A&P 9

Skeletal system

A complex network of bones, joints, ligaments, and cartilage that provides structure, support, and protection to the human body.

Number of bones in the human skeleton

206

Main components of the skeletal system

Bones, joints, ligaments, and cartilage.

Joints

Connect bones and promote movement.

Ligaments

Fibrous connective tissues that connect bones to bones, providing stability.

Cartilage

Smooth, elastic tissue that cushions joints and reduces friction.

Primary functions of the skeletal system

Support and structure, movement, protection, mineral storage, blood cell production, and fat storage.

How does the skeletal system support and structure the body?

It provides a rigid framework that supports organs and muscles.

Hematopoiesis

The process of blood cell production that occurs in the red bone marrow found within bones.

Minerals are stored in bones

Calcium and phosphorus, essential for bone health and overall body function.

What type of marrow is responsible for fat storage?

Yellow bone marrow, found within bones.

Function of yellow bone marrow

Store fat

How does the skeletal system protect vital organs?

The skull, rib cage, and spine protect vital organs like the brain, heart, and lungs.

Divisions of the skeletal system

Axial and appendicular

Components of axial skeleton

Skull

Vertebral column

Thoracic (rib) cage

Hyoid bone

Hyoid bone

Unique bone in the throat that doesn't articulate with any other bone but provides attachment for muscles of the tongue and neck

Functions of axial skeleton

Protection

Support

Attachment

Balance and movement

Appendicular skeleton

Comprises bones of the upper and lower extremeties

Number of bones in the appendicular skeleton

126

Functions of the appendicular skeleton

Locomotion

Weight transmission

Muscle attachment

Locomotion

The lower limbs are adapted for standing and walking, while the upper limbs are used for grasping and manipulating objects

Weight Transmission

The pelvic girdle helps to support the body's weight and transmit it to the ground through the lower limbs

Muscle Attachment

Provides attachment points for many muscles, allowing for a wide range of movements

Bone fusing

A baby's body has 270-300 bones at birth, some of which are made entirely of cartilage. These bones eventually fuse to form the 206 bones that adults have.

Long bones

Cylinder-like shape, longer than it is wide; function in leverage. Examples include femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges.

Short bones

Cube-like shape, approximately equal in length, width, and thickness; provide stability, support, while allowing for some motion. Examples include carpals, tarsals.

Flat bones

Thin and curved; points of attachment for muscles and protectors of internal organs. Examples include sternum, ribs, scapulae, cranial bones.

Irregular bones

Complex shape; protect internal organs. Examples include vertebrae, facial bones.

Sesamoid bones

Small and round; embedded in tendons; protect tendons from compressive forces. Example includes patellae.

Bone density

The total amount of bone tissue continues to increase slowly until the late 20s.

Bone growth cessation

Bones stop growing in length between the ages of 16 and 18.

Joints/articulations

Connections between two or more bones

Structural classification of joints

Based on the structure of joints.

Fibrous joints

Joints connected by dense connective tissue, which are immovable (e.g., skull sutures) or slightly movable (e.g., radioulna joint).

Cartilaginous joints

Joints connected by cartilage, which are partially movable (e.g., spine).

Synovial joints

Joints with a fluid-filled capsule and ligaments, which are freely movable (e.g., shoulder and hip joints).

Functional classification of joints

Classification based on the function of joints.

Synarthrosis

Immovable joints (e.g., skull sutures).

Amphiarthrosis joint

Slightly movable joints (e.g., between the two halves of the pelvis).

Diarthrosis

Freely movable joints (e.g., shoulder and hip joints).

Sutures

Fibrous joints found between the bones of the skull, allowing minimal movement in infants but not adults.

Gomphoses

Fibrous joints occurring between teeth and their sockets in the jawbone, providing support for teeth.

Syndesmoses

Fibrous joints where two parallel bones are joined by connective tissue, allowing slight movement (e.g., tibio-fibula joint).

Synchondrosis

A temporary cartilaginous joint formed by hyaline cartilage (e.g., epiphyseal plates in children).

Symphysis

A permanent cartilaginous joint formed by fibrocartilage (e.g., intervertebral discs).

Ball and socket joint

A synovial joint where one bone fits into a socket of another bone (e.g., hip, shoulder).

Hinge joint

A synovial joint where one bone moves back and forth on another (e.g., elbow, knee).

Pivot joint

A synovial joint where one bone rotates around another (e.g., neck).

Condyloid joint

A synovial joint where one bone moves in two directions on another (e.g., wrist).

Saddle joint

A synovial joint where one bone moves in two directions on a saddle-shaped bone (e.g., thumb).

Functions of joints

Flexion and extension, abduction and adduction, rotation, and gliding, and provide cushioning, stability, and lubrication.

Why is cartilage considered a slow-healing tissue?

Due to its lack of blood supply.

What conditions can result from damage to cartilage?

