Chapter 7: Cells, Ossification, Remodeling & Calcium Homeostasis

What are bones primarily composed of?

Bones are composed of several tissue types, including compact bone, spongy bone, connective tissues, bone marrow, nervous tissue, and blood.

What are the two subtypes of osseous tissue?

Compact bone and spongy bone.

What is the function of osteoprogenitor cells?

Osteoprogenitor cells are bone stem cells that can divide by mitosis to produce more osteoprogenitor cells and osteoblasts.

What are osteoblasts?

Osteoblasts are bone-building cells derived from osteoprogenitor cells that cannot divide by mitosis.

What happens to osteoblasts when they become trapped in bone matrix?

They are called osteocytes and are responsible for maintaining bone tissue.

Where are osteocytes located?

Osteocytes are located in lacunae, trapped within the bone matrix.

What is the role of osteoclasts?

Osteoclasts are cells that resorb bone tissue and originate from blood cells called monocytes.

What is intramembranous ossification?

Intramembranous ossification is a process where bone tissue is formed directly from mesenchyme, creating flat bones of the skull and most of the clavicle.

What is endochondral ossification?

Endochondral ossification is the process of bone formation from a hyaline cartilage model, producing most bones of the skeletal system, including long bones.

What is appositional growth?

Appositional growth is the process by which bones widen, involving the action of osteoblasts and osteoclasts.

What are primary ossification centers?

Primary ossification centers are active during fetal development and are located near the center of the diaphysis.

What are secondary ossification centers?

Secondary ossification centers become active around the time of birth and are located in the epiphysis.

What is the function of collagen in bones?

Collagen provides tensile strength and flexibility to bones.

What is the function of hydroxyapatite in bones?

Hydroxyapatite provides compressional strength and rigidity to bones.

What is bone remodeling?

Bone remodeling is the continuous process of bone resorption and formation throughout a person's life.

How do osteocytes communicate and receive nutrients?

Osteocytes communicate through canaliculi and receive nutrients via diffusion from blood vessels.

What is the difference between the epiphyseal line and the epiphyseal plate?

The epiphyseal plate is a layer of cartilage that allows for bone lengthening, while the epiphyseal line is the remnant of the plate after growth has ceased.

What is the significance of mechanical stress on bone architecture?

Bone architecture is determined by the mechanical stresses placed upon the bone, influencing its shape and density.

What is the role of periosteum in bone formation?

Periosteum is formed after some spongy bone is made and plays a role in bone growth and repair.

What is osteoid?

Osteoid is uncalcified bone matrix that serves as a precursor to calcified bone.

What condition is characterized by brittle bones due to insufficient components?

Osteogenesis imperfecta is characterized by brittle bones due to insufficient collagen.

What cells are responsible for appositional growth?

Osteoblasts are responsible for appositional growth.

Where are osteoblasts and osteoprogenitor cells found in bone?

Osteoblasts and osteoprogenitor cells are found on the bone surface.

What are the two processes through which long bones grow?

Long bones grow by both intramembranous ossification and endochondral ossification.

How do flat bones of the skull develop?

Flat bones of the skull develop only through intramembranous ossification.

What condition is characterized by proportional head and trunk size but shorter arms and legs?

Achondroplastic Dwarfism.

What is the genetic process affected in achondroplastic dwarfism?

The gene responsible for endochondral ossification is affected.

What role do calcium ions play in the body?

Calcium ions are important in cell signaling and maintaining calcium homeostasis.

What triggers the body to produce parathyroid hormone (PTH)?

The need to maintain calcium homeostasis triggers the production of PTH.

What organs are affected by PTH, calcitonin, and calcitriol?

PTH, calcitonin, and calcitriol affect the bones, kidneys, and intestines.

Where is calcitriol made in the body?

Calcitriol is made in the kidneys, with involvement from the liver and skin.

What is the relationship between vitamin D3 and calcitriol?

Vitamin D3 is converted to calcitriol in the kidneys.

Describe the negative feedback loop involving PTH.

When calcium levels drop, PTH is released to increase calcium levels; when levels are sufficient, PTH secretion decreases.

What is the role of osteoclasts in calcium homeostasis?

Osteoclasts break down bone tissue to release calcium into the bloodstream.

What is osteoporosis?

Osteoporosis is characterized by severe bone tissue loss, leading to increased fracture risk.

What are the two main characteristics of stem cells?

Self-renewal and potency.

What is the difference between totipotent and unipotent stem cells?

Totipotent stem cells can differentiate into any cell type, while unipotent stem cells can only become one type of cell.

What is the function of mesenchyme in intramembranous ossification?

Mesenchyme serves as the precursor tissue that differentiates into bone.

What is a soft callus in bone healing?

A soft callus is a temporary tissue formed during the healing process before hard callus formation.

What is a hard callus in bone healing?

A hard callus is a bony tissue that replaces the soft callus during the later stages of fracture healing.

How does a marrow cavity form in a long bone?

A marrow cavity forms as osteoclasts break down bone tissue in the center of the developing bone.

What is the primary role of PTH?

The primary role of PTH is to increase calcium levels in the blood.

What is the function of calcitriol?

Calcitriol increases calcium absorption in the intestines and promotes calcium release from bones.

What is the process of endochondral ossification?

Endochondral ossification is the process where cartilage is replaced by bone during the development of long bones.

What is the role of blood vessels in intramembranous ossification?

Blood vessels supply nutrients and oxygen, and help in the formation of bone tissue.

What is the structure and function of the periosteum?

The periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints; it provides attachment for muscles and contains nerves and blood vessels.

What is the function of collagen in bone tissue?

Collagen provides tensile strength and flexibility to bone tissue.