Skeletal System Test

A

Diaphysis: shaft

• Compact bone

• Covers the medullary cavity

  • Storage for yellow marrow in adults (adipose)

  • Red marrow in infants up to age 7

H

Periosteum

• fibrous connective tissue membrane

• covers diaphysis

• sharpey’s fibers secure it to the bone

• contains nerves and capillaries

Sharpey’s fibers

thick, strong bundles of collagen fibers that connect the periosteum or soft tissues like tendons and ligaments directly into the underlying bone matrix

B

Epiphyses

• bulbous ends

• thin layer of compact bone around spongy bone

7

Epiphyseal plate (growth plate)

• thin line of hyaline cartilage

• site of long bone growth

• ossifies (becomes bone) in puberty and becomes epiphyseal line

8

articular cartilage

• hyaline cartilage

• covers epiphyses

• decreases friction at joints

osteon

one unit/circle of bone structure compact bone

osteocytes

mature bones cells

lacunae

cavities in matrix that house osteocytes

haversian canal

microscopic hollow tube in compact bone

canaliculi

tiny canals that radiate out from Haversian canal to the lacunae — permits circulation to osteocytes

lamellae

concentric circle arrangement of lacunae around Haversian canal

osteoblasts

bone building cells

• becomes osteocytes when surrounded by matrix

compact bone

dense, looks uniform

forms diaphysis of long bone

creates a sturdy external shell that shield soft internal organs and inner spongy bone

80% of human skeleton

spongy bone

small, needle-like trabeculae and lots of open space filled with red marrow

porous, lightweight bone tissue that makes up the interior framework of bones

skeletal system functions

• support

• protection

• movement (with muscular system)

• storage of calcium and phosphate

• hematopoiesis (blood cell production)

short bones

cube-shaped, mostly spongy

• carpals

• tarsals

• patella

flat bones

thin, curved

layer of spongy between compact, no medullary cavity

• skull

• ribs

• sternum

• spaculae

• pelvis

irregular

• pelvis

• vertebrae

• mandible, maxilla, sphenoid

sesamoid bones

small, embedded in tendons

• patella

• pisiform carpal bone

long bones

act as levers pulled by contracting muscles, longer than they are wide

• limbs

• phalanges, metacarpals/metatarsals

where is red bone marrow

in spongy bones

where is yellow bone marrow

found in the medullary cavity

sacrum

• 5 fused vertebrae

• posterior wall of pelvis

• articulates with ilium of hip to form sacroiliac joint

coccyx

• “tailbone”

• 3-5 fused vertebrae

shoulder girdle

• clavicle and scapula

  • scapula articulates with clavicle at acromion process and humerus at glenoid cavity

  • clavicle articulates with sternum (sternoclavicular joint) and scapula to brace arm away from thorax

pelvic girdle

• fused ilium, ischium, and pubis

functional classification

what kind of movement it allows

for joints

synarthroses, amphiarthrosis, diarthroses

structural classification

what tissue types the joint holds together

for joints

fibrous, cartilaginous, synovial

synarthroses

immovable

functional classification of joint

cranial joints

amphiarthrosis

allows a little movement

intervertebral joints

diarthroses

freely moveable

acetabulofemoral (hip joint)

fibrous

mostly synarthroses

bones joined by fibrous tissue

sutures of skull

cartilaginous joints

mostly amphiarthroses

bones joined by cartilage

• pubic symphysis, intervertebral joints, between ribs and sternum

synovial joints

mostly diarthroses

bones are connected by a joint cavity containing synovial fluid

osteoclasts

cells that remove bones

• originate in the bone marrow

• primary function is bone resorption, the process of breaking down and removing old or damaged bone tissue

• essential role in bone health

• release calcium and phosphate from bone into the blood

osteoblasts

• responsible for bone formation, the process of creating new bone tissue

• during their lifecycle, some osteocytes embed themselves within the bone matrix they’ve created instead of dying off

  • these embedded cells release enzymes that help maintain healthy bone tissue and transform into osteocytes

• use minerals like calcium and phosphate to harden the bone matrix

osteocytes

• function as the bone’s monitoring system

• manage bone formation and resorption

• can survive for up to 25 years within the bone matrix

• detect microscopic damage and stress in bone tissues and send signals to both osteoclasts and osteoblasts

functions of bone remodeling

• allows for growth

• repair microscopic cracks

• meet changing mechanical needs

• maintain constant blood calcium levels

wolff’s law

bone changes its structure in response to the mechanical loads placed on it

• increased stress stimulates osteoblast activity, helping bones become stronger in areas experiencing greater load

