Human Skeletal System: Structure & Functions

Human Skeletal System: Parts, Functions, Diagram, Facts

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:46 PM IST

The human skeletal system forms the structural framework of the body, providing support, protection, and shape. It consists of 206 bones organized into the axial and appendicular skeleton. Along with cartilage, ligaments, and joints, the skeletal system facilitates movement and protects vital organs. In this article, the definition of the skeletal system, skeletal system anatomy, and the physiology of the skeletal system are discussed. The Human Skeletal System is a topic of the chapter Locomotion And Movement in Biology.

This Story also Contains

Definition of Skeletal System
Skeletal System Anatomy
Skeletal System Physiology

Human Skeletal System: Parts, Functions, Diagram, Facts

Definition of Skeletal System

In humans, the skeletal system forms one of the most complex structures or frameworks of bones and connective tissues functioning for structuring, protection, and mobility. The human adult skeleton is composed of 206 bones connected by a system of joints, yet held together with cardiovascular, cartilaginous, ligamentary, and tendinous parts.

It supports the body to take shape and maintain posture, protects vital organs like the brain, heart, and lungs and provides for movement via the articulation of bones and the associated action of bones and muscles. It is also relevant to the foremost physiological processes of human beings, offering storage for minerals and producing blood cells inside the bone marrow.

Skeletal System Anatomy

The structure is discussed below-

Number of Bones in the Human Body

Adult vs. Newborn Skeletal System: Whereas an adult has 206 bones, in a newborn it is about 270 bones. With increasing maturity, some of the bones fuse and hence the number decreases.

Simple Classification of Bones: The bones can be simply classified into four major groups by their shapes, long bones, for example, femur, and short bones, for example. carpals, flat bones, for example. skull, and irregular bones, for example. vertebrae.

Major Components of the Skeletal System

The components are discussed below-

Axial Skeleton

The components of the axial skeleton are:

Skull

This is made up of 22 bones, all together, protecting the brain, and generally forming the structure of the face.

Vertebral column

This is composed of 33 vertebrae, each of which supports the spinal cord a provides protection. These could be grouped into cervical-7, thoracic-12, lumbar-5, sacral-5 fused into the, and coccygeal-4 fused into the coccyx.

Rib cage

This structure is composed of 24 ribs in 12 pairs and the sternum, protects the heart and lungs and supports respiration or breathing.

Appendicular Skeleton

The components of the appendicular skeleton are:

Pectoral girdle

This is made of the clavicles and scapulae. These bones serve to support the limbs of the upper part of the body, hence making wide-ranging movements at the shoulder possible.

Pelvic girdle

The hip bones are created by the ilium, ischium, and pubis. These bones convey the weight from the upper body to the lower extremities while on the same note serving to protect the pelvic organs.

Limbs

The upper limbs consisting of arms, forearms, wrists and hands and the lower limbs consisting of thighs, legs, ankles, and feet are made up of long and short bones that offer locomotion and contact with the environment

Also Read:

NEET Highest Scoring Chapters & Topics

Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis.

Know More

Skeletal System Physiology

The functions are discussed below-

Support and Shape

The skeleton provides a great framework that helps to support the shape and structure of the body. Since the bones are the chief constituent structure of the body, they are easily able to provide support against the force of gravity and bear other external forces upon it.

Protection of Vital Organs

The skull covers, overlays, and protects one of the most important organs in the human body, the brain, against damage.
The protective function of the rib cage shields from direct physical trauma heart and lungs—key molecular structures to cardiovascular and respiratory functions.

Movement and Locomotion

The skeletal system makes movements and locomotions possible through its interaction with the muscular system. More precisely, bones are attachment sites for muscles; when these muscles contract, they will pull on the bones, generating movement at joints.

Mineral Storage

Bones act as a storage site for several crucial minerals, primarily calcium and phosphorus, both of which are critical to many bodily functions in general. This mineral content might then be resorbed back into the bloodstream when required and therefore help in the maintenance of mineral balance and metabolism.

