers that resemble membranes. - a bone develops directly within mesenchyme - non-differentiate "stem cells" form directly into bone - flat bones of the skull, the mandible (lower jawbone), and clavicle (collar bone) are formed in this way Frontanel - soft areas in infants skull that develop after your born 2. Endochondral Ossification (mesenchyme -> hyaline cartilage -> bone) - the replacement of cartilage by osseous tissue - bone develops within cartilage (cartilage starts to calcify in primary ossification site...then starts to breakdown) - differentiates into hyaline cartilage first, then breaks down into bone - most bones of the body are formed in this way, the process is best observed in a long bone - During endochondral ossification, osseous tissue gradually replaces a hyaline cartilage model

What are the two major types of bone tissue? SPONGY BONE

2. Spongy Bone - doesn't contain osteons - matrix is arranged in lattice (a lot of openings + much lighter) - consists of lamellae arranged in an irregular lattice of thin columns called trabeculae Trabeculae - have bigger spaces filled with red/white blood cells - form plate like structures Red Bone Marrow

What are the major events of intramembranous ossification? Of endochondral ossification?

A. 1. development of the ossification center, calcification, formation of trabeculae, and development of the periosteum; B. 1. development of the cartilage model, growth of the cartilage model, development of the primary ossification center 2. development of the medullary cavity, development of the secondary ossification centers, formation of articular cartilage and the epiphyseal plate

How are compact and spongy bone tissues different in microscopic appearance, location, and function?

Compact bone tissue is arranged into osteons packed closely together while spongy bone tissue contains trabeculae arranged in a lattice-like network with spaces filled with red marrow. Compact bone tissue found beneath the periosteum of all bones and makes up the bulk of the diaphyses of long bones. Spongy bone tissue is found in the epiphyses of long bones and in the interior of short, flat, and irregular bones. Compact bone tissue protects and supports while spongy bone tissue supports and protects red bone marrow.

What are the anatomical regions of a long bone?

Diaphysis (shaft) - body-the long (middle), cylindrical, main portion of the bone - rich supply of blood vessels Epiphysis - proximal and distal ends of the bone (rounded ends associated w/ joints) Metaphysis - regions between the diaphysis and the epiphysis - each metaphysis contains an epiphyseal plate -> epiphyseal line (a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length) Articular Cartilage - thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone - reduces friction and absorbs shock at freely movable joints Periosteum - sheath that surrounds the bone surface - contains bone-forming cells that enable bone to grow in thickness - protects the bone, assists in fracture repair, helps nourish osseous tissue, and serves as an attachment point for ligaments and tendons Medullary Cavity - a hollow, cylindrical space within the diaphysis that contains yellow bone marrow in adults Endosteum - a thin membrane that lines the internal bone surface facing the medullary cavity

What are the processes by which bones grow in length and in thickness?

Growth in Length: 1. epiphyseal plate (growth plate -- b/n epiphysis and diaphysis) - growth of cartilage on the epiphyseal side of the epiphyseal plate - replacement of cartilage on the diaphyseal side of the epiphyseal plate with osseous tissue - continuously adding compact bone b/n diaphysis which calcifies into bone tissue (lengthening the diaphysis) - new chondrocytes are formed on the epiphyseal side of the plate, while old chondrocytes on the diaphyseal side of the plate are replaced by osseous tissue 2. epiphyseal line - the cartilage in the epiphyseal plate is replaced by osseous tissue and the resulting bony structure is known as the epiphyseal line Growth in Thickness "Diameter" (width and girth) - osteoclasts break the inside & osteoblasts add tissue to outside (this keeps bone strong + sturdy) - Bones grow in thickness (diameter) by the deposition of osseous tissue on the outer surface of the bone

What are the major functions of bone tissue and the skeletal system?

Support - framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles Protection - protects internal organs from injury ex: cranial bone protecting brain, vertebrae (backbones) protect the spinal cord, and the rib cage protects the heart and lungs Movement - skeletal muscles attach to bones; when they contract, they pull on bones to produce movement Homeostasis of Calcium and Phosphorus - osseous tissue stores minerals that strengthen the bone - Bones can release minerals on demand into the bloodstream to maintain critical mineral balances (homeostasis) and to distribute minerals to other parts of the body Production of blood cells - red bone marrow produces red blood cells, white blood cells, and platelets by a process called hemopoiesis ("blood making")

What body functions depend on proper levels of calcium?

bone growth and remodeling, muscle and nerve cell function, and blood clotting

Which nutrients are important for bone growth and remodeling?

calcium, phosphorus, fluoride, magnesium iron, manganese, vitamins A, C, B12, D, and K

Where are the diaphysis, epiphyses, and metaphyses each located on a long bone?

diaphysis is the long cylindrical main portion of the bone epiphyses are at the proximal and distal ends of the bone metaphyses are between the diaphysis and each of the epiphyses

How do the two major types of bone tissue differ in terms of their structure?

different in the way the matrix is set up

Describe the location, composition, and function of the epiphyseal plate, articular cartilage, and periosteum.

epiphyseal plate: located in the metaphysis, composed of hyaline cartilage, is the growth plate articular cartilage: covers the part of the epiphysis where the bone forms an articulation with another bone, composed of hyaline cartilage, reduces friction and absorbs shock at freely movable joints periosteum: surrounds the bone surface wherever it is not covered by articular cartilage, is a sheath of connective tissue containing osteoblasts, functions to protect the bone, assists in fracture repair, nourishes bone tissue, and serves as an attachment point for ligaments and tendons

Which type of bone provides a large, flat surface area for muscle attachment?

flat bone

Which kind of bone marrow is in spongy bone tissue?

hemopoietic (red) bone marrow

How does human growth hormone regulate bone growth?

human growth hormone stimulates the production and release of insulin-like growth factors, which stimulate bone growth

Why is bone remodeling necessary when a person reaches adulthood?

it renews osseous tissue before deterioration sets in, it heals injured bone, it redistributes bone along lines of mechanical stress

Which activities of the epiphyseal plate account for the lengthwise growth of the diaphysis?

new chondrocytes are formed on the epiphyseal side of the plate, while old chondrocytes on the diaphyseal side of the plate are replaced by osseous tissue

How do bones grow in diameter?

osteoblasts beneath the periosteum add new extracellular matrix to the surface of the bone

List the functions of osteoblasts, osteocytes, and osteoclasts.

osteoblasts: form extracellular matrix osteocytes: maintain daily metabolism osteoclasts: break down extracellular matrix

Which bone cell type is derived from white blood cells?

osteoclasts

How does the medullary cavity enlarge during bone growth?

osteoclasts in the endosteum breaking down osseous tissue lining the medullary cavity

How do the primary and secondary ossification centers differ?

primary ossification center forms in the diaphysis, secondary ossification centers form in the epiphysis

How does the epiphyseal line develop?

the epiphyseal cartilage cells stop dividing and bone replaces the cartilage

How do the medullary cavities in a long bone form?

through the action of osteoclasts

What is the composition of the extracellular matrix of osseous tissue?

water, collagen fibers, and crystalized mineral salts called hydroxyapatite (mainly, calcium phosphate and calcium hydroxide)