Human Skeletal System PDF

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‘Human Skeletal System’ is an important topic under general science. Often 2-3 questions asked about this topic in most of the competitive exams like SSC, Banking, Rail and State government exams etc. Dear Aspirants, at the end of this topic ‘Human Skeletal System‘ there is a link through which you can download the full PDF of the topic.

Human Skeletal System
Human Skeletal System

Introduction of Human Skeletal System

What is Human Skeletal system?

☞ The skeletal system is a network of bones and Cartilages.

☞ The skeletal system played a crucial role in movement shown by the body.

☞ The human skeletal System composed of around 270 bones at birth.

In adulthood, some of the bones get fused together, and the total number of bones decreases to around 206 bones.

☞ This 270 bones (at birth) or 206 bones (Adult) worked together and build a framework, which protects soft organs in our body.

Composition of Skeletal System

☞ The human skeletal system consists of bones, cartilage.

☞ Bone and cartilage are specialized connective tissues.

☞ The Bone has a very hard matrix due to calcium salts.

☞ And the Cartilage has slightly pliable matrix due to chondroitin salts.
☞ In human beings, the skeletal system is made up of 206 bones and a few cartilages.

Composition of Human Bones

☞ Bone consists of a 30% flexible matrix and 70% bound minerals.

☞ This Bone matrix is composed of 90 to 95% elastic collagen fibers.

☞ Collagen fibers also known as ossein.

☞ An inorganic salt, Calcium phosphate hardens this bone matrix.

☞ So, Collagen and Calcium phosphate are the two principal components of bone.

99 percent of our body calcium is held in our bones and teeth.

☞ Bones have an internal structure similar to a honeycomb.

Important Fact about Human Bones

• The longest bone in the Human Body – Femur (in thigh)

• The smallest bone in the human body – Stapes (in the middle ear)

• The adult human skeleton is made up of – 206 bones

• The human infants is made up of – 270 bones

• Two principal components of bone – Collagen and Calcium phosphate

• The study of bones is called – Osteology

Types of Human Bones

☞ Human body consists of five types of bones.They are _
• 1 – Long Bones
• 2 – Short bones
• 3 – Flat bones
• 4 – Sesamoid bones
• 5 – Irregular bones.

◘ Long bones
• A long bone is a bone that has a shaft (diaphysis) and 2 expanded ends (epiphyses).

• It has a thick outside layer of compact bone and a bone marrow filled inner medullary cavity.

• These bones tend to support body weight and helps in movement.

• Example – Femur, Ulna.
• Femur is the longest bone in human body.

◘ Short bones
• Short bones are as wide as they are long.

• Their primary function is to provide support and stability.
• Example – Carpals, Tarsals.

 Flat bones
• Flat bones are thin and curved.
• Flat bones have three layers.
• Two outer layers of compact bone,
• and an inner layer of spongy bone.

• It’s principal function is to provide protection of the muscular attachment of our body.

• Example – Cranium (skull), the ilium (pelvis), sternum and the rib cage.

◘ Sesamoid bones
• A sesamoid bone is a bone embedded within a tendon or a muscle.

• The name sesamoid is derived from the Arabic word sesamum (“sesame seed”), indicating the small size of most sesamoids.
 Example – Patella or kneecap

◘ Irregular bones
• As their name implies, these are completely irregular in shape.

• They are often protecting organs or tissues.

• Example – Hip bone, base of skull.

Types of Skeletal Systems

☞ Skeletal System is divided into two types_ They are
1. Exoskeleton
2. Endoskeleton

◘ Exoskeleton
• An exoskeleton (Exo means outer) is the external skeleton that is present on the body surface.

• Exoskeleton supports and protects animal’s body.

Exoskeleton which have a larger size are known as “shells”.

• Examples – exoskeleton of grasshoppers , cockroaches, crabs , lobsters, and shells of snails, clams.

Tortoise and Turtle, have both an endoskeleton and an exoskeleton.

◘ Endoskeleton
• The skeleton found inside the body is called endoskeleton.
It originates from the mesoderm.
• The vertebrate endoskeleton is made up of bones and cartilages.

◘ Difference between Endoskeleton and Exoskeleton

Endoskeleton Exoskeleton
Present inside the body Present outer surface of the body
Endoskeleton is made up of bones and cartilage. Exoskeleton is made up of scales, chitinous cuticle and calcified shells.
It is found in vertebrates. It is mainly found in arthropods (Spiders, millipedes, centipedes, crabs, insects etc)
It is a living structure. It is a non-living structure..
It develops from the endoderm. It develops from the ectoderm
Animals with endoskeleton do not undergo molting. Animals with exoskeleton molted periodically during growth.

