neurotransmitters stress
stressors
L E A R N I N G O B J E C T I V E S
On completion of this chapter, the reader will
● Explain homeostasis.
● List four categories of stressors that affect homeostasis.
● Identify two beliefs about the body and mind based on the concept of holism.
● Identify the purpose of adaptation and two possible outcomes of unsuccessful adaptation.
● Trace the structures through which adaptive changes take place.
● Differentiate between sympathetic and parasympathetic adaptive responses.
● Define stress.
● List 10 factors that affect the stress response.
● Discuss the three stages and consequences of the general adaptation syndrome.
● Name three levels of prevention that apply to the reduction or management of stress-related disorders.
● Explain psychological adaptation and two possible outcomes.
● List eight nursing activities helpful to the care of clients prone to stress.
● List four approaches to preventing, reducing, or eliminating a stress response.
HEALTHis a tenuous state. To sustain it, the body continuously adapts to stressors
(changes with the potential to disturb equilibrium). As long as stressors are minor, the body’s responses are negligible and generally unnoticed. When stressors are intense or numerous, efforts to restore balance may cause uncomfortable signs and symptoms.
With prolonged stress, related disorders and even death may occur.
Homeostasisis a relatively stable state of physiologic equilibrium; it literally means
“staying the same.” Although it sounds contradictory, staying the same requires con- stant physiologic activity. The body maintains constancy by adjusting and readjust- ing in response to changes in the internal and external environment that foster disequilibrium.
Holism
Although homeostasis is associated primarily with a person’s physical status, emo- tional, social, and spiritual components also affect it. As discussed in Chapter 4, holism implies that entities in all these areas contribute to the whole of a person. Based on the principles of holism, stressors may be physiologic, psychological, social, or spiritual (Table 5-1).
HOMEOSTASIS
60
C H A P T E R 5 ● Homeostasis, Adaptation, and Stress 61
Holism is the foundation of two commonly held beliefs:
(1) both the mind and body directly influence humans, and (2) the relationship between the mind and body can potentially sustain health as well as cause illness. Conse- quently, it is helpful to understand how the mind perceives information and makes adaptive responses. Both physical and psychological mechanisms of perception and adapta- tion are discussed later in this chapter.
COMMON STRESSORS
TABLE 5-1
PHYSIOLOGIC PSYCHOLOGICAL SOCIAL SPIRITUAL Prematurity
Aging Injury Infection Malnutrition Obesity Surgery Pain Fever Fatigue Pollution
Fear
Powerlessness Jealousy Rivalry Bitterness Hatred Insecurity
Gender, racial, age discrimination Isolation Abandonment Poverty
Conflict in relationships Political instability Denial of human rights Threats to safety Illiteracy Infertility
Guilt Doubt Hopelessness Conflict in values Pressure to join, abandon,
or change religions Religious discrimination
Stop • Think + Respond BOX 5-1 List physiologic, psychological, social, and spiritual stress- ors that can affect homeostasis among nursing students.
Adaptation
Adaptation(how an organism responds to change) requires the use of self-protective properties and mechanisms for regulating homeostasis. Neurotransmitters mediate homeostatic adaptive responses by coordinating functions of the central nervous system, autonomic nervous system, and endocrine system.
Neurotransmitters
Neurotransmitters(chemical messengers synthesized in the neurons) allow communication across the synaptic cleft between neurons, subsequently affecting thinking, behav- ior, and bodily functions. When released, neurotransmit- ters temporarily bind to receptor sites on the postsynaptic neuron and transmit their information. After this is accomplished, the neurotransmitter is broken down, recaptured for later use, or weakened (Fig. 5-1).
Common neurotransmitters include serotonin, dopa- mine, norepinephrine, acetylcholine, gamma-aminobutyric acid, and glutamate. Other chemical messengers, called neuropeptides, are actually a separate type of neuro- transmitter. Neuropeptides include substance P, endor- phins, enkephalins, and neurohormones.
Synapse
Axon Axon
Dendrite Dendrites
Vesicles Synaptic cleft
Dendrite
Neurotransmitters Receptor
sites Axon Direction of
nerve impulse
FIGURE 5-1
•
Neurotransmitter activity. (From Timby, B. K., & Smith, N. E. [2007]. Introductory medical-surgical nursing[9th ed.]. Philadel- phia: Lippincott Williams and Wilkins)62 U N I T 2 ● Integrating Basic Concepts
Neurotransmitters and neuropeptides exert different effects. Serotonin stabilizes mood, induces sleep, and reg- ulates temperature. Norepinephrine heightens arousal and increases energy. Acetylcholine and dopamine pro- mote coordinated movement. Gamma-aminobutyric acid inhibits the excitatory neurotransmitters, such as nor- epinephrine and dopamine, which are classified as cat- echolamines. Substance P transmits the pain sensation, whereas endorphins and enkephalins interrupt the trans- mission of substance P and promote a sense of well-being.
Different brain areas contain different neurons that contain specific neurotransmitters. Receptors for these chemical messengers are found throughout the central ner- vous, endocrine, and immune systems, suggesting a highly integrated communication system sometimes referred to as the hypothalamus-pituitary-adrenal (HPA) axis.
Central Nervous System
The central nervous system is composed of the brain and spinal cord. The brain is divided into the cortex and the structures that make up the subcortex (Fig. 5-2).
CORTEX. The cortex is considered the higher-functioning portion of the brain. It enables people to think abstractly, use and understand language, accumulate and store mem- ories, and make decisions about information received.
The cortex also influences other primitive areas of the brain located in the subcortex.
SUBCORTEX. The subcortex consists of the structures in the midbrain and brainstem. The midbrain, which lies between the cortex and brainstem, includes the basal ganglia, thalamus, and hypothalamus. The brainstem, so named because it resembles a stalk, contains the cere- bellum, medulla, and pons. The subcortical structures are primarily responsible for regulating and maintaining physiologic activities that promote survival. Examples
include regulation of breathing, heart contraction, blood pressure, body temperature, sleep, appetite, and stimula- tion and inhibition of hormone production.
RETICULAR ACTIVATING SYSTEM. The reticular activating system (RAS), an area of the brain through which a net- work of nerves passes, is the communication link between body and mind. Information about a person’s internal and external environment is funneled through the RAS to the cortex on both a conscious and an unconscious level (Fig. 5-3). The cortex processes the information and gen- erates behavioral and physiologic responses through acti- vation by the hypothalamus. The hypothalamus, in turn, influences the autonomic nervous system and endocrine functions (Fig. 5-4).
Autonomic Nervous System
The autonomic nervous system is composed of peripheral nerves affecting physiologic functions that are largely auto- matic and beyond voluntary control. It is subdivided into the sympathetic and parasympathetic nervous systems.
Both the sympathetic and parasympathetic divisions supply organs throughout the body with nerve pathways.
Each division takes a turn being functionally dominant, depending on the appropriate physiologic response. For example, when increased heart rate is needed, the sym- pathetic division dominates; when heart rate needs to be slowed, the parasympathetic division takes over.
SYMPATHETIC NERVOUS SYSTEM. When a situation occurs that the mind perceives as dangerous, the sympathetic nervous system prepares the body for fight or flight. It
Cortex
Basal ganglia Thalamus Hypothalamus
Cerebellum Pons Medulla
Spinal cord Brain stem Midbrain
Pituitary gland
FIGURE 5-2
•
Central nervous system structures.FIGURE 5-3
•
The reticular activating system is the link in the mind–body connection.
however, does not produce an opposite reaction for every sympathetic effect (Table 5-2). For this reason, some believe that the parasympathetic nervous system offers an alternate but equally effective mechanism for responding to threats from the internal or external environment. For example, physiologic deceleration, produced by the para- sympathetic nervous system, has been likened to the manner in which opossums and other animals “play dead”
when they sense that predators are stalking them. Simu- lating the appearance of death often causes the predator to leave the animal alone, thus saving its life. Therefore, it has been proposed that humans, too, may respond to stimuli not only by speeding physiologic responses but also by slowing them down (Nuernberger, 1981).
Endocrine System
The autonomic nervous system provides the initial and immediate response to a perceived threat through either sympathetic or parasympathetic pathways. The endocrine system, a group of glands found throughout the body that produce hormones, sustains the response (Fig. 5-5). Hor- mones are chemicals manufactured in one part of the body whose actions have physiologic effects on target cells elsewhere.
NEUROENDOCRINE CONTROL. The pituitary gland, located in the brain, is considered the master gland, producing hormones that influence other endocrine glands. The pitu- itary gland is connected to the hypothalamus, a subcortical structure, through both vascular connections and nerve endings. For pituitary function to occur, the cortex first stimulates the hypothalamus that then activates the pitu- itary gland.
FEEDBACK LOOP. A feedback loopis the mechanism for controlling hormone production (Fig. 5-6). Feedback can be negative or positive. Most hormones are secreted in response to negative feedback; when a hormone level
Stress Hypothalamus
Autonomic nervous system
Catecholamines
Bone marrow Thymus
Thyroid Parathyroid
Heart and lungs
Adrenal medulla Adrenal
cortex
Kidneys Liver Stomach Pancreas Pituitary
Adrenocorticotrophic hormone (ACTH)
Corticosteroids, including cortisol
FIGURE 5-4
•
Homeostatic adaptive pathways.SYMPATHETIC AND PARASYMPATHETIC EFFECTS
TABLE 5-2
TARGET STRUCTURE SYMPATHETIC EFFECT PARASYMPATHETIC EFFECT
Iris of the eye Dilates pupils Constricts pupils
Sweat glands Increases perspiration None
Salivary glands Inhibits salivation Increases salivation
Digestive glands Inhibits secretions Stimulates secretions
Heart Increases rate and force of contraction Decreases rate and force of contraction Blood vessels in skin Constrict, causing pale appearance Dilate causing blush or flushed appearance
Skeletal muscles Increased tone Decreased tone
Bronchial muscles Relaxed (bronchodilation) Contracted (bronchoconstriction)
Digestive motility (peristalsis) Decreased Increased
Kidney Decreased filtration None
Bladder muscle (detrusor) Inhibited (suppressed urination) Stimulated (urge to urinate)
Liver Release of glucose None
Adrenal medulla Stimulated None
accelerates the physiologic functions that ensure survival through enhanced strength or rapid escape. The person becomes active, aroused, and emotionally charged.
PARASYMPATHETIC NERVOUS SYSTEM. The parasympa- thetic nervous system restores equilibrium after danger is no longer apparent. It does so by inhibiting the physiologic stimulation created by its counterpart, the sympathetic nervous system. The parasympathetic nervous system,
C H A P T E R 5 ● Homeostasis, Adaptation, and Stress 63
COMMON SIGNS AND SYMPTOMS OF STRESS
TABLE 5-3
PHYSICAL EMOTIONAL COGNITIVE Rapid heart rate
Rapid breathing Increased blood
pressure Difficulty falling
asleep or excessive sleep Loss of appetite
or excessive eating Stiff muscles Hyperactivity or
inactivity Dry mouth Constipation or
diarrhea Lack of interest
in sex
Irritability Angry outbursts Hypercritical Verbal abuse Withdrawal Depression
Impaired attention and concentration Forgetfulness Preoccupation Poor judgment
64 U N I T 2 ● Integrating Basic Concepts
decreases, the releasing gland is stimulated. In positive feedback, the opposite occurs, keeping concentrations of hormones within a stable range at all times. Homeosta- sis is maintained when hormones are released as needed or inhibited when adequate.
As long as demands on the central nervous, autonomic nervous, and endocrine systems are within adaptive capac- ity, the body maintains homeostasis. When internal or external changes overwhelm homeostatic adaptation,