LECTURE 7 Flashcards
Why is it that a particular bone, such as the humerus, is considered to be an organ?
They consist of multiple tissue types that are working for the same general purpose.
List and briefly describe four of the many components of the skeletal system.
- 206 bones
- Three types of cartilage
- Ligaments (bone to bone)
- red & yellow bone marrow
- Blood and nervous tissue
3 types of cartilage in the body
hyaline cartilage
elastic cartilage
fibrocartilage
Functions of the skeletal system
- Support: Of muscles, teeth, and body as a whole
- Mineral/energy storage, and ion balance: Calcium and phosphate. Yellow bone marrow has lipids to store energy.
- Hemopoiesis: Aka hematopoiesis. Blood cell production in red marrow.
- Protection: cranial bones protect the brain, vertebral column protects the spinal cord. Protects CNS, thoracic and pelvic viscera, and bone marrow.
- Locomotion: Skeletal muscles act on bones allowing for movement around articulations.
Name the two ways that the bones of the body are classified.
- structure/shape
- internal composition (compact/spongy)
Longer than wide. Shaft and two ends. Most important for movement.
(femur, humerus, radius, ulna, tibia, fibula)
long bones
Roughly cube-shaped
(wrist in carpals, ankle in tarsals)
short bones
Thin, flat, and often curved
(sternum, scapulae, ribs, hip, and skull bones)
flat bones
Found between sutures of skull bones. Small, numerous, and irregularly shaped. Not included in the 206 bones.
(coronal, sagittal, squamous, lambdoid sutures)
sutural bones
Complex shapes with processes. Vertebrae, ethmoid bone (separates the nasal cavity from the brain), and sphenoid bone from the skull.
irregular bones
Small bones formed in tendons. In the shape of a sesame seed.
Patellas- largest sesamoid bones, and only ones included in 206 bones
sesamoid bones
Shaft of the long bone. Walls made of compact bone (dense bone)
diaphysis
The head of the long bone. Distal and proximal ends. Wall is compact and the interior is spongy bone. Red marrow found in spongy bone.
Articular cartilages (hyaline that lack perichondrium) cover articular surfaces of epiphyses.
epiphyses
-a hollow space to the interior of diaphysis
-Yellow marrow found here. Was red marrow as a child. Can revert back to red marrow in severe anemia to produce more red blood cells
-Tiny amount of spongy (cancellous) bone close to medullary cavity
medullary cavity
“growth plate” made of hyaline cartilage
epiphyseal plate
very dense spongy bone, used to be an epiphyseal plate
epiphyseal line
Describe the distribution of both compact and spongy bone in a typical long bone.
Compact bone lines the entire outer surface
Spongy bone within, especially in the epiphysis.
There is a little lining of spongy bone within the diaphysis around the medullary cavity.
Describe the distribution of both yellow and red bone marrow in a typical long bone
(Describe the composition and functions)
RED BONE MARROW
-typically found in the proximal epiphysis.
-reticular connective tissue
-produces blood.
YELLOW BONE MARROW
-in the medullary cavity and distal epiphysis
-adipose tissue
-energy storage
Describe the make-up of a typical flat bone
2 layers of compact bone. Outer compact bone, spongy bone (diploe), inner compact bone
Why is it difficult to completely break through one of the flat bones of the skull?
because the outer bone may take initial force and crack, but the diploe is excellent at dispersing the force of an impact, so that the interior compact bone is typically left intact.
outer surface of compact bone
periosteum
structure of a periosteum
White collagenous fibers. Blood vessels are prominent in the periosteum and enter matrix through nutrient foramina to allow for exchange of materials. Lymph vessels and nerves present in bone travel through the periosteum and enter bone.
periosteum layers and cell types
Outer fibrous layer of dense irregular connective tissue. Perforating fibers from the outer layer enter the bone matrix to have a solid connection to the bone.
Inner cellular layer that has 3 of the 4 cell types. Those cell types include: osteogenic (osteoprogenitor) cells, osteoblasts, and osteoclasts.
You do NOT find the osteocytes in the periosteum.
functions of periosteum
Outer layer serves as an attachment for tendons and ligaments. Inner layer allows for remodeling and healing of fractures. Inner layer makes a bone matrix or breaks it down.
location of endosteum
-Any open spaces in the bone are going to be lined with the endosteum. -lines medullary cavities of long bones
-Surrounds trabeculae of spongy bone
-Lines canals of compact bone.
structure of endosteum
Analogous to the osteogenic layer of periosteum, but technically made of reticular connective tissue.
endosteum layers and cell types
Osteogenic cells, osteoblasts, and osteoclasts are located here
functions of endosteum
bone growth, repair, and remodeling
stem cells that give rise to osteoblasts
derived from mesenchymal cells and located in both bone membranes
osteogenic cells
(osteoprogenitor) cells
(Mesenchymal cells -> osteogenic cells)
Build new bone matrix.
