Anatomy Lecture Exam 2 (1/3) - Chapter 6 The Skeletal System

Components of skeletal system

Four components: Bone, Cartilage, Tendons, Ligaments

Functions of the skeletal system

Support, protection, movement, storage (calcium), blood cell production

Classification of bones

Long, short, flat, irregular, sesamoid

Long Bone

Features: Cylinder like shape, longer than it is wide
Functions: Leverage
Examples: Femur (thigh bone) & Phalanges (finger and toe bones)

Short Bone

Features: Cube-like shape, about equal in length, width, and thickness
Functions: Stability, support, while allowing for some motion
Examples: Carpals (wrist bones) & Tarsals (ankle bones)

Flat Bone

Features: Thin and curved
Functions: Points of attachments for muscles; protects internal organs
Examples: Sternum & Ribs

Irregular Bone

Features: Complex shape
Functions: Protect internal organs
Examples: Vertebrae & Facial bones

Sesamoid Bone

Features: Small and round; embedded in tendons
Functions: Protect tendons from compressive force
Examples Patellae (kneecap)

Spongy bone

Made up of trabeculae (interconnecting rods or plates of bone looks like scaffolding)

Additional Features: Spaces filled with marrow, Covered with endosteum (thin membrane of connective tissue), Orientated along stress lines

Compact bone

Made up of osteons (cylindrical units of bone)

Additional Features: Blood vessel-filled central canal

Diaphysis

The shaft or central part of the long bone; made up of compact bone

Epiphysis

The end of a long bone; made up of spongy bone

Proximal and distal epiphysis ends

Epiphyseal plate

A layer of cartilage in long bones that is responsible for bone growth and length.

Becomes the epiphyseal line when the bone stops growing

Medullary Cavity

The hollow space in the center of a long bone that contains bone marrow

Periosteum

A dense fibrous membrane covering the surface of bones and serving as an attachment for tendons and muscles.

Long Bone: Periosteum

Dense, white fibrous membrane that covers bone

Endosteum

A thin membrane of connective tissue that lines the inner surface of a bone

Long Bone: Endosteum

lines the medullary cavity

Proximal epiphysis

The end of bone closest to the trunk of the body

Distal epiphysis

The end of bone furthest to the trunk of the body

Epiphysis is covered with...

articular cartilage, this acts a shock absorber

Flat Bone Structure

No diaphyses or epiphyses. Sandwich of spongy bone between compact bone.

Irregular bone Structure

Spongy bone that is covered with a thin layer of compact bone

Spongy bone and medullary cavity receive nourishment from...

arteries that pass through the compact bone

Nutrient foramen

A small opening in the shaft of a long bone that allows a nutrient artery to pass through and supply the bone with nutrition

Bone matrix

The tissue that surrounds bone cells, and is made up of minerals and collagen fibers that give bones their strength and stiffness

If mineral is removed bone becomes too bendable
If collagen is removed bone becomes too brittle

Osteocytes

mature bone cells

Lacuna

A small cavity or space in bone or cartilage that contains an osteocyte, which is a bone cell

Osteocytes are located in...

lacunae

Canaliculi

Hair like canals that connect lacunae to each other and the central canal, used for communication and nutrition distribution

Osteoblasts

Cells that form and grow bone tissue

Ossification

Process of bone formation by osteoblasts

Osteoclasts

Cells that break down bone tissue to help maintain a healthy skeleton

Osteogenic cells

Stem cells that differentiate (become) into osteoblasts and osteocytes

Osteoblasts and osteocytes are incapable of...

mitosis, osteogenic cells are used to replace them

Bone Markings

Surface features on a bone

Bone Marking Classes

Three: Articulations, Projections, Holes

Articulation

A joint, or the place where two or more bones meet

Projections

A part of a bone that sticks out from the bone's surface

Holes

Refers to foramens (literal holes or gaps)

Foramen

A hole through which nerves and blood vessels pass

Intramembranous ossification

A process that forms bones directly from mesenchymal tissue (embryonic tissue)

Takes place in connective tissue membrane

Produces flat bones of skull and clavicle (collarbone)

Intramembranous ossification forms...

Forms many skull bones, part of mandible, diaphysis of clavicles (collarbone)

Intramembranous ossification takes place in...

