Week 7 - The Skeletal System

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Questions and Answers

What is the primary function of hematopoiesis in bones?

Blood cell production (correct)

Support and protection

Calcium storage

Facilitating movement

Which type of bone is characterized by being greater in length than width?

Long bones (correct)

Short bones

Irregular bones

Flat bones

Which of the following serves as a mineral reservoir in bones?

Cartilage

Osteocytes

Calcium and phosphate (correct)

Red bone marrow

What is the shape characteristic of irregular bones?

Elaborate and complex shapes Signup and view all the answers

Which terminology indicates the process of making blood?

Hematopoiesis Signup and view all the answers

Which type of bone is defined by having length nearly equal to width?

Short bones Signup and view all the answers

What do osteocytes primarily relate to?

Bone maintenance Signup and view all the answers

Which term refers to tissues involved in bone formation?

Osseous Signup and view all the answers

What is the first step in the process of bone formation?

Secretion of osteoid Signup and view all the answers

Which nutrient is directly responsible for enhancing calcium absorption from the gastrointestinal tract?

Vitamin D Signup and view all the answers

What enzyme is primarily involved in the process of bone resorption?

Proteolytic enzymes Signup and view all the answers

What is the structural unit of mature compact bone?

Osteon Signup and view all the answers

What is the primary function of the central canal within an osteon?

Transmission of blood vessels and nerves Signup and view all the answers

How are the collagen fibers arranged in concentric lamellae?

90 degrees to each other between lamellae Signup and view all the answers

Which mineral is essential for the calcification process of bone?

Calcium Signup and view all the answers

What role does hydrochloric acid play in the process of bone resorption?

Dissolves calcium and phosphate Signup and view all the answers

What is the primary role of osteoclasts in bone tissue?

Resorbing (breaking down) bone Signup and view all the answers

Which component of the bone matrix is responsible for providing tensile strength and flexibility?

Collagen protein Signup and view all the answers

Which statement about hydroxyapatite is correct?

It is formed by the interaction of calcium phosphate and calcium hydroxide. Signup and view all the answers

Where are osteoclasts located in relation to bone structure?

In resorption lacunae adjacent to bone pits Signup and view all the answers

Which of the following is NOT a characteristic of the bone matrix?

It is devoid of any inorganic components. Signup and view all the answers

The ruffled border of osteoclasts aids in which essential process?

Increasing surface area for bone resorption Signup and view all the answers

Which of the following types of bone tissue is typically involved in initial fracture repair?

Woven bone Signup and view all the answers

What best describes the formation of the inorganic component of bone?

Mineral crystals deposit around collagen fibers within the matrix. Signup and view all the answers

What is the primary role of the diaphysis in a long bone?

To offer leverage and support weight Signup and view all the answers

Which nutrients are essential for the process of calcification in bone formation?

Calcium and phosphorus Signup and view all the answers

Which part of the long bone contains red bone marrow in children?

Medullary cavity Signup and view all the answers

What is the primary function of osteoclasts within bone tissue?

Breaking down bone matrix during resorption Signup and view all the answers

What characterizes the function of the articular cartilage in long bones?

It reduces friction and absorbs shock Signup and view all the answers

How do concentric lamellae contribute to the strength of compact bone?

They interlace collagen fibers for added resilience. Signup and view all the answers

Where is the epiphyseal plate located?

Within the metaphysis Signup and view all the answers

What occurs when blood calcium levels are low?

Bone resorption increases to release calcium. Signup and view all the answers

Which of the following is true regarding the metaphysis?

It connects the diaphysis and epiphysis Signup and view all the answers

What shape is typically associated with mature compact bone due to the arrangement of osteons?

Concentric circles Signup and view all the answers

What is the composition of the epiphysis in a long bone?

Outer compact bone and inner spongy bone Signup and view all the answers

Which component is found at the center of an osteon and is crucial for its function?

Central (Haversian) canal Signup and view all the answers

What happens to the epiphyseal plate in adults?

It transforms into the epiphyseal line Signup and view all the answers

Which characteristic of the diaphysis is specifically important for its function?

It has a cylindrical shape for optimal strength Signup and view all the answers

What role do proteolytic enzymes play in bone resorption?

Breaking down collagen and organic matrix components Signup and view all the answers

Which vitamin is required for collagen formation, essential in the bone matrix?

Vitamin C Signup and view all the answers

What is the primary function of canaliculi in bone connective tissue?

Facilitating intercellular contact and nutrient exchange Signup and view all the answers

Which statement correctly describes interstitial lamellae?

They are found between osteons or partially resorbed osteons Signup and view all the answers

What distinguishes circumferential lamellae in long bones?

They are found in both external and internal regions of the bone Signup and view all the answers

Osteocytes reside in small spaces called lacunae. What is their main role?

To help maintain the bone matrix Signup and view all the answers

Which feature is characteristic of trabeculae in spongy bone?

They are filled with bone marrow Signup and view all the answers

What structural characteristic of perforating (Volkmann) canals is significant?

