HEALTH AND AGING TEXTBOOK NOTES
Chapter 7: Aging and the Regulatory Systems
¾ In order for the organs to function properly, they must recognize changes in both the external and
internal environment and be able to communicate with each other to maintain homeostasis, avert
dangers, and manage growth.
¾ The regulatory systems that manage this communication are the sensory, nervous, endocrine, and
¾ The sensory system is composed of five senses: touch, smell, taste, hearing, and vision.
¾ Sensory organs allow the nervous system to gain information about the external environment.
¾ The skin is the sense organ for touch.
¾ There are age-related changes in both touch receptors and pressure receptors.
¾ With age, these receptors decrease both in number and in sensitivity, resulting in degradation of the
send of touch, with decreased ability to detect, locate or identify objects.
¾ Impaired ability to manipulate small objects is also developed.
¾ Modest changes in the sense of smell occur with age, averaging at about only a 10% decline.
¾ There are decreases in both the number of sensory neurons in the nasal lining and in the olfactory
pathways to the brain.
¾ Large individual differences occur in the preservation of the sense of smell however.
¾ Smoking degrades it, although some function may return if an individual quits smoking.
¾ The olfactory bulb is very close to the hippocampus, and one of the first indicators or incipient
¾ There may be neurological changes in the olfactory bulb as well.
¾ The ability to smell is also important in detecting when food has gone bad.
¾ Most of what we consider taste is actually a function of smell.
glutamate, best known in the form of monosodium glutamate (MSG) often used in Chinese cuisine.
¾ There are differing opinions on whether the sense of taste diminishes with age.
¾ At worst, aging may cause slight decreases in the sensitivity of these neurons, which may be below the
sensory threshold and thus undetectable.
¾ Any gradual losses in taste may actually be due to smoking, periodontal disease, illness, or use of
medications, whereas a sudden loss may be indicative of a brain tumor.
¾ Age-related changes in the auditory structures affect not only hearing but balance as well.
¾ Sound is transmitted through the outer ear via the ear canal into the middle ear through vibrations in
¾ The middle ear contains three ossicles, or little bones, that pass vibrations to the oval window, a
flexible membrane that is the beginning of the inner ear.
¾ A highly complex structure in the inner ear, called the vestibule, allows organisms to sense gravity and
¾ Many age-related changes can affect hearing and balance.
¾ Cells in the ear canal generate earwax, a lubricant that thickens with age and can build up, decreasing
sensitivity to sound.
¾ Although the eardrum itself can become stiffer and the ossicles a bit arthritic, this does not tend to
HEALTH AND AGING TEXTBOOK NOTES
¾ The structures of the inner ear that sense gravity and head position can also degrade overtime, leading
to dizziness and falls.
¾ Presbycusis, or hearing loss with age, is the most common hearing problem.
¾ On average, men lose 80% of hearing capacity by age 90, but women only lose about 30%.
¾ Severe loss can result from exposure to loud noises such as factory machinery, jet planes, military
equipment and even music.
¾ The damage can be temporary, as in the loss of hearing for a day or two after a rock concert, but over
time such damage can become permanent.
¾ Risk factors included ototoxic drug use and occupations with high noise exposure, whereas exercise
was protective, probably due to its positive effects on blood flow.
¾ One may lose a sense of connection to the environment.
¾ A decreased willingness to communicate with others, or to mingle in social settings, frequently
accompanies diminished hearing. Use of hearing aids can migrate hear loss, but people often complain
that aids do not allow then to focus or screen out unwanted sounds.
¾ Tinnitus, often defined as ringing in the ears with no discernable cause, is another common problem
with age. It has many sources, including ear infections, high blood pressure, diabetes, tumors,
atherosclerosis, malnutrition, medications, and toxic chemicals.
¾ If tinnitus becomes severe, however, it can be very distracting and interfere with sleep and everyday
¾ Light passes through the cornea, a transparent structure that protects the eye. By contracting and
dilating, muscles in the iris regulate the amount of light that enters the eye.
¾ At the back of the eye is the retina, which contains photoreceptors (rods and cones).
¾ The lens focuses the image on the retina, adjusting for the distance of the object. The photoreceptors
then translate light energy into action potentials in the optic nerve.
¾ Cones are responsible for the colour vision, whereas rods only transmit information in black and white,
although they are more sensitive to light. Cones are most numerous in the macula.
¾ Rods are typically found in the more peripheral regions of the retina.
¾ The whole structure is supported by gel-like substances called humors in the chamber in the eye.
¾ Aqueous (watery) humor not only provides support but also transport nutrients and wastes, whereas the
more gel-like vitreous humor protects the eye against shock.
¾ The conjunctiva, a clear mucus membrane inside the eyelids, also provides protection.
¾ The cornea, lens, and vitreous humor all diminish in transparency, reducing the amount of light
entering the eye also scattering the light that does come in, making the eye more sensitive to glare.
¾ Yellowing of the lens also decreases its transparency and makes it difficult to differentiate blues,
greens, and violets.
¾ The lens loses elasticity with age, making it more difficult to focus on near objects. This is called
presbyopia and is the most common age-related visual problem.
