CHAPTER 5: THE SKELETAL SYSTEM INTRO

cartilage

-dense connective tissue found in joints,ribcage,ear,nose,throat -purpose: reduce friction at joints by providing smooth surface for two bones meeting at that joint

Functions of Periosteum

-protection -attaches to fascia (provides surface for muscle attachment) -attachment site for circulatory&nervous supply

Calcium Homeostasis feedback loop system: what happens if your blood calcium levels rise above homeostatic level?

1) The thyroid gland stimulates the release of calcitonin. 2)Calcitonin stimulated bone deposition and reduces calcium uptake in kidneys

Two types of bone:

1)Compact bone (cortical bone); denser with fewer spaces 2)Spongy bone (cancellous/trabecular bone); lighter/has many spaces

Bone maintenance & remodeling phases:

1)Resting phase: nothing is happening 2)Resorption: osteaclasts eat/resorb bone 3)Reversal: transitional phase where mononuclear cells help smooth things out 4)Matrix Deposition: bone is deposited when osteoblasts secrete bone matrix 5)Mineralization: osteoblasts become osteocytes to maintain the bone tissue

Five basic functions of the skeleton:

1)Support 2)Protection(skull+ribcage) 3)Movement 4)Blood cell production by red marrow 5)Mineral Storage/Homeostasis

Calcium Homeostasis feedback loop system: what happens if your blood calcium levels drop below homeostatic level?

1)The parathyroid gland stimulated PTH to be released. 2) PTH stimulates calcium release in bones (resorption), increased calcium uptake in kidneys and intestines 3)blood level rises, balance is restored

What is the homeostatic blood calcium level?

10mg/100mL

The skeletal system is made up of

Bones (Osseous Tissue) Connective Tissues

Types of connective tissues

Cartilage Ligaments Other for skeletal stabilization

Describe the first stage {steps 1-4} of endochondral ossification:

Concerned mostly with formation of diaphysis Step 1: chondrocytes near center of diaphysis increase in size. surrounding matrix begins to calcify. chondrocytes die & disintegrate due to lack of nutrients, forming cavities within the cartilage. Step 2: Blood vessels grow around the edges of the cartilage&bring in nutrients. The perichondrium differentiates into osteoblasts (that start laying down bone)&now becomes a functioning periosteum. The osteoblasts start secreting osteoid, which forms the bone collar, a thin layer of compact bone around the shaft of the cartilage. Step 3: there is increased blood supply; capillaries invest inside of the bone& osteoblasts migrate to the center of the cartilage and invade the spaces left behind by chondrocytes, forming the primary ossification center. In the primary ossification center, cartilaginous matrix is replaced by spongey bone produced by osteoblasts(increases from middle to the ends). Step 4: shaft is filled with spongy bone. Osteoclasts create the medullary cavity. Further growth; increase in length and diameter enlargement.

Factors that affect bone remodeling and growth:

Essential nutrients : calcium, phosphorus, magnesium,sodium Vitamins: A, C & D Hormones: parathyroid(releases stored minerals;osteoclasts), calcitonin(associated with osteablasts; for matrix deposition) sex hormones(testosterone+estrogen)

Types of bones: categorized by shape ; list examples of each

Flat bones: cranial vault(top) bones (parietal, occipital & frontal bones) ribs, scapula&sternum Irregular bones: vertebrae, hips bones, bones at the base of the cranium/face Long Bones: limbs; humerus, upper limb,radius,ulna,brachium , tibia, fibula, clavicles** Short bones: (made up of all spongy bone inside) carpal bones& tarsal bones Sesamoid bones: (found at joints, form inside of tendons) purpose is to reduce friction at joints, example is the patella

What kind of connective tissue are the bone linings? What does this mean? State both kinds of bone linings and their locations.

