Introduction to the Skeletal System. Support: Bones support the weight of the body and structures...
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Transcript of Introduction to the Skeletal System. Support: Bones support the weight of the body and structures...
Chapter 7 Part 1Introduction to the Skeletal System
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
All About Bones
Many tissues are contained within bones◦ Bone tissue◦ Nervous tissue (nerves)◦ Blood vessels (and blood)◦ Cartilage ◦ Dense connective tissue
Tissues Within Bones
There are 5 types of bones: Long (ex: femur) Short (ex: carpals) Flat (ex: scapula) Irregular (ex: vertebrae) Sesamoid (ex: patella)
Five Types of Bones
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
Long Bones
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
Long Bone Structure
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.
Epiphyseal Plate
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.
Diaphysis & Periosteum
Bone Marrow 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
Bone Marrow Transplant Clip
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
REVIEW
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
Blast vs. Clast
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
Microscopic Structure of Compact Bone
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).
Microscopic Structure of Compact Bone (continued)
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
Canals, canals, canals
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
Microscopic Structure of Spongy Bone
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
Compact vs Spongy Bone
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
Similarities
Bone Development & Growth 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
1. Membrane like layers of connective tissue appear at the site of future bones (ex: skull)2. Cells differentiate into osteoblasts3. Osteoblasts deposit bony matrix around themselves4. 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 bone6. Osteocytes form when extracellular matrix completely surrounds osteoblasts
Intramembranous Bone Formation
1. Hyaline Cartilage forms at the site of future bones2. Cartilage grows and begins to change3. Blood vessels invade the tissue 4. Osetoblasts form spongy bone at the primary ossification center of the diaphysis5. Secondary ossification occurs in the spongy bone of the epiphyses6. The epiphyseal plate separates the two ossification centers7. Accumulation of the bone cells forces the death of the cartilaginous cells
Endochondral Bone Formation
8. Bones continue to lengthen while cartilaginous cells of the epiphyseal plate are active9. Bone growth ceases when the primary and secondary ossification centers meet
Endochondral Bone Formation (continued)
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.
In summation…
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
Homeostasis of Bone Tissue
Bones shape, support, and protect body structures
Bones aid in body movement Bones house tissues that produce blood
cells and store salts
Bone Function
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
Support & Protection
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?
Hematopoiesis
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
Inorganic Salt Storage
Bones are good accumulators of heavy metals such as lead, radium, or strontium (bad news)
Poison Storage
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
Lead Poisoning
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
Fractures
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
Fractures (continued)
Greenstick: an incomplete fracture usually occurring in the developing bones of children
Types of Fractures
Compound: a severe fracture in which the bone breaks through the skin
Types of Fractures
Comminuted: a fracture in which the bone is broken into several pieces
Types of Fractures