Page 116 - 84 human physiolofy part-1

Chapter 6

to 300 moles of ATP daily. This means that each ATP molecule is recycled 2000 to 3000 times during
a single day. ATP cannot be stored, hence its consumption must closely follow its synthesis. On a per-
hour basis, 1 kilogram of ATP is created, processed and then recycled in the body. Looking at it
another way, a single cell uses about 10 million ATP molecules per second to meet its metabolic needs,
and recycles all of its ATP molecules about every 20-30 seconds.

Lactic Acid

Catabolized carbohydrates is known as glycolysis. The end product of glycolysis, pyruvate can go
into different directions depending on aerobic or anaerobic conditions. In aerobic it goes through the
Krebs cycle and is anaerobic it goes through the Cori cycle. In the Cori cycle pyruvate is converted to
lactate, this forms lactic acid, lactic acid causes muscle fatigue. In the aerobic conditions pyruvate goes
through the Krebs cycle. For more about Krebs cycle refer to chapter 2 Cell Physiology.

Muscle Disorders

DERMATOMYOSITIS AND POLYMYOSITIS — Dermatomyositis and polymyositis cause
inflammation of the muscles. They are rare disorders, affecting only about one in 100,000 people per
year. More women than men are affected. Although the peak age of onset is in the 50s, the disorders
can occur at any age.

Signs and symptoms — Patients complain of muscle weakness that usually worsens over several
months, though in some cases symptoms come on suddenly. The affected muscles are close to the trunk
(as opposed to in the wrists or feet), involving for example the hip, shoulder, or neck muscles. Muscles
on both sides of the body are equally affected. In some cases, muscles are sore or tender. Some patients
have involvement of the muscles of the pharynx (throat) or the esophagus (the tube leading from the
throat to the stomach), causing problems with swallowing. In some cases, this leads to food being
misdirected from the esophagus to the lungs, causing severe pneumonia.

In dermatomyositis, there is a rash, though sometimes the rash resolves before muscle problems
occur. A number of different types of rash can occur, including rashes on the fingers, the chest and
shoulders, or on the upper eyelids (show picture 1-3). In rare cases, the rash of dermatomyositis
appears but myopathy never develops.

Other problems sometimes associated with these diseases include fever, weight loss, arthritis, cold-
induced color changes in the fingers or toes (Raynaud phenomenon), and heart or lung problems.

Muscle Atrophy

Alternative names : Atrophy of the muscles, Muscle wasting, Wasting

The majority of muscle atrophy in the general population results from disuse. People with
sedentary jobs and senior citizens with decreased activity can lose muscle tone and develop significant
atrophy. This type of atrophy is reversible with vigorous exercise. Bed-ridden people can undergo
significant muscle wasting. Astronauts, free of the gravitational pull of Earth, can develop decreased
muscle tone and loss of calcium from their bones following just a few days of weightlessness.

116 | Human Physiology