Week 4 - Skeletal System (Chapter 6)
- Supports soft tissue (attachment for skeletal muscles)
- Protects internal organs
- Assists in movement
- Stores & releases minerals
- Contains red bone marrow (produce red blood cells) and yellow
Functions of bone tissue
Unspecialized bone cells, only ones that undergo tell division; resulting in osteoblasts, found along inner osteogenic layer of periosteum, endosteum, blood vessel canals
Osteoprogenitor cells
long, cylindral main portion of the bone
Diaphysis
Proximal and distal regions of the bone between diaphysis & epiphyseal line
Epiphyses
Thin layer of hyaline cartilage covering the part of the epiphyses where there is a joint; reduces friction & absorbs shock. lacks perichondrium and blood vessels.
Articular cartilage
- Tough connective tissue sheath with blood supply surrounding bone surface not covered by articular cartilage
- Composed of an outer fibrous layer of dense irregular connective tissue and osteogenic cells inside
- Can grow in thickness but not length.
Periosteum
Hollow space within the diaphysis containing yellow/red bone narrow
- Minimizes weight of bone by reducing the dense, bony material where least needed.
- Tubular shape provides max strength & min weight
Medullary Cavity
Thin membrane that lines the medullary cavity & internal spaces of spongy bone. Contains layer of osteoprogenitor cells and small amount of connective tissue
The endosteum
Unspecialized bone stem cells
- They are the only bone cells to undergo cell division; the resulting cells develop into osteoblasts.
- These cells are found along the inner osteogenic layer of the periosteum, in the endosteum, and in the canals in bone that contain blood vessels
Osteoprogenitor cells
Bone - building cells.
- Synthesize & secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue
- Initiate calcification.
- As they surround themselves with extracellular matrix, they become trapped in their secretions & become osteocytes.
Osteoblasts
Mature bone cells, are the main cells in bone tissue & maintain its daily metabolism, such as exchange of nutrients & wastes with the blood. Like osteoblasts, they do not undergo in division
Osteocytes
Huge cells derived from the fusion of monocytes in the endosteum.
- On the side of the cell that faces the bone surface
Osteoclasts
Contains few spaces
Strongest type of bone tissue
Found beneath the periosteum Makes up the bulk of the diaphyses of long bones
Compact bone tissue
_______ are the building blocks of compact bone, made up of layers of hard material arranged around a central canal that contains blood vessels and nerves.
Osteons
Circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels & nerves located in the osteonic canal.
Concentric bone lamellae
Calcium builds up in body tissues, causing them to harden
Calcification
4 Cell types in bone tissue
Osteoprogenitor cells, Osteoblasts, Osteocytes, Osteoclasts
Between the concentric bone lamallae are small spaces called _____ which contain osteocytes
Bone lacunae
Radiating in all directions from the bone lacunae are tiny ____ which are filled with extracellular fluid. Inside ______ are slender fingerlike processes of osteocytes
They connect bone lacunae with one another & with the oste canals, forming an intricate, miniature system of interconnected canals throughout the bone. This system provides many routes for nutrients & oxy to reach the osteocytes and for removal of wastes.
Bone canaliculi
Also cancellous bone tissue - does not contain osteons.
- Located in the interior of a bone, protected by a covering of compact bone.
- Consists of bone lamellae
- Makes up most of the interior bone tissue of short, flat, sesamoid and irregularly shaped bones. - In long bones it forms the core of the epiphyses
Spongy Bone Tissue
Spongy bone tissue is located in ______
In hip bones, ribs, sternum, vertebrae, skull, proximal ends of the humerus & femur (only site where red bone marrow is stored and where hemopoiesis / blood cell production
Characteristics of spongy bone tissue:
Light, reduced weight, located where bones are not heavily strained Bone can move more readily when pulled by skeletal muscle, supports & protects red bone marrow
Blood vessels (abundant in portions of bone containing red bone marrow) pass into bones from the _____
Periosteum
_________ are small canals that carry small arteries from the periosteum into the bone.
Perforating canals
One or two nutrient veins accompany the nutrient artery & exit through the _____
Diaphysis
Numerous epiphyseal veins & metaphysical veins accompany their respective arteries and exit through the _____ and _____
epiphyses and metaphases
Many small periosteal veins accompany their respective arteries & exit through the ______
Periosteum
The process by which bone forms is called ____ or _____
Ossification or Osteogenesis
Bone formation occurs in four situations:
Initial formation of bones in an embryo & fetus
The growth of bones during infancy, childhood and adolescence
The remodeling of bone (replacement of old bone by new bone tissue throughout life) The repair of fractures throughout life
The first type of ossification is ________ - the method of bone formation in which the bone is formed directly in mesenchyme arranged in sheet-like layers that resemble membranes. Creates flat bones like the Skull, Facial bones, mandible, part of the clavicle.
