Skeletal System Anatomy and Functions

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Questions and Answers

Which type of bone is characterized by being small and cubical, typically articulating with more than one bone?

Irregular bones

Short bones (correct)

Long bones

Flat bones

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

Medullary cavity (correct)

Articular surface

Spongy bone composition

Cartilage covering

What component of bone is primarily responsible for its flexibility and resilience against tension?

Mineral salts

Inorganic matrix

Water

Collagen fibers (correct)

Which bone type includes the patella and the bones at the first metatarsophalangeal joint?

Sesamoid bones Signup and view all the answers

Which layer of bone is primarily responsible for protecting and nourishing the bone and provides attachment for tendons and ligaments?

Periosteum Signup and view all the answers

What is the significance of Wolff's Law in relation to bone properties?

Bones reshape based on stress placed upon them. Signup and view all the answers

What type of bone is characterized by being flat and varying in thickness depending on tendon attachment?

Flat bones Signup and view all the answers

Which part of the bone serves as the region where the diaphysis joins the epiphysis?

Metaphyses Signup and view all the answers

Which component of bone makes up 60 to 85% of the net weight of articular cartilage?

Water Signup and view all the answers

What type of bone has a high porosity and contains 30 to 90% non-mineralized tissue?

Cancellous bone Signup and view all the answers

What is primarily responsible for the longitudinal growth of bones during adolescence?

Endochondral ossification at the epiphyseal plate Signup and view all the answers

Which zone of articular cartilage has fibers that are randomly oriented and homogeneously dispersed?

Middle Zone Signup and view all the answers

What is the primary component of articular cartilage that occupies the inter-fibrillar space?

Water Signup and view all the answers

What process allows the diameter of bones to continue to increase throughout life?

Periosteal apposition Signup and view all the answers

Which type of bone is characterized by developing from hyaline cartilage?

Endochondral bones Signup and view all the answers

What is the main characteristic of the superficial tangential zone of articular cartilage?

Densely packed fibers parallel to the surface Signup and view all the answers

Which of the following processes describes the absorption of old bone by specific cells?

Osteoclast activity Signup and view all the answers

What happens to the water content in articular cartilage as a person ages?

It decreases Signup and view all the answers

Study Notes

Skeletal System

Axial skeleton & Appendicular Skeleton:
- Adult skeleton comprised of the Axial (e.g., skull, vertebral column, ribs, sternum) and Appendicular (e.g., limbs) skeletons.
Bony Variations:
- The number of bones in the skeleton can vary slightly between individuals.
Skeletal Functions:
- Provides protection for vital organs (e.g., heart, lungs, brain).
- Supports posture and body weight.
- Facilitates movement by providing points for muscle attachment and acting as levers.
- Stores minerals like calcium and phosphorus.
- Plays vital role in hemopoiesis (blood cell formation) in specific bones (e.g., vertebrae, femurs, humerus, ribs, sternum).

Bone Types

Long bones:
- Feature a long cylindrical shaft (diaphysis) and wider protruding ends (epiphyses).
- Contain a medullary canal within the shaft.
Short bones:
- Typically small and cubical in shape.
- Have a proportionally large articular surface allowing articulation with multiple bones.
Flat bones:
- Characterized by curved surfaces varying in thickness, with thicker areas for tendon attachments.
Irregular bones:
- Include bones with unique shapes found in the spine, pelvis, and maxilla.
Sesamoid bones:
- Small bones embedded within tendons, like the patella (kneecap) and bones in the foot.

Typical Bony Features

Diaphysis: The main shaft or body of a long bone.
Epiphysis: Ends of long bones composed of cancellous (spongy) bone.
Metaphyses: Region where the diaphysis and epiphysis join.
Periosteum:
- A tough fibrous membrane covering the outer surface of the diaphysis.
- Contains an outer fibrous layer of dense irregular connective tissue, providing blood vessels, lymphatic vessels, and nerves for bone nourishment.
- An inner osteogenic layer contains elastic fibers, blood vessels, and bone-forming cells (osteoblasts).
Endosteum:
- Thin membrane lining the medullary cavity.
- Contains osteoprogenitor cells (precursors to bone cells) and osteoclasts (bone-resorbing cells).
Medullary cavity: Space within the shaft of a long bone that contains yellow bone marrow.