Blood Cell Production

The process of hematopoiesis occurs within the red bone marrow in some bones. It is the area where blood cells are formed. Every day, millions of red blood cells are produced by this process for carrying oxygen, many white blood cells for immune defence, and thousands of platelets required for blood clotting

Also Read:

Ribs and Rib Cage	Vertebral Column
List of 206 Bones in Body	Pectoral Girdle
Axial Skeleton System	Appendicular Skeleton System

Frequently Asked Questions (FAQs)

1. What are the main functions of the human skeletal system?

The important roles played by the human skeleton would include serving to structurally support and give form to the body, protect vital organs, facilitate motion via the joints and attach to the muscles, act as a store of essential minerals like calcium and phosphorus, and produce blood cells within the bone marrow itself.

2. How many bones are in the human body?

There are 206 bones in the human adult. At birth, there are about 270 bones, but some of them fuse during growth and hence bring down this number in adults.

3. What is the difference between the axial and appendicular skeleton?

Axial skeleton incorporates the bones of the skull and vertebral column and case; it mainly serves to support and protect the central nervous system and thoracic organs. The appendicular skeleton consists of the pectoral girdle, pelvic girdle, and bones of limbs. One of the main functions is movement and interaction with the environment.

4. What is osteoporosis, and how can it be prevented?

It is a bone disorder whereby the bone weakens and gets very prone to fracture. This includes its prevention by a healthy diet rich in calcium and Vitamin D, performing weight-bearing exercises regularly, refraining from smoking and excessive consumption of alcohol, and even medication if a doctor advises.

5. What are the types of joints in the human body?

Types of joints in the human body include:

Ball-and-Socket Joints: Allow rotational movement. Example: shoulder, hip.
Hinge Joints: Allow bending and straightening. Example: elbow, knee.
Pivot Joints: Allow rotation around a single axis. Example: neck.
Saddle Joints: Allow for back-and-forth and side-to-side movements. Example: thumb.
Plane Joints: These allow gliding movements; for example, that between the tarsal bones of the foot.
Condyloid Joints: This allows motion but no rotation; for example, that at the wrist.

6. What is osteoporosis and how does it affect the skeletal system?

Osteoporosis is a condition where bones become weak and brittle due to loss of bone density. It affects the skeletal system by increasing the risk of fractures, especially in the hip, spine, and wrist. This condition occurs when bone breakdown outpaces bone formation, often due to age, hormonal changes, or nutritional deficiencies.

7. What is the difference between endochondral and intramembranous ossification?

Endochondral and intramembranous ossification are two processes of bone formation. Endochondral ossification involves the replacement of cartilage with bone tissue and is responsible for the formation of most bones in the body, including long bones. Intramembranous ossification, on the other hand, involves the direct transformation of mesenchymal tissue into bone without a cartilage intermediate. This process forms flat bones like those in the skull.

8. How do ligaments and tendons differ in their roles within the skeletal system?

Ligaments and tendons are both types of connective tissue, but they serve different roles. Ligaments connect bone to bone, providing stability to joints and limiting excessive movement. Tendons, on the other hand, connect muscle to bone, transmitting the force of muscle contractions to create movement. Both are crucial for the proper functioning of the musculoskeletal system.

9. What is the role of osteoclasts in bone health and disease?

Osteoclasts are cells responsible for bone resorption, breaking down bone tissue. In healthy bone metabolism, they work in balance with osteoblasts (bone-building cells) to maintain bone density and shape. However, overactive osteoclasts can lead to excessive bone loss, contributing to conditions like osteoporosis. Conversely, underactive osteoclasts can result in overly dense, brittle bones, as seen in osteopetrosis.

10. What is the significance of Wolff's Law in understanding bone adaptation?

Wolff's Law, proposed by German anatomist Julius Wolff in the 19th century, states that bone in a healthy person or animal will adapt to the loads under which it is placed. In

11. What is the primary function of the human skeletal system?

The primary function of the human skeletal system is to provide structural support for the body, protect vital organs, enable movement through muscle attachment, produce blood cells in bone marrow, and store minerals like calcium and phosphorus.

12. What is the function of the vertebral column?

The vertebral column, or spine, has several crucial functions: it supports the body's weight, protects the spinal cord, allows for flexibility and movement of the torso, and serves as an attachment point for ribs, muscles, and ligaments.

