Monday, 6 April 2020

SKELETAL SYSTEM - HUMAN ENDOSKELETON - VERTEBRAL COLUMN - ENGLISH MEDIUM BIOLOGY

SKELETAL SYSTEM
- Skeletal system constitutes hard internal or external living or non-living parts that form the supporting framework of body.
- It is divided into 2 parts.

- Exoskeleton: Which is produced by ectoderm. It is present on the outside of the body (made of either dead tissues or biochemical secretion). Found in both invertebrates and vertebrates
- Endoskeleton: Which is produced by mesoderm. It occurs inside the body and is made of cartilages and bones.

HUMAN ENDOSKELETON
- Divided into two main parts: Axial Skeleton and Appendicular Skeleton.

A. AXIAL SKELETON (Total 80 bones) SKULL

- Skull consists of two main parts cranium and face.
- Cranium (brain box) is formed by 8 bones and provides a bony protection for the brain.
- Face: There are 14 bones which form the skeleton of face.
- There are also present 6 ear ossicles in the skull.
- Another bone is hyoid.

VERTEBRAL COLUMN
- It is made up of 33 vertebrae in which 26 bones are visible because five sacral vertebrae are fused to form one sacrum and four coccygeal vertebrae are fused to form one coccyx

RIBS - Ribs are 12 pairs (12 x 2) of bony bars which form the sides of chest cage. They protect the delicate organs (heart, lungs, etc)

STERNUM or Breast Bone

It is a narrow, elongated and flattened structure, present just under the skin in the middle front of the chest.

B. Appendicular Skeleton (Total 126 bones)
- This skeleton lies laterally and is attached to axial skeleton at an angle. It is made up of girdles (pectoral and pelvic) and limb bones (forelimb and hindlimb)

PECTORAL GIRDLE
- Shoulder girdle - Has 4 bones (two in each pectoral girdle)

 LIMB BONES:
- Forelimbs – Consists of 60 bones.
- Hindlimbs – Consists of 60 bones.
Femur (2) – Thigh (longest bone in the body)
Fibula (2) – Shank (thinnest bone) PELVIC GIRDLE – Has 2 hip bones

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