what is the difference between an endoskeleton and an exoskeleton

what is the difference between an endoskeleton and an exoskeleton

Studying Outcomes

  • Determine the three widespread skeleton designs

Hydrostatic Skeleton

Photo shows a white sea star with red bumps along the tops and tips of its arms.

Determine 1. The skeleton of the red-knobbed sea star (Protoreaster linckii) is an instance of a hydrostatic skeleton. (credit score: “Amada44”/Wikimedia Commons)

A hydrostatic skeleton is a skeleton fashioned by a fluid-filled compartment throughout the physique, referred to as the coelom. The organs of the coelom are supported by the aqueous fluid, which additionally resists exterior compression. This compartment is underneath hydrostatic strain due to the fluid and helps the opposite organs of the organism. The sort of skeletal system is present in soft-bodied animals resembling sea anemones, earthworms, Cnidaria, and different invertebrates (Determine 1).

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Motion in a hydrostatic skeleton is offered by muscle tissues that encompass the coelom. The muscle tissues in a hydrostatic skeleton contract to vary the form of the coelom; the strain of the fluid within the coelom produces motion. For instance, earthworms transfer by waves of muscular contractions of the skeletal muscle of the physique wall hydrostatic skeleton, referred to as peristalsis, which alternately shorten and lengthen the physique. Lengthening the physique extends the anterior finish of the organism. Most organisms have a mechanism to repair themselves within the substrate. Shortening the muscle tissues then attracts the posterior portion of the physique ahead. Though a hydrostatic skeleton is well-suited to invertebrate organisms resembling earthworms and a few aquatic organisms, it isn’t an environment friendly skeleton for terrestrial animals.


Photo shows a crab with orange legs and a black body crawling on a tree.

Determine 2. Muscle mass connected to the exoskeleton of the Halloween crab (Gecarcinus quadratus) enable it to maneuver.

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An exoskeleton is an exterior skeleton that consists of a tough encasement on the floor of an organism. For instance, the shells of crabs and bugs are exoskeletons (Determine 2). This skeleton sort supplies defence towards predators, helps the physique, and permits for motion by means of the contraction of connected muscle tissues. As with vertebrates, muscle tissues should cross a joint contained in the exoskeleton. Shortening of the muscle adjustments the connection of the 2 segments of the exoskeleton. Arthropods resembling crabs and lobsters have exoskeletons that encompass 30-50 p.c chitin, a polysaccharide by-product of glucose that could be a sturdy however versatile materials. Chitin is secreted by the epidermal cells. The exoskeleton is additional strengthened by the addition of calcium carbonate in organisms such because the lobster. As a result of the exoskeleton is acellular, arthropods should periodically shed their exoskeletons as a result of the exoskeleton doesn’t develop because the organism grows.


Photo shows a human skeleton riding a bucking horse skeleton.

Determine 3. The skeletons of people and horses are examples of endoskeletons. (credit score: Ross Murphy)

An endoskeleton is a skeleton that consists of onerous, mineralized constructions positioned throughout the smooth tissue of organisms. An instance of a primitive endoskeletal construction is the spicules of sponges. The bones of vertebrates are composed of tissues, whereas sponges don’t have any true tissues (Determine 3).

Endoskeletons present assist for the physique, defend inner organs, and permit for motion by means of contraction of muscle tissues connected to the skeleton.

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The human skeleton is an endoskeleton that consists of 206 bones within the grownup. It has 5 primary capabilities: offering assist to the physique, storing minerals and lipids, producing blood cells, defending inner organs, and permitting for motion.

The skeletal system in vertebrates is split into the axial skeleton (which consists of the cranium, vertebral column, and rib cage), and the appendicular skeleton (which consists of the shoulders, limb bones, the pectoral girdle, and the pelvic girdle).

Go to the Anatomy Explorer: Skeletal System to be taught the person bones in nice element. See precisely the place they’re discovered within the human physique and be taught extra concerning the goal of every.

In Abstract: Sorts of Skeletal Methods

The three sorts of skeleton designs are hydrostatic skeletons, exoskeletons, and endoskeletons. A hydrostatic skeleton is fashioned by a fluid-filled compartment held underneath hydrostatic strain; motion is created by the muscle tissues producing strain on the fluid. An exoskeleton is a tough exterior skeleton that protects the outer floor of an organism and allows motion by means of muscle tissues connected on the within. An endoskeleton is an inner skeleton composed of onerous, mineralized tissue that additionally allows motion by attachment to muscle tissues.

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