13. How does the skeletal system interact with the muscular system?

The skeletal and muscular systems work together in a system called the musculoskeletal system. Muscles attach to bones via tendons, and when muscles contract, they pull on bones, causing movement. This interaction allows for all voluntary movements of the body.

14. How do weight-bearing exercises benefit bone health?

Weight-bearing exercises, such as walking, jogging, or dancing, benefit bone health by stimulating bone formation. When bones experience stress from these activities, they respond by building more bone tissue, increasing density and strength. This helps prevent conditions like osteoporosis and maintains overall skeletal health.

15. How do joints allow for movement in the skeletal system?

Joints are the meeting points between bones that allow for movement. They work in conjunction with muscles, tendons, and ligaments. Different types of joints allow for various ranges of motion, from the ball-and-socket joint of the hip allowing multi-directional movement to the hinge joint of the elbow permitting bending and straightening.

16. How many bones are in an adult human skeleton?

An adult human skeleton typically consists of 206 bones. However, this number can vary slightly between individuals due to factors like age, genetics, and the presence of accessory bones.

17. What's the difference between the axial and appendicular skeleton?

The axial skeleton includes the bones of the skull, vertebral column, and rib cage, forming the central axis of the body. The appendicular skeleton consists of the bones of the limbs, shoulders, and pelvis, which are attached to the axial skeleton.

18. What is the difference between compact and spongy bone tissue?

Compact bone tissue is dense and forms the outer layer of bones. It provides strength and protection. Spongy bone tissue, found inside bones, has a honeycomb-like structure. It's lighter, allows for blood vessel passage, and houses bone marrow where blood cells are produced.

19. Why are babies born with more bones than adults?

Babies are born with about 300 bones, which fuse together as they grow. This process, called ossification, allows for easier passage through the birth canal and accommodates rapid growth during childhood. For example, the skull bones are not fully fused in infants, allowing for brain growth.

20. What is the role of calcium in bone health?

Calcium is crucial for bone health as it's the primary mineral component of bones. It provides strength and rigidity to the skeleton. Adequate calcium intake and absorption are essential for maintaining bone density and preventing conditions like osteoporosis.

21. How do bones grow and repair themselves?

Bones grow and repair through a process called remodeling. This involves two types of cells: osteoblasts, which build new bone tissue, and osteoclasts, which break down old bone tissue. This continuous process allows bones to adapt to stress, heal from injuries, and maintain strength throughout life.

22. How does the skeletal system change with age?

The skeletal system undergoes several changes with age: bone density tends to decrease, especially after age 30, increasing the risk of osteoporosis; joints may become less flexible due to changes in cartilage; and the spine may compress, leading to a loss in height. These changes can affect posture, mobility, and overall skeletal health.

23. How do hormones influence the skeletal system?

Hormones play a significant role in regulating the skeletal system. For example, parathyroid hormone and calcitonin control calcium levels in the blood and bones. Growth hormone and sex hormones (estrogen and testosterone) influence bone growth and density. Thyroid hormones affect bone turnover rates. Imbalances in these hormones can lead to various skeletal disorders.

24. How does the skeletal system adapt to different physical activities?

The skeletal system adapts to physical activities through a process called Wolff's Law. This principle states that bone will adapt to the loads under which it is placed. For instance, weight-bearing exercises stimulate bone formation, increasing bone density and strength. Conversely, lack of physical activity or prolonged weightlessness (as in space) can lead to bone loss.

25. What is the role of bone marrow in the skeletal system?

Bone marrow, found within the spongy interior of bones, has two crucial roles. Red bone marrow is responsible for producing blood cells (hematopoiesis), including red blood cells, white blood cells, and platelets. Yellow bone marrow primarily stores fat, which can be converted to energy if needed.

26. How does the skeletal system contribute to mineral homeostasis?

The skeletal system acts as a reservoir for important minerals, particularly calcium and phosphorus. When blood levels of these minerals drop, bones can release them to maintain balance. Conversely, when levels are high, bones can absorb and store these minerals. This process is crucial for maintaining proper function of nerves, muscles, and other body systems.