¾ The muscles in the iris decrease in number and strength with age, and its collagen stiffens, reducing the
ability of the pupil to enlarge.
¾ These changes in the iris also decrease the speed at which it responds to light, so it stays open
fractionally too long when the eye is exposed to bright light and does not expand quickly enough when
the light dims. This makes older adults more vulnerable to glare and reduces their ability to see at
¾ The fluids in the eye also show age-related changes.
¾ The rate at which aqueous humor is generated also declines, and there might not be enough to properly
maintain the shape of the cornea. Vitreous humor also decreases in size and becomes more liquid.
¾ The retina also undergoes age-related changes. Cones and rods loss sensitivity progressively from
adolescents through the remainder of the lifespan.
¾ Cones are stable, but rods in the central retina are vulnerable to aging.
light. Optic nerve fibers are also lost, decreasing the quality of vision.
¾ The four most common serious diseases of the eye in late life are cataracts, macular degeneration,
glaucoma, and diabetic retinopathy.
HEALTH AND AGING TEXTBOOK NOTES
¾ Cataract is characterized by cloudiness or opacity of the lens; the can occur at any age but is found
much more frequently in later years. Although painless, with time, cataracts can interfere with vision,
particularly at night or in bright sunlight.
¾ The main risk factors for developing cataracts, beside age, are exposure to UV-B light and
environmental pollutants, topical or internal steroids, diabetes, smoking, dehydration, etc.
¾ Cataracts are easily treatable by surgery, which involves removal of the damaged lens and its
replacement by an artificial one.
¾ Cataracts are the leading cause of blindness among elders in developing countries.
¾ In this country glaucoma is a leading cause of blindness in adults over the age of 50.
¾ It is caused by buildup of aqueous humor in the eye, which results in intraocular pressure and damage
to the retina and optic nerve.
¾ There are several ways to control the damages of glaucoma, including medications and laser therapy,
but early detection is the key to prevention of retinal damage.
¾ One of the most deleterious retinal diseases is age-related macular degeneration (AMD), a disease that
accounts for about 40% of visual impairment in people over the age of 80 and is the leading cause of
severe vision loss in people over 60.
¾ The wet form is responsible to the most cases in which there is severe vision loss.
¾ It appears that free radicals damage the supply of nutrients to the retina, and the macula of the eye
degenerates, destroying central vision.
¾ Exposure to UV rays and smoking are probably the major risk factors, but there is some evidence that
the ingestion of vegetable fats also increases the risk of AMD.
Basic Anatomy and Physiology
¾ The nervous system is the primary regulator of the body.
¾ It monitors and provides communication between all the systems and regulates homeostasis.
¾ It also permits voluntary movement and underlies all cognitive processes, including sensation,
attention, language, memory, emotions, and problem solving.
¾ The central nervous system (CNS) consists of the brain and the spinal cord; the peripheral nervous
system (PNS) consists of sensory and motor neurons.
¾ The autonomic nervous system (ANS) is responsible for all regulatory functions, including monitoring
and controlling blood pressure, digestion, respiration, and temperature; it includes components of both
the CNS and PNS.
¾ There are several types of neuronal cells, but each consists of a cell body or coma, and axon, and
¾ Neurons communicate with each other across interneuronal junctions called synapses.
¾ Communication across synapses is primarily chemical, but can be electrical, especially outside of the
¾ Cerebrospinal fluid (CSF) also provides support for the brain.
¾ The ventricles serve as a type of internal cushion from the brain, protecting it from injury.
¾ Wrapped around the brain stem is the cerebellum which controls balance, body position, and
movement in space and may store certain types of procedural memory related to movement, such as
riding a bicycle.
¾ The limbic system is wrapped around the thalamus, which helps initiate consciousness and sort
¾ The cerebrum is by far the largest part of the brain and is divided into two hemispheres connected by
the corpus callosum.
¾ The cerebrum consists largely of white matter and is covered by the cortex, which consists of gray
¾ Each half of the cortex is divided into several lobes, including the occipital, parietal, temporal, and
¾ The occipital lobe processes visual information; the parietal lobe processes somatosensory
information; the frontal lobes control voluntary motor behaviour language production, and high-order
cognitive and emotional processing, and the temporal lobes process hearing, recognition of faces, and
higher-order visual processing and may be involved in emotional control.
In order for the organs to function properly, they must recognize changes in both the external and internal environment and be able to communicate with each other to maintain homeostasis, avert dangers, and manage growth. The regulatory systems that manage this communication are the sensory, nervous, endocrine, and immune systems. The sensory system is composed of five senses: touch, smell, taste, hearing, and vision. Sensory organs allow the nervous system to gain information about the external environment. The skin is the sense organ for touch. There are age-related changes in both touch receptors and pressure receptors. With age, these receptors decrease both in number and in sensitivity, resulting in degradation of the send of touch, with decreased ability to detect, locate or identify objects. Impaired ability to manipulate small objects is also developed. Modest changes in the sense of smell occur with age, averaging at about only a 10% decline.