SKELETAL SYSTEM (part 1)

Anatomical terms, Function of the Skeletal System, Bone Histology

Skeletal System

provides support and protection for the body’s internal organs while also serving as an attachment point for muscles.

In humans, it consists of bones, joints, and associated cartilage.

Superior

ANATOMICAL TERM: near vertex/topmost point

Cranial

ANATOMICAL TERM: towards the head

inferior

ANATOMICAL TERM: near sole of foot

Caudal

ANATOMICAL TERM: towards feet/tail region

Posterior

ANATOMICAL TERM: back surface/near the back

Anterior

ANATOMICAL TERM: front surface

Medial

ANATOMICAL TERM: nearer to median plane

Lateral

ANATOMICAL TERM: farther away from median plane

Proximal

ANATOMICAL TERM: near to trunk or point of origin

Distal

ANATOMICAL TERM: farther from trunk or point of origin

Bilateral

ANATOMICAL TERM: both sides of the body

Unilateral

ANATOMICAL TERM: one side of the body

Ipsilateral

ANATOMICAL TERM: on the same side of the body

Contralateral

ANATOMICAL TERM: on the opposite side of the body

Body support, Organ protection, Body movement, Mineral and Fat storage, and Blood cell production

Function of Skeletal System

Bones

for bearing weight and the major supporting tissue of the body

Cartilage

provides a firm yet flexible support. Examples nose, external ear, thoracic cage, and trachea.

Ligaments

strong bands of fibrous connective tissue, hold bones together

allow some movement between bones but prevent excessive movements.

Skull

encloses and protects the brain

Vertebrae

surround the spinal cord

Rib cage

protects the heart, lungs, and other organs of the thorax.

Tendon

attach skeletal muscles to bones for body movement through muscle contraction.

Joint

allow movement between two or more joined bones.

Smooth cartilage

covers the ends of bones within some joints, allowing the bones to move freely.

Calcium and phosphorus

Mineral and fat storage: what can we be found in the bone matrix.

Lipids

Mineral and fat storage: what can be found in the adipose tissue, also the energy source for glycolysis

Bone marrow

gives rise to blood cells and platelets

Hyaline cartilage, fibrocartilage, and elastic cartilage

Types of Cartilage

Hyaline cartilage

is the most associated with bone formation.

First step

Cartilage formation: Chondroblasts (derived from stem cells) secrete a matrix to surround itself.

Second step

Cartilage formation: Chondroblasts differentiates to chondrocytes(responsible for the maintenance of matrix/cartilage) following the complete matrix deposition.

Third step

Cartilage formation: Continued growth through matrix deposition and cell division.

Lacuna or Lacunae

the space occupied by the chondrocytes within the matrix.

Collagen

Matrix composition which provides strength

Proteoglycans

Matrix composition which provides cartilage resiliency by trapping water

Articular cartilage

is hyaline cartilage that covers the ends of bones, has no perichondrium, blood vessels, or nerves.

Appositional growth

Cartilage growth: chondroblasts in the perichondrium add new cartilage to the outside edge of the existing cartilage

Interstitial growth

Cartilage growth: chondrocytes in the center of the tissue divide and add more matrix in between the existing cells

Bone matrix

About 35% organic and 65% inorganic material

Organic material

Bone matrix: The _________ consists primarily of collagen and proteoglycans.

Inorganic material

Bone matrix: The _________ consists primarily hydroxyapatite(a calcium phosphate crystal with the molecular formula Ca10(PO4)6(OH)2

Collagen fibers, Mineral components

Bone matrix: The ________ lend flexible strength to the matrix like concrete, the __________ give the matrix weight-bearing strength.

Osteoblast

Bone-building cells

produce collagen and proteoglycans which are packaged into vesicles by the Golgi apparatus and secreted by exocytosis

secrete matrix vesicles – contain high concentrations of Ca2+ and PO 4 3- à hydroxyapatite crystals form.

derived from osteochondral progenitor cells

Ossification

formation of new bone by osteoblasts, also known as osteogenesis

Osteocytes

account for 90–95% of bone cells and are very long-lived, with a life span of up to 25 years.

________ are connected to neighboring ________ through their cell extensions.

derived from osteoblasts.

Osteoclast

are bone-destroying cells – cells break down bone.

are massive, multinucleated cells whose differentiation follows a complex pathway.

Bone Reabsorption

Breakdown of bone is called _________

Podosomes

develop and form a sealed compartment under the osteoclast.

Ruffled border

The osteoclast plasma membrane then further differentiates into a highly folded form called the _______.

Mesenchymal cells

Connective tissue develops embryologically from ________

Osteochondral progenitor cells

can become osteoblasts or chondroblasts.

Locations:

1. Inner layer of the perichondrium;

2. In the layers of connective tissue that cover bone (periosteum and endosteum).

Woven bone and Lamellar bone

Types of bone formed during ossification

Woven bone

the first type of bone that osteoblasts form during ossification. It is fairly weak bone because the collagen fibers are randomly oriented in many directions.

Lamellar bone

mature bone. It is organized into thin, concentric sheets or layers approximately 3–7 micrometers (μm) thick called lamellae

Spongy bone

Appears porous, has less bone matrix and more space than compact bone.

The spaces are filled with bone marrow and blood vessels.

Trabeculae

Spongy bone consists of interconnecting rods or plates of bone called ______.

The surfaces of ________ are covered with a single layer of cells consisting mostly of osteoblasts with a few osteoclasts.

Canaliculi

In spongy bones, usually, no blood vessels penetrate the trabeculae, so osteocytes must obtain nutrients through their ________.

Compact bone

It is the solid, outer layer surrounding each bone. It has more matrix and is denser with fewer pores than spongy bone.

Osteon

The functional unit of compact bone is an _______ or haversian system.

composed of concentric rings of matrix, which surround a central tunnel. Osteocytes are “sandwiched” between the rings of matrix.

Central canal

In cross section, an osteon resembles a circular target; the bull’s-eye of the target is the ________.

Concentric lamellae

Surrounding the central canal are rings of bone matrix called ________.

Each osteon has from 4 to 20

Osteocytes

are located in lacunae between the lamellar rings, and canaliculi radiate between lacunae across the lamellae, looking like minute cracks across the rings of the target.

Circumferential lamellae

form the outer surfaces of compact bone, which are thin plates that extend around the bone.

Perforating canals (Volkmann canals)

deliver blood to the central canals of the osteons