Chapter 7: Bone Tissue Flashcards
1
Q
Bone Tissue
A
- often associated with death
- bones and teeth are durable and remain once other tissues are gone
- a living skeleton is made of dynamic tissue, full of cells, and permeated with nerves & blood vessels
2
Q
Tissues and Organs of the Skeletal System
A
- Osteology: the study of bones.
- the skeletal system consists of:
- bones
- cartilage:
forerunner of
most bones;
covers many joint
surfaces of mature
bones
- ligaments:
holds bones
together at joints - (tendons attach to muscles at bones)
3
Q
Functions of the Skeleton
A
- support: holds up the body, supports muscle and teeth (mandible and maxilla)
- protection: brain, spinal cord, heart, lungs
- movement: action of muscle on bone enables limb movement and breathing
- electrolyte balance: calcium and phosphate ions
- acid-base balance: buffers blood against excessive pH changes
- blood formation: red bone marrow is the chief producer of blood cells
4
Q
Bones as Organs
A
- individual bones are organs that consist of bone tissue plus blood, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.
- metabolically active
- permeated with nerves and blood vessels, which attest to its sensitivity and metabolic activity.
- constantly changing in response to the environment
- interacts physiologically with all the other organ systems
5
Q
Categories of Bones (the organs)
A
- flat bones: curved but wide and thin; protects soft organs (brain)
- long bones: longer than wide; rigid levers acted upon by muscles
- short bones: equal in length and width; glide across one another in multiple directions
- irregular bones: elaborate shapes don’t fit into any category; unity of shape and function
6
Q
features of long bones
A
- epiphysis: enlarged end of long bone
- strengthens joint and allows room for ligaments and tendons to attach
- diaphysis (shaft): cylinder of compact bone to provide leverage
- epiphyseal plate (growth plate): area of hyaline cartilage between marrow spaces of the epiphysis and diaphysis
- epiphyseal plate: in children/young people
- epiphyseal line: in adults (a bony scar left where the growth plates used to be)
7
Q
features of long bone cont.
A
- articular cartilage: layer of hyaline cartilage that covers the surfaces of joints (where bones meet)
- allows joints to move more freely and relatively friction-free
- nutrient foramina: minute holes in the bone surface that allow blood vessels to penetrate
- medullary (marrow) cavity: marrow-containing chamber in diaphysis
8
Q
feature of long bone cont.
A
- periosteum: external sheath, covers bone except where there is articular cartilage
- outer fibrous layer
- strong link between bone –> tendon–> muscle
- inner osteogenic layer
- bone-forming cells important to growth of bone and healing of fractures
- outer fibrous layer
- endosteum: thin layer of reticular connective tissue lining the medullary cavity and covering spongy bone tissues
9
Q
General Features of Flat Bone
A
- sandwich-like construction
- 2 layers of compact bone enclosing a middle layer of spongy bone
- both surfaces of flat bone covered with periosteum
- diploe: spongy layer in cranium
- absorbs shock
- marrow spaces lined with endosteum
10
Q
Composition of Bone (Osseous) Tissue
A
- connective tissue with few cells, lots of matrix
- matrix: 1/3 organic, 2/3 inorganic
- organic materials: collagen and protein-carbohydrate complexes
- collagen fibers synthesized by bone building cells (osteoblasts)
- gives bones some flexibility
- osteogenesis imperfecta (brittle bone disease): defect in collagen deposition
- inorganic materials: minerals
- 85% hydroxyapatite (crystallized calcium phosphate salt)
- 10% calcium carbonate (plus some F, Na, Mg, etc. ions)
- gives bone strength
- rickets = diminished mineral deposition (due to vitamin D deficiency)
–> soft bones
11
Q
two types of bone tissue
A
- compact bone: dense outer shell of bone
- spongy (cancellous) bone: under the compact bone in the ends of long bone and in the middle of other bones. space is filled with marrow
- together these make bone strong with minimal weight
- 3/4 of skeletal dry weight is from compact bone
12
Q
compact vs spongy bones
A
- compact bone is composed of osteons
- spongy bone has few osteons, bone tissue is in thin spicules and trabeculae with spaces between
13
Q
histology of compact bone
A
- each osteon is actually cylinder of matrix tissue organized around the central canal
- collagen fibers wrap around in opposite directions, making it stronger
- perforating (Volkmann) canal: diagonal canals that connect central canals to each other
14
Q
histology of compact bone cont.
