Chapter 9 - Study Guide
The Approach
1. First read the summary and questions.
2. Next read bolded headings.
3. Finally read the chapter–once through, look up unfamiliar words in the chapter’s key terms.
4. Lastly, re-read the chapter a second time using the support given below
Consider the expectations of Chapter 9
Chapter 9 seeks to teach the following:
a) The cardiovascular (CV) system anatomically consists of the heart, blood vessels of many sizes and thickness, and nerves; CV function depends on these structures to maintain appropriate blood pressure to assure blood flow (and oxygen/carbon dioxide exchange) under rest and stress.
b) Multiple anatomic and physiologic changes occur in the heart with age to include shape change, altered mode of contraction, and accumulation of senescent cells.
c) Blood vessels carrying oxygenated blood from the heart to the tissues are altered with age, becoming less elastic, thicker, and less functional. These changes reduce blood flow and prime the system for CV disease.
d) The benefits of high-intensity aerobic exercise are numerous and serve to dramatically slow CV aging.
Read the pre-sections for Chapters 9, 10 and 11, Internal Organ Systems.
Important points
1. The CV, pulmonary (lungs), GI and renal (kidneys, etc.) systems appear perfectly normal in an elderly person AT REST! It is when these systems are stressed, as in exercise, anxiety, physical activities during the day, that deficits due to aging become evident.
2. One recurrent age change in internal organs is ‘remodeling’ or shape change. Recall that structure determines function, so when structure changes, changes in function (not for the best) are expected.
3. A proven pathway to minimization of aging in internal organs and reduction in vulnerability to disease is with a serious, chronic exercise program (aerobic and resistance).
Overview
Take to heart (no pun intended) the italicized statement that ‘CV maintenance or preservation is key to successful aging,’ so results of interventional studies addressing this provide extremely valuable information for the elderly.
Study Figure 9.1 to appreciate the layout and flow of blood/nutrients/etc. in the closed CV system.
The word homeostasis is important as it refers to the basal or normal range of functional operation (in this case, the CV system). The normal ranges for CV function are given in Table 9.2. You are probably familiar with most of these values. The important point is that higher or lower values are tolerated, but only for fairly short periods of time.
The Heart
Essential points here are:
a) Please note the variety of cell types that make up the heart; of course, each type will be uniquely affected by age.
b) The most abundant cell type in the heart (surprise, surprise) is the fibroblast. Similar to senescent fibroblasts in the dermis of the skin, senescent cardiac fibroblasts contribute to the stiffness of the heart (termed fibrosis).
c) The contractile cells of the heart, called cardiac myocytes, constantly renew themselves. However, this impressive regenerative phenomenon slows with age, and additionally with age renewed cells progress to senescence at a faster rate (recall replicative senescence of Chapter 5). Thus, despite impressive renewal, the staying power of older myocytes declines with age–that is, renewed cells become SASP more quickly.
d) Two conditions–enlargement of heart mass (hypertrophy, usually of the left side) and fibrosis of the heart valves on the left side of the heart–are not generally attributed to aging per se. The exception is aortic valve stenosis.
e) It is important to read the two paragraphs under Cardiac Cycle, etc. This provides very basic physiology of the CV system. There are two important age changes in cardiac function:
· Early diastolic (relaxation) filling time increases due to changes in function of specific myocyte groups; contractions of the aged heart (systole) are too great, leaving less time for the heart to relax (diastole) and therefore, requiring the atria to add more and more blood to the ventricles. The latter requirement creates an enlarged atria (hypertrophy) as well as contributing to diastolic heart failure.
· Cardiac reserve needed for prolonged exercise declines with age. This means that an increase in heart rate, an increase in heart contractility and associated physiological changes will still occur with exercise in the elderly, but the necessary changes are smaller in the elderly compared to that of younger individuals.
NOTE: Re-read paragraph (e) as this is important: in physically inactive elderly people, any stress (exercise, running for the bus, climbing stairs, grocery shopping) encountered that requires an increase in CV function will be limited.
The outcome: decreased blood flow to tissues (hypoxia and inflammation), reduction of independence, inability to continue exercise (exercise intolerance) and desire to stop the physical activity, which leads to more problems (vicious downward spiral).
f) The heart rate fails to increase in exercise in elderly, and may be the biggest contributor to reduced cardiac reserve (exercise intolerance). This has been attributed to several possible changes:
· The disappearance of specific receptors, termed beta-adrenergic receptors. If receptors are not present, the neurotransmitter, norepinephrine, cannot bring about an increase in heart rate.
· Slowing of the innate rhythm of the heart from the SA node.
g) Preconditioning is like hormesis–a small insult protects against a larger insult. This seems to work in young individuals, but some aspects of preconditioning are lost or reduced in the elderly. Thus, a brief bout of oxygen shortage prior to a heart attack reduces the severity of the heart attack in a young person but may not help this way in an older person.
The vasculature
Essential points here are:
a) Understand the blood flow route from the left ventricle to the tissues and back to the right ventricle, then to the lungs. Note the flow of nutrients, oxygen, and carbon dioxide. Learn that blood vessels generally have three layers (the exception is the capillary).
b) Note that the middle layer of arterial blood vessels contains connective tissue. The function here is for support, elasticity, and flexibility. Age-related changes in collagen (as with connective tissue elsewhere, e.g., skin) cause loss of function, or in this case, stiffness. Arterial stiffness is measured by pulse wave velocity (PWV; how fast the pressure wave, generated when the heart contracts, travels through the system and back to the heart). It is a serious problem if the PWV increases, since this means that all of the recipient tissues get their nutrients at higher pressures, leading to tissue damage/inflammation.
c) A phenomena called intimal-medial thickening (an accumulation of artery cells called smooth muscle cells in a space called the intima) occurs with age. Note that many other conditions favor this change (heart disease, unfavorable lipid profile), so it is difficult to sort out the age influence.
d) Small blood vessels called arterioles change with age. This is important because they contribute to optimal tissue blood flow and regulation of the overall system pressure. The cell type here of interest is the endothelial cell; when it becomes replicative senescent, normal endothelial function declines (also stated as a loss of homeostasis). There is a loss of ability of the blood vessel to dilate to allow more blood through, an increased chance for blood clots to form, and permits toxins to enter the vessel wall, leading to plaque formation and artery wall remodeling.
e) Standing up rapidly and feeling light-headed is an example of the baroreceptor reflex in action, but not quite getting the job done. Basically, on sudden standing the blood pressure falls and is rapidly corrected by a reflex (baroreceptor reflex) so that the bold pressure returns to normal. This avoids fainting. This reflex declines with age (and with certain medications).
f) Note the age-related changes that create a vulnerability to disease: senescent endothelial cell assists with promoting atherosclerosis; stiffening heart and blood vessels assists with hypertension and heart failure.
Interventions
Essential points here are:
a) Read over all the data showing that chronic aerobic exercise optimizes heart and blood vessel structure and function. Clearly, an aerobic exercise program can be initiated at any age and found to be beneficial. However, professional advice is wise for those with physical limitations, diseases, and medications.
b) Future work looks to specific drugs (called ACE inhibitors) and to calorie restriction (CR) or CR-mimetics.