Introduction
People have no doubt heard everything they need to know about bones. Then why do some people find it confusing to differentiate bone and cartilage? Probably because they read about bone tissue, which is a specialized type of connective tissue. Cartilages are a type of connective tissue (that connects and supports all other tissues in the body), too.
So, what is the difference? Well, for one, bones are not made only of bone tissues. They also consist of nervous, muscle, epithelial, and fibrous tissue that combine to perform a function; this makes bones an organ, whereas cartilage is not.
Bone Vs. Cartilage
Bones are organs that protect the various other organs of the body. They help maintain the body shape, as they form part of the skeleton. Cartilage is a connective tissue that protects the ends of long bones by covering them.
Difference Between Bone And Cartilage In Tabular Form
| Parameters of Comparison | Bone | Cartilage |
| Growth | Bones grow in both directions (bi-directional). | Cartilage grows only in one direction (unidirectional). |
| Type | It is an organ and a tissue. | It is a tissue. |
| Blood vessels and nerves | Bones have blood vessels and nerves. | Cartilages do not have either blood vessels or nerves. |
| Matrix (material between an eukaryotic organism’s cells) | The matrix present in bones may be organic or inorganic. Furthermore, the matrix contains calcium phosphate. | Only organic matrix is present in cartilages and does not contain calcium phosphate. |
| Function | Bones facilitate movement, protect the body from mechanical damage, store minerals, and produce red and white blood cells (aside from protecting organs and providing body shape). | Cartilages reduce friction and act as shock absorbers. |
What Is A Bone?
Simply put, bones are the body’s framework (in vertebrates). They are made up of living tissues that constantly change, grow, and reshape. Bones keep the body stable at all times; it does not matter whether people are active or resting at a given moment. One of the most famous bones of all time is the skull. Sure, they became cool after pirates began using them on their flags, but people have always wanted to crack open another person’s skull (literally and figuratively) for centuries when angered.
Anyway, the skull protects people’s precious brains, and the rib cage protects their hearts. However, the bones are not only meant for protecting organs. Bones have bone marrow (a spongy substance/soft, fatty tissue), which produces white blood cells, platelets, and red blood cells. These cells help build stronger immunity systems, control bleeding, and carry oxygen to all parts of the body (oxygen deprivation is no joke, that is one horrible way to die!).
The bones are made up of bone tissues called cortex/compact bones and cancellous bones. The cortical bones form the hard outer layer of bones and are denser than cancellous bones. 80% of the total bone mass in an adult skeleton is attributed to these bones. When speaking about bones in general, people are referring to compact bones. These bones are responsible for a bone’s white and smooth appearance. The cancellous bones are the inner tissues of the skeletal bone. They are found mostly near the ends of long bones and contain the bone marrow responsible for blood cell production.
Types Of Bones
A newborn baby has 300 bones in its body that fuse as they grow. An adult has 206 bones in the body; however, all these bones are classified under five categories. The five bone types are as follows:
Long Bones
Bones that are longer than they are wide are referred to as long bones. The femur (thighbone), tibia (shinbone), fibulae (calf bone), humeri (the bone that runs from shoulder to elbow), radii and ulnae (forearm bones), metacarpals (palm bones), and metatarsals (group of bones located in the midfoot) make up the long bone category of the human body.
Periosteum, a connective tissue covers the compact bones in long bones. Under the cortical bone layer is the spongy cancellous bone. Long bones grow when the diaphysis (the shaft/midsection) elongates. Epiphysis (rounded ends or tips) are present at each end of the long bones and are covered by hyaline/articular cartilage.
The vertebrae, skull, and long bones are the components that determine an adult’s height. The long bones account for nearly half of a person’s height. So, underdevelopment of bones can lead to a person being short for their age. That is why it is critical to ensure children receive enough nourishment for their bones to grow. After all, no one likes being called shorty.