A
- osteon: the structural and functional unit of the bone
- concentric lamellae: layers of matrix, laid in concentric circles around a central canal
- central canal (haversian or osteonic canal): contains blood vessels and nerves
- osteocytes in lacunae
- slide of compact bone contains matrix but no cells
- osteocytes are destroyed in the slide-making process
- empty lacunae are left behind
15
Q
histology of spongy bone
A
- spongy bone consists of: slivers of bone called spicules, thin plates of bone called trabeculae, spaces filled with red bone marrow
- provides strength with minimal weight
- few osteons and no central canal
- all osteocytes are close to bone marrow
16
Q
bone marrow
A
- soft tissue that occupies the marrow cavities in bone
- red bone marrow: occupies the empty spaces within the spongy bone, produces blood cells (hemopoietic), in almost every bone of children, in adult: persists of skull, vertebrae, ribs, sternum, hips, proximal heads of humorous and femur
- yellow marrow: in adults, replaces red marrow in rest of skeleton; becomes fatty, no more hemopoiesis
17
Q
bone cell types
A
- osteogenic cells, osteoblasts, osteocytes
- same cells at different stages of differentiation
- builds bone
- osteoclasts: develop from different stem cells (in marrow); dissolve bone
- osteogenic cell: type of cell found in endosteum and inner periosteum; multiply continuously to produce new osteoblasts
- osteoblasts: differentiated, non-mitotic bone-forming cells; single layer of cells under endosteum and periosteum; synthesizes soft organic matter matrix (collagen) to be hardened by mineral deposition
18
Q
bone-forming by osteoblasts
A
- osteoblasts produce collagen fibers that spiral the length of the osteon
- mineral deposition: calcium, phosphate and other ions from blood plasma (via. tissue fluid) are spontaneously deposited along the collagen fibers as these minerals precipitate (come out of solution)
- form hydroxyapatite crystals
- the matrix hardens as the collagen fibers become encrusted with the crystals
19
Q
osteocytes
A
- former osteoblasts that have become trapped in the hardened matrix they have deposited
- lacunae: tiny cavities where osteocytes reside
- canaliculi: cytoplasmic channels that allow communication between lacunae
20
Q
osteoclasts
A
- bone-dissolving cells on bone surface
- develop from the bone marrow stem cells that give rise to blood cells (not osteogenic cells)
- formed from the fusion of several stem cells
- typically, very large; have 3-50 nuclei
- sit in resorption bays which are pits on the surfaces of bone
21
Q
mineral deposition and resorption
A
- mineral deposition/resorption exerts a profound influence over the rest of the body by exchanging minerals with tissue fluid (tissue fluid occupies space that is not in blood vessels nor within cells)
- mineral deposition: Ca^2+ (calcium ion) and PO4^3- (phosphate ion) concentration in tissue fluid + various other signals > crystal formation
- first few crystals (seed crystals) attract more and more calcium and phosphate from solution (positive feedback!!)
- ectopic ossification: abnormal calcification occurring in lungs, brain, eyes, muscles, tendons, or arteries (arteriosclerosis)
- calculus: calcifies mass in a soft organ such as the lung
22
Q
mineral deposition and resorption cont.
A
- mineral resorption: the process of dissolving bone and releasing minerals into tissue fluid –> blood
- performed by osteoclasts at their ruffled borders
- hydrogen pumps in membranes secrete H+ into space between the osteoclasts and bone surface
- chloride ions follow by electrical attraction
- hydrochloric acid (HCI, pH 4) dissolves bone minerals
- protease enzyme digests the collagen
- orthodontic appliances (braces) reposition teeth: tooth moves because osteoclasts dissolve bone ahead of the tooth & osteoblasts deposit bone behind the tooth
23
Q
ossification (osteogenesis)
A
- formation of bone; development and growth of bone that starts in the human fetus
bone develops by two methods: - endochondral ossification: develops from hyaline cartilage model mesenchyme (embryonic CT) –> hyaline cartilage –> bone; produces most bones (limbs, pelvic girdle, ribs, etc.); occurs from 6 weeks (fetal development) until full height is achieved
- intramembranous ossification: develops from mesenchyme surrounding blood vessels; produces flat bone of the skull and clavicle.