They connect central canals of different osteons Signup and view all the answers

How do osteocyte projections contribute to bone function?

They connect lacunae with nearby blood supply Signup and view all the answers

Which statement accurately describes the arrangement of collagen fibers in concentric lamellae?

They are arranged parallel to each other and alternate in orientation Signup and view all the answers

What is the role of osteoblasts during the primary ossification center formation?

They produce and secrete osteoid around the calcified cartilage shaft. Signup and view all the answers

What happens during the transition from the primary ossification center to the formation of the medullary cavity?

Osteoclasts resorb some bone matrix. Signup and view all the answers

What characterizes the secondary ossification centers compared to the primary ossification center?

They develop later and not all of them are present at birth. Signup and view all the answers

At what stage does lengthwise growth of bone continue until the epiphyseal plates ossify into epiphyseal lines?

Throughout adolescence and into puberty. Signup and view all the answers

What is the consequence of chondrocyte death in the calcified cartilage matrix?

Creation of hollow spaces within the cartilage shaft. Signup and view all the answers

During the endochondral ossification process, which structure primarily displaces the calcified, degenerating cartilage?

Osteoid tissue. Signup and view all the answers

What is the primary role of the periosteal bud during long bone development?

It facilitates the entry of blood vessels and osteoprogenitor cells into the cartilage shaft. Signup and view all the answers

What indicates that a long bone has reached its adult length?

The ossification of epiphyseal plates into epiphyseal lines. Signup and view all the answers

What primarily drives the lengthening of long bones during interstitial growth?

Cartilage growth in the epiphyseal plate Signup and view all the answers

Which of the following zones of the epiphyseal plate is characterized by chondrocytes undergoing rapid mitotic division?

Zone of proliferating cartilage Signup and view all the answers

What occurs in the zone of hypertrophic cartilage during bone growth?

Chondrocytes cease dividing and enlarge Signup and view all the answers

Which term best describes the initial state of cartilage that secures the epiphysis to the epiphyseal plate?

Mature hyaline cartilage Signup and view all the answers

Which characteristic of the zone of resting cartilage is important for its function?

Its position nearest to the epiphysis Signup and view all the answers

During endochondral ossification, what role do chondrocytes in the zone of hypertrophic cartilage play?

Support the apoptosis of neighboring cells Signup and view all the answers

What is the primary function of the columns formed in the zone of proliferating cartilage?

To organize chondrocytes for effective growth Signup and view all the answers

What changes characterize the transition from the zone of hypertrophic cartilage to the zone of calcified cartilage?

Increased vascularization and cell death Signup and view all the answers

Study Notes

Functions of Bone

Support and Protection: Bones provide structural support for the body and protect internal organs.
Levers for Movement: Bones act as levers for muscle attachment, allowing for movement.
Hematopoiesis:
- Blood cell production occurs in red bone marrow, a type of connective tissue.
Storage of Mineral and Energy Reserves:
- Bones store essential minerals like calcium and phosphate.
- They also store energy reserves in the form of lipids.

Bone Classification

Long Bones: Length is greater than width, examples include femur and humerus.
Short Bones: Length is nearly equal to width, examples include carpals and tarsals.
Flat Bones: Flat and thin, may be slightly curved, examples include cranial bones.
Irregular Bones: Complex and elaborate shapes, examples include vertebrae.

Bone Connective Tissue Cells

Osteoblasts: Responsible for the formation of bone matrix.
Osteocytes: Mature bone cells, maintain the bone matrix.
Osteoclasts: Large multinucleated cells responsible for bone resorption or breakdown.
- They have a ruffled border that increases surface area for contact with bone.
- Located in resorption lacunae (depressions/pits) on the bone surface.

Composition of Bone Matrix

Organic Components:
- Osteoid, produced by osteoblasts, contains collagen protein and a semisolid ground substance of proteoglycans and glycoproteins.
- Provides tensile strength and flexibility to bone.
Inorganic Components:
- Primarily composed of calcium phosphate crystals that deposit around collagen fibers.
- Contribute to bone rigidity and hardness.

Bone Formation and Resorption

Bone Formation (Ossification):
- Starts with secretion of osteoid.
- Calcification (mineralization) occurs, with deposition of hydroxyapatite crystals.
- Requires calcium, phosphate, vitamin D (for calcium absorption), and vitamin C (for collagen formation).
Bone Resorption:
- Bone matrix is broken down by osteoclasts.
- Proteolytic enzymes from lysosomes within osteoclasts digest the organic components.
- Hydrochloric acid released by osteoclasts dissolves calcium and phosphate.
- Released calcium and phosphate enter the bloodstream.
- Occurs when blood calcium levels are low.

Compact Bone Microscopic Anatomy

Osteons (Haversian Systems):
- Basic functional and structural unit of mature compact bone.
- Cylindrical structures oriented parallel to the diaphysis (shaft) of long bones.
- Contain central canals, concentric lamellae, and osteocytes within lacunae.

