Skeletal System

skeletal system

is mostly thought to be the framework of the body. But along with the bones, the system consists of their associated connective tissues, which include cartilage, tendons, and ligaments that contribute to the myriad of functions of the skeletal system.

skeletal system

makes up 20% of the body weight.

Body Support

Organ Protection

Body Movement

Mineral Storage

Blood Cell Production

Functions of skeletal system

Rigid, strong bones

suited for bearing weight and are the major supporting tissue of the body.

Cartilage

provides firm yet flexible support within certain structures:

○ Nose

○ External Ear

○ Thoracic Cage

○ Trachea

Ligaments

are strong bands of fibrous connective tissue that hold bones together.

Tendons

are strong bands of connective tissue which attach bones to the skeletal muscles to provide movement through contraction.

Joints

are formed when two or more bones come together.

Ligaments

restrict excessive movement.

Calcium and phosphorus

are the principal minerals stored in the bone and are essential for many physiological activities.

Adipose tissues

are also stored within bone cavities in the form of fat embolism

Red bone marrow

produces red blood cells and platelets and fill the bone cavities of many bones.

BONE HISTOLOGY (matrix)

which exists in skeletal tissue, is produced by cells which become entrapped in them. Its composition is responsible for its characteristics

35% organic and 65% inorganic material

Mature bone matrix is normally about — organic and —- inorganic material

Collagen

Proteoglycans

Organic Material in bone matrix

Hydroxyapatite

Inorganic Material in bone matrix

Collagen

Provides flexibility but resists pulling or compression. Essential for the attachment functions of tendons and ligaments and shock-absorption of the cartilage.

Proteoglycans

Water-trapping protein molecules that help cartilage be smooth and resilient.

Hydroxyapatite

calcium phosphate crystal that has a molecular formula of Ca10(PO4)6(OH)2.

Brittle Bone Disease

imperfect bone formation is a rare disorder caused by one of them any number of faulty genes that results in: Little collagen formation and Poor quality collagen

1. Osteoblasts

2. Osteocytes

3. Osteoclasts

The different types of bone cells include:

OSTEOBLASTS

Bone building cells for bone formation, repair, and remodelling.

OSTEOBLASTS

Produces collagen and proteoglycans.

OSTEOBLASTS

Packaged into vesicles by the Golgi apparatus and secreted by exocytosis

OSTEOBLASTS

Has an extensive endoplasmic reticulum and numerous ribosomes.

OSTEOBLASTS

High concentrations of Ca2+and phosphate ions.

Ossification

The formation of new bone by osteoblasts.

Ossification

Can occur during the fetal stage, growth, and fractures

Ossification

Occurs by appositional growth on the surface of the old bone or cartilage, resulting in a new layer of bone.

OSTEOCYTES

Account for 90-95% of bone cells and have a lifespan of 25years

OSTEOCYTES

Produces the components needed to maintain the bone matrix

Lacunae

houses the osteocyte cell bodies within the bone matrix

Canaliculi

are narrow, long spaces housing the osteocyte cell extensions. These extensions form a “mold” around which the matrix is formed where nutrients and gases can pass through.

OSTEOCLASTS

Bone destroying cells that break down bone.

Ruffled border

is formed which is a specialized reabsorption-specific area of the membrane.

Lamellar Bones

are the mature bones which are organized into thin, concentric sheets called lamellae.

lamellae

Lamellar bodies are organize into thin, concentric sheets

SPONGY BONE

Appears porous and has less bone matrix

Trabeculae

are thin, interconnecting rods or plates of bone that make up the spongy bone.

Trabeculae

The spaces in between are filled with bone marrow and blood vessels

Trabeculae

The surface is covered with a single layer of cells consisting of mostly osteoblasts and a few osteoclasts.

COMPACT BONE / CORTICAL BONE

The solid, outer layer surrounding each bone.

COMPACT BONE / CORTICAL BONE

It has more matrix, is denser, and has fewer pores.

COMPACT BONE / CORTICAL BONE

The blood vessels enter the bone itself, where the lamellae cater to these blood vessels

osteon or the haversian system

primary functional unit of the compact bone

Central canals

which are surrounded by rings of bone matrix, are lined with endosteum and contain blood vessels, nerves, and loose connective tissue.

canaliculi

Nutrients in the blood vessels are delivered to the osteocytes and are passed from cell to cell through the

Diaphysis

Medullary Cavity

Epiphyses

Articular Cartilage

Epiphyseal Plate

Epiphyseal Line

Red Bone Marrow

Yellow Bone Marrow

Periosteum

Endosteum

STRUCTURE OF A LONG BONE

Diaphysis

The center portion of the bone

Diaphysis

At both ends of the this, growth in length of bones of the arm, forearm, thigh, and leg occurs.

Diaphysis

At one end of the this, Growth in length of the hand and foot bones occurs.

Medullary Cavity

The hollow center of the bone is surrounded by compact bone tissue.

Epiphyses

The ends of a long bone composed of mostly spongy bone with an outer layer of compact bone.

Articular Cartilage

Covers the end of long bones within joints

Epiphyseal Plate

The growth plate exists between the epiphysis and diaphysis where growth in bone length occurs.

Epiphyseal Line

Signals the stop in growth of length in bones when it ossifies.

Red Bone Marrow

Site of red blood cell formation and fills the cavities of spongy bone and medullary cavity, especially in fetuses.

hip bone

The __ has large distributions of red bone marrow and is a source of donated red bone marrow.

Yellow Bone Marrow

Endosteum Single cell layer of connective

tissue that lines the medullary

cavities and smaller cavities of

spongy and compact bone.

