Exam 2 Structure and function Bone/Muscle Tissue

What is osteoid?

The soft, unmineralized organic portion of bone matrix secreted by osteoblasts. It is mainly collagen and other organic molecules.

What is osseous tissue?

Mineralized bone tissue. It contains organic matrix that has been hardened by calcium phosphate and other minerals.

What is the main difference between osteoid and osseous tissue?

one is unmineralized, while the other tissue is mineralized and hardened with calcium phosphate and other minerals.

Where is trabecular bone located relative to compact bone?

Located deep to compact bone. It is found especially at the ends of long bones and inside flat, short, and irregular bones.

What is the epiphysis of a long bone?

Expanded end of a long bone. It helps strengthen the joint and provides attachment surfaces for tendons and ligaments.

What is the diaphysis of a long bone?

the shaft, or long central portion, of a long bone.

What is the medullary cavity?

the hollow cavity inside the diaphysis that contains bone marrow.

What is the endosteum?

thin connective tissue membrane that lines the internal surfaces of bone, including the medullary cavity, trabeculae, and internal canals.

What is the periosteum?

a connective tissue membrane covering the outer surface of bone, except where articular cartilage is present. It contains an outer fibrous layer and an inner osteogenic layer.

What cells are found in the periosteum?

The inner osteogenic layer contains osteogenic cells and bone-forming cells such as osteoblasts.

What cells are found in the endosteum?

osteogenic cells, osteoblasts, and osteoclasts involved in bone growth, repair, and remodeling.

What are the two major components of the bone extracellular matrix?

Organic components and inorganic components.

What percentage of bone matrix is organic?

About one-third of the bone matrix

What are the main organic components of bone matrix?

Mostly collagen, along with glycosaminoglycans, proteoglycans, and glycoproteins.

What is the function of the organic portion of bone matrix

provides flexibility and tensile strength, helping prevent bone from being excessively brittle.

What percentage of bone matrix is inorganic?

About two-thirds of the bone matrix by dry weight.

What is the main inorganic component of bone matrix?

Hydroxyapatite, a crystallized calcium phosphate mineral.

What is the function of the inorganic portion of bone matrix?

It provides hardness and compressive strength, allowing bone to support weight without bending easily.

What happens to bone if it loses most of its minerals?

It becomes soft and flexible because the mineral component normally provides hardness.

What happens to bone if it loses its collagen?

It becomes excessively brittle because collagen provides flexibility and tensile strength

What is an osteon?

Haversian system, is the basic structural unit of compact bone

What is found at the center of an osteon?

A central, or Haversian, canal.

What is a central canal?

A canal running through the center of an osteon that contains blood vessels and nerves and provides nutrients to bone cells.

What are lamellae?

layers of bone matrix arranged concentrically around the central canal in an osteon.

Why do collagen fibers run in different directions in adjacent lamellae?

The alternating directions increase the strength of bone and help it resist different types of mechanical stress.

What are canaliculi?

tiny channels connecting the lacunae of osteocytes.

Why are canaliculi important?

They allow osteocytes to communicate and exchange nutrients, gases, chemical signals, and wastes with one another and with nearby blood vessels.

Where are osteocytes located?

Osteocytes are located in small spaces called lacunae within the bone matrix.

What are perforating, or Volkmann, canals?

They are canals that run transversely or diagonally through compact bone and connect central canals with one another and with blood vessels entering from the surface.

What is the purpose of the central and perforating canals?

They provide pathways for blood vessels and nerves, allowing bone cells to receive nutrients and remove wastes.

What are trabeculae?

thin plates or rods of bone that form the framework of spongy, or trabecular, bone.

Does trabecular bone contain osteons with central canals?

No. Its trabeculae are thin enough that osteocytes can receive nutrients by diffusion from nearby blood vessels in the marrow spaces. The PowerPoint specifically notes that no central canals are needed.

What are some functions of trabecular bone?

