Skeletal System Video Lecture - Class 11

you
the skeletal system includes all the
bones of the body plus the joints where
they attach to each other our skeleton
protects our internal organs provides a
framework or scaffolding that allows us
to stand upright and move stores
minerals that our body needs to function
properly and produces blood cells our
muscles pulling this way or that way on
our bones produce movement and without
the protection of our skeleton
even a simple bump on the head or chest
could injure vital internal organs pound
for pound the bones of the skeletal
system are stronger than steel
the skeletal system is made up of 206
different bones which come in four basic
shapes long bones such as the femur
short bones like the wrist and ankle
bones flat bones such as those in the
skull or scapula and irregular bones
like the vertebrae there are two types
of bone tissue compact bone which is
dense smooth and very strong and
cancellous bone which is spongy and
lightweight both types of bone tissue
contain living cells which help make
repairs if a bone is injured or broken a
typical long bone has a main shaft
called the diaphysis composed of compact
bone and two ends called epiphysis
composed of cancellous bone the main
shaft is covered with a membrane of
living cells called periosteum to which
muscles and tendons attach themselves
inside the main shaft is a cavity called
the medullary cavity which contains bone
marrow bone marrow stores fat produces
blood cells and plays an important part
in the body's immune system
the skeletal system is divided into two
divisions the axial skeleton which
consists of bones that form the
longitudinal axis of the body and the
appendicular skeleton which consists of
bones that are appended to the axial
skeleton the axial skeleton includes 80
bones comprising the skull vertebral
column and thorax
the appendicular skeleton consists of
the bones of the shoulders upper
extremities hips and lower extremities
the bones of the upper extremities or
arms are connected to the axial skeleton
via the shoulder girdle this consists of
the scapula or shoulder blade and the
clavicle or collarbone the arm itself is
composed of the humerus or upper arm and
the radius and ulna of the forearm plus
the wrist in hand which consists of 27
separate bones because of this large
number of small bones our hands are
capable of more movement than any other
part of our body the bones of the lower
extremities or legs are connected to the
axial skeleton via the pelvic girdle
which is formed by the two hip bones it
protects the bladder reproductive organs
lower colon and rectum in the male the
pubic arch of the pelvis is less than 90
degrees wide
in the female greater than 90 degrees
this difference in width is necessary
for the female pelvis to accommodate
childbirth the longest heaviest and
strongest bone in the body is the femur
commonly called the thigh bone at one
end it is connected to the pelvis and at
the other end to the lower leg which is
made up of the tibia or shin bone and
fibula the tibia bears all of our body's
weight the fibula bears no weight at all
the patella or kneecap is a large bone
between the femur and fibula it protects
the knee joint and tendons that form the
knee the bones of the ankle and foot
must carry all of our body weight as we
stand walk or run and the 26 bones and
33 joints that make up our ankle and
foot enable it to do just that the
entire skeletal system of an average
adult weighs less than 10 kilograms if
you attempted to replace this with a
steel skeleton that was just as strong
it would weigh 400 kilograms and still
would not have the resilience of bone or
the ability to repair itself harder than
reinforced concrete lighter than
stainless steel able to repair itself
bone is the near-perfect material to
provide the framework for the human body
you