Skeletal System Flashcards
Percentage composition of the bone from the body weight
20%
Skeletal system is composed of
interconnected system of bones, cartilage, joints, and associated ligaments.
Osteology
is the branch of science that deals with the study of the skeletal system structure and function
Bone composition
Bone connective tissue (Mineralized)
Cells: Osteocytes
Matrix: Collagen fibers within a matrix of calcium phosphate.
Bone function
Provides firmness and support.
(Can be compact or spongy.)
Cartilage composition
Cartilage Connective tissue
Cells: Chondrocytes
Matrix: Collagen fibres within a rubbery gelatinous substance called chondrin.
Cartilage function
-Covers bone tips and reduces friction.
-Provides smooth and flexible cushioning.
Ligament composition
Dense connective tissue
Cells: Fibroblasts
Matrix: Dense collagen fibers
Ligament function
Connects bone to bone, stabilizes joints.
(Holds bones together)
Function of the bones
Protects vital organs (such as the skull protecting the brain and vertebrae protecting the spinal cord)
Storage of fat and minerals (Ca)
Fat Storage: Bones serve as a storage site for fat, primarily within their internal yellow marrow cavity
Calcium and Phosphorous Storehouse: Most of the body’s calcium is stored in bones in the form of calcium salts.
Blood cell formation (Hematopoiesis): occur within the red marrow cavities of certain bones.
Movement:Skeletal muscles, when attached to bones, facilitate movement and act as mechanical force multipliers.
Support: Provides a hard framework that supports and anchors the soft organs of the body.
Why do we need a small amount of calcium ions (Ca2+) to be present in the blood at all times
To support various bodily functions, including:
1. Transmitting messages within the nervous system
2. Enabling muscle contraction
3. Supporting blood clotting (converting prothrombin to thrombin)
The movement of calcium is regulated by
Hormones
No. of bones at birth and in adulthood
270
206
Division of the skeleton system
Axial skeleton (80 bones)
Appendicular skeleton (126 bones)
Axial skeleton bones and function
Bones
Skull
Vertebral column
Thoracic cage
Function
Protection of the internal organs
The appendicular skeleton bones and function
Bones
Shoulder grindle
Upper limbs
Pelvic girdle
Lower limbs
Function
Facilitate movements
Types of bone tissues
Compact bone
Spongy bone
Description and function of the compact bone
Description
Dense, hard, smooth, homogenous
Function
Provide structural support
Description and function of the spongy bone
Description
Has a spiky, open appearance like a sponge
Function
Provide structural support and store bone marrow
Periosteum
Tough membrane that covers and protects the outside of the bone
Bones are classified according to their shape into ____ groups
Four
Bones shapes
Long - humerus
Short - talus
Flat - sternum
Irregular - vertebra
Long bones
mostly compact bone (the outside part) surrounding spongy bone (red marrow).
Inside a long bone is a medullary cavity filled with yellow bone marrow.
Long bones of the appendicular system
Upper limb - Humerus, radius, ulna, metacarpals, phalanges
Lower limbs - Femur, tibia, fibula, metatarsals, phalanges
Function: Supporting body weight and facilitating movement
What is the longest and heaviest bone in the body?
Femur
Short bones
• Are generally cube-shaped
• Contain mostly spongy bone
• Include bones of the wrist and ankle
• short bones provide stability and some movement.
Ex: carpals/ tarsals
Sesamoid bones
are a special type of short bone that form within tendons
Ex: patella
Flat bones
Are thin, flattened, and usually curved (protects internal organs)
Have two thin layers of compact bone that surround a layer of spongy bones
Examples
Cranial bones (skull)
Ribs
Sternum (breastbone)
Scapula
Irregular bones
Have irregular shape
Examples:
Vertebrae
Hip bones
Gross anatomy of a long bone (structures)
Diaphysis
Periosteum
Endosteum
Medullary cavity in adults
Medullary cavity in infants
Red Marrow in Adults
Epiphysis
Diaphysis
Main shaft of the bone (Composed of compact bone)
Periosteum
A layer of fibrous connective tissue covering the diaphysis; also involved in bone formation and repair
Endosteum
A layer of epithelial tissue lining the inside wall of the medullary cavity; houses bone cells
Medullary Cavity in Adults
Primarily contains yellowbone marrow, which serves as a storage area for adipose (fat) tissue
Medullary Cavity in Infants
Contains red marrow where blood cells are formed, playing a role in blood cell formation
Red Marrow in Adults
Confined to cavities in the spongy bone of flat bones and the epiphysis of some long bones
Location of the epiphysis
The ends of the bone
Composition of the epiphysis
Consists of a thin layer of compact bone enclosing an area of spongy bone (filled with red marrow) that produces red and white blood cells
External surface of the epiphysis
Covered by an articular cartilage, made of hyaline cartilage that decreases friction at joint surfaces
epiphyseal line is in what type of bones?