24
Q
endochondral ossification
A
- early cartilage model: mesenchyme develops into area of hyaline cartilage covered by perichondrium which chondrocytes
- chondrocytes inflate, calcify & die leaving cavity; perichondrium is now periosteum, creates osteoblasts which deposits a ring of bone
- osteoclasts arrive & dissolve calcifies cartilage; osteoclasts thicken the outer bone
- At birth: chondrocytes death has also occurred at an epiphysis, forming a secondary marrow cavity
- in infancy and childhood: epiphyses fill with spongy bone; remaining cartilage = epiphyseal plate and articular cartilage
25
intramembranous ossification
1. mesenchyme cells line up around blood vessels, become osteoblasts; secrete osteoid tissue (includes collagen fibers)
2. minerals crystalize on collagen fibers; osteoblasts become osteocytes
3. continue mineralization --> spongy bone; mesenchyme at surface forms periosteum
4. osteoblasts beneath periosteum form zone of compact zone
26
Flat bones
- flat bones of the skull are formed by intramembranous ossification
27
Bone growth: elongation
- in long bones, interstitial growth (interior growth) occurs at the epiphyseal plate
- in the x-rays of long bone
- x-ray shows epiphyseal in a child's hand
- cartilage is precursor to bone
- hyaline cartilage calcified and is replaced by bone
- lengthening of long bones continues as long as the epiphyseal plates have cartilage
- until about 16-20 yrs old (different ages for different bone)
28
metaphysis
- transition area found on either side of the epiphyseal plate
29
zones of the metaphysis
1. zone of reserve cartilage: typical histology of resting hyaline cartilage
2. zone of cell proliferation: chondrocytes multiplying and lining up in rows of small flattened lacunae
3. zone of cell hypertrophy: cessation of mitosis, enlargement of chondrocytes & removing of lacuna walls
4. zone of calcification: temporary calcification of cartilage matrix between columns of lacunae
5. zone of bone deposition: breakdown of lacuna walls, leaving open channels; death of chondrocytes; bone deposition by osteoblasts, forming trabeculae of spongy bones
30
transformation
- growing bone to adult bone
- by late teens to early 20s, all remaining bone in the epiphyseal plate
- gap between epiphyses and diaphysis closes leaving behind an epiphyseal line
- single marrow cavity
- no more increase in height
31
dwarfism
achondroplastic dwarfism:
- long bones stop growing in childhood
- normal torso; short limbs
- failure of cartilage growth in metaphysis
- due to spontaneous DNA mutation
pituitary dwarfism:
- lack of growth hormone
- normal proportions with short stature
32
bone growth: widening and thickening
appositional growth = new bone tissue at surface
- this type of growth occurs throughout life
- occurs by intramembranous ossification
deposition of new bone occurs when osteoblasts on the inner side of periosteum deposit osteoid tissue.
- osteoblast become trapped as the tissue calcifies
- matrix is laid down in layers parallel to surface form circumferential lamellae over surface
as bone widens, osteoclasts dissolve bone tissue to increase the marrow cavity
33
bone remodeling
a mature bone remains metabolically active
- involved in its own growth and constant remodeling
collaborative effort between osteoblasts (bone builders) & osteoclasts (bone dissolves)
wolfs law of bone: architecture of bone is determined by mechanical stresses placed on it
- trabeculae develop along the bones lines of stress
- bony processes grow larger in response to mechanical stress
34
bone remodeling cont.
10% of skeleton is remodeled each year.
- renew old bones, repair microfractures, release minerals into the blood
osteoblasts strengthen bone
- increase in number with stress and fractures because osteogenic cells are stimulated to produce more osteoblasts to reinforce or rebuild bones
osteoclasts release minerals
- secrete proteases that dissolve the organic components
- secrete acids that dissolve the inorganic components
35
importance of bone minerals
calcium and phosphate are used for much more than bone structure
- phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers
- calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis
the skeleton acts as a storage unit for minerals
- minerals are deposited in the skeleton and withdrawn when they are needed for other purposes
36
phosphate homeostasis
occurs as HPO4^2- (monohydrogen and dihydrogen phosphate ions)
phosphate levels are not regulated as tightly as Ca^2+
- no immediate functional disorders
regulated by calcitriol & parathyroid hormone (PTH)
- calcitriol (forms vitamin D) promotes phosphate absorption by the small intestine --> increase blood phosphate levels (making phosphate available for bone deposition)
- PTH promotes urinary excretion of phosphate --> lowers blood phosphate levels
37
calcium homeostasis
99% of body calcium is in the skeleton
- most bone calcium is in hydroxyapatite -- very stable
- small Amont is exchangeable calcium (Ca^2+) - easily released into tissue fluid <--> blood
normal blood calcium
- 45% is calcium that can diffuse across capillary walls and affect other tissues
- the rest is in reverse, bound to plasma proteins
balance between:
- dietary intake of calcium
- urinary and fecal losses of calcium
- exchange between osseous tissue & blood
regulated by 3 hormones:
- calcitriol
- parathyroid hormone (PTH)
- calcitonin
38
calcium imbalances
hypocalcemia: calcium deficiency in blood
- even moderate hypocalcemia can cause problems
- can cause overexcitability of the nervous system and muscle systems resulting in muscle spasms, trousseau sign, tetany (inability of muscles to relax)
hypercalcemia: excessive calcium in blood
- rarely occurs
- can cause under-excitability of the nervous and muscle systems resulting in muscle weakness, reduced neural reflexes and non-responsiveness
39