27. What is the function of the skull in the skeletal system?

The skull serves several vital functions in the skeletal system: it protects the brain and sensory organs (eyes, ears, nose), provides a structure for facial features, allows for mastication (chewing) through the mandible (jaw bone), and houses the organs of the vestibular system which controls balance and spatial orientation.

28. How do bones act as levers in the body?

Bones act as levers in the body by providing rigid structures that muscles can pull on to create movement. In this system, joints serve as fulcrums, muscles provide the force, and bones are the lever arms. This arrangement allows for various types of movements and the ability to lift and manipulate objects with different mechanical advantages.

29. What is the process of bone remodeling and why is it important?

Bone remodeling is the continuous process of bone tissue being broken down (by osteoclasts) and rebuilt (by osteoblasts). This process is crucial for maintaining bone strength, repairing micro-damage from daily stress, and adapting bone structure to changing mechanical needs. It also plays a role in calcium homeostasis in the body.

30. What is the role of vitamin D in skeletal health?

Vitamin D plays a crucial role in skeletal health by enhancing the absorption of calcium and phosphorus from the intestines. It also helps maintain proper calcium levels in the blood and promotes bone mineralization. Without adequate vitamin D, bones can become thin, brittle, or misshapen, leading to conditions like rickets in children or osteomalacia in adults.

31. How do fractures heal in the skeletal system?

Fracture healing is a complex process involving several stages: 1) Inflammation, where blood clots form and cells clean the injury site; 2) Soft callus formation, where cartilage forms around the fracture; 3) Hard callus formation, where the cartilage is replaced by spongy bone; 4) Bone remodeling, where the bone is reshaped to its original form. This process can take weeks to months depending on the severity of the fracture and overall health of the individual.

32. What is the function of cartilage in the skeletal system?

Cartilage serves several functions in the skeletal system: it provides a smooth surface at joints to reduce friction during movement, acts as a shock absorber to protect bones during impact, gives shape and support to certain structures (like the nose and ears), and allows for bone growth in children and adolescents through the process of endochondral ossification.

33. How does the skeletal system contribute to the body's immune defense?

The skeletal system contributes to immune defense primarily through the bone marrow. Red bone marrow produces various types of white blood cells, which are crucial components of the immune system. Additionally, bones provide a protective environment for this blood cell production, shielding it from external threats.

34. What is the purpose of the fontanelles in a baby's skull?

Fontanelles are soft spots on a baby's skull where bones haven't yet fused. They serve several purposes: they allow the skull to compress slightly during birth, facilitating passage through the birth canal; they accommodate rapid brain growth in infancy; and they serve as a clinical indicator of hydration and intracranial pressure in young infants.

35. What is the role of osteocytes in bone tissue?

Osteocytes are the most abundant cells in bone tissue. They are former osteoblasts that have become trapped in the bone matrix. Their main functions include: maintaining bone tissue, detecting mechanical stress on the bone, and communicating with other bone cells to initiate remodeling when necessary. They play a crucial role in bone homeostasis and adaptation.

36. How does the skeletal system contribute to acid-base balance in the body?

The skeletal system helps maintain acid-base balance by acting as a buffer. When the body becomes too acidic, bones can release alkaline minerals (like calcium) to neutralize the acid. Conversely, if the body becomes too alkaline, bones can absorb these minerals. This process helps maintain the body's pH within a narrow, healthy range.

37. What is the function of red bone marrow versus yellow bone marrow?

Red bone marrow is primarily responsible for hematopoiesis, the production of blood cells including red blood cells, white blood cells, and platelets. It's found mainly in the spongy bone of flat and short bones, and the epiphyses of long bones. Yellow bone marrow, on the other hand, consists mainly of fat cells and serves as an energy reserve. It's found primarily in the medullary cavity of long bones.

38. What is the role of the periosteum in bone health and repair?

The periosteum is a thin, tough membrane that covers the outer surface of bones (except at joints where cartilage is present). It plays several important roles: it contains blood vessels that nourish the bone, houses nerves that make bones sensitive to pain, contains bone-forming cells (osteoblasts) that aid in bone growth and repair, and provides an attachment point for muscles, tendons, and ligaments.

