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Questions and Answers
Which of the following is NOT a primary function of the skeletal system?
The study of bone structure is called osteology.
True
What type of tissue primarily makes up bone?
Osseous tissue
The mineral salts that contribute to the hardness of bone include __________ and __________.
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Match the following components of long bones with their descriptions:
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What percentage of bone is made up of cells?
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Yellow bone marrow primarily stores triglycerides.
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The __________ cavity may contain yellow bone marrow and blood vessels.
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Which of the following is a consequence of a sedentary lifestyle?
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Calcium is stored primarily in muscle tissue.
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What is the role of parathyroid hormone in calcium homeostasis?
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The ______ phase of bone repair involves the formation of a hematoma.
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Match the following types of fractures with their description:
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Which vitamin deficiency leads to rickets?
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Osteoporosis is characterized by increased bone density.
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What happens to plasma calcium levels when they drop below the normal range?
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A lack of mechanical stress shifts the balance between bone building and resorption toward ______.
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Which treatment is NOT a method for preventing osteoporosis?
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Which process describes the formation of most bones, including long bones?
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The primary ossification center forms after birth.
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What do osteoblasts secrete to form bone tissue?
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Bone remodeling includes both bone resorption and __________.
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Match the type of growth with its description:
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Which zone of the epiphyseal plate contains actively dividing chondrocytes?
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The periosteum is formed from mesenchymal tissue surrounding forming trabeculae.
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At what age does the epiphyseal plate typically close in females?
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_____________ cells are responsible for the destruction of the bone ECM.
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Which hormone can inhibit bone resorption and promote the apoptosis of osteoclasts?
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Osteoprogenitor cells mature into osteoclasts.
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What type of cartilage remains at joints and becomes articular cartilage?
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The ____________ plate is where interstitial growth of long bones occurs.
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What do osteoblasts primarily secrete?
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Osteocytes are mature bone cells that continue to divide.
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What is the process of bone formation called?
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The structural unit of compact bone is called an __________.
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Which type of bone tissue is lighter and helps muscles to move more easily?
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Osteoclasts are involved in bone formation.
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What do osteocytes use to communicate with each other?
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The __________ artery nourishes the periosteum.
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Which of the following is NOT a function of blood supply in bones?
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Match the following types of ossification with their descriptions:
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What type of bone tissue is packed tightly and strongest?
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Red bone marrow contains stem cells for blood formation.
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What provides passage for blood vessels and nerves in bone?
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The smallest structural unit of spongy bone is __________.
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Which of the following statements about osteoclasts is true?
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Name the types of lamellae surrounding long bones.
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Study Notes
Bone Structure and Function
- Bone is a dynamic organ composed of osseous tissue, cartilage, dense connective tissue, epithelial tissue, adipose tissue, and nervous tissue.
- The study of bone structure is called osteology.
- The skeletal system provides support, protection, assists movement, regulates mineral homeostasis, produces red blood cells, and stores triglycerides.
Structure of Long Bones
- Long bones consist of a diaphysis (shaft), epiphyses (ends), metaphyses (connecting diaphysis to epiphyses), articular cartilage, periosteum (outer covering), medullary cavity (hollow diaphysis), and endosteum (lining of medullary cavity).
Bone Tissue Composition
- Bone tissue is a connective tissue with sparsely distributed cells within a hard extracellular matrix (ECM).
- The ECM of bone contains water, collagen fibers, and mineral salts, with mineral salts deposited on a network of collagen fibers, conferring hardness and tensile strength.
- This process of mineral deposition is called calcification.
Mineral Composition of Bone
- The mineral salts of bone ECM include hydroxyapatite (Ca10(PO4)6(OH)2), calcium phosphate (Ca3(PO4)2), calcium hydroxide (Ca(OH)2), and calcium carbonate (CaCO3).
Bone Cells
- Bone cells comprise 2% of bone tissue.
- Osteoprogenitor cells are the stem cells of bone, located deep to the periosteum.
- Osteoblasts secrete collagen and other components of bone ECM, becoming osteocytes once immobilized by their own secretions.
- Osteocytes are mature bone cells that do not divide or secrete, responsible for nutrient acquisition and waste removal.
- Osteoclasts catabolize bone, formed by fusion of monocytes, secreting lysosomal enzymes and acids that release minerals into the blood, a process called bone resorption.
Types of Bone Tissue
- There are two types of bone tissue: compact bone tissue and spongy bone tissue.
- Compact bone tissue is the strongest type, resistant to mechanical stress, and densely packed.
- Spongy bone tissue is lighter than compact bone, supporting and protecting bone marrow, and handling stress along multiple axes.
Structure of Compact Bone Tissue
- The structural unit of compact bone is the osteon, arranged along lines of stress.
- Osteons contain a central canal with blood vessels and concentric lamellae, rings of ECM.
- Interstitial lamellae are old concentric lamellae from prior osteons, while circumferential lamellae, joined to the periosteum via perforating fibers, surround the long bone.
- Osteocytes reside in lacunae within the ECM, communicating via canaliculi.
- Interosteonic canals provide passage for blood vessels and nerves, contributing to the fast healing of bone tissue due to extensive vascularization.