Osteoarthritis and joint pain.

Cells that produce cartilage

Chondrocytes, which are produced by chondroblasts.

Main components of the extracellular matrix (ECM) of cartilage

Collagen, proteoglycans, ground substance, elastin fibers, and hyaluronic acid.

What type of collagen is primarily found in cartilage?

Type II collagen.

Function of proteoglycans in cartilage

Retain water and provide cushioning.

Properties of cartilage

Avascular (lack blood vessels) and aneural (lack nerves).

Three main types of cartilage

Hyaline cartilage, fibrocartilage, and elastic cartilage.

Hyaline cartilage

Most common type, somewhat flexible, rich in type II collagen, found in joints, nose, ribs, and trachea. Provides smooth, low-friction movement in joints.

Fibrocartilage

A dense network of thick type I collagen fibers, making it the strongest type of cartilage, least flexible. Provides support and shock absorption to intervertebral discs, pubic symphysis, and menisci.

Elastic cartilage

Provides flexibility and support, found in the ear, epiglottis, and larynx.

Fibroelastic cartilage

A type that combines properties of elastic and fibrocartilage, found in the temporomandibular joint.

Functions of cartilage

Cushioning joints, supporting and protecting bones, maintaining joint flexibility, and shaping body structures.

What role does cartilage play in the shape of body structures?

It contributes to the shape and support of structures like the nose, ears, and trachea.

Two parts of long bone

Diaphysis and epiphysis

What does the periosteum contain?

Blood vessels, nerves, and lymphatic vessels

What type of cartilage is articular cartilage?

Hyaline cartilage

Flat bone

Consist of a layer of diploe (spongy bone). Protect internal organs.

Facet

Small, flat articular surface

Trochlea

Smooth, grooved articular process

Sulcus

A narrow groove

Sinus

Air-filled space in the bone

Fissue

Deep furrow, clef or slit

Osteoblasts

Responsible for forming new bone tissue and secrete proteins and minerals that mineralize and create bone matrix. Located on surface of bones.

Osteocytes

Mature bone cells that reside within the bone matrix. Maintain bone tissue and regulate mineral content. Connected to each other through a network of channels called canaliculi.

Osteoclasts

Break down and resorb bone tissue. Multi-nucleated cells that release enzymes to dissolve bone matrix. Essential for bone remodeling and repair

Osteogenic cell

Only bone cells that divide

Two types of bone tissue that make up the human skeleton

Compact bone and spongy bone.

Primary function of compact bone/Cortical

To provide strength and protection to the skeleton.

Compact/Cortical bone location

It forms the hard, dense outer shell of all bones, including long bones, ribs, and flat bones of the skull.

Osteon

The primary functional and structural unit of compact bone, forming a cylindrical structure.

Haversian canal

A central canal within each osteon containing blood vessels, nerves, and lymphatic vessels.

Lamellae

Concentric rings of hardened bone matrix surrounding the Haversian canal.

Lacunae

Small spaces where osteocytes are located within compact bone.

Canaliculi

Tiny, branched canals that connect the lacunae, allowing for the transport of nutrients and removal of waste from osteocytes.

Perforating canals

Channels that run perpendicular to Haversian canals, connecting them to the periosteum and endosteum.

Spongy bone

A porous, honeycomb-like tissue found at the ends of long bones and in the middle of other bones, containing osteocytes in a lattice-like network.

Function of trabeculae in spongy bone

Provide strength to the bone by forming along lines of stress and making bones lighter.

Hematopoiesis

The process of blood cell formation that occurs in the red marrow found in some spongy bones.

How do spongy bone and medullary cavity receive nourishment?

Through arteries that pass through the compact bone via nutrient foramina and from blood vessels of the periosteum.

Role of nerves in bone

Sense pain and help regulate blood supplies and bone growth, concentrating in metabolically active regions.

Ossification

The process of bone development that begins in the sixth or seventh week of embryonic life.

Intramembranous ossification

The direct development of bone from mesenchymal connective tissue, forming flat bones like those of the skull.

Steps of intramembranous ossification

Formation of ossification center

Osteoid secretion

Mineralization and osteoblast trapping

Osteocyte formation

Blood vessel incorporation

Spongy bone formation

Compact bone formation.

Bones formed through intramembranous ossification

Flat bones such as the skull bones, clavicle, mandible, and maxilla.

Endochondral ossification

The process where cartilage is converted into bone, occurring in long and short bones.

Stages of endochondral ossification

Formation of cartilage

Maturation of chondroblasts

Hypertrophy and matrix calcification

Death of chondrocytes

Blood vessel invasion

Formation of primary ossification center

Formation of secondary ossification center

Bones are formed through endochondral ossification

Long bones like femur, tibia, humerus, and short bones like tarsals and carpals.

Age do humans typically stop increasing in height

Between the ages of 18 and 20, due to the closure of growth plates.