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Human skeleton

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Human skeleton
The human skeleton consists of both fused and individual bones supported and
supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which
supports organs, anchors muscles, and protects organs such as the brain, lungs and heart.
The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes
bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body
weight and half of this weight is water.
Fused bones include those of the pelvis and the cranium. Not all bones are interconnected
directly: there are three bones in each middle ear called the ossicles that articulate only
with each other. The hyoid bone, which is located in the neck and serves as the point of
attachment for the tongue, does not articulate with any other bones in the body, being
supported by muscles and ligaments.
Muscle
Muscle (from Latin musculus, diminutive of mus "mouse") is the contractile tissue of
animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells
contain contractile filaments that move past each other and change the size of the cell.
They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce
force and cause motion. Muscles can cause either locomotion of the organism itself or
movement of internal organs. Cardiac and smooth muscle contraction occurs without
conscious thought and is necessary for survival. Examples are the contraction of the heart
and peristalsis which pushes food through the digestive system. Voluntary contraction of
the skeletal muscles is used to move the body and can be finely controlled. Examples are
movements of the eye, or gross movements like the quadriceps muscle of the thigh. There
are two broad types of voluntary muscle fibers: slow twitch and fast twitch. Slow twitch
fibers contract for long periods of time but with little force while fast twitch fibers
contract quickly and powerfully but fatigue very rapidly.
Muscles are predominately powered by the oxidation of fats and carbohydrates, but
anaerobic chemical reactions are also used, particularly by fast twitch fibers. These
chemical reactions produce adenosine triphosphate (ATP) molecules which are used to
power the movement of the myosin heads.

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Integumentary system
"Integument" redirects here; in botany, an integument refers to an outer membrane of an
ovule, which later develops into a seed coat.
The integumentary system (From Latin integumentum, from integere 'to cover'; from in-
+ tegere 'to cover) is the organ system that protects the body from damage, comprising
the skin and its appendages (including hair, scales, feathers, and nails). The
integumentary system has a variety of functions; it may serve to waterproof, cushion, and
protect the deeper tissues, excrete wastes, and regulate temperature, and is the attachment
site for sensory receptors to detect pain, sensation, pressure, and temperature. In humans
the integumentary system also provides vitamin D synthesis.
The integumentary system is the largest organ system. In humans, this system accounts
for about 16 percent of total body weight and covers 1.5-2m
2
of surface area. It
distinguishes, separates, protects and informs the animal with regard to its surroundings.
Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer
layer (integument). This gas exchange system, where gases simply diffuse into and out of
the interstitial fluid, is called integumentary exchange.
Circulatory system
The circulatory system is an organ system that passes nutrients (such as amino acids and
electrolytes), gases, hormones, blood cells, etc. to and from cells in the body to help fight
diseases and help stabilize body temperature and pH to maintain homeostasis.
This system may be seen strictly as a blood distribution network, but some consider the
circulatory system as composed of the cardiovascular system, which distributes blood,
and the lymphatic system, which distributes lymph. While humans, as well as other
vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the
network of arteries, veins and capillaries), some invertebrate groups have an open
cardiovascular system. The most primitive animal phyla lack circulatory systems. The
lymphatic system, on the other hand, is an open system.
Two types of fluids move through the circulatory system: blood and lymph. The blood,
heart, and blood vessels form the cardiovascular system. The lymph, lymph nodes, and
lymph vessels form the lymphatic system. The cardiovascular system and the lymphatic
system collectively make up the circulatory system.

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Human skeleton The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart. The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight and half of this weight is water. Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: there are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments. Muscle Muscle (from Latin musculus, diminutive of mus "mouse") is the contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause either locomotion of the organism itself or movement of internal organs. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Examples are the contraction of th ...
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Very useful material for studying!

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