Short Bones
Short bones are bones approximately equal in length, width, and thickness. Typically, these bones are named after their shapes. A distinct characteristic of short bones is the absence of a bone shaft. Most argue that short bones are located only in carpals (wrist bones) and tarsals (seven bones located between the metatarsals and the lower end of the tibia).
However, others put forward the view that certain long bones that are shorter than the standard ones may be classified as short bones even though they have a bone shaft. Some consider the patellae (kneecap) and the phalanges (finger and toe bones) to be short bones. (Most people are completely uninterested in these debates; to them, bones are just bones. Can’t argue with that logic!)
Flat Bones
Flat bones consist of varying quantities of cancellous bone enclosed between two thin layers of compact bones. These bones have only red bone marrow, unlike the long bones with red and yellow bone marrow. Osteoclast, a type of bone cell found in flat bones, destroys the bone parts making reparation of the rest of the bones challenging. Moreover, they dissolve bone sections that protrude or need to grow and change (who knew that bone cells have such fascinating functions? Now, people know why their professors kept yelling at them to pay attention in class).
Flat bones include the occipital (main cranial bone that forms the back and lower skull part), sternum (breastbone), ribs, hipbone, nasal (nose bridge), vomer (part of the nasal septum), scapulae (shoulder blade), lacrimal (fragile bone of the facial skeleton), frontal (part of the forehead, orbital cavity and the nose), and parietal (the cranium’s sides and roof) bones.
Sesamoid Bones
Sesamoid bones are the bones embedded within a tendon or muscle. The patella (found in the knee) is the largest bone of this category. Other sesamoid bones are found in the wrist, hand, and foot. The red panda and the giant pandas have enlarged radial sesamoid bones (false thumb).
Irregular Bones
The bones that do not fall into the other four categories are called irregular bones (so, they are basically misfits?). They protect nerve tissues, maintain tongue attachment, and join the spinal column’s parts together. Irregular bones are made up of cancellous tissues within a cortex bone layer.
The following are the irregular bones: temporal, sacrum (large triangular bone at the spine’s base), vertebrae (spinal column), coccyx (tailbone), ethmoid (bone that separates nasal cavity from brain), zygomatic (cheekbone), mandible (lower jaw), sphenoid (unpaired bone in neurocranium), maxilla (upper jaw), hyoid (horseshoe-shaped bone in the neck), palatine, and inferior nasal concha.
What Is Cartilage?
In non-complex terms, cartilage is a connective tissue that acts as a shock absorber. They cushion the bone joints and help them function smoothly without rubbing against each other. A membrane called Perichondrium covers the cartilage. Compared to other connective tissues, cartilage takes a longer time to repair.
Cartilage is found in the rib cage, nose, windpipe, ear, etc. The cricoid cartilage forms the back of the voice box in humans. Cartilaginous fish divided into Elasmobranchii (sharks, their close relatives – the rays, skates, and sawfish/carpenter sharks) and Holocephali (chimeras/ghost sharks) have skeletons made of cartilage alone.
Types Of Cartilage
Cartilages are classified into three types with different amounts of collagen (a protein that makes 25 – 35% of whole-body proteins in mammals) and proteoglycan. They are as follows:
Hyaline Cartilage
Predominantly found on joint surfaces, these cartilages are glass-like (hence, the name hyaline) and translucent (allowing light to pass through without scattering it much). They are also found in the larynx/voice box (the cricoid cartilage is an example of hyaline cartilage), ribs, nose, and trachea (windpipe). Hyaline cartilage is composed of Type II collagen and chondroitin sulfate (made up of a chain of alternating sugar). Among the three cartilage types, hyaline is the most abundant one. It forms the temporary embryonic skeleton that bones eventually replace as people grow. The articular cartridge that covers the bones’ articular surface is a type of hyaline cartilage.
Elastic Cartilage
Elastic/fibro elastic/yellow fibrocartilage is present in the pinnae (visible part of the ear) providing its shape and epiglottis (a larynx part). It contains type II collagen, elastin (a protein type that allows tissues to resume their original shape after stretching), fibrillin, etc. The elastic cartilage in the ears supports them and helps maintain their shape/bounce back to their original shape when bent or compressed. That is, they provide strength and elasticity. (Sometimes, babies and toddlers pull their ears. That does not mean they are experimenting with the ear’s elasticity. It’s probably a case of earwax build-up.)