Takes place in connective tissue membrane

Endochondral ossification

The process of replacing hyaline cartilage with bone

Takes place in cartilage

Endochondral ossification takes place in...

cartilage, specifically hyaline cartilage

Hyaline cartilage

Translucent cartilage found on many joint surfaces

Ossification (osteogenesis)

Process of bone formation; created from cartilage or fibrous tissue

Methods of Ossification

intramembranous ossification and endochondral ossification

Centers of ossification

locations in membrane where ossification begins

Fontanels

Soft spots on a baby's skull where the skull bones are not yet joined together

Intramembranous Ossification Steps

1. Early osteoblasts appear in the ossification center.
2. Osteoblasts secrete uncalcified matrix that hardens in a few days (calcification)
3. Once hardened, osteoblasts become osteocytes.
4. Osteogenic cells differentiate into new osteoblasts.
5. Trabecular bone forms (scaffold like bone) and compact bone develops on the surface.

Endochondral Ossification Steps

The process where a baby's bones develop from a cartilage template, essentially "replacing" the cartilage with bone as the body grows

1. Around 6-8 weeks after conception, mesenchymal cells become chondrocytes.
2. The perichondrium forms and becomes vascularized (gets blood supply).
3. Blood vessels cause mesenchymal cells to turn into osteoblasts, forming a bone collar.
4. Chondrocytes die as the matrix hardens, creating space in the center of the bone.
5. Blood vessels invade, bringing osteogenic cells with them.
6. A secondary ossification center forms at the ends of the bone (the cartilage remains until after birth).
7. The epiphyseal plate remains between the primary and secondary ossification centers for bone growth

Chondrocytes

Cells that make up cartilage

a connective tissue that provides structural support and protects bones at joints

Perichondrium

A dense layer of fibrous connective tissue that covers the surface of most of the cartilage in the body

Periosteal bud

A vascular tissue that contains blood vessels, osteoprogenitor cells, and hemopoietic cells that invade the center of a developing bone

Hematopoietic cells

Blood forming cells

Osteoprogenitor cells

Bone stem cells

Zones of the Epiphyseal Plate

1. Zone of resting cartilage
2. Zone of proliferating cartilage
3. Zone of hypertrophic cartilage
4. Zone of calcified cartilage
5. Zone of ossification

Zone of resting cartilage

Slowly dividing chondrocytes

Zone of proliferating cartilage

New cartilage is made as chondrocytes divide and form stacks of cells

Zone of hypertrophic cartilage

Chondrocytes grow larger and mature.

Zone of calcified cartilage

The matrix hardens (calcifies), and chondrocytes die.

Zone of ossification

The cartilage is replaced by bone tissue.

Wolff's law

Bone is modeled and remodeled based on stresses applied to it

Paget's disease

A disease of unknown origin that is characterized by abnormal bone growth and weakening

Incomplete Fracture

Bone is not broken all the way through

Complete Fracture

Bone is broken all the way through

Communited fracture

Bone is splintered or crushed

Bone Repair

1. Hematoma formation
2. callus formation
3. callus ossification (Callus replaced by spongy bone)
4. bone remodeling (Replacement of spongy bone and damaged material by compact bone & sculpting by osteoclasts)

Hematoma

A solid swelling of clotted blood within the tissues.

Factors affecting bone growth

Hormones (Estrogen and testosterone) and vitamins (Vitamin D, Vitamin C)

Three hormones that control blood calcium levels

Parathyroid hormone (PTH), Calcitriol, Calcitonin

Parathyroid Hormone

Released when blood calcium levels are too low and activates osteoclasts, causes calcitriol to be released

Hypocalcemia

Low levels of calcium

Hypercalcemia

High levels of calcium, can cause kidney stones

Calcitriol

A hormone produced from vitamin D that, increases blood calcium by stimulating intestinal absorption of calcium

(Acts in essentially the same manner as parathyroid hormone)

Calcitonin

Lowers blood calcium levels, counter acts the parathyroid hormone by inhibiting osteoclast

Effects of aging on the skeletal system...

Bone Matrix decreases
Bone Mass decreases
Increased bone fractures
Bone loss causes deformity, loss of height, pain, stiffness
Stooped posture
Loss of teeth

Homeostatic relationship between skeletal system and other organ systems...

1. Skeletal System provides support for body organs including the skin.
2. Skeletal system is dependent upon skin to provide vitamin D
3. Skeletal system works with muscles to provide movement