Adult bones
Epiphyseal line
is a remnant of the epiphyseal plate (a flat plate of hyaline cartilage seen in a young, growing bone)
Epiphyseal plates
cause the lengthwise growth of a long bone
Bone connective tissues cells
Osteocytes
Bone connective tissue matrix
• One-third is composed of organic components (collagen fibre), which provide bone flexibility and great tensile strength.
• Inorganic components mainly composed of hydroxyapatite (a form of calcium phosphate), it provides bones with rigidity and strength, making them resistant to compression
• Water 25%
The central (harvesian) canal
A compact bone tissue contains passageways (called central (harvesian) canal) carrying nerves, blood vessels, which provide the living bone cells with nutrients and a route for waste disposal.
Arrangement of Lacunae
Lacunae are arranged in concentric circles called lamellae
Lamellae are circles around the central (Haversian) canal
Haversian system
Each complex consisting of a central canal is called an osteon, or Haversian system.§ Because of this network of canals, bone cells are well nourished in spite of the hardness of the matrix, and bone injuries heal quickly.
The human skeleton is composed of two strong and supportive tissue
Cartilage
Bone
Ossification
Formation of Long Bone
In embryonic stages, the skeleton consists primarily of _________, but as fetal growth to continue, most of the cartilage is replaced by _______.
hyaline cartilage, bone
Ossification
Long bones develop using hyaline cartilage as a template
Ossification involve 2 phases in the
Embryo and fetus
Embryo phase
In the embryo, osteoblasts create a bone matrix cover ‘collar’ around the entire hyaline cartilage model
Fetus stage
In the fetus, the hyaline cartilage model is gradually replaced by bone tissue, and the central region is digested away, creating a medullary cavity within the newly formed bone
Postnatal bone formation
By birth or shortly thereafter, most hyaline cartilage models have been transformed into bone, except for two regions - the articular cartilages covering bone ends and the epiphyseal plates
Bone growth
Lengthwise
Sideways
Hormonal control
Bone growth lengthwise
Grow in length as infant develops into a child
- New Cartilage Formation: On the external face of the articular cartilage, and on the surface of the epiphyseal plate, new cartilage is consistently formed.
- Old Cartilage Replacement: At the same time, the old cartilage next to the inner part of the articular cartilage and near the medullary cavity is slowly broken down and substituted with bone material.
Bone Growth-sideways
• Osteoblasts in the periosteum build bone on the outer surface of the diaphysis.
• Osteoclasts in the endosteum simultaneously remove bone from the inner surface of the diaphysis.
• These two cell types work at a similar pace, resulting in the expansion of the long bone’s diameter, and the bone widens due to this coordinated activity of osteoblasts and osteoclasts. • This process by which bones increase in diameter is called appositional growth.
Bone Growth- Hormonal control
• The growth is controlled by growth hormone and, during puberty, the sex hormones.
• The growth ends during adolescence, when the epiphyseal plates are completely converted to bone (become epiphyseal line).
Are bone static structures or dynamic tissues?
They are dynamic tissues that continuously change
Bone remodeling occurs in response to two main factors:
1) The blood calcium levels.
2) The influence of gravity and muscle tension on the skeleton.
Hypercalcemia
In cases of high blood calcium levels (hypercalcemia), the thyroid gland releases calcitonin, which stimulates osteoblasts to deposit excess calcium into the bone matrix as hard calcium salts.
Hypocalcemia
When blood calcium levels decrease, the parathyroid glands release parathyroid hormone (PTH) into the blood. PTH activates osteoclasts, which break down bone matrix to calcium ions into the blood.
What happens to bones in bedridden or physically inactive individuals?
They tend to atrophy and lose mass.
Mechanism of Bone Remodeling- Type of cells
Osteoclast
Osteoblast
Osteocytes
Osteoclasts
multinucleated cells
destroy bones
They contain numerous mitochondria and lysosomes.
Osteoblasts
bone forming cells
uninucleated cells
Considered part of the periosteum.
Osteocytes
mature bone cells (inside the bone matrix).
found in lacunae between the concentric lamellae of osteons.
Resorption
Old bone is resorbed by osteoclasts in a process called resorption
Ossification
new bone”is deposited by osteoblasts in a process called ossification (bone formation).
Location of osteoclasts
present on the outer layer of bone, underneath the periosteum.
Resorptionprocess
Attachment of the osteoclast to the osteon begins the process of resorption.
The osteoclast then secretes collagenase and other enzymes important in the resorption process.
As a result, high levels of calcium, phosphate and products of collagen will be released into the extracellular fluid.