Endoskeleton Definition

An endoskeleton is a skeleton uncovered within the inner of the body; it offers structural support and protection because that the internal organs and also tissues of an organism.

You are watching: Which of these has an endoskeleton?

Endoskeletons deserve to take numerous forms, and can different in complexity, shape and also function, relying on the demands of the animal. Many vertebrates have actually an endoskeleton, i beg your pardon is consisted of of mineralized tissue in the form of bone and cartilage. This ‘true skeleton’ is developed from the mesoderm throughout embryogenesis.

The image shows a chart of a person endoskeleton v the significant bones labeled.

Fish in ~ the course chondrichthyes (sharks, rays and chimaeras) have actually an endoskeleton; although, quite than bone, their skeletons are consisted of of cartilage, muscle and connective tissues.

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

Porifera (sponges) and cnidarians (jellyfish) space invertebrates that have actually a kind of endoskeleton referred to as a hydrostatic skeleton. Instead of bone or cartilage, it is composed of a cavity dubbed the coelom, i m sorry is filled v a gelatinous substance referred to as mesohyl, and is supported by liquid pressure.

An benefit that endoskeletons have over exoskeletons is that—as life tissue— the endoskeleton grows in tandem with the rest of the body. In order to prosper from infancy come adulthood, organisms v exoskeletons must shed or ‘molt’ their external skeletons and then prosper a brand-new one. This is not necessary with an endoskeleton. Throughout the molting process, an pet is there is no an exoskeleton and also is therefore an especially vulnerable. Additionally, it have the right to be really costly in state of sources to prosper or gain a brand-new exoskeleton,

While still being lightweight, endoskeletons are additionally able come support better body weights 보다 exoskeletons. This permits vertebrate organisms to thrive to much bigger sizes than those with external skeletons, such together insects.


There room two varieties of bone tissue within the endoskeleton the humans:

The Cortical Bone

The cortical bone—also called the ‘compact bone’— is the thick bone organization that forms the tough exterior and gives long bones their strength.

Compact bone is developed of a calcified matrix containing very couple of spaces, although the does contain many tiny cylindrical columns of just a couple of millimeters wide called lamellae. This lamellae type the osteon or the haversian system.

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

Surrounding the haversian canal room the osteocytes, which keep the mineral organization of skeletal such as calcium. These osteocytes are associated to each various other in a network of small canals referred to as canaliculi, which allows them to deliver minerals, fat acids and waste and between every other.

Compact spongy bone

The Cancellous Bone

The cancellous bone, also known as trabecular bone or ‘spongy bone’, provides up the interior of the bone structure. Cancellous bone is commonly found at the end of the long bones as well as the rubs, skull, pelvic bones and the vertebrae that the spinal column.

It is a lightweight and also porous bone with the organization arranged right into a honeycomb-like procession with huge spaces; these spaces are often filled through blood vessels and bone marrow. The main structure of the cancellous bone is developed of thin rod-like bones referred to as trabeculae.

Functions the the Endoskeleton

Protection and Support

The endoskeleton offers the structural assistance for the body, allowing its owner to stand up; there is no it, the human body would have actually no shape.

Although the skeleton does no necessarily prevent damages to outer organs such together the skin, it offers a good deal of protection for the within organs.

The vertebrate skeleton is formed of two different parts:

The axial skeleton is the ‘inner skeleton’. This is comprised of the skull, the ribcage and also the vertebral column. Its main protective duty is for the central nervous system and 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 also arm bones and the legs and also feet. This part of the endoskeleton protects and also supports the limbs.

Appendicular skeleton diagram


Bones, as soon as supported by the role of muscles, provide the volume of locomotion (movement). The muscles space attached come the bone via tendons or ligaments.

Since the structure of bones is mostly rigid, activity of the skeleton is made possible by connecting bones dubbed joints. There are numerous different varieties of joint, allowing different arrays of movement.

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

The wrist has a ‘condyloid’ joint. This is comparable in structure to the ball and also socket, and also although it has a wide variety of movements, it does not enable the wrist to rotate 360-degrees.

A ‘saddle’ share is the share that enables movement in the thumb. This gives the same selection of activities as the condyloid joints return cannot bending backwards.

The ‘hinge’ joint is found within the fingers and toes. This allows movement favor the hinge of a door—bending in and also straightening, although no backwards or sideways. The knee and also ankle joints, return hinges, allow a degree of movement when the body is organized in a particular position.

A ‘pivot’ joint permits rotational movement. This joint deserve to be discovered at the elbow, and also at the vertebrae straight under the skull permitting the head to relocate in a rotation.


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

The bone is consisted of of calcium, phosphorus and also other fatty acids, every one of which are stored in ~ the osteocytes in the compact bone. As soon as the human body is in require of this nutrients, they have the right to be bring away from this stores and utilized.


Within the cancellous bone is the versatile tissue called bone marrow. There space two types of bone marrow: yellow marrow and red marrow.

Within the bone marrow, there are special cells referred to as ‘stem cells’. This are distinctive in that they have actually the ability to become any kind of other kind of cell.

Yellow bone marrow is composed primarily of fat, which gives it the yellow color. This fat contains a resource of power that deserve to be provided in times of starvation. The yellow marrow includes stem cells called stroma, which can produce fat, cartilage and bone tissue).

Red bone marrow—also dubbed myeloid tissue—contains hemopoietic stem cells, which produce an assortment of various blood cells with haematopoiesis. This system frequently produces around 500 exchange rate blood cells per day.

Some of this blood cells are the red blood cells associated with carrying oxygen around the body, while others, such as lymphocytes, are crucial for assistance of the immune system.


The skeletal of the endoskeleton hold approximately 99% that the body calcium, for this reason they pat a vital part in the regulation that 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 cell (those responsible for the malfunction of bone tissue) in ~ the osteon, and stimulates the osteoblast cell (responsible because that the structure of bone tissue), thus absorbing calcium come the bone and decreasing the calcium level in the blood.

When calcium levels room too high, the thyroid gland release parathyroid hormone, i m sorry acts to inhibit osteoblasts and also stimulate osteoclasts, and also reducing the calculation of calcium from the kidneys and increasing the quantity of calcium absorbed by the little intestine, thereby boosting the blood calcium levels.

Related biology Terms

Exoskeleton – A rigid exterior skeleton, which plot to defend the soft inner of one animal. Cartilage – A smooth simple tissue v elastic qualities that forms component of the endoskeleton, or the totality endoskeleton in the situation of chondricthyes. Hydrostatic Skeleton – The endoskeleton of certain soft-bodied animals, which consists of fluid-filled cavities fairly than bone or cartilage.


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

See more: How Far Is Myrtle Beach South Carolina From Atlanta Georgia, It'S 362 Miles From Atlanta To Myrtle Beach

Cortical Bone D. Joints