The Skeletal System

Donya Razinoubakht
6 th block
 Your Skeletal system is all of the bones in the body and
the tissues such as tendons, ligaments and cartilage
that connect them.
The teeth are also considered part of your skeletal
system but they are not counted as bones.
 Support:
The main job of the skeleton is to provide support for
the body. Without your skeleton your body would
collapse into a heap.
 Protection:
The skeletal system works closely with all the systems
in the body to protect them. The brain, eyes, lungs,
and spinal cord are all protected by the skeletal
system. For example, the cranium protects the brain
and eyes and the vertebrae protect the spinal cord.
 Movement
The bones of the skeletal system act as attachment points
for the skeletal muscles of the body. Almost every skeletal
muscle works by pulling two or more bones either closer
together or further apart. Joints act as pivot points for the
movement of the bones.
 To help the body move freely, the skeletal system works
very closely with the muscular system. Without the skeletal
system, the human body would not be able to support
itself, but without muscles, the skeletal system wouldn't be
able to move.
 Storage:
Bones have their own nerves and blood vessels . The skeletal system’s
cell matrix acts as our calcium bank by storing and releasing calcium
ions into the blood as needed. Proper levels of calcium ions in the
blood are essential to the proper function of the nervous and muscular
systems, and bones help regulate blood calcium levels to maintain
homeostasis. The yellow bone marrow inside of our hollow long bones
is used to store energy in the form of lipids.
 Hematopoiesis:
Red bone marrow produces red and white blood cells in a process
known as hematopoiesis. Red bone marrow is found in the hollow
space inside of bones known as the medullary cavity. The calcified
bones of the skeleton work closely with the circulatory system and
immune system. Red and white blood cells are necessary for the body
to function properly, and these cells couldn't be circulated through the
body unless the bones of the skeletal system first created marrow
 Endocrine Regulation
Bone cells release osteocalcin, a hormone that helps
regulate blood sugar and fat deposition
 The skeleton begins to form early in fetal development
as a flexible skeleton made of hyaline cartilage and
dense irregular fibrous connective tissue. These tissues
act as a soft, growing framework and placeholder for
the bony skeleton that will replace them. At birth, the
skeleton of a newborn has more than 300 bones; as a
person ages, these bones grow together and fuse into
larger bones, leaving adults with only 206 bones.
 A typical bone has an outer layer of hard or compact
bone, which is very strong and dense. Inside this is a
layer of spongy bone, which is lighter and slightly
flexible. In the middle of some bones is jelly-like bone
marrow, where new cells are constantly being
produced for the blood.
 Cartilage is a connective tissue that supports the
structure of many body parts and functions like the
bones, ribs, ears and nose.
A tendon is a is a tough band of fibrous connective
tissue that connects muscle to bones. Tendons
withstand pressure and tension; they work with
muscles to enable rigorous movement.
Ligaments are fibrous tissues that provide stability to
joints throughout the body during rest and active
An articulation, or joint, is a point of contact
between bones, between a bone and cartilage, or
between a bone and a tooth. Types of joints are:
synovial joints, fibrous joints, and cartilaginous joints
The teeth help with digesting.
All of the bones of the body can be broken down into
five types:
 The oldest human skeleton ever found is the Ardipithecus
ramidus or “Ardi” fossils discovered in Ethiopia. Ardi lived
4.4 million ears ago.
 The biggest surprise about Ardipithecus's biology is its
bizarre means of moving about.
 Hominids after Ardi all walked upright as we do, but Ardi’s
feet, pelvis, legs and hands suggest she was a biped on the
ground but a quadruped when moving about the trees. All
previously known hominids—members of our ancestral
lineage—walked upright on two legs, like us. But Ardi's
feet, pelvis, legs, and hands suggest she was a biped on the
ground but a quadruped when moving about in the trees.
Later hominids could more efficiently walk on two legs due
to losing some bones that Ardi had.
Bipedal adaptation
 There are few features to do with the spine which allow the human skeleton to
be bipedal. The modern human spine has dual curvature, which allows us to
stand erect. This also means that we can conserve energy as it will require less
to remain upright due to the fact that the spine naturally curves that way
 Also, the foramen magnum is positioned in the centre of the basicranium (the
bottom of the skull). This is a change from the foramen magnum being further
back as it is in normal quadrupeds. It helps keep the head right and in
optimum visual poison.
 The structure of the human foot is also significantly different in comparison to
other modern mammals. Humans have evolved platform feet with enlarged big
toes and large arches which act as propulsive levers and allow us to spring
forward when walking. Again, this conserves more energy than if we had apelike flat feet like the other great apes.
 Other adaptations of the human skeleton to accommodate bipedalism include
a shorter, broader, pelvis, longer legs, and lock knees.

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