Page 173 - 86 human physiology part-2

Chapter 19

The effects of Aging on the Bodys System

Cardiovascular System

The heart looses about 1% of its reserve plumbing capacity every year after we turn 30. Change in
blood vessels that serve brain tissue reduce nourishment to the brain, resulting in the malfunction and
death of brain cells. By the time we turn 80, cerebral blood flow is 20% less, and renal blood flow is
50% less than when we were 30. Decreased blood supply may be a factor in age-related changes
through out the body.

Heart Attack / Myocardial infarction
Acute myocardial infarction (AMI or MI), commonly known as a heart attack, is a disease that
occurs when the blood supply to a part of the heart is interrupted, causing death of heart tissue. It
is the leading cause of death for both men and women all over the world. The term myocardial
infarction is derived from myocardium (the heart muscle) and infarction (tissue death). The
phrase "heart attack" sometimes refers to heart problems other than MI, such as unstable angina
pectoris and sudden cardiac death.

Congestive Heart Failure
In the elderly, ventricular diastolic stiffness can lead to pulmonary circulatory congestion. Aortic
stenosis and aortic insufficiency, elevate left ventricular preload to the point where the left
ventricle becomes stiff and noncompliant, and is common in people 75 years of age or older.
Elevated pressures are transmitted to the pulmonary vasculature and lead to pulmonary edema.

Musculoskeletal System

Bones
Aging is acccompanied by the loss of bone tissue. The haversian systems in compact bone
undergo slow erosion, lacunae are enlarged, canals become widened, and the endosteal cortex
converts to spongy bone. The endosteal surface gradually erodes until the rate of loss exceeds the
rate of deposition. Bone remodeling cycle takes longer to complete because bone cells slow in the
rate of resorption and deposition of bone tissue. The rate of mineralization also slows down. The
number of bone cells also decreases because the bone marrow becomes fatty and unable to
provide an adequate supply of precursor cells. Because bones become less dense, they become
more prone to fractures.

Joints
Cartilage becomes more rigid, fragile, and susceptible to fibrillation. Loss of elasticity and
resiliency is attributed to more cross-linking of collagen to elastin, decrease in water content, and
decreasing concentrations of glycosaminoglycans. Joints are also more prone to fracture due to
the loss of bone mass.

Muscles
Decrease in the range of motion of the joint is related to the change of ligaments and muscles. As
the body ages, muscle bulk and strength declines especially after the age of 70. As much as 30%
of skeletal muscle are lost by age 80. Muscle fibers, RNA synthesis and mitochondrial volume
loss may all be contributors to muscle decline. Other factors that could contribute to muscle loss

388 | Human Physiology