1. Introduction to the Skeletal System

2.  Support: Bones support the weight of the body and structures such as the head and face  Protection: Bones protect delicate organs such as the brain and spinal cord, heart and lungs  Muscle Attachment & Movement: Bones act as levers to which muscles are attached  Blood Production: Blood cells are produced within red bone marrow (hematopoeisis)  Store Minerals: Minerals such as calcium and phosphorus, etc. are stored in bone matrix

3.  Many tissues are contained within bones ◦ Bone tissue ◦ Nervous tissue (nerves) ◦ Blood vessels (and blood) ◦ Cartilage ◦ Dense connective tissue

4.  There are 5 types of bones:  Long (ex: femur)  Short (ex: carpals)  Flat (ex: scapula)  Irregular (ex: vertebrae)  Sesamoid (ex: patella)

5.  Those classified as Long Bones must meet this criteria: ◦ Must have a body (diaphysis) that is longer than it is wide; Diaphysis must have a hard covering (periosteum) made of compact bone ◦ Must have growth plate (epiphysis) at either end; Epiphysis must contain marrow and be made of spongy bone with a thin covering of compact bone  Example: femur, humerus

6.  Epiphysis: Expanded end of bones that form joints with adjacent bones ◦ Covered by articular cartilage (hyaline) at the joint  Diaphysis: The long shaft of the bone ◦ Covered in compact bone

7.  The epiphysis is at the end of long bones.  The epiphyseal plate is the part of the epiphysis where lengthwise bone growth occurs.  Usually referred to as ‘the growth plate’.  The epiphyseal plates fuse in early adulthood and no further lengthening of the bones occurs.

8.  The diaphysis is the long, shaft portion of a long bone.  The diaphysis contains a hollow medullary cavity that is lined with endosteum and filled with marrow.  A tough layer of vascular connective tissue, called the periosteum, covers the bone and is continuous with ligaments and tendons.

10.  There are two types of bone marrow: ◦ Red Bone Marrow-responsible for the production of red blood cells, white blood cells and blood platelets; is found in spongy bone (epiphysis) ◦ Yellow Bone Marrow-stores fat and is not active in blood cell production; found in the medullary cavities

12.  Ends of long bones: ◦ Epiphyses  Shaft of long bones: ◦ Diaphysis  Inner cavity of long bones: ◦ Medullary Cavity  Outer covering of bones: ◦ Periosteum  Inner covering of medullary cavity: ◦ Endosteum

13.  Osteoblasts are cells that build bone tissue ◦ They become active in connective tissue membranes and deposit bone matrix around themselves-this leads to the branching appearance of spongy bone  Osteoclasts destroy bone tissue by secreting acid that dissolves the inorganic bone matrix  These two cells usually work well together but malfunctions can lead to bone cancer

14.  Bone cells called osteocytes are located within spaces called lacunae that lie in concentric circles around Haversian canals that contain blood vessels, and nerves  These systems are organized into columns called osteons that are cemented together

15.  These osteonic/Haversian systems contain blood vessels & nerve fibers and extend longitudinally through bone  Osteonic canals are interconnected by transverse perforating canals (Volkmann’s canals).

16.  Scientists like to name things after themselves…  Haversian canals=central canals ◦ run longitudinally through bone  Volkmann’s canals=perforating canals ◦ these are transverse canals that run between individual Haversian systems

18.  Osteocytes are scattered in no particular order and pass nutrients and wastes back and forth in passageways in the matrix called canaliculi.  Important sites for spongy bone include: ◦ the skull ◦ the ribs ◦ the vertebrae ◦ the sternum

19.  Compact bone ◦ Osteocytes and extracellular matrix cluster around Haversian canals ◦ Many of these units cemented together makes up compact bone  Spongy bone ◦ Also composed of osteocytes and extracellular matrix, but the units do not aggregate around canals ◦ They form cross connections called trabeculae

