Lectures 1 Flashcards
4 categories of tissues in animals
Nervous tissue
Epithelial tissue
Muscle tissue
Connective tissue
Types of connective tissue
Bone Blood Cartilidge Dense connective tissue Loose connective tissue
Loose connective tissue
large amounts of ground substance and fewer fibers
Aerolar
Adipose
Reticular
DENSE connective tissue
large amounts of fibers and less ground substance
Dense Regular
Dense Irregular
Elastic CT
Cartilidge
specialized cells called chondrocytes are within the matrix (cartilage cells)
Hyaline Cartilage
Elastic Cartilage
Fibrocartilage
Bone
strongest connective tissue with little ground substance, hard matrix of calcium and phosphorous and specialized bone cells called osteocytes
Blood
fluid connective tissue, no fibers – only ground substance (plasma) and cells (red, white, and platelets)
Bone matrix - 2 components
INORGANIC/mineral – hydroxyapatite, compression strength , without it= bone is too flexible
ORGANIC – collagen and proteoglycans, flexible strength , without it = bone is brittle and will shatter
Bone classification
1.LONG BONES
Longer than wide. Formed from compact bone with spongy bone in the center and at the end long shaft. E.g. tibia
- FLAT BONES
Flat and thin, slightly curved, 2 thin layers of compact bone surrounding a thin layer of spongy bone e.g. skull, ribs - IRREGULAR BONE
Bones that don’t fit into any other category. Made from spongy bone covered with compact bone. E.g. vertebrae and pelvis - SHORT BONE
Cuboidal and contain mainly spongy bone with a surface layer if compact bone
SEASAMOID bones are types of short bones that are found where there’s lots of friction/ tension e.g. within the patella, modify and reduce pressure in joints
2 parts to a skeleton
AXIAL skeleton – forms the long axis of the body and contains the skull, vertebral column and ribs
APPENDICULAR SKELETON – consists of the limb bines and their attachments or girdles, the pelvis and scapula and clavicle
Cellular component of bone
Osteochondral progenitor cells Osteoblasts Osteocytes Osteoclasts Bone lining cells
Osteochondral progenitor cells
undifferentiated stem cells, derived from mesenchymal cells. Found in the periosteum and endosteum ( lining the medullary cavity) of the bone and in canals within the bone that contain blood vessel and differentiate into osteoblasts.
Osteoblasts
make new bone matrix , synthesize and secrete collagen fiber’s and other organic components, derived from mesenchymal stem cells
Osteocysts
Found in the more mature bone and were once osteoblasts, now surrounded in their OWN matrix. No longer secrete matrix they maintain the daily cellular activities of the bone tissue and to sense the stresses placed on bone matrix. E.g. exchange of nutrients and waste products with blood. 25 years
osteoclasts
remove old bone. Large, multinucleated, concentrated in the endosteum( layer of connective tissue LINING the bone medullary cavity
Bone lining cells
regulate movement of Ca2+ and Po4- ions
Long bone consits of ? parts
Diaphysis = shaft of long bone and main portion
Epiphyses= distal and proximal ends of the bone
Metaphyses= regions in the mature bone where the diaphysis joins the epiphysis. In a growing bone the metaphysis is occupied by the epiphyseal growth plate
Periosteum
Medullary cavity
Endostenum
Articular cartilidge in long bone
thin layer of hyaline Cartlidge
covers the epiphyses. Reduces the friction at the joints and acts as a shock absorber at freely moveable joints
Periosteum
tough dense layer of irregular connective tissue surrounding the bone surface where its not covered by articular Cartlidge .Contains the osteogenic proteginor cells. Helps protect the bone, assists in fracture repair, helps nourish the bone tissue and serves as an attachment point for tendons and ligaments
Medullary cavity
center of bones, sometimes called the marrow cavity, space within the diaphysis that contains BONE MARROW
2 types of bone marrow
RED marrow : produces red and white blood cells and platelets
YELLOW marrow: contains fat and connective tissue and produces some white blood cells
At birth, there is only red bone marrow present and as the person grows the red marrow in many of the bones is replaced by yellow. Increase in a haemopoetic stimulant that regulates red cell mitosis and differentiation, reducing with age.
Endostenum
membrane that lines the medullary cavity and contains bone forming cells , the equivalent of the periosteum surrounding the outside of the bone.
Compact/cortical bone
outer layer of all bones,
provides support and protection to the spongy bone in center and resists the stresses produced by weight and movement.
Formed of collagen. Organized into osteons/ harversian systems
In the center of the haversian system there’s a central canal (haversian canal) running through the bone LONGITUDINALLY. Blood and lymph vessels and nerves run in these central canals. Around the canal the bone is arranged into concentric layers (lamellae)
Spongey/cancellous/trabecular bone
Does not contain true osteons and consists of lamellae arranged in an irregular lattice of thin interconnecting struts ( trabeculae)
Spaces between trabeculae are filled with red and yellow bone marrow
Within each trabecula osteocytes lie in lacunae with radiating canaliculi, like in osteons of compact bone
Osteocytes receive nutrients directly from the blood circulating through the medullary cavity
Trabeculae along the lines of stress, helps bone resist stresses and transfer the force without breaking
Where is spongy bone found
Makes up majority of bony tissue in short, flat, irregularly shaped bones and the epiphysis of the long bones, and lines the medullary cavity of diaphysis of the long bones
Blood supply to bone
From periosteum into the interior of the bone
Bone marrow
Periosteal arteries
Enter diaphysis through perforating volkmann canals
Supply the periosteum and the compact bone
Large nutrient artery that passes obliquely through the compant bone through a hole- nutrient foramen
When the nutrient artery reaches the medullary cavity it divides into proximal and distal branches, supplying the inner layers of compact bone and spongey bone
ends are supplied by metaphyseal and epiphyseal arteries
Nervous supply
Accompany the blood vessels of the bone
Periosteum has a rich supply of sensory nerves, some of which transmit pain sensations
Bone development/formation ( ossification)
Intramembranous - direct ossification of mesenchymal cells
Endochondral - replacement of hyaline cartildige with bone tissue
Endochondral ossification
Hyaline cartilage forms an initial model of the future bone from mesenchymal cells that differentiate into chondroblasts
Once hyaline model has formed, osteoblasts gradually replace the cartildige with bone matrix, which is then ossified.
