Skeletal System Functions and Components

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Questions and Answers

What are the main minerals stored in bones?

Calcium and zinc

Calcium and phosphorus (correct)

Magnesium and Phosphorus

Calcium and magnesium

Which component of the bone imparts flexible strength to the bone matrix?

Proteoglycan

Collagen (correct)

Hydroxyapatite

Elastic fibers

Intramembranous ossification is the mode of development in these bones, except:

Mandible

Humerus bone (correct)

Diaphysis of clavicle

Frontal bones of the skull

Active bone resorption is a function of which of the following bone cells?

Osteoclast Signup and view all the answers

Blood calcium levels depend on the movement of this mineral in and out of the bone. Levels of calcium in the blood is controlled by?

Parathyroid hormone Signup and view all the answers

What is one of the primary functions of the skeletal system?

Movement Signup and view all the answers

Which structure is primarily responsible for holding bones together?

Ligaments Signup and view all the answers

Which part of the skeletal system protects the brain?

Skull Signup and view all the answers

Which function of the skeletal system allows the body to maintain upright posture?

Support Signup and view all the answers

What type of cartilage is known for providing flexibility and is found in structures like the ear?

Elastic cartilage Signup and view all the answers

Which component of the skeletal system lies between muscles and bones, providing connectivity?

Tendons Signup and view all the answers

Which element is most directly stored in bones and released as needed for various bodily functions?

Calcium Signup and view all the answers

What type of growth results in the increase of cartilage size by adding new layers of matrix?

Appositional growth Signup and view all the answers

In the process of blood cell production, which part of the skeletal system is primarily responsible?

Bone marrow Signup and view all the answers

What function of the skeletal system is directly achieved by the presence of joints?

Movement Signup and view all the answers

Which cell type is responsible for maintaining the cartilage matrix?

Chondrocytes Signup and view all the answers

The ribs protect which of the following organs?

Heart and lungs Signup and view all the answers

What characteristic does the matrix of cartilage contain to enhance its properties?

Collagen and proteoglycans Signup and view all the answers

What type of growth is characterized by the addition of new matrix at the surface of cartilage by chondroblasts?

Appositional growth Signup and view all the answers

What percentage of the bone matrix is organic constituents, primarily collagen and proteoglycans?

35% Signup and view all the answers

Which cell type is primarily responsible for bone formation?

Osteoblasts Signup and view all the answers

How do osteocytes primarily communicate with one another?

Through gap junctions Signup and view all the answers

What role do osteoclasts play in bone tissue?

Bone resorption Signup and view all the answers

What is the main component of the inorganic part of the bone matrix?

Hydroxyapatite Signup and view all the answers

What initiates the recruitment of osteoclasts during bone remodeling?

Osteoblast signaling Signup and view all the answers

Which of the following structures is NOT associated with osteocytes?

Ruffled border Signup and view all the answers

What is the function of matrix vesicles secreted by osteoblasts?

To provide a high concentration of calcium and phosphate Signup and view all the answers

Which cell type is a bone stem cell that can differentiate into bone-forming cells?

Osteoprogenitor cells Signup and view all the answers

What is the primary method by which long bones increase in length?

Growth at the epiphyseal plate Signup and view all the answers

Which of the following hormones is primarily responsible for stimulating interstitial cartilage growth?

Growth hormone Signup and view all the answers

What are osteoclasts primarily responsible for in the context of calcium homeostasis?

Breaking down bone Signup and view all the answers

What condition results from a deficiency of vitamin D in childhood?

Rickets Signup and view all the answers

At what age does the closure of the epiphyseal plate typically occur, marking the cessation of growth in length for long bones?

12-25 years of age Signup and view all the answers

What is the primary role of osteoclasts in bone physiology?

To attach and resorb bone Signup and view all the answers

Which type of bone is characterized by collagen fibers that are randomly oriented?

Woven bone Signup and view all the answers

What structure is associated with spongy bone?

Trabeculae Signup and view all the answers

Which of the following is true regarding compact bone compared to spongy bone?

Compact bone has more matrix and less space Signup and view all the answers

What features characterize an osteon?

It consists of concentric lamellae surrounding a central canal Signup and view all the answers

What are canaliculi primarily responsible for in compact bone?