Osteon Components

Central (Haversian) Canal:
- Cylindrical channel at the center of the osteon.
- Contains blood vessels and nerves.
Concentric Lamellae:
- Rings of bone connective tissue surrounding the central canal.
- Collagen fibers are arranged at 90 degrees from the previous and next lamellae.
- Contribute to bone strength and resilience.

Regions of a Long Bone

The diaphysis is the elongated shaft of a long bone, providing leverage and weight support. It is made primarily of compact bone with thin layers of spongy bone.
The medullary cavity is the hollow space within the diaphysis. It contains red bone marrow in children and yellow bone marrow in adults.

Epiphysis

The epiphysis is the knobby region at each end of a long bone.
The proximal epiphysis is the end closest to the body trunk, while the distal epiphysis is the end farthest from the trunk.
The epiphysis is composed of an outer layer of compact bone and an inner region of spongy bone.
Articular cartilage is a thin layer of hyaline cartilage that covers the joint surface of the epiphysis, reducing friction and absorbing shock in movable joints.

Metaphysis

The metaphysis is the region where the bone widens and transfers weight between the diaphysis and epiphysis.
The epiphyseal plate, or growth plate, is located within the metaphysis. It is responsible for lengthwise bone growth in children.
The epiphyseal line is the remnant of the epiphyseal plate in adults, indicating that the bone has stopped growing in length.

Bone Formation

Bone formation begins with the secretion of osteoid, which subsequently undergoes calcification (mineralization) through the deposition of hydroxyapatite crystals.
This process requires essential nutrients including vitamin D for calcium absorption, vitamin C for collagen formation, and calcium and phosphate for calcification.

Bone Resorption

Bone resorption involves the breakdown of bone matrix by osteoclasts, which release proteolytic enzymes and hydrochloric acid.
Proteolytic enzymes digest organic matrix components while hydrochloric acid dissolves calcium and phosphate, releasing them into the bloodstream.
This process is essential for maintaining blood calcium levels.

Compact Bone

Compact bone is composed of small cylindrical structures called osteons (Haversian systems), which are the basic functional and structural unit of mature compact bone.
Osteons are oriented parallel to the bone diaphysis and have a bull's-eye target appearance.

Osteon Components

The central (Haversian) canal runs parallel to the osteon and houses blood vessels and nerves.
Concentric lamellae are rings of bone connective tissue surrounding the central canal, with collagen fibers arranged at 90 degrees to those of the previous and next lamellae for strength and resilience.
Osteocytes are mature bone cells located in small spaces between concentric lamellae called lacunae. They maintain the bone matrix.
Canaliculi are tiny, interconnecting channels within bone connective tissue, extending from each lacuna and connecting to other lacunae and the central canal. They allow for the exchange of nutrients, minerals, gases, and waste.

Structures in Long Bone, Not Part of an Osteon

Perforating (Volkmann) canals extend perpendicular to central canals, connecting central canals within different osteons.
Circumferential lamellae are rings of bone that encircle the entire bone, with external lamellae running immediately internal to the periosteum and internal lamellae running internal to the endosteum.
Interstitial lamellae are components of compact bone between osteons or partially resorbed osteons.

Spongy Bone

Spongy bone is composed of trabeculae, which are open latticework of narrow rods and plates of bone containing bone marrow.
Trabeculae provide resistance to stresses and are formed by parallel lamellae with bone matrix and osteocytes.

Endochondral Ossification

Endochondral ossification is the process by which most bones develop from a hyaline cartilage model.
In long bone development, the process involves five key steps:
Formation of cartilage model: Hyaline cartilage forms the shape of the future bone.
Calcification of cartilage: Cartilage calcifies, and a periosteal bone collar forms around the shaft.
Formation of primary ossification center: A periosteal bud containing blood vessels and osteoblasts invades the calcified cartilage shaft, forming the primary ossification center.
Formation of secondary ossification centers: Secondary ossification centers develop in the epiphyses, similar to the process in the primary ossification center.
Bone replaces cartilage: Bone replaces cartilage, except for articular cartilage and epiphyseal plates. Lengthwise growth continues until the epiphyseal plates ossify and form epiphyseal lines, indicating that the bone has reached its adult length.

Interstitial Growth

Interstitial growth is the process of long bone growth in length and is dependent on cartilage growth in the epiphyseal plate.
The epiphyseal plate has five zones:
Zone of resting cartilage: This zone is closest to the epiphysis. It contains small chondrocytes distributed throughout the matrix, resembling mature hyaline cartilage.
Zone of proliferating cartilage: Chondrocytes in this zone undergo rapid mitotic division, aligning into columns parallel to the diaphysis.
Zone of hypertrophic cartilage: Chondrocytes in this zone cease dividing and enlarge, with their lacunae walls becoming thin.
Zone of calcified cartilage: The matrix of this zone calcifies, the chondrocytes die, and the calcified cartilage is eroded by osteoclasts.
Zone of ossification: Osteoblasts in this zone lay down bone matrix on the calcified cartilage, replacing it with bone tissue.

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