Structure of Spongy Bone Tissue
- Spongy bone tissue is not composed of osteons, but rather trabeculae, plates or projections of bone tissue arranged along areas of stress.
- Trabeculae are surrounded by red bone marrow and blood vessels, containing blood stem cells.
Nerve and Blood Supply of Bone
- Bone is well vascularized, with periosteal arteries nourishing the periosteum, nutrient arteries penetrating the diaphysis and branching into bone marrow, entering through the nutrient foramen, epiphyseal and metaphyseal arteries nourishing the internal tissues of the epiphyses, and veins exiting through the same entrance as the arteries.
- Nerves run similar paths to blood vessels through bones.
Functions of Blood Supply and Nerve Supply
- The blood supply of bone is vital for nutrient delivery, waste removal, bone remodeling, hormone transport, and immune function.
- The nerve supply of bone enables pain perception, regulation of bone metabolism, response to mechanical stimuli, vascular regulation, and communication with other systems.
Ossification: Bone Formation
- The process of bone formation is called ossification, occurring during embryonic development, childhood, adolescence, bone remodeling, and fracture repair.
- The embryonic skeleton is initially composed of mesenchymal tissue.
- There are two types of ossification: intramembranous and endochondral.
Intramembranous Ossification
- Intramembranous ossification occurs directly from mesenchymal tissue, forming the embryonic cranium and facial bones.
- It involves formation of an ossification center, calcification of mineral salts, formation of trabeculae, and formation of the periosteum.
Endochondral Ossification
- Endochondral ossification forms most bones, including long bones, from a hyaline cartilage intermediate.
- It involves mesenchymal cells differentiating into chondroblasts, secreting collagen to form hyaline cartilage, chondroblast ECM secretion leading to interstitial growth, penetration of a nutrient artery stimulating osteoprogenitor cells, primary ossification extending towards the ends of the bones, secondary ossification occurring at birth, and hyaline cartilage at joints becoming articular cartilage while cartilage remaining at the metaphysis continues to ossify.
Bone Growth During Childhood and Adolescence
- Bones can grow interstitially (lengthwise) or appositionally (circumferentially).
- Interstitial growth occurs at the epiphyseal plate of long bones, containing zones of resting cartilage, proliferating cartilage, hypertrophic cartilage, and calcified cartilage.
- At maturity, the epiphyseal plate closes, marking the end of interstitial growth.
- Appositional growth, or circumferential growth, involves periosteal cells becoming osteoblasts forming ridges of ECM, ridges fusing and forming the endosteum, endosteal osteoblasts secreting ECM, and new concentric lamellae being formed, increasing the diameter of the bone.
Factors Affecting Bone Growth
- Bone growth is affected by nutrition, hormones, and exercise.
- Nutrition includes adequate calcium, vitamin D, and protein intake.
- Hormones influencing bone growth include growth factors, thyroid hormones (T3 and T4), estrogen, and testosterone.
- Exercise is crucial for bone remodeling, with weight-bearing exercise stimulating bone adaptation.
Bone Remodeling: A Lifelong Process
- Bone remodeling is a dynamic, lifelong process involving the destruction (resorption) and building (deposition) of bone ECM.
- It occurs during growth, injury, and with changes in exercise and diet.
- Osteoclasts resorb bone, releasing minerals into the blood, while osteoblasts deposit new bone along lines of mechanical stress.
Importance of Bone Remodeling
- Bone remodeling aids in bone repair, adaptation to mechanical stress, and calcium homeostasis.
- A sedentary lifestyle or injury can lead to bone loss due to increased bone resorption.
- Bone stores 99% of the body’s calcium, which is essential for nerve and muscle cell function, blood clotting, and enzyme catalysis.
- Calcium homeostasis is carefully regulated through a negative feedback loop involving parathyroid hormone (PTH), calcitonin, and vitamin D.
Fractures and Bone Repair
- Fractures are breaks in bones, ranging from microscopic stress fractures to compound fractures.
- Fractures are treated by reduction, either closed (non-surgical) or open (surgical).
- Bone repair involves a reactive phase (hematoma and inflammation), reparative phase (fibrocartilaginous callus formation and bony callus formation), and bone remodeling phase (osteoclast removal of dead bone and replacement with compact bone).
Bone Disorders
- Osteoporosis is a loss of bone density due to increased resorption compared to deposition, increasing fracture risk.
- Rickets (childhood) and osteomalacia (adult) are vitamin D deficiency diseases, leading to inefficient calcium absorption and bone softening.
Key Takeaways
- Bones are dynamic organs of the skeletal system.
- There are two types of bone tissue: spongy and compact.
- Ossification occurs through intramembranous or endochondral processes.
- Bone growth is influenced by nutrition, hormones, and exercise.
- Bone remodeling is essential for calcium homeostasis, repair, and adaptation.
- Bone disorders include osteoporosis, rickets, and osteomalacia.
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Description
Test your knowledge on the composition and purpose of bones in the human body. This quiz covers topics such as osteology, the structure of long bones, and the various tissue types involved in bone function. Explore how bone tissue contributes to overall health and movement.