 

Functions of Skeleton

◘ Protective Function
The skeletal system protects the internal organs from injury by covering or surrounding them.

For example – Ribs protect our lungs and heart, Cranial bones and Spinal cord is protected by vertebral column (spine). and the cranial bones (skull) protects our brain.

◘ Supportive Function
☞ The bones and cartilages of the skeletal system provide supports to the soft body organs.

◘ Helps in Movement
Semi-rigid connective tissue found on the skeleton support movement.

◘ Mineral reservation
☞ The tissue present in bones acts as a reservoir of important minerals, like calcium, and phosphorus.

☞ These minerals, stores into bone tissue.

☞ To maintain the level of these minerals , the stored minerals in bone released back into the bloodstream.

Calcium ions, are essential for muscle contractions and are involved in the transmission of nerve impulses.

◘ Haematopoiesis
☞ The red bone marrow present in bone produced Red blood cells, white blood cells, and platelets. Production of red blood cells known as hematopoiesis. [ hemato- = “blood”, -poiesis = “to make”]

◘ Other function
☞ The skeletal system also gives the body its shape and size, provide the balance features to the body, and helps in breathing and hearing. (for an example the ear bones transmit the sound vibrations from the tympanic membranes to the internal ear)

Counting of 206 Human bones (Table format)

☞ The adult human skeleton consists of 206 bones.

☞ This 206 bones are grouped into , the axial skeleton and appendicular skeleton.

☞ Parts of Appendicular skeleton
• Bones of the limbs
• Shoulders
• Pelvic girdle.

☞ Parts of Axial skeleton
• Bones of the skull
• Vertebral column
• Thoracic cage

Appendicular Skeleton

Part of Body Part of Endoskeleton Region Number of Bones Number
Thorax
Hip
Forelimbs
Pectoral girdle
Pelvic girdle
Shoulder Scapula-Clavicle 2 * 2
Pelvis Osinnominatum 2
Upper Arm Humerus 2
Fore arm Radius-Ulna 4
Wrist Carpals 16
Palm Metacarplas 10
Fingers Phalanges 28 * 2
Thigh Femur 2
Shank Tibio-Fibula 4
Knee Patella 2
Ankle Tarsals 14
Sole Metatarsals 10
Total 126
Appendicular Skeleton
Appendicular Skeleton
Appendicular Skeleton
Appendicular Skeleton

Axial Skeleton

Part of Body Part of Endoskeleton Region Names of Bones Number
Head Skull Cranium Occipital 1
Parietal 2
Frontal 1
Temporal 2
Sphenoid 1
Ethmoid 1
Facial region Nasal 2
Vomer 1
Turbinal 2
Lacrymal 2
Zygomatic 2
Palatine 2
Maxila 2
Mandible 1
Ear
Ossicles
Malleus 2
Incus 2
Stapes 2
Back bone Vetebral column Hyoid Hyoid body 1
Neck Cervical vertebrae 7
Thorax Thoracic vertebrae 12
Waist Lumber vertebrae 5
Sacrum Sacral vertebra Sacrum 1
Tail Caudal vertebrae
/ Coccyx
1
Thorax Sternum
Ribs
Sternum 1
Ribs 24
Total 80
Total Bone = Appendicular Skeleton + Axial Skeleton = 126 + 80 = 206

Diagram of Axial and Appendicular skeletal system of Human

Diagram of Axial and Appendicular skeletal system of Human 
Diagram of Axial and Appendicular skeletal system of Human

Counting of 206 Human bones (Simplified format)

Appendicular Skeleton

• The appendicular skeleton, comprising the arms and legs, including the shoulder and pelvic girdles, contains 126 bones.

■ Bones in Arms
◘ Human Arms consist of 64 bones (32 in each arm)

◘ Bones in Upper Arm [ 3 × 2 = 6 bones , 3 on each side]
☞ Humerus – 2
♦ Under Pectoral girdle (shoulder)
☞ Scapula – 2
☞ Clavicles – 2

◘ Bones in Lower Arm( 2× 2 = 4 bones, 2 on each side)
☞ Ulna – 2
☞ Radius – 2

◘ Bones in Hand (27 × 2 = 54 bones, 27 in each hand)
♦ Under Carpals
☞ Scaphoid bone – 2.
☞ Lunate bone – 2.
☞ Triquetral bone – 2
☞ Pisiform bone – 2
☞ Trapezium – 2
☞ Trapezoid bone – 2
☞ Capitate bone – 2
☞ Hamate bone – 2
☞ Metacarpals ( 5 × 2 =10 bones, 5 on each side)

♦ Under Phalanges of the hand
☞ Proximal phalanges ( 5 × 2 =10 bones , 5 on each side)

☞ Intermediate phalanges (4 × 2 = 8 bones, 4 on each side)

☞ Distal phalanges (5 × 2 = 10 bones , 5 on each side)

✪ Total = 6 (upper arm) + 4 (lower arm) + 54 (both hands) = 64

■ Bones in Pelvis (pelvic girdle)
☞ Pelvis region contain Two coxal bone.

