Question

explain how the two growth plates in a long bone account for the ability of a long bone to lengthen. Explain what causes rigor mortis.

Answer 1

Long bones are the bones which are hard,dense and lengthier whose main function is to provide required strength,structure and movement to the body. Long bones are usually cylindrical in shape . It is longer than being wide.

Where are the long bones present :

In the arms - humerus,ulna,radius

In the legs - femur,tibia,fibula.

How the growth plates account for the ability of a long bone to lengthen :

Now, you know about the long bone and its function, we will know how it helps in growth.

The growth plate is surrounded by hard bone as well as porous bone. At the side of this growth plate, is bone shaft which is invaded by osteoblasts. The function of this osteoblast is it deposits mineral at one face of the growth plate. This deposit causes thinning of the growth plate in growing years and the chondrocytes in the growth plate is responsible for cartilage synthesizing which gives the necessary mass to the growth plate. These changes causes the long bone to lengthen.

The effect of these changes result in growth of human being and this occurs during growth years. The growth plate is replaced by porous bone in when the person reaches adulthood and thus the height of person remains same .

Well, this was about the growth plates action in lengthening of long bones.

Causes of Rigor mortis :

Rigor mortis is stiffening of limbs of the corpse (dead body) usually occuring at the third stage of death.

The respiration processes stops after death which causes reduced oxygen levels in the body which is required to make Adenosine TriPhosphate (ATP). ATP is needed for the seperation of actin-myosin cross bridges which helps in relaxation of muscles. When there is no oxygen , the body continues to make this ATP via anaerobic glycolysis. Now when the glycogen in the body is used up and no longer glycogen is available, the body stops making ATP. Thus, unable to break the actin - myosin bridges which is necessary for relaxation of muscles .

Calcium is released into cystol because of reduction in sarcoplasmic reticulum. The calcium activates the formation of actin-myosin cross bridging. Once calcium enters cytosol, it binds with the troponin of thin filaments which cause the troponin -tropomyosin complex to change its shape allowing the myosin heads to continue binding with active sites of actin. Normal relaxation would occur in presence of ATP. Since ATP is absent, the muscles remain contracted.

Rigor mortis usually occurs three to four hours after death which peaks at 12 hours and dissipates after 48 hours .