Bio 111 Skeletal System (1)

6 Functions of bones

1. Framework for the body

2. Mechanical protection for internal organs

3. Provides points of attachment for skeletal muscles → produces movement

4. Storage of calcium & phosphorus

5. Production of blood cells by red bone marrow (contains stem cells)

6. Storage of energy in yellow bone marrow

Red bone marrow mother cells form

red blood cells, white blood cells, platelets

Type of bone: Long

longer than they are wide, e.g. all bones of the arms and legs except carpals and tarsals

Type of bone: Short

nearly equal in width and length; cube shape, e.g. bones of hand (carpals) and foot (tarsals: talus & calcaneus)

Type of bone: Flat

thin and flat; e.g. ribs, scapula, parietal, occipital, temporal

Type of bone: Irregular

don’t fit in any previous categories; complex in shape, e.g. hip bone, vertebrae

Type of bone: Sesamoid bone

develop in the tendons under friction and stress to protect the tendons, e.g. patella & small hand bones

Bone tissue

type of connective tissue, bone cells, matrix: fibers: collagen, ground substance: calcium (makes the bones the hardest tissue)

compact bone

hard, dense, forms shafts of long bones & outer layer of other bones and is found wherever stress arrives from one direction of the bone

lamellae

rings of calcified matrix in compact bone

Haversian system/ osteon

supportive columns of compact bone in which osteocytes are present

Haversian (central) canal

contains blood vessels and nerves, surrounded by haversian system/osteon

Volkman’s (perforating) canals

small diffusion channels that radiate outward from a central canal to facilitate nutrient, gas and waste exchange between osteocytes and the blood

Spongy bone

forms structure of short, flat, irregular bones & the epiphyses ends of long bones. Does not contain osteons

where are bone cells located?

inside small spaces in the matrix called lacunae

Trabeculae

bony struts that form a lattice surrounding many red marrow filled spaces. found in spongy bone

red bone marrow

Connective tissue found between the trabeculae of spongy bones. Made from stem cells & has precursor cells to produce red blood cells, platelets, and white blood cells

Yellow bone marrow

Adipose connective tissue, storage for fat/energy. Found in medullary cavity

osteogenic cells

precursor/ mother cells that are very active in mitosis and develop into osteoblasts during mitosis

osteoblasts

(develop from osteogenic cells) bone-building cells, secrete fibers of bone matrix then mature into osteocytes

Osteocytes

(develop from osteoblasts) mature bone cells, main cell of the bone tissue, maintains the bone tissue

Osteoclasts

(Develop from monocytes (white blood cells)) Break down bone tissue by secreting enzymes & stimulating the release of calcium & phosphorus into interstitial fluid.. Also helps with calcium homeostasis

Bone resorption

breakdown of bone tissue by osteoclasts through secreting enzymes that dissolve the malcium salts in the bone matrix

Bone remodelling

A lifelong process where old bone tissue is removed from the skeleton by osteoclasts, and new bone tissue is formed by osteoblasts

Bone matrix is formed by:

25% water
25% collagen fibers

50% crystallized mineral salts deposited from the blood: hydroxyapatite, calcium carbonate

Anatomy of long bone: Diaphysis

the shaft

Anatomy of long bone: Epiphysis

the end of a long bone

Anatomy of long bone: Metaphysis

the area between epiphysis and diaphysis and include the epiphyseal plate in growing bones

Anatomy of long bone: Medullary cavity

marrow cavity inside shaft, contain yellow bone marrow formed of fat

Anatomy of long bone: Endostenum

thin membrane lining the medullary cavity

Anatomy of long bone: Periosteum (fiberous layer)

tough membrane covering bone formed of dnese irregular connective tissue

Anatomy of long bone: Periosteum (osteogenic layer)

tough membrane covering bone formed of blood vessels that nourish and help with repairs by proliferation of its cells

Epipyseal plate

1. Proliferation of hyaline cartilage cells by mitosis on epipyseal side of the plate increases the thickness of the epiphyseal plate

2. cartilage on the diaphyseal side of the plate is replaced by bone

3. cycle is repeated until the cartilage cells stop dividing and bone replaces the whole cartiage. Bone has completed its growth in length.

Epiphyseal line

in adults who have stopped growing, the epiphyseal plate is replaced by the epiphyseal line

Epiphyseal closure

Replacement of the epiphyseal plate by the epiphyseal line. Complete closure happens at ages 12-18 for girls and 14-19 for boys.

Nutrition needed for bone growth

• Adequate levels of minerals and vitamins

• Calcium and phosphorus for bone growth

• Vitamin C for collagen formation

• Vitamin K and B12 for protein synthesis

Sufficient levels of specific hormones needed for bone growth

• growth hormone (secreted from pituitary gland): stimulates mitosis of the epiphyseal plate of cartilage

• thyroid hormones (T3 & T4): stimulate maturation of bone cells, regulate bone remodeling by adjusting activity of osteoclasts and osteoblasts to maintain mineral density of bone

(calcium homeostasis) Parathyroid hormone

Released from parathyroid gland

Effect: elevates the blood calcium Ca²+ levels

Stimulus: low blood calcium levels

Action:

1. Inhibits osteoclast activity, reducing bone breakdown (bone resorption).

2. Encourages calcium to be deposited into bones.

3. Increases calcium excretion by the kidneys.

(calcium homeostasis) Calcitonin hormone

Released from thyroid gland

Effect: lowers the blood calcium Ca²+ levels

Stimulus: high blood calcium levels

Action:

1. Bone: activation of osteoclasts to dissolve matrix freeing Ca²+ to the blood

2. Intestine: activation of vitamin D which enhances intestinal Ca²+ absorption

3. Kidney: reabsorption of Ca²+

Low calcium effects

weak teeth/ bones

High calcium effects:

kidney stones/ deposits calciumin valve of heart or bones

2 Effects of aging on the bone

1. Loss of calcium and other minerals from the bone matrix (demineralization)

Rapid in women ages 40-45 bc they lose estrogen, and estrogen inactivates osteoclasts, leading to osteoporosis

2. decreased rate of protein synthesis

decrease in collagen production. Bone becomes brittle & susceptible to fracture

Axial skeleton divided into:

• Skull

• Hyoid

• Vertebral Column

• Ribs

• Sternum

Appendicular Skeleton divided into;

• Bones of upper and lower limbs

• Bones of shoulder and pelvic girldles

What are fontanelles?

Membrane-filled spaces between the cranial bones of infants. They allow for overlapping of the skull bones during delivery of the baby and allow for rapid brain growth during infancy. Later they fill in with bone and become sutures.

Anterior fontanel

Between parietal and occipital bones at point of meeting of saggital and lambdoid sutures

Which bones of the skull form the zygomatic arch?

Temporal process of zygomatic bone and zygomatic process of temporal bone

What are the 4 bones that make up the Pterion and why is it significant?

Frontal, parietal, temporal, and sphenoid bones meet here. It is very thin area that can be injured severly