Intramembranous Ossification
The second type of ossification is ________ - bone forms Within hyaline cartilage that develops from mesenchyme. Most bones of body are formed this way, best observed in a long bone. Bone development from a cartilage model.
Endochondral ossification
_______ Formation: The extracellular matrix forms trabeculae that fuse to create spongy bone, Surrounding a network of blood vessels. Connective tissue around these vessels differentiates into red bone marrow.
Bone Trabeculae Formation
_________ Development: As trabeculae form, mesenchyme condenses at the bone’s surface to become the periosteum. Eventually, a thin layer of compact bone replaces the outer spongy bone, while spongy bone remains in the centre. The bone undergoes remodelling to achieve its adult shape.
Periosteum
Formation of __________ & __________: the hyaline cartilage covering the epiphyses becomes ________, while the cartilage between the diaphysis & epiphysis forms the _______, which is crucial for the lengthwise growth of long bones
Articular cartilage and epiphyseal plate
Development of the ___________ cavity: osteoclasts break down some spongy bone creating the this cavity in the diaphysis, while compact bone replaces much of the diaphysis wall
Medullary cavity
The epiphyseal plate allows the diaphysis of a bone to increase in _______
Length
1. Differentiation: Osteoprogenitor cells in the osteogenic layer of the periosteum differentiate into osteoblasts
2. Matrix secretion: Osteoblasts secrete collagen fibers & organic molecules forming the bone extracellular matrix and becoming surrounded by it
3. Formation of ridges: bone ridges form on either side of a periosteal blood vessel as osteoblasts secrete matrix
4. Groove Creation: The ridges enlarge, creating a groove for the periosteal blood vessel
5. Tunnel Formation: The ridges fold together and fuse, turning the groove into a tunnel that
encloses the blood Vessel
6. Endosteum Development: The former periosteum now becomes the endosteum lining the tunnel
7. Lamellae Formation: Osteoblasts in the endosteum deposit bone extracellular matrix, forming
new concentric bone lamellae
8. Osteon Creation: Additional Concentric lamellae fill in the tunnel, creating a new
osteon
Growth in Thickness steps
During endochondral ossification, bone gradually replaces a _____ model
Cartilage
As new bone is deposited on the outer surface of bone by ______, the bone tissue lining the medullary cavity is destroyed by ______ in the endosteum
Osteoblasts and osteoclasts
Remodeling of bone involves:
Bone resorption and bone deposition
Ongoing replacement of old bone by new bone tissue is called _______
Bone Remodeling
Removal of materials & collagen fibers from bone by osteoclasts
Bone resporption
The addition of materials & collagen fibers to bone by osteoblasts.
Bone desposition
___________ attach to bone surfaces & create a sealed environment to release enzymes & acids that break down old bone. After resorption, _________ rebuild the area, ensuring the bone remains strong & adaptive to stress.
Osteoclasts and osteoblasts
Factors Affecting Bone Growth & Remodeling:
Minerals, vitamins, hormones (Especially estrogen, parathyroid and calcitonin hormones)
_________ is the process of aligning fractured ends:
Reduction
The repair of bone fracture occurs in three phases:
Reactive, reparative, bone remodelling phase
_______ phase - blood vessels are damaged, forming a fracture hematoma (mass of clotted blood) around the fracture site, triggering inflammation & the removal of dead tissue by phagocytes and osteoclasts. This can be several weeks
Reactive
_______ phase: Fibrous cartilage callus formation: fibroblasts produce collagen, and chondroblasts create a soft callus bridging the fracture (takes three weeks). Bony callus formation: osteoprogenitor cells develop into osteoblasts, producing spongy bone that replaces the fibrous callus. Bony callus lasts three to four months
Reparative Phase
Bone helps regulate ________ levels through two processes (resorption and deposition) in order to maintain homeostasis.
Blood calcium
Functions of skeletal system:
• Support
• Movement
• Mineral homeostasis
• Blood cell production – hemopoiesis
• Fat storage – triglycerides in yellow bone marrow
Region between epiphyses & diaphysis. Has epiphyseal growth plate (layer of hyaline cartilage) which allows diaphysis to
grow long. Around age 24, this plate replaced by bone and appears as epiphyseal line
Metaphyses
Spaces between lamellae are bone ______, which has osteocytes.
lacunae
Bone formation occurs in 4 situations:
1. Fetal development
2. Bone growth prior to adulthood
3. When bones remodel
4. When fractures heal
Bones store _____% of body's calcium
99
The ________ gland secretes PTH when calcium levels drop
Parathyroid gland
PTH stimulates production of:
Calcitriol
Disease where bone resorption outpaces formation, mainly affects women
Osteoporosis
Disease where degeneration of articular cartilage occurs (leads to friction)
Osteoarthritis
Infection of bone is called _____
Osteomyelitis
Disease where bone mass is reduced beyond normal:
Osteopenia
Bone cancer affecting osteoblasts
Osteosarcoma