Cuboidal cells that line up like epithelium in the osteogenic layer of the periosteum, and in the endosteum. Amitotic, so osteogenic cells multiply in damaged areas of bone, and then differentiate.
osteoblasts
(Mesenchymal cells -> osteogenic cells -> osteoblasts)
Mature bone cells that maintain the existing bone matrix
Formed when osteoblasts surrounds self with matrix to form a lacuna. Communicate with neighboring osteocytes with cytoplasmic processes and gap junctions. Sense bone stress and release chemical signals that result in bone remodeling by other cells.
osteocytes
(Mesenchymal cells -> osteogenic cells -> osteoblasts -> osteocytes)
Not related to the previous 3 cell types.
- Osteoclasts secrete enzymes and acids to break down existing bone matrix along the borders of cellular periosteum and endosteum. They use hydrochloric acid and enzymes.
- Large, multinucleate, and derived from the fusion of up to 50 monocytic stem cells.
- Think of them like macrophages for the bone, but instead of breaking down bacteria, they break down bone matrix.
- Have a ruffled border which increases SA for dissolving matrix. Osteoclasts have calcium receptors that are stimulated by declining calcium.
- Pump hydrogen ions across ruffled border and chloride ions follow.
- Acid phosphatase from osteoclasts digest collagen matrix.
- Balance between activity of osteoblasts and osteoclasts is important in bone remodeling
osteoclasts
Describe the composition of bone extracellular matrix (ECM).
What are the approximate percentages of the entire ECM for each of the main components?
- Osseous tissue is 35% organic (cells, collagen - primary ingredient, GAGs, proteoglycans, etc.)
- Remaining 65% is inorganic (calcium phosphate salts, main one being hydroxyapatite)
Why are both the main components of bone ECM needed for healthy and strong bones?
What effect does breaking down the hydroxyapatite in bone have on the organ?
What technique could one use to do this?
What effect does breaking down the collagen in bone have on the organ?
What technique could one use to do this?
- Think of bone as steel-reinforced concrete where collagen is like the steel rebar and the concrete is the calcium phosphate salt hydroxyapatite.
- Calcium can be compressed, but cannot withstand bending or twisting
- Collagen can withstand bending/twisting, but doesn’t compress much
- Without the protein bone will not bend and will shatter, but without the salts, bones are limp. The two components compliment each other.
- Ratio of protein to salt varies throughout bone, in relation to stress
- Breaking down the hydroxyapatite would make the bone soft and flexible, this could be done by soaking the bone in vinegar (the acetic acid would break down the calcium phosphate salt)
- Breaking down the collagen in bone would cause it to be rigid and shatter when dropped, this could be done by baking the bone in the oven (the heat would denature the collagen protein)
Arranged in circular layers of matrix known as concentric lamellae
osteons
(Haversian system) is a functional unit of compact bone.
-Surround a central (Haversian) canal
-Lamellae have alternating orientations of collagen fibers for added strength.
concentric lamellae
contains blood vessels, nerves, and lymphatics
central canal
(Volkmann’s) travel transversely or diagonally and connect adjacent central canals
perforating canal
Found near periosteum and endosteum, very outer layers that encompass the entire circumference of the shaft of the long bone for example. They are also found along the marrow cavity.
circumferential lamellae
-incomplete lamellae that you find situated between adjacent osteons
-remnants of old osteons.
interstitial lamellae
small cavities that contain osteocytes
lacunae
Small channels across lamellae which connect lacunae. Can pass nutrients and electrical communication.
canaliculi
Describe the composition of spongy bone
Define trabeculae
- Spongy bone is sandwiched between layers of compact bone. Matrix composition is the same for both.
- Red marrow is found in spongy bone (some of it also has yellow marrow)
- Trabeculae: struts and plates of bone that form lattice of spongy bone. Built to resist stress from multiple angles.
- Contains osteoblasts, osteoclasts, osteocytes, lamellae, canaliculus
- No osteons are present in trabeculae
Struts and plates of bone that form lattice of spongy bone. Built to resist stress from multiple angles.
trabeculae
