skeletal system Flashcards
what does the skeletal system provide
the framework and overall structure for our body, and in coordination with our skeletal muscles, allows movement
what is the skeletal system made of
connective tissues, including bone, cartilage and dense fibrous CT. these are arranged to form skeletons and joints
what is cartilage
composed of mostly water- allows it to regain shape after compression. it has no blood supply but
it is surrounded by perichondrium, a layer of dense irregular CT
which contains blood vessels from which gases and nutrients diffuse into the cartilage.
what are the 3 types of cartilage
hyaline cartilage- the most abundant type, consists of mostly collagen fibres and provides flexibility, support and resilience
elastic cartilage- contains high proportion of elastic fibres and can withstand repeated stretching and bending while retaining shape
fibrocartilage- has an intermediate structure between hyaline and elastic cartilage. it is compressible with great tensile strength and is located in areas subject to heavy pressure and stretch
what is bone
a CT composed of bone cells embedded in the rigid ECM. it is vascularised (has a blood supply) and has a nerve supply
functions of bone
forms a supportive framework for the body, protects soft tissue, mineral storage, hematopoiesis (production of blood cells), act as levers which are moved by skeletal muscles
4 types of bone cells
osteogenic cells, osteoblasts, osteocytes, osteoclasts
what are osteogenic cells
the main cells undergoing continuous mitosis. each division of the cell results in one cell that becomes an osteoblast and one that remains an osteogenic cell that will continue with the mitosis process
what are osteoblasts
the bone builders. they produce and lay down osteoid, incorporating the mineral salts to build bone around themselves. when cells are active they take calcium out of the blood to incorporate into the ECM of bone
what are osteocytes
they are osteoblasts that have finished laying down ECM and are considered mature bone cells. when the osteoblast has completely surrounded itself with a calcified matrix and can no longer produce more, it becomes trapped in lacunae in the ECM and will stay there as an osteocyte. they maintain the bone by communicating with each other and other bone cells, coordinate bone building and remodelling.
what are osteoclasts
the bone destroyers that break down the ECM of bone. in the process of bone resorption, osteoclasts release the mineral salts- mainly calcium- into the blood
bone structure
the internal and external surfaces of the bones are lined with dense connective tissue membranes which contain working bone cells. between these membranes is the calcified matrix of bone, laid down into sheets called lamellae which contain the osteocytes within lacunae. lamellae are arranged in 2 ways within the bone- compact and spongy
compact bone
dense, smooth superficial layer of bone. consists of numerous units called osteons which are packed together between circumferential lamellar sheets. covered by both periosteum and endosteum
spongy bone
fills the interior portion of a bone and holds bone marrow. blood vessels run around the outside of the trabeculae. bone marrow fills gaps between the trabeculae. lamellae form trabeculae. also known as cancellous bone. it is covered in endosteum only.
what is ossification
the formation of bone, it involves remodelling and it occurs via 2 methods which are intramembranous ossification and endochrondral ossification
intramembranous ossification
occurs only to the flat bones of the skull, the mandible (jaw) and the clavicles. it begins within the fibrous dense CT
endochondral ossification
occurs within the cartilage preforms (blobs of hyaline cartilage), beginning in the embryo and continuing into adolescence. Cartilage dies from the inside where there is no blood flow and is replaced by bone tissue. Cartilage keeps growing externally and the bone keeps growing on the inside known as the first center of ossification. Then bone may start to grow in another spot in the cartilage called the second center of ossification. They continue growing through childhood and more bone centers grow until eventually the cartilage stops growing but the bone inside keeps growing and then overtakes almost all of the cartilage and the first and second centers of bone will merge together and form lines which will then disappear and will become a full bone with a tiny bit of cartilage around the outside of the bone.
what do hormones do in bone remodelling
facilitate the homeostasis of blood calcium levels. parathyroid hormone (PTH)
what does mechanical stress do in bone remodelling
induces the tension generated by skeletal muscles and forces of gravity on the bones. bone grows in response to demands (stress) placed on it
shapes/ bone types
long bones- long and wide
short bones- roughly cuboil/ roundish in shape
flat bones- contain a large flat (usually gently curved) surface
irregular bones- dont easily fit into any of the other categories. tend to have lots of different angles or bits sticking out in different directions and have holes where the body structure pass through it.
sesamoid bones- small, seed shaped bones that form with tendons typically in the hands and feet
sutural bones- small flat bones found along the structure lines between the major bones of the skull
axial skeleton
forms the longitudinal axis of the body, consists of bones of the skull, vertebrae and rib cage
appendicular skeleton
consists of the bones of the upper and lower limbs and the pectoral and pelvic girdles
what are the two types of cartilaginous growth
appositional growth- new cartilage is formed on the exterior surface
interstitial growth- new cartilage is formed internally (growth from inside out)
where is hyaline cartilage found
nasal cartilages, laryngeal cartilages (voice box), costal cartilages (between ribs and sternum), precursor to bone, articular cartilages (found on the surfaces surfaces of bone contained within joints)