Osteogenic connective tissue ; means the linings generate bone in specific parts of the body Periosteum (lines outside of bone) Endosteum (very thin, lines medullary cavity/inside of bone)

Describe the second stage of endochondral ossification:

Secondary ossification is for formation of epiphysis; Step 5: migration of capillaries & osteoblasts into epiphysis centers. Step 6:epiphysis/secondary ossification center is filled with spongy bone&the epiphyseal cartilage (epi.plate) is formed between the epiphysis and diaphysis. This forms an area so that the bone can be laid down (*metaphysis). Osteoblasts invade the shaft side of the bone, replace the cartilage with bone as the epiphyseal cartilage simultaneously enlarges. This enlargement increases distance between epiphysis&diaphysis, resulting in increased length. Step 7: decreased rate of epiphyseal cartilage enlargement/increased rate of osteoblast activity to close up the epiphyseal plate. The epiphyseal cartilage narrows/disappears and leaves behind the epiphyseal line. The epiphyseal plate remains cartilaginous until skeletal maturity(skeletal maturity depends on the bone bc bones grow at different rates). The articular cartilage remains on the ends of the bone to prevent damage from bone-to-bone contact with joint.

endochondral ossification: two main stages of the process

Steps 1-4: initiation of ossification in developing bone -building bone around hyaline cartilage model Steps 5-7: increasing length of developing bone

what is the epiphyseal plate?

The line that separates the metaphysis from the diaphysis. consists of cartilage until skeletally mature. [once skeletally mature, it fuses up and becomes bone and the individual cannot grow more]

what is the metaphysis of the bone?

The widened portion of the diaphysis , where bone is added during growth.

Main minerals stored in bone

body must store extra calcium and phosphorus in the bone

how is bone tissue replaced throughout your life time? why does this happen?

bone remodeling; a coordinated removal and replacement of bone tissue by osteoclasts (removes old bone) and osteoblasts(builds new bone). Functions: -to change the shape of the bone&adapt to environment -replace old/damaged bone -release mineral stores in any scenario where you need to increase minerals in your blood stream

Two parts of the matrix of the bone

calcium phosphate collagen fibers

what is the mineral component of the bone? What does it do?

calcium phosphate eventually converts to hydroxyapetite crystals in mature bone; makes bone hard/tough; responsible for homeostasis of the bone during production of bone

what are the ends of the long bones called?what is the middle called?

epiphysis; made of mostly spongy bone but covered in cortical bone diaphysis; made of mostly cortical bone

What are the three long bones present at birth/ the three longest bones in the body?

femur, tibia, humerus

what do collagen fibers provide for bones?

flexibility

before six weeks of development, the skeleton is made up of _____.

hyaline cartilage

where is bone marrow found?

in the spaces between the cortical and cancellous bone

state the two types of ossification and describe them

intramembranous ossification: involved in development of clavicle, mandible, skull and face endochondral ossification: involved in development of limbs, vertebrae and hips

what kind of bones are in your limbs?

long bones ex:femur

osteons; describe structure

long tubes of bone that run the full length of the bone are the basic functional unit of bone are made of up lamellae (thin sheets of bone laid down in concentric circles) have a central canal that allows blood/nutrient supply into the bone osteocytes that maintain the lamellae/tissue canaliculli connect osteocytes and allow communication between cells

Compact (cortical bone) is made of ___ and found on the _____ of bone.

made up of osteons; found on the outside of bone for protection.

articular cartilage is where? what does it do?

on surface of epiphysis; prevents friction between connecting bones

after six weeks of development, cartilage cells are replaced by bone cells in a process called ______/_______.

ossification/osteogenesis

Spongy (cancellous/trabecular) bone is arranged in____ and found on the ___ of the bone.

parallel struts(looks like a sponge); inside of the bone

homeostasis

process by which your body maintains an internal environment in response to its external environment

ligaments

short bands of tough fibrous connective tissue; connect bones to other bones at joints

Structure of the bone

supporting connective tissue specialized cells solid matrix bone linings

bone cell functions; describe types of bone cells and each of their functions

to maintain the bone matrix osteocytes-live inside the matrix, provide nutrients for the tissue osteoblasts-bone building; secretes osteoid that mineralizes calcium phosphate/hydroxyapetite crystals to become osteous tissue(bone)..eventually become osteocytes osteoclasts-big multinucleated cells that release enzymes that eat away at bone; for the removal of bone or in the case where we need to release minerals stored in bones

parallel struts form a branching network called _____.

trabeculae; makes bones lightweight

calcification

when calcium ions are deposited into the bone tissue