Facilitating nutrient exchange Signup and view all the answers

Which type of lamellae forms the outer surfaces of compact bone?

Circumferential lamellae Signup and view all the answers

What occurs during the differentiation of osteoclast plasma membranes?

They develop into a ruffled border for bone resorption Signup and view all the answers

Which statements correctly describe lamellar bone?

Collagen fibers are parallel and it is organized into thin sheets Signup and view all the answers

How do perforating (Volkmann) canals contribute to the overall function of the bone?

They connect osteons and facilitate blood delivery Signup and view all the answers

Which function of the skeletal system primarily aids in the body's movement?

Movement Signup and view all the answers

What is the role of hydroxyapatite in bone structure?

Providing compressive strength Signup and view all the answers

What role do ligaments play in the skeletal system?

Holding bones together Signup and view all the answers

Which of the following is a characteristic of the skeletal system's role in calcium homeostasis?

Controlling calcium ion movement in bones Signup and view all the answers

How do osteoblasts contribute to bone physiology?

Bone formation Signup and view all the answers

What is the primary component of bone that aids in its resilient structure?

Collagen Signup and view all the answers

What condition is caused by a lack of adequate vitamin D during childhood?

Rickets Signup and view all the answers

Which type of bone is essential for bearing weight and providing structural integrity during movement?

Compact bone Signup and view all the answers

What is the key feature of intramembranous ossification compared to endochondral ossification?

It starts within embryonic connective tissue membranes. Signup and view all the answers

Which hormone is primarily involved in increasing blood calcium levels?

Parathyroid hormone Signup and view all the answers

At what point does the closure of the epiphyseal plate typically occur?

12-25 years of age Signup and view all the answers

Which vitamin deficiency is associated with osteomalacia in adults?

Vitamin D Signup and view all the answers

What process describes the replacement of old bone with new bone tissue?

Bone remodeling Signup and view all the answers

What is the primary role of chondrocytes in cartilage?

Maintain the cartilage matrix Signup and view all the answers

Which type of cartilage is known for providing strength and is often found in intervertebral discs?

Fibrocartilage Signup and view all the answers

What function does the perichondrium serve in the skeletal system?

Enclose cartilage and supply it with nutrients Signup and view all the answers

What are the primary functions of tendons in the skeletal system?

Attach muscles to bones Signup and view all the answers

Which component of the skeletal system is primarily responsible for blood cell production?

Bone marrow Signup and view all the answers

What is one way that bones act as a storage system in the body?

They sequester calcium and phosphorus Signup and view all the answers

What do ligaments do in relation to skeletal function?

Connect bone to bone and limit excessive movement Signup and view all the answers

What types of cartilage are primarily found in the skeletal system?

Hyaline, fibrocartilage, and elastic cartilage Signup and view all the answers

What benefits does the matrix of cartilage provide?

Resilience and strength Signup and view all the answers

Which of these components is NOT considered part of the skeletal system?

Blood vessels Signup and view all the answers

What structural characteristic differentiates lamellar bone from woven bone?

Collagen fibers arranged parallel to one another Signup and view all the answers

Which structure is primarily associated with spongy bone?

Trabeculae Signup and view all the answers

What is the primary role of the ruffled border in osteoclasts?

Enhancing bone resorption Signup and view all the answers

Which type of bone contains more bone matrix and less space?

Compact bone Signup and view all the answers

Which of the following statements is true regarding the organization of osteocytes in lamellar bone?

Osteocytes are arranged in layers between lamellae Signup and view all the answers

Which structure does NOT play a role in connecting osteons?

Lamellae Signup and view all the answers

What do canaliculi facilitate in bone tissue?

Exchange of nutrients Signup and view all the answers

What type of lamellae forms the outer surface of compact bone?

Circumferential lamellae Signup and view all the answers

What defines an osteon in compact bone?

Concentric layers of osteocytes with a central canal Signup and view all the answers

What defines the process of ossification in bone tissue?

The formation of new bone by osteoblasts Signup and view all the answers

What role do osteocytes play in bone maintenance?

They maintain the bone matrix and communicate with other cells Signup and view all the answers

What is the primary component of the inorganic matrix of bone?

Hydroxyapatite Signup and view all the answers

Which statement correctly describes osteoclasts?

They are derived from monocyte/macrophage lineage stem cells Signup and view all the answers

Which cellular structure allows osteocytes to obtain nutrients?

