The Skeletal System



The skeleton, is the passive part of the locomotor system, it's not what makes our body to move (Like the muscles), but it's what gives a structure to your body.
The skeleton has four main tasks:

1) Support. The skeleton is the scaffolding of the human body, it supports our body, just like the main walls of a building.

2) Protection. The skeleton protects our organs, expecially the organs located in the chest (Lungs, heart, stomach, liver, and spleen.), and in the skull (The brain).
There's a bad side for the rib cage though: If some ribs break, they can pierce important organs, causing massive bleeding (Spleen and liver expecially), or even
putting the subject in a near-death stage ( Lungs and heart ).

3) Mineral source. The bones are a mineral source, expecially calcium, that are grabbed by the organism in case of necessity.

4) Blood cells factory. The bone marrow inside the bones performs this task, called hematopoiesis.

The skeleton is made of two types of connective tissues: cartilaginous tissue, and bone tissue.

The cartilaginous tissue is a solid (but flexible) tissue, great part of it is collagen, an organic substance in which there are cells, the chondrocytes.

The bone tissue cells are called osteocytes, and they are relatively far from eachother, and get in contact by branched extensions. They are contained in an abundant intracellular
substance, organized in lamellae, which is made by osseine and minerals.
The intracellular substance, or matrix, gives the bones the needed features for their tasks, in-fact, the bone must stay hard and compact (due to minerals), but also elastic and shockproof.
There are two types of bone tissue: Sponge-like tissue, and compact tissue.
The compact tissue is arranged in concentric lamellae, around small canals (Havers' canals), in which are located blood vessels and nerve endings.
The sponge-like tissue is known for its reticle of lamellae, that gives it the sponge-like appearance (Remember that it only looks like a sponge, but it doesn't have the same density: The sponge-like
tissue is hard.).

The bones are attached togheter by joints, and they are classified on their functions, which are: synarthrosis, amphiarthrosis, and diarthrosis.

Synarthrosis joints allow very little or no movement, such as skull joints.
Amphiarthrosis joints allow sight movement, such as cartilaginous structures (the beginning of the ribs, and the vertebrae)
Diarthrosis joints allow a variety of movements, such as knees, elbows, hips, shoulders, etc.)