Bones and Skeletal Tissues

endochondral ossification

"inside cartilage" ossification, make bone cartilage bone forms by replacing hyaline cartilage forms most of skeleton turning cartilage into bone 1. Bone collar forms around hyaline cartilage model (WEEK 9) 2. Cartilage in the center of the diaphysis calcifies and then develops cavities 3. The personal bud invades the internal cavities and spongy bones begins to form 4. The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stag 5 5. The epiphyses ossify. When completed hyaline cartilage remains only in the epiphyseal plates and articular cartilages

Classification of Bone Fractures

1. position of bone ends after fracture. The bone ends can be nondisplaced which means the ends retain normal position and alignment. Or they can be displaced, meaning the ends are out of normal alignment. 2. Fractures can also be classified by completeness of break. A complete break is is broken all the way through. An incomplete break is a fracture that doesn't go all the way thru the thickness of the bone. 3. orientation of the break to the long axis of the bone. A linear fracture is parallel to the long axis of the bone. A transverse fracture is perpendicular to the long axis of the bone. 4. bone ends penetrate the skin. If the fracture is open (compound), the ends penetrate the skin. A simple (or closed) fracture is where the ends of the broken bone do not penetrate the skin. Additoinally, fractures can be described as particular "types". Here we see a comminuted fracture. These fractures occur when the bone breaks in three or more pieces. This fracture type is common in the elderly, when bones become brittle and frail. Compression fractures are when the bone is crushed. This is common in porous bones, and often occurs as a result of a fall.

Hamstrings- biceps femoris

2 heads (long and short) Origin: Ischial tuberosity and linea aspera Insertion: Head of fibula, lateral condyle of tibia Action: Extends thigh, flexes leg

appositional growth, type of postnatal bone growth

Appositional growth is growth in thickness of bone and also includes remodeling of bones by osteoblasts and osteoclasts. Here we see a cross section thru the diaphysis of a long bone. In infancy, the long bone is thin = easy to break. As the infant ages and become a child, new bone is deposited on the outer edges of the bone (just inside the periosteum), and the bone against the medullary cavity gets resorbed. This is to keep the bone from getting to thick and clunky and heavy. And finally, as adults, the balance between laying down new bone and resorbing old bone has hopefully maintained a balance.

bone deposit

Bone deposit occurs where bone is injured or added strength is needed. It requires a diet rich in protein, vitamins A, C, & D, calcium, phosphorus, and manganese. -Osteoblasts lay down new bone matrix on top of old bone matrix.

Blood Cell Formation

Hematopoietic Tissue (Red Marrow) • Red marrow cavities of adults • Trabecular cavities of heads of femur & humerus • Trabecular cavities of diploe (intermediate layer) of flat bones • Red marrow of newborn infants • Medullary cavities & all spaces in spongy bone

bone marrow

It is the place where new blood cells are produced. two types of stem cells: hemopoietic (which can produce blood cells) and stromal (which can produce fat, cartilage and bone). There are two types of bone marrow: red marrow (also known as myeloid tissue) and yellow marrow. Red marrow - Red blood cells, platelets and most white blood cells Yellow marrow - helps store fat and some white blood cells develop in yellow marrow Both types of bone marrow contain numerous blood vessels and capillaries. At birth, all bone marrow is red. With age, more and more of it is converted to yellow. HAVE TO BUILD IMMUNITY In cases of severe blood loss, the body can convert yellow marrow back to red marrow in order to increase blood cell production. The normal bone marrow architecture can be displaced by malignancies or infections such as tuberculosis, leading to a decrease in the production of blood cells and blood platelets. In addition, cancers of the hematologic progenitor cells in the bone marrow can arise; these are the leukemias.

Locational names for bones

Spiral fractures occur when the bone is subject to twisting forces and it breaks in a ragged spiral. This is common in sports injuries where a person zigs instead of zags. Epiphyseal fracturs occur when the diaphysis separates from the epiphyseal plate. Depression fractures occur when the bone is pressed inward. This is common in bar fights and car accidents. And finally, greenstick fractures often occur in children, whose bones are still somewhat soft and flexible (not as much calcification of bone has occurred.) Here, the bone breaks incompletely, much like a green twig doesn't fully break.