It provides strength while keeping bones relatively lightweight, absorbs shock, participates in calcium and phosphate homeostasis, and adapts to mechanical stress.

What is red bone marrow?

hematopoietic tissue that produces red blood cells, white blood cells, and platelets.

Where is red bone marrow found in children?

found throughout the marrow cavities and in the spaces between trabeculae.

Where is red bone marrow found in adults?

mainly found in the skull, vertebrae, ribs, sternum, pelvis, and proximal ends of the femur and humerus.

What happens to red bone marrow in the medullary cavity as a person ages?

Much of it changes into yellow bone marrow, which is primarily fatty tissue.

What are the four major types of bone cells?

Osteogenic cells, osteoblasts, osteocytes, and osteoclasts.

What are osteogenic cells?

stem cells that can divide and develop into osteoblasts.

Where are osteogenic cells located?

They are found in the endosteum and inner layer of the periosteum.

What is the function of osteogenic cells?

They produce new osteoblasts/claytes for bone growth and repair.

What are osteoblasts?

Bone-forming cells that synthesize osteoid and promote its mineralization

What is the function of osteoblasts?

They deposit new bone matrix and are primarily responsible for bone deposition.

What are osteocytes?

mature bone cells that develop from osteoblasts after becoming trapped in the matrix they produced.

What is the main function of osteocytes?

They maintain bone matrix and monitor mechanical stress, helping regulate bone remodeling

What are osteoclasts?

large, multinucleated cells that break down bone matrix.

What is the function of osteoclasts

They perform bone resorption, breaking down bone and releasing minerals such as calcium into the blood.

Which bone cells are responsible for bone deposition?

Osteoblasts

Which bone cells are responsible for bone resorption?

Osteoclasts

What is bone deposition?

the formation of new bone matrix by osteoblasts, followed by mineralization.

What is bone resorption?

the breakdown of bone matrix by osteoclasts, releasing minerals into the blood.

What is ossification?

or osteogenesis, is the process of bone formation.

What are the two types of ossification?

Intramembranous ossification and endochondral ossification.

What tissue does intramembranous ossification begin with?

Embryonic mesenchymal connective tissue.

What tissue does endochondral ossification begin with?

A preexisting hyaline cartilage model.

What bones primarily form through intramembranous ossification?

Flat bones of the skull and most of the clavicle.

What bones primarily form through endochondral ossification

Most bones of the body, including vertebrae, ribs, sternum, scapula, pelvic bones, and limb bones.

What happens during intramembranous ossification?

Mesenchymal cells become osteoblasts, osteoblasts secrete osteoid, the osteoid mineralizes, osteoblasts become osteocytes, and the developing bone forms trabeculae and then compact bone.

What happens during endochondral ossification?

A hyaline cartilage model is formed first, then cartilage is gradually replaced by bone as ossification centers develop.

What is the major difference between intramembranous and endochondral ossification?

One forms bone directly from mesenchymal tissue, while the other one forms bone by replacing a hyaline cartilage model.

What are the two types of bone growth?

Interstitial growth and appositional growth.

What is the purpose of interstitial growth?

It increases the length of bones during childhood and adolescence.

Where does interstitial growth occur?

It occurs in the cartilage of the epiphyseal plate.

How does interstitial growth increase bone length?

Chondrocytes multiply and produce new cartilage on the epiphyseal side of the growth plate. The cartilage then undergoes hypertrophy, calcification, and replacement by bone on the diaphyseal side.

What is appositional growth

increases the width or thickness of a bone by adding new bone to its outer surface.

Which type of bone growth continues in adults?

Appositional growth.

What happens to the epiphyseal plate when a person becomes an adult?

The cartilage of the epiphyseal plate is depleted and replaced by bone, leaving an epiphyseal line

Why can adults no longer increase the length of their long bones?

Their epiphyseal plates have closed, so cartilage can no longer grow to lengthen the bone

How do adult bones differ from children’s bones?

one has open epiphyseal plates and more red bone marrow, while the other have closed epiphyseal plates and much of the marrow cavity contains yellow marrow.