The ones in the larynx facilitate smooth movements of vocal cords and are responsible for voice quality and pitch. The epiglottis (composed of elastic cartilage) covers the opening in the larynx when a person swallows, preventing the food or saliva from entering the windpipe. (Try saying ‘blame the epiglottis’ when someone accidentally chokes on their food; their reactions are hilarious. They do not have a clue what one is talking about! However, a punch to the nose is another possible reaction. So, pick the target carefully.)
Fibrocartilage
Fibrocartilage is unique, as it is the only cartilage with type I collagen in addition to the type II collagen found in other types. It is a connective tissue with a mixture of fibrous and cartilaginous tissues. Fibrocartilage is inflexible and tough due to its resemblance to fibrous tissues, and its elasticity is due to the structural properties it shares with other cartilaginous tissues.
Fibrocartilage is classified into intra-articular, connecting, stratiform, and circumferential fibrocartilage, and each one has a specific function. The intra-articular fibrocartilage acts as buffers and spacers in high-impact, frequently moving bone joints. The C-shaped cartilage in the knee called meniscus (menisci in plural form) is an example of this fibrocartilage type. Meniscus tear is the most common knee injury. That is why many players and athletes wear kneepads/braces (if already injured) to protect/take pressure off their knees when playing.
Connective fibrocartilage cushions limited-movement joints such as the intervertebral discs that cushion each vertebra of the spinal column. The stratiform fibrocartilage is found where tendons glide over bones and help reduce friction. Circumferential fibrocartilage is a ring-shaped, protective tissue that improves how the end of one bone fits into the cavity of another one.
Main Difference Between Bone And Cartilage (In Points)
- Bones are rigid and inelastic, whereas cartilages are soft, elastic, and flexible.
- Cartilage damage is slower to repair as it lacks blood supply. On the other hand, bone damage heals comparatively faster.
- Haversian and Volkmann canals are present in bones; however, cartilage lacks them.
- Cartilages may or may not contain calcium salts, whereas bones have calcium salt deposits.
- Bones make up most of the axial and appendicular skeleton. On the other hand, cartilages are found between bone joints, respiratory tract, etc.
Conclusion
Ultimately, people have no doubts when it comes to bones. After all, nearly everyone has seen and interacted with the creepy skeletons in their science labs (and bones are the easily recognizable part). However, hearing the word ‘cartilage’ may make their brains grind to a halt, as it is not something people generally talk about (unless they are science nerds). Remember, they are merely a type of connective tissue that make up the skeletal system together with bones and ligaments.
People who know the difference between bones and cartilage gain the distinct advantage of being able to annoy everyone around them. Moreover, they can use that ability to shut down any conversationalist who does not heed polite dismissals. Of course, many enthusiastic persons study everything to do with the human body, but people rarely bring up bones and cartilage in general conversation, if they ever do.
References
- https://en.wikipedia.org/wiki/Bone
- https://en.wikipedia.org/wiki/Flat_bone
- https://en.wikipedia.org/wiki/Short_bone
- https://en.wikipedia.org/wiki/Sesamoid_bone
- https://en.wikipedia.org/wiki/Irregular_bone
- https://en.wikipedia.org/wiki/Long_bone
- https://en.wikipedia.org/wiki/Cartilage
- https://en.wikipedia.org/wiki/Elastic_cartilage
- https://en.wikipedia.org/wiki/Hyaline_cartilage
- https://en.wikipedia.org/wiki/Fibrocartilage
- https://my.clevelandclinic.org/health/body/23173-cartilage#
- https://biologydictionary.net/elastic-cartilage/
- https://www.sciencedirect.com/topics/immunology-and-microbiology/fibrocartilage
- https://www.britannica.com/science/fibrocartilage
