Unit 4The Skeletal System

Lecture 1- Bone Structure, Formation and Growth

(Chapters 7 & 8)

The Skeletal System- OverviewThe Skeletal System- Overview The skeleton contains 206 bones

Parts of the skeletal system

Bones (skeleton)

Joints

Cartilages

Ligaments (bone to bone)

Divided into two divisions

Axial skeleton

Appendicular skeleton – limbs and girdle

Classification of Bones on the Classification of Bones on the Basis of ShapeBasis of Shape

Figure 5.1

Classification of Bones- ShapeClassification of Bones- Shape

Long bones

Typically longer than wide

Have a shaft with heads at both ends

Contain mostly compact bone

• Examples: Femur, humerus

Classification of Bones- ShapeClassification of Bones- Shape

Short bones

Generally cube-shape

Contain mostly spongy bone

Examples: Carpals, tarsals

Sesamoid bones

Small, round

Example: patella

Classification of Bones- ShapeClassification of Bones- Shape

Flat bones

Thin and flattened

Usually curved

Thin layers of compact bone around a layer of spongy bone

Examples: Skull, ribs, sternum

Classification of Bones- ShapeClassification of Bones- Shape

Irregular bones

Irregular shape

Do not fit into other bone classification categories

Example: Vertebrae and hip

Classification of Bones on the Classification of Bones on the Basis of ShapeBasis of Shape

Classification of Bones- MarkingsClassification of Bones- Markings

Projections

grow out from a bone surface

site of muscle and ligament attachments

help form joints

Examples: process, crest, facet, ramus, condyle

Classification of Bones- MarkingsClassification of Bones- Markings Openings

Hollows, cavities or passageways

allow blood vessels and nerves to pass through

Examples: sinus, meatus, foramen, groove, fissure

Depressions

Indentations

articulates with a process

Examples: fossa

Functions of BonesFunctions of Bones

Support of the body

Protection of soft organs

Movement due to attached skeletal muscles

Storage of minerals and fats

Blood cell formation

Mineral StorageMineral Storage Bone matrix is made of collagen and inorganic mineral

salts

Salt = 70% of matrix weight

Mostly calcium phosphate

Calcium is vital in the body

Muscle cell contraction

Nerve impulse conduction

Blood clot formation

Low blood calcium = osteoclasts break down bone

High blood calcium = osteoblasts form bone

Blood Cell FormationBlood Cell Formation Process of blood cell formation is called

hematopoiesis

Begins in yolk sac, outside of embryo

Blood cells are later manufactured in the live and spleen

Eventually form bone marrow

Marrow is a soft mass of connective tissue

Blood Cell FormationBlood Cell Formation Types of Marrow:

Red Marrow

Forms blood cells (red, white and platelets)

Yellow Marrow

Stores fat

Does not produce blood cells

Marrow distribution changes with age

Infants- most marrow is red

Over time yellow marrow replaces red marrow

Adults- red marrow found in spongy bone of skull, ribs, sternum, clavicle, vertebrae and hips

Bone TissueBone Tissue Two basic types of bone tissue

Compact bone

Homogeneous

Dense

Outer bone

Spongy bone

Small needle-like pieces of bone

Many open spaces, porous

Inner bone

Gross Anatomy of a Long BoneGross Anatomy of a Long Bone Diaphysis

Shaft

Composed of compact bone

Epiphysis

Ends of the bone

Composed mostly of spongy bone

Metaphysis

Between diaphysis and epiphysis

Structures of a Long BoneStructures of a Long Bone Periosteum

Outside covering of the diaphysis

Fibrous connective tissue membrane

Endosteum

Lines medullary cavity

Sharpey’s fibers

Secure periosteum to underlying bone

Arteries

Supply bone cells with nutrients

Structures of a Long BoneStructures of a Long Bone

Medullary cavity

Cavity of the shaft

Contains yellow marrow (mostly fat) in adults

Contains red marrow (for blood cell formation) in infants

Structures of a Long BoneStructures of a Long Bone

Articular cartilage

Covers the external surface of the epiphyses

Made of hyaline cartilage

Decreases friction at joint surfaces

Microscopic Anatomy of BoneMicroscopic Anatomy of Bone

Osteon

A unit of bone

Central (Haversian) Canal

Opening in the center of an osteon

Carries blood vessels and nerves

Microscopic Anatomy of BoneMicroscopic Anatomy of Bone Lacunae

Cavities containing bone cells (osteocytes)

