Bone Structure and Functions
Terms in this set (70)
Composed of bones, cartilages, and ligaments joined tightly to form a strong, flexible framework for the body.
Forerunner for most bones in embryonic development; forms a growth zone in the bones of children; and it covers many joint surfaces in the mature skeleton
Collagenous bands that hold bones together at the joints.
Structure similarly to ligaments but attach muscle to bone.
Soft bloody or fatty material enclosed in the bones.
Functions of the Skeletal System
Support, Protection, Movement, Blood Formation, & Electrolyte Balance
The hard, calcified tissue of a bone
Osseous tissue is made up of:
Compact (dense) & spongy bone
Compact (dense) bone
Solidly filled with opaque matrix
Porous lattice honeycombed with spaces. Always found in interior of a bone.
4 Kinds of Bone Cells:
Osteogenic, Osteoblasts, Osteocytes, & Osteoclasts
Occur on bone surface, beneath the fibrous connective tissue membranes that cover a bone. Stem cells that give rise to osteoblasts. Only bone cells capable of dividing and making more bone cells.
Develop from osteogenic cells & lie in a single layer on the bone surface.
Have an active role in adults and produce bone matrix
Synthesize the organic matter of bone and deposit matrix. Has lots of mitochondria and rough endoplasmic reticulum.
Former osteoblasts that have become trapped in the matrix they deposited.
Resides in cavities called lacunae (pocket within matrix), which are connected to each other by slender channels called canaliculi.
Pass nutrients, wastes, and chemical signals to each other through gap junctions at the tips of their cytoplasmic processes.
Bone-dissolving cells that develop from a separate line of bone marrow stem cells.
Very large, have multiple nuclei, & lie on the bone surface like osteoblasts.
Often lies in pits that they have eroded into bone surface.
Develop from macrophage-like cells
Degrade bone matrix
On side facing the bone, an osteoclast has an unusual comb like row of infoldings of the plasma membrane.
On this surface the cell secretes hydrochloric acid and enzymes to dissolve osseous tissue.
The stony matter that surrounds the osteocytes and lacunae.
⅓ Organic & ⅔ inorganic matter by weight.
Organic matter of bone matric
Collagen & large protein-carbohydrates complexes
Inorganic matter of bone matric
85% calcium phosphate, w/ lesser amounts of calcium carbonate, magnesium, potassium, and fluoride.
Gives bone flexibility and strength.
Rickets & osteomalacia
Minerals resist compression and mineral-deficient can results in easily deformed bones of childhood rickets and the similar adult disease osteomalacia.
Spongy (cancellous) bone
Consists of trabeculae
Permeated by tiny spaces that give it a sponge-like appearance
These spaces are filled w/ bone marrow & small blood vessels
Trabeculae align along planes that give the bone the best strain resistance.
All osteocytes are close to the blood supply in the marrow cavity, so no need for central canals or osteons.
Porous lattice of slender rods and plates; trabeculae align along planes that give the bone the best strain resistance.
Compact (dense) bone
Forms outer shell that surrounds the spongy bone.
Prevents bone marrow from seeping out and provides solid attachment surfaces for muscles, tendons, & ligaments.
Look like onion slices - layers called lamellae arranged concentrically around a central (osteonic or haversian) canal.
Canal = small blood vessels & nerves.
Occupy lacunar b/w the lamellae.
Osteons (haversian systems)
Deeper in compact bone and is organized in cylindrical units
Look like onion slices - layers
Leverage & movement
Covered with articular cartilage, the distal and proximal portions at each end of a typical long bone
Shaft or diaphysis
Elongated midsection; Provides leverage
Head or epiphysis
Each expanded end of bone
Enlarged to strengthen a joint and provide added surface area of the attachment of tendons and ligaments
Ends where two bones meet are covered w/ a thin layer of hyaline cartilage called the articular cartilage (eases join movement).
Bone marrow occupies the medullary cavity of the shaft and the spaces in the spongy bone of the head.
Of an adult bone mark the former growth zones of the child's bone
Protective armor-like plates covering delicate organs beneath, such as the sternum anterior to the heart and the cranial bones enclosing the brain.
Short & irregular bone
Bones that neither fit the description of neither long nor flat bones (i.e. wrist bone & vertebrae)
A fibrous sheath that covers the bone externally
Covers both sides of a flat bone (i.e. skull)
Connective tissue that wraps around bone
A thin layer of reticular connective tissue.
Covers spongy bone trabeculae in the middle layer.
Red bone marrow
Produce blood cells & platelets
Has more limited distribution in adults
Yellow bone marrow
Dominates in long limbs bones of adults
The formation of bone; Two types of ossification & both begins w/ a soft embryonic connective tissue called mesenchyme (forerunner of adult bone, muscle, blood, and many other tissues b/w skin & gut)
Direct, within membranes (flat bones of the skull)
Produces the flat bones of the skull and most of the clavicle (collarbone).