What is Wolff’s Law?

bone architecture is determined by the mechanical stresses placed on it, and bone adapts to withstand those stresses.

How does exercise affect bone according to Wolff’s Law?

Repeated mechanical stress stimulates bone deposition and can make bones stronger and denser.

What happens to a bone that is not used very much?

Osteoclast activity removes unnecessary bone matrix, reducing bone mass.

What happens to a bone that experiences consistent mechanical stress?

Osteoblasts deposit new bone and the bone becomes thicker and stronger in areas experiencing stress.

What is bone remodeling?

Bone remodeling is the continuous process of bone resorption and bone deposition that replaces old bone with new bone.

Why does the body remodel bone?

To repair microfractures, reshape bone according to use and disuse, and help regulate calcium and phosphate levels.

Approximately how much of the skeleton is remodeled each year?

About 10%

Which cells work together during bone remodeling?

Osteoclasts resorb old bone, while osteoblasts deposit new bone.

What is gigantism?

Occurs when excessive growth hormone is present before the epiphyseal plates close, causing excessive longitudinal bone growth.

What is acromegaly?

occurs when excessive growth hormone is present after the epiphyseal plates have closed, causing thickening of bones and soft tissues, especially in the hands, feet, and face.

What is the difference between gigantism and acromegaly?

One occurs before epiphyseal closure and causes excessive height. another occurs after epiphyseal closure and causes thickening of bones and soft tissues.

What is osteoporosis?

a condition in which bone resorption exceeds bone formation, resulting in decreased bone mass and strength.

Why is spongy bone especially vulnerable to osteoporosis?

Spongy bone has a large surface area available for osteoclast activity, making it especially susceptible to bone loss.

What is osteogenesis imperfecta?

Aka brittle bone disease, is a disorder involving defective collagen deposition that makes bones unusually brittle and prone to fractures.

What is rickets?

a childhood disease involving soft, poorly mineralized bones, commonly associated with vitamin D and calcium deficiency.

What is osteomalacia?

the adult form of defective bone mineralization associated with inadequate vitamin D and mineral availability.

What is achondroplastic dwarfism?

a condition in which the long bones of the limbs stop growing normally because cartilage growth in the metaphysis is impaired. The head and trunk remain relatively normal in size.

What part of bone growth is affected in achondroplastic dwarfism?

Cartilage growth in the zones of chondrocyte proliferation and hypertrophy is impaired

What is hyperparathyroidism?

excessive secretion of parathyroid hormone, which increases osteoclast activity indirectly and increases bone resorption and blood calcium levels.

What happens to bone when PTH levels remain excessively high?

Bone resorption increases, which can reduce bone density and release more calcium into the blood.

What is hypoparathyroidism?

insufficient secretion of PTH, which can contribute to low blood calcium levels.

What is hypercalcemia?

abnormally high concentration of calcium in the blood.

What effect does hypercalcemia have on neuromuscular excitability?

It decreases neuromuscular excitability and can cause muscle weakness and impaired reflexes.

What is hypocalcemia?

an abnormally low concentration of calcium in the blood.

What effect does hypocalcemia have on neuromuscular excitability?

It increases neuromuscular excitability and can cause muscle tremors, spasms, and tetany

What is ectopic ossification?

abnormal formation or calcification of bone tissue in tissues where bone normally should not form.

What is a fracture?

break or crack in a bone.

What are the four stages of fracture healing?

Hematoma formation, formation of granulation tissue, callus formation, and remodeling.

What happens during hematoma formation?

Blood vessels in the bone and periosteum break, causing bleeding and the formation of a fracture hematoma.

What happens during the formation of granulation tissue?

Blood vessels grow into the hematoma, macrophages clean up tissue debris, and osteoclasts and osteogenic cells migrate into the area.

What is a soft callus?

A soft mass of fibrocartilage that forms as blood vessels and connective tissue grow into the fracture area.