Chapter 6- Bones Physiology

What is the living skeleton made of?

Dynamic ossified tissue full of cells, permeated with nerves and blood vessels

What are the main tissues that make up the skeletal system?

Bones, cartilage, ligaments, and connective tissue

What is the role of cartilage in the skeletal system?

It is the forerunner of most bones and covers many joint surfaces of mature bone

Why does cartilage take longer to heal?

Because it is avascular (lacks blood vessels)

How many bones are in the human skeleton at birth?

Approx. 300 bones

How many bones are in the adult human skeleton?

Approx. 300 bones

What are the two mineral-related functions of the skeletal system?

Storing and releasing minerals

What is a major protective function of bones

Protect internal organs, produce blood cells, supports the body, facillitates movement

What are the example of long bones?

The upper and lower limbs

What are examples of short bones

Carpals and Tarsals

What are examples of flat bones

Ribs, sternum, skull, scapulae

What are examples of irregular bones?

Vertebrae and facial bones

What is the structural arrangement of a flat bone?

A “sandwhich” of spongy bone between compact bone

What is the structural arrangement of short and irregular bones

Compact bone surrounds a spongy center

What is a diploe

Spongy bone in the cranium that absorbs shock

What percentage of total bone mass do bone cells make up?

only about 2%

How many types of bone cells are there?

4 Types

What are the 4 types of bone cells

Osteo(chondral) progenitor/osteogenic cells, osteoblasts, osteocytes, osteoclasts

What 3 main components make up bone as a connective tissue?

Cells, fibers, and ground substance

What are osteogenic (osteochondral progenitor) cells>

Stem cells that multiply continuously to produce new osteoblasts

Where in the bone are osteogenic cells found

In the endosteum, periosteum, and central canals

What are osteoblasts?

Bone-forming cells

Are osteoblasts mitotic or nonmitotic?

nonmitotic (they do not divide)

What is the primary function of osteoblasts?

They synthesize the soft organic matter of matrix, which then hardens by mineral deposition

How do stress and fractures affect bone cells

They stimulate osteogenic cells to multiply more rapidly and increase the number of osteoblasts to reinforce/rebuild bone

What are osteocytes?

Older osteoblasts that have become trapped in the matrix they deposited

What dual function can osteocytes perform regarding the bone matrix?

Some reabsorb bone matrix while others deposit it

What homeostatic mechanism do osteocytes contribute to

The regulation of bone density and calcium and phosphate ions

What are osteoclasts and where are they found?

Bone-dissolving cells found on the bone surface

What is the origin of osteoclasts

They develop from bone marrow stem cells (a different origin than other bone cells)

What are 2 distinct physical characteristics of osteoclasts?

They are unusually large cells formed by the fusion of several stem cells and have many nuclei

What are resorption bays (how ship lacunae)

pits on the surface of bone where osteoclasts reside

What two processes must balance to maintain bone homeostasis?

Bone building (by osteoblasts) and bone recycling (by osteoclasts)

What is osteoporosis?

Occurs when the creation of new bone does not keep up with the loss of old bone

Which demographic has a higher risk of osteoporosis?

Older Caucasian and Asian women

What is rickets/osteomalacia

Soft bones, usually due to deficiency of Vitamin D

What is Osteogenesis Imperfect?

Brittle bone disease, causing excessively brittle bones due to lack of protein (collagen)

By dry weight, what is the ratio of the bone matrix, and what does it include?

1/3 Organic Matter

2/3 Inorganic Matter

What synthesizes the organic matter in bone matrix, and what does it include?

Synthesized by osteoblasts; includes collagen and carbohydrates-protein complexes (glycosaminoglycans, proteoglycans, glycoproteins)

What is the primary component of inorganic matter in bone matrix?