• reduced stress can cause bone loss because less bone formation is needed

why is blood calcium regulation important

• calcium ions are essential for normal nervous system and muscular system functioning

• calcium helps neurotransmitter release at synapses, and calcium is necessary for muscle contraction (including contraction of the heart muscle)

• body regulates blood calcium through hormones

• if blood calcium becomes too low, neurons become excessively excitable, potentially causing tetany

PTH — parathyroid hormone

• raises blood calcium levels when they drop too low

• low blood calcium stimulates the parathyroid glands to release PTH

• how PTH increases blood calcium

  • increases osteoclast activity indirectly, causing bone resorption and releasing stored calcium into the blood

  • kidneys increase calcium reabsorption, meaning less calcium is lost in urine

  • stimulates the kidneys to activate vitamin D, which increases calcium absorption from food in the small intesting

What substances do osteoclasts release to breakdown the components of bone

• organic component: collagen that makes bone flexible/resilient

  • digested away by acid proteases (enzymes)

  • flexibility and resilience

• inorganic component: hydroxyapatite crystals (calcium salts) that make bone hard and able to bear weight

  • dissolved out by HCl

  • hardness and weight-bearing strength

how does PTH activate osteoclasts

1. PTH (messenger) binds to an osteoblast

2. osteoblast sends signal

• increases RANKL

• releases M-CSF (helps immature osteoclasts survive and develop)

• decreases OPG (blocks osteoclast activation)

3. RANKL binds to RANK on the pre-osteclast

• signal to develop into an osteoclast

4. M-CSF helps the pre-osteoclast develop

• binds to its receptor on the pre-osteoclast

• helps the cell survive, multiple, and develop into a mature osteoclast

5. mature osteoclast breaks down bone

how do osteoclasts work

1. osteoclast moves to the surface of the bone where it will break down old bone

• integrins and vitronectin help with attachment

2. osteoclast “ruffles” the membrane

• changes the shape of its cell membrane, creating a folded area called the ruffled border

• the folds increase the surface area of the cell membrane which allows the osteoclast to release more acid and enzymes onto the bone

• maximizes the amount of bone it can break down

3. osteoclast uses adhesion molecules to attach tightly to the bone, creating a sealed-off area so its acids and enzymes don’t leak into surrounding tissue (creates resorption lacuna)

4. release acid, enzymes, and HCl

• acid (HCl) dissolves the inorganic mineral component of the bone, hydroxyapatite crystals

• acid proteases (lysosomal enzymes) break down organic component/collagen

caclitonin

• antagonist hormone to PTH

• releases by thyroid gland when blood calcium levels are high

• increases osteoblast activity

• plays a bigger role in kids than adults

vitamin D3

• made from cholesterol by skin when exposed to UV light

• can be consumed in our diet

• inactive in this form

how to activate vitamin D3

• active vitamin D increase calcium absorption from food in the small intestine, helping maintain normal blood calcium levels

1. liver - first hydroxylation

• vitamin D3 travels to liver

• an enzyme adds a hydroxyl group to it

• it becomes 25-hydroxyvitamin D (calcidiol) but is still not active in this form

2. kidney - second hydroxylation

• 25-hydroxyvitamin D travels to kidneys

• another enzyme called 1-alpha-hydroxylase adds a second hydroxyl group

• it becomes 1,25-dihydroxyvitamin D (calcitriol)

• this is the active form of vitamin D

PTH activates the enzyme 1-alpha-hydroxylase in the kidney which produces more active vitamin D

what does vitamin D do

helps your body absorb calcium from the food you eat and move it into your bloodstream

1. increases the enzyme in the intestine that break down calcium complexes into free Ca2+ for absorption

• releases calcium from complexes to free it up

2. increases calbindin in intestinal cells

• calbindin is a protein that binds to calcium

• transport protein that helps bring calcium through the intestinal cells

3. increases ATPase pumps that move calcium into the blood

• once calcium reaches the other side of the intestinal cell, it needs to enter the bloodstream

• vitamin D increases the production of calcium ATPase pumps

• these pumps use ATP/energy to move calcium out of the intestinal cell and into the blood