Canaliculi Signup and view all the answers

What initiates the process of bone remodeling?

The recruitment of osteoclasts Signup and view all the answers

Which part of the bone is responsible for secretion of matrix vesicles?

Osteoblasts Signup and view all the answers

What is the primary role of osteoprogenitor cells?

To differentiate into osteoblasts Signup and view all the answers

Which feature of osteoclasts enhances their ability to absorb bone tissue?

Ruffled border Signup and view all the answers

In which location can osteochondral progenitor cells be found?

In the inner portion of the periosteum Signup and view all the answers

Study Notes

Skeletal System Functions

Provide support and protection for the body
Enable body movement by facilitating the attachment of muscles to bones
Store calcium and phosphorus, which are essential for various bodily functions
Produce blood cells, which are essential for oxygen transport and immune function

Components of the Skeletal System

Bone: Hard and rigid tissue that provides support and protection.
Cartilage: Firm and flexible tissue that cushions joints, supports the shape of the nose and ears, and provides the framework for developing bones.
- Types: Hyaline, Fibrocartilage, Elastic cartilage.
- Cells: Chondroblasts and Chondrocytes.
Ligaments: Connective tissue that connects bones to each other and help stabilize joints.
Tendons: Connective tissue that connects muscles to bones, enabling muscle to move the skeleton.

Bone Histology

Bone Matrix: The extracellular material that surrounds bone cells.
- Organic (35%): Collagen and proteoglycans for tensile strength and flexibility.
- Inorganic (65%): Hydroxyapatite (calcium phosphate crystals) for hardness and rigidity.
Bone Cells:
- Osteochondral Progenitor Cells: Undifferentiated bone stem cells.
- Osteoblasts: Bone-building cells that synthesize and secrete bone matrix.
- Osteocytes: Mature bone cells that maintain the bone matrix and help regulate calcium homeostasis.
- Osteoclasts: Bone-resorbing cells that break down bone tissue.

Bone Types

Woven Bone: Collagen fibers are randomly oriented, found in developing bones and fracture sites, weaker than compact bone.
Lamellar Bone: Stronger type of bone with collagen fibers arranged in parallel sheets (lamellae), found in mature bones.
Spongy Bone: Lighter type of bone with a porous structure, contains trabeculae (interconnected bony plates) filled with bone marrow.
Compact Bone: Dense and solid bone that forms the outer layer of bones, contains osteons (functional units of compact bone) with central canals containing blood vessels.

Bone Development

Intramembranous Ossification: Formation of bone directly from mesenchymal tissue (connective tissue), occurs in skull bones, part of the mandible, and clavicle.
Endochondral Ossification: Formation of bone from cartilage, occurs in most bones, including long bones and the base of the skull.

Bone Growth

Growth in Length: Occurs at the epiphyseal plate (growth plate) of long bones, involves endochondral ossification, and ends with the closure of the epiphyseal plate, marking the end of long-bone growth.
Growth in Width: Occurs through appositional growth, involves the deposition of new bone tissue by osteoblasts beneath the periosteum, contributing to bone thickness and circumference.

Factors Affecting Bone Growth

Nutrition:
- Vitamin D: Essential for calcium absorption from the intestines, deficiency leads to rickets (children) or osteomalacia (adults).
- Vitamin C: Necessary for collagen synthesis, deficiency leads to scurvy.
Hormones:
- Growth Hormone (GH): Promotes bone growth, especially at the epiphyseal plate, deficiency leads to dwarfism, excess leads to gigantism.
- Thyroid Hormone: Required for normal bone growth and development.
- Reproductive Hormones (Estrogen and Testosterone): Promote bone growth during puberty, eventually lead to closure of the epiphyseal plate and cessation of long-bone growth.

Calcium Homeostasis

Bone: Serves as the major storage site for calcium.
Blood Calcium Levels: Regulated by the movement of calcium in and out of bone.
Hormones:
- Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating osteoclast activity, promoting calcium reabsorption in the kidneys, and indirectly promoting the activation of calcitriol (a hormone that increases calcium absorption from the intestines).
- Calcitriol (Vitamin D3): Increases calcium absorption in the intestines.
- Calcitonin: Lowers blood calcium levels by inhibiting osteoclast activity.