Bone Composition & Structure

Mineral salts (Inorganic components):
- Provide rigidity and strength to the bone, comprising most of the dry weight.
Organic components:
- Collagen fibers (Type I) contribute to flexibility and resistance to tension, making up 90% of the extra-cellular matrix.
Water:
- Significant component of bone tissue, contributing to its overall composition.

Bone Properties

Cortical bone:
- Outer layer of bone with low porosity (small spaces).
- Has a higher strength but lower strain tolerance than cancellous bone.
Cancellous bone:
- Spongy bone with a high porosity (larger spaces).
- Can withstand greater strain before fracturing compared to cortical bone.
Wolff’s Law:
- States that bones adapt their structure based on the stresses placed upon them.
- Increased stress leads to increased bone mass.

Articular (Hyaline) Cartilage

Location: Smooth layer covering the epiphysis of long bones.
Function: Reduces friction, absorbs shocks, provides flexibility and support.
Composition:
- Composed of a bluish-white, shiny ground substance with fine collagen fibers.
- Chondrocytes (cartilage cells) are sparsely distributed within the extracellular matrix.
Extracellular matrix:
- Contains a network of fine collagen fibrils and a concentrated solution of proteoglycans.
- Also includes water, inorganic salts, other matrix proteins, glycoproteins, and lipids.

Articular Cartilage Organization

Superficial Tangential Zone:
- Contains fine, densely packed collagen fibers parallel to the articular surface.
Middle Zone:
- Features randomly oriented and homogeneously dispersed collagen fibers.
Deep Zone:
- Characterized by larger, radially oriented fiber bundles that cross the tidemark.

Water in Articular Cartilage

Properties:
- Most abundant component of articular cartilage.
- Concentration is higher near the articular surface (~80%) and lower in the deep zone (~65%).
- Water occupies spaces within the extracellular matrix and moves readily in response to pressure gradients.
- Amount of water decreases with age.

Molecular Organization of Articular Cartilage

Interactions of components create a material that is:
- Porous and permeable, permitting water flow.
- A fiber-reinforced solid matrix swollen with water and ions.

Bone Growth: Endochondral Bones

Process:
- Develop from hyaline cartilage.
- Embryonic cartilage masses rapidly grow into bone-like structures.

Epiphyseal Plate (Growth Plate)

Location: Thin cartilaginous plate separating the diaphysis and epiphyses.
Role: Responsible for longitudinal bone growth.

Bone Growth

Longitudinal growth:
- Continuously occurring while epiphyseal plates are open.
- Ceases after adolescence with the closure and disappearance of the plates (typically around age 18).
Growth in diameter:
- Continues throughout life.
- Internal layer of periosteum builds new bone layers while bone is resorbed from the medullary cavity sides, increasing diameter.
Role of cells:
- Osteoblasts: Responsible for bone formation.
- Osteoclasts: Involved in bone resorption.

Common Bone Markings

Joints:
- Condyle: Rounded articular projection.
- Facet: Smooth, flat articular surface.
- Head: Rounded, prominent articular projection.
Attachments:
- Angle: Sharp, pointed projection.
- Border: Ridge or margin.
- Crest: Prominent, sharp ridge.
- Epicondyle: Projection above a condyle.
- Line: Narrow, linear elevation.
- Process: Projection that extends beyond the main body of the bone.
- Spine: Sharp, pointed projection.
- Trochanter: Large, blunt projection found on the femur.
- Tubercle: Small, rounded projection.
- Tuberosity: Large, rough projection for tendon attachment.
Cavities:
- Facet: Smooth, flat articular surface.
- Foramen: Opening for passage of nerves or blood vessels.
- Fossa: Shallow depression.
- Fovea: Small, shallow pit.
- Notch: Indentation or notch in the margin of a bone.
- Sinus: Air-filled cavity within a bone.
- Groove: Shallow, elongated depression or furrow.

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Description

Explore the intricate details of the skeletal system, focusing on the axial and appendicular skeletons. This quiz covers various bone types, their functions, and the importance of bones in protecting vital organs and facilitating movement.