LONG BONES in arms and legs
Intramembranous ossification
FLAT BONES of the skull, clavicle and scapula
Bone forms directly condensed mesenchymal cells without first going through a cartilage step
Bone growth
WIDTH - appositional
Length - endochondral
Endochondral growth
Requires intestitial growth from cartilage first
Occurs at epiphysial growth plates
Stops when growth plates ossify
Appositional growth
Osteoblasts in periosteum secrete matrix and become trapped as osteocytes
Osteoclasts increase diameter of medullary cavity
Increases diameter of bones until skeletal maturity
Bone remodelling- new bone
WOVEN BONE
Osteoblasts lay down bone and osteoblasts remove bone
Mature bone - bone remodelling
Old bone is constantly being replaced by new bone
Factors affecting bone growth and remodelling
Mechanical factors Genes Hormones Aging Diseases Diet
Mechanical factors affecting bone growth and remodelling
More stress increases osteoblast activity = more bone
Less stress decreases osteoblast activity= less bone
Gene factors affecting bone growth and remodelling
Determines potential size and shape
Height and bone mass is multifactorial ( many genes involved and other factors)
Genes influence:
Growth hormone release
Hormone receptors on bone cells
Ability to absorb nutrients ( e.g. calcium ) from the gut
Hormones - bone growth and remodelling
Growth, sex and thyroid hormones influence cell differentiation and metabolism
Ageing - bone growth and remodelling
Osteoblast matrix production slows in comparison to osteoclast matrix resorption
Decreased collagen deposition results in more BRITTLE bone ( less flexible strength )
Bone mass peaks at 25-30 years and then falls
Diseases- bone growth and remodelling
Bone mass is reduced particularly in women after menopause ( decreased oestrogen production )
Smoking, extreme exercise, anorexia and removal of ovaries also reduce estrogen levels
Cancellous bone is most affected as its severely weakened if connections are lost
Cartilage
More elastic than bone
Cartilage is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bones at the joints and nerves
Forms a semi rigid part of the skeleton and a protective layer at many joint surfaces
2 types of cartilidge cells
CHONDROBLASTS- secrete extracellular matrix of Cartlidge, composed of collagen fibers, elastic fibers and other proteinaceous components.
CHONDROCYTES- mature Cartlidge cells located in spaces called lacunae. Derived from chondroblasts that have become trapped within extracellular matrix
Does cartilidge have blood vessels
NO -all metabolites exchanged by diffusion
Types of cartilidge
Hyaline
White fibrocartilidge
Elastic yellow cartilidge
Hyaline cartilidge
Covers the ends of synovial joints, glassy, connects the ribs to the sternum, forms the larynx, and part of the nose and reinforces trachea and bronchi
White fibrocartilidge
Less matrix and more collagen than other cartilidge, makes it more compressible and able to resist high pressures. Found in areas of high stress
Elastic yellow cartilidge
External ear and throat epiglottis)
Growth and development of cartilidge - appositional
Chondroblasts
Growth and development of cartilidge- intestitial
Chondrocytes
Perichondrium
Outer and inner layer
the connective tissue that envelops cartilage where it is not at a joint
Outer layer - dense irregular CT with fibroblasts
Inner layer- fewer fibers with chondrocytes
Articular cartilidge
Type of hyaline cartildige
On articular surfaces of bones
No perichondrium ( membrane
Growth of articular cartildge
Similar to growth plate
Columns of cells – calcified Cartlidge- bone
Type 2 collagen fibrils anchor proteoglycan matrix to bone
Growth plate stops at a similar time to growth plate but never ossifies
function of articular cartilidge
Smooth – reduces friction ( heat causes protein damage )
Deformable and elastic which distributes the load evenly
factors affecting cartilidge metabolism
mechanical factors
Injury
Aging
Disease
Mechanical factors influencing cartilage
Anabolic and catabolic processes adjust to adapt matrix to mechanical demands
Load below 1mPa may be catabolic wheras load above may be anabolic stimulus
HIGH strain = matrix deposition = increased stiffness
Low strain = matrix resorption - reducedstiffness
Injury and repair - influencing cartilidge
Lack capillaries within cartildge
Nutrients from diffusion ( synovium not bone )
Chondrocytes do not normally divide in adult but still secrete matrix ( repairs normal wear )
Tears/ lesions never fully heal
Ageing and diseases- influencing cartilidge
Decreased proteoglycan and collagen turnover
Collagen disruption, PG’s lost, water lost on compression, tissue damage
Increased non enzymatic glycation ( NEG)
Impaired joint lubrication
- Friction/ heat
- Fibrillation
- Osteoarthiritis
Osteoporosis
reduction in mass of bones
deficiency of vitamin D
Ostemalacia
Softening of bones
deficiency of calcium and phosphorus
