You have a set of glands in your body that have a lot to do with your moods, your emotional states, and your behavior in general. Working together, these glands are called the endocrine system. The glands themselves are called endocrine glands because they secrete their substances directly into the bloodstream with- out ducts. (Endomeans “within” or “inside.” In contrast, exocrine glands,such as salivary or digestive glands, secrete their substances “outside” of the blood- stream.) The substances secreted by the endocrine glands are called hormones.
These, like neurotransmitters, act as chemical messengers.
The pineal glandis a tiny gland located nearly in the center of the brain. It is called “pineal” because it is shaped something like a pine cone. Of historical interest is the fact that the philosopher René Descartes suggested, perhaps because it is small and centered, that the pineal gland is the place where the soul
Pineal gland Pituitary gland Thyroid gland
Adrenal glands Kidneys Pancreas gland Ovaries (female)
Testes (male) Gonads
Locations of the endocrine glands.
interacts with the body. Today’s research indicates that the pineal gland secretes a hormone called melatonin.This hormone plays a role in controlling the bio- logical timetable for sexual maturation. Another of its functions is to regulate the sleep cycle.
(a) The endocrine glands secrete their substances (without ducts) directly into the .
(b) The pineal gland secretes a hormone called . Answers: (a) bloodstream; (b) melatonin.
The pituitary gland, about the size of a pea, is located in front of the hypo- thalamus. As already noted, it is called the “master gland” because it secretes a group of hormones that affect the action of the other glands. Among these hor- mones there are adrenocorticotrophic hormone (ACTH), a hormone that acts on the adrenal glands, thyrotrophin, a hormone that acts on the thyroid gland, and follicle-stimulating hormone,a hormone that acts on the gonads.
One of the hormones secreted by the pituitary gland is growth hormone (GH). GH has an effect on growth and stature. People who are abnormally tall have a pathology of the pituitary gland and are said to suffer from the disease of giantism.
The thyroid glandis located toward the base and front of the neck. It is a rel- atively large gland and is shaped somewhat like a butterfly. In areas of the world where the soil is deficient in iodine, some individuals develop a disease of the thy- roid gland called goiter.The gland can swell to the size of an orange or larger.
One of the reasons that salt is often iodized is to prevent goiter.
The principal function ofthyroxin,the hormone secreted by the thyroid gland, is to regulate metabolism,the rate at which you burn food. If not enough thyroxin is secreted, and your metabolic rate is abnormally low, you will tend to gain weight easily; at a behavioral level you may be sluggish and unenthusiastic. If too much thy- roxin is secreted, and your metabolic rate is abnormally high, you will have difficulty gaining weight; at a behavioral level you may be impulsive and hyperactive.
(a) What hormone secreted by the pituitary gland is associated with a disease such as giantism?
(b) The principal function of the hormone thyroxin is to regulate . Answers: (a) Growth hormone (GH); (b) metabolism.
There are two adrenal glands, and these are located on top of the kidneys.
The adrenal glands produce such hormones as the corticosteroid hormones and epinephrine. The corticosteroid hormonesregulate the way the body utilizes such substances as glucose, salt, and water during times of stress. Epinephrine
induces an increased sense of arousal and excitement. It plays an important role in the fight-or-flight reaction,an involuntary process in which the body prepares itself to cope with threatening situations. (The word adrenalin is synonymous with epinephrine. However, when the word Adrenalinappears in capitalized form, it refers to a specific drug with a trade name.)
Psychology has given increased attention to the role that the adrenal glands play in the body’s adaptation to stress because of the work of the Canadian researcher Hans Selye (1907–1982). Using rats as subjects, Selye discovered that under conditions of chronic stress the body goes through a series of stages, including resistance and eventual exhaustion, that lead to an early death. The reaction pattern is called the general adaptation syndrome. Postmortem examinations revealed that the adrenal glands of the subjects were damaged and enlarged.
(a) Epinephrine induces an increased sense of . (b) What reaction pattern is associated with chronic stress?
Answers: (a) arousal and excitement; (b) The general adaptation syndrome.
The pancreas glandis a large gland located under the stomach. One of the hormones secreted by the pancreas is insulin. Insulin helps to regulate blood sugar. The disease diabetes is associated with an inadequate insulin production.