Endochondral ossification = bone forms by replacing hyaline cartilage that was laid down earlier in development.....responsible for formation of most bones of skeleton. Wk 9 > hyaline cartilage model has been formed and it has a perichondrium >forms periosteum >osteogenic cells >osteoblasts > bone collar around primary ossification site > chondrocytes hypertrophy > ECM calcifies > cartilage deteriorates >cavity forms 3 Months > periosteal bud> spongy bone forms Birth >diaphysis formed and elongates >medullary cavity > secondary ossification in epiphyses > chondrocytes hypertrophy, ECM, periosteal bud Childhood/Adolescence > epiphysis ossify > epiphyseal plate between diaphysis and epiphysis allowing for growth > plate becomes line around 18-20 years and no more growth

Steps

Intramembranous Ossification à early stages of embryonic development, embryo's skeleton consists of fibrous membranes and hyaline cartilage. bone develops from a fibrous membrane that was already laid down earlier in development. This type of ossification forms flat bones such as the clavicles and cranial bones A = Ossification center = Mesenchymal cells and collagen fibers>osteogenic cells > osteoblast (builders)> produce matrix (osteoid) B = Calcification = Osteoblasts >produce matrix > lacunae(osteocytes home) > osteocytes > canaliculi to nearby osteocytes and calcium phosphates to harden ECM > nearby osteogenic cells turn into osteoblasts C = Trabeculae (laticework) formed = ECM becomes porous > form trabeculae > form spongy bone > blood vessels intrude spaces > deposit CT cells > develop into Red Bone marrow (blood and white cells, more as an adult) D = Periosteum formed = Mesenchyme condenses > forms periosteum > osteoblasts within produce thin layer of compact bone

Steps

inoragnic

The inorganic components of bone include hydroxyapatites (which is a fancy name for mineral salts), which mainly includes calcium phosphate crystals. The inorganic components make up 65% of bone by mass and is responsible for hardness and resistance to compression. Healthy bone is incredibly strong. it is 1/2 as strong as steel in resisting compression and as strong as steel in resisting tension.

Organic

The organic material of bone includes the bone cells— namely: osteogenic stem cells, osteoblasts, osteocytes, and osteoclasts. osteoid— the organic bone matrix secreted by osteoblasts. This includes ground substance (such as proteoglycans and glycoproteins) and collagen fibers— which provide tensile strength and flexibility.

Stages of bone healing

There are four main stages of bone healing, and these occur over several weeks and months. 1. hematoma forms >tearing of blood vessels as the bone was broken open. The blood from those vessels hemorrage and a clot forms. The site becomes painful, swollen, and inflammed. 2. fibrocartilaginous callus forms > phagocytic cells clear the debris (dead cells, damaged ECM, bone chards, etc) that resulted from the break. Osteoblasts begin forming spongy bone—within one week following injury. Fibroblasts secrete collagen fibers to connect the bone ends. Chondrocytes begin to lay down new cartilage. New blood vessels begin to form. The entire mass of repair tissue = fibrocartilaginous callus. 3. bony callus forms > new trabeculae form a bony (hard) callus where the fibrocartilaginous callus was. This bony callus formation continues until the two ends are rejoined usually complete around 2 months after the injury. 4. bone remodeling occurs > shape and structure bone takes on, in response to mechanical stressors (such as the exercises performed in physical therapy following the injury and a return to normal activities.) The final structure of the bone, ideally, resembles the original.

Mechanical Regulation of Bone Remodeling

There is a scientific "law" called Wolff's law, that states, a bone grows or remodels in response to the forces or demands placed upon it. -This is why we see things like the wrists and forearms of tennis players being larger on their dominant hand (the bones of limbs used more grow thicker and stronger.) This phenomenon is called "handedness." -Also, supporting wolff's law is that curved bones are thickest where they are most likely to buckle (and that thickness helps prevent its buckling) and that trabeculae form along lines of stress. -And finally, large bone projections occur where heavy, active muscles attach— bone grows in places where there are increased demands placed upon it (such as a strongly contracting muscle.)

appendicular skeleton

appendages pectoral girdle brachium, ante brachium pelvic leg feet

osteoclast

bone-resorbing cell resorption, breakdown tissue and put nutrients back into the blood reabsorption

long bone structure

compact bone (diaphysis/shaft of bone) within medullar cavity line by endosteum where yellow marrow spongy bone (epiphyseal/ end of bone), sit of red blood cell formation red marrow=blood cells eventually turns into yellow marrow=adipose tissue and energy storage

skeletal system

composed of bones, cartilages, and ligaments form strong, flexible framework of body Cartilage-forerunner of most bones •Covers many joint surfaces of mature bone •Ligaments—hold bones together at joints •Tendons—attach muscle to bone

canaliculi

connects osteocytes with one another so they can share nutrients

endosteum

delicate membrane on internal surfaces of bone container osteoblasts (Build) and osteoclasts (Cut)