85% hydroxyapatite (crystalized calcium phosphate salt),10% calcium carbonate, plus other minerals (fluoride, sodium, potassium, magnesium)

What is the basic structural unit of compact bone?

an osteon

How are osteocytes arranged within an osteon

In concentric lamellae around a central canal containing blood vessels

What are perforating canals (volkmann canals)

Canals perpendicular to the central canal that carry blood vessels into bone and marrow

What are trabeculae in spongy bone?

Lamellae arranged as interconnecting rods or plates of bone

What are spicules in spongy bone

slivers of bone

What filles the spaces in spongy bone?

Bone marrow

What membrane covers the structures within spongy bone?

Endosteum

What are concentric lamallae?

Rings of matrix surrounding the central canal in an osteon

What are lacunae?

“Black Dots” or small spaces in the matric where bone cells (osteocytes) reside

When is skeletal maturity reached?

At about age 20 (though females reach it sooner)

What happens to the epiphyseal cartilage when a long bone stops growing after puberty?

It disappears (leaving an epiphyseal line that is visible on x-rays)

What are the two methods of bone development (ossification) in the human fetus?

Intramembranous ossification and endochondral ossification

Where does intramembranous ossification take place?

In connective tissue membrane?

What is endochondral ossification?

The major embryonic process of bone formation where bone develops from a pre-existing hyaline cartilage model?

What bones are produced by intramembraneous ossification in the fetus?

Flat bones of the skull, part of the mandible, and the clavicle

Which bones come from endochondral ossification?

Most bones of the body, including long bones, vertebrae, and pelvic bones

What is appositional growth?

Bone growth where bones increase in width and thickness

When does appositional growth happen?

Throughout life, particularly with increased load on the skeleton (stress, weight gain, and muscle mass)

How do osteoblasts contribute to bone widening?

— In the Periosteum deposit osteoid tissue, which becomes trapped as the tissue calcifies

How often does bone remodeling occur?

Throughout life, at a rate of about 10% per year

What are the main functions of bone remodeling?

It repairs microfractures, releases minerals into blood, and reshapes bone in response to use and disuse

What is Wolff’s law of bone?

The architecture of bone is determined by mechanical stresses placed on it; bones will adapt to withstand those stresses

Which cells work together during bone remodeling?

Osteoclasts and osteoblasts

What is the ultimate goal of bone remodeling according to Wolff’s Law?

Bone remodels itself to become stronger

What is the primary storage site for calcium in the body?

Bone

How does calcium enter vs. leave the bone?

Enters bone - when osteoblasts create new bone

Leaves bone - when osteoblasts break down new bone

What three hormones control blood calcium levels?

Parathyroid hormone (PTH), Calcitriol, Calcitonin

Where is parathyroid hormone (PTH) secreted from?

Secreted by cells in the parathyroid gland

What triggers/stimulates the release of PTH

A reduction (low level) in blood calcium

What happens to bone and blood calcium when PTH activates osteoclasts?

bone is reabsorbed and calcium is released into the blood

How does PTH directly affect calcium in the kidneys?

It stimulates the reabsorption of calcium from urine in the kidney tubules

How does PTH affect blood phosphate levels?

It lowers blood phosphate levels by promoting its urinary excretion

What is an indirect effect of PTH on calcium levels?

Promotes activation of calcitriol (a hormone that increases calcium absorption in the small intestine) (vitamin D)

How does calcitonin affect blood calcium levels?

When blood calcium levels reach high levels, releases hormone to lower it

What are the three structural classification of joints based on connective tissue type?

Fibrous, Cartilaginous, and synovial joints

What is a synarthrosis joint?

A non-movable joint

What is an amphiarthrosis joint?

Slightly moveable joint

What is a diarthrosis joint?

A freely moveable joint

How are bones joined together in fibrous joints?

They are unified by fibrous connective tissue

Do fibrous joints have a joint cavity, and how much movement do they allow

No joint cavity, allow little to no movement

What are the 4 main types of sutures in the skull

Lambdoid, sagittal, coronal, and squamous suture

What is a syndeme=