The disorder chronic hypoglycemia, or low blood sugar, is, paradoxically, aggravated when one consumes either too much dietary sugar or too many refined carbohydrates. A person suffering from low blood sugar finds it difficult to concentrate, feel energetic, or otherwise function well.
The gonads are the sexual glands. In females the gonads are called the ovaries. In males the gonads are called the testes. Estrogen is one of the prin- cipal hormones produced by the ovaries. The secondary sexual characteristics in females, such as minimal facial hair and larger breasts, are determined by estrogen.
Testosteroneis one of the principal hormones produced by the testes. The sec- ondary sexual characteristics in males, such as lack of breast development and the presence of facial hair, are determined by testosterone. There is also evidence to suggest that testosterone is associated, particularly in youth, with aggressive behav- ior. (It is important to note that both sexes produce estrogen and testosterone;
however, the relative amounts differ.)
(a) Insulin helps to regulate .
(b) Identify a hormone associated principally with the ovaries.
(c) Identify a hormone associated principally with the testes.
Answers: (a) blood sugar; (b) Estrogen; (c) Testosterone.
SELF-TEST
1. An axon
a. can be found in the cell body of a neuron b. is a motor neuron
c. sends information in the direction of the cell body d. sends information away from the cell body
2. Which one of the following is said to be a chemical messenger?
a. A cell nucleus b. A neurotransmitter
c. A metabolic cell d. A connector neuron
3. Informally, a neuron is said to “fire.” The formal term for “fire” is a. signal recentering
b. depolarize c. repolarize d. adaptation
4. The two main divisions of the nervous system are a. the brain and the spinal cord
b. the somatic and the parasympathetic divisions
c. the central nervous system and the peripheral nervous system d. the right hemisphere and the left hemisphere
5. What structure functions like both a light switch and a rheostat?
a. The medulla b. The thalamus
c. The reticular activating system d. The cerebellum
6. The hypothalamus is associated primarily with a. the regulation of biological drives
b. abstract intelligence c. the curiosity drive d. motor coordination
7. The cerebral cortex is associated primarily with a. the inhibition of respiration
b. the regulation of biological drives c. primal impulses
d. thinking
8. The right hemisphere of the brain tends to mediate a. nonverbal patterning
b. verbal thinking
c. mathematical thinking d. symbolic logic
9. What hormone is associated with the pineal gland?
a. Thyroxin b. Melatonin
c. Growth hormone d. Insulin
10. The ovaries belong to what larger general category of endocrine glands?
a. Stress glands b. Adrenal glands
c. Gonads
d. Pituitary glands
ANSWERS TO THE SELF-TEST
1-d 2-b 3-b 4-c 5-c 6-a 7-d 8-a 9-b 10-c
ANSWERS TO THE TRUE-OR-FALSE PREVIEW QUIZ
1. True.
2. False. The sympathetic division and the parasympathetic division refer to the two divi- sions of the autonomic nervous system. The two divisions of the brain are called the right hemisphere and the left hemisphere.
3. False. There is only one pituitary gland, and it is located in the brain. The two adrenal glands are located on top of the kidneys.
4. True.
5. True.
KEY TERMS
adrenal glands adrenalin
adrenocorticotrophic hormone (ACTH) afferent nerves
anhedonia (or ahedonia) association neurons autonomic nervous system axon
Broca’s area
central nervous system cerebellum
cerebral cortex chronic hypoglycemia corpus callosum
corticosteroid hormones dendrite
depolarize dopamine efferent nerves end foot
endocrine glands endocrine system epinephrine estrogen exocrine glands fight-or-flight reaction follicle-stimulating hormone general adaptation syndrome giantism
goiter gonads
growth hormone (GH) hormones
hypothalamus id
insulin
left hemisphere limbic system medulla melatonin
metabolism motor neurons nerve
nervous system neuron
neurotransmitter ovaries
pancreas gland
parasympathetic division peripheral nervous system pineal gland
pituitary gland pons
receptor site
reticular activating system (RAS) right hemisphere
selective serotonin reuptake inhibitors (SSRIs)
sensory neurons serotonin soma
somatic nervous system spinal cord
sympathetic division synapse
synaptic cleft testes
testosterone thalamus thyroid gland thyrotrophin thyroxin