skeletal system

Functions of the skeletal system:

• Support (structural framework)

• Protection (e.g., skull protects the brain)

• Movement (muscle attachment for leverage)

• Electrolyte balance (stores calcium/phosphate)

• Blood formation (hematopoiesis in marrow)

Ligaments connect bone to ______ whereas tendons connect ____________ to _________.

• Ligaments connect bone to bone.

• Tendons connect muscle to bone.

The shaft of the long bone is called the ______________ and the ends are called the ____________.

• Diaphysis (shaft)

• Epiphyses (ends)

The ends of long bones contain _____________ bone and the spaces are filled with _________________.

• pongy (cancellous) bone

• Red bone marrow (hematopoietic tissue)

The growth plate is called the ____________________.

• Epiphyseal plate (hyaline cartilage in children; becomes epiphyseal line in adults).

In adults, red bone marrow can be found at the end of ____________ bones and in the middle of ____________ bones.

• Long bones (e.g., proximal femur/humerus)

• Flat bones (e.g., sternum, pelvis)

_________________ form around stress points in spongy bone.

• Trabeculae (align along lines of mechanical stress).

Spongy bone is ___________ and ______________ than compact bone.

• Lighter and less dense.

Compact bone is a composite material made up of ______________ which is the ceramic portion and _______________ which gives it flexibility.

• Hydroxyapatite (ceramic mineral)

• Collagen (protein polymer)

________________ are bone stem cells.

• Osteogenic cells (found in periosteum/endosteum).

________________ are buried in the matrix of bone.

• Osteocytes (mature bone cells in lacunae).

______________ are bone-forming cells.

• Osteoblasts.

________________ resorb the bone.

• Osteoclasts (multinucleated cells with ruffled borders).

The basic unit of compact bone is the ______________.

• Osteon (Haversian system).

It is like a layer cake and consists of ___________ and ______________ where osteocytes reside.

• Concentric lamellae (matrix rings)

• Lacunae (tiny cavities housing osteocytes)

Bones growing lengthwise is _______________ growth and widening is _______________ growth.

• Interstitial (lengthwise, via epiphyseal plate)

• Appositional (widthwise, via periosteal osteoblasts)

In fetal development, ____________________ forms flat bones and _______________ forms long bones.

• Intramembranous ossification (skull, clavicle)

• Endochondral ossification (limbs, vertebrae)

What is Wolff’s law of bone?

• Bone remodels its structure in response to mechanical stresses (e.g., exercise thickens bones).

Difference between mineralization and mineral resorption:

• Mineralization: Osteoblasts deposit calcium/phosphate into bone matrix.

• Resorption: Osteoclasts dissolve bone, releasing minerals into blood.

What is calcium needed for in the body?

• Nerve function, muscle contraction, blood clotting, enzyme activity.

What is phosphate needed for in the body?

• ATP production, DNA/RNA synthesis, pH buffering.

Calcitriol is the most active form of vitamin ___ which causes the ________________ to absorb more calcium.

• Vitamin D

• Small intestine

If calcium levels are high, the _________ releases ____________ which inhibits ___________ and stimulates ___________ to deposit calcium in the bones.

• Thyroid gland releases calcitonin → inhibits osteoclasts → stimulates osteoblasts.

. If calcium levels are low, the _________ releases ____________ which inhibits ___________ and stimulates ___________ to make a withdrawal of calcium.

• Parathyroid glands release PTH → inhibits osteoblasts → stimulates osteoclasts.

______ and __________ raise blood calcium levels while _________ lowers blood calcium levels.

• PTH and calcitriol raise calcium.

• Calcitonin lowers calcium.

___________ raises blood phosphate levels while ____________ lowers blood phosphate levels.

• Calcitriol raises phosphate.

• PTH lowers phosphate (via urinary excretion).

A fracture broken in multiple pieces would be a ________ fracture.

• Comminuted fracture.

Process of bone healing (heal soft into hard bone):

1. Hematoma forms at fracture site.

2. Fibrocartilaginous callus (soft tissue bridges gap).

3. Bony callus (osteoblasts form spongy bone).

4. Remodeling (compact bone replaces spongy bone).

Why are post-menopausal women more prone to osteoporosis?

• Estrogen decline reduces osteoclast inhibition → accelerated bone resorption.

• Peak bone mass is typically lower in women, and aging exacerbates loss.