Arranged in concentric rings

Lamellae

Rings around the central canal

Sites of lacunae

Canaliculi

Tiny canals

Connect lacunae

Microscopic Anatomy of BoneMicroscopic Anatomy of Bone

Figure 5.3

Types of Bone CellsTypes of Bone Cells Osteocytes

Mature bone cells

Osteoblasts Bone-forming cells

Osteoclasts Bone-destroying cells

Break down bone matrix for remodeling and release of calcium

Bone remodeling is a process by both osteoblasts and osteoclasts

Osteoblast

Osteocyte

OsteoclastEats bone

Builds new bone

Mature bone cell

Bone Development and GrowthBone Development and Growth Osteogenesis- development of bone

Intramembranous bones

originate within layers of connective tissue

Flat bones of skull, clavicles, sternum and some facial bones

Endochondral bones

Develop from hyaline cartilage

Shaped like future bones

Initial growth is rapid

Endochondral Bone FormationEndochondral Bone Formation1. Perichondrium becomes a periosteum and a

bone collar forms around the cartilage model.

2. Cavity begins to form within cartilage.

3. Periosteal bud invades marrow cavity.

4. Osteoblasts lay down spongy bone in the bone interior.

5. Osteoclast eventually remove the spongy bone and leave a cavity to house fat.

Endochondral Bone FormationEndochondral Bone Formation

Bone Development and Growth- FetusBone Development and Growth- Fetus

The skeleton begins to form during the first few weeks of prenatal development

In embryos, the skeleton is primarily hyaline cartilage

Cartilage remains in isolated areas

Bridge of the nose

Parts of ribs

Joints

Bone structures continue to develop into adulthood

Fetal SkeletonFetal Skeleton

275 bones12 weeks (6-9 inches long)

Bone Growth in ChildhoodBone Growth in Childhood

Epiphyseal plates allow for growth of long bone during childhood

New cartilage is continuously formed

Older cartilage becomes ossified

Cartilage is broken down

Bone replaces cartilage

Long Bone Formation and GrowthLong Bone Formation and Growth

Bone Growth in AdulthoodBone Growth in Adulthood

Bone formation and growth stops between 23-25 years of age

Bone remodeling continues throughout life

Osteoclasts resorb bone tissue

Osteoblasts replace/deposit new bone

10%-20% of the skeleton is replaced annually

Factors Affecting Bone Factors Affecting Bone Development, Growth and RepairDevelopment, Growth and Repair

Nutrition

Vitamin D

Needed for calcium absorption

Lack of calcium softens and deforms bones

Vitamin A and C

A is needed for osteoblast and osteoclast activity

Deficiency slows bones development

C is needed for collagen formation

Deficiency leads to slender, fragile bones

Factors Affecting Bone Development, Factors Affecting Bone Development, Growth and RepairGrowth and Repair

Hormones

Pituitary gland secretes growth hormone

Stimulates division of cartilage cells

Pituitary dwarfism

Absence of growth hormone

Very short, normal body proportions

Pituitary gigantism

Excess growth hormone

Height over 8 feet

In adults, enlarged hands, feet or jaw

Factors Affecting Bone Factors Affecting Bone Development, Growth and RepairDevelopment, Growth and Repair

(Hormones cont.)

Sex hormones promote bone formation

Abundant during puberty, so long bone growth increases

Also stimulate ossification and eventually stop bone growth

Estrogen is stronger, so females reach maximum height sooner

Physical Stress

Factors Affecting Bone Development, Factors Affecting Bone Development, Growth and RepairGrowth and Repair

Physical Stress

Contraction of skeletal muscles cause bone tissue to thicken and strengthen

Hypertrophy

Bones of athletes are stronger and heavier

Lack of exercise cause bone tissue to waste

Atrophy

Fractures can cause shortening of bones

Astronauts experience a 1% loss of bone mass per month in space