elastic tissue

ears, nose

interstitial growth, type of postnatal bone growth

five distinct zones can be microscopically identified within the epiphyseal plate. 1.Resting zone—normal, resting hyaline cartilage. 2. Proliferation zone — chondrocytes undergo rapid mitosis and the cells stack onto of one another. 3. Maturation and Hypertrophy - hypertrophy and secrete an enzyme (alkaline phosphatase) that causes calcification of the ECM. 4. Calcification zone à chondrocytes die (because they can't receive nutrients) and they leave behind cavities that will be invaded by osteoprogenitor stem cells. 5. Ossification zone à osteoprogenitor cells invade the cavities from the dead chondrocytes and differentiate into osteoblasts, secreting osteoid that becomes calcified on the surface of the calcified cartilage. The calcified cartilage is resorbed and the bone remains. This process results in growth in bone length— its as though the diaphysis of long bone gets stretched in both directions, because the growth happens in each epiphyseal plate of the bone. *Interstitial growth is regulated by hormones. Growth hormone stimulates epiphyseal plate activity. Thyroid hormone modulates the activity of growth hormone And testosterone and estrogens (at puberty) promote the adolescent growth spurt, and they contribute to the end of growth by inducing closure of the epiphyseal plate.

fribrocartalige

intervertebral discs menisucs pubic symphysis

lacunae

lacunae (lake)- osteocytes live

lamellae

lamellae, rings of collagen fibers run in different directions that aid in fracture resistance

trabeculae

layers of bones

bone remodeling and repair

lifelong two mechanisms involved with bone remodeling and repair— bone deposit and bone resorption.

classification of bones

long bones (femur, humerus) short bones (carpals, tarsals) flat bones (scapula, sternum, cranial bones) irregular bones (pelvis, vertebrae) sesamoid bones (patella, inside tendons)

osteoblast

matrix-synthesis cell responsible for bone growth

osteocyte

mature bone cell that maintains he bone matrix, gets trapped within lacunae depend on on surround cells that communicate through canaliculi

intramembranous ossification

membrane bone develops from fibrous membrane forms flat bone (ex. clavicles and cranial bones) from mesenchymal cell 1. development of ossification center 2. Calcification, osteoblast surround self by matrix of calcium 3. Formation of trabeculae (layers) 4. Development of periosteum

periosteum

outer fibrous layer of bones, dense irregular connective tissue -nerve fibers, blood, and lymph vessels, enter via nutrient foramina -secured by Sharpey's fiber -inner osteogenic (create bone/ osteoblast) layer

volkman cannals

perforating canals (volkman cannals), allows blood flow and communication between osteon

structure of short, irregular and flat bones

periosteum- covered compact bone on outside endosteum- covered spongy bone within bone marrow between trabecular resist compression and tension in many different ways

osteogenesis

process of bone formation endochondrial ossification intramembranous ossification

Bone resorption

release lysosomal enzymes which digest the organic bone matrix release acids which convert calcium salts into soluble forms. dissolved matrix is transcytosed (endocytosed and then exocytosed) across the osteoclast and enters the ISF and then the blood.

axial skeleton

skull thoracic cage vertebrae

osteogenic cell

stem cell

osteon

structural unit group of hollow tubes of bone matrix one inside next like growth rings of a tree trunk

F(X)

support protection movement storage electrolyte balance- calcium and phosphate acid-base balance-buffers against excessive ph changes blood cell formation (hematopoiesis)

hylaine cartilage

synovial joints aka articulations of bones, trachea and larynx intercostal connection -perichondrium(LCT), allow vessels to move through tissue and allow diffusion -chondrocytes (chondroblasts) mature cartilage cells -chondrocytes live within lacunae

osteology

the study of bone orthopedic docots- focus on caring for your bones, joints, ligaments, neverves, and tendons=muschuloskeltal system

postnatal bone growth

until early adulthood There are two types of postnatal bone growth— interstitial growth and appositional growth. Interstitial growth is growth in the length of long bones. Appositional growth is growth in the thickness of bone and usually requires some aspect of bone breakdown and remodeling to accompany the growth.

Hormonal Regulation of bone remodeling

••Means of regulating Blood Calcium •Controlled by Parathyroid Hormone (PTH) & Calcitonin, endocrine (stimulate calcium salt deposits in bone) Thyroid gland: simply cuboidal The remodeling of bone (laying down new bone or breaking down old bone) is used by the body to regulate blood calcium levels. The body cares about blood calcium homeostasis because calcium is used in vital processes like neuron communication, and muscle contraction, and blood coagulation, glandular secretion, and cell division. Blood calcium levels are controlled by parathyroid hormone and calcitonin