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Macroscopic Structure of the Skeletal System

The overall function of the musculoskeletal system is simply to provided us with movements and structure of our form. In this post we will focus on the skeletal system covering the macroscopic and microscopic bone structure, bone formation, and bone remodeling. Related posts soon to come are: Microscopic Structure of the Skeletal System: What makes our bones Strong?; Joints; Skeletal, Smooth, and Cardiac Muscle.

Skeletal System:

Our skeletal system can be identified into the axial and appendicular section. Axial skeleton categorizes the skull, spine, and ribcage. Appendicular skeleton section comprises of the arms, legs, pelvic area. I usually remember it as: axial skeleton is within the mid axis of our body, while the appendicular skeleton is anything that deals with the appendages or extension from our body.

CARTILAGE

Cartilage is firm, but unlike bone, it is a lot more flexible. You obviously can bend your forearm, but surely easily bend your ears! The material that makes up cartilage is an elastic matrix called chondrin (comes from cells called chondrocytes)

Fun fact #1: Babies’ skeletal system begins with cartilage since it needs to be a tad bit more easily pushed out of a female’s vaginal opening. I would imagine it would hurt plenty if they weren’t.

Fun fact #2: Cartilage does eventually break down, of course some of them dont break down like your ears. However, some cartilage are found in between joints (articular cartilage) which degrade with age and may cause arthritis.

BONE

Strength: Stronger than cartilage

How many: Adults have 206 bones, Children have 300+ bones

Structure (Macroscopic)

Without using a microscope, macroscopically, we can see the compact bone & cancellous or spongy bone. See the imagine on the right.

1. Compact bone appears to be a lot more dense (compact) and strong compared to that of the spongy or cancellous bone.

2. Cancellous or Spongy bone appears to be a lot more hollow, spider web like, sort of like a real sponge. These thin spicules are known as trabeculae. In between these cavities contains bone marrow (red or yellow).

Red bone marrow is where hematopoietic stem cells, which gives rise to all cells in our blood. Yellow bone marrow is the house of fats and does not appear to have any sort of function.

Side note: Bone marrow transplants are highly encouraged since the possibility of finding a match for patients needing stem cells are fairly low. The process of how bone marrow transplant works can be further discussed with your doctor. The simplest explanation would be: anesthetics required and a long needle to extract that marrow from your hip.

A good example of how all these interrelates is by looking at the long bone (appendicular skeleton).

Long bones is the major make up of the appendicular skeleton. The ends of the long bones are epiphysis, its shaft is called the diaphysis. The surroundings or periphery of the epiphysis and diaphysis are made up of compact bone.

Differences between the diaphysis and epiphysis is the content in its interior.

Diaphysis:

– Marrow rich interior (home of B cells maturation)

Epiphysis:

– Spongy bone interior (helps with absorbing pressure in between joints)

In between long bones are epiphyseal plate (depicted as articular cartilage). It is in this region where bone growth occurs. (Yes, the bone grows by extending its ends).

The entire long bone is covered of the fibrous sheath called periosteum, which further protects the bone and allows the attachment with other bones. In order for bone growth and effective bone healing, the periosteum must be healthy.

Fun fact#2:  A thin hairline fracture of the bone may be easily repaired by the bone itself. The fractured area is less likely to fracture again since the healing area is much stronger compared to the not-yet-fractured area of the bone. Of course, this does that mean that it is encouraged to break your bone so you can be invincible!

Read on for more information on the skeletal system in these related posts (soon to come):

1. Microscopic Structure of the Skeletal System: What makes our bones Strong?

2. Joints

3. Skeletal, Smooth, and Cardiac Muscle

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