Human Physiology

Lesson 11 : Bone Structure

Bone Growth

As a young animal grows it becomes taller and longer, due primarily to the growth of the bones. Bone growth occurs by two routes.

• Firstly, new layers of bone can be laid down around the circumference of the shaft, so increasing its diameter.
• Secondly, longitudinal growth occurs from a layer of cartilage, called the growth plate, which lies between the epiphysis and diaphysis. The cartilage cells divide, expand and then die, to be replaced by bone. This process causes the bone to lengthen. The growth plate is radiolucent (allows X-rays through). At skeletal maturity, the growth plate stops dividing, and is replaced by bone, leading to fusion of the epiphysis and diaphysis.
• No. of Bones in skeletal system:
• Total 206 bones in entire skeleton are further categorized as below:
• Axial skeleton - 80 no.
• Appendicular skeleton - 126 no.
Axial Skeleton

1.		1. Crani	-08
		2. Face	- 14
		3. Auditory ossicles	-06
		4. Hyoid	-01
2	Thorax- 25	1. Sternum	-01
		2. Ribs	-24
3	Vertebral Column-26	1. Cervical	-07
		2. Thoracic	-12
		3. Lumbar	-05
		4. Sacrum	-01
		5. Coccygeal	-01

Appendicular Skeleton

1.	Pectoral Girdle- 04	1. Clavicles	-02
		2. Scapula	-02
2	Upper limbs -60	1. Humerus	-02
		2. Radius	-02
		3. Ulna	-02
		4. Carpals	-16
		5. Metacarpals	-10
		6. Phalanges	-28
3	Pelvic Girdle -02
4	Lower limb- 60	1. Femur	- 02
		2. Patella	- 02
		3. Tibia	- 02
		4. Fibula	-02
		5. Tarsal	-14
		6. Metatarsals	-10
		7. Phalanges	-28