Collagen is like a soft, stretchy rope inside bones. It lets bones bend a little so they don’t break when you move or fall.
Hydroxyapatite is a hard mineral that surrounds collagen. It makes bones tough and strong, able to hold your body weight and protect organs.

So together, collagen keeps bones flexible, and hydroxyapatite makes them strong.

Explain the function of each of the following: osteogenic cells, osteoblasts, osteoclasts, and osteocytes.

Bone Cell Functions (Quick & Simple)

Osteogenic cells – Stem cells that become osteoblasts.
Osteoblasts – Build new bone (make collagen + add minerals).
Osteocytes – Maintain bone; former osteoblasts trapped in bone.
Osteoclasts – Break down bone and release calcium.

Where are the osteogenic layers of bone?

1. Inner layer of the periosteum

The periosteum is the outer covering of bones.
Its inner layer has osteogenic cells (bone stem cells).
These cells make osteoblasts to build bone on the outside.

2. Endosteum

The endosteum is a thin lining inside bones.
It also has osteogenic cells.
These help repair or rebuild bone from the inside.

Periosteum → builds bone outside
Endosteum → repairs bone inside

What different connective tissues make up the skeletal system?

Connective Tissues in the Skeletal System:

Bone (Osseous Tissue) – Hard tissue that makes up bones. Supports and protects the body.
Cartilage – Smooth and flexible. Found at joints to reduce friction.

Hyaline (most common), fibrocartilage (spine), elastic (ear).

Dense Regular CT – Found in tendons and ligaments. Strong, rope-like tissue for connection.
Dense Irregular CT – Found in the periosteum (outer layer of bone). Gives strength in many directions.
Adipose (Fat) – Found in yellow bone marrow. Stores energy.

Blood – Found in red bone marrow. Makes blood cells.

Be able to label the parts of a typical long bone. Describe the function of each part.

Parts of a Typical Long Bone & Their Functions:

Diaphysis

What it is: The long, middle shaft of the bone.
Function: Provides strength and supports weight.

Epiphysis (plural: epiphyses)

What it is: The enlarged ends of the bone.
Function: Forms joints with other bones and contains spongy bone (for shock absorption).

Medullary Cavity

What it is: The hollow center of the diaphysis.
Function: Holds yellow bone marrow (fat storage).

Endosteum

What it is: The thin lining inside the medullary cavity.
Function: Contains osteogenic cells for bone growth and repair.

Periosteum

What it is: Tough outer covering of the bone (except at joints).
Function: Protects bone, anchors tendons/ligaments, and helps with bone growth and healing (contains osteogenic layer).

Compact Bone

What it is: Dense, hard outer layer of bone.
Function: Provides strength and protection.

Spongy Bone

What it is: Light, porous bone found in the epiphysis.
Function: Reduces weight and contains red marrow (makes blood cells).

Articular Cartilage

What it is: Smooth cartilage covering the joint surface of epiphyses.
Function: Reduces friction and absorbs shock at joints.

Epiphyseal Plate (in kids) / Line (in adults)

What it is: Growth plate made of cartilage (plate) or bone (line).
Function: Site where the bone grows in length during childhood.

Red Bone Marrow

What it is: Found in spongy bone of epiphyses.
Function: Makes red and white blood cells (hematopoiesis).

Describe the anatomy and physiology of spongy bone (trabeculae) and compact bone (osteons).

Spongy Bone (Trabeculae)

Structure: Looks like a sponge; made of thin branches called trabeculae. Has spaces filled with red bone marrow.
Function:
- Lightweight support.
- Makes blood cells (hematopoiesis).
- Found in ends of long bones and inside flat bones.

Compact Bone (Osteons)

Structure: Hard, dense outer layer of bone. Made of osteons (circular units).

Each osteon has a central canal with blood vessels, surrounded by layers called lamellae.

Function:

Gives strength and protection.
Handles pressure in one direction.
Found in the outer part of all bones.

Distinguish between the two main types of bone marrow.

Red Bone Marrow

Makes blood cells (red, white, and platelets).
Found in spongy bone (hip, ribs, skull, ends of long bones).
Active in blood cell production.

Yellow Bone Marrow

Stores fat.

Found in the medullary cavity of long bones.
Can change back to red marrow if the body needs more blood.

Explain how the effect of calcitriol, calcitonin and PTH on blood calcium levels. Explain what structure or gland produces each of these hormones?

🧬 1. Calcitriol (active vitamin D)

Made by: Skin → Liver → Kidney
Effect: Raises blood calcium
How: Helps absorb calcium from food and tells bones to release calcium.

🧪 2. Parathyroid Hormone (PTH)

Made by: Parathyroid glands
Effect: Raises blood calcium
How: Activates bone breakdown (osteoclasts) and helps kidneys keep calcium.

❄ 3. Calcitonin

Made by: Thyroid gland
Effect: Lowers blood calcium
How: Stops bone breakdown and helps store calcium in bone.

Briefly describe the steps of intramembranous bone formation.

Cells gather — Special cells called mesenchymal cells come together.

Make bone builders — These cells change into osteoblasts (cells that make bone).

Build soft bone — Osteoblasts make a soft bone material called osteoid.

Make it hard — The soft bone gets hardened by adding calcium.

Cells get stuck — Some osteoblasts get trapped inside and become osteocytes (bone cells).

Bone forms — The bone grows into a spongy shape with spaces (trabeculae).

Cover bone — The outside layer forms into periosteum (protective layer).

Briefly describe the steps of endochondral bone formation.

Your body first makes a cartilage model shaped like the bone.

The cartilage in the middle gets hard and starts to die.

Blood vessels come in carrying bone cells.

Bone cells replace the dead cartilage with real bone in the middle.

Later, the bone also forms at the ends of the cartilage model.

The bone keeps growing longer at special growth areas (growth plates) until you’re fully grown.

Basically:
Cartilage → hardens → blood brings bone cells → bone replaces cartilage → bone grows

What is the function of canaliculi in compact bone?

Bone cells live inside the bone.

They need a way to get food and send out trash.

Canaliculi are tiny tiny tubes that connect the bone cells.

Through these tubes, bone cells get food and send out waste
So canaliculi = tiny tubes that help bone cells get what they need and stay healthy

Briefly explain how bone repair occurs.

When a bone breaks, blood collects to stop bleeding and forms a clot.

The body makes a soft bridge of cartilage to connect the broken pieces.

This soft bridge turns into hard bone over time.

Finally, the bone is shaped back to normal.

What are the risk factors associated with osteoporosis? Rickets?

🦴 Osteoporosis Risk Factors

Happens mostly in older adults, especially women after menopause
Not enough calcium or vitamin D
Not enough exercise (especially weight-bearing)
Smoking and drinking too much alcohol
Low hormone levels (like estrogen)
Family history of weak bones

🌞 Rickets Risk Factors

Lack of vitamin D (main cause)
Not enough sunlight to make vitamin D
Poor diet low in calcium or phosphorus
Babies only breastfed without vitamin D supplements
Problems with nutrient absorption in the gut

Quick recap:

Osteoporosis: Bones get thin and weak in adults
Rickets: Bones stay soft and weak in children because of vitamin D or mineral deficiency

Why do you store minerals in your bones? In other words…What are the functions of calcium ions in the body? What are the functions of phosphate ions in the body? What are the functions of bicarbonate ions in the body?