39. How does the skeletal system contribute to blood pH regulation?

The skeletal system helps regulate blood pH through a process called bone buffering. When blood becomes too acidic, bones release alkaline minerals like calcium and phosphate to neutralize the acid. Conversely, if blood becomes too alkaline, bones can absorb these minerals. This mechanism helps maintain the blood's pH within the narrow range necessary for proper bodily function.

40. What is the significance of the axial skeleton in human evolution?

The axial skeleton, particularly the spine and skull, has undergone significant changes during human evolution. The curvature of the spine and the position of the foramen magnum (the hole at the base of the skull where the spinal cord enters) have adapted to allow for bipedal locomotion. The skull has also changed to accommodate increased brain size and altered jaw mechanics for speech and diverse diets.

41. How do sesamoid bones function in the skeletal system?

Sesamoid bones are small, round bones embedded within tendons. The most well-known example is the patella (kneecap). They function to protect tendons from wear and tear, reduce friction, and alter the direction of muscle pull, thereby increasing the mechanical advantage of the associated muscles. This allows for smoother joint movement and increased force production.

42. How does the skeletal system interact with the endocrine system?

The skeletal system and endocrine system have a complex interrelationship. Bones respond to various hormones like parathyroid hormone, calcitonin, and vitamin D to regulate calcium levels. Growth hormone and sex hormones influence bone growth and density. Conversely, bone cells produce hormones like osteocalcin, which affects glucose metabolism and male fertility, demonstrating that bones also function as an endocrine organ.

43. What is the purpose of synovial fluid in joints?

Synovial fluid is a viscous, clear liquid found in synovial joints (like the knee or elbow). Its primary functions are to reduce friction between articulating cartilage surfaces, absorb shock, and provide nutrients to the avascular cartilage. It also helps remove metabolic wastes from the joint space, maintaining joint health and facilitating smooth movement.

44. How does the skeletal system contribute to thermoregulation?

While not its primary function, the skeletal system contributes to thermoregulation in several ways. The bone marrow, particularly yellow marrow, can act as an insulator. Additionally, shivering, a mechanism for generating heat, involves rapid contraction of skeletal muscles attached to bones. The skeletal system also plays a role in storing and releasing calcium, which is involved in muscle contraction, including those contractions that generate heat.

45. What is the significance of Haversian systems in compact bone?

Haversian systems, also known as osteons, are the fundamental functional units of compact bone. They consist of concentric layers of bone matrix (lamellae) surrounding a central canal containing blood vessels and nerves. This structure allows for the efficient distribution of nutrients throughout the dense bone tissue, maintains bone strength, and facilitates the repair and remodeling of bone.

46. How does the skeletal system adapt to microgravity environments?

In microgravity environments, such as during space travel, the skeletal system undergoes significant changes. Without the constant stress of gravity, bones begin to lose density and strength, a condition known as spaceflight osteopenia. This occurs because the lack of mechanical stress reduces the stimulus for bone formation, while bone resorption continues. Astronauts must engage in specialized exercise routines and may require dietary supplements to mitigate these effects.

47. What is the role of collagen in bone structure and function?

Collagen, particularly Type I collagen, is the main organic component of bone, making up about 90% of the organic matrix. It provides a flexible framework for bone, contributing to its ability to resist tensile stress. Collagen fibers also serve as a scaffold for mineral deposition, particularly hydroxyapatite crystals, which give bone its strength and rigidity. The arrangement of collagen fibers in bone tissue significantly influences its mechanical properties.

48. How does the skeletal system contribute to mineral homeostasis beyond calcium?

While calcium is the most well-known mineral associated with bones, the skeletal system also plays a crucial role in the homeostasis of other minerals. Phosphorus, which combines with calcium to form hydroxyapatite crystals, is stored and regulated by bones. Magnesium, another important mineral for bone health, is also stored in bones. Additionally, bones serve as a reservoir for other trace minerals like zinc, copper, and fluoride, releasing them as needed for various bodily functions.