Lecture 8/ Chapter 7 - Skeletal System 1 (Bones Structure & Function)

what are the five homeostatic functions of bone?

Support/protection, movement (levers), hematopoiesis, mineral & energy storage, calcium homeostasis.

hematopoiesis

blood cell production occurs in red bone marrow

How does PTH affect blood calcium levels?

Stimulates osteoclasts → increases blood calcium.

Which hormones regulate calcium homeostasis?

Parathyroid hormone (PTH), Calcitonin, and Vitamin D (Calcitriol).

How does Calcitonin affect blood calcium levels?

Stimulates osteoblasts, inhibits osteoclasts → lowers blood calcium.

What role does Vitamin D (Calcitriol) play in calcium homeostasis?

Increases calcium absorption in the intestines.

what are the four types of bones?

long, short, flat and irregular

examples of long bones are—

femur, humerus

examples of short bones are—

carpals & tarsals

examples of flat bones are—

Skull, sternum, ribs.

examples of irregular bones are—

vertebrae & pelvis

What is the diaphysis of a long bone?

The shaft; provides leverage and weight support.

What is the medullary cavity?

Hollow space in diaphysis; contains red marrow (children) or yellow marrow (adults).

What is the difference between the epiphyseal plate and line?

Plate = growth site in children; line = remnant in adults.

What is the periosteum?

Outer covering with fibrous and cellular layers; anchors tendons/ligaments.

What is the endosteum?

Thin connective tissue lining inside of bone, containing bone cells.

What are the parts of flat bone?

Compact bone on outside, spongy bone (diploë) inside; no medullary cavity.

What are the organic components of bone matrix?

Osteoid: collagen + ground substance (flexibility & tensile strength).

What are the inorganic components of bone matrix?

Hydroxyapatite crystals (rigidity & compressive strength).

What is the central canal?

Channel containing blood vessels and nerves.

What are concentric lamellae?

Rings of calcified matrix around the central canal.

Where are osteocytes located?

In lacunae between lamellae.

What are canaliculi?

Tiny channels for communication and nutrient exchange between osteocytes.

What are perforating (Volkmann’s) canals?

Perpendicular canals connecting osteons.

What are circumferential lamellae?

Rings running around the entire bone.

What are interstitial lamellae?

Remnants of old osteons between newer ones.

What is compact bone?

Dense, forms outer surface, organized into osteons, provides strength (80% of bone mass).

What is spongy bone?

Porous, lattice of trabeculae, contains marrow, reduces weight (20% of bone mass).

What are osteoprogenitor cells?

Stem cells that differentiate into osteoblasts.

What are osteoblasts?

Bone-forming cells; secrete osteoid, initiate calcification

What are osteocytes?

Mature bone cells; maintain matrix, detect stress.

What are osteoclasts?

Bone-resorbing cells; break down matrix using enzymes and acid.

What is red bone marrow and where is it found?

Hematopoietic tissue that produces blood cells; found in spongy bone and medullary cavities of children, and only in certain axial bones in adults (e.g., sternum, pelvis).

What is yellow bone marrow?

Fatty marrow derived from red marrow with age; can revert to red marrow during severe anemia.

Why is calcium homeostasis important?

Necessary for bone formation/remodeling, blood clotting, nerve impulse transmission, and muscle contraction.

How do bones help regulate calcium?

Osteoblasts remove calcium from blood during bone formation; osteoclasts release calcium into blood during resorption.

What is bone remodeling?

Continuous replacement of old bone with new bone through the coordinated activity of osteoclasts and osteoblasts.

What is Rickets and what causes it?

Childhood disease from vitamin D deficiency; leads to poor calcification, bowed legs, and growth disturbances.

What is Osteoporosis?

Age-related bone disease with reduced bone mass, increased fracture risk, especially in postmenopausal women.