Includes osteoblasts and

osteoclasts

composed of adipose tissues and fills the cavities of spongy bone, gradually replacing the red bone marrow beginning before birth to adulthood.

Yellow Bone Marrow

Completely replaces the red bone marrow in long bones except for the proximal part of arm and thigh bones.

Periosteum

Connective tissue membrane that covers the outer surface of the bone.

Outer Layer

the layer of periosteum that contains blood vessels and nerves

Inner Layer

the layer of periosteum that contains single layer of bone cells, including osteoblasts and osteoclasts

1. Intramembranous Ossification

2. Endochondral Ossification

Bone formation in fetuses follows two process:

INTRAMEMBRANOUS OSSIFICATION

Starts within the embryonic connective tissue membranes

INTRAMEMBRANOUS OSSIFICATION

Forms many skull bones, part of the mandible (lower jaw), and diaphyses of clavicles (collarbones).

INTRAMEMBRANOUS OSSIFICATION

The centers of ossification are locations in membranes where this ossification begins.

Fontanels

soft spots that are larger, membrane-covered spaces that have not yet ossified.

Fontanels

this closes by 2 years of age

At 5th week of embryonic development:

The skull begins to form from a membrane of connective tissue with delicate, randomly oriented collagen fibers surrounds the brain

At 8th week of embryonic development:

early skull membrane begins

PROCESS OF INTRAMEMBRANEOUS OSSFICIATION

1. Osteoblast Activity

2. Spongy Bone Formation

3. Compact Bone Formation

At 8th week of embryonic development: early skull membrane begins (process)

Osteoblast Activity

osteoblasts begin to produce the bone matrix thus covering the existing connective tissue membranes and results in many tiny trabeculae.

Spongy Bone Formation

additional osteoblasts continue to form the bone matrix, thus making the trabeculae stronger thus forming the spongy bone.

Compact Bone Formation

Cells in spaces form the bone marrow, cells surrounding developing bone form the periosteum, and osteoblasts lay down more matrix to form compact bone.

ENDOCHONDRAL OSSIFICATION

Ossifies the cartilage at the 8th week of embryonic development.

18-20

Some cartilage ossify as late as __ years of age.

ENDOCHONDRAL OSSIFICATION

Develops the bones of the base of the skull, part of the mandible, the epiphyses of the clavicles, and most of the remaining skeletal system.

1. Cartilage Model Formation

2. Bone Collar Formation

3. Primary Ossification

4. Secondary Ossification Center Formation

5. Adult Bone

ENDOCHONDRAL OSSIFICATION Processes:

Cartilage Model Formation

cells called chondrocytes produce the hyaline cartilage model that has the approximate shape of future bone.

Bone Collar Formation

osteoblasts produce compact bone on the surface of the cartilage model. The cartilage model increases in size due to interstitial and appositional growth and the chondrocytes at the center absorb some of the cartilage matrix and enlarge (hypertrophy). Hydroxyapatite crystals form in the cartilage matrix and convert it into calcified cartilage. These chondrocytes then die, leaving enlarged lacunae.

Hydroxyapatite crystals

form in the cartilage matrix and convert it into calcified cartilage.

Primary Ossification

osteoblasts begin to produce bone as they migrate into the calcified cartilage through the blood vessels and transform it into the diaphysis of spongy bone. Osteoclasts remove bone from the diaphysis to form the medullary cavity and the cells within form red bone marrow.

Secondary Ossification Center Formation:

osteoblasts migrate to the epiphysis and continue to form bone to replace the cartilage, except in the epiphyseal plate and articular surfaces.

Adult Bone

spongy and compact bone are fully developed and the epiphyseal plate becomes the epiphyseal line. The only cartilage present is the articular cartilage at the end of bones. The perichondrium that once surrounded the cartilage becomes the periosteum.

both interstitial and appositional

Bones undergo ______________ growth unlike cartilage.

Appositional growth

is a process where the osteoblasts form a new layer of bone on the surface of old bone.

Interstitial growth

New cartilage is formed and is followed by appositional bone growth on the surface of the existing cartilage.

Zone of Resting Cartilage

Zone of Proliferation

Zone of Hypertrophy

Zone of Calcification

Ossified Bone

ZONES OF THE EPIPHYSEAL PLATE

Zone of Resting Cartilage

Contains slowly dividing chondrocytes

Zone of Proliferation

Chondrocytes produce new cartilage by dividing and forming columns

Zone of Hypertrophy

Chondrocytes mature and enlarge

Zone of Calcification

Very thin and contain hypertrophied chondrocytes and calcified cartilage matrix. They eventually die and blood vessels from the diaphysis grow into the area.

Ossified Bone

Osteoblasts line up on the surface of the calcified cartilage and produce a new bone matrix, which is later remodeled.

12-25 years of age

The closure of the epiphyseal plate to the epiphyseal line occurs between ______________, depending on the bone and individual.

TRUE

The cartilage growth of the epiphyseal plate is equal to the rate of bone formation in the diaphyseal plate, thus the thickness of the epiphyseal plate remains.

BONE REMODELLING

Process where old bone is replaced with new bone.

BONE REMODELLING

Osteoclasts remove old bone and osteoblasts deposit new bone

○ Bone Growth

○ Changes in Bone Shape

○ Adjustment of Bone to Stress

○ Bone Repair

○ Calcium ion Regulation

bone remodelling converts woven bone into lamellar bone and is involved in several important functions:

1. Lighter in weight than a solid rod

2. Can support much more weight without bending

The hollow cylinder with a medullary cavity in long bones have two mechanical advantages:

Compact bone remains its thickness because osteoclasts remove bone from the inside while osteoblasts add bone from the outside.

How does compact bone remain its thickness