Bone Remodeling

Continuous process of replacing old bone with new bone tissue involving both bone resorption by osteoclasts and bone formation by osteoblasts.
Essential for bone growth, shaping, repair, adaptation to stress, and maintaining calcium homeostasis.
Basic Multicellular Unit (BMU): Functional unit of bone remodeling, composed of osteoclasts and osteoblasts working together, responsible for the continuous renewal of the skeleton, estimated to replace the entire skeleton every 10 years.

The Skeletal System

The skeletal system is a vital structure that provides numerous functions including:
- Support
- Protection
- Movement
- Storage
- Blood cell production
It is comprised of four main components:
- Bone
- Cartilage
- Tendons
- Ligaments

Cartilage

Cartilage is a type of connective tissue that supports and protects joints.
It is composed of three types:
- Hyaline cartilage
- Fibrocartilage
- Elastic cartilage
The cells within cartilage are called chondrocytes, which are responsible for maintaining the cartilage matrix.
Chondroblasts are responsible for forming new cartilage matrix.
Cartilage growth can occur through two processes:
- Appositional growth, where new matrix is added to the existing cartilage from the perichondrium.
- Interstitial growth, where chondrocytes divide and produce additional matrix within the existing cartilage.

Bone

Bone is made of a matrix composed of organic material (collagen and proteoglycans) and inorganic material (hydroxyapatite).
Bone cells include:
- Osteochondral progenitor cells:
  - Bone stem cells derived from mesenchymal cells.
  - Found in the inner portion of periosteum, endosteum, and perichondrium.
  - Can undergo cell division.
- Osteoblasts:
  - Bone-building cells.
  - Derived from osteochondral progenitor cells.
  - Secrete collagen and proteoglycans.
  - Secrete matrix vesicles containing high concentrations of calcium and phosphate.
- Osteocytes:
  - Mature bone cells.
  - Relatively inactive, but can still produce small amounts of matrix.
  - Connected to each other through canaliculi.
  - Get nutrients through the canaliculi, lacunae, and gap junctions.
- Osteoclasts:
  - Bone-destroying cells
  - Massive, multinucleated cells.
  - Derived from monocyte/macrophage lineage stem cells.
  - Have a ruffled border, which is the main site of bone resorption.
The process of bone formation is called ossification.
- Intramembranous ossification begins with connective tissue membranes during embryonic development, and forms many skull bones, parts of the clavicle and mandible.
- Endochondral ossification starts with a cartilage model, and forms the base of the skull, parts of the clavicle and mandible, and most of the remaining skeleton.

Bone Growth

Growth in length:
- Occurs at the epiphyseal plate, a region of cartilage growth between the diaphysis and epiphysis of long bones.
- The process involves endochondral ossification, where interstitial cartilage growth is followed by appositional bone growth.
- The epiphyseal plate closes during late adolescence or early adulthood, forming the epiphyseal line.
Growth in width:
- Occurs at the periosteum, the outer layer of the bone.

Bone Remodeling

Bone remodeling is a continuous process where old bone is replaced with new bone.
This process is essential for:
- Converting woven bone into lamellar bone.
- Supporting bone growth and repair.
- Adjusting bone shape in response to stress.
- Maintaining calcium homeostasis.
It is performed by a functional unit called the Basic Multicellular Unit (BMU), which is made up of coordinated osteoclasts and osteoblasts.
The entire skeleton is renewed approximately every 10 years.

Calcium Homeostasis

Bone is a primary storage site for calcium.
Blood calcium levels are controlled by three main hormones:
- Parathyroid hormone (PTH):
  - Released by the parathyroid gland when blood calcium levels decrease.
  - Increases blood calcium levels by stimulating osteoclast activity, increasing calcium reabsorption in the kidneys, and promoting calcitriol activation in the intestines.
- Calcitriol (vitamin D3):
  - Increases blood calcium levels by increasing intestinal absorption of calcium.
- Calcitonin:
  - Released by the thyroid gland when blood calcium levels are high.
  - Decreases blood calcium levels by inhibiting osteoclast activity.

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Description

Explore the essential functions of the skeletal system, including support, protection, and movement facilitation. Learn about the various components such as bones, cartilage, ligaments, and tendons, and understand their roles in maintaining the body's structure and function.