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39.2 The Human Skeletal System -- Part 1
Members of the cat family walk on their toes, which is an adaptation to running and chasing prey.
Hoofed mammals, such as horses and deer, have long legs and run on the tips of their phalanges.
The lowest part of the horse's body is a modified third digit.
Humans walk on the soles of their feet.
The monkeys and apes' habit of using only forelimbs as they swing through the branches of trees may have evolved from this form of locomotion.
The ancestral mammal has a Dexterity of hands and feet.
The bones of the hands and feet are not fused in humans and apes.
There are different types of skeletons found in animals.
There are five major functions of the skeletal system.
The body's shape is largely determined by the internal framework of the rigid skeleton.
The brain is protected by the skull's bones and rib cage.
The spine protects the cord.
The bones have muscles that pull them.
Body movement is associated with jointed appendages.
There is a matrix in the bones that contains calcium sulphide and calcium sulphide in the blood.
Blood cells and other blood elements are produced in the red bone marrow of the skull.
We describe the characteristics of human bones, the components of various regions of the skeleton, and the different types and functions of joints in this section.
The bones of the human skeleton are composed of cartilage.
These structures are shaped like the bones of the future.
The models are converted to bones after the calcium salts are deposited in the matrix.
The conversion of cartilaginous models to bones is called ossification.
This type of ossification occurs in the skin.
During intramembranous ossification, the tissues give support.
The primary ossification center is located in the middle of the cartilaginous model.
In the primary ossification center, the cells in the area mature into bone-forming osteoblasts.
Secondary ossification centers form at the end of the model.
Growth is possible if the plates remain.
Sex hormones and growth hormones control the rate of growth.
The bone stops growing when the primary and secondary centers of ossification are fused.
The adult's bone is being broken down and built up again.
The cells that absorb bone are called (Gk.
Break down bone, remove worn cells, and deposit calcium in the blood.
osteoclasts help maintain the blood calcium level.
Calcium ion plays a major role in muscle contraction.
The blood calcium level is regulated by hormones.
The activity of osteoclasts is promoted by PTH and the activity of calcitonin is reduced by PTH.
If the blood calcium level is normal, bone destruction caused by the work of osteoclasts is repaired by osteoblasts.
Some of the osteoblasts get caught in the matrix as they form bone.
These cells live in the lacunae of osteons, where they affect the timing and location of bone remodeling.
The rate of bone formation is higher than the rate of bone breakdown.
The mass increases until the age of 30.
The rate of formation and breakdown of bone mass are the same until 50.
The total bone mass slowly decreases as resorption exceeds formation.
As people age, osteoporosis can lead to an increased risk of broken bones, especially of the wrist, spine, and pelvis.
Osteoporosis results in 1.5 million broken bones each year in the United States.
One in four women will experience an osteoporosis-related break in their lifetime, and women are twice as likely as men to have such a break.
The reason for this is that women have less bone mass than men.
Women lose 2% of their bone mass each year after menopause because sex hormones play an important role in maintaining bone strength.
Estrogen replacement therapy has been shown to increase bone mass and reduce fractures, but it can also increase the risk of cardiovascular disease and certain types of cancer.
Other strategies for decreasing osteoporosis risk include consuming 1,000-1,200mg of calcium per day, obtaining sufficientvitamin D, and engaging in regular physical exercise.
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