Endoskeleton Definition

An endoskeleton is a skeleton discovered within the inner of the body; it gives structural support and protection for the interior organs and also tissues of one organism.

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Endoskeletons deserve to take several forms, and also can different in complexity, shape and function, relying on the demands of the animal. Many vertebrates have an endoskeleton, which is consisted of of mineralized tissue in the form of bone and cartilage. This ‘true skeleton’ is formed from the mesoderm during embryogenesis.

The image shows a diagram of a human being endoskeleton through the significant bones labeled.

Fish within the class chondrichthyes (sharks, rays and also chimaeras) have actually an endoskeleton; although, rather than bone, your skeletons are consisted of of cartilage, muscle and connective tissues.

While the majority of invertebrates have a non-cartilaginous exoskeleton, a select couple of invertebrates have endoskeletons, including squid and octopus, as well as echinoderms such as starfish and also sea urchins.

Porifera (sponges) and cnidarians (jellyfish) are invertebrates that have a type of endoskeleton called a hydrostatic skeleton. Instead of bone or cartilage, it is composed of a cavity referred to as the coelom, i beg your pardon is filled with a gelatinous substance called mesohyl, and is supported by liquid pressure.

An benefit that endoskeletons have over exoskeletons is that—as living tissue— the endoskeleton grow in tandem with the rest of the body. In stimulate to grow from infancy come adulthood, organisms v exoskeletons must melted or ‘molt’ their outer skeletons and also then grow a new one. This is not important with an endoskeleton. During the molting process, an pet is there is no an exoskeleton and is therefore specifically vulnerable. Additionally, it deserve to be very costly in terms of resources to thrive or obtain a brand-new exoskeleton,

While still gift lightweight, endoskeletons are likewise able come support greater body weights 보다 exoskeletons. This permits vertebrate organisms to prosper to much larger sizes than those with external skeletons, such together insects.


There are two species of bone organization within the endoskeleton of humans:

The Cortical Bone

The cortical bone—also dubbed the ‘compact bone’— is the thick bone tissue that creates the difficult exterior and also gives lengthy bones your strength.

Compact bone is created of a calcified matrix containing very couple of spaces, although that does save on computer many little cylindrical columns of only a couple of millimeters wide called lamellae. These lamellae type the osteon or the haversian system.

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

Surrounding the haversian canal room the osteocytes, which keep the mineral tissue of skeletal such together calcium. These osteocytes are associated to each other in a network of small canals called canaliculi, which permits them to carry minerals, fatty acids and waste and also between every other.

Compact spongy bone

The Cancellous Bone

The cancellous bone, additionally known together trabecular bone or ‘spongy bone’, renders up the interior of the bone structure. Cancellous bone is frequently found at the end of the long bones and also the rubs, skull, pelvic bones and the vertebrae of the spinal column.

It is a lightweight and porous bone v the tissue arranged right into a honeycomb-like matrix with huge spaces; these spaces are regularly filled with blood vessels and bone marrow. The main structure that the cancellous bone is developed of slim rod-like bones dubbed trabeculae.

Functions the the Endoskeleton

Protection and also Support

The endoskeleton gives the structural assistance for the body, allowing its owner to stand up; without it, the human body would have no shape.

Although the skeleton does no necessarily prevent damages to external organs such as the skin, it provides a good deal of protection for the inside organs.

The vertebrate skeleton is developed of two various parts:

The axial skeleton is the ‘inner skeleton’. This is consisted of of the skull, the ribcage and also the vertebral column. Its main protective role is because that the main nervous system and also the vital organs such as the lungs, heart, kidneys and liver.

Axial skeleton diagram

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

Appendicular skeleton diagram


Bones, once supported through the role of muscles, supply the capacity of locomotion (movement). The muscles room attached come the bone via tendons or ligaments.

Since the structure of bones is greatly rigid, activity of the skeleton is made possible by connecting bones dubbed joints. There are several different types of joint, permitting different varieties of movement.

The hip and also shoulder have ‘ball and also socket’ joints. The ‘ball’ component of the joint is a spherical bone, i beg your pardon fits within the ‘socket’, and can relocate in almost all directions.

The wrist has actually a ‘condyloid’ joint. This is similar in framework to the ball and socket, and also although it has actually a wide selection of movements, it does not allow the wrist to rotate 360-degrees.

A ‘saddle’ joint is the joint that allows movement in the thumb. This gives the same selection of movements as the condyloid joints back cannot bending backwards.

The ‘hinge’ share is discovered within the fingers and also toes. This allows movement favor the hinge the a door—bending in and also straightening, although not backwards or sideways. The knee and also ankle joints, although hinges, enable a degree of movement when the limb is organized in a particular position.

A ‘pivot’ joint allows rotational movement. This joint have the right to be discovered at the elbow, and also at the vertebrae directly under the skull enabling the head to relocate in a rotation.


The osteocyte cells—star shaped cells that kind a network bordering the haversian canals—are the cell that room responsible because that the maintain of maturation bone.

The bone is comprised of calcium, phosphorus and also other fatty acids, all of which room stored in ~ the osteocytes in the compact bone. Once the body is in require of this nutrients, they can be taken from these stores and also utilized.


Within the cancellous bone is the flexible tissue referred to as bone marrow. There space two types of bone marrow: yellow marrow and also red marrow.

Within the bone marrow, there space special cells called ‘stem cells’. This are unique in the they have the capability to become any type of other form of cell.

Yellow bone marrow is composed primarily the fat, which provides it the yellow color. This fat contains a resource of power that have the right to be offered in time of starvation. The yellow marrow contains stem cells called stroma, i m sorry can develop fat, cartilage and also bone tissue).

Red bone marrow—also dubbed myeloid tissue—contains hemopoietic stem cells, which produce an assortment of different blood cells v haematopoiesis. This system typically produces roughly 500 exchange rate blood cells per day.

Some of these blood cells room the red blood cells connected with transferring oxygen around the body, when others, such as lymphocytes, are important for assistance of the immune system.


The skeletal of the endoskeleton hold about 99% that the body calcium, so they pat a key part in the regulation the calcium levels in ~ the body v the procedure of homeostasis.

When blood calcium levels end up being too high, the hormone calcitonin is exit from the thyroid gland. Calcitonin inhibits the osteoclast cells (those responsible because that the breakdown of bone tissue) within the osteon, and also stimulates the osteoblast cell (responsible for the structure of bone tissue), thus taking in calcium come the bone and decreasing the calcium level in the blood.

When calcium levels are too high, the thyroid gland publication parathyroid hormone, i m sorry acts come inhibit osteoblasts and stimulate osteoclasts, and reducing the calculation of calcium indigenous the kidneys and increasing the lot of calcium absorbed by the small intestine, thereby raising the blood calcium levels.

Related biologic Terms

Exoskeleton – A rigid external skeleton, which plot to safeguard the soft interior of one animal. Cartilage – A smooth malleable tissue through elastic attributes that forms component of the endoskeleton, or the entirety endoskeleton in the instance of chondricthyes. Hydrostatic Skeleton – The endoskeleton of specific soft-bodied animals, which is composed of fluid-filled cavities quite than bone or cartilage.


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

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Cortical Bone D. Joints