20.  The intercellular material consists of collagen and inorganic salts. ◦ Calcium Phosphate & Calcium Carbonate  Most bones contain a mixture of compact and spongy bone ◦ the epiphyses of long bones all contain spongy bone covered by compact bone ◦ the diaphysis of a long bone is made of compact bone

22.  Bones begin to form during the first few weeks of prenatal development  Bones form in one of two ways ◦ Intramembranous bones originate between sheet- like layers of connective tissues ◦ Endochondral bones begin as masses of cartilage that ossify

23. 1. Membrane like layers of connective tissue appear at the site of future bones (ex: skull) 2. Cells differentiate into osteoblasts 3. Osteoblasts deposit bony matrix around themselves 4. Cells outside the developing bone give rise to the outer periosteum 5. Osteoblasts on the inside of the bone form the outer compact covering over spongy bone 6. Osteocytes form when extracellular matrix completely surrounds osteoblasts

24. 1. Hyaline Cartilage forms at the site of future bones 2. Cartilage grows and begins to change 3. Blood vessels invade the tissue 4. Osetoblasts form spongy bone at the primary ossification center of the diaphysis 5. Secondary ossification occurs in the spongy bone of the epiphyses 6. The epiphyseal plate separates the two ossification centers 7. Accumulation of the bone cells forces the death of the cartilaginous cells

25. 8. Bones continue to lengthen while cartilaginous cells of the epiphyseal plate are active 9. Bone growth ceases when the primary and secondary ossification centers meet

26.  Epiphyseal (growth) plates are responsible for lengthening bones while increases in thickness are due to intramembranous ossification underneath the periosteum.  A medullary cavity forms in the region of the diaphysis due to the activity of the cells called osteoclasts.

27.  Osteoclasts and osteoblasts remodel bone tissue throughout life  Hormones that regulate blood calcium (PTH- Parathyroid Hormone and calcitonin) help control resorption and deposition of bone matrix

28.  Bones shape, support, and protect body structures  Bones aid in body movement  Bones house tissues that produce blood cells and store salts

29.  Supporting weight: bones of the lower limbs, pelvis, and backbone  Protecting the senses: bones of the skull protect the eyes, ears, and brain  Vital organ protection: bones of the thoracic cavity and pectoral girdle protect the heart and lungs  Reproductive organs: protected by the pelvic girdle

30.  Blood cell formation begins in the yolk sac  As a fetus grows, blood cells are manufactured in the liver and spleen ◦ The liver does not perform digestive processes because the fetus does not consume meals directly, but receives nourishment from the mother via the placenta  After birth, blood cells form in bone marrow ◦ Which kind?

31.  The thyroid gland regulates blood calcium levels via two hormones  When blood calcium is low, parathyroid hormone (PTH) stimulates osteoclasts to break down bone tissue to release calcium salts  When blood calcium is too high, calcitonin stimulates osteoblasts to form bone tissue, storing excess calcium salts

32.  Bones are good accumulators of heavy metals such as lead, radium, or strontium (bad news)

33.  The use of lead-based paints for homes, children's toys and household furniture has been banned in the United States since 1978  Lead-based paint is still on walls and woodwork in many older homes and apartments  Lead is sometimes found in toys and other products produced abroad

34.  A fracture is a break in a bone  Blood vessels within the bone and the periosteum rupture forming a 1)hematoma  Fibrocartilage fills in the gap between the ends of the broken bone with a 2)cartilaginous callus  Osteoblasts and osteoclasts go to work and the cartilaginous callus breaks down and a 3)bony callus fills the space

35.  Bone healing can be aided by doctors ◦ First cast used in Philadelphia in 1876 ◦ More recently, screws and plates have been used to internally align healing bones parts ◦ Rods, wires and nails are used by surgeons today  They are lighter and smaller and usually built of titanium

36.  Greenstick: an incomplete fracture usually occurring in the developing bones of children

37.  Compound: a severe fracture in which the bone breaks through the skin

38.  Comminuted: a fracture in which the bone is broken into several pieces