The method of depositing new tissue on the bone surface even past the age where our bones can no longer grown in length.
Step 1 of intramembranous ossification
An ossification center occurs within the embryonic tissue where mesenchymal cells cluster together, differentiate into osteoblasts, and secrete bone matrix. Some of the osteoblasts become trapped in the bone matrix and become osteocytes.
Step 2 of intramembranous ossification
Blood vessels grow into the area to supply the cells and matrix with oxygen and nutrients. These blood vessels get trapped within the developing bone.
Step 3 of intramembranous ossification
The bone assumes a foundation of spongy bone
Step 4 of intramembranous ossification
Remodeling creates compact bone and the finalized form of the bone
Indirect, replacing hyaline cartilage (most of the skeleton below the head)
Produces most other bones, including the vertebrae, ribs, scapulae, pelvic bones, bones of the limb, & some parts of the skull.
Method in which mesenchyme first transforms into a hyaline cartilage "model" in the approximate shape of the bone to come.
Cartilage is then broken down and replaced by osseous tissue.
Step 1 of endochondral Ossification
Early cartilage model
Forerunner of future bone is a body of hyaline cartilage that approximate its shape. Covered w/ a fibrous perichondrium.
Step 2 of endochondral Ossification
Formation of Primary ossification center, bony collar, and periosteum
Cartilage cells begin the process of dying
They enlarge and die, leaving behind open space
Primary ossification center
Near the middle of this cartilage, chondrocytes begin to inflate & die, while the thin walls b/w them calcify.
Step 3 of endochondral Ossification
Blood vessels grow inward from the periosteum and invade the ossification center.
Osteoclasts arrive & digest calcified tissue in the shaft, hollowing it out and creating the primary marrow cavity. Also deposit layers of bone lining the cavity, thickening the shaft.
Secondary ossification center develops at one end of the bone.
vascular invasion: Blood vessels coming in
Step 4 of endochondral Ossification
At each end of the primary marrow cavity is a transitional zone called a metaphysis - where cartilage is undergoing replacement by bone (undergo cartilage tissue to bone tissue)
Appearance of secondary marrow cavity
Where cartilage is undergoing replacement by bone.
Step 5 of endochondral Ossification
Childhood & adolescence - the primary & secondary marrow cavities are separated by a wall called the epiphyseal plate.
Consists of a middle layer of hyaline cartilage w/ metaphysis on each side. The plate functions as a growth zone enabling the individual to grow in limb length and height.
Step 6 of endochondral Ossification
Late teens to early twenties → Reserve cartilage in the epiphyseal plate is depleted and the primary & secondary marrow cavities are no longer separated.
Only remnant of the original cartilage model is the articular cartilage that covers the joint surfaces of the bone.
Bone elongation results from cartilage growth
Inter = Inside
Chondrocytes multiply, enlarge, & secrete new matrix b/w them.
Bone elongation results from cartilage growth
When bone can then no longer grow & the epiphyseal plate leaves behind an internal mark
Deposition of new bone/cartilage on the surface of existing cartilage/bone
Appositional = Around the outside
A crystallization process in which osteoblasts extract calcium, phosphate, and other ions from the blood and deposit them in the osseous tissue.
A process in which the osteoclasts dissolve bone, releasing minerals into the blood and making them available for other uses.
Calcium deficiency → Causes dysfunctions ranging from muscle tremors to tetanus - inability of muscle to relax.
Calcium excess → depresses nervous, muscular, and cardiac function.
Calcium homeostasis is regulated by 2 hormones:
Calcitriol & parathyroid hormones (PTH) - both raises blood calcium levels.
Release when Ca is low
The most active form of vitamin D.
Raises blood calcium by promoting calcium absorption from digested food, reducing urinary loss of calcium, & stimulating osteoclasts to release calcium from the bones to the blood.
Also necessary for bone deposition because w/o its effects on the kidneys and small intestine, blood calcium levels are too low for normal deposition.
Parathyroid hormone (PTH)
Secreted by the parathyroid glands, which adhere to the posterior surface of the thyroid.
Respond to drop in blood calcium level by secreting PTH. PTH them stimulates bone resorption by osteoclasts, promotes calcium reabsorption by the kidneys, and promotes calcitriol synthesis.
Secreted by the thyroid gland in response to elevated blood calcium levels.
Promotes deposition of the excess calcium into the skeleton and thereby lowers the blood calcium level.
Has little influence on adult bone, but regulates blood calcium in children and may help to reduce bone loss in pregnant women.
Where dendrites reside
Pocket within matrix
Osteogenesis imperfecta (brittle bone disease)
Excessively brittle bones resulting from improperly formed collagen
Releases minerals into blood
Architecture of bone determined by mechanical stresses placed on it and bones adapt to withstand those stresses
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