☞ These 2 coxal bone is made up of 3 region (fused together), They are: ilium, ischium, and pubis.

■ Bones in Leg
◘ There are a total of 30 × 2 = 60 bones , 30 in each leg.

☞ Femur – 1× 2 = 2 bones
☞ Patella or kneecap – 1× 2 = 2 bones
☞ Tibia – 1× 2 = 2 bones
☞ Fibula – 1× 2 = 2 bones.

♦ Bones in Foot (26 × 2 = 52 bones, 26 per foot)

♦ Human foot consists of Tarsals , Metatarsals and phalanges

➧ Bones in Tarsals (7 × 2 = 14 bones, 7 in each Tarsals )

☞ Calcaneus or heel bone – 1 × 2 bones
☞ Talus – 1 × 2 = 2 bones
☞ Navicular bone – 1 × 2=2 bones

☞ Medial cuneiform bone – 1 × 2=2 bones

☞ Intermediate cuneiform bone – 1 × 2 =2 bones

☞ Lateral cuneiform bone – 1 × 2=2 bones

☞ Cuboid bone – 1 × 2 = 2 bones

➧ Bones in Metatarsals – 10 bones

➧ Bones in Phalanges of the foot (14 × 2= 28 bones, 14 in each Phalanges )

☞ Proximal phalanges – 5 × 2 = 10 bones

☞ Intermediate phalanges – 4 × 2 = 8 bones

☞ Distal phalanges – 5 × 2 = 10 bones

Axial Skeleton

The axial skeleton, comprising the spine, chest and head, contains 80 bones.

■ Bones in Spine
◘ A fully grown adult have 26 bones in the spine.☞ Cervical vertebrae – 7 bones
☞ Thoracic vertebrae – 12 bones
☞ Lumbar vertebrae – 5 bones
☞ Sacrum – 1 bones (Adult)
☞ Coccygeal vertebrae – 1 bone

■ Bones in Chest (Thorax)
◘ There are 25 bones in the chest.
☞ Sternum – 1
☞ Ribs – 24, in 12 pairs

■ Hyoid Bone – 1

■ Bones in Skull
◘ Human skull made up of 22 bones

◘ Human Head contains 28 bones, including the bones of the middle ear.

Axial Skeleton
Axial Skeleton
28 bones in Head ➥ 22 + 6 = 28
22 bones in Skull ➥ 14 + 8 = 22 6 bones in Ear
8 Cranial Bones 14 Facial Bones 3 × 2 = 6 Bones
• Occipital bone
• Parietal bones – 2
• Frontal bone
• Temporal bones – 2
• Sphenoid bone
• Ethmoid bone
• Nasal bones – 2
• Maxillae – 2
• Lacrimal bone – 2
• Zygomatic bone – 2
• Palatine bone – 2
• Inferior nasal concha – 2
• Vomer – 1
• Mandible – 1
• Malleus – 2
• Incus – 2
• Stapes – 2
Bones in Skull and Bones in Hand
Bones in Skull and Bones in Hand
Human Skeletal Systems
Human Skeletal Systems

Disorders of Human Skeletal Systems

Disease Description
Osteoporosis It is an age-related disorder in which bones lose mineral density, weaken, and break more easily than normal bones.
Osteoarthritis Osteoarthritis occurs due to breakdown of joint cartilage and bone. The most common symptoms are joint pain and stiffness include joint swelling.
Paget’s disease Paget’s disease is a chronic bone disorder that causes affected bones to become large and misshapen.
Bursitis Bursitis is the painful swelling of a small, fluid-filled sac called a bursa due to physical injury.The most common locations for bursitis are in the shoulder, elbow and hip
Rickets Rickets is a skeletal disorder in which the development of bone disrupted. Rickets caused by the lack of vitamin D. It is a common disease in children. It causes bone pain, poor growth and soft, weak bones that can lead to bone deformities
Osteomalacia Osteomalacia is the most common nutritional deficiency among adults. Osteomalacia is a disorder of “bone softening” occurs due to prolonged deficiency of vitamin D.

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