SKELETAL SYSTEM Flashcards
Skeletal system
Body system composed of bones, cartilage, and ligaments of body that supports and give shape to body and body structures
Bone
Hard, dense connective tissue that forms most of adult skeleton
Cartilage
Semi-rigid connective tissue that provides flexibility and smooth surfaces found in areas where bones move
Functions of skeletal system (6)
- Support
- Movement
- Protection
- Mineral storage
- Energy storage
- Hematopoiesis
Support
Bones and cartilage support the rest of the body
Movement
Bones facilitate movement by serving as points of attachment for muscles and they also act as levers
Protection
Bones protect internal organs from injury by covering/surrounding them (eg. Ribs protect lungs and heart, vertebrae protect spinal cord, skull protect brain)
Mineral storage
Bone matrix acts as reservoir for some minerals which is important to functioning of body like calcium and phosphorus; these minerals can be released back into bloodstream to maintain levels needed to support physiological processes
Energy storage
Bone marrow in softer connective tissue that fills interior of bone contains yellow bone marrow which has adipose tissue and the triglycerides stored here serve as energy source
Hematopoiesis
Red bone marrow is where hematopoiesis is where production of blood cells occur; RBC, WBC and platelets are all produced in red marrow
How many bones are in adult skeleton and how many categories
206 bones divided into 5 broad categories based on shape
Bone classification (5):
- Long
- Short
- Flat
- Irregular
- Sesamoid
Long (8)
Cylinder like shape, functions in leverage (eg. Tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges)
Short (2)
Cube like shape equal in width length thickness, functions in providing stability and support while allowing motion (eg. Carpals, tarsals)
Flat (4)
Thin and curved, functions in points of attachment for muscles and protects internal organs (eg. Sternum, rib, scapulae, cranial bone)
Irregular
Complex shape, functions in protecting internal organs (eg. Vertebrae, facial bone)
Sesamoid
Small and round embedded in tendons, functions in protecting tendons from compressive forces (eg. Patallae)
Long bone
Contains two parts (diaphysis and epiphysis)
Diaphysis structure
Is a tubular shaft that runs between proximal and distal ends of bone and contains a hollow region called medullary cavity which is filled with yellow marrow. Walls are composed of dense and hard compact bone
Epiphysis structure
Wider section at each end of bone filled with spongy bone with spaces filled of red marrow
Metaphysis
Where the epiphysis and diaphysis meet that contains epiphyseal plate (layer of hyaline cartilage in a growing bone)
Epiphyseal line
Serves as indicator of boundary between epiphysis and diaphysis. Epiphyseal plate becomes epiphyseal line when bone as matured (stops growing) in early adulthood and cartilage is replaced by osseous tissue
Endosteum
Delicate membranous lining in medullary cavity where bone growth, repair, and remodelling occur
Periosteum
Fibrous membrane covering the outer surface of bone (except where epiphyses meet) containing blood vessels, nerves, and lymphatic vessels that nourish compact bone
Articular cartilage
Thin layer of cartilage that covers epiphyses to reduce friction and absorb shock
Spongy bone and compact bone
Two layers of compact bone and interior spongy bone work together to protect internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the inner layer
Bone cells structure
Relatively small number of cells that are entrenched in a matrix of collagen fibers
Hydroxyapatite
Inorganic salt crystals made of calcium phosphate (hydroxyapatite) that adhere to collagen and gives bones their hardness and strength
Collagen fiber function in bones
Impart flexibility so that bones are not brittle
4 types of bone cells:
- Osteocyte
- Osteoblast
- Osteogenic cell
- Osteoclast
Osteoblast
Responsible for forming new bones found in growing portions of bone, including periosteum and endosteum; Secretes organic compounds of matrix
Function of osteoblasts that don’t divide
Synthesize and secrete the collagen matrix and calcium salts
Osteocyte
A mature and the most common bone cell that results from when a trapped osteoblast changes in structure and becomes osteocyte; Maintains bone matrix and lives in lacunae
Lacuna
Spaces where osteocytes are found and surrounded by bone matrix
Osteogenic cell
Undifferentiated cells that develop into osteoblasts
Osteoclast
Functions in bone resorption and found on bone surfaces, multinucleated, and originate from two types of white blood cells and not from osteogenic cells; Secrete acid and enzymes to dissolve bone matrix
Spongy bone
Contains open spaces and supports shifts in weight distribution. It contains osteocytes housed in lacunae arranged in a lattice network of matrix spikes called trabeculae
Compact bone
Dense and can withstand compressive forces; found deep in periosteum and in diaphyses
Osteon
Structural unit of compact bone, composed of concentric rings of calcified matrix called lamellae
Central canal
Found in each center of osteon that contains blood vessels, nerves, and lymphatic vessels that branch off at right angles through the perforating canal
Canaliculi
Connect with canaliculi of other lacunae and eventually with central canal which allows nutrients to be transported to the osteocytes and wastes to be removed from them
Trabeculae
Refers to the lattice like network of matrix spikes of lacunae and osteocytes in spongy bone providing strength to bone and the spaces in between makes bones lighter so that muscles can move them more easily. Some also contain red marrow
Nutrient arteries
Pass through nutrient foramen (small opening in diaphysis) that nourish the spongy bone and medullary cavity
How are osteocytes in spongy bone nourished
Blood vessels of the periosteum that penetrate spongy bone and blood that circulate in marrow cavities
Nerve supply to bone
Nerves also follow the same path into the bone through nutrient foramen and concentrate into more metabolically active regions
Skeleton in embryonic early stages
Consists of only fibrous membranes and hyaline cartilage. By week 6 or 7 of development, ossification (formation of bones begins)
2 pathways of ossification:
- Intramembranous ossification
- Endochondral ossification
Cartilage templates (2)
- Bone is a replacement tissue; uses model of cartilage on which to lay down matrix
- Framework of flexible semi solid cartilage is laid down to determine where born will form during fetal development –> replaced with bone as fetus is born
Intramembranous ossification
Occurs in flat bones of face, most cranial bones and clavicles
7 Steps of intramembranous ossification -
- Mesenchymal cells differentiate into specialized cells (osteogenic cells and capillary forming cells)
- Osteoblasts form clusters called ossification centers
- Osteoblasts secrete osteoid which calcifies and traps osteoblasts and transforming them into osteocytes
- Surrounding osteogenic cells differentiate into new osteoblasts
- Osteoid secretion around capillaries forms trabecular matrix, and osteoblasts on surface become periosteum
- Periosteum forms protective layer of compact bone
- Trabecular bone crowds nearby blood vessels which condense into red marrow
Endochondral ossification
Occurs at bones on base of the skull long bones and involves bone development by replacing hyaline cartilage template and takes longer than intramembranous ossification
9 steps of endochondral ossification:
- Mesenchymal cells differentiate into chondrocytes that form cartilaginous skeletal precursor
- Perichondrium appears and chondrocytes in center grow in size
- Matrix calcifies, leading to chondrocyte death and disintegration of surrounding cartilage
- Blood vessels invade spaces, enlarging them and carrying osteogenic cells
- Space combines to form medullary cavity and capillaries penetrate cartilage
- Perichondrium transforms into periosteum and periosteal collar of compact bone forms around cartilage
- Primary ossification center forms deep in periosteal collar
- Similar events occur in secondary ossification centers in epiphyseal regions
- Cartilage remains at joint surfaces as articular cartilage and between diaphysis and epiphysis as growth plate responsible for bone lengthening
Epiphyseal plate
Area of growth in long bone and is a layer of hyaline cartilage where ossification occurs in immature bones (longitudinal)
Bone growth on epiphyseal side of epiphyseal plate
Cartilage is formed
Bone growth on diaphyseal side of epiphyseal plate
Cartilage is ossified and diaphysis grows in length
Growth plate zones (4)
- Reserve zone
- Proliferative zone
- Maturation and hypertrophy zone
- Calcified zone
Reserve zone
Closest to epiphysis consisting of resting chondrocytes that anchor the growth plate to bone
Chondrocyte function in reserve zone
Do not participate in bone growth but secure the growth plate to the osseous tissue of epiphysis
Proliferative zone
Chondrocytes undergo rapid cell division leading to formation of new chondrocytes
Zone of maturation and hypertrophy
Chondrocytes are older and larger and contribute to lengthening of bones
Cause of longitudinal growth of bone
Result of cell division in the proliferative zone and the maturation of cells in zone of maturation and hypertrophy
Calcified zone
Cartilage matrix becomes calcified and chondrocytes die. Serves as bridge for invasion of blood vessels and transformation of cartilage into bone
When does longitudinal growth stop
When the chondrocytes in the epiphyseal plate cause proliferation and bone replaces the cartilage; bones will continue to grow in length until early adulthood
Appositional growth
Bone growth in diameter; bones increase in diameter as they grow in length and even after growth in length ceases