Endoskeleton Definition

An endoskeleton is a skeleton found within the internal of the body; it provides structural assistance and also protection for the inner organs and tissues of an organism.

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Endoskelelots can take several forms, and also have the right to differ in complexity, form and attribute, relying on the requirements of the animal. Many vertebrates have an endoskeleton, which is consisted of of mineralized tproblem in the form of bone and cartilage. This ‘true skeleton’ is created from the mesoderm during embryogenesis.

The photo shows a diagram of a humale endoskeleton with the major bones labeled.

Fish within the course chondrichthyes (sharks, rays and also chimaeras) have an endoskeleton; although, fairly than bone, their skeleloads are made up of cartilage, muscle and connective tconcerns.

While the majority of invertebrates have actually a non-cartilaginous exoskeleton, a choose few invertebprices have actually endoskelelots, including squid and octopus, and echinoderms such as starfish and sea urchins.

Porifera (sponges) and also cnidarians (jellyfish) are invertebprices that have a type of endoskeleton called a hydrostatic skeleton. Instead of bone or cartilage, it consists of a cavity called the coelom, which is filled via a gelatinous substance dubbed mesohyl, and is sustained by liquid press.

An advantage that endoskelelots have over exoskelelots is that—as living tissue— the endoskeleton grows in tandem with the remainder of the body. In order to thrive from inintricate to adulthood, organisms through exoskeleloads have to melted or ‘molt’ their outer skelelots and then thrive a brand-new one. This is not important with an endoskeleton. During the molting procedure, an pet is without an exoskeleton and also is therefore specifically fragile. Additionally, it can be extremely costly in terms of sources to thrive or obtain a brand-new exoskeleton,

While still being lightweight, endoskeletons are additionally able to assistance better body weights than exoskeletons. This allows vertebrate organisms to flourish to a lot bigger sizes than those with external skeleloads, such as insects.


Tright here are 2 forms of bone tconcern within the endoskeleton of humans:

The Cortical Bone

The cortical bone—additionally dubbed the ‘compact bone’— is the dense bone tconcern that forms the difficult exterior and gives long bones their stamina.

Compact bone is created of a calcified matrix containing very few spaces, although it does contain many small cylindrical columns of just a couple of millimeters wide dubbed lamellae. These lamellae form the osteon or the haversian system.

Within the osteon is the haversian canal, the central canal which surrounds blood cells and nerves.

Surrounding the haversian canal are the osteocytes, which save the mineral tproblem of bones such as calcium. These osteocytes are linked to each other in a netoccupational of tiny canals called canaliculi, which permits them to transfer minerals, fatty acids and also waste and in between each other.

Compact spongy bone

The Cancellous Bone

The cancellous bone, likewise known as trabecular bone or ‘spongy bone’, renders up the inner of the bone structure. Cancellous bone is frequently discovered at the ends of the lengthy bones and the rubs, skull, pelvic bones and also the vertebrae of the spinal column.

It is a lightweight and porous bone through the tworry arranged right into a honeycomb-prefer matrix with large spaces; these spaces are frequently filled through blood vessels and also bone marrowhead. The primary structure of the cancellous bone is formed of thin rod-like bones referred to as trabeculae.

Functions of the Endoskeleton

Protection and also Support

The endoskeleton provides the structural assistance for the body, permitting its owner to stand up; without it, the body would certainly have no shape.

Although the skeleton does not necessarily prevent damage to outer organs such as the skin, it provides a good deal of defense for the inner organs.

The vertebrate skeleton is formed of 2 different parts:

The axial skeleton is the ‘inner skeleton’. This is consisted of of the skull, the ribcage and the vertebral column. Its primary protective attribute is for the main nervous device and the vital organs such as the lungs, heart, kidneys and also liver.

Axial skeleton diagram

The appendicular skeleton is composed of the pelvic girdle, the shoulder blades and arm bones and the legs and also feet. This component of the endoskeleton protects and also supports the limbs.

Appendicular skeleton diagram


Bones, as soon as sustained by the function of muscles, deliver the capacity of locomovement (movement). The muscles are attached to the bone via tendons or ligaments.

Due to the fact that the framework of bones is greatly rigid, activity of the skeleton is made possible by connecting bones called joints. Tright here are a number of various types of joint, allowing different varieties of activity.

The hip and also shoulder have ‘round and socket’ joints. The ‘ball’ part of the joint is a spherical bone, which fits within the ‘socket’, and can move in nearly all directions.

The wrist has actually a ‘condyloid’ joint. This is equivalent in framework to the sphere and socket, and although it has actually a wide array of movements, it does not allow the wrist to turn 360-degrees.

A ‘saddle’ joint is the joint that enables movement in the thumb. This gives the very same range of activities as the condyloid joints although cannot bfinish backwards.

The ‘hinge’ joint is found within the fingers and also toes. This enables movement like the hinge of a door—bending in and straightening, although not backwards or sidemeans. The knee and also ankle joints, although hinges, enable a level of movement when the limb is hosted in a particular place.

A ‘pivot’ joint enables rotational movement. This joint can be discovered at the elbow, and at the vertebrae straight under the skull allowing the head to relocate in a rotation.


The osteocyte cells—star shaped cells that form a network bordering the haversian canals—are the cells that are responsible for the maintenance of mature bone.

The bone is comprised of calcium, phosphorus and various other fatty acids, all of which are stored within the osteocytes in the compact bone. When the body is in require of these nutrients, they deserve to be taken from these stores and also used.


Within the cancellous bone is the functional tissue referred to as bone marrow. Tright here are two kinds of bone marrow: yellow marrowhead and red marrowhead.

Within the bone marrow, there are unique cells called ‘stem cells’. These are distinctive in that they have actually the ability to become any type of various other kind of cell.

Yellow bone marrowhead is composed primarily of fat, which provides it the yellow color. This fat has a resource of power that can be supplied in times of starvation. The yellow marrowhead consists of stem cells referred to as stroma, which deserve to produce fat, cartilage and bone tissue).

Red bone marrow—likewise referred to as myeloid tissue—contains hemopoietic stem cells, which produce an assortment of various blood cells with haematopoiesis. This mechanism typically produces roughly 500 billion blood cells per day.

A few of these blood cells are the red blood cells connected with transferring oxygen roughly the body, while others, such as lymphocytes, are necessary for support of the immune system.


The bones of the endoskeleton hold around 99% of the body’s calcium, so they play a key part in the regulation of calcium levels within the body with the process of homeostasis.

When blood calcium levels end up being as well high, the hormone calcitonin is released from the thyroid gland also. Calcitonin inhibits the osteoclast cells (those responsible for the break dvery own of bone tissue) within the osteon, and stimulates the osteoblast cells (responsible for the structure of bone tissue), hence taking in calcium to the bone and decreasing the calcium levels in the blood.

When calcium levels are also high, the thyroid gland also releases parathyroid hormone, which acts to inhilittle bit osteoblasts and stimulate osteoclasts, as well as reducing the output of calcium from the kidneys and enhancing the amount of calcium took in by the little intestine, thereby enhancing the blood calcium levels.

Related Biology Terms

Exoskeleton – A rigid outside skeleton, which acts to protect the soft internal of an animal. Cartilage – A smooth malleable tconcern through elastic characteristics that develops component of the endoskeleton, or the whole endoskeleton in the case of chondricthyes. Hydrostatic Skeleton – The endoskeleton of specific soft-bodied pets, which consists of fluid-filled cavities quite than bone or cartilage.


1. The calcium-storing osteocytes are found within the: A. Bone marrowhead B. Cancellous